Patent Publication Number: US-2023159674-A1

Title: Multiple Reactor and Multiple Zone Polyolefin Polymerization

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of and claims priority to U.S. Pat. Application No. 17/074,809, filed Oct. 20, 2020, now U.S. Pat. Application Publication No. 2021/0032380 A1, which is a continuation of and claims priority to U.S. Pat. Application No. 16/866,980, filed May 5, 2020, now U.S. Pat. No. 10,844,147, which is a continuation of and claims priority to U.S. Pat. Application No. 16/538,429 filed Aug. 12, 2019, now U.S. Pat. No. 10,703,832, which is a continuation of and claims priority to U.S. Pat. Application No. 16/234,153 filed Dec. 27, 2018, now U.S. Pat. No. 10,781,273, all entitled “Multiple Reactor and Multiple Zone Polyolefin Polymerization,” all of which are hereby incorporated by reference herein in their entirety. 
     The present application is a continuation of and claims priority to U.S. Pat. Application No. 17/074,809, filed Oct. 20, 2020, now U.S. Pat. Application Publication No. 2021/0032380 A1, which is a continuation of and claims priority to U.S. Pat. Application No. 16/867,015, filed May 5, 2020, now U.S. Pat. No. 10,844,148, which is a continuation of and claims priority to U.S. Pat. Application No. 16/538,467 filed Aug. 12, 2019, now U.S. Pat. No. 10,696,759, which is a continuation of and claims priority to U.S. Pat. Application No. 16/234,153 filed Dec. 27, 2018, now U.S. Pat. No. 10,781,273, all entitled “Multiple Reactor and Multiple Zone Polyolefin Polymerization,” all of which are hereby incorporated by reference herein in their entirety. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     BACKGROUND 
     Field of the Invention 
     This disclosure generally relates to the polymerization of polyolefins in multiple reaction zones. 
     Background of the Invention 
     Polyolefins have various applications such as use in pipe, films, large and small containers, cups, bottles, molded articles, and the like. There is an ongoing need for polyolefin compositions having improved properties and processability, especially when formed into the aforementioned items. 
     SUMMARY 
     A process for producing a multimodal polyolefin includes (a) polymerizing ethylene in a first reactor to produce a first polyolefin, (b) polymerizing ethylene in a first reaction mixture in a riser of a second reactor to produce a second polyolefin, (c) passing the first reaction mixture through an upper conduit from the riser to a separator, (d) recovering, in the separator, the second polyolefin from the first reaction mixture, (e) passing the second polyolefin from the separator into a downcomer of the second reactor, optionally via a liquid barrier, (f) polymerizing ethylene in a second reaction mixture in the downcomer to produce a third polyolefin, (g) passing the second reaction mixture through a lower conduit from the downcomer to the riser, and (h) one of (1) after step (a) and before steps (b)-(g), receiving the first polyolefin into the second reactor, or (2) before step (a) and after steps (b)-(g), receiving the second polyolefin and the third polyolefin into the first reactor. 
     Another process for producing a multimodal polyolefin includes (a) polymerizing ethylene in a first reactor to produce a first polyolefin, (b) polymerizing ethylene in a first reaction mixture in a riser of a second reactor to produce a second polyolefin contained in a riser product mixture, (c) passing the riser product mixture through an upper conduit from the riser to a separator, (d) recovering, in the separator, the second polyolefin from the riser product mixture, (e) passing the second polyolefin from the separator into a downcomer of the second reactor, optionally via a liquid barrier, (f) polymerizing ethylene in a second reaction mixture in the downcomer to produce a third polyolefin in a downcomer product mixture, (g) passing the downcomer product mixture through a lower conduit from the downcomer to the riser, and (h) one of (1) after step (a) and before steps (b)-(g), receiving the first polyolefin into the second reactor, or (2) before step (a) and after steps (b)-(g), receiving the second polyolefin and the third polyolefin into the first reactor. 
     Another process for producing a multimodal polyolefin, performed with i) a first reactor having a first polymerization zone, and ii) a second reactor having a second polymerization zone in a riser and a third polymerization zone in a downcomer, includes (a) polymerizing ethylene in the first polymerization zone to produce a first polyolefin, (b) passing a first reaction mixture upward through the second polymerization zone of the riser, wherein a second polyolefin is produced in the second polymerization zone, (c) receiving the first reaction mixture from the second polymerization zone in a separator, (d) separating, by the separator, a first polyolefin product from the received first reaction mixture, (e) passing the first polyolefin product through a barrier section of the second reactor and into the third polymerization zone, (f) adding, in the third polymerization zone, the first polyolefin product to a second reaction mixture, (g) passing the second reaction mixture downward through the third polymerization zone of the downcomer, wherein a third polyolefin is produced in the third polymerization zone, (h) repeating steps (b)-(g) n times, wherein n=1 to 100,000 and (i) one of 1) adding the first polyolefin to the second reactor at a location upstream of the second polymerization zone with respect to a direction of flow of the first reaction mixture in the second polymerization zone, and withdrawing the multimodal polyolefin from the downcomer, or 2) withdrawing a portion of a second polyolefin product from the second reactor, adding the portion of the second polyolefin product to the first polymerization zone of the first reactor, and withdrawing the multimodal polyolefin from the first reactor. 
     An apparatus for producing a multimodal polyolefin includes a first reactor configured to produce a first polyolefin, a second reactor configured to produce a second polyolefin and a third polyolefin, where the second reactor comprises a riser configured to produce the second polyolefin, an upper conduit having an end fluidly connected to a top portion of the riser, a separator fluidly connected to an opposite end of the upper conduit, a downcomer configured to produce the third polyolefin, wherein a top portion of the downcomer is fluidly connected to the separator, optionally via a liquid barrier in the top portion of the downcomer, and a lower conduit having an end fluidly connected to a bottom portion of the downcomer and an opposite end fluidly connected to a bottom portion of the riser, wherein the second reactor is configured to receive the first polyolefin from the first reactor, or, the first reactor is configured to receive the second polyolefin and the third polyolefin from the second reactor. 
     A multimodal polyolefin can comprise the first polyolefin (e.g., a low molecular weight component), the second polyolefin (e.g., an intermediate molecular weight component), and the third polyolefin (e.g., a high molecular weight component) made in accordance with an above apparatus and/or process. The multimodal polyolefin can have one or more of: a density in a range of from about 0.930 to about 0.970 g/ml, a melt index in a range of from about 0.1 to about 30 g/10 min when tested under a force of 2.16 kg and at a temperature of 190° C., a high load melt index of from about 1 to about 45 g/10 min under a force of 21.6 kg and a temperature of 190° C., a comonomer content in a range of from 0 to about 6 wt.%, a M w  in a range of from about 250 to about 1,500 kg/mol, a M z  in a range of from about 500 to about 5,000 kg/mol, a Mw/Mn in a range of from about 18 to about 52, a long chain branching index in a range of from 0 to about 0.96, and a shear induced crystallization (SIC) index in a range of from about 0.15 to about 8. The multimodal polyolefin can be in the form of a polyethylene resin. 
     Another multimodal polyolefin in the form of a polyethylene resin can have a low molecular weight (LMW) component, an intermediate molecular weight (IMW) component, and a high molecular weight (HMW) component; wherein the LMW component is present in an amount of from about 20 wt.% to about 75 wt.%; wherein the IMW component is present in an amount of from about 5 wt.% to about 40 wt.%; wherein the HMW component is present in an amount of from about 10 wt.% to about 60 wt.%; wherein the LMW component has a weight average molecular weight of from about 20 kg/mol to about 150 kg/mol; wherein the IMW component has a weight average molecular weight of from about 85 kg/mol to about 350 kg/mol; wherein the HMW component has weight average molecular weight of greater than about 350 kg/mol; wherein the weight average molecular weight of the IMW component is greater than the weight average molecular weight of the LMW component; wherein the LMW component has a short chain branching content of from about 0 to about 5 short chain branches per 1,000 carbon atoms; wherein the IMW component has a short chain branching content of from about 0.1 to about 10 short chain branches per 1,000 carbon atoms; wherein the HMW component has a short chain branching content of from about 1 to about 15 short chain branches per 1,000 carbon atoms; and wherein the polyethylene resin has a magnitude of slip-stick of from about 300 psi to about 1,000 psi (about 2.07 MPa to about 6.89 MPa). 
     Another multimodal polyolefin in the form of a polyethylene resin can have a low molecular weight (LMW) component, an intermediate molecular weight (IMW) component, and a high molecular weight (HMW) component; wherein the LMW component is present in an amount of from about 40 wt.% to about 60 wt.%; wherein the IMW component is present in an amount of from about 5 wt.% to about 15 wt.%; wherein the HMW component is present in an amount of from about 30 wt.% to about 50 wt.%; wherein the LMW component has a weight average molecular weight of from about 25 kg/mol to about 65 kg/mol; wherein the IMW component has a weight average molecular weight of from about 100 kg/mol to about 200 kg/mol; wherein the HMW component has weight average molecular weight of from about 400 kg/mol to about 925 kg/mol; wherein the LMW component has a short chain branching content of from about 0 to about 2 short chain branches per 1,000 carbon atoms; wherein the IMW component has a short chain branching content of from about 0.1 to about 5 short chain branches per 1,000 carbon atoms; wherein the HMW component has a short chain branching content of from about 2 to about 12 short chain branches per 1,000 carbon atoms; and wherein the polyethylene resin has a resistance to slow crack growth of equal to or greater than about 3,000 h, when tested in accordance with ASTM F1473, wherein the resistance to slow crack growth is defined as the polyethylene notch tensile test (PENT) failure time. 
     Another multi-modal polyolefin in the form of a polyethylene resin can have a low molecular weight (LMW) component, an intermediate molecular weight (IMW) component [from riser], and a high molecular weight (HMW) component; wherein the LMW component is produced in a first reaction zone in the substantial absence of a comonomer, and wherein the LMW component is present in an amount of from about 20 wt.% to about 75 wt.%; wherein the IMW component is produced in a second reaction zone in the presence of a first amount of comonomer and a first amount of hydrogen, and wherein the IMW component is present in an amount of from about 5 wt.% to about 40 wt.%; wherein the HMW component is produced in a third reaction zone in the presence of a second amount of comonomer and a second amount of hydrogen, wherein the second amount of comonomer is greater than the first amount of comonomer, wherein first amount of hydrogen is greater than the second amount of hydrogen, and wherein the HMW component is present in an amount of from about 10 wt.% to about 60 wt.%; wherein the LMW component has a weight average molecular weight of from about 20 kg/mol to about 150 kg/mol; wherein the IMW component has a weight average molecular weight of from about 85 kg/mol to about 350 kg/mol; wherein the HMW component has weight average molecular weight of greater than about 350 kg/mol; wherein the weight average molecular weight of the IMW component is greater than the weight average molecular weight of the LMW component; wherein the LMW component has a short chain branching content of from about 0 to about 5 short chain branches per 1,000 carbon atoms; wherein the IMW component has a short chain branching content of from about 0.1 to about 10 short chain branches per 1,000 carbon atoms; wherein the HMW component has a short chain branching content of from about 1 to about 15 short chain branches per 1,000 carbon atoms; and wherein the polyethylene resin has an ƞ 251  (eta_251) of less than about 1.5 × 10 3  Pa-s. 
     The foregoing has outlined rather broadly the features and technical advantages of the disclosed inventive subject matter in order that the following detailed description may be better understood. The various characteristics described above, as well as other features, will be readily apparent to those skilled in the art upon reading the following detailed description of the preferred embodiments, and by referring to the accompanying drawings. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       For a detailed description of the preferred embodiments of the disclosed processes and apparatuses, reference will now be made to the accompanying drawings in which: 
         FIG.  1    illustrates a multiple reactor and multiple zone polyolefin polymerization according to the disclosure, where a multi-zone circulating reactor is connected downstream of a first reactor. 
         FIG.  2    illustrates another multiple reactor and multiple zone polyolefin polymerization according to the disclosure, where a multi-zone circulating reactor is connected upstream of a first reactor. 
         FIG.  3    illustrates a multi-zone circulating reactor having various additional aspects that can be utilized in  FIG.  1    and/or  FIG.  2   . 
         FIG.  4    illustrates a multi-zone circulating reactor having various additional aspects that can be utilized in  FIG.  1    and/or  FIG.  2    and with any combination of aspects shown in  FIG.  3   . 
         FIGS.  5 A and  5 B  illustrate cross-sectional views of embodiments of an eductor. 
         FIG.  5 C  illustrates a perspective view of a standpipe. 
         FIGS.  5 D to  5 H  illustrate various aspects of the multi-zone circulating reactor having an eductor that can be utilized in  FIG.  1    and/or  FIG.  2    and with any combination of other aspects described herein. 
         FIGS.  5 I and  5 J  illustrate embodiments of the multi-zone circulating reactor having a standpipe that can be utilized in  FIG.  1    and/or  FIG.  2    and with any combination of other aspects described herein. 
         FIG.  6 A  illustrates a configuration of the multi-zone circulating reactor having a transition conduit that can be utilized in  FIG.  1    and/or  FIG.  2   , along with any combination of aspects described herein. 
         FIG.  6 B  illustrates the configuration of the multi-zone circulating reactor in  FIG.  6 A , having an eductor and standpipe instead of the transition conduit. 
         FIG.  6 C  illustrates the configuration of the multi-zone circulating reactor in  FIG.  6 A , having a standpipe placed inside the transition conduit. 
         FIG.  7    illustrates an isolated view of an elbow connector having a smart elbow configuration. 
         FIG.  8 A  is a side view of the separator of the multi-zone circulating reactor, embodied as a cyclone separator. 
         FIG.  8 B  is a top cross-sectional view of the cyclone separator of  FIG.  8 A , taken along sight line i—i shown in  FIG.  8 A . 
         FIG.  9    illustrates an embodiment of a product separation system depicted in  FIG.  1    and  FIG.  2   . 
         FIG.  10 A  illustrates the first reactor in a gas phase configuration for use in  FIG.  1   , utilizing a settling leg to move the reactor effluent to a separator for polyolefin recovery. 
         FIG.  10 B  illustrates the first reactor in a gas phase configuration for use in  FIG.  1   , utilizing a lock hopper to move the reactor effluent to a separator for polyolefin recovery. 
         FIG.  10 C  illustrates the first reactor in a gas phase configuration for use in  FIG.  1   , utilizing a take-off valve to move the reactor effluent to a separator for polyolefin recovery. 
         FIG.  10 D  illustrates the first reactor in a gas phase configuration for use in  FIG.  2   , utilizing a settling leg to move the reactor effluent to a separator for polyolefin recovery. 
         FIG.  10 E  illustrates the first reactor in a gas phase configuration for use in  FIG.  2   , utilizing a lock hopper to move the reactor effluent to a separator for polyolefin recovery. 
         FIG.  10 F  illustrates the first reactor in a gas phase configuration for use in  FIG.  2   , utilizing a take-off valve to move the reactor effluent to a separator for polyolefin recovery. 
     
    
    
     DETAILED DESCRIPTION 
     Disclosed herein are apparatuses and processes for multiple reactor and multiple zone polyolefin polymerization, as well as the polyethylene resins that can be produced by the apparatus and processes. The description may be in context of the apparatus or in context of process steps; however, it is contemplated that aspects of the disclosed process can include aspects discussed in apparatus context and that aspects of the disclosed apparatus can include aspects discussed in the process context. Also, while polyethylene resins are described herein, it is contemplated that the disclosed apparatuses and processes can produce various other polyethylene resins and otherwise various other multimodal polyolefins by utilizing different embodiments and aspects of the discloses apparatuses and processes. 
     The disclosed apparatus and processes are configured to produce a multimodal polyolefin, and particular the polyethylene resins, disclosed herein. This is accomplished by using two reactors in series, where one of the reactors is a multi-zone circulating reactor that can implement two polymerization zones having two different flow regimes in order to produce two polyolefins that have different molecular weights so that the final multimodal polyolefin has improved product properties, improved product homogeneity, and a reduced the number of gels compared to a bimodal polyolefin. 
     The term “polyolefin” as used herein refers to unimodal or multimodal polymers such as polyethylene, ethylene-alpha olefin copolymers, ethylene copolymers having at least about 50 percent by weight of ethylene polymerized with a lesser amount of a comonomer, polypropylene, polybutene, and other polymeric resins within the “olefin” family classification. 
     The term “unimodal” as used herein refers to a polyolefin homopolymer having a molecular weight distribution curve showing a single peak in a molecular weight distribution curve. Molecular weight distribution curves can be displayed in a graph of the polyolefin weight fraction as a function of its molecular weight, as measured by, e.g., gel permeation chromatography (GPC). The polyolefin weight fraction refers to the weight fraction of polyolefin molecules of a given size. 
     The term “multimodal” as used herein refers to a polyolefins having a molecular weight distribution curve showing more than one peak in a molecular weight distribution curve. It is acknowledged that, in some instances, a multimodal polyolefin may appear to have a single peak via, for example, GPC analysis, when in fact the polyolefin is multimodal, and the single peak is due to overlap of multiple peaks. The term “multimodal” includes a polyolefin having a curve showing two distinct peaks, also referred to as a bimodal or a bimodal-like polyolefin, and a polyolefin having a curve showing three distinct peaks, also referred to as trimodal or a trimodal-like polyolefin. 
     The term “polymerization zone” as used herein refers to a volume of space inside a polymerization reactor where conditions are such that an olefin polymerization reaction occurs. 
     The terms “conduit” and “line” are interchangeable, and as used herein, refer to a physical structure configured for the flow of materials therethrough, such as pipe or tubing. The materials that flow in the “conduit” or “line can be in the gas phase, the liquid phase, the solid phase, or a combination of these phases. 
     The term “stream” as used herein refers to a physical composition of materials that flow through a “conduit” or “line”. 
     The term “diameter” as used herein refers to an inner diameter. Thus, a pipe or conduit having a diameter disclosed herein refers to the inner diameter of the pipe or conduit. Wall thicknesses of the pipe or conduit can be separately specified or otherwise can be a wall thickness appropriate for the application. 
     The term “length” as used herein refers to the distance of a first end of a straight section of pipe or tube to the second end of the straight section of pipe or tube and includes any straight portions that may be part of an elbow. For avoidance of doubt, no arcuate portions of an elbow are included in the length of an elbow. 
       FIG.  1    illustrates multiple reactor and multiple zone polyolefin polymerization according to the disclosure, where a multi-zone circulating reactor  300  is connected downstream of a first reactor  100 .  FIG.  2    illustrates another multiple reactor and multiple zone polyolefin polymerization according to the disclosure, where the multi-zone circulating reactor  300  is connected upstream of the first reactor  100 . Each of the reactors  100  and  300  is a polymerization reactor configured to polymerize one or more olefins in the presence of one or more polymerization catalysts at conditions suitable for the production of one or more polyolefins. 
     Multiple polymerization zones are present in each of  FIG.  1    and  FIG.  2   . That is, the first reactor  100  has at least one polymerization zone  112 , and the multi-zone circulating reactor  300  has two polymerization zones  321  and  341 . Each polymerization zone  112 ,  321 , and  341  can be configured to produce a different polyolefin than the other zones. For example, polymerization zone  112  of the first reactor  100  can produce a first polyolefin, second polymerization zone  321  of the MZCR  300  can be configured to product a second polyolefin, and third polymerization zone  341  of the MZCR  300  can be configured to product a third polyolefin. Alternatively, polymerization zone  112  of the first reactor  100  can be configured to produce a first polyolefin and the second and third polymerization zones  321  and  341  of the MCZR  300  can be configured to produce a second polyolefin. 
     In aspects, the ratio of the amount of the first polyolefin produced in the first reactor  100  that becomes part of the multimodal polyolefin to the amount of the polyolefin(s) produced in the MZCR  300  that becomes part of the multimodal polyolefin can be about 10/90 wt.%, about 20/80 wt.%, about 30/70 wt.%, about 40/60 wt.%, about 50/50 wt.%, about 60/40 wt.%, about 70/30 wt.%, about 80/10 wt.%, or about 90/10 wt.% of the multimodal polyolefin. 
     In aspects, the ratio of the amount of the second polyolefin produced in the riser  320  of the MZCR  300  to the amount of the third polyolefin produced in the downcomer  340  of the MZCR  300  can be about 10/90 wt.%, about 20/80 wt.%, about 30/70 wt.%, about 40/60 wt.%, about 50/50 wt.%, about 60/40 wt.%, about 70/30 wt.%, about 80/10 wt.%, or about 90/10 wt.% based on the total weight of the second polyolefin and the third polyolefin that becomes part of the multimodal polyolefin. 
       FIG.  1    shows the MZCR  300  is configured to receive the first polyolefin from the first reactor  100 .  FIG.  2    shows the first reactor  100  can be configured to receive the second polyolefin and the third polyolefin from the MCZR  300 . 
     The first reactor  100  can be embodied as one or more loop slurry reactors, one or more fluidized bed reactors, one or more autoclave reactors, one or more tubular reactors, one or more horizontal gas phase reactors, one or more continuous stirred-tank reactors, one or more solution reactors, or a combination thereof. Configurations for these types of polymerization reactors are known, each capable of having the polymerization zone  112  that produces the first polyolefin. In an aspect, the first reactor  100  can be embodied as two or more reactors operated in parallel, each having a polymerization zone, and each having a product discharge conduit  110  that feed the first reactor product mixture to a product separation system  200 . In one such aspect, the polymerization zone  112  can produce a low molecular weight (LMW) component of the multimodal polyolefin (e.g., a polyolefin resin). 
     Polymerization of olefin monomer and optional olefin comonomer in the first reactor  100  occurs by contacting a polymerization catalyst and the olefin monomer(s) in the polymerization zone  112  under polymerization conditions. Polymerization conditions in the polymerization zone  112  can include a temperature ranging from about 20° C. (68° F.) to about 260° C. (500° F.) and a pressure ranging from about 14.7 psia to about 4,000 psia (0.101 MPaa to about 27.6 MPaa); alternatively, a temperature ranging from about 60° C. (140° F.) to about 110° C. (230° F.) and a pressure ranging from about 250 psia to about 600 psia (about 1.7 MPaa to about 4.1 MPaa). In one or more aspects, polymerization in the polymerization zone  112  can be conducted batchwise such as in a continuous-stirred tank reactor or continuously such as in a loop slurry reactor or a gas phase reactor. 
     The olefin monomer polymerized in the first reactor  100  can be an aliphatic 1-olefin containing from 2 to 8 carbon atoms, e.g., ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, or 1-octene. In an embodiment, the olefin monomer is ethylene or propylene. 
     Polymerization of the olefin monomer can optionally be performed with one or more comonomers that are an aliphatic 1-olefin containing from 3 to about 10 carbon atoms, e.g., propylene, 1-butene, 1-pentene, 1-hexene, 1-pentene, 1-heptene, 1-octene, 1-nonene, or 1-decene. In embodiments, the olefin comonomer can be ethylene, propylene, 1-butene, 1-hexene, 1-octene, or a combination thereof. 
     Polymerization in the polymerization zone  112  can occur in the presence of a hydrocarbon diluent that is inert to the polymerization reaction. Examples of a diluent include propane, isobutane, n-butane, n-pentane, isopentane, neopentane, n-hexane, cyclohexane, n-heptane, methylcyclohexane, or combinations thereof. 
     The olefin monomer used to produce the first polyolefin can be fed to the reactor  100  via conduit  102 . The optional olefin comonomer used to produce the first polyolefin can be fed to the reactor  100  via conduit  106 . The diluent can be fed to the reactor  100  via conduit  104 . The polymerization catalyst can be fed to the reactor  100  in a catalyst feed conduit  108 . The polymerization catalyst can be fed via conduit  108  in a solution (e.g., catalyst dissolved in solvent liquid), in a slurry (e.g., solid catalyst particles suspended in a liquid medium such as a hydrocarbon suitable for use as the polymerization diluent), or in gas mixture (e.g., solid catalyst particles in a carrier gas such as nitrogen). Equipment such as metering valves and/or control valves can be utilized in any of conduits  102 ,  104 ,  106 , and  108  to regulate the flow of the respective component into the reactor  100 . 
     Additional conduits can be utilized for feeding hydrogen and nitrogen to the reactor  100 . Hydrogen can be used to regulate the molecular weight of the polyolefin produced in the reactor  100 . Nitrogen can be used as a pressure source when controlling the pressure of the reactor  100 . Additional conduits and equipment can also be utilized when reactor  100  is a continuous gas phase reactor. For example, when reactor  100  is in a gas phase reactor configuration that operates in condensing mode, additional conduits can be configured for recycle of gases recovered from the top of the reactor  100  back to the bottom of the reactor  100  in the form of a liquid phase. In such configuration, the conduits can be configured to remove gas from a top of the reactor  100 , and a compressor and heat exchanger can be interconnected among the conduits and configured to condense and cool the gas for recycle as a liquid phase back to the bottom of reactor  100 . 
     In aspects, the first reactor  100  is configured to produce the first polyolefin such that the first polyolefin has an average residence time in the polymerization zone  112  of about 1 second to about 14 hours; alternatively, about 1 second to about 12 hours; alternatively, about 1 second to about 10 hours; alternatively, about 1 second to about 8 hours; alternatively, about 2 hours to about 14 hours; alternatively, about 4 hours to about 14 hours; alternatively, about 4 hours to about 12 hours; alternatively, from about 1 hour to about 3 hours; alternatively, about 1 second to about 5 minutes; alternatively, less than 10 hours; alternatively, greater than 1 hour. 
     A product mixture containing polyolefin particles (e.g., the first polyolefin or the multimodal polyolefin) is withdrawn from the reactor  100  via the product discharge conduit  110 . In  FIG.  1   , a product mixture containing the first polyolefin is withdrawn from the first reactor  100  via the product discharge conduit  110 .  FIG.  1    shows the product discharge conduit  110  located on a bottom of the first reactor  100 ; however, it is contemplated that the product discharge conduit  110  can be located anywhere on the reactor  100  of  FIG.  1   , such as a side of the reactor  100 . In  FIG.  2   , a product mixture containing the multimodal polyolefin is withdrawn from the first reactor  100  via the product discharge conduit  110 .  FIG.  2    shows the product discharge conduit  110  located on the side of the first reactor  100 ; however, it is contemplated that the product discharge conduit  110  can be located anywhere on the reactor  100  of  FIG.  2   , such as the bottom of the reactor  100 . In an embodiment, the product discharge conduit  110  can include a take-off valve that is configured as a continuous take-off valve or a discontinuous take-off valve. A continuous take-off valve can regulate the removal of the produce mixture from the first reactor  100  such that product mixture is removed on a continuous basis. A discontinuous take-off valve can regulate the removal of the product mixture on a discontinuous basis, for example, opening and shutting such that the flow of the product mixture through the discontinuous take-off valve is not continuous. 
     In aspects, at least a portion of the reactor  100  can be made carbon steel, stainless steel, or a combination of these materials. In a further aspect the carbon steel can be a low temperature carbon steel. In an embodiment, an internal surface  109  of the reactor  100  can have a rust inhibitor coating. 
     The multi-zone circulating reactor (MZCR)  300  generally polymerizes olefin monomer and optional olefin comonomer in gas phase polymerization and has two interconnected polymerization zones  321  and  341 . The direction of flow of the reaction mixture(s) in the MZCR  300  is shown in  FIG.  1    and  FIG.  2    by arrows A and B. The flow path for the reaction mixture(s) in the MCZR  300  is in the form of a loop, formed by a lower conduit  310  fluidly connected to a riser  320 , the riser  320  additionally being fluidly connected an upper conduit  330 , the upper conduit  330  additionally being fluidly connected to a downcomer  340 , and the downcomer  340  additionally being fluidly connected to the lower conduit  310 . A separator  350  can be fluidly connected to each of the upper conduit  330  and to a liquid barrier  360  (interchangeably referred to as a barrier section  360 ) of the downcomer  340 . 
     In an aspect, the polymerization zone  321  of the riser  320  can produce an intermediate molecular weight (IMW) component, and the polymerization zone  341  of the downcomer  340  can produce a high molecular weight (HMW) component of the multimodal polyolefin (e.g., a polyethylene resin). 
     As illustrated in both  FIG.  1    and  FIG.  2   , an end  312  of the lower conduit  310  can be fluidly connected to a bottom portion  329  of the riser  320 , a top portion  328  of the riser  320  can be fluidly connected an end  331  of the upper conduit  330 , the separator  350  can be fluidly connected to an end  332  of the upper conduit  330 , the separator  350  additionally can be fluidly connected to a top portion  348  of the downcomer  340  via the liquid barrier  360  that is in the top portion  348  of the downcomer  340 , and a bottom portion  349  of the downcomer  340  can be fluidly connected to the end  311  of the lower conduit  310 . 
     An elbow connector  302  is fluidly connected to the end  312  of the lower conduit  310  and to the bottom portion  329  of the riser  320 ; an elbow connector  304  is fluidly connected to the top portion  328  of the riser  320  and to an end  331  of the upper conduit  330 ; the separator  350  is fluidly connected to the end  332  of the upper conduit  330  and to the liquid barrier  360 ; the liquid barrier  360  is additionally fluidly connected to a top portion  348  of the downcomer  340 ; and an elbow connector  306  is fluidly connected to the bottom portion  349  of the downcomer  340  and to the end  311  of the lower conduit  310 . The scope of this disclosure includes interpretations where the elbow connectors  302 ,  304 , and  306  are pieces of equipment that are separate from the portions of the loop formed by the lower conduit  310 , riser  320 , upper conduit  330 , and downcomer  340 . Alternatively, the scope of this disclosure includes interpretations where the elbow connectors  302 ,  304 ,  306  are formed as part of an adjacent piece of the loop, e.g., elbow connector  302  can be part of the lower conduit  310  or part of the riser  320 , elbow connector  304  can be part of the upper conduit  330  or part of the riser  320 , and elbow connector  306  can be part of the downcomer  340  or part of the lower conduit  310 . 
     The lower conduit  310  can be embodied as a tubular structure through which a reaction mixture (e.g., downcomer product mixture, optionally with added recycled monomer, comonomer, and/or diluent) passes from end  311  to end  312 . The longitudinal axis of the lower conduit  310  can be oriented substantially horizontally, as shown in  FIG.  1    and  FIG.  2   . Alternatively, the longitudinal axis of the lower conduit  310  can be oriented at an angle greater than 0° and less than 90° with respect to horizontal, as is discussed in  FIG.  4   . The lower conduit  310  can have a length-to-diameter ratio of greater than about 5; alternatively, greater than about 10; alternatively, greater than about 15; alternatively, in a range of from about 5 to about 20. This ratio can be calculated for embodiments of the lower conduit  310  where the length of the lower conduit  310  does not include the length of elbow connectors  302  and  306 . Alternatively, this ratio can be calculated for embodiments of the lower conduit  310  where the elbow connector  302  and/or elbow connector  306  is considered to be part of the lower conduit  310 , and the length of the lower conduit  310  includes the length of the tubular structure that is not curved. 
     The riser  320  can be embodied as a tubular structure through which the reaction mixture (e.g., beginning as the downcomer product mixture, optionally with added recycled monomer, comonomer, and/or diluent, and changing in composition along the length of the riser  320 ) passes from bottom  329  to top  328 . The longitudinal axis of the riser  320  can be oriented substantially vertically, as is shown in  FIG.  1    and  FIG.  2   . The riser  320  can have a width-to-height ratio of less than about 0.1; alternatively, less than about 0.06; alternatively, less than about 0.05; alternatively, less than about 0.03; alternatively, in a range of from about 0.03 to about 0.1. The width of the riser  320  can be the diameter of the tubular structure. The height of the riser  320  can be the height of the polymerization zone  321 . This width-to-height ratio can be calculated for embodiments of the riser  320  where the height of the riser  320  does not include the height of elbow connectors  302  and  304 . Alternatively, this ratio can be calculated for embodiments of the riser  320  where the elbow connector  302  and/or elbow connector  304  is considered to be part of the riser  320 , and the height of the riser  320  includes the height of the tubular structure and the height of one or both of elbow connectors  302  and  304 . 
     The upper conduit  330  can be embodied as a tubular structure through which a reaction mixture (e.g., the riser product mixture) passes from end  331  to end  332 . The longitudinal axis of the upper conduit  330  can be oriented substantially horizontally, as shown in  FIG.  1    and  FIG.  2   . Alternatively, the longitudinal axis of the upper conduit  330  can be oriented at an angle greater than 0° and less than 15° with respect to horizontal, as is discussed in  FIG.  10   . The upper conduit  330  can have a length-to-diameter ratio of greater than about 5; alternatively, greater than about 10; alternatively, greater than about 15; alternatively, in a range of from about 5 to about 20. This ratio can be calculated for embodiments of the upper conduit  330  where the length of the lower conduit  330  does not include the length of the elbow connector  304 . Alternatively, this ratio can be calculated for embodiments of the upper conduit  330  where the elbow connector  304  is considered to be part of the upper conduit  330 , and the length of the upper conduit  330  includes the length of the tubular structure and the length of the elbow connector  304 . 
     The liquid barrier, or barrier section,  360  is part of the downcomer  340 , located in the top portion  348  of the downcomer  340  above the polymerization zone  341 . The liquid barrier  360  can be embodied as part of the tubular structure of the downcomer  340  and having a liquid therein, through which polyolefin particles settle and subsequently flow into the polymerization zone  341 . The diameter of the tubular structure of the liquid barrier  360  can correspond to the diameter of the downcomer  340 . The height of the liquid barrier  360  can contribute to the height of the downcomer  340 . The liquid in the liquid barrier  360  can be an inert liquid, in that, the liquid is inert to the polymerization of the olefins. The inert liquid can be any of the hydrocarbons described herein that are suitable for use as a diluent (e.g., one or a combination of alkanes having 2 to 7 carbon atoms, being straight chain or branched, such as propane, isobutane, n-butane, n-pentane, isopentane, neopentane, n-hexane, cyclohexane, n-heptane, methylcyclohexane, or combinations thereof). In an aspect, the concentration of the inert liquid in the liquid barrier  360  is greater than a concentration of the inert liquid in the downcomer  340  and in the riser  320 . 
     The downcomer  340  can be embodied as a tubular structure through which the reaction mixture (e.g., changing in composition along the length of the downcomer  340 ) passes from top  348  to bottom  349 . The longitudinal axis of the downcomer  340  can be oriented substantially vertically, as is shown in  FIG.  1    and  FIG.  2   . The downcomer  340  can have can have a width-to-height ratio of less than about 0.1; alternatively, less than about 0.06; alternatively, less than about 0.05; alternatively, less than about 0.03; alternatively, in a range of from about 0.03 to about 0.1. The width of the downcomer  340  can be the diameter of the tubular structure. The height of the downcomer  340  can be the sum of the height of the polymerization zone  341  and the height of the liquid barrier  360 . The width-to-height ratio can be calculated for embodiments of the downcomer  340  where the height of the downcomer  340  does not include the height of elbow connector306. Alternatively, this ratio can be calculated for embodiments of the downcomer  340  where the elbow connector  306  is considered to be part of the downcomer  340 , and the height of the downcomer  340  includes the height of the tubular structure and the height of the elbow connector  306 . 
     In an alternative aspect, the downcomer  340  can have a diameter than varies from top to bottom of the downcomer  340 , such as a conical shape. In another alternative aspect, a portion of the downcomer  340  can have a diameter than varies from top to bottom of said portion. In such an aspect, the downcomer  340  may have another portion (e.g., a tubular structure) above the varied portion (e.g., conical structure) and/or another portion (e.g., a tubular structure) below the varied portion. For example, as shown in  FIG.  5 D , a bottom portion  349  of the downcomer  340  can be conical in shape, while the remaining portion of the downcomer  340  that is above the bottom portion  340  can be a tubular structure. In aspects where both a portion above and a portion below the varied portion are used, the diameter of the portion above the varied portion can be greater than the diameter of the portion below the varied portion. Without being limited by theory, it is believed that varying the diameter of the downcomer  340  such that the diameter decreases in a vertically downward direction at least for a portion of the downcomer  340  can facilitate an increase in the velocity of the polymer bed than moves downwardly through the downcomer  340 . 
     Each of elbow connectors  302 ,  304 , and  306  can be embodied as a tubular structure that changes the direction of flow of the reaction mixture in the MZCR  300 . Elbow connector  302  can change the direction of flow of the reaction mixture from the direction of flow provided in lower conduit  310  to the direction of flow in the riser  320 . Elbow connector  304  can change the direction of flow of the reaction mixture from the direction of flow provided in the riser  320  to the direction of flow in the upper conduit  330 . Elbow connector  306  can change the direction of flow of the reaction mixture from the direction of flow provided in the downcomer  340  to the direction of flow in the lower conduit  310 . The angle between the ends of each elbow connector  302 ,  304 ,  306  can independently vary from about 45° to about 135°. 
     Elbow connector  302  can connect to the bottom portion  329  of the riser  320  and to the end  312  of the lower conduit  310 . More specifically, end  302   a  of the elbow connector  302  can connect to the bottom portion  329  of the riser  320 , and end  302   b  of the elbow connector  302  can connect to the end  312  of the lower conduit  310 . Elbow connector  304  can connect to the top portion  328  of the riser  320  and to the end  331  of the upper conduit  330 . More specifically, end  304   a  of the elbow connector  304  can connect to the top portion  328  of the riser  320 , and end  304   b  of the elbow connector  304  can connect to the end  331  of the upper conduit  330 . Elbow connector  306  can connect to the bottom portion  349  of the downcomer  340  and to the end  311  of the lower conduit  310 . More specifically, end  306   a  of the elbow connector  306  can connect to the bottom portion  349  of the downcomer  340 , and end  306   b  of the elbow connector  306  can connect to the end  311  of the lower conduit  310 . 
     In an aspect, at least one of the elbow connectors  302 ,  304 , or  306  has an inner diameter (d) and a radius (R c ) of an inner curvature such that the elbow connector  302 ,  304 , or  306  configured to maintain a Dean number (D n ) of the reaction mixture flowing therein to be a value in a range of about 1,000,000 to about 5,000,000, where D n =ρVd/µ*(d/2R c ) ½  and where ρ is a density of the reaction mixture, V is a circulation velocity of the reaction mixture, and µ is a dynamic viscosity of the reaction mixture. The density, circulation velocity, and the dynamic viscosity are the values for the reaction mixture in the respective elbow connectors  302 ,  304 , or  306 . 
     The separator  350  of the MZCR  300  can be embodied as a flash tank, a flash vessel, a flash chamber, a cyclone, a high efficiency cyclone, or a centrifuge. The end  332  of the upper conduit  330  can be fluidly connected to the separator  350  proximate a top  354  of the separator  350 . The separator  350  is configured to separate the reaction mixture (e.g., the riser product mixture comprising solid polyolefin particles and a gas mixture) received from the upper conduit  330  into polyolefin particles and gases. The gases are removed from the separator  350  via vapor conduit  353 . The polyolefin particles settle in bottom of the separator  350  and flow downwardly through an outlet  352  of the separator  350  into the liquid barrier  360 . 
     The MZCR  300  has various feed lines that can be configured to inject components of a reaction mixture for polymerization in the polymerization zone  321  of the riser  320  and to inject components of a reaction mixture for polymerization in the polymerization zone  341  of the downcomer  340 . 
       FIG.  1    shows a catalyst feed line  322  configured to feed catalyst for polymerization of an olefin in the polymerization zone  321  of the riser  320 .  FIG.  1    also shows an olefin monomer feed line  342 , an olefin comonomer feed line  343 , a hydrogen feed line  344 , and a diluent feed line  345  configured to feed each of the respective components to the downcomer  340  for polymerization of one or more olefins in the polymerization zone  341  of the downcomer  340 . 
       FIG.  2    shows additional inlet feed lines can be configured to deliver components for polymerization in the polymerization zone  321  of the riser  320 . An olefin monomer feed line  323 , an olefin comonomer feed line  324 , and a diluent feed line  345  configured to feed each of the respective components to the downcomer  340  for polymerization of one or more olefins in the polymerization zone  321  of the riser  320 . 
     While  FIG.  1    and  FIG.  2    show one feed line  322 ,  323 ,  324 ,  325 ,  342 ,  343 , and  344  configured to inject the respective component into the riser  320  and downcomer  340 , it is contemplated that more than one feed line can be used to inject any of the olefin monomer, olefin comonomer, polymerization catalyst, diluent, and hydrogen. Further, in aspects where multiple feed lines for a component are used, it is contemplated that the feed lines for a given components are placed in multiple locations. For example, multiple comonomer feed lines  343  can be located at various locations on the downcomer  340  of the MZCR  300 . 
     Alternative configurations in  FIG.  1    include no feed lines for the riser  320 . Alternative configurations in  FIG.  1    also include additional feed lines  323 ,  324 , and  325  configured to feed components as discussed above into the reaction mixture that flows through the riser  320 . 
     The MZCR  300  includes a product discharge conduit  370  fluidly connected to the bottom portion  349  of the downcomer  340 . A product mixture containing polyolefin particles is withdrawn from the MZCR  300  via the product discharge conduit  370 . In  FIG.  1   , a product mixture containing the multimodal polyolefin is withdrawn from the MZCR  300  via the product discharge conduit  370 . In  FIG.  2   , a product mixture containing a polyolefin is withdrawn from the MZCR  300  via the product discharge conduit  370 .  FIG.  1    and  FIG.  2    show the product discharge conduit  370  fluidly connected to a bottom portion  349  of the MZCR  300 . However, it is contemplated that the product discharge conduit  370  can fluidly connected anywhere on the MZCR  300  of  FIG.  1   , such as i) to a bottom half of the downcomer  340 , ii) on or near a bottom tangent of the downcomer  340 , or iii) somewhere along the outer radius of the elbow connector  306  or on the lower conduit  310 . 
     In an aspect, the bottom tangent of the downcomer  340  is the location at the bottom of the downcomer  340  that is the tangent before any curvature or deviation from vertical. 
     In aspects, the product discharge conduit  370  can be located at or above the bottom tangent of the downcomer  340 . More specification, the product discharge conduit  370  can be located above the bottom tangent of the downcomer  340  for a distance that is 0% to 50% of the total height of the downcomer  340 . In an alternative aspect, the product discharge conduit  370  can be located on a curvature of the downcomer  340 , such as on the elbow connector  306 . In an alternative aspect, the product discharge conduit  370  can be located on a curvature of the elbow connector  306  that is connected to the downcomer  340 . 
     In an embodiment, the product discharge conduit  370  can include a take-off valve that is configured as a continuous take-off valve or a discontinuous take-off valve. A continuous take-off valve can regulate the removal of the produce mixture from the MZCR  300  such that product mixture is removed on a continuous basis. A discontinuous take-off valve can regulate the removal of the product mixture from the MZCR  300  on a discontinuous basis, for example, opening and shutting such that the flow of the product mixture through the discontinuous take-off valve is not continuous. In an aspect, the take-off valve can be part of the polyolefin product separation system  400 , such as take-off valve  410  described in  FIG.  9    below. 
     In an aspect, the product mixture in the product discharge conduit  370  can have a concentration of solid polyolefin particles greater than 50 wt.%, 60 , wt.%, 70 wt.%, 80 wt.%, 90 wt.% based on a total weight of the mixture. 
     Polymerization conditions in the polymerization zone  321  and polymerization zone  341  of the MZCR  300  can include the conditions suitable for gas phase polymerization reactions. In aspects, the polymerization zone  321  and the polymerization zone  341  can each operate with a temperature ranging from about 50° C. (122° F.) to about 120° C. (248° F.) and a pressure ranging from about 14.7 psia to about 1,000 psia (0.101 MPaa to about 6.9 MPaa). 
     The olefin monomer polymerized in polymerization zone  321  and/or polymerization zone  341  of the MZCR  300  can be an aliphatic 1-olefin containing from 2 to 8 carbon atoms, e.g., ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, or 1-octene. In an embodiment, the olefin monomer is ethylene or propylene. 
     Polymerization of the olefin monomer in the polymerization zone  321  and/or polymerization zone  341  of the MZCR  300  can optionally be performed with one or more comonomers that are an aliphatic 1-olefin containing from 3 to about 10 carbon atoms, e.g., propylene, 1-butene, 1-pentene, 1-hexene, 1-pentene, 1-heptene, 1-octene, 1-nonene, or 1-decene. In embodiments, the olefin comonomer can be propylene, 1-butene, 1-hexene, 1-octene, or a combination thereof. 
     Polymerization in the polymerization zone  321  and/or polymerization zone  341  of the MZCR  300  can occur in the presence of a hydrocarbon diluent that is inert to the polymerization reaction. Examples of a diluent include propane, isobutane, n-butane, n-pentane, isopentane, neopentane, n-hexane, cyclohexane, n-heptane, methylcyclohexane, or combinations thereof. 
     A reaction mixture containing polyolefin particles and a gas mixture can flow upwardly through the second polymerization zone  321  in the riser  320 , through the upper conduit  330 , and into the separator  350 . The reaction mixture in the riser  320  (e.g., the riser reaction mixture) can have a gas mixture of at least two components selected from olefin monomer, diluent, and a polymerization catalyst. The reaction mixture exiting the riser  320  (e.g., the riser product mixture) can likewise have a gas mixture of at least two components selected from olefin monomer, diluent, and a polymerization catalyst. 
     Gases recovered from the reaction mixture (e.g., the riser product mixture) are removed from the separator  350  via vapor conduit  353 , while polyolefin particles recovered from the reaction mixture fall to the bottom of the separator  350  and flow downwardly through an outlet  352  of the separator  350  into the liquid barrier  360 . The polyolefin particles settle downwardly through the liquid in the liquid barrier  360  by gravity and flow into the top  348  of the downcomer  340 . The polyolefin particles become part of a separate reaction mixture in the downcomer  340 . 
     The reaction mixture in the downcomer  340  (e.g., the downcomer reaction mixture) can have a gas mixture of at least two components selected from hydrogen, olefin monomer, olefin comonomer, diluent, and a polymerization catalyst. The reaction mixture exiting the downcomer  340  (e.g., the downcomer product mixture) can likewise have a gas mixture of at least two components selected from hydrogen, olefin monomer, olefin comonomer, diluent, and a polymerization catalyst. The polyolefin particles in the downcomer reaction mixture can flow through the polymerization zone  341  of the downcomer  340  downwardly by gravity, through the lower conduit  310 , and back into the polymerization zone  321 . A circulation of polyolefin(s) is established in the flow path defined by the lower conduit  310 , riser  320 , upper conduit  330 , separator  350 , downcomer  340 , and any pieces of conduit considered separate from the lower conduit  310 , riser  320 , upper conduit  330 , and downcomer  340  (e.g., any connecting pieces such as elbow connectors  302 ,  304 , and  306 ). In an aspect, the reaction mixture in the downcomer  340  (e.g., the downcomer reaction mixture) can have a gas composition that is different than the gas composition in the riser  320  (e.g., the riser reaction mixture). 
     The MZCR  300  affords the flexibility that the reaction mixture of the downcomer  340  can have a different gaseous composition than the reaction mixture in the riser  320 , which advantageously provides for producing two different polyolefins in the MZCR  300 . In this aspect, the polyolefin particles flowing in the loop of the MZCR  300  can include the polyolefin made in the riser  320 , the polyolefin made in the downcomer  340 , and optionally for the order of reactors  100  and  300  shown in  FIG.  1   , the first polyolefin produced in the first reactor  100 . Alternatively, the reaction mixture of the downcomer  340  can have the same gaseous composition as the reaction mixture in the riser  320 . Thus, in this aspect, the polyolefin particles flowing in the loop of the MZCR  300  can include the polyolefin made in the MZCR  300 , and optionally for the order of reactors  100  and  300  shown in  FIG.  1   , the polyolefin produced in the first reactor  100 . It is believed that the configuration of the MZCR  300  in combination with the first reactor  100  can improve product properties, improve product homogeneity, and reduce the number of gels. 
     The flow in the second polymerization zone  321  in the riser  320  can be under fast fluidization conditions. The conditions for fast fluidization are obtained when the velocity of the fluidizing gas (e.g., the diluent and/or condensing agent) is higher than the transport velocity of the polyolefin solids, and the pressure gradient along the direction of flow is a monotonic function of the quantity of solid, for equal flow rate and density of the fluidizing gas. In contrast, conventional fluidized-bed technology utilized in gas phase reactors maintains the fluidizing-gas velocity well below the transport velocity, in order to avoid solids entrainment and particle carryover into the gas recycle system of the gas phase reactor. 
     The flow in the third polymerization zone  341  in the downcomer  340  can be under plug flow conditions. The polyolefin particles can form a moving bed of solid particles that move downwardly through the polymerization zone  341  in the downcomer  340 , where polyolefin particles exiting the bed of solid particles into the lower conduit  310  make room for polyolefin particles entering the bed from the liquid barrier  360 . It is contemplated that a positive gain in pressure obtained by the downward flow of the reaction mixture in the downcomer  340  can provide momentum of the polyolefin particles that is suitable to reintroduce the polyolefin particles into the riser  320  via the lower conduit  310 . In this way, a “loop” circulation is established. For the order of reactors  100  and  300  shown in  FIG.  1   , the circulation back to the riser  320  can be facilitated by one or more of: 1) the introduction of the first polyolefin produced in the first reactor  100  into the MCZR  300  via conduit  202 , 2) the introduction of one or more of unreacted olefin monomer, unreacted olefin comonomer, and diluent via conduit  502  and/or conduit  503 . For the order of reactors  100  and  300  shown in  FIG.  2   , the circulation back to the riser  320  can be facilitated by the introduction of one or more of unreacted olefin monomer, unreacted olefin comonomer, and diluent via conduit  502  and/or conduit  503 . Alternative or additional embodiments of the MZCR  300  can include equipment for facilitating the recirculation of the polyolefin particles from the downcomer  340  to the riser  320 , such as the eductor  375  shown in  FIGS.  5 A,  5 B,  5 D- 5 H, and  6 B  and/or standpipe shown in  FIGS.  5 C,  5 I,  5 J, and  6 B- 6 C . 
     In an aspect, the polyolefin particles of the moving bed of solid particles can have a packed bed configuration. That is, the polyolefin particles can have a high concentration in the mixture of solids and gas/liquid moving through the downcomer  340  as compared to the concentration of gas and/or liquid that is contained in the mixture. The concentration of solid polyolefin particles in the moving mixture can be greater than 50 wt.%, 60 , wt.%, 70 wt.%, 80 wt.%, 90 wt.% based on a total weight of the mixture (e.g., based on a “plug” of the moving mixture). An advantage of having a high concentration of polyolefin particles in the mixture is that the portion(s) of the mixture removed in the product discharge conduit  370  require smaller capacity for downstream equipment configured to separate the polyolefin particles from the gas and any liquid. 
     In aspects, the lower conduit  310  can be configured such that the reaction mixture (e.g., the downcomer product mixture, optionally with added recycled components) can flow in the lower conduit  310  at a velocity that is i) greater than a saltation velocity of the reaction mixture and up to about 30.48 m/s (100 ft/sec), ii) i) greater than a saltation velocity of the reaction mixture and greater than about 0.508 m/s (20 ft/sec),iii) greater than a saltation velocity of the reaction mixture and greater than about 0.762 m/s (30 ft/sec), iv) greater than a saltation velocity of the reaction mixture and greater than about 1.016 m/s (40 ft/sec), v) greater than a saltation velocity of the reaction mixture and greater than about 1.27 m/s (50 ft/sec), vi) greater than a saltation velocity of the reaction mixture and greater than about 1.52 m/s (60 ft/sec), vi) from about 1.52 m/s (60 ft/sec) to about 30.48 m/s (100 ft/sec), vii) from about 0.762 m/s (30 ft/sec) to about 1.27 m/s (50 ft/sec), or viii) greater than 110% of the saltation velocity of the reaction mixture. In further aspects of the disclosure, the upper conduit  330  is configured such that the reaction mixture (e.g., the riser product mixture) can flow in the upper conduit  330  at a velocity that is i) greater than a saltation velocity of the reaction mixture and up to about 30.48 m/s (100 ft/sec), ii) i) greater than a saltation velocity of the reaction mixture and greater than about 0.508 m/s (20 ft/sec),iii) greater than a saltation velocity of the reaction mixture and greater than about 0.762 m/s (30 ft/sec), iv) greater than a saltation velocity of the reaction mixture and greater than about 1.016 m/s (40 ft/sec), v) greater than a saltation velocity of the reaction mixture and greater than about 1.27 m/s (50 ft/sec), vi) greater than a saltation velocity of the reaction mixture and greater than about 1.52 m/s (60 ft/sec), vi) from about 1.52 m/s (60 ft/sec) to about 30.48 m/s (100 ft/sec), vii) from about 0.762 m/s (30 ft/sec) to about 1.27 m/s (50 ft/sec), or viii) greater than 110% of the saltation velocity of the reaction mixture. 
     Circulation of polyolefin particles in the loop of the MZCR  300  can be about 50 to about 250 times the multimodal polyolefin production rate. In aspects, the polyolefin particles can circulate the loop from 1 to about 250 cycles before being withdrawn from the MZCR  300 . In a particular aspect, the polyolefin particles can circulate about 40, 50, 60, 70, 80, 90, or 100 cycles before being withdrawn from the MZCR  300 . In aspects, the time for a polyolefin particle to circulate the loop of the MZCR  300  can be from about 0.5 minutes to about 10 minutes; alternatively, about 1 minute to about 8 minutes; alternatively, about 1 minute to about 7 minutes; alternatively, about 1 minute to about 6 minutes; alternatively, about 1 minute to about 5 minutes; alternatively, about 1 minute to about 4 minutes; alternatively, about 1 minute to about 3 minutes; alternatively, about 1 minute to about 2 minutes; alternatively, about 2 minutes to about 3 minutes; alternatively, about 2 minutes. 
     In aspects, the average residence time of polyolefin particles in the MZCR  300  can range from about 0.25 hours to about 5 hours; alternatively, about 0.5 hours to about 4 hours; alternatively, about 1 hour to about 3 hours; alternatively, about 2 hours. In aspects, the average residence time of the riser reaction mixture in the polymerization zone  321  of the riser  320  during a single pass through the polymerization zone  321  is in a range of about 1 second to about 5 minutes. In additional aspects, the residence time of the downcomer reaction mixture in the polymerization zone  341  of the downcomer  340  during a single pass through the polymerization zone  341  is in a range of about 5 second to about 15 minutes. The polyolefin particles can be circulated in the loop of the MZCR  300  from 1 to about 100,000 cycles. The total average residence time of polyolefin particles in the MZCR  300  can be on the order of hours. 
     In aspects, at least a portion of the MZCR  300  can be made carbon steel, stainless steel, or a combination of these materials. In a further aspect the carbon steel can be a low temperature carbon steel. 
     In an aspect, an internal surface  379  of the MZCR  300 , and optionally any flanges of the MZCR  300 , can have a rust inhibitor coating. The rust inhibitor coating can be applied during manufacture of the components of the MZCR  300  and be configured to inhibit rust of the components, for example, during transport to and assembly at a plant site. 
     In an aspect, the internal surface  379  of the MZCR  300  can be polished to a root mean square of less than about 3.8 microns (150 microinches); alternatively, less than about 2.54 microns (100 microinches); alternatively, less than about 1.27 microns (50 microinches); alternatively, in a range of from about 0.254 m (10 microinches) to about 1.27 microns (50 microinches). 
     In an aspect, only the internal surface of the downcomer  340  of the MZCR  300  is polished to a root mean square value disclosed herein; alternatively, only the internal surface of the riser  320  of the MZCR  300  is polished to a root mean square value disclosed herein; alternatively, only the internal surfaces of the downcomer  340  and the riser  320  are polished to a root mean square value disclosed herein. In an additional aspect, the internal surface  109  of the first reactor  100  can be polished to a root mean square value disclosed herein. 
     The multiple zone polyolefin polymerization in  FIG.  1    and in  FIG.  2    also can include polyolefin product separation systems  200  and  400 .  FIG.  1    and  FIG.  2    generally illustrate that one of reactors  100  and  300  is upstream of the other. The product separation system  200  is configured to recover polyolefin product from the product mixture withdrawn from the upstream reactor and between the reactors  100  and  300  such that the polyolefin produced in the upstream reactor can be fed to the downstream reactor. The product separation system  400  is configured to recovery the multimodal polyolefin from the product mixture withdrawn from the downstream reactor. 
     The product separation system  200  can be configured to separate one or more components in the product mixture (e.g., unreacted monomer, unreacted comonomer, diluent, catalyst, co-catalyst, or combinations thereof) from the polyolefin produced in the upstream reactor such that the amount of these components fed to the downstream reactor is controlled, which can affect the composition of the polymerization zone(s) in the downstream reactor. 
     In  FIG.  1   , the product separation system  200  is configured to receive a product mixture containing the first polyolefin via the product discharge conduit  110 , and to separate gaseous components of the product mixture from the first polyolefin. The gaseous components can include one or more of unreacted olefin monomer, unreacted olefin comonomer, diluent, hydrogen, nitrogen, and any additive for the polymerization of the olefin monomer in the first reactor  100 . The gaseous components can flow from the product separation system  200  in conduit  201 . The first polyolefin can flow in conduit  202  for injection into the MZCR  300 . 
     In  FIG.  2   , the product separation system  200  is configured to receive a product mixture containing the second polyolefin and the third polyolefin via the product discharge conduit  370 , and to separate gaseous components of the product mixture from the second and third polyolefins. The gaseous components can include one or more of unreacted olefin monomer, unreacted olefin comonomer, diluent, hydrogen, nitrogen, and any additive for the polymerization of the olefin monomer in the MZCR  300 . The gaseous components can flow from the product separation system  200  in conduit  201 . The second and third polyolefins can flow in conduit  202  for injection into the first reactor  100 . 
     More detailed embodiments and aspects of the product separation system  200  are discussed for  FIGS.  10 A to  10 C . 
     The product separation system  400  is configured to recover the multimodal polyolefin product of this disclosure from the effluent of whichever reactor  100  or  300  is the downstream reactor (e.g., the MZCR  300  in  FIG.  1    or the first reactor  100  in  FIG.  2   ). The product separation system  400  can be configured to separate one or more components in the reaction effluent (e.g., unreacted monomer, unreacted comonomer, diluent, catalyst, co-catalyst, or combinations thereof) from the multimodal polyolefin. The multimodal polyolefin can then be further treated, sent to a container, processed (e.g., processed into pellets), or a combination thereof. 
     In  FIG.  1   , the first polyolefin is circulated in the MZCR  300  in the reaction mixtures which flow through the riser  320  and the downcomer  340 , so that the second polyolefin is formed in the riser  320  and the third polyolefin is formed in the downcomer  340  in the presence of the first polyolefin to produce a multimodal polyolefin of this disclosure. In  FIG.  1   , the product separation system  400  is configured to receive a product mixture containing the multimodal polyolefin via the product discharge conduit  370 , and to separate the gaseous components of the product mixture from the multimodal polyolefin. The gaseous components can include one or more of unreacted olefin monomer, unreacted olefin comonomer, diluent, hydrogen, anti-static agent, nitrogen, and any additive for the polymerization of the olefin monomer in the MZCR  300 . 
     In its simplest form, the product separation system  400  can be configured to separate polyolefin particles from the gaseous components such that the multimodal polyolefin flows in conduit  401  and the gaseous components flow in another conduit for fluidly coupled for recycle of the components back to the first reactor  100  and/or the MZCR  300 .  FIG.  1    and  FIG.  2    show an alternative recovery in that the product separation system  400  can be configured to separate polyolefin particles from the gaseous components, and the gaseous components can be separated from one another. The multimodal polyolefin can flow in conduit  401  for transport, storage, or processing (e.g., treatment). The product separation system  400  can be configured to separate the gaseous components into olefin monomer that flows in conduit  402 , olefin comonomer that flows in conduit  403 , diluent that flows in conduit  404 , hydrocarbons that are heavier than the diluent that flow in heavies conduit  405 , and light gases that are lighter than the unreacted monomer that flow in a waste gas conduit  406 . 
     In  FIG.  2   , the first polyolefin is formed in the first reactor  100  in the presence of the second and third polyolefins to produce a multimodal polyolefin of this disclosure. In  FIG.  2   , the product separation system  400  is configured to receive a product mixture containing the multimodal polyolefin via the product discharge conduit  110 , and to separate the gaseous components of the product mixture from the multimodal polyolefin. The gaseous components can include one or more of unreacted olefin monomer, unreacted olefin comonomer, diluent, hydrogen, anti-static agent, nitrogen, and any additive for the polymerization of the olefin monomer in the first reactor  100 . The multimodal polyolefin can flow in conduit  401  for transport, storage, or processing (e.g., treatment). Like that shown in  FIG.  1   , the product separation system  400  of  FIG.  2    can separate the gaseous components from one another. In an aspect, the product separation system  400  can separate the gaseous components into olefin monomer that flows in conduit  402 , olefin comonomer that flows in conduit  403 , diluent that flows in conduit  404 , hydrocarbons that are heavier than the diluent flow in heavies conduit  405 , and light gases that are lighter than the unreacted monomer flow in waste gas conduit  406 . 
     More detailed embodiments and aspects of the product separation system  400  are described for  FIG.  9   . 
     In both  FIG.  1    and  FIG.  2   , the vapor recycle system  500  is configured to recycle gases recovered from the separator  350  of the MZCR  300 . Gases flow in vapor conduit  353  and into the vapor recycle system  500 . The vapor recycle system  500  can be configured to condense at least a portion of the gases in the vapor conduit  353  (e.g., using a compressor, heat exchanger, or both) such that liquid diluent can optionally flow to the liquid barrier  360  in diluent recycle conduit  345 . The vapor recycle system  500  can also be configured to recycle other gases recovered from the vapor conduit  353  back to the MZCR  300  via conduits  501 ,  502 , and  503 . Particularly, unreacted monomer and optionally unreacted comonomer can be recycled back to the MZCR  300  at the elbow connector  306  via conduit  502  and at the elbow connector  302  via conduit  503 . In embodiments, the vapor recycle system  500  can be configured similar to a gas recycle system of a gas phase reactor such as that described for  FIGS.  10 A to  10 C . The vapor recycle system  500  can be configured to condense the diluent for use in the liquid barrier  360  while leaving the unreacted monomer and optional unreacted comonomer in the gas phase. 
     Having separately described each of the first reaction  100 , product separation system  200 , MZCR  300 , product separation system  400 , and vapor recycle system  500  above, the process flow of the multiple zone polymerizations in  FIG.  1    and in  FIG.  2    is now discussed. 
     In  FIG.  1   , the first reactor  100  is operated under polymerization conditions so as to produce the first polyolefin in the polymerization zone  112 . Product separation system  200  is configured to receive a product mixture from the first reactor  100  via the product discharge conduit  110  and to separate gaseous components in the product mixture from the first polyolefin in the product mixture. The gaseous components can flow from the product separation system  200  via conduit  201  for further separation, for recycling to the first reactor  100 , or combination thereof. The first polyolefin can flow from the product separation system  200  via conduit  202 . The MZCR  300  can be configured to receive the first polyolefin, for example, in the elbow connector  302  or in the lower conduit  110 . The MZCR  300  can circulate the first polyolefin in one or more reaction mixtures through the loop of the MZCR  300  (discussed above), while operating under polymerization conditions to concurrently produce polyolefin(s) in the polymerization zone  321  of the riser  320  and in the polymerization zone  341  of the downcomer  340 . The vapor recycle system  500  is configured to recycle diluent, unreacted monomer, and any unreacted comonomer recovered from the separator  350  of the MZCR  300  back to the elbow connector  302  and elbow connector  306  of the MZCR  300 . The resulting polymer that is comprised of the first polyolefin produced in the first reactor  100  and the polyolefin(s) produced in the riser  320  and downcomer  340  of the MZCR  300  is the multimodal polyolefin product of the disclosure. The MZCR  300  is configured to discharge the multimodal polyolefin via the product discharge conduit  370 . Product separation system  400  is configured to receive the product mixture from the MZCR  300  via the product discharge conduit  370  and to separate gaseous components in the product mixture from the multimodal polyolefin in the product mixture. The multimodal polyolefin can flow from the product separation system  400  via conduit  401 . The gaseous components can flow from the product separation system  400  via conduits  402 ,  403 ,  404 ,  405 , and  406 , for further use such as treatment and/or for recycle to the first reactor  100  and/or the MZCR  300 . 
     In  FIG.  2   , the MZCR  300  can circulate polyolefin particles through the loop of the MZCR  300  in the various reaction mixtures (discussed above, e.g., downcomer reaction mixture, downcomer product mixture, riser reaction mixture, and riser product mixture), while operating under polymerization conditions to produce one or more polyolefins in the polymerization zone  321  of the riser  320  and in the polymerization zone  341  of the downcomer  340 . The vapor recycle system  500  is configured to recycle diluent, unreacted monomer, and any unreacted comonomer recovered from the separator  350  of the MZCR  300  back to the elbow connector  302  and elbow connector  306  of the MZCR  300 . Product separation system  200  is configured to receive a product mixture from the MZCR  300  via the product discharge conduit  370  and to separate gaseous components in the product mixture from the polyolefin(s) in the product mixture. The gaseous components can flow from the product separation system  200  via conduit  201  for further separation, for recycling to the MZCR  300 , or combination thereof. The polyolefin(s) can flow from the product separation system  200  via conduit  202 . The first reactor  100  can be configured to receive the polyolefin(s). The first reactor  100  is operated under polymerization conditions so as to produce the first polyolefin in the polymerization zone  112  in the presence of the polyolefin(s) produced in the MZCR  300 . The resulting polymer that is comprised of the first polyolefin produced in the first reactor  100  and the polyolefin(s) produced in the riser  320  and downcomer  340  of the MZCR  300  is the multimodal polyolefin product of the disclosure. The first reactor  100  is configured to discharge the multimodal polyolefin via the product discharge conduit  110 . Product separation system  400  is configured to receive the product mixture from the first reactor via the product discharge conduit  110  and to separate gaseous components in the product mixture from the multimodal polyolefin in the product mixture. The multimodal polyolefin can flow from the product separation system  400  via conduit  401 . The gaseous components can flow from the product separation system  400  via conduits  402 ,  403 ,  404 ,  405 , and  406 , for further use such as treatment and/or for recycle to the first reactor  100  and/or the MZCR  300 . 
     In an aspect, an amount of from about 20 to about 80 wt.%, alternatively from about 40 to about 60 wt.%, alternatively from about 45 to about 55 wt.%, alternatively about 50 wt.% of the multimodal polyolefin can comprise the first polyolefin produced in the first reactor  100  and an amount of from about 80 to about 20 wt.%, alternatively from about 60 to about 40 wt.%, alternatively from about 55 to about 45 wt.%, alternatively about 50 wt.% of the multimodal polyolefin can comprise the second polyolefin and the third polyolefin produced in the MZCR  300 . 
     The concentration of the olefin monomer, olefin comonomer, hydrogen, or combinations thereof can differ between the first reactor  100  and the MZCR  300 . Moreover, the concentration of the olefin monomer, olefin comonomer, hydrogen, or combinations thereof can differ between the riser  320  and the downcomer  340  of the MZCR. In an aspect, the concentration of the olefin monomer (e.g., ethylene, propylene, or butene) in the first reactor  100  can be from 0.1 to 10 wt.% on solids-free basis (i.e., the basis is the amount of gas or liquid to the exclusion of any solid polyolefin particles); the concentration of the olefin comonomer (e.g., 1-butene, 1-hexene, or 1-octene) in the first reactor  100  can be from 0.0 to 5 wt.% on a solids-free basis; the concentration of hydrogen in the first reactor  100  can be from 0.0 to about 5 mole% on a solids-free basis; or a combination thereof. In an aspect, the concentration of the olefin monomer (e.g., ethylene, propylene, or butene) in the MZCR  300  can be from 0.1 to 10 wt.% on solids-free basis (i.e., the basis is the amount of gas or liquid to the exclusion of any solid polyolefin particles); the concentration of the olefin comonomer (e.g., 1-butene, 1-hexene, or 1-octene) in the MZCR  300  can be from 0.0 to 5 wt.% on a solids-free basis; the concentration of hydrogen in the MZCR  300  can be from 0.0 to about 5 mole% on a solids-free basis; or a combination thereof. In aspects, the concentration of olefin monomer in the first reactor  100  can vary in the range disclosed above; the concentration of olefin comonomer in the first reactor  100  can vary in the range disclosed above; the concentration of hydrogen in the first reactor  100  can vary in the range disclosed above; the concentration of olefin monomer in the MZCR  300  can vary in the range disclosed above; the concentration of olefin comonomer in the MZCR  300  can vary in the range disclosed above; the concentration of hydrogen in the MZCR  300  can vary in the range disclosed above; or combination thereof. 
     In a particular aspect, the concentration of olefin monomer (e.g., ethylene, propylene, or butene) in the first reactor  100  can have from 1 to 6 wt.% ethylene, 0.0 to 1 wt.% olefin comonomer, and no hydrogen on a solids-free basis; the riser  230  of the MZCR  300  can have 2 to 10 wt.% ethylene, 0.1 to 3 wt.% olefin comonomer, and 0.2 to 2 mole% hydrogen on a solids-free basis; and the downcomer  340  of the MZCR  300  can have 3 to 20 wt.% ethylene, 0.5 to 8 wt.% olefin comonomer, and 0.0 to 0.5 mole% hydrogen. 
     In an aspect, the concentration of ethylene can be lowest in the first reactor  100  or in the downcomer  340  of the MZCR  300 . In another aspect, the concentration of ethylene can be greatest in the first reactor  100  or in the riser  320  of the MZCR  300 . 
     In an aspect, the concentration of hydrogen in the first reactor  100  can be greater than the concentration of hydrogen in the riser  320  of the MZCR  300 , and the concentration of hydrogen in the riser  320  of the MZCR  300  can be greater than the concentration of hydrogen in the downcomer  340  of the MZCR  300 . 
     In an aspect, the concentration of olefin comonomer in the first reactor  100  can be less than the concentration of olefin comonomer in riser  320  of the MZCR  300 , and the concentration of olefin comonomer in the riser  320  of the MZCR  300  can be less than the concentration of the olefin comonomer in the downcomer  340  of the MZCR  300 . 
     As discussed for the first reactor  100 , hydrogen can be used to regulate the molecular weight of the polyolefin produced in the MZCR  300 . In an aspect, the concentration of hydrogen in the first reactor  100  can be different than the concentration of hydrogen in the MZCR  300 . For example, the concentration of hydrogen in the first reactor  100  can be lower than the concentration of hydrogen in at least a part of the MZCR  300  (e.g., the downcomer  340 ). Additionally, the concentration of hydrogen in the MZCR  300  can be different in different parts of the MZCR  300  (e.g., a first concentration in the riser  320  and a second concentration in the downcomer  340 ). 
     In an aspect, the concentration of hydrogen can be on a gradient along a flow path in the MZCR  300 . For example, the concentration of hydrogen can decrease in a downward direction in the downcomer  340  downstream of the injection point for hydrogen feed line  344 ; the concentration of hydrogen can decrease in an upward direction in the riser  320 ; the concentration of hydrogen can decrease in the direction of arrow A in the lower conduit  310 ; the concentration of hydrogen can decrease in the direction of arrow B in the upper conduit  330 ; or combinations thereof. 
     In an aspect, the concentration of comonomer in the first reactor  100  can be different than the concentration comonomer in the MZCR  300 . For example, the concentration of comonomer in the first reactor  100  can be lower than the concentration of comonomer in at least a part of the MZCR  300  (e.g., the downcomer  340 ). Additionally, the concentration of comonomer in the MZCR  300  can be different in different parts of the MZCR  300  (e.g., a first concentration in the riser  320  and a second concentration in the downcomer  340 ). 
     In an aspect, the concentration of comonomer can be on a gradient along a flow path in the MZCR  300 . For example, the concentration of comonomer can decrease in a downward direction in the downcomer  340  downstream of the injection point for comonomer feed line  343 ; the concentration of comonomer can decrease in an upward direction in the riser  320 ; the concentration of comonomer can decrease in the direction of arrow A in the lower conduit  310 ; the concentration of comonomer can decrease in the direction of arrow B in the upper conduit  330 ; or combinations thereof. 
     Catalyst(s) 
     One or more polymerization catalyst can be used to polymerize olefin monomer(s) in the reactor  100  and in the MZCR  300 . The polymerization catalyst can be delivered to the reactor  100  or MZCR  300  in solution (e.g., catalyst dissolved in a solvent liquid), in suspension (e.g., a slurry of the catalyst in a carrier liquid), or in gaseous mixture (e.g., a mixture of particulate catalyst in a carrier gas). 
     Each polymerization catalyst used to polymerize olefin(s) in the reactor  100  and/or MZCR  300  can be a transition metal-based catalyst system. The transition metal(s) included in the transition metal-based catalyst systems can be selected from Groups IIIB, IVB, VB, VIB, VIIB, or VIIIB. More particularly, the transition metal(s) included in the transition metal-based catalyst systems can be selected from nickel, chromium, titanium, zirconium, hafnium, vanadium, or a combination thereof. Examples of such catalyst systems include, but are not limited to, Ziegler-Natta based catalyst systems (e.g., Ziegler-based catalyst systems), chromium-based catalyst systems, metallocene-based catalyst systems, Phillips catalyst systems, coordination compound catalyst systems, post-metallocene catalyst systems, and the like, including combinations thereof. 
     The transition metal-based catalyst system can include a solid oxide support for the transition metal compounds. The solid oxide used to produce the support can comprise oxygen and one or more elements from Groups 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15 of the Periodic Table of Elements, or can comprise oxygen and one or more elements from the lanthanide or actinide elements. For instance, the solid oxide can comprise oxygen and at least one element selected from Al, B, Be, Bi, Cd, Co, Cr, Cu, Fe, Ga, La, Mn, Mo, Ni, Sb, Si, Sn, Sr, Th, Ti, V, W, P, Y, Zn, and Zr. Examples of solid oxide materials that can be used to form the activator-support can include, but are not limited to, Al 2 O 3 , B 2 O 3 , BeO, Bi 2 O 3 , CdO, Co 3 O 4 , Cr 2 O 3 , CuO, Fe 2 O 3 , Ga 2 O 3 , La 2 O 3 , Mn 2 O 3 , MoO 3 , NiO, P 2 O 5 , Sb 2 O 5 , SiO 2 , SnO 2 , SrO, ThO 2 , TiO 2 , V 2 O 5 , WO 3 , Y 2 O 3 , ZnO, ZrO 2 , and the like, including mixed oxides thereof, and combinations thereof. This includes co-gels or co-precipitates of different solid oxide materials. Accordingly, the solid oxide can comprise silica, alumina, silica-alumina, silica-coated alumina, aluminum phosphate, aluminophosphate, heteropolytungstate, titania, zirconia, magnesia, boria, zinc oxide, any mixed oxide thereof, or any combination thereof. The silica-alumina which can be used typically can have an alumina content from about 5 to about 95% by weight. In one embodiment, the alumina content of the silica-alumina can be from about 5 to about 50%, or from about 8% to about 30%, alumina by weight. In another embodiment, high alumina content silica-alumina compounds can be employed, in which the alumina content of these silica-alumina compounds typically can range from about 60% to about 90%, or from about 65% to about 80%, alumina by weight. According to yet another embodiment, the solid oxide component can comprise alumina without silica, and according to another embodiment, the solid oxide component can comprise silica without alumina. Moreover, as provided hereinabove, the solid oxide can comprise a silica-coated alumina. The solid oxide can have any suitable surface area, pore volume, and particle size, as would be recognized by those of skill in the art. 
     In another or additional aspect, the solid oxide support can be treated with an electron-withdrawing component. The electron-withdrawing component used to treat the solid oxide so as to form the activator-support can be any component that increases the Lewis or Brønsted acidity of the solid oxide upon treatment (as compared to the solid oxide that is not treated with at least one electron-withdrawing component). According to one aspect, the electron-withdrawing component can be an electron-withdrawing anion derived from a salt, an acid, or other compound, such as a volatile organic compound, that serves as a source or precursor for that anion. Examples of electron-withdrawing anions can include, but are not limited to, sulfate, bisulfate, fluoride, chloride, bromide, iodide, fluorosulfate, fluoroborate, phosphate, fluorophosphate, trifluoroacetate, triflate, fluorozirconate, fluorotitanate, phospho-tungstate, and the like, including mixtures and combinations thereof. In addition, other ionic or non-ionic compounds that serve as sources for these electron-withdrawing components also can be employed. It is contemplated that the electron-withdrawing component can comprise sulfate, bisulfate, fluoride, chloride, bromide, iodide, fluorosulfate, fluoroborate, phosphate, fluorophosphate, trifluoroacetate, triflate, fluorozirconate, fluorotitanate, and the like, or combinations thereof. Specific examples of the activator-support include, but are not limited to, fluorided alumina, chlorided alumina, bromided alumina, sulfated alumina, fluorided silica-alumina, chlorided silica-alumina, bromided silica-alumina, sulfated silica-alumina, fluorided silica-zirconia, chlorided silica-zirconia, bromided silica-zirconia, sulfated silica-zirconia, fluorided silica-titania, fluorided silica-coated alumina, sulfated silica-coated alumina, phosphated silica-coated alumina, and the like, as well as any mixture or combination thereof. 
     In additional aspects, the transition metal-based catalyst system can comprise an activator selected from an aluminoxane compound (e.g., methylaluminoxane), an organoboron compound, an organoborate compound (e.g., borate), an ionizing ionic compound, the solid oxide support treated with an electron-withdrawing component (referred to as an activator support), the like, or any combination thereof. 
     In additional aspects, the transition metal-based catalyst system can include one or more co-catalysts. Commonly used polymerization co-catalysts can include, but are not limited to, metal alkyl, or organometal, co-catalysts, with the metal encompassing boron, aluminum, zinc, and the like. Representative boron-containing co-catalysts include, but are not limited to, tri-n-butyl borane, tripropylborane, triethylborane, and combinations thereof. Representative aluminum-containing co-catalysts can include, but are not limited to, the organoaluminum compounds of trimethylaluminum, triethylaluminum, tri-n-propylaluminum, tri-n-butylaluminum, triisobutylaluminum, tri-n-hexylaluminum, tri-n-octylaluminum, diisobutylaluminum hydride, diethylaluminum ethoxide, diethylaluminum chloride, and the like, as well as any combination thereof. Representative zinc-containing co-catalysts include, but are not limited to, diethylzinc. 
     Each of the polymerization zones  112 ,  321 , and  341  can independently use any one or a combination of the polymerization catalysts disclosed herein. In an aspect of the multiple zone polymerization which produces the multi-modal polyolefin disclosed herein, a Ziegler-Natta catalyst can be used in each of the polymerization zone  112  of the first reactor  100 , the polymerization zone  321  of the riser of the MZCR  300 , and the polymerization zone  341  of the downcomer  340  of the MZCR. In an alternative aspect of the multiple zone polymerization, a chromium-based catalyst can be used in each of the polymerization zone  112  of the first reactor  100 , the polymerization zone  321  of the riser of the MZCR  300 , and the polymerization zone  341  of the downcomer  340  of the MZCR. In an alternative aspect of the multiple zone polymerization, a metallocene catalyst can be used in each of the polymerization zone  112  of the first reactor  100 , the polymerization zone  321  of the riser of the MZCR  300 , and the polymerization zone  341  of the downcomer  340  of the MZCR. In an alternative aspect of the multiple zone polymerization, a chromium-based catalyst, a Ziegler-Natta catalyst, or a metallocene catalyst can be used in the polymerization zone  112  of the first reactor  100 ; in combination with a chromium-based catalyst, a Ziegler-Natta catalyst, or a metallocene catalyst used in the polymerization zone  321  of the riser of the MZCR  300 ; in combination with a chromium-based catalyst, a Ziegler-Natta catalyst, or a metallocene catalyst used in the polymerization zone  341  of the downcomer  340  of the MZCR. In a particular aspect, a chromium-based catalyst can be used in the polymerization zone  112  of the first reactor  100 , in combination with a Ziegler-Natta or metallocene catalyst in the polymerization zone  321  of the riser, in combination with a Ziegler-Natta or metallocene catalyst in the polymerization zone  341  of the downcomer  340 . 
       FIG.  3    illustrates the MZCR  300  having various additional aspects that can be utilized in the MZCR  300  of  FIG.  1    and/or  FIG.  2   . Feed lines  323 ,  324 , and  325  are shown with dashed lines to indicate the optional use of these lines, since it is intended that the aspects and embodiments of the MZCR  300  shown in  FIG.  3    can be implemented in the MCZR  300  shown in  FIG.  1    and/or  FIG.  2   . 
     In embodiments, the MZCR  300  can include a heat apparatus  371  configured to add or remove heat from the riser  320  and/or a heat apparatus  372  configured to add or remove heat from the downcomer  340 . The heat apparatus  371  and/or the heat apparatus  372  can be embodied as heat exchange jackets and/or an electric heater placed around the riser  320  and around the downcomer  340 , respectively. 
     During startup of the MZCR  300 , the heat apparatus  371  and/or the heat apparatus  372  can be configured to supply heat to the riser  320  and/or to the downcomer  340 , respectively, in order raise the temperature of the polymerization zone  321  and/or polymerization zone  341  to the temperature for polymerization. When embodied as heat exchange jackets, a heating fluid such as steam or hot water may be circulated through an annulus between the heat apparatus  371  and riser  320  and/or between the heat apparatus  372  and the downcomer  340 . The circulation of the heating fluid can add heat to the polymerization zone  321  and/or polymerization zone  341  via heat transfer through the reactor wall of the MZCR  300 . The heating fluid may be circulated to a heating system configured to reheat the heating fluid before returning to the annular region in a heating cycle. When embodied as an electric heater, the heat apparatus  371  and/or the heat apparatus  372  can be appropriately connected to an electrical power supply that supplies power to raise the temperature of electrical heating elements. The heated heating elements can add heat to the polymerization zone  321  and/or polymerization zone  341  via heat transfer through the reactor wall of the MZCR  300 . 
     During operation of the MZCR  300  at polymerization conditions, the heat apparatus  371  and/or the heat apparatus  372  apparatus can be configured to remove excess heat generated by the exothermic polymerization reactions. When embodied as heat exchange jackets, a cooling fluid may be circulated through the annulus between the heat apparatus  371  and riser  320  and/or between the heat apparatus  372  and the downcomer  340 . The circulation of the cooling fluid can remove heat from the polymerization zone  321  and/or polymerization zone  341  via heat transfer through the reactor wall of the MZCR  300 . The cooling fluid may be circulated to a cooling system configured to cool the cooling fluid before returning to the annular region in a cooling cycle. 
     In an aspect, the heat apparatus  371  may only cover a portion of the riser  320  and other portions of the riser  320  may not be subject to heat transfer. Likewise, the heat apparatus  372  may only cover a portion of the downcomer  340  and other portions of the downcomer  340  may not be subject to heat transfer. In further aspects, about 10% to about 100%; alternatively, about 20% to about 100%; alternatively, about 30% to about 100%; alternatively, about 40% to about 100%; alternatively, about 50% to about 100%; alternatively, about 60% to about 100%; alternatively, about 70% to about 100%; alternatively, about 70% to about 100%; alternatively, about 80% to about 100%; alternatively, about 90% to about 100% of the outer surface of the riser  320  may be subject to heat exchange via the heat transfer apparatus  371 . In further aspects, about 10% to about 100%; alternatively, about 20% to about 100%; alternatively, about 30% to about 100%; alternatively, about 40% to about 100%; alternatively, about 50% to about 100%; alternatively, about 60% to about 100%; alternatively, about 70% to about 100%; alternatively, about 70% to about 100%; alternatively, about 80% to about 100%; alternatively, about 90% to about 100% of the outer surface of the downcomer  340  may be subject to heat exchange via the heat transfer apparatus  372 . 
       FIG.  3    also illustrates that the MZCR  300  can include a thermowell  374 . The thermowell  374  is shown on the lower conduit  310 ; however, it is contemplated than any number of thermowells can additionally or alternatively be included in the lower conduit  310 , riser  320 , upper conduit  330 , separator  350 , downcomer  340 , elbow connector  302 , elbow connector  304 , elbow connector  306 , or a combination thereof. A temperature sensing element, such as a thermocouple or a resistance temperature detector (RTD) can be housed in each thermowell  374  and configured to sense a temperature at the location in the MZCR  300  at which the temperature sensing element is placed. Each temperature sensing element can be appropriately connected to a process control system or processes monitoring system for reading and/or control of the MZCR  300 . The multiple sensed temperature values can be assembled into a temperature profile for any portion or the whole MZCR  300 . 
       FIG.  3    additionally illustrates that the MZCR  300  can include a gas density meter  373 . The gas density meter  373  can be configured to measure a density of the reaction mixture at the point where the gas density meter  373  is located. In  FIG.  3   , the gas density meter  373  is located in the riser  320  and thus measures the gas density of the riser reaction mixture. Gas can flow into the gas density meter  373  via sample conduit  373   a . Additionally or alternatively, it is contemplated that the gas density meter  373  can be located in other parts of the MZCR  300 , e.g., i) one or more meters in the lower conduit  310  to measure the gas density of the downcomer product mixture along with any added recycled components, ii) one or more meters in the upper conduit  330  to measure the gas density of the riser product mixture, and iii) one or more meters in the downcomer  340  to measure the gas density in the downcomer  340 . A commercial embodiment of the gas density meter  373  is an EMERSON® Micro Motion Gas Density Meter based on Coriolis effect. Other suitable gas density meters include on magnetic flow meters or thermodynamic flow meters. 
       FIG.  4    illustrates the MZCR  300  having various additional aspects that can be utilized in  FIG.  1    and/or  FIG.  2    and with any combination of aspects shown in  FIG.  3   . Feed lines  323 ,  324 , and  325  are shown with dashed lines to indicate the optional use of these lines, since it is intended that the aspects and embodiments of the MZCR  300  shown in  FIG.  4    can be implemented in the MCZR  300  shown in  FIG.  1    and/or  FIG.  2   . 
       FIG.  4    shows that the product discharge conduit  370  can be connected to the downcomer  340  such that an angle of the product discharge conduit  370  with respect to horizontal is in a range of -60° to 60°; alternatively, -45° to 45°; alternatively, -35° to 35°; alternatively, -25° to 25°; alternatively, 0° to 45°; alternatively, in a range of 10° to 35°; alternatively, in a range of 20° to 25°. For example, the angle of the product discharge conduit  370  with respect to horizontal can be -60°, -59°, -58°, -57°, -56°, -55°, -57°, -56°, -55°, -54°, -53°, -52°, -51°, -50°, -49°, -48°, -47°, -46°, -45°, -44°, -43°, -42°, -41°, -40°, -39°, -38°, -37°, -36°, -35°, -34°, -33°, -32°, -31°, -30°, -29°, -28°, -27°, -26°, -25°, -24°, -23°, -22°, -21°, -20°, -19°, -18°, -17°, -16°, -15°, -14°, -13°, -12°, -11°, -10°, -9°, -8°, -7°, -6°, -5°, -4°,-3°, -2°, -1°, 0°, 1°, 2°, 3°, 4°, 5°, 6°, 7°, 8°, 9°, 10°, 11°, 12°, 13°, 14°, 15°, 16°, 17°, 18°, 19°, 20°, 21°, 22°, 23°, 24°, 25°, 26°, 27°, 28°, 29°, 30°, 31°, 32°, 33°, 34°, 35°, 36°, 37°, 38°, 39°, 40°, 41°, 42°, 43°, 44°, 45°, 46°, 47°, 48°, 49°, 50°, 51°, 52°, 53°, 54°, 55°, 56°, 57°, 58°, 59°, or 60°. In an additional or alternative aspect, the product discharge conduit  370  can be connected to the downcomer  340  such that an angle of the product discharge conduit  370  with respect to a longitudinal axis of the downcomer  340  is in a range of 45° to 90°; alternatively, in a range of 55° to 80°; alternatively, in a range of 65° to 70°. For example, the angle of the product discharge conduit  370  with respect to the longitudinal axis of the downcomer  340  can be 45°, 46°, 47°, 48°, 49°, 50°, 51°, 52°, 53°, 54°, 55°, 56°, 57°, 58°, 59°, 60°, 61°, 62°, 63°, 64°, 65°, 66°, 67°, 68°, 69°, 70°, 71°, 72°, 73°, 74°, 75°, 76°, 77°, 78°, 79°, 80°, 81°, 82°, 83°, 84°, 85°, 86°, 87°, 88°, 89°, or 90°. 
       FIG.  4    also shows that a sample analyzer  377  configured to: i) analyze a sample of the a reaction mixture at one or more locations in the MZCR  300 , ii) determine a concentration of gas, liquid, or solid in the reaction mixture, and iii) determine a concentration of monomer, comonomer, diluent, hydrogen, inert component, or polymer in the reaction mixture. The reaction mixture analyzed by the sample analyzer  377  can be the reaction mixture from the lower conduit  310  (e.g., the downcomer product mixture and any added recycled components), the reaction mixture from the riser  320  (e.g., the riser reaction mixture), the reaction mixture from the upper conduit  330  (e.g., the riser product mixture), or the reaction mixture from the downcomer  340  (e.g., the downcomer reaction mixture). In an aspect, the sample analyzer  377  can be configured to i) analyze a sample of the reaction mixture of the riser  320  and/or the reaction mixture of the downcomer  340  at one or more locations in the MZCR  300 , ii) determine a concentration of gas, liquid, or solid in the reaction mixture of the riser  320  and/or the reaction mixture of the downcomer  340 , and iii) determine a concentration of monomer, comonomer, diluent, hydrogen, inert component, or polymer in the reaction mixture of the riser  320  and/or the reaction mixture of the downcomer  340 . In aspects, multiple sample analyzers similar to sample analyzer  377  can be included at various locations on the MZCR  300 . In additional or other aspect, one or more sample analyzers can be included on the product discharge conduit  110  and/or product discharge conduit  370 . The sample analyzer  377  can include a gas chromatograph (GC) configured to determine the concentration of the gases sampled via a conduit  377   a  that is connected to the interior of the MZCR  300 . The analysis method can be Raman analysis, for example. The sample analyzer  377  can be configured to analyze a sample at a set frequency of time, i.e., at designated periods of time (e.g., every 1, 5, 10, 15, 20, 30, or 60 minutes). A commercially available sample analyzer  377  is a THERMO FISHER SCIENTIFIC® Raman gas analyzer or other commercially available infrared spectrometer. 
       FIG.  4    also shows a level controller  378  configured to control a level of polyolefin product in the separator  350  of the MZCR  300 . The level controller  378  can be coupled to the separator  350  and configured such that the polyolefin product has a residence time in an range of from about 1 to about 30 minutes; alternatively, from about 1 to about 5 minutes; alternatively, from about 5 to about 10 minutes; alternatively, from about 10 to about 30 minutes in the separator  350 . 
     The level controller  378  can be embodied as a valve, a level sensor, and a computer device connected to both the valve and the level sensor. 
     The valve of the level controller  378  can be positioned at the bottom of the separator  350  and configured to operate between an open position and a closed position. In the open position, the valve allows polyolefin product to pass from the separator  350  to the liquid barrier  360  of the downcomer  350 . In the closed position, the valve prevents the polyolefin product from passing from the separator  350  into the liquid barrier  360 . In operation, the valve of the level controller  380  can actuate between the open and closed positions in order to control the amount of polyolefin product that passes from the separator  350  into the liquid barrier  360 . The valve can be electrically and/or pneumatically connected to the computer device of the level controller  378  such that actuation of the valve can be accomplished. 
     The level sensor of the level controller  378  can be configured to sense an amount (e.g., the level) of the polyolefin product in the separator  350 . The level sensor can be a pressure sensor or pressure transducer positioned on the bottom of the separator  350  that measures a pressure or weight of the polyolefin product that accumulates in the bottom of the separator  350 . Alternatively, the level sensor can be an electro-optical sensor positioned anywhere on the separator  350  so as to measure the presence of the polyolefin product at a threshold level in the separator  350 . For example, an electro-optical sensor can be located on the wall of the separator  350  and configured to measure a disruption in light caused by the presence of the polyolefin product in front of the sensor, i.e., the amount of polyolefin product is at a threshold height in the in the separator  350  such that actuation of the valve into the open position is made by the level controller  378 . Regardless how the level sensor is embodied, the level controller  378  can be configured to actuate the valve between the open position and the closed position in response to input from the level sensor (e.g., in the form of a pressure sensor, transducer, or electro-optical sensor). The level sensor can be electrically and/or pneumatically connected to the computer device of the level controller  378  such that measurement of the level of the polyolefin product in the separator  350  can be made. 
     The computer device of the level controller  378  can be specially configured with an input port that connects to the level sensor and an output port than connects to the valve. The computer device of the level controller  378  can be programmed to receive signals (e.g., electrical and/or pneumatic signals) from the level sensor, to analyze the received signals based on a control algorithm, and to send signals (e.g., electrical and/or pneumatic signals) to the valve of the level controller  378  that cause the valve either to actuate to the open position or to the closed position. 
       FIG.  4    shows additionally that an anti-static agent feed line  346  can be configured to inject an anti-static agent into the MZCR  300 . While  FIG.  4    shows the feed line  346  fluidly connected near the top portion  348  of the downcomer  340 , it is contemplated that the feed line  346  can be connected anywhere on the MZCR  300 . Additionally, it is contemplated that the feed line  346  can comprise more than one line configured to inject the anti-static agent at various locations along the downcomer  340  or anywhere along the MZCR  300 . In an embodiment, the feed line  346  can be configured to inject a mixture comprising an anti-static agent and a carrier fluid. In an aspect of such embodiment, the concentration of the anti-static agent in feed line  346  (or each feed line when more than one is used) is in an range of from about 1 ppm to about 50 ppm; alternatively, from about 1 ppm to about 5 ppm; alternatively, about 5 ppm to about 10 ppm; alternatively, about 10 ppm to about 50 ppm, based on weight of the carrier fluid in the feed line  346 . In an additional or alternative aspect of such embodiment, the concentration of the anti-static agent in feed line  346  (or each feed line when more than one is used) is about 1 ppm to about 50 ppm; alternatively, from about 1 ppm to about 5 ppm; alternatively, about 5 ppm to about 10 ppm; alternatively, about 10 ppm to about 50 ppm, based on weight of the carrier fluid in the MZCR  300 . In an aspect, the anti-static agent can be STADIS® 425, STADIS® 450, STATSAFE™ 2000, STATSAFE™ 3000, STATSAFE™ 6000, ammonium salts, or other commercially available anti-static agent. 
       FIG.  4    also shows that a reactor deactivator feed line  347  can be included on the MZCR  300 . The feed line  347  is shown as connecting to the downcomer  340 ; however, it is contemplated that the reactor deactivator feed line  347  can be placed anywhere on the MZCR  300 . It is also contemplated that the MZCR  300  can have multiple reactor deactivator feed lines  347 . The reactor deactivator feed line  347  is useful on the MZCR  300  when the multiple zone configuration of  FIG.  1    is utilized, since the MZCR  300  is the last of the two reactors  100  and  300 . It is contemplated that a deactivator feed line can additionally or alternatively be included on the first reactor  100  when the multiple zone configuration of  FIG.  2    is utilized. 
     In and aspect, the reactor deactivation agent introduced via feed line  347  can be carbon monoxide or an alcohol. In an aspect, the reactor deactivation agent is not water, so as to prevent the internals of the MZCR  300  (or first reactor  100 ) from rusting. 
     A reactor deactivation agent is useful when the MZCR  300  (and/or the first reactor  100 ) must be shut down. The reactor deactivation agent can lead to a stoppage of the polymerization reactions, which then can enable stoppage of the reactors. In another aspect, the reactor deactivation agent is useful to partially reduce, or moderate, the polymerization reactions in the MZCR  300  (and/or the first reactor  100 ). Moderation enables slowing the polymerization reaction enough that the MZCR  300  and/or the first reactor  100  can be stopped for about 20 to about 60 minutes and then restarted, for example, to start a new polyolefin product run. The amount of reactor deactivation agent required for a total stoppage is greater than the amount required for moderation. 
       FIGS.  5 A and  5 B  illustrate cross-sectional views of embodiments of an eductor  375 , and  FIG.  5 C  illustrates a perspective view of a standpipe  390 . The eductor  375  and/or standpipe  390  can be used with the MZCR  300  in  FIG.  1    and/or  FIG.  2   , along with any combination of aspects shown in  FIGS.  3  and  4   . The configuration of the eductor  375  differs in various aspects between  FIG.  5 A  and  FIG.  5 B , as is discussed below. 
     The eductor  375  of  FIG.  5 A  is configured to increase a velocity of the fluids entering the eductor  375  such that the velocity of the fluids exiting the eductor  375  is higher than the velocity of the fluids entering the eductor  375 . The design of the eductor  375  shown in  FIG.  5 A  is intended to be exemplary and non-limiting, and other designs that function to increase the velocity of fluids that enter the eductor  375  are contemplated. The eductor  375  has two inlets  375   a  and  375   b , and one outlet  375   c . The inlet  375   b  and outlet  375   c  generally share the same longitudinal axis. The longitudinal axis of the inlet  375   b  is generally at an angle, for example 15° to 90°, relative to the longitudinal axis of the inlet  375   b  and outlet  375   c . 
     Referring still to the eductor  375  in  FIG.  5 A , a reaction mixture containing polyolefin particles can enter the eductor  375  at inlet  375   a . A motive fluid, for example, of recycled monomer/comonomer from conduit  502  or  503  in  FIG.  1    or  FIG.  2   , can enter the eductor  375  at inlet  375   b . The inlet  375   b  of the eductor  375  in  FIG.  5 A  can be configured such that a portion  375   d  of the inlet  375   b  extends into the interior of the eductor  375  and is contoured in the shape of a nozzle such that the motive fluid is forced to flow at a higher velocity in the direction of arrow C. The flow of the motive fluid out of the nozzle-shaped portion  375   d  creates suction at inlet  375   a  that aids in drawing the reaction mixture into the eductor  375 . The reaction mixture mixes with the motive fluid in the interior of the eductor  375 , and the mixture flows in the direction of arrow C and out of the outlet  375   c  of the eductor  375  at an exit velocity that is higher than either or both of the inlet velocity of the motive fluid and the inlet velocity of the reaction mixture. In an aspect, a portion  375   e  of the body of the eductor  375  in  FIG.  5 A  can be tapered such that the inner diameter of the portion  375   e  of the eductor  375  decreases in the direction of arrow C. In another aspect, a portion  375   f  of the body of the eductor  375  in  FIG.  5 A  can be tapered such that the inner diameter of the portion  375   f  of the eductor  375  increases in the direction of arrow C. In another aspect, the motive fluid can be pressurized before entering the eductor  375 , for example, by a pump or compressor positioned upstream of the eductor  375 . In a further aspect, the eductor  375  of  FIG.  5 A  can be oriented in the MZCR  300  such that the direction of flow indicated by arrow C is horizontal, vertical, or at an angle with respect to horizontal. 
     The eductor  375  of  FIG.  5 B  is configured to increase a velocity of the fluids entering the eductor  375  such that the velocity of the fluids exiting the eductor  375  is higher than the velocity of the fluids entering the eductor  375 . The design of the eductor  375  shown in  FIG.  5 B  is intended to be exemplary and non-limiting, and other designs that function to increase the velocity of fluids that enter the eductor  375  are contemplated. The eductor  375  has two inlets  375   a  and  375   b , and one outlet  375   c . The inlet  375   b  and outlet  375   c  generally share the same longitudinal axis. The longitudinal axis of the inlet  375   b  is generally at an angle, for example perpendicular, relative to the longitudinal axis of the inlet  375   b  and outlet  375   c . 
     Referring still to the eductor  375  in  FIG.  5 B , a motive fluid, for example, of recycled monomer/comonomer from conduit  502  or  503  in  FIG.  1    or  FIG.  2   , can enter the eductor  375  at inlet  375   a . A reaction mixture containing polyolefin particles can enter the eductor  375  at inlet  375   b . This is the opposite configuration of the eductor  375  in  FIG.  5 A , where the reaction mixture enters inlet  375   a  and the motive fluid enters inlet  375   b . 
     The inlet  375   a  of the eductor  375  in  FIG.  5 B  can be configured such that a portion 375 g of the inlet  375   a  extends into the interior of the eductor  375 . The portion 375 g bends within the interior of the eductor  375  such that the end  375   h  of the inlet  375   a  has a longitudinal axis that is parallel to or the same as the longitudinal axis of the inlet  375   b  and outlet  375   c . The end  375   h  can also be contoured in the shape of a nozzle such that the motive fluid is forced to flow at a higher velocity in the direction of arrow C. The flow of the motive fluid out of the nozzle-shaped end  375   h  creates suction at inlet  375   b  that aids in drawing the reaction mixture into the eductor  375 . The reaction mixture mixes with the motive fluid in the interior of the eductor  375 , and the mixture flows in the direction of arrow C and out of the outlet  375   c  of the eductor  375  at an exit velocity that is higher than either or both of the inlet velocity of the motive fluid and the inlet velocity of the reaction mixture. In an aspect, a portion  375   e  of the eductor  375  can be tapered such that the inner diameter of the portion  375   e  of the eductor  375  decreases in the direction of arrow C. In another aspect, the motive fluid can be pressurized before entering the eductor  375 , for example, by a pump or compressor positioned upstream of the eductor  375 . In further aspect, the eductor  375  of  FIG.  5 B  can be oriented in the MZCR  300  such that the direction of flow indicated by arrow C is horizontal, vertical, or at an angle with respect to horizontal. 
       FIG.  5 C  illustrates a perspective view of a standpipe  390 . The standpipe  390  is generally a length of pipe having a wall thickness adequate for high pressure fluid. That is, the wall  391  of the standpipe  390  can have a thickness that is greater than the wall of the conduits which form the MZCR  300 , due to the higher pressure of fluid that passes through the channel  392  of the standpipe  390 . In aspects, the diameter of the standpipe  390  can be from about 2 to about 48 inches (about 5 to about 122 cm); alternatively, from about 12 to about 24 inches (about 30.5 to about 61 cm); alternatively, from about 6 to about 12 inches (about 15.2 to about 30.5 cm). In an aspect, a diameter of the standpipe  390  can be less than a diameter (e.g., inner diameter and/or outer diameter) of the lower conduit  310  of the MZCR  300 . Generally, the standpipe  390  can have a uniform diameter along a length thereof such that end  390   a  of the standpipe  390  has an outer diameter and inner diameter that is equal to the outer diameter and inner diameter of the opposite end  390   b . The thickness of the wall  391  of the standpipe  390  can be, for example, from about 0.1, 0.2, 0.3, 0.4, or 0.5 inches (about 0.254, 0.508, 0.762, 1.02, or 1.27 cm) to about 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, or 5 inches (about 2.54, 3.81, 5.08, 6.35, 7.62, 8.89, 10.2, 11.4, or 12.7 cm). In a further aspect, the length of the standpipe  390  can be any length suitable for delivering the high pressure fluid to the MZCR  300 , for example, 0.328, 1.64, 3.28, 4.92, 6.56, 8.20, 9.84, 11.5, 13.1, 14.8, or 16.4 ft (0.1, 0.5, 1, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, or 5.0 meters). In yet a further aspect, it is contemplated that the standpipe  390  can include bends, elbow connectors, straight portions, or combinations thereof. Further, it is contemplated that the standpipe  390  can be formed from multiple piping segments, for example, to traverse the distance between a compressor and the MZCR  300  in the plant. 
       FIGS.  5 D to  5 J  illustrate embodiments of the MZCR  300  that utilize the eductor  375  and/or standpipe  390  in various configurations and aspects. The configurations shown in  FIGS.  5 D to  5 J  can be utilized in the MZCR  300  of  FIG.  1    and/or  FIG.  2   , along with any combination of aspects shown in  FIGS.  3  and  4   . Feed lines  323 ,  324 , and  325  in each of  FIGS.  5 D to  5 J  are shown with dashed lines to indicate the optional use of these lines, since it is intended that the aspects and embodiments of the MZCR  300  shown in  FIGS.  5 D to  5 J  can be implemented in the MCZR  300  shown in  FIG.  1    and/or  FIG.  2   . 
     In  FIG.  5 D , the eductor  375  of  FIG.  5 A  is placed in the MZCR  300  such that inlet  375   a  is fluidly connected to the bottom portion  349  of the downcomer  340  and such that outlet  375   c  is fluidly connected to the end  311  of the lower conduit  310 . The bottom portion  349  of the downcomer  340  can be tapered in a conical manner so as to facilitate flow of the downcomer product mixture into the inlet  375   a  of the eductor  375 . Inlet  375   b  of the eductor  375  is fluidly connected to conduit  502  such that unreacted olefin monomer, unreacted olefin comonomer, diluent, or a combination thereof enters the eductor  375 . 
     The flow of the unreacted olefin monomer, unreacted olefin comonomer, diluent, or a combination thereof out of the nozzle-shaped portion  375   d  creates suction at inlet  375   a  that aids in drawing the downcomer product mixture into the eductor  375 . The downcomer product mixture mixes with the unreacted olefin monomer, unreacted olefin comonomer, diluent, or a combination thereof in the interior of the eductor  375  to form an eductor reaction mixture, and the eductor reaction mixture flows in the direction of arrow C and out of the outlet  375   c  of the eductor  375  and into the lower conduit  310 . The eductor  375  helps the eductor reaction mixture exit the eductor  375  at an exit velocity that is i) greater than a saltation velocity of the eductor reaction mixture and up to about 30.48 m/s (100 ft/sec), or ii) greater than 110% of the saltation velocity of the eductor reaction mixture. The exit velocity of the eductor reaction mixture moves the mixture through the lower conduit  310  in the direction of arrow A, where the eductor reaction mixture mixes with additional unreacted olefin monomer, unreacted olefin comonomer, diluent, or a combination thereof provided by conduit  503  to form a lower conduit reaction mixture. The lower conduit reaction mixture mixes with feed components provided by feed lines  322 ,  323 ,  324 , and/or  325  to form the riser reaction mixture. For the polymerization of  FIG.  1   , the first polyolefin received from conduit  202  can additionally mix with the eductor reaction mixture flowing in the lower conduit  310  such that the first polyolefin and the eductor reaction mixture flow in the lower conduit reaction mixture. 
     The angle between the longitudinal axis of the inlet  375   a  and inlet  375   b  in  FIG.  5 D  is perpendicular, and the direction of flow of arrow C is horizontal. 
     The eductor  375  of  FIG.  5 D  replaces the elbow connector  306  shown in  FIG.  1    and  FIG.  2   . 
     In  FIG.  5 E , the eductor  375  of  FIG.  5 A  is placed in the MZCR  300  such that inlet  375   a  is fluidly connected to the end  312  of the lower conduit  310  and such that outlet  375   c  is fluidly connected to the bottom portion  329  of the riser  320 . The bottom portion  329  of the riser  320  can be tapered in a conical manner so as to facilitate connection to the outlet  375   c  of the eductor  375 . Inlet  375   b  of the eductor  375  is fluidly connected to conduit  503  such that unreacted olefin monomer, unreacted olefin comonomer, diluent, or a combination thereof enters the eductor  375 . 
     The flow of the unreacted olefin monomer, unreacted olefin comonomer, diluent, or a combination thereof out of the nozzle-shaped portion  375   d  creates suction at inlet  375   a  that aids in drawing the lower conduit reaction mixture (e.g., containing the downcomer product mixture and any recycled components added via conduit  502 ) from the lower conduit  310  into the eductor  375 . The lower conduit reaction mixture mixes with the additional unreacted olefin monomer, unreacted olefin comonomer, diluent, or a combination thereof in the interior of the eductor  375  to form the eductor reaction mixture, and the eductor reaction mixture flows in the direction of arrow C and out of the outlet  375   c  of the eductor  375 . The eductor reaction mixture exits the eductor  375  at an exit velocity that is i) greater than a saltation velocity of the eductor reaction mixture and up to about 30.48 m/s (100 ft/sec), or ii) greater than 110% of the saltation velocity of the eductor reaction mixture. The eductor reaction mixture mixes with any added feed components via conduits  322 ,  323 ,  324 , and/ 325  to form the riser reaction mixture. The exit velocity of the eductor reaction mixture helps move the riser reaction mixture (which contains the eductor reaction mixture and any components added via conduits  322 ,  323 ,  324 , and/or  325 ) through riser  320  in an upward direction. The momentum of the riser reaction mixture through the riser  320  helps move the riser product mixture through the upper conduit  330 . For the polymerization of  FIG.  1   , the first polyolefin received from conduit  202  can mix with the lower conduit reaction mixture flowing in the lower conduit  310  such that the first polyolefin and the lower conduit reaction mixture flow into the eductor  375 . 
     The angle between the longitudinal axis of the inlet  375   a  and inlet  375   b  in  FIG.  5 E  is perpendicular, and the direction of flow of arrow C is vertical. 
     It is contemplated that embodiments of the MZCR  300  can have an eductor  375  placed as shown in  FIG.  5 D  in combination with an eductor placed as shown in  FIG.  5 E . 
     The eductor  375  of  FIG.  5 E  replaces the elbow connector  302  shown in  FIG.  1    and  FIG.  2   . 
     In  FIG.  5 F , the eductor  375  of  FIG.  5 B  is placed in the MZCR  300  such that inlet  375   b  is fluidly connected to the end  311  of the lower conduit  310  and such that outlet  375   c  is fluidly connected to the end  312  of the lower conduit  310 . Inlet  375   a  of the eductor  375  is fluidly connected to conduit  502  such that unreacted olefin monomer, unreacted olefin comonomer, diluent, or a combination thereof enters the eductor  375  via the inlet  375   a . 
     The flow of the unreacted olefin monomer, unreacted olefin comonomer, diluent, or a combination thereof out of the portion 375 g of the inlet  375   a  that extends into the interior of the eductor  375  creates suction at inlet  375   b  that aids in drawing the downcomer product mixture from the end  311  of the lower conduit  310  into the eductor  375 . The downcomer product mixture mixes with the unreacted olefin monomer, unreacted olefin comonomer, diluent, or a combination thereof in the interior of the eductor  375  to form an eductor reaction mixture, and the eductor reaction mixture flows in the direction of arrow C and out of the outlet  375   c  of the eductor  375  and into the end  312  of the lower conduit  310 . The eductor reaction mixture flows out of the eductor  375  at an exit velocity that is i) greater than a saltation velocity of the eductor reaction mixture and up to about 30.48 m/s (100 ft/sec), or ii) greater than 110% of the saltation velocity of the eductor reaction mixture. The exit velocity of the eductor reaction mixture moves the mixture through the lower conduit  310  and into the riser  320  (e.g., via the elbow connector  302 ). The eductor reaction mixture can combine with the additional unreacted olefin monomer, unreacted olefin comonomer, diluent, or a combination thereof provided by conduit  503 , forming a lower conduit reaction mixture, and the lower conduit reaction mixture mixes with any feed components from lines  322 ,  323 ,  324 , and/or  325  to form the riser reaction mixture. The riser reaction mixture moves through the riser  320  in an upward direction. The momentum of the riser reaction mixture through the riser  320  moves the riser product mixture through the upper conduit  330 . For the polymerization of  FIG.  1   , the first polyolefin received from conduit  202  can mix with the eductor reaction mixture flowing in the lower conduit  310  such that the first polyolefin and the eductor reaction mixture flow in the lower conduit reaction mixture into the eductor  375 . 
     The angle between the longitudinal axis of the inlet  375   a  and inlet  375   b  in  FIG.  5 F  is less than 90°, and the direction of flow of arrow C is horizontal. 
     It is contemplated that embodiments of the MZCR  300  can have the eductor  375  as shown in  FIG.  5 F  in combination with an eductor  375  placed as shown in  FIG.  5 D  and/or with an eductor placed as shown in  FIG.  5 E . 
     In  FIG.  5 G , the eductor  375  of  FIG.  5 B  is placed in the MZCR  300  such that inlet  375   b  is fluidly connected to the bottom portion  349  of the downcomer  340  and such that outlet  375   c  is fluidly connected to the end  311  of the lower conduit  310  (e.g., via the elbow connector  306 ). Inlet  375   a  of the eductor  375  is fluidly connected to conduit  502  such that unreacted olefin monomer, unreacted olefin comonomer, diluent, or a combination thereof enters the eductor  375  via the inlet  375   a . 
     The flow of the unreacted olefin monomer, unreacted olefin comonomer, diluent, or a combination thereof out of the portion  375   g  of the inlet  375   a  that extends into the interior of the eductor  375  creates suction at inlet  375   b  that aids in drawing the downcomer product mixture from the downcomer  340  into the eductor  375 . The downcomer product mixture mixes with the unreacted olefin monomer, unreacted olefin comonomer, diluent, or a combination thereof in the interior of the eductor  375  to for an eductor reaction mixture, and the eductor reaction mixture flows in the direction of arrow C and out of the outlet  375   c  of the eductor  375  and into the end  311  of the lower conduit  310 . The eductor reaction mixture exits the eductor  375  at an exit velocity that is i) greater than a saltation velocity of the eductor reaction mixture and up to about 30.48 m/s (100 ft/sec), or ii) greater than 110% of the saltation velocity of the eductor reaction mixture. The exit velocity helps to move the educator reaction mixture through the lower conduit  310 . The eductor reaction mixture combines with the unreacted olefin monomer, unreacted olefin comonomer, diluent, or a combination thereof provided by conduit  503  to for the lower conduit reaction mixture. The lower conduit reaction mixture mixes with feed components added be any of feed conduits  322 ,  323 ,  324 , and/or  325  to form the riser reaction mixture. The riser reaction mixture moves through the riser  320  in an upward direction. The riser reaction mixture exits the riser  320  as the riser product mixture, and the riser product mixture flows through the upper conduit  330  to the separator  350 . For the polymerization of  FIG.  1   , the first polyolefin received from conduit  202  can mix with the eductor reaction mixture flowing in the lower conduit  310 . 
     The angle between the longitudinal axis of the inlet  375   a  and inlet  375   b  in  FIG.  5 G  is less than 90°, and the direction of flow of arrow C is vertical. 
     It is contemplated that embodiments of the MZCR  300  can have the eductor  375  as shown in  FIG.  5 G  in combination with an eductor  375  placed as shown in  FIG.  5 D , with an eductor  375  placed as shown in  FIG.  5 E , with an eductor  375  placed as shown in  FIG.  5 F , or a combination thereof. 
     In  FIG.  5 H , the eductor  375  of  FIG.  5 B  is placed in the MZCR  300  such that inlet  375   b  is fluidly connected to the end  312  of the lower conduit  310  and such that outlet  375   c  is fluidly connected to the bottom portion  329  of the riser  320  (e.g., via the elbow connector  302 ). Inlet  375   a  of the eductor  375  is fluidly connected to conduit  503  such that unreacted olefin monomer, unreacted olefin comonomer, diluent, or a combination thereof enters the eductor  375  via the inlet  375   a . 
     The flow of the unreacted olefin monomer, unreacted olefin comonomer, diluent, or a combination thereof out of the portion  375   g  of the inlet  375   a  that extends into the interior of the eductor  375  creates suction at inlet  375   b  that aids in drawing the lower conduit reaction mixture from the lower conduit  310  into the eductor  375 . The lower conduit reaction mixture received at inlet  375   b  can contain i) the downcomer product mixture, ii) unreacted olefin monomer, unreacted olefin comonomer, diluent, or a combination thereof provided by conduit  502 , and optionally iii) the first polyolefin delivered via conduit  202  (see the polymerization in  FIG.  1   ). The lower conduit reaction mixture received at inlet  375   b  mixes with the unreacted olefin monomer, unreacted olefin comonomer, diluent, or a combination thereof provided by conduit  503  in the interior of the eductor  375  to for the eductor reaction mixture, and the eductor reaction mixture flows in the direction of arrow C and out of the outlet  375   c  of the eductor  375 . The eductor reaction mixture exits the eductor  375  at an exit velocity that is i) greater than a saltation velocity of the eductor reaction mixture and up to about 30.48 m/s (100 ft/sec), or ii) greater than 110% of the saltation velocity of the eductor reaction mixture. The eductor reaction mixture mixes with any feed components provided by feed conduits  322 ,  323 ,  324 , and/or  325  to form the riser reaction mixture. The riser reaction mixture flows into the riser  320  and upward therethrough. The riser reaction mixture exits the riser  320  as the riser product mixture. The exit velocity of the riser product mixture helps to move the riser product mixture through the upper conduit  330  to the separator  350 . 
     The angle between the longitudinal axis of the inlet  375   a  and inlet  375   b  in  FIG.  5 H  is less than 90°, and the direction of flow of arrow C is vertical. 
     It is contemplated that embodiments of the MZCR  300  can have the eductor  375  as shown in  FIG.  5 H  in combination with an eductor  375  placed as shown in  FIG.  5 D , with an eductor  375  placed as shown in  FIG.  5 E , with an eductor  375  placed as shown in  FIG.  5 F , with an eductor  375  placed as shown in  FIG.  5 G , or a combination thereof. 
     In  FIG.  5 I , the standpipe  390  of  FIG.  5 C  is fluidly connected to the lower conduit  310  (e.g., via the elbow connector  306 ). The outlet  390   b  of the standpipe  390  connects to the MZCR  300 . The inlet  390   a  of the standpipe  390  is fluidly connected to conduit  502 , optionally via a compressor or pump  502   a . The compressor or pump  502   a  is configured to increase the pressure of the unreacted olefin monomer, unreacted olefin comonomer, diluent, or a combination thereof received from conduit  502 . The inlet  390   a  of the standpipe  390  can be directly connected to the outlet of the compressor or pump  502   a  so as to deliver the pressurized components to the interior of the MZCR  300  in the direction of arrow C. The pressured components enter the MZCR  300  and increase the velocity of the downcomer product mixture traveling out of the downcomer  340  and into the lower conduit  310  such that the velocity of the downcomer product mixture reaches a velocity that is i) greater than a saltation velocity of the downcomer product mixture and up to about 30.48 m/s (100 ft/sec), or ii) greater than 110% of the saltation velocity of the downcomer product mixture. 
     The direction of flow of arrow C in  FIG.  5 I  is horizontal. It is contemplated that embodiments of the MZCR  300  can have the standpipe  390  as shown in  FIG.  5 I  in combination with an eductor  375  placed as shown in  FIG.  5 D , with an eductor  375  placed as shown in  FIG.  5 E , with an eductor  375  placed as shown in  FIG.  5 F , with an eductor  375  placed as shown in  FIG.  5 G , with an eductor  375  placed as shown in  FIG.  5 H , or a combination thereof. 
     In  FIG.  5 J , the standpipe  390  of  FIG.  5 C  is fluidly connected to the lower conduit  310  (e.g., via the elbow connector  302 ). The outlet  390   b  of the standpipe  390  connects to the MZCR  300 . The inlet  390   a  of the standpipe  390  is fluidly connected to conduit  503 , optionally via a compressor or pump  503   a . The compressor or pump  503   a  is configured to increase the pressure of the unreacted olefin monomer, unreacted olefin comonomer, diluent, or a combination thereof received from conduit  502 . The inlet  390   a  of the standpipe  390  can be directly connected to the outlet of the compressor or pump  502   a  so as to deliver the pressurized components to the interior of the MZCR  300  in the direction of arrow C. The pressured components enter the MZCR  300  and increase the velocity of the lower conduit reaction mixture traveling out of the lower conduit  310  such that a velocity of the lower conduit reaction mixture is i) greater than a saltation velocity of the lower conduit reaction mixture and up to about 30.48 m/s (100 ft/sec), or ii) greater than 110% of the saltation velocity of the lower conduit reaction mixture. 
     The direction of flow of arrow C in  FIG.  5 J  is vertical. It is contemplated that embodiments of the MZCR  300  can have the standpipe  390  as shown in  FIG.  5 J  in combination with an eductor  375  placed as shown in  FIG.  5 D , with an eductor  375  placed as shown in  FIG.  5 E , with an eductor  375  placed as shown in  FIG.  5 F , with an eductor  375  placed as shown in  FIG.  5 G , with an eductor  375  placed as shown in  FIG.  5 H , the standpipe  390  as shown in  FIG.  5 I , or a combination thereof. 
       FIGS.  6 A to  6 C  illustrate the MZCR  300  having various additional aspects that can be utilized in  FIG.  1    and/or  FIG.  2    and with any combination of aspects shown in  FIGS.  3 ,  4 , and  5 A to  5 J . Feed lines  323 ,  324 , and  325  are shown with dashed lines to indicate the optional use of these lines, since it is intended that the aspects and embodiments of the MZCR  300  shown in  FIG.  6 A  can be implemented in the MCZR  300  shown in  FIG.  1    and/or  FIG.  2   . 
     In  FIG.  6 A , the MZCR  300  that includes a transition conduit  376 . The transition conduit  376  can be fluidly connected to the end  311  of the lower conduit  310  and to the bottom portion  349  of the downcomer  340 . An angle of the lower conduit  310  with respect to horizontal can be less than about 90°; alternatively, greater than about 0° and less than about 90°; alternatively, in a range of from about 0° to about 45°; alternatively, in a range of from about 45° to about 67.5°. An angle of the transition conduit  376  with respect to horizontal can be less than about 90°; alternatively, greater than about 0° and less than about 90°; alternatively, in a range of from about 0° to about 45°; alternatively, in a range of from about 45° to about 67.5°. In an aspect, the lower conduit  330  and the transition conduit  376  are the same angle value with respect to horizontal. A length of the transition conduit  376  can be from about 0.305 m (1 ft) to about 4.57 m (15 ft); alternatively, about 1.83 m (6 ft) to about 4.57 m (15 ft); alternatively, from about 0.305 m (1 ft) to about 1.5 m (5 ft); alternatively, about 1.5 m (5 ft) to about 3.05 m (10 ft).  FIG.  6 A  also shows that the transition conduit  376  can be fluidly connected to the conduit  502 . In an aspect, part of the transition conduit  376  can be a flush and clean out chamber having a length of from about 0.305 m (1 ft) to about 1.5 m (5 ft); alternatively, about 1.5 m (5 ft) to about 3.05 m (10 ft). 
       FIG.  6 A  illustrates that the MZCR  300  can have elbow connector  302 , elbow connector  304 , and tee connector  307  (e.g., elbow connector  306  is replaced by tee connector  307  due to the presence of the transition conduit  376 ). As can be seen, elbow connector  302  can connect to the bottom portion  329  of the riser  320  and to the end  312  of the lower conduit  310 . More specifically, end  302   a  of the elbow connector  302  can connect to the bottom portion  329  of the riser  320 , and end  302   b  of the elbow connector  302  can connect to the end  312  of the lower conduit  310 . Elbow connector  304  can connect to the top portion  328  of the riser  320  and to the end  331  of the upper conduit  330 . More specifically, end  304   a  of the elbow connector  304  can connect to the top portion  328  of the riser  320 , and end  304   b  of the elbow connector  304  can connect to the end  331  of the upper conduit  330 . Tee connector  307  can connect to the bottom portion  349  of the downcomer  340 , to the end  311  of the lower conduit  310 , and to an end  376   a  of the transition conduit  376 . More specifically, end  307   a  of the tee connector  307  can connect to the bottom portion  349  of the downcomer  340 , end  307   b  of the tee connector  307  can connect to the end  311  of the lower conduit  310 , and end  307   c  of the tee connector  307  can connect to the end  376   a  of the transition conduit  376 . In an aspect, the a first angle θ A  formed between the end  307   a  and the end  307   b  of the tee connector  307  is equal to or less than about 90°, and an angle θ B  between the end  307   a  and the end  307   c  is equal to or greater than 90°. 
     In  FIG.  6 B , an eductor  375  is used in combination with a transition conduit  376  embodied as a standpipe  390 . The eductor  375  is similar to that illustrated in  FIG.  5 A , except the angle between the longitudinal axis of the inlet  375   a  and inlet  375   b  in  FIG.  6 B  is angle θ B  (angle θ B  is discussed for  FIG.  6 A ). In an aspect, the angle θ B  in  FIG.  6 B  that is between the longitudinal axis of inlet  375   a  and the longitudinal axis of inlet  375   b  is greater than 90° and less than 180°. 
     The eductor  375  is placed in the MZCR  300  such that inlet  375   a  is fluidly connected to the bottom portion  349  of the downcomer  340  and such that outlet  375   c  is fluidly connected to the end  311  of the lower conduit  310 . The bottom portion  349  of the downcomer  340  can be tapered in a conical manner so as to facilitate flow of the reaction mixture into the inlet  375   a  of the eductor  375 . The inlet  375   b  of the eductor  375  is fluidly connected to the outlet  390   b  of the standpipe  390 . The inlet  390   a  of the standpipe  390  can be fluidly connected to a compressor or pump  502   a . 
     The configuration and operation of the eductor  375  in  FIG.  6 B  is similar to that described for  FIG.  5 D , except the recycled components are received at the inlet  375   b  at a higher pressure due to use of the standpipe  390  and compressor or pump  502   a . The downcomer product mixture received in the inlet  375   a  from the downcomer  340  mixes with the pressurized unreacted olefin monomer, unreacted olefin comonomer, diluent, or a combination thereof in the interior of the eductor  375  to form a pressurized eductor reaction mixture, and the pressurized eductor reaction mixture flows in the direction of arrow C and out of the outlet  375   c  of the eductor  375  and into the lower conduit  310 . The eductor reaction mixture exits the eductor  375  at an exit velocity that is i) greater than a saltation velocity of the eductor reaction mixture and up to about 30.48 m/s (100 ft/sec), or ii) greater than 110% of the saltation velocity of the eductor reaction mixture. The exit velocity of the pressurized eductor reaction mixture (containing recycled components and the downcomer product mixture) exiting the eductor  375  is higher than an inlet velocity of the reaction mixture at inlet  375   a  and the inlet velocity of the recycled components at inlet  375   b . 
     The exit velocity helps to move the eductor reaction mixture through the lower conduit  310  in the direction of arrow A, where the eductor reaction mixture mixes with unreacted olefin monomer, unreacted olefin comonomer, diluent, or a combination thereof provided by conduit  503  to form the lower conduit reaction mixture. The lower conduit reaction mixture mixes with any feed components provided by conduits  322 ,  323 ,  324 , and/or  325  to form the riser reaction mixture. For the polymerization of  FIG.  1   , the first polyolefin received from conduit  202  can additionally mix with the eductor reaction mixture flowing in the lower conduit  310 . 
     In  FIG.  6 B , the eductor  375  replaces the tee connector  307  shown in  FIG.  6 A , and the transition conduit  376  of  FIG.  6 A  is embodied as the standpipe  390  in  FIG.  6 B . 
     In alternative aspect for  FIG.  6 B , it is contemplated that the inlet  375   b  of the eductor  375  can be fluidly connected to conduit  502  such that unreacted olefin monomer, unreacted olefin comonomer, diluent, or a combination thereof enters the eductor  375  (i.e., in an embodiment, there is no standpipe  390 ) directly from the conduit  502 . Alternatively still, it is contemplated that the outlet  390   b  of the standpipe  390  can be fluidly connected to the tee connector  307  of the MZCR  300  shown in  FIG.  6 A  such that unreacted olefin monomer, unreacted olefin comonomer, diluent, or a combination thereof enters the MZCR  300  directly from the standpipe  300 . 
     In  FIG.  6 C , a standpipe  390  of  FIG.  5 C  is used in combination with the transition conduit  376  having the configuration shown in  FIG.  6 A . The standpipe  390  is fluidly connected to the lower conduit  310  (e.g., via the tee connector  307 ), and the outlet  390   b  of the standpipe  390  extends into the interior of the transition conduit  376 . The inlet  390   a  of the standpipe  390  is fluidly connected to conduit  502 , optionally via a compressor or pump  502   a . The compressor or pump  502   a  is configured to increase the pressure of the unreacted olefin monomer, unreacted olefin comonomer, diluent, or a combination thereof received from conduit  502 . While the inlet  390   a  of the standpipe  390  is shown in  FIG.  6 C  as being inside the transition conduit  376 , it is contemplated that the standpipe  390  can have portions that extend both inside and outside the transition conduit  376  such that the inlet  390   a  is outside the transition conduit  376  and the outlet  390   b  of the standpipe  390  is inside the transition conduit  376 . 
     The inlet  390   a  of the standpipe  390  can be directly connected to the outlet of the compressor or pump  502   a  so as to deliver the pressurized components to the interior of the MZCR  300  in the direction of arrow C. The pressurized components enter the MZCR  300  and increase the velocity of the downcomer product mixture traveling out of the downcomer  340  and into the lower conduit  310  such that a velocity of the downcomer product mixture is i) greater than a saltation velocity of the downcomer product mixture and up to about 30.48 m/s (100 ft/sec), or ii) greater than 110% of the saltation velocity of the downcomer product mixture 
       FIG.  7    illustrates an isolated view of an elbow connector  700  having a smart elbow configuration. Any of elbow connectors  302 ,  304 , and  306  can have the smart elbow configuration shown in  FIG.  7    for elbow connector  700 . That is, the elbow connector  700  can be the elbow connector  302  connected to the bottom portion  329  of the riser  320  and to the opposite end  312  of the lower conduit  310 , the elbow connector  304  connected to the top portion  328  of the riser  320  and to the end  331  of the upper conduit  330 , or the elbow connector  306  connected to the bottom portion  349  of the downcomer  340  and to the end  311  of the lower conduit  310 . 
     In the smart elbow design, the elbow connector  700  can have a first tap  701  on an outside radius  702  of the elbow connector  700  and a second tap  703  on an inside radius  704  of the elbow connector  700 . The taps  701  and  702  can generally be holes or openings formed in the wall of the tubular structure than forms the elbow connector  700  in order to fluidly connect the interior space  705  of the elbow connector  700  with the differential pressure meter  708  via sensing legs  706  and  707 . The legs  706  and  707  can be constructed of conduit such as pipe or tubes. The sensing leg  706  on the outside radius  702  of the elbow connector  700  can be a high pressure leg, and sensing leg  707  on the inside radius  704  of the elbow connector  700  can be a low pressure leg. 
     As fluid passes through the elbow connector  700 , the pressure at the outside radius  702  increases due to centrifugal force. A first pressure on the high pressure side of the elbow connector  700  is indicated by pressure in the sensing leg  706 , and a second pressure on the low pressure side of the elbow connector  700  is indicated by a pressure in the sensing leg  707 . The pressure in the sensing leg  706  is sensed by a sensing element on the meter  708 , and the pressure in the sensing leg  707  is likewise sensed by a sensing element on the meter  708 . The meter  708  can be configured to calculate the flow rate of the reaction mixture flowing through the elbow connector  700  based on the difference in the pressures sensed by the sensing elements of the differential pressure meter  708 . In aspects, the differential pressure meter  708  can include a transmitter for transmitting a signal indicative of the pressure sensed by and/or flow rate calculated by the meter  708 , for example, to a computer in a process control system and/or process monitoring system. 
     A flushing system can be included in the sensing legs  706  and  707  that is configured to flush polyolefin particles from the legs  706  and  707 , for example, using a component in the reaction mixture, such as the olefin monomer, olefin comonomer, diluent, or an inert gas. In addition to the flushing system, screens can be included in the hole or opening formed by each of the taps  701  and  703 . The screen can be a wire mesh metal material (e.g., Johnson® type screens) configured to allow gaseous components of the reaction mixture to pass while holding back solid polyolefin particles from flowing into the legs  706  and  707 . 
     Alternatively, a diaphragm can be placed in each hole or opening formed by the tap  701  and/or tap  703  to mitigate the plugging of the taps  701  and/or  703  or plugging of the sensing legs  706  and/or  707  with polyolefin particles. The diaphragm(s) may be a flexible and relatively thin piece of material, and generally circular in shape, such as a disc. The diaphragm can be constructed of a metal (e.g., stainless steel) or polymer. In embodiments with diaphragms, sensing legs  706  and  707  can be filled with a fluid such as diluent, a hydraulic fluid (oil, mineral oil, etc.), or other fluid suitable for transmitting the pressure force for the length of the sensing legs  706  and  707  to the differential pressure meter  708 . The fluid in the legs  706  and  707  may be generally hydraulically full. Therefore, as pressure is exerted on the diaphragm, the fluid inside the legs  706  and  707  then exerts pressure on the sensing elements of the differential pressure meter  708 . 
     While  FIG.  7    shows the taps  701  and  703  formed in the elbow connector  700 , it is contemplated that the taps  701  and  703 , sensing legs  706  and  707 , and the differential pressure meter  708  can be located alternatively or additionally at other points in the MZCR reactor  300 , such as the lower conduit  310 , the riser  320 , the upper conduit  330 , the downcomer  340 , or the tee connector  307  (of  FIG.  4   ). 
       FIG.  8 A  illustrates a side view of a cyclone separator  850 , which can be a particular embodiment of the separator  350  shown in  FIG.  1    and  FIG.  2   .  FIG.  8 B  illustrates a top cross-sectional view of the cyclone separator  850  of  FIG.  8 A , taken along sight line i-i. The following discussion about the cyclone separator is with respect to both  FIG.  8 A  and  FIG.  8 B . 
     As can be seen in  FIGS.  8 A and  8 B , the cyclone separator  850  can be a hollow vessel having a conical shape. The top  854  of the cyclone separator  850  has a diameter that is greater than a diameter of the bottom  852  of the separator  850 . In an aspect, the cone angle θc of the cyclone separator  850  can be about 45° to about 80°; alternatively, about 50° to about 75°; alternatively, about 60° to about 65°; alternatively, about 45° to about 60°; alternatively, about 60° to about 70°; alternatively, about 70° to about 80°. 
     The riser  320  is configured to produce a riser product mixture that flows from the riser  320 , through the upper conduit  330 , and into the cyclone separator  850 . Thus, cyclone separator  850  can be configured to receive the riser product mixture (e.g., comprising solid particles of polyolefin particles and catalyst particles, and a gas mixture) at the separator inlet  851  via the upper conduit  330  and to separate the riser product mixture such that the gas mixture exits via the outlet  855  at the top  854  of the separator  850  (in line  353 ) and the solid particles exit the cyclone separator  850  via the bottom  852  of the cyclone separator  850  (e.g., into the liquid barrier). 
     The riser product mixture can enter the inner chamber  856  of the cyclone separator  850  via the inlet  851  and near the top  854  of the cyclone separator  850 . A tangential velocity of the riser product mixture entering the inner chamber  856  forces the solid particles to flow in a downward spiral path  858 , due to inward radial acceleration of the solid particles, and concurrently, due to gravitational force imparts downward acceleration on the solid particles in the inner chamber  856  of the cyclone separator  850 . The result is a downward movement of separated solid particles along the inner wall  857  in the downward spiral path  858 , while the gas mixture of the riser product mixture separates and moves upward in the chamber  856  and exits via the outlet  855 . In an aspect, the cyclone separator  850  can particularly be a high efficiency cyclone configured to separate 99 wt.% or more of the solid particles which have a size of from about 2 µm to about 10 µm from the gas mixture. 
     In another aspect, an angle θc with respect to horizontal of the end  332  of the upper conduit  330  than connects to the cyclone separator  850  can be about 0° to about 15°. In yet another aspect, a vertical distance h between the top  854  of the separator  850  and where the upper conduit  330  connects to the separator  850  can be from about 0 m (0 ft) to about 6.10 m (20 ft); alternatively, from about 0.305 m (1 ft) to about 3.048 m (10 ft); alternatively, from about 0.305 m (1 ft) to about 1.52 m (5 ft). 
     In an aspect, cyclone separator  850  is a tangential flow cyclone, and inlet  851  is a tangential inlet. The tangential inlet  851  can have an entrance angle θ E  of about 0° to about 15°; alternatively, about 7° to about 11°, with respect to a tangent of the cyclone separator  850 . Configuring the cyclone separator  850  as a tangential flow cyclone separator entails that the inlet  851  is a tangential inlet. The tangential inlet  351  can guide the riser product mixture entering the cyclone separator  850  toward the inner wall  857  to promote separation of the solid particles from the gas mixture in cyclone fashion as described above. 
     In another aspect, the tangential entrance velocity of the riser product mixture into the cyclone separator  850  can be from about 15.24 m/s (50 ft/sec) to about 30.48 m/s (100 ft/sec); alternatively, about 18.29 m/s (60 ft/sec) to about 27.43 m/s (90 ft/sec); alternatively, about 21.34 m/s (70 ft/sec) to about 24.39 m/s (80 ft/sec). 
       FIG.  9    illustrates an embodiment of the product separation system  400  depicted in  FIG.  1    and  FIG.  2   . As can be seen, the product separation system  400  can be configured to separate the a product mixture containing the multimodal polyolefin received from the product discharge conduit  370  (if referring to the embodiment in  FIG.  1   ) or product discharge conduit  110  (if referring to the embodiment in  FIG.  2   ) into various streams, including a multimodal polyolefin conduit  401 , an olefin monomer conduit  402 , an olefin comonomer conduit  403 , a diluent conduit  404 , a heavies conduit  405 , and a waste gas conduit  406 .  FIG.  9    illustrates additional conduits that are present in the product separation system  400 , including side conduit  451  that can contain olefin monomer, gaseous components that are lighter than the olefin monomer, and optionally, diluent. 
     Equipment in the product separation system  400  can include one or more of a take-off valve  410 , a heater  420 , a separation vessel  430 , a degassing vessel  440 , a heavies distillation column  450 , a lights distillation column  460 , and a polishing apparatus  470 . 
     In  FIG.  9   , the take-off valve  410  can be configured to receive the product mixture from the product discharge conduit  370  and to control the flow of the product mixture therethrough. The take-off valve  410  can be any type of control valve known in the art to be useful for controlling flow of the product mixture. Such valves include ball valves, v-ball valves, plug valves, globe valves and angle valves. In an aspect, the take-off valve  410  can have a diameter when 100% open in a range of from about 1.27 cm (0.5 inches) to about 7.62 cm (3 inches). In an aspect, the take-off valve  410  can have a flow channel diameter greater than the largest expected polymer particle size even when the valve  410  is required to be only a small amount open (for example, 20-25% open), which gives a wide control range for the range of openness of the take-off valve  410  (e.g., 20-100% open). The take-off valve  410  may be actuated by a signal from a controller configured to operate the take-off valve  410  in a continuous or a discontinuous (e.g., intermittently opened) manner. The controller may be configured to fully close and then fully open the take-off valve  410  at set intervals and for a certain duration, to actuate the take-off valve  410  to a percentage of openness, e.g., 20-100% open. 
     The product mixture can flow from the take-off valve  410  in conduit  411  to a heater  420 . In an optional embodiment, one or more of a catalyst poison (also referred to as a catalyst deactivator) and a cocatalyst poison (also referred to as a cocatalyst deactivator) can be added to the conduit  411  via conduit  412 . In such an embodiment, the product mixture with catalyst/cocatalyst poison/deactivator can flow from the take-off valve  410  in conduit  411  to the heater  420 . It is contemplated that the poison and/or deactivator added via line  412  can be added anywhere in or upstream of the heater  420 . Examples of the catalyst poison and/or cocatalyst poison include water and any alcohol. 
     The heater  420  can be coupled to the product discharge conduit  370 , either directly, or as depicted in  FIG.  9   , via take-off valve  410  and conduit  411 . In  FIG.  9   , the end  421  of the heater  420  is connected to the conduit  411 . The heater  420  can be configured to receive the product mixture and to add heat to the product mixture as the product mixture passes through the heater  420 . An objective of the heater  420  is to discharge the multimodal polyolefin in the product mixture at a temperature i) of about 54.4° C. (130° F.) to about 104.4° C. (220° F.), or ii) below a melting point of the multimodal polyolefin. 
     The heater  420  can have any configuration according to any configuration recognized in the art with the aid of this disclosure. For example, heater  420  can be an electric heater wrapped around portions of the conduit  411 , a heat exchanger such as a shell and tube heat exchanger (e.g., where a heating medium is separated by structural elements which transfer heat to the product mixture flowing through the heater  420 ), a flashline heater (e.g., with heat added by steam into a jacket, by electric heaters, or by both in alternating portions along the heater  420 ), or combinations thereof. Flashline heater configurations are discussed further in U.S. Pat. Nos. 8,597,582 and 8,883,940, each of which is incorporated by reference in its entirety. In an aspect, the heater  420  can be configured as an open flow channel flashline heater, which is a jacketed pipe of a constant diameter that is heater with steam injected in the jacket at end  421  and condensate collected from the jacket at end  422  of the heater  420 . In the open flow channel configuration, the jacket can include a common collection system for the steam that condenses to water in the jacket after transferring heat to the product mixture that moves through the heater  420 . The collection system can comprise an open downward angle flow section configured to collect the condensate. 
     The separation vessel  430  can be coupled to the end  422  of the heater  420  either directly or, as shown in  FIG.  9   , via conduit  423 . The separation vessel  430  is configured to separate the heated product mixture into a plurality of streams (e.g., conduit  431  and conduit  432 ) comprising vapor, a polymer product, or both vapor and polymer product. The vapor can include the gases separated from the multimodal polyolefin, and the polymer product can include the multimodal polyolefin. The separation vessel  430  can be embodied as a flash tank configured to provide a reduction in pressure of the product mixture such that olefin monomer, any optional olefin comonomer, diluent, and other components (e.g., nitrogen, hydrogen, oxygen, methane, ethane, propane, butane, isobutane, pentane, hexane, heavier hydrocarbons, or combinations thereof) separate from the multimodal polyolefin so as to yield conduit  431  comprising one or more of these gaseous components. To the extent that any liquid is contained in the heated product mixture, the pressure reduction provided in the flash tank can flash the liquid into the gas phase for flow in conduit  431 . 
     The separation vessel  430  can be a hollow vessel having a cone-shaped bottom portion that directs the flow of the multimodal polyolefin to conduit  432 . In an aspect, the separation vessel  430  can operate without a pressure reduction, for example, when the product mixture contains gas components and the multimodal polyolefin and no or a minimal amount of liquid, since a reduction in pressure is not needed for flashing a liquid component to a gas phase. 
     The multimodal polyolefin in conduit  432  can optionally flow to a degassing vessel  440  that can be configured to receive the polymer product (e.g., the multimodal polyolefin) from the separation vessel  430  and to remove at least a portion of a hydrocarbon (e.g., olefin monomer, any optional olefin comonomer, diluent, ethane, or combinations thereof) entrained within the polymer product. Conduit  441  can provide an inert gas (e.g., nitrogen or an inert hydrocarbon such as ethane, propane, n-butane, or isobutane) to the degassing vessel  440 . The degassing vessel  440  can be operated at appropriate conditions (e.g., temperature, pressure, inert gas flow rate) such that the inert gas flows through the collection of polyolefin particles present in the degassing vessel  440 , removes entrained hydrocarbon from the polyolefin particles, moves upwardly through the degassing vessel  440  with the removed hydrocarbon(s), and exits the degassing vessel  440  along with the previously entrained hydrocarbon in conduit  442 . The degassed polymer product (e.g., multimodal polyolefin) can be recovered via conduit  401 . The degassing vessel  440  can be configured for plug flow of polymer product from top to bottom. The residence time of polymer product in the degassing vessel  440  can be at least 10 minutes, at least 30 minutes, about 1 hour, or from about 1 hour to about 6 hours. The operating pressure of the degassing vessel  440  can be a vacuum pressure, atmospheric pressure, or greater than atmospheric pressure. In a particular aspect, the pressure of the degassing vessel  400  can be a pressure in the range of from about 0 psia to about 50 psia (about -0.101 MPaa to about 0.345 MPaa). 
     In an optional aspect, conduit  201  containing gaseous components recovered from the product mixture of the first reactor  100  in  FIG.  1    or the product mixture of the MZCR  300  in  FIG.  2    can be combined with the gaseous components in conduit  431  such that the vapor that flows in conduit  431  additionally contains said gaseous components from conduit  201 . 
     The gaseous components in the vapor in conduit  431  can flow to a monomer recovery system  480 . The monomer recovery system  480  can be configured to recover one or more of the olefin monomer, the olefin comonomer, the diluent, and other gaseous components (e.g., nitrogen, oxygen, hydrogen, or combinations thereof) from the vapor in conduit  431 . 
     The monomer recovery system  480  in  FIG.  9    is described in the context of recovery of the olefin monomer, olefin comonomer, diluent, and other gaseous components from conduit  431  by recovering these components in various streams to a desired purity via separation techniques such as distillation, absorption, membrane separation, flash separation, compression, condensation, or combinations thereof. The exact configuration of the monomer recovery system  480  can depend on which olefin monomer, which olefin comonomer, and which diluent are used in the polymerizations in the first reactor  100  and the MZCR  300 . For example, for polymerization of ethylene monomer and 1-hexene comonomer with an isobutane diluent, the monomer recovery system  480  as illustrated in  FIG.  9    can be utilized (as will be described in more detail below). Alternatively, when the olefin comonomer is closer in molecular weight to the olefin monomer (e.g., 1-butene or propylene is used as the comonomer instead of 1-hexene), a lights distillation column can be utilized where ethylene and lighter gaseous components are recovered from the top of the lights distillation column, isobutane is recovered from the bottom of the distillation column, and 1-butene or propylene can be recovered from the bottom and/or optionally from a side draw of the lights distillation column. In such as aspect, the ethylene and lighter components can be separately recovered in a polishing apparatus (embodiments and aspects are described for polishing apparatus  470  in  FIG.  9   ). Alternatively, it is contemplated that the monomer recovery system  480  can be embodied simply as a compressor or series of compressors that recycle the vapor in conduit  431  to one or both of the first reactor  100  and MZCR  300 , such as is described in the monomer recovery process in U.S. Pat. No. 5,376,742. 
     In the embodiment of the monomer recovery system  480  illustrated in  FIG.  9   , the monomer recovery system  480  includes a heavies distillation columns  450 , a lights distillation column  460 , and polishing apparatus  470 . 
     The heavies distillation column  450  can be configured to separate at least one gaseous component from the group of gaseous components received into the column  450  from conduit  431 . The components in conduit  431  can be introduced into the heavies distillation column  450  at a pressure in a range of from about 0.101 MPa (14.7 psi) to about 3.64 MPa (527.9 psi), alternatively, from about 0.108 MPa (15.7 psi) to about 2.40 MPa (348 psi), alternatively, from about 0.586 MPa (85 psi) to about 2.00 MPa (290 psi). 
     The heavies distillation column  450  can be operated at conditions (e.g., temperature, pressure, number of trays, reflux rate, heating rate, and other parameters for controlling the operation of a distillation column) suitable to recover heavy hydrocarbons in conduit  405 , the olefin comonomer in conduit  403 , and components lighter than the olefin comonomer in conduit  451 . For example, the heavies distillation column  450  can be operated at a temperature in a range of from about 15° C. (59° F.) to about 233° C. (451.4° F.), alternatively, from about 20° C. (68° F.) to about 200° C. (392° F.), alternatively, from about 20° C. (68° F.) to about 180° C. (356° F.), and/or a pressure in a range of from about 0.101 MPa (14.7 psi) to about 3.64 MPa (527.9 psi), alternatively, from about 0.108 MPa (15.7 psi) to about 2.40 MPa (348 psi), alternatively, from about 0.586 MPa (85 psi) to about 2.00 MPa (290 psi). 
     In an aspect, the heavy hydrocarbons in conduit  405  include hydrocarbons heavier than the olefin comonomer (e.g., C 6+  hydrocarbons), the olefin comonomer in conduit  403  is 1-hexene, and the components lighter than the olefin comonomer in conduit  451  can include nitrogen, hydrogen, oxygen, methane, ethane, ethylene, propane, propylene, butane, 1-butene, isobutane, pentane, pentene or combinations thereof. In an additional aspect, the components in conduit  405  are in the liquid phase, the components in conduit  403  are in the liquid phase, and the components in conduit  451  are in the gas phase. 
     Components lighter than the olefin monomer may be present in conduit  451  in an amount of from about 80 wt.% to about 100 wt.% based on a total weight of the components in conduit  451 ; alternatively, from about 90 wt.% to about 99.999999 wt.%; alternatively, from about 99 wt.% to about 99.9999 wt.%. Components including C 5  and heavier hydrocarbons may be present in the conduit  451  in an amount from 0 wt.% to about 20 wt.% based on a total weight of the intermediate hydrocarbon stream; alternatively, from about 10 wt.% to about 0.000001 wt.%; alternatively, from about 1.0 wt.% to about 0.0001 wt.%. 
     Components including hexane and heavier hydrocarbons may be present in conduit  405  in an amount greater than about 85 wt.% based on a total weight of the components in conduit  405 ; alternatively, greater than about 90 wt.%; alternatively, greater than about 95 wt.%. In an embodiment, the components in conduit  405  can be directed to additional processing steps or processes, or alternatively they may be disposed of, as appropriate. 
     The components present in conduit  403  can include the olefin comonomer of 1-hexene. 1-hexene can be present in conduit in an amount of from about 20 wt.% to about 98 wt.% based on a total weight of the components in conduit  403 ; alternatively from about 40 wt.% to about 95 wt.%; alternatively, from about 50 wt.% to about 95 wt.%. 
     Either of conduits  403  and  405  can be routed so as to recycle the components therein to the first reactor  100  and/or to the MZCR  300 . 
     The lights distillation column  460  can be configured to separate at least one gaseous component from the group of gaseous components received into the column  460  from conduit  451 . The lights distillation column  460  can be operated at conditions (e.g., temperature, pressure, number of trays, reflux rate, heating rate, and other parameters for controlling the operation of a distillation column) suitable to recover olefin-free diluent in conduit  404 , the diluent in conduit  461 , and the olefin monomer combined with components lighter than the olefin comonomer in conduit  462 . For example, the lights distillation column  460  can be operated at a temperature in a range of from about 50° C. (122° F.) to about 20° C. (68° F.); alternatively, from about 40° C. (104° F.) to about 10° C. (50° F.); alternatively, from about 30° C. (86° F.) to about 5° C. (41° F.), and a pressure in a range of from 0.101 MPa (14.7 psi) to about 3.64 MPa (527.9 psi), alternatively, from about 0.108 MPa (15.7 psi) to about 2.40 MPa (348 psi), alternatively, from about 0.586 MPa (85 psi) to about 2.00 MPa (290 psi). 
     In an aspect, the light components in conduit  462  include hydrocarbons lighter than the diluent, the components in conduit  461  can include the diluent and olefin monomer, and the components in conduit  404  can include the diluent. In an additional aspect, the components in conduit  404  are in the liquid phase, the components in conduit  461  are in the liquid phase, and the components in conduit  462  are in the gas phase. 
     The components emitted from the lights distillation column  460  in light hydrocarbon conduit  462  may comprise the olefin monomer (e.g., ethylene) and other light gases (e.g., ethane, methane, carbon dioxide, nitrogen, hydrogen, or combinations thereof). In an aspect, ethylene may be present in light hydrocarbon conduit  462  in an amount from about 50 wt.% to about 99 wt.% based on a total weight of components in the light hydrocarbon conduit  462 ; alternatively, from about 60 wt.% to about 98 wt.%; alternatively, from about 70 wt.% to about 95 wt.%. 
     The components emitted from the lights distillation column  460  in bottoms conduit  404  may comprise propylene, propane, butane, isobutane, pentane, or combinations thereof. In an aspect, the bottoms conduit may be free of olefins (i.e., “olefin-free”), alternatively, substantially free of olefins, alternatively, essentially free of olefins. For example, olefin(s) may be present in bottoms conduit  404  in an amount less than about 1.0 wt.% based on a total weight of the components in the bottoms conduit  404 ; alternatively, less than about 0.5 wt.%; alternatively, less than about 0.1 wt.%. The diluent may be present in the bottom conduit in an amount greater than about 99.0 wt.% based on a total weight of the components in the bottoms conduit  404 ; alternatively, greater than about 99.5 wt.%; alternatively, greater than about 99.9 wt.%. 
     The components emitted from the lights distillation column  460  in side draw conduit  461  can include isobutane and ethylene. For example, isobutane can be present in the side conduit  461  in an amount of greater than about 85 wt.% based on a total weight of components in the conduit  461 ; alternatively, greater than about 90 wt.%; alternatively, greater than about 95 wt.%. Ethylene can be present in the side conduit  461  in an amount of less than about 15 wt.% based on a total weight of components in the conduit  461 ; alternatively, less than about 10 wt.%; alternatively, less than about 5 wt.%. 
     Either of conduits  404  and  461  can be routed so as to recycle the components therein to the first reactor  100  and/or to the MZCR  300 . 
     The polishing apparatus  470  can be configured to receive the conduit  462  and to separate the received gaseous components into olefin monomer in conduit  402  and waste gases in conduit  406 . The polishing apparatus  470  can utilize any technique for separating the olefin monomer from the waste gases, for example, compression, distillation (e.g., utilizing cryogenic and/or vacuum conditions), absorption, membrane separation, condensation, or combinations thereof. 
     An example of the polishing apparatus  470  is found in U.S. Pat. No. 9,598,514, which is incorporated by reference in its entirety. In aspects, the polishing apparatus  470  can include an absorption reactor configured to selectively absorb the olefin monomer from among the components in conduit  462 . Non-limiting examples of suitable absorption reactors and/or absorption reactor configurations include an absorption (distillation) tower, a pressure-swing absorption (PSA) configuration, a sparger tank, an agitation reactor, one or more compressors, one or more recycle pumps, or combinations thereof. The absorption reactor can contain a liquid absorption solvent system configured to selectively absorb the olefin monomer, and the components in conduit  462  can enter the absorption reactor so that the components (in the gas phase) bubble upwardly through the liquid absorption solvent system. The olefin monomer can be absorbed in the liquid absorption solvent system until saturation with the olefin monomer is reached. In an aspect, the olefin monomer can be liberated from the solvent by a reduction in pressure (e.g., pressure swing absorption) and/or by elevating the solvent temperature (e.g., the olefin monomer liberates as a gas from the solvent at elevated temperature). In an alternative aspect, a solvent circulation system can be utilized in the polishing apparatus  470  to circulate saturated liquid absorption solvent system to a regenerator of the polishing apparatus  470 . The olefin monomer can be liberated from the solvent in the regenerator, and in such as aspect, the olefin monomer can flow in conduit  402  from the regenerator of the polishing apparatus  470 . 
     In further aspects, the absorption reactor of the polishing apparatus  470  can include a packed bed or column configured to maintain smaller bubble sizes (e.g., of the gas components received from conduit  462 ), for example, so as to maintain a relatively large surface area of contact between the gas and the liquid solvent and to maintain an efficiency of mass transfer and/or absorption of the gas into the liquid. In aspects, the packing material of the packed bed or column can include a polymeric material, a metallic material, or combinations thereof. It is contemplated that in the pressure swing absorption configuration, the polishing apparatus  470  can include multiple absorption reactors operating in parallel such that at least one reactor can be taken off-line to liberate the olefin monomer from the liquid absorption solvent system while at least another reactor in parallel can be on-line to capture the olefin monomer received from conduit  462 . An example of a suitable absorption reactor is illustrated in the Gas Processors Association, “Engineering Data Book” 10 th  ed. at  FIGS.  19 - 16   , which is incorporated by reference in its entirety. 
     In aspects where the components in conduit  462  include ethylene as the olefin monomer and ethane is among the other gases, the absorption solvent system may be characterized as having a selectivity of ethylene to ethane where ethylene and ethane are present at the same partial pressure of about 40:1 at about 96.5 kPa (14 psi); alternatively, about 12:1 at about 138 kPa (20 psi); alternatively, about 6:1 at about 276 kPa (40 psi); alternatively, about 3:1 at about 1.24 MPa (180 psi) partial pressure. 
     In aspects, the absorption reactor of the polishing apparatus  470  can be configured to operate in a temperature range of from about 4.4° C. (40° F.) to about 43.3° C. (110° F.); alternatively, from about 4.4° C. (40° F.) to about 15.6° C. (60° F.); alternatively, from about 7.2° C. (45° F.) to about 12.8° C. (55° F.); alternatively, from about 10° C. (50° F.) to about 12.8° C. (55° F.); alternatively about 10° C. (50° F.). 
     In aspects, the absorption reactor of the polishing apparatus  470  can be configured to operate in a pressure range of from about 34.5 kPag (5 psig) to about 3.45 MPag (500 psig); alternatively, from about 0.345 MPag (50 psig) to about 3.10 MPag (450 psig); alternatively, from about 0.517 MPag (75 psig) to about 2.76 MPag (400 psig). In aspects that involve ethylene as the olefin monomer recovered in conduit  402  of the polishing apparatus  470 , the absorption reactor can be configured to provide or maintain a suitable partial pressure of ethylene in a range of from about 6.89 kPaa (1 psia) to about 2.76 MPaa (400 psia); alternatively, from about 0.207 MPaa (30 psia) to about 1.38 MPaa (200 psia); alternatively, from about 0.276 MPaa (40 psia) to about 1.72 MPaa (250 psia); alternatively, from about 0.276 MPaa (40 psia) to about 0.517 MPaa (75 psia); alternatively, from about 0.276 MPag (40 psig) to about 0.414 MPag (60 psig); alternatively about 0.276 MPag (40 psig); alternatively, about 0.414 MPag (60 psig). 
     In aspects, the liquid absorption solvent system contains a solvent. The solvent can be an amine or an amine complex, an aromatic hydrocarbon, an olefin, or combinations thereof. Non-limiting examples of solvent amines include pyridine, benzylamine, and aniline. For example, the amine may comprise an aniline (phenylamine, aminobenzene); alternatively, aniline combined with dimethylformamide (DMF), and in embodiments, aniline and N-methylpyrrolidone (NMP). In aspects where the solvent comprises an aromatic hydrocarbon, the aromatic hydrocarbon may comprise an unsubstituted or alkyl substituted aryl groups. The aromatic hydrocarbon may be in the liquid phase under normal, ambient conditions. Suitable non-limiting examples include toluene, xylene, and the like. In aspects where the solvent comprises an olefin, non-limiting examples include olefins having 10 to 16 carbon atoms. For example, the olefin functioning as a solvent (which is not the olefin monomer from conduit  462  being absorbed) can comprise propylene tetramer, dodecene, tetradecene, hexadecene, or combinations thereof. In aspects, the solvent may be characterized as aprotic, that is, as not including a dissociable hydrogen atom. Not intending to be bound by theory, a dissociable hydrogen solvent may result in the hydrogenation of the double bond between carbons in an olefin such as ethylene. Further, the solvent may be characterized as polar, as having a slight polarity, or as having unidirectional, electric charge. Not intending to be bound by theory, a polar solvent may interact with and at least partially solubilize the salt. 
     In additional aspects, the liquid absorption solvent system can additionally include a complexing agent in addition to the solvent. In this configuration, the liquid absorption solvent can be capable of reversibly complexing with the olefin monomer. The complexing agent may include a metallic salt. The metallic salt can include a salt of one or more transition metals and a weakly-ionic halogen. Non-limiting examples of suitable transition metals include silver, gold, copper, platinum, palladium, and nickel. Non-limiting examples of suitable weakly-ionic halogens include chlorine and bromine. In aspects, a suitable transition metal salt may be characterized as having a high specificity for olefins. Non-limiting examples of suitable transition metal-halogen salts include silver chloride (AgCl) and copper chloride (CuCl). In a particular aspect, the salt employed in the liquid absorption solvent system comprises CuCl. Not seeking to be bound by theory, such a metallic salt may interact with the double carbon bonds of olefin monomers (e.g., ethylene). 
     In an aspect, the complexing agent may comprise a copper (I) carboxylate. Suitable copper (I) carboxylates include salts of copper (I) and mono-, di-, and/or tri-carboxylic acids containing 1-20 carbon atoms. The carboxylic acid component of the salt may comprise an aliphatic constituent, a cyclic constituent, an aryl constituent, or combinations thereof. Other suitable examples of copper (I) carboxylates include Cu(I) formate, Cu(I) acetate, Cu(I) propionate, Cu(I) butyrate, Cu(I) pentanoate, Cu(I) hexanoate, Cu(I) octanoate, Cu(I) decanoate, Cu(I) 2-ethyl-hexoate, Cu(I) hexadecanoate, Cu(I) tetradecanoate, Cu(I) methyl formate, Cu(I) ethyl acetate, Cu(I) n-propyl acetate, Cu(I) n-butyl acetate, Cu(I) ethyl propanoate, Cu(I) octoate, Cu(I) benzoate, Cu(I) p-t-butyl benzoate, and the like. Additionally, the complexing agent can include an adduct of a copper (I) carboxylate, for example, as disclosed herein, and boron trifluoride (BF 3 ). 
     In an additional and/or alternative aspect, the complexing agent may comprise a copper (I) sulfonate. Non-limiting examples of suitable copper (I) sulfonates include the copper (I) salts of sulfonic acids having 4 to 22 carbon atoms. The sulfonic acid component of the salt can include an aliphatic constituent, a cyclic constituent, an aryl constituent, or combinations thereof. The aliphatic sulfonic acids can be straight chain or branched. Examples of suitable aliphatic sulfonic acids include, but are not limited to, n-butanesulfonic acid, 2-ethyl-1-hexanesulfonic acid, 2-methylnonanesulfonic acid, dodecanesulfonic acid, 2-ethyl-5-n-pentyltridecanesulfonic acid, n-eicosanesulfonic acid, and the like. Examples of suitable aromatic sulfonic acids include benzenesulfonic acid, alkylbenzenesulfonic acids wherein the alkyl member contains from 1 to 16 carbon atoms, such as p-toluenesulfonic acid, dodecylbenzenesulfonic acid (o-, m-, and p-), p-hexadecylbenzenesulfonic acid, and the like, naphthalenesulfonic acid, phenolsulfonic acid, naphtholsulfonic acids, and halobenzenesulfonic acids, such as p-chlorobenzenesulfonic acid, p-bromobenzenesulfonic acid, and the like. 
     In an aspect, the complexing agent can also include a hindered olefin. For example, the complexing agent may additionally include a hindered olefin when the complexing agent without the hindered olefin forms a copper complex with insufficient solubility in the solvent. An example of such a hindered olefin is a propylene tetramer (i.e. dodecene). Not intending to be bound by theory, the hindered olefin may increase the solubility of the copper complex while being easily displaced by ethylene. 
     In various embodiments, the absorption solvent system can utilize one or more of the complexing agents disclosed in U.S. Pat. Nos. 5,104,570; 5,191,153; 5,259,986; and 5,523,512, each of which is incorporated by reference in its entirety. 
     Particular embodiments of the liquid absorption solvent system include copper chloride, aniline, and dimethylformamide (CuCl/aniline/DMF); alternatively, copper chloride, aniline, and N-methylpyrrolidone (CuCl/aniline/NMP); alternatively, copper (I) carboxylate and an aromatic solvent such as toluene or xylene; alternatively, copper (I) sulfonate and an aromatic solvent such as toluene or xylene; alternatively, an adduct of copper (I) carboxylate and BF 3  in an aromatic solvent such as toluene or xylene; alternatively, copper (I) 2-ethyl-hexanoate and propylene tetramer; alternatively, copper (I) 2-ethyl-hexanoate and dodecene; alternatively, copper (I) hexadecanoate and hexadecene; alternatively, copper (I) tetradecanoate and tetradecene. 
     Another example of the polishing apparatus  470  is found in U.S. Pat. No. 5,769,927. In aspects, the polishing apparatus  470  can include a condenser, a flash tank, and a membrane filtration unit. The components of conduit  462  can be subject to condensation in the condenser so that a portion of the components condenses to a liquid phase while another portion of the components remains in the gas phase. The resulting liquid from condensation can then be subjected to flash separation in the flash tank to form a vapor from the condensed liquid and residual liquid portion. The resulting gas from condensation can be subjected to membrane separation to recover the waste gases from the resulting gases. The residual liquid portion recovered from the flash step can include the olefin monomer in conduit  402 , which can be recycled to the first reactor  100  and/or the MZCR  300 , or otherwise consumed, treated, processed, and/or stored. The waste gases recovered from the membrane separation step can include hydrogen, oxygen, nitrogen, carbon dioxide, or combinations thereof in conduit  406 . These waste gases can be flared. 
     When utilizing a polishing apparatus  470  that has a condenser, flash tank, and membrane filtration unit, the components in conduit  462  can be compressed prior to feeding to the condenser. The temperature and pressure of the components in conduit  462  exiting the lights distillation column  460  can be a temperature which can range from about 5° C. (41° F.) to about 20° C. (68° F.) and a pressure which can range of from about 0.101 MPa (14.7 psi) to about 0.586 MPa (85 psi). The pressure after compression can be in a range of from about 0.689 MPag (100 psig) to about 6.89 MPag (1,000 psig); alternatively, from about 0.689 MPag (100 psig) to about 3.45 MPag (500 psig); alternatively, from about 0.689 MPag (100 psig) to about 1.72 MPag (250 psig); alternatively, from about 1.38 MPag (200 psig) to about 6.89 MPag (1,000 psig); alternatively, from about 1.38 MPag (200 psig) to about 3.45 MPag (500 psig); alternatively, from about 1.38 MPag (200 psig) to about 1.72 MPag (250 psig). The temperature of the components in conduit  462  after compression may be slightly higher due to heat of compression. 
     In aspects, the condenser of the polishing apparatus  470  can be operated at a temperature in a range of from about -100° C. (-148° F.) to about 20° C. (68° F.); alternatively, from about -60° C. (-76° F.) to about 20° C. (68° F.); alternatively, from about -40° C. (-40° F.) to about 20° C. (68° F.). In additional aspects, the condenser of the polishing apparatus  470  can be operated at a pressure in a range of from about 0.689 MPag (100 psig) to about 6.89 MPag (1,000 psig); alternatively, from about 0.689 MPag (100 psig) to about 3.45 MPag (500 psig); alternatively, from about 0.689 MPag (100 psig) to about 1.72 MPag (250 psig); alternatively, from about 1.38 MPag (200 psig) to about 6.89 MPag (1,000 psig); alternatively, from about 1.38 MPag (200 psig) to about 3.45 MPag (500 psig); alternatively, from about 1.38 MPag (200 psig) to about 1.72 MPag (250 psig). 
     The temperature and pressure for operation of the flash tank of the polishing apparatus  470  can be that which is suitable to bring the olefin monomer in the residual condensed liquid in a range of about 0 MPa (0 psig) to about 0.345 MPag (50 psig) above the saturation vapor pressure of the olefin monomer at the temperature at which the flash tank is operated. 
     In aspects, the membrane filtration unit of the polishing apparatus  470  can contain a membrane that exhibits a substantially different permeability for the olefin monomer gas than for the other gases (e.g., nitrogen, hydrogen, carbon dioxide, oxygen, or combinations thereof) that are in the residual gas phase. The pressure of the residual gas components exiting the condenser can be sufficient to drive the pressure drop across the membrane of the membrane filtration unit. The waste gas stream  406  exiting the membrane filtration unit can be greater than 5° C. (41° F.), alternatively, greater than 10° C. (50° F.) colder than the temperature of the residual gas components that feed from the condenser to the membrane filtration unit. 
     The membrane can be relatively permeable to the olefin monomer and relatively impermeable to the other gases, or relatively permeable to the other gases and relatively impermeable to the monomer. When relatively permeable to the olefin monomer, the conduit  406  used to recover the waste gases is connected to the retentate side of the membrane filtration unit; whereas, when relatively permeable to the other gases, the conduit  406  used to recover the waste gases is connected to the permeate side of the membrane filtration unit. 
     Examples of membranes that are relatively permeable to the olefin monomer include polymers that can be used to make elastomeric membranes, for example, nitrile rubber, neoprene, polydimethylsiloxane (silicone rubber), chlorosulfonated polyethylene, polysilicone-carbonate copolymers, fluoroelastomers, plasticized polyvinylchloride, polyurethane, cis-polybutadiene, cis-polyisoprene, poly(butene-1), polystyrene-butadiene copolymers, styrene/butadiene/styrene block copolymers, styrene/ethylene/butylene block copolymers, thermoplastic polyolefin elastomers, block copolymers of polyethers, polyamides, polyesters, or combinations thereof. Examples of membranes that are relatively permeable to the other gases include polymers that can be used to make glassy membranes, for example, polysulfones, polyimides, polyamides, polyaramides, polyphenylene oxide, polycarbonates, ethylcellulose, cellulose acetate, or combinations thereof. 
       FIGS.  10 A to  10 F  illustrate the first reactor  100  having various additional aspects not shown in  FIG.  1    and  FIG.  2   . 
       FIGS.  10 A to  10 F  show the first reactor  100  is in a fluidized bed reactor configuration (also referred to as a gas phase reactor configuration). In such a configuration, and as described for the first reactor  100  in the description for  FIGS.  1 - 2   , the fluidized bed reactor can include a gas recycle system, which in  FIGS.  10 A to  10 F  is formed by equipment  120 ,  130 ,  122 ,  140 ,  124 ,  150 , and  126 . Equipment  120 ,  122 ,  124 , and  126  are conduits; equipment  130  is a separator; equipment  140  is a condenser; and equipment  150  is a compressor. Feed components feed into the gas recycle system at conduit  124  via a combined feed conduit  107 . The combined feed conduit  107  contains a mixture of the olefin monomer from conduit  102 , the optional olefin comonomer from conduit  104 , the diluent from conduit  106 . The catalyst (optionally as art of a catalyst system) can be fed directly to the reaction vessel of the fluidized bed reactor  100  via conduit  108 . While  FIGS.  10 A to  10 F  show conduits  102 ,  104 , and  106  feeding to the gas recycle system via conduits  107  and  124 , it is contemplated that the components in conduits  102 ,  104 ,  106  can be fed to the first reactor  100  at any suitable location, including i) directly to the reaction vessel of the first reactor  100 , or ii) any of conduits  120 ,  122 ,  124 ,  126 , and  133 . Similarly, while  FIGS.  10 A to  10 F  show conduit  108  feeding to directly to the reaction vessel, it is contemplated that the catalyst can be fed in conduit  108  to the first reactor  100  at any suitable location, such as via any of conduits  107 ,  120 ,  122 ,  124 ,  126 , and  133 . 
     In operation, gaseous components flow from the top  101  of the first reactor  100  into conduit  120  of the gas recycle system. While the first reactor  100  can include a disengagement zone  114  configured to disengage the gaseous components in the fluidized bed from the solid polyolefin particles for flow in conduit  120 , it is possible that some polyolefin particles can flow along with the gaseous components out of the top  101  of the first reactor  100  and into conduit  120 . 
     In the gas recycle system of  FIGS.  10 A to  10 F , an optional separator  130  can be included to separate the polyolefin particles from the gaseous components before the gaseous components enter downstream equipment such as the condenser  140  and compressor  150  (e.g., to avoid fouling of this equipment). The separator  130  can be configured as a settling tank or a cyclone separator as described herein. The solid polyolefin particles fall with the aid of gravity in the separator  130  and can separate from the gaseous components such that the solid olefin particles flow from the separator  130  in conduit  131 , while the gaseous components continue along the gas recycle system in conduit  122 . The gaseous components in conduit  122  can then flow into a condenser  140  in the gas recycle system that is configured to condense at least one of the gaseous components, for example, the diluent or condensing agent, used in the gas phase polymerization reactor. Condensation of the gaseous components forms a gas/liquid mixture that flows from the condenser  140  via conduit  124 . The gas/liquid mixture can be combined with any components fed to the first reactor  100  via conduit  107 . The conditions of conduit  124  can be such that diluent added via conduit  106  is in the liquid phase, while the olefin monomer added via conduit  102  is in the gas phase. It is contemplated that the optional olefin comonomer, if present, can be in the liquid phase or gas phase in conduit  124 , depending on the boiling point of the olefin comonomer relative to the diluent/condensing agent. The gas/liquid mixture can then flow to in conduit  124  to compressor  150 . The compressor  150  is configured to increase the pressure of the gas/liquid mixture so as to provide additional conditions under which the diluent/condensing agent condenses in the gas recycle system. The compressed gas/liquid mixture flows from the compressor  150  via conduit  126 , back into the first reactor  100 . 
     The solid polyolefin particles in conduit  131  can flow to a motive device  132 . In an embodiment, the motive device  132  can be an eductor of a configuration as described in  FIG.  5 A  or  FIG.  5 B . A motive device  132  embodied as an eductor can be appropriately sized for the smaller solids flow rate than the comparative solids flow of eductor  375  described in  FIGS.  5 D to  5 H . In an eductor embodiment, the motive device  132  can receive the solid polyolefin particles in end  132   a , a carrier gas in end  132   b . The solid/gas mixture can exit end  132   c  and can flow back into the first reactor  100  via conduit  133 . In an aspect, the carrier gas can be sourced from the gaseous components in conduit  122 , conduit  201  (see  FIGS.  1  and  2   ), conduit  501  (see  FIGS.  1  and  2   ), conduit  502  (see  FIGS.  1  and  2   ), or combinations thereof. In another embodiment, the motive device  132  can be a solids pump configured to receive the solid polyolefin particles from conduit  131  and to pump the solid polyolefin particles to the first reactor  100  via conduit  133 . 
     The first reactor  100  in  FIGS.  10 A,  10 B, and  10 C  can be used in  FIG.  1   , where the first reactor product mixture exits the reactor  100  in product discharge conduit  110 . In each of  FIGS.  10 A,  10 B, and  10 C , a portion of the first reactor product mixture can flow from the product discharge conduit  110  into a sampling system  1000  while the remaining portion of the first reactor product mixture can flow from the product discharge conduit  110  into the product separation system  200 . 
     The first reactor  100  as shown in  FIGS.  10 D,  10 E, and  10 F  can be used in  FIG.  2   , where the first reactor product mixture containing the multimodal polyolefin exits the reactor  100  in product discharge conduit  370 . In each of  FIGS.  10 D,  10 E, and  10 F , a portion of the first reactor product mixture can flow from the product discharge conduit  370  into a sampling system  1000  while the remaining portion of the first reactor product mixture can flow from the product discharge conduit  370  into the product separation system  400 . 
     The sampling system  1000  in each of  FIGS.  10 A to  10 F  can be fluidly connected to the product discharge conduit  110  and configured to analyze a sample of the first polyolefin (for  FIGS.  10 A to  10 C ) or a sample of the multimodal polyolefin (for  FIGS.  10 D to  10 F ). The sampling system  1000  can include a sample conduit  110  through which a portion of the first reactor product mixture flows to a sample flash tank  1010 . The sample flash tank  1010  can be configured to separate the solid polyolefin (e.g., the first polyolefin for  FIGS.  10 A to  10 C  or the multimodal polyolefin for  FIGS.  10 D to  10 E ) from the gaseous components such that the gaseous components can flow from the flash tank  1010  via conduit  1011  and such that the solid polyolefin can flow from the flash tank  101  via conduit  1012 . The solid polyolefin in conduit  1012  can flow to a sample analyzer  1020  that can be configured to analyze a sample of the first polyolefin to determine the one or more properties of the solid polyolefin received via conduit  1012 . The sample analyzer  1020  can be configured to perform a Raman analysis, configured as a gas chromatograph, or configured as a spectroscopy device. Commercially available examples of the sample analyzer  1020  include the RAMANRXN3™ Analyzer and the RAMANRXN4™ Analyzer. 
       FIGS.  10 A to  10 F  also show a gas distributor  111  can be located inside a bottom portion  115  of the fluidized bed reactor (i.e., the first reactor  100 ). The gas distributor  111  can be configured with channels  111   a  through which the recycled gaseous components received from conduit  126  can be distributed inside the reactor  100  as the gaseous components pass through the gas distributor  111  into the polymerization zone  112  of the first reactor  100 . 
     The unique aspects and product separation system  200  in each of  FIGS.  10 A,  10 B, and  10 C  will now be described. 
       FIG.  10 A  shows a settling leg  113  placed partially within the bottom portion  115  of the fluidized bed reactor. At least a portion of the settling leg  113  can be placed inside the first reactor  100  such that an end  113   a  of the settling leg  113  opens to the gas distributor  111  and/or to the polymerization zone  112  and an opposite end  113   b  extends outside the first reactor  100 . While the settling leg  113  is shown in  FIG.  10 A  as being positioned in a center of the gas distributor  111 , it is contemplated that the settling leg  113  can be placed off-center with respect to the gas distributor  111  and/or the reaction vessel of the first reactor  100 . 
     The settling leg  113  can be in the form of a pipe. In an aspect, a diameter of the settling leg  113  is the same along the length of the settling leg  113 ; while in another aspect, the end  113   b  of the settling leg  113  can be conically tapered such that the diameter of the end  113   b  decreases in the downward direction. In an aspect, the settling leg  113  can have an inner diameter along the length of the settling leg in the range of from about 10.16 cm (4 inches) to about 30.48 cm (12 inches); alternatively, from about 15.24 cm (6 inches) to about 20.32 cm (8 inches); alternatively, from about 23.32 cm (8 inches) to about 30.48 cm (12 inches), including any portion (e.g., end  113   b ) that has an inner diameter than changes along the length of said portion. 
     Solid polyolefin particles of the first polyolefin can fall by force of gravity into the settling leg as the particles become too large for the fluidization forces to keep them fluidized in the polymerization zone  112 . The particles that settle out of the fluidized bed in the first reactor  100  can flow into the end  113   a  of the settling leg  113  to the opposite end  113   b  of the settling leg  113   b . The particles can move downward in the settling leg  113  from end  113   a  to end  113   b  as a moving bed in a plug-flow manner. The particles then can flow from the first reactor  100  via product discharge conduit  110  to the product separation system  200 . 
     The product separation system  200  in  FIG.  10 A  can include a take-off valve  210 , a conduit  211 , a separation vessel  230 , conduit  201 , and conduit  202 . The product separation system  200  in  FIG.  10 B  can optionally further include the treater  1030 . 
     The take-off valve  210  can be configured to receive the first reactor product mixture from the product discharge conduit  110  and to control the flow of the first reactor product mixture therethrough. The take-off valve  210  can be any type of control valve known in the art to be useful for controlling flow of the product mixture. Such valves include ball valves, v-ball valves, plug valves, globe valves and angle valves. In an aspect, the take-off valve  210  can have a diameter when 100% open in a range of from about 1.27 cm (0.5 inches) to about 7.62 cm (3 inches). In an aspect, the take-off valve  210  can have a flow channel diameter greater than the largest expected polymer particle size even when the valve  210  is required to be only a small amount open (for example, 20-25% open), which gives a wide control range for the range of openness of the take-off valve  210  (e.g., 20-100% open). The take-off valve  210  may be actuated by a signal from a controller configured to operate the take-off valve  210  in a continuous or a discontinuous manner. The controller may be configured to fully close and then fully open the take-off valve  210  at set intervals and for a certain duration, to actuate the take-off valve  210  to a percentage of openness, e.g., 20-100% open. 
     The separation vessel  230  can be coupled to the end  113   b  of the settling leg  113  via conduits  110  and  211  as well as via the take-off valve  210 . The separation vessel  230  can be configured to separate the first reactor product mixture into the first polyolefin in conduit  202  and into a gas mixture in conduit  201 . The gas mixture in conduit  201  can include the gases separated from the first polyolefin. The separation vessel  230  can be embodied as a flash tank configured to provide a reduction in pressure of the product mixture such that olefin monomer, any optional olefin comonomer, diluent, and other components (e.g., nitrogen, hydrogen, oxygen, methane, ethane, propane, butane, isobutane, pentane, hexane, heavier hydrocarbons, or combinations thereof) separate from the first polyolefin so as to yield one or more of these gaseous components in conduit  201 . To the extent that any liquid is contained in the first reactor product mixture, the pressure reduction provided in the flash tank can flash the liquid into the gas phase for flow in conduit  201 . In an aspect, the separation vessel  230  can be a hollow vessel having a cone-shaped bottom portion that directs the flow of the first polyolefin to conduit  202 . In an aspect, the separation vessel  230  can operate without a pressure reduction, for example, when the first reactor product mixture contains gas components and the first polyolefin and no or a minimal amount of liquid, since a reduction in pressure is not needed for flashing a liquid component to a gas phase. 
     In an optional aspect,  FIG.  10 A  illustrates a treater  1030  that can be configured to treat the gas mixture in conduit  201 . That is, the treater  1030  can be fluidly connected to the conduit  201 . In aspects, the treater  1030  can be a flare stack, a ground flare, a pressure swing absorber, a membrane, or a combination thereof. In another optional aspect, it is contemplated that the conduit  201  can flow to the product separation system  400  for treatment of the gas mixture, as is described for  FIG.  9   . 
       FIG.  10 B  shows the product discharge conduit  110  placed on the side  116  of the fluidized bed reactor. While placed on the side  116  of the vessel of the fluidized bed reactor, it is contemplated that the product discharge conduit  110  can be placed on the bottom of the reactor vessel. The product discharge conduit  110  can be connected to the fluidized bed reactor such that an angle of the product discharge conduit  110  with respect to horizontal is in a range of -60° to 60°; alternatively, -45° to 45°; alternatively, -35° to 35°; alternatively, -25° to 25°; alternatively, 0° to 45°; alternatively, in a range of 10° to 35°; alternatively, in a range of 20° to 25°. For example, the angle of the product discharge conduit  110  with respect to horizontal can be -60°, -59°, -58°, -57°, -56°, -55°, -57°, -56°, -55°, -54°, -53°, -52°, -51°, -50°, -49°, -48°, -47°, -46°, -45°, -44°, -43°, -42°, -41°, -40°, -39°, -38°, -37°, -36°, -35°, -34°, -33°, -32°, -31°, -30°, -29°, -28°, -27°, -26°, -25°, -24°, -23°, -22°, -21°, -20°, -19°, -18°, -17°, -16°, -15°, -14°, -13°, -12°, -11°, -10°, -9°, -8°, -7°, -6°, -5°, -4°,-3°, -2°, -1°, 0°, 1°, 2°, 3°, 4°, 5°, 6°, 7°, 8°, 9°, 10°, 11°, 12°, 13°, 14°, 15° 16°, 17°, 18°, 19°, 20°, 21°, 22°, 23°, 24°, 25°, 26°, 27°, 28°, 29°, 30°, 31°, 32°, 33°, 34°, 35°, 36°, 37°, 38°, 39°, 40°, 41°, 42°, 43°, 44°, 45°, 46°, 47°, 48°, 49°, 50°, 51°, 52°, 53°, 54°, 55°, 56°, 57°, 58°, 59°, or 60°. 
     The product separation system  200  in  FIG.  10 B  can include a lock hopper  240 , cycling valves  241  and  243 , conduit  242 , conduit  244 , conduit  245 , a separation vessel  230 , conduit  201 , and conduit  202 . The product separation system  200  in  FIG.  10 B  can optionally further include the treater  1030 . 
       FIG.  10 B  shows that a lock hopper  240  can be coupled to the product discharge conduit  110 . In an aspect, the lock hopper  240  can be coupled to the product discharge conduit  110  by a first cycling valve  241  and a conduit  242 . The lock hopper  240  can additionally be coupled to a separation vessel  230  via a second cycling valve  243  and conduits  244  and  245 . The first cycling valve  241  can be coupled to an inlet  247  of the lock hopper  240 , and the second cycling valve  243  can be coupled to an outlet  246  of the lock hopper  240 . The first cycling valve  241  and the second cycling valve  243  can be configured to pass the first reactor product mixture into and out of the lock hopper  240  while keeping the contents inside the lock hopper  240  isolated from the conditions of the fluidized bed reactor and from the conditions of the separation vessel  230 . That is, at no time is the interior space of the lock hopper  240  fluidly connected to the interior of the fluidized bed reactor or the interior of the separation vessel  230 . For example, the cycling valves  241  and  243  can each have a plurality of chambers  248  and  249  that can be cycled, for example if there are four chambers, by a quarter rotation (if two chambers, then a half rotation and so on for more chambers). Upon each partial rotation, one of the chambers  248  of the first cycling valve  241  can fluidly connect to the product discharge conduit  110  so as to receive first reactor product mixture therein, while another one of the chambers  248  can fluidly connect with the lock hopper  240  via conduit  242  so that the first reactor product mixture falls down into the lock hopper  240  via conduit  242 . In a similar matter, upon each partial rotation, one of the chambers  249  of the second cycling valve  243  can fluidly connect to the lock hopper  240  via conduit  244  so as to receive first reactor product mixture therein, while another one of the chambers  249  can fluidly connect with the separation vessel  230  via conduit  245  so that the first reactor product mixture falls down into the separation vessel  230 . A controller can be configured to control the partial rotation of each of the first cycling valve  241  and the second cycling valve  243  so as to maintain or change a desired amount of the first reactor product mixture inside the lock hopper  240 . 
     The lock hopper  240  can be a vessel configured to receive the first reactor product mixture and then pass the mixture out of the lock hopper  240  according to actuation of the first cycling valve  241  and the second cycling valve  243 . 
     The separation vessel  230  can be coupled to the lock hopper  240  via the second cycling valve  243  and conduits  244  and  245 . The separation vessel  230  can be configured to separate the first reactor product mixture into the first polyolefin in conduit  202  and into a gas mixture in conduit  201 . The gas mixture in conduit  201  can include the gases separated from the first polyolefin. The separation vessel  230  can be embodied as a flash tank configured to provide a reduction in pressure of the product mixture such that olefin monomer, any optional olefin comonomer, diluent, and other components (e.g., nitrogen, hydrogen, oxygen, methane, ethane, propane, butane, isobutane, pentane, hexane, heavier hydrocarbons, or combinations thereof) separate from the first polyolefin so as to yield one or more of these gaseous components in conduit  201 . To the extent that any liquid is contained in the first reactor product mixture, the pressure reduction provided in the flash tank can flash the liquid into the gas phase for flow in conduit  201 . In an aspect, the separation vessel  230  can be a hollow vessel having a cone-shaped bottom portion that directs the flow of the first polyolefin to conduit  202 . In an aspect, the separation vessel  230  can operate without a pressure reduction, for example, when the first reactor product mixture contains gas components and the first polyolefin and no or a minimal amount of liquid, since a reduction in pressure is not needed for flashing a liquid component to a gas phase. 
     In an optional aspect,  FIG.  10 B  illustrates a treater  1030  that can be configured to treat the gas mixture in conduit  201 . That is, the treater  1030  can be fluidly connected to the conduit  201 . In aspects, the treater  1030  can be a flare stack, a ground flare, a pressure swing absorber, a membrane, or a combination thereof. In another optional aspect, it is contemplated that the conduit  201  can flow to the product separation system  400  for treatment of the gas mixture, as is described for  FIG.  9   . 
       FIG.  10 C  shows the product discharge conduit  110  placed on the side  116  of the fluidized bed reactor. While placed on the side  116  of the vessel of the fluidized bed reactor, it is contemplated that the product discharge conduit  110  can be placed on the bottom of the reactor vessel. The product discharge conduit  110  can be connected to the fluidized bed reactor such that an angle of the product discharge conduit  110  with respect to horizontal is in a range of -60° to 60°; alternatively, -45° to 45°; alternatively, -35° to 35°; alternatively, -25° to 25°; alternatively, 0° to 45°; alternatively, in a range of 10° to 35°; alternatively, in a range of 20° to 25°. For example, the angle of the product discharge conduit  110  with respect to horizontal can be -60°, -59°, -58°, -57°, -56°, -55°, -57°, -56°, -55°, -54°, -53°, -52°, -51°, -50°, -49°, -48°, -47°, -46°, -45°, -44°, -43°, -42°, -41°, -40°, -39°, -38°, -37°, -36°, -35°, -34°, -33°, -32°, -31°, -30°, -29°, -28°, -27°, -26°, -25°, -24°, -23°, -22°, -21°, -20°, -19°, -18°, -17°, -16°, -15°, -14°, -13°, -12°, -11°, -10°, -9°, -8°, -7°, -6°, -5°, -4°,-3°, -2°, -1°, 0°, 1°, 2°, 3°, 4°, 5°, 6°, 7°, 8°, 9°, 10°, 11°, 12°, 13°, 14°, 15° 16°, 17°, 18°, 19°, 20°, 21°, 22°, 23°, 24°, 25°, 26°, 27°, 28°, 29°, 30°, 31°, 32°, 33°, 34°, 35°, 36°, 37°, 38°, 39°, 40°, 41°, 42°, 43°, 44°, 45°, 46°, 47°, 48°, 49°, 50°, 51°, 52°, 53°, 54°, 55°, 56°, 57°, 58°, 59°, or 60°. 
     The product separation system  200  in  FIG.  10 C  can include a continuous take-off valve  212 , conduit  211 , a separation vessel  230 , conduit  201 , and conduit  202 . The product separation system  200  in  FIG.  10 C  can optionally further include the treater  1030 . 
       FIG.  10 C  shows a continuous take-off valve  212  fluidly connected to the product discharge conduit  110 . The continuous take-off valve  212  can be configured to receive the first reactor product mixture from the product discharge conduit  110  and to control the flow of the first reactor product mixture therethrough. The continuous take-off valve  212  can be any type of control valve known in the art to be useful for controlling flow of the product mixture on a continuous basis. Such valves include ball valves, v-ball valves, plug valves, globe valves and angle valves. In an aspect, the continuous take-off valve  212  can have a flow channel diameter greater than the largest expected polymer particle size even when the valve  212  is required to be only a small amount open (for example, 20-25% open), which gives a wide control range for the range of openness of the continuous take-off valve  212  (e.g., 20-100% open). The continuous take-off valve  212  may be actuated by a signal from a controller configured to operate the continuous take-off valve  212  such that the first reactor product mixture flows in the product discharge conduit  110  in a continuous manner. The controller may be configured to actuate the continuous take-off valve  212  to a percentage of openness, e.g., 20-100% open. 
     The separation vessel  230  can be coupled to the continuous take-off valve  212  via conduit  211 . The separation vessel  230  can be configured to separate the first reactor product mixture into the first polyolefin in conduit  202  and into a gas mixture in conduit  201 . The gas mixture in conduit  201  can include the gases separated from the first polyolefin. The separation vessel  230  can be embodied as a flash tank configured to provide a reduction in pressure of the product mixture such that olefin monomer, any optional olefin comonomer, diluent, and other components (e.g., nitrogen, hydrogen, oxygen, methane, ethane, propane, butane, isobutane, pentane, hexane, heavier hydrocarbons, or combinations thereof) separate from the first polyolefin so as to yield one or more of these gaseous components in conduit  201 . To the extent that any liquid is contained in the first reactor product mixture, the pressure reduction provided in the flash tank can flash the liquid into the gas phase for flow in conduit  201 . In an aspect, the separation vessel  230  can be a hollow vessel having a cone-shaped bottom portion that directs the flow of the first polyolefin to conduit  202 . In an aspect, the separation vessel  230  can operate without a pressure reduction, for example, when the first reactor product mixture contains gas components and the first polyolefin and no or a minimal amount of liquid, since a reduction in pressure is not needed for flashing a liquid component to a gas phase. 
     In an optional aspect,  FIG.  10 C  illustrates a treater  1030  that can be configured to treat the gas mixture in conduit  201 . That is, the treater  1030  can be fluidly connected to the conduit  201 . In aspects, the treater  1030  can be a flare stack, a ground flare, a pressure swing absorber, a membrane, or a combination thereof. In another optional aspect, it is contemplated that the conduit  201  can flow to the product separation system  400  for treatment of the gas mixture, as is described for  FIG.  9   . 
       FIG.  10 D  shows a settling leg  113  placed partially within the bottom portion  115  of the fluidized bed reactor. At least a portion of the settling leg  113  can be placed inside the first reactor  100  such that an end  113   a  of the settling leg  113  opens to the gas distributor  111  and/or to the polymerization zone  112  and an opposite end  113   b  extends outside the first reactor  100 . While the settling leg  113  is shown in  FIG.  10 D  as being positioned in a center of the gas distributor  111 , it is contemplated that the settling leg  113  can be placed off-center with respect to the gas distributor  111  and/or the reaction vessel of the first reactor  100 . 
     The settling leg  113  can be in the form of a pipe. In an aspect, a diameter of the settling leg  113  is the same along the length of the settling leg  113 ; while in another aspect, the end  113   b  of the settling leg  113  can be conically tapered such that the diameter of the end  113   b  decreases in the downward direction. In an aspect, the settling leg  113  can have an inner diameter along the length of the settling leg in the range of from about 10.16 cm (4 inches) to about 30.48 cm (12 inches), including any portion (e.g., end  113   b ) that has an inner diameter than changes along the length of said portion. 
     Solid polyolefin particles of the first polyolefin can fall by force of gravity into the settling leg as the particles become too large for the fluidization forces to keep them fluidized in the polymerization zone  112 . The particles that settle out of the fluidized bed in the first reactor  100  can flow into the end  113   a  of the settling leg  113  to the opposite end  113   b  of the settling leg  113   b . The particles can move downward in the settling leg  113  from end  113   a  to end  113   b  as a moving bed in a plug-flow manner. The particles then can flow from the first reactor  100  via product discharge conduit  370  to the product separation system  200 . 
     The product separation system  400  in  FIG.  10 D  can include a take-off valve  410 , a conduit  411 , a separation vessel  430 , conduit  431 , and conduit  401 . The product separation system  400  in  FIG.  10 D  can optionally further include the treater  1030  and/or any combination of equipment shown in and described for  FIG.  9   . 
     The take-off valve  410  can be configured to receive the first reactor product mixture from the product discharge conduit  370  and to control the flow of the first reactor product mixture therethrough. The take-off valve  410  in  FIG.  10 D  can be of a configuration for the take-off valve described for  FIG.  9   . 
     The separation vessel  430  can be coupled to the end  113   b  of the settling leg  113  via conduits  110  and  411  as well as via the take-off valve  410 . The separation vessel  430  can be configured to separate the first reactor product mixture into the multimodal polyolefin in conduit  401  and into a gas mixture in conduit  431 . The gas mixture in conduit  431  can include the gases separated from the first polyolefin. The separation vessel  430  can be a configuration for the separation vessel  430  described for  FIG.  9   , for example, embodied as a flash tank configured to provide a reduction in pressure of the product mixture such that olefin monomer, any optional olefin comonomer, diluent, and other components (e.g., nitrogen, hydrogen, oxygen, methane, ethane, propane, butane, isobutane, pentane, hexane, heavier hydrocarbons, or combinations thereof) separate from the multimodal polyolefin so as to yield one or more of these gaseous components in conduit  431 . To the extent that any liquid is contained in the first reactor product mixture, the pressure reduction provided in the flash tank can flash the liquid into the gas phase for flow in conduit  431 . In an aspect, the separation vessel  430  can be a hollow vessel having a cone-shaped bottom portion that directs the flow of the multimodal polyolefin to conduit  401 . In an aspect, the separation vessel  430  can operate without a pressure reduction, for example, when the first reactor product mixture contains gas components and the multimodal polyolefin and no or a minimal amount of liquid, since a reduction in pressure is not needed for flashing a liquid component to a gas phase. 
     In an optional aspect,  FIG.  10 D  illustrates a treater  1030  that can be configured to treat the gas mixture in conduit  431 . That is, the treater  1030  can be fluidly connected to the conduit  431 . In aspects, the treater  1030  can be a flare stack, a ground flare, a pressure swing absorber, a membrane, or a combination thereof. In alternative aspects, the treater  1030  can be the train of equipment shown in  FIG.  9    that processes the gaseous components received from conduit  431 . 
       FIG.  10 E  shows the product discharge conduit  370  placed on the side  116  of the fluidized bed reactor. While placed on the side  116  of the vessel of the fluidized bed reactor, it is contemplated that the product discharge conduit  370  can be placed on the bottom of the reactor vessel. The product discharge conduit  370  can be connected to the fluidized bed reactor such that an angle of the product discharge conduit  370  with respect to horizontal is in a range of -60° to 60°; alternatively, -45° to 45°; alternatively, -35° to 35°; alternatively, -25° to 25°; alternatively, 0° to 45°; alternatively, in a range of 10° to 35°; alternatively, in a range of 20° to 25°. For example, the angle of the product discharge conduit  370  with respect to horizontal can be -60°, -59°, -58°, -57°, -56°, -55°, -57°, -56°, -55°, -54°, -53°, -52°, -51°, -50°, -49°, -48°, -47°, -46°, -45°, -44°, -43°, -42°, -41°, -40°, -39°, -38°, -37°, -36°, -35°, -34°, -33°, -32°, -31°, -30°, -29°, -28°, -27°, -26°, -25°, -24°, -23°, -22°, -21°, -20°, -19°, -18°, -17°, -16°, -15°, -14°, -13°, -12°, -11°, -10°, -9°, -8°, -7°, -6°, -5°, -4°,-3°, -2°, -1°, 0°, 1°, 2°, 3°, 4°, 5°, 6°, 7°, 8°, 9°, 10°, 11°, 12°, 13°, 14°, 15°, 16°, 17°, 18°, 19°, 20°, 21°, 22°, 23°, 24°, 25°, 26°, 27°, 28°, 29°, 30°, 31°, 32°, 33°, 34°, 35°, 36°, 37°, 38°, 39°, 40°, 41°, 42°, 43°, 44°, 45°, 46°, 47°, 48°, 49°, 50°, 51°, 52°, 53°, 54°, 55°, 56°, 57°, 58°, 59°, or 60°. 
     The product separation system  400  in  FIG.  10 E  can include a lock hopper  490 , cycling valves  491  and  493 , conduit  492 , conduit  494 , conduit  495 , a separation vessel  430 , conduit  401 , and conduit  431 . The product separation system  400  in  FIG.  10 E  can optionally further include the treater  1030  and/or any combination of equipment shown in and described for  FIG.  9   . 
       FIG.  10 E  shows that a lock hopper  490  can be coupled to the product discharge conduit  370 . In an aspect, the lock hopper  490  can be coupled to the product discharge conduit  370  by a first cycling valve  491  and a conduit  492 . The lock hopper  490  can additionally be coupled to a separation vessel  430  via a second cycling valve  493  and conduits  495  and  495 . The first cycling valve  491  can be coupled to an inlet  497  of the lock hopper  490 , and the second cycling valve  493  can be coupled to an outlet  496  of the lock hopper  490 . The first cycling valve  491  and the second cycling valve  493  can be configured to pass the first reactor product mixture into and out of the lock hopper  490  while keeping the contents inside the lock hopper  490  isolated from the conditions of the fluidized bed reactor and from the conditions of the separation vessel  430 . That is, at no time is the interior space of the lock hopper  490  fluidly connected to the interior of the fluidized bed reactor or the interior of the separation vessel  430 . For example, the cycling valves  491  and  493  can each have a plurality of chambers  498  and  499  that can be cycled, for example if there are four chambers, by a quarter rotation (if two chambers, then a half rotation and so on for more chambers). Upon each partial rotation, one of the chambers  498  of the first cycling valve  491  can fluidly connect to the product discharge conduit  370  so as to receive first reactor product mixture therein, while another one of the chambers  498  can fluidly connect with the lock hopper  490  via conduit  492  so that the first reactor product mixture falls down into the lock hopper  490  via conduit  492 . In a similar matter, upon each partial rotation, one of the chambers  499  of the second cycling valve  493  can fluidly connect to the lock hopper  490  via conduit  494  so as to receive first reactor product mixture therein, while another one of the chambers  499  can fluidly connect with the separation vessel  430  via conduit  495  so that the first reactor product mixture falls down into the separation vessel  430 . A controller can be configured to control the partial rotation of each of the first cycling valve  491  and the second cycling valve  493  so as to maintain or change a desired amount of the first reactor product mixture inside the lock hopper  490 . 
     The lock hopper  490  can be a vessel configured to receive the first reactor product mixture and then pass the mixture out of the lock hopper  490  according to actuation of the first cycling valve  491  and the second cycling valve  493 . 
     The separation vessel  430  can be coupled to the lock hopper  490  via the second cycling valve  493  and conduits  494  and  495 . The separation vessel  430  can be a configuration for the separation vessel  430  described for  FIG.  9   , for example, embodied as a flash tank configured to provide a reduction in pressure of the product mixture such that olefin monomer, any optional olefin comonomer, diluent, and other components (e.g., nitrogen, hydrogen, oxygen, methane, ethane, propane, butane, isobutane, pentane, hexane, heavier hydrocarbons, or combinations thereof) separate from the multimodal polyolefin so as to yield one or more of these gaseous components in conduit  431 . To the extent that any liquid is contained in the first reactor product mixture, the pressure reduction provided in the flash tank can flash the liquid into the gas phase for flow in conduit  431 . In an aspect, the separation vessel  430  can be a hollow vessel having a cone-shaped bottom portion that directs the flow of the multimodal polyolefin to conduit  401 . In an aspect, the separation vessel  430  can operate without a pressure reduction, for example, when the first reactor product mixture contains gas components and the multimodal polyolefin and no or a minimal amount of liquid, since a reduction in pressure is not needed for flashing a liquid component to a gas phase. 
     In an optional aspect,  FIG.  10 E  illustrates a treater  1030  that can be configured to treat the gas mixture in conduit  431 . That is, the treater  1030  can be fluidly connected to the conduit  431 . In aspects, the treater  1030  can be a flare stack, a ground flare, a pressure swing absorber, a membrane, or a combination thereof. In another optional aspect, it is contemplated that the conduit  431  can flow to the product separation system  400  for treatment of the gas mixture, as is described for  FIG.  9   . 
       FIG.  10 F  shows the product discharge conduit  370  placed on the side  116  of the fluidized bed reactor. While placed on the side  116  of the vessel of the fluidized bed reactor, it is contemplated that the product discharge conduit  370  can be placed on the bottom of the reactor vessel. The product discharge conduit  370  can be connected to the fluidized bed reactor such that an angle of the product discharge conduit  370  with respect to horizontal is in a range of -60° to 60°; alternatively, -45° to 45°; alternatively, -35° to 35°; alternatively, -25° to 25°; alternatively, 0° to 45°; alternatively, in a range of 10° to 35°; alternatively, in a range of 20° to 25°. For example, the angle of the product discharge conduit  370  with respect to horizontal can be -60°, -59°, -58°, -57°, -56°, -55°, -57°, -56°, -55°, -54°, -53°, -52°, -51°, -50°, -49°, -48°, -47°, -46°, -45°, -44°, -43°, -42°, -41°, -40°, -39°, -38°, -37°, -36°, -35°, -34°, -33°, -32°, -31°, -30°, -29°, -28°, -27°, -26°, -25°, -24°, -23°, -22°, -21°, -20°, -19°, -18°, -17°, -16°, -15°, -14°, -13°, -12°, -11°, -10°, -9°, -8°, -7°, -6°, -5°, -4°,-3°, -2°, -1°, 0°, 1°, 2°, 3°, 4°, 5°, 6°, 7°, 8°, 9°, 10°, 11°, 12°, 13°, 14°, 15°, 16°, 17°, 18°, 19°, 20°, 21°, 22°, 23°, 24°, 25°, 26°, 27°, 28°, 29°, 30°, 31°, 32°, 33°, 34°, 35°, 36°, 37°, 38°, 39°, 40°, 41°, 42°, 43°, 44°, 45°, 46°, 47°, 48°, 49°, 50°, 51°, 52°, 53°, 54°, 55°, 56°, 57°, 58°, 59°, or 60°. 
     The product separation system  400  in  FIG.  10 F  can include a continuous take-off valve  413 , conduit  411 , a separation vessel  430 , conduit  401 , and conduit  431 . The product separation system  400  in  FIG.  10 E  can optionally further include the treater  1030  and/or any combination of equipment shown in and described for  FIG.  9   . 
       FIG.  10 F  shows a continuous take-off valve  413  fluidly connected to the product discharge conduit  370 . The continuous take-off valve  413  can be configured to receive the first reactor product mixture from the product discharge conduit  370  and to control the flow of the first reactor product mixture therethrough. The continuous take-off valve  413  can be any type of control valve known in the art to be useful for controlling flow of the product mixture on a continuous basis. Such valves include ball valves, v-ball valves, plug valves, globe valves and angle valves. In an aspect, the continuous take-off valve  413  can have a flow channel diameter greater than the largest expected polymer particle size even when the valve  413  is required to be only a small amount open (for example, 20-25% open), which gives a wide control range for the range of openness of the continuous take-off valve  413  (e.g., 20-100% open). The continuous take-off valve  413  may be actuated by a signal from a controller configured to operate the continuous take-off valve  413  such that the first reactor product mixture flows in the product discharge conduit  370  in a continuous manner. The controller may be configured to actuate the continuous take-off valve  413  to a percentage of openness, e.g., 20-100% open. 
     The separation vessel  430  can be coupled to the continuous take-off valve  413  via conduit  411 . The separation vessel  430  can be configured to separate the first reactor product mixture into the first polyolefin in conduit  401  and into a gas mixture in conduit  431 . The gas mixture in conduit  431  can include the gases separated from the first polyolefin. The separation vessel  430  can be embodied as a flash tank configured to provide a reduction in pressure of the product mixture such that olefin monomer, any optional olefin comonomer, diluent, and other components (e.g., nitrogen, hydrogen, oxygen, methane, ethane, propane, butane, isobutane, pentane, hexane, heavier hydrocarbons, or combinations thereof) separate from the first polyolefin so as to yield one or more of these gaseous components in conduit  431 . To the extent that any liquid is contained in the first reactor product mixture, the pressure reduction provided in the flash tank can flash the liquid into the gas phase for flow in conduit  431 . In an aspect, the separation vessel  430  can be a hollow vessel having a cone-shaped bottom portion that directs the flow of the first polyolefin to conduit  401 . In an aspect, the separation vessel  430  can operate without a pressure reduction, for example, when the first reactor product mixture contains gas components and the first polyolefin and no or a minimal amount of liquid, since a reduction in pressure is not needed for flashing a liquid component to a gas phase. 
     In an optional aspect,  FIG.  10 F  illustrates a treater  1030  that can be configured to treat the gas mixture in conduit  431 . That is, the treater  1030  can be fluidly connected to the conduit  431 . In aspects, the treater  1030  can be a flare stack, a ground flare, a pressure swing absorber, a membrane, or a combination thereof. In another optional aspect, it is contemplated that the conduit  431  can flow to the product separation system  400  for treatment of the gas mixture, as is described for  FIG.  9   . 
     The disclosed apparatuses and processes are configured to produce multimodal polyolefins. 
     In aspect, the multimodal polyolefins can comprise high density polyethylene (HDPE), medium density polyethylene (MDPE), low density polyethylene (LDPE), linear low density polyethylene (LLDPE), or combinations thereof. Any of the HDPE, MDPE, LDPE, LLDPE can be produced as a homopolymer or a copolymer (e.g., a polyolefin containing ethylene monomer units and comonomer units of a comonomer disclosed herein such as 1-hexene). 
     Other aspects and embodiments of the multimodal polyolefin compositions produced according to this disclosure are described as polyethylene resins A, B, C, D, and E below. Each polyethylene resin A, B, C, D, and E can comprise the first polyolefin made in polymerization zone  112  of the first reactor  100 , the second polyolefin made in the polymerization zone  321  of the riser  320  of the MZCR  300 , and the third polyolefin made in the polymerization zone  341  of the downcomer  340  of the MZCR  300 . 
     In an aspect, the first polyolefin can be a HDPE resin and the second and third polyolefins can together form a LLDPE. 
     In an aspect, the first polyolefin in each polyethylene resin A, B, C, D, and E can be a low molecular weight (LMW) component of the multimodal polyolefin, the second polyolefin in each polyethylene resin A, B, C, D, and E can be an intermediate molecular weight (IMW) component of the multimodal polyolefin, and the third polyolefin in each polyethylene resin A, B, C, D, and E can be a high molecular weight component (HMW) of the multimodal polyolefin. It is contemplated that an amount or number of other components of the multimodal polyolefin may be present due to residual polymerization reactions that can occur in MZCR  300 , for example, in one or more of the lower conduit  310 , the upper conduit  330 , and the separator  350  of the MZCR  300 . Thus, in an aspect, the multimodal polyolefin (and thus in each polyethylene resin A, B, C, D, and E) can have from three to six molecular weight components and can be characterized as a trimodal polyolefin, a quadramodal polyolefin, a pentamodal polyolefin, or a hexamodal polyolefin. 
     In an aspect, the first polyolefin in each polyethylene resin A, B, C, D, and E can be a low molecular weight (LMW) component of the multimodal polyolefin, the second polyolefin in each polyethylene resin A, B, C, D, and E can be an intermediate molecular weight (IMW) component of the multimodal polyolefin, and the third polyolefin in each polyethylene resin A, B, C, D, and E can be a high molecular weight component (HMW) of the multimodal polyolefin. It is contemplated that an amount of other components of the multimodal polyolefin may be present due to residual polymerization reactions that can occur in MZCR  300 , for example, in one or more of the lower conduit  310 , the upper conduit  330 , and the separator  350  of the MZCR  300 . 
     In additional or alternative aspects, the first polyolefin (e.g., the LMW component) in each polyethylene resin A, B, C, D, and E that is produced in the polymerization zone  112  of the first reactor  100  can be a lower molecular weight polyethylene, and the third polyolefin (e.g., the HMW component) in each polyethylene resin A, B, C, D, and E that is produced in the polymerization zone  341  of the downcomer  340  can be a higher molecular weight polyethylene. The second polyolefin (e.g., the IMW component) in each polyethylene resin A, B, C, D, and E that is produced in the polymerization zone  321  of the riser  320 . The terms “lower” and “higher” are used to describe the average molecular weight of a polyolefin relative to the average molecular weight of other polyolefins in the multimodal polyolefin composition, and are not meant to include only absolute values as recognized by those skilled in the art (e.g., “lower molecular weight” does not necessarily mean the average molecular weight has a “low” molecular weight, although very well could be). Thus, when the polyolefin produced in the polymerization zone  112  has a “lower molecular weight”, it is intended that the polyolefin has an average molecular weight that is lower than the average molecular weight of other polyolefins in the multimodal polyolefin composition, e.g., lower than the “higher molecular weight” of the polyolefin made in the downcomer  340  and the intermediate molecular weight of the polyolefin made in the riser  320 . Likewise, when the polyolefin produced in the polymerization zone  341  of the downcomer  340  has a “higher molecular weight” it is intended that the polyolefin has an average molecular weight that is higher than the molecular weight of other polyolefins in the multimodal polyolefin composition, e.g., higher than the “lower molecular weight” of the polyolefin made in the first reactor  100  and the intermediate molecular weight of the polyolefin made in the riser  320 . 
     The multiple polymerization zones (e.g., polymerization zones  112 ,  321 , and  341 ) in the disclosed apparatuses and processes give great flexibility in the properties of the multimodal polyolefins that can be made. The residence times, gas compositions, catalyst, catalyst injection rate, ratio of olefin monomer to catalyst, comonomer concentration, hydrogen concentration, and other parameters in the polymerization zones  112 ,  321 , and  341  can be determined to produce a multimodal polyolefin having desirable properties. 
     One advantage of the multimodal polyolefins disclosed herein is their use in lightweighting. Lightweighting occurs when less of a multimodal polyolefin is used to form a pipe, film, or article than would otherwise be used, for example with a bimodal polyolefin, to form the same size of pipe, film, or article. The multimodal polyolefins that can be produced herein can have advantageous stiffness and Young’s, Secant, and/or Flexural modulus values that enable lightweighting when forming a pipe, film, or article, while still having desired impact strength and environmental stress cracking resistance (ESCR) in the formed pipe, film, or article. Without being limited by theory, it is believed that the disclosed processes and apparatuses can be used to control the amount of the first polyolefin (also can be referred to as the low molecular weight (LMW) component) that is incorporated into the multimodal polyolefin. The control can be for an amount of the LMW component that advantageously leads to lightweighting when the multimodal polyolefin is used to produce pipe, film, or an article. 
     Another advantage of the multimodal polyolefins disclosed herein is a lower amount of gels in resins suitable for use as pipe. The lower gel count results in improved mechanical properties, aesthetics, and surface finish of the product. Generally, gels are higher molecular weight and/or crosslinked polymers (e.g., polyethylene) in the form of discrete particles. For purposes of counting these discrete particles, a countable gel has greater than 200 microns in size. Gels in the multimodal polyolefins (including the polyethylene resins disclosed herein) can be measured by extruding a 1 mm thick cast film on a 1.25” Killion single screw extruder with a slot die. An FS5 model OCS (Optical Control Systems, GmbH) gel counter with a light source can be used in transmission mode with the grey level set at 170 to detect the number of gels. Fewer gels are formed because the multiple zone polyolefin polymerizations disclosed herein produce a more homogeneous product. The multimodal molecular weight distribution can allow bridging of the low molecular weight (LMW) component and the high molecular weight (HMW) component with one or more other components such that the multimodal polyolefin has fewer gels that result when mixing components having disparate molecular weights (e.g., a HMW component and a LMW component). 
     Polyethylene resins A, B, C, D, and E are discussed below as exemplary embodiments of the multimodal polyolefins that can be made in the disclosed apparatuses and processes, and it is contemplated that other polyolefin resins can be made. In aspect, any multimodal polyolefin and any polyolefin resin made herein can be suitable for use as a film, a pipe, or an article formed by blow molding, small part blow molding, large part blow molding, extrusion molding, rotational molding, thermoforming, cast molding, and the like. 
     In an aspect, an amount of from about 20 to about 80 wt.%, alternatively from about 40 to about 60 wt.%, alternatively from about 45 to about 55 wt.%, alternatively about 50 wt.% of polyethylene resin A can comprise the first polyolefin and an amount of from about 80 to about 20 wt.%, alternatively from about 60 to about 40 wt.%, alternatively from about 55 to about 45 wt.%, alternatively about 50 wt.% of polyethylene resin A can comprise the second polyolefin and the third polyolefin. Stated another way, an amount of from about 20 to about 80 wt.%, alternatively from about 40 to about 60 wt.%, alternatively from about 45 to about 55 wt.%, alternatively about 50 wt.% of polyethylene resin A can comprise the LMW component and an amount of from about 80 to about 20 wt.%, alternatively from about 60 to about 40 wt.%, alternatively from about 55 to about 45 wt.%, alternatively about 50 wt.% of polyethylene resin A can comprise the IMW component and the HMW component. Stated another way, the LMW component of polyethylene resin A can be present in an amount of from about 20 wt.% to about 75 wt.%, the IMW component of polyethylene resin A can be present in an amount of from about 5 wt.% to about 40 wt.%, and the HMW component of polyethylene resin A can be present in an amount of from about 10 wt.% to about 60 wt.%. 
     In an aspect, the portion of polyethylene resin A that is made of the second polyolefin and the third polyolefin can include an amount of from about 1 to about 30 wt.% of the second polyolefin and an amount of from about 10 to about 79 wt.% of the third polyolefin. 
     In an aspect, the portion of polyethylene resin A that is made of the IMW component and the HMW component can include an amount of from about 1 to about 30 wt.% of the IMW component and an amount of from about 10 to about 79 wt.% of the HMW component. 
     In an aspect, polyethylene resin A can have a density in a range of about 0.930 to about 0.970 g/ml, when tested in accordance with ISO  1183  at 23° C. 
     In an aspect, polyethylene resin A can have a melt index (MI 2 ) in a range of from about 0.1 to about 30 g/10 min, when tested in accordance with ISO  1133  at 190° C. under a force of 2.16 kg. 
     In an aspect, polyethylene resin A can have a high load melt index (HLMI) of from about 1 to about 45 g/10 min, when tested in accordance with ISO  1133  at 190° C. under a force of 2.16 kg. 
     In an aspect, polyethylene resin A can have a comonomer content in a range of from about 0 to about 6 wt.%. 
     In an aspect, polyethylene resin A can have a weight average molecular weight (M w ) in a range of from about 250 to about 1,500 kg/mol. 
     In an aspect, polyethylene resin A can have a number average molecular weight (M n ) in a range of from about 4.8 to about 84 kg/mol. 
     In an aspect, polyethylene resin A can have a z-average molecular weight (M z ) in a range of from about 500 to about 5,000 kg/mol. 
     In an aspect, polyethylene resin A can have a polydispersity index (dispersity or PDI or M w /M n ) in a range of from about 18 to about 52. 
     In an aspect, polyethylene resin A can have a long chain branching index in a range of from about 0 to about 0.96. 
     In an aspect, polyethylene resin A can have a shear induced crystallization (SIC) index in a range of from about 0.15 to about 8. The SIC index is determined by the following equation: SIC index=(t onset,SIC @1000 × t onset,quiescent ) / (HLMI * 100) where t onset,SIC @1000 is measured in seconds and is the time required for crystallization onset under shear rate of 1000 s -1 , and where t onset,   quiescent  is measured in seconds and is the crystallization onset time at a temperature of 125° C. under no shear, determined in isothermal mode by differential scanning calorimetry. 
     In an aspect, the second polyolefin (e.g., the IMW component) of polyethylene resin A that is produced in polymerization zone  321  of the riser  320  can have an average molecular weight (M w , M n , or M z ) greater than an average molecular weight (M w , M n , or M z ) of the first polyolefin (e.g., the LMW component) of polyethylene resin A that is produced in the polymerization zone  112  of the first reactor  100  and less than an average molecular weight (M w , M n , or M z ) of the third polyolefin (e.g., the HMW component) of polyethylene resin A that is produced in the polymerization zone  341  of the downcomer  340 . 
     In an aspect, polyethylene resin A can have an environmental stress cracking resistance (ESCR) of equal to or greater than about 800 hours; alternatively, greater than about 900 hours; alternatively, greater than about 1,000 hours, when tested in accordance with ISO 16770. 
     In an aspect, polyethylene resin A can have a value for rapid crack propagation (RCP) that is at least 100%; alternatively, at least 110%; alternatively, at least 120%; alternatively, at least 130%; alternatively, at least 140 % of the value for RCP of a bimodal polyethylene. 
     In an aspect, polyethylene resin A can have a value for rapid crack propagation (RCP) that is at least 100%; alternatively, at least 110%; alternatively, at least 120%; alternatively, at least 130%; alternatively, at least 140 % of the value for RCP of a bimodal polyethylene. 
     In an aspect, polyethylene resin A can have a resistance to slow crack growth of at least 100%; alternatively, at least 110%; alternatively, at least 120%; alternatively, at least 130%; alternatively, at least 140 % of the value for resistance to slow crack growth of a bimodal polyethylene, when tested in accordance with ASTM F1473, with the caveat that the resistance to slow crack growth is defined as the polyethylene notch tensile test (PENT) failure time. 
     In an aspect, polyethylene resin A can have a tensile impact strength of from about 135 to about 165 kJ/m 2 . 
     In an aspect, polyethylene resin A can have a gel count of less than about 950 gels/m 2 . Alternatively, polyethylene resin A can have a gel count of less than about 900 gels/m 2 ; alternatively, less than about 850 gels/m 2 ; alternatively, less than about 800 gels/m 2 ; alternatively, less than about 750 gels/m 2 ; alternatively, a gel count of less than about 700 gels/m 2 ; alternatively, less than about 650 gels/m 2 ; alternatively, less than about 600 gels/m 2 . 
     In an aspect, polyethylene resin A can be made by an embodiment of the process having a combination of the aspects described herein. 
     In an aspect, polyethylene resin A can be suitable for use as a film, a pipe, or an article formed by blow molding, small part blow molding, large part blow molding, extrusion molding, rotational molding, thermoforming, cast molding, and the like. 
     In an aspect, an amount of from about 20 to about 75 wt.% of polyethylene resin B can comprise the first polyolefin, an amount of from about 5 to about 40 wt.% of polyethylene resin B can comprise the second polyolefin, and an amount of from about 10 to about 60 wt.% of polyethylene resin B can comprise the third polyolefin. Stated another way, an amount of from about 20 to about 75 wt.% of polyethylene resin B can comprise the LMW component, an amount of from about 5 to about 40 wt.% of polyethylene resin B can comprise the IMW component, and an amount of from about 10 to about 60 wt.% of polyethylene resin B can comprise the HMW component. Stated another way, the LMW component of polyethylene resin B can be present in an amount of from about 20 wt.% to about 75 wt.%, the IMW component of polyethylene resin B can be present in an amount of from about 5 wt.% to about 40 wt.%, and the HMW component of polyethylene resin B can be present in an amount of from about 10 wt.% to about 60 wt.%. 
     In an aspect, polyethylene resin B can be a trimodal polyethylene resin. 
     In aspect, an amount of from about 40 to about 60 wt.% of polyethylene resin B can comprise the first polyolefin, an amount of from about 20 to about 40 wt.% of polyethylene resin B can comprise the second polyolefin, and an amount of from about 10 to about 30 wt.% of polyethylene resin B can comprise the third polyolefin. Stated another way, an amount of from about 40 to about 60 wt.% of polyethylene resin B can comprise the LMW component, an amount of from about 20 to about 40 wt.% of polyethylene resin B can comprise the IMW component, and an amount of from about 10 to about 30 wt.% of polyethylene resin B can comprise the HMW component. Stated another way, the LMW component of polyethylene resin B can be present in an amount of from about 40 wt.% to about 60 wt.%, the IMW component of polyethylene resin B can be present in an amount of from about 20 wt.% to about 40 wt.%, and the HMW component of polyethylene resin B can be present in an amount of from about 10 wt.% to about 30 wt.%. 
     In aspect, an amount of from about 50 wt.% of polyethylene resin B can comprise the first polyolefin, an amount of from about 30 wt.% of polyethylene resin B can comprise the second polyolefin, and an amount of from about 20 wt.% of polyethylene resin B can comprise the third polyolefin. Stated another way, an amount of from about 50 wt.% of polyethylene resin B can comprise the LMW component, an amount of from about 30 wt.% of polyethylene resin B can comprise the IMW component, and an amount of from about 20 wt.% of polyethylene resin B can comprise the HMW component. Stated another way, the LMW component of polyethylene resin B can be present in an amount of from about 50 wt.%, the IMW component of polyethylene resin B can be present in an amount of from about 30 wt.%, and the HMW component of polyethylene resin B can be present in an amount of from about 20 wt.%. 
     In an aspect, polyethylene resin B can have a long chain branching content of less than about 0.01 long chain branches per 1,000 carbon atoms. 
     In an aspect, polyethylene resin B can be a copolymer formed using a comonomer in at least one of the first reactor  100  and the MZCR  300 . The copolymer can have a comonomer content of from greater than about 0 wt.% to about 20 wt.%; alternatively, from greater than about 0 wt.% to about 6 wt.%; alternatively, from about 2 wt.% to about 6 wt.%; alternatively, from about 1 wt.% to about 5 wt.%; alternatively, from greater than about 6 wt.% to about 20 wt.%; alternatively, from greater than about 6 wt.% to about 15 wt.%; or alternatively, from greater than about 6 wt.% to about 10 wt.%. 
     In an aspect, the comonomer for polyethylene resin B can be 1-butene, 1-hexene, 1-octene, or combinations thereof. 
     In an aspect, polyethylene resin B can have density of from about 0.900 g/cc to about 0.980 g/cc, when tested in accordance with ASTM D1505; alternatively, a density of less than about 0.960 g/cc, when tested in accordance with ASTM D1505; alternatively, a density of from greater than about 0.940 g/cc to about 0.960 g/cc, when tested in accordance with ASTM D1505; alternatively, a density of from about 0.920 g/cc to about 0.940 g/cc, when tested in accordance with ASTM D1505. 
     In an aspect, polyethylene resin B can have a melt index (MI 2 ) of less than about 1 g/10 min, when tested in accordance with ASTM D1238 under a force of 2.16 kg. 
     In an aspect, polyethylene resin B can have a high load melt index (HLMI) of from about 1 g/10 min to less than about 20 g/10 min, when tested in accordance with ASTM D1238 under a force of 21.6 kg. 
     In an aspect, polyethylene resin B can have a weight average molecular weight (M w ) of from about 150 kg/mol to about 1,000 kg/mol. 
     In an aspect, polyethylene resin B can have a number average molecular weight (M n ) of from about 7.5 kg/mol to about 30 kg/mol. 
     In an aspect, polyethylene resin B can have a z-average molecular weight (M z ) of from about 1,000 kg/mol to about 5,000 kg/mol; alternatively, from about 1,000 kg/mol to about 3,500 kg/mol. 
     In an aspect, polyethylene resin B can have a (z+1)-average molecular weight (M z+1 ) of from about 2,000 kg/mol to about 9,000 kg/mol. 
     In an aspect, polyethylene resin B can have a polydispersity index (dispersity or PDI or M w /M n ) of from about 5 to about 60. 
     In an aspect, polyethylene resin B can have a polydispersity index (dispersity or PDI or M w /M n ) of less than about 18. 
     In an aspect, polyethylene resin B can have a magnitude of slip-stick of from about 300 psi to about 1,000 psi (about 2.07 MPa to about 6.89 MPa). 
     In an aspect, the LMW component of polyethylene resin B is a homopolymer. 
     In an aspect, the LMW component of polyethylene resin B can have a density of less than about 0.960 g/cc or alternatively, from equal to or greater than about 0.960 g/cc to about 0.985 g/cc, when tested in accordance with ASTM D1505. 
     In an aspect, the LMW component of polyethylene resin B can have a melt index (MI 2 ) of from about 3 g/10 min to about 400 g/10 min, when tested in accordance with ASTM D1238 under a force of 2.16 kg. 
     In an aspect, the LMW component of polyethylene resin B can have a high load melt index (HLMI) of from about 160 g/10 min to about 41,000 g/10 min, when tested in accordance with ASTM D1238 under a force of 21.6 kg. 
     In an aspect, the LMW component of polyethylene resin B can have a weight average molecular weight (M w ) of from about 20 kg/mol to about 150 kg/mol. 
     In an aspect, the LMW component of polyethylene resin B can have a number average molecular weight (M n ) of from about 5 kg/mol to about 25 kg/mol; alternatively, from about 5 kg/mol to about 15 kg/mol. 
     In an aspect, the LMW component of polyethylene resin B can have a z-average molecular weight (M z ) of from about 100 kg/mol to about 340 kg/mol. 
     In an aspect, the LMW component of polyethylene resin B can have a polydispersity index (dispersity or PDI or M w /M n ) of from about 1 to about 30; alternatively, from about 1 to about 15. 
     In an aspect, the LMW component of polyethylene resin B can have a short chain branching content of from about 0 to about 5 short chain branches per 1,000 carbon atoms; alternatively, from about 0 to about 4 short chain branches per 1,000 carbon atoms; alternatively, from about 0 to about 3 short chain branches per 1,000 carbon atoms; alternatively, from about 0 to about 2 short chain branches per 1,000 carbon atoms; alternatively, from about 0 to about 1 short chain branches per 1,000 carbon atoms. 
     In an aspect, the IMW component of polyethylene resin B can be a copolymer. 
     In an aspect, the IMW component of polyethylene resin B can have a first comonomer content of from greater than about 0 wt.% to about 10 wt.%; alternatively, from greater than about 0 wt.% to about 4 wt.%. 
     In an aspect, the IMW component if polyethylene resin B can have a density of from equal to or greater than about 0.915 g/cc to about 0.970 g/cc, when tested in accordance with ASTM D1505. 
     In an aspect, the IMW component of polyethylene resin B can have a melt index (MI 2 ) of from about 0.1 g/10 min to about 30 g/10 min, when tested in accordance with ASTM D1238 under a force of 2.16 kg. 
     In an aspect, the IMW component of polyethylene resin B can have a high load melt index (HLMI) of from about 5 g/10 min to about 1,500 g/10 min, when tested in accordance with ASTM D1238 under a force of 21.6 kg. 
     In an aspect, the IMW component of polyethylene resin B can have a weight average molecular weight (M w ) of from about 85 kg/mol to about 350 kg/mol. 
     In an aspect, the weight average molecular weight (M w ) of the IMW component of polyethylene resin B can be greater than the weight average molecular weight (M w ) of the LMW component of polyethylene resin B. 
     In an aspect, the IMW component of polyethylene resin B can have a number average molecular weight (M n ) of from about 10 kg/mol to about 185 kg/mol; alternatively, from about 10 kg/mol to about 100 kg/mol; alternatively, from about 10 kg/mol to about 35 kg/mol. 
     In an aspect, the IMW component of polyethylene resin B can have a z-average molecular weight (M z ) of from about 215 kg/mol to about 2,300 kg/mol. 
     In an aspect, the IMW component of polyethylene resin B can have a polydispersity index (dispersity or PDI or M w /M n ) of from about 2.5 to about 35; alternatively, from about 2.5 to about 25. 
     In an aspect, the IMW component of polyethylene resin B can have a short chain branching content of from about 0.1 to about 10 short chain branches per 1,000 carbon atoms; alternatively, from about 0.1 to about 8 short chain branches per 1,000 carbon atoms; alternatively, from about 0.2 to about 7 short chain branches per 1,000 carbon atoms; alternatively, from about 0.3 to about 6 short chain branches per 1,000 carbon atoms; alternatively, from about 0.4 to about 5 short chain branches per 1,000 carbon atoms. 
     In an aspect, the HMW component of polyethylene resin B can be a copolymer. 
     In an aspect, the HMW component of polyethylene resin B can have a comonomer content of greater than about 0 wt.% to about 10 wt.%; alternatively, from about 1 wt.% to about 10 wt.%. 
     In an aspect, the comonomer content in the HMW component of polyethylene resin B can be greater than the comonomer content of the IMW component of polyethylene resin B. 
     In an aspect, the HMW component of polyethylene resin B can have a density of from equal to or greater than about 0.900 g/cc to about 0.960 g/cc; alternatively, from equal to or greater than about 0.900 g/cc to about 0.940 g/cc; or alternatively, from equal to or greater than about 0.900 g/cc to about 0.930 g/cc, when tested in accordance with ASTM D1505. 
     In an aspect, the HMW component can have a melt index (MI 2 ) of less than about 0.1 g/10 min, when tested in accordance with ASTM D1238 under a force of 2.16 kg. 
     In an aspect, the HMW component of polyethylene resin B can have a high load melt index (HLMI) of from about 0.005 g/10 min to about 2 g/10 min, when tested in accordance with ASTM D1238 under a force of 21.6 kg. 
     In an aspect, the HMW component of polyethylene resin B can have weight average molecular weight (M w ) of greater than about 350 kg/mol; alternatively, from greater than about 350 kg/mol to about 1,500 kg/mol. 
     In an aspect, the HMW component of polyethylene resin B can have a number average molecular weight (M n ) of from about 75 kg/mol to about 200 kg/mol. 
     In an aspect, the HMW component of polyethylene resin B can have a z-average molecular weight (M z ) of from about 1,700 kg/mol to about 4,600 kg/mol. 
     In an aspect, the HMW component of polyethylene resin B can have a polydispersity index (dispersity or PDI or M w /M n ) of from about 2 to about 20; alternatively, from about 2 to about 15. 
     In an aspect, the HMW component of polyethylene resin B can have a short chain branching content of from about 1 to about 15 short chain branches per 1,000 carbon atoms; alternatively, from about 2 to about 13 short chain branches per 1,000 carbon atoms; alternatively, from about 3 to about 12 short chain branches per 1,000 carbon atoms; alternatively, from about 4 to about 11 short chain branches per 1,000 carbon atoms; alternatively, from about 5 to about 10 short chain branches per 1,000 carbon atoms. 
     In an aspect, polyethylene resin B can have a Young’s modulus (E) of equal to or greater than about 900 MPa; alternatively from about 900 MPa to about 1350 MPa, when tested in accordance with ASTM D638. 
     In an aspect, polyethylene resin B can have a tensile yield stress of equal to or greater than about 20 MPa; alternatively, from about 20 MPa to about 30 MPa, when tested in accordance with ASTM D638. 
     In an aspect, polyethylene resin B can have a tensile yield strain of from about 5% to about 25%, when tested in accordance with ASTM D638. 
     In an aspect, polyethylene resin B can have a tensile natural draw ratio at room temperature of from about 300% to about 600%, when tested in accordance with ASTM D638. 
     In an aspect, polyethylene resin B can have a tensile natural draw ratio at 80° C. of less than 500%; alternatively, of less than about 400%; alternatively, from about 250% to about 400%; alternatively, less than about 300%, when tested in accordance with ASTM D638. 
     In an aspect, polyethylene resin B can have a strain hardening modulus of from about 50 MPa to about 90 MPa, when tested in accordance with ISO 18488-2015(E). 
     In an aspect, polyethylene resin B can have an environmental stress cracking resistance (ESCR) of equal to or greater than about 1,000 hours, when tested in accordance with ASTM D1693 (condition A). 
     In an aspect, polyethylene resin B can have a resistance to slow crack growth of equal to or greater than about 800 h; alternatively, equal to or greater than about 2,000 h; alternatively, equal to or greater than about 5,000 h; or alternatively, equal to or greater than about 10,000 h, when tested in accordance with ASTM F1473, with the caveat that the resistance to slow crack growth is defined as the polyethylene notch tensile test (PENT) failure time. 
     In an aspect, polyethylene resin B can have a resistance to slow crack growth of equal to or greater than about 8,760 h; alternatively, equal to or greater than about 10,000 h; alternatively, equal to or greater than about 15,000 h; alternatively, equal to or greater than about 25,000 h; alternatively, equal to or greater than about 50,000 h; alternatively, equal to or greater than about 100,000 h; or alternatively, equal to or greater than about 500,000 h, when tested in accordance with ISO 16770 at 80° C. and 6 MPa, with the caveat that the resistance to slow crack growth is defined as the full notch creep test (FNCT) failure time. 
     In an aspect, polyethylene resin B can have a resistance to slow crack growth of equal to or greater than about 100 h; alternatively, equal to or greater than about 500 h; alternatively, equal to or greater than about 1,000 h; alternatively, equal to or greater than about 5,000 h; alternatively, equal to or greater than about 10,000 h; or alternatively, equal to or greater than about 15,000 h, when tested in accordance with ISO 13479:2009(E) at 4.6 MPa, with the caveat that the resistance to slow crack growth is defined as the notched pipe test (NPT) failure time. 
     In an aspect, polyethylene resin B can have a viscous relaxation time of from about 0.5 s to about 7.5 s. 
     In an aspect, polyethylene resin B can have an η 0  (eta_0) of equal to or greater than about 0.7×10 5  Pa-s; alternatively, equal to or greater than about 1.0×10 5  Pa-s; alternatively from about 0.7×10 5  Pa-s to about 2.0×10 6  Pa-s. 
     In an aspect, polyethylene resin B can have an η 251  (eta_251) of less than about 1.5×10 3  Pa-s. 
     In an aspect, polyethylene resin B can have a storage modulus (G′) of from about 225,000 Pa to about 325,000 Pa, wherein G′ is measured at 190° C. and 251 rad/s in accordance with ASTM D4440. 
     In an aspect, polyethylene resin B can have a loss modulus (G″) of from about 100,000 Pa to about 200,00 Pa, wherein G″ is measured at 190° C. and 251 rad/s in accordance with ASTM D4440. 
     In an aspect, polyethylene resin B can have a tanδ of from about 0.3 to about 0.7; wherein tanδ is the ratio of the loss modulus (G″) to storage modulus (G′), wherein G″ and G′ are measured at 190° C. and 251 rad/s in accordance with ASTM D4440. 
     In an aspect, polyethylene resin B can be suitable for use as a film, a pipe, or an article formed by blow molding, small part blow molding, large part blow molding, extrusion molding, rotational molding, thermoforming, cast molding, and the like. 
     In an aspect, polyethylene resin B can have a gel count of less than about 950 gels/m 2 . Alternatively, polyethylene resin B can have a gel count of less than about 900 gels/m 2 ; alternatively, less than about 850 gels/m 2 ; alternatively, less than about 800 gels/m 2 ; alternatively, less than about 750 gels/m 2 ; alternatively, a gel count of less than about 700 gels/m 2 ; alternatively, less than about 650 gels/m 2 ; alternatively, less than about 600 gels/m 2 . 
     In an aspect, polyethylene resin B can be made by an embodiment of the process having a combination of the aspects described herein. 
     In an aspect, an amount of from about 40 to about 60 wt.% of polyethylene resin C can comprise the first polyolefin, an amount of from about 5 to about 15 wt.% of polyethylene resin C can comprise the second polyolefin, and an amount of from about 30 to about 50 wt.% of polyethylene resin C can comprise the third polyolefin. Stated another way, an amount of from about 40 to about 60 wt.% of polyethylene resin C can comprise the LMW component, an amount of from about 5 to about 15 wt.% of polyethylene resin C can comprise the IMW component, and an amount of from about 30 to about 50 wt.% of polyethylene resin C can comprise the HMW component. Stated another way, the LMW component of polyethylene resin C can present in an amount of from about 40 wt.% to about 60 wt.%, the IMW component of polyethylene resin C can be present in an amount of from about 5 wt.% to about 15 wt.%, and the HMW component of polyethylene resin C can be present in an amount of from about 30 wt.% to about 50 wt.%. 
     In aspect, an amount of from about 40 to about 60 wt.% of polyethylene resin C can comprise the first polyolefin, an amount of from about 5 to about 35 wt.% of polyethylene resin C can comprise the second polyolefin, and an amount of from about 15 to about 50 wt.% of polyethylene resin C can comprise the third polyolefin. Stated another way, an amount of from about 40 to about 60 wt.% of polyethylene resin C can comprise the LMW component, an amount of from about 5 to about 35 wt.% of polyethylene resin C can comprise the IMW component, and an amount of from about 15 to about 50 wt.% of polyethylene resin C can comprise the HMW component. Stated another way, the LMW component of polyethylene resin C can be present in an amount of from about 40 wt.% to about 60 wt.%, the IMW component of polyethylene resin C can be present in an amount of from about 5 wt.% to about 35 wt.%, and the HMW component of polyethylene resin C can be present in an amount of from about 15 wt.% to about 50 wt.%. 
     In aspect, an amount of from about 50 wt.% of polyethylene resin C can comprise the first polyolefin, an amount of from about 30 wt.% of polyethylene resin C can comprise the second polyolefin, and an amount of from about 20 wt.% of polyethylene resin C can comprise the third polyolefin. Stated another way, an amount of from about 50 wt.% of polyethylene resin C can comprise the LMW component, an amount of from about 30 wt.% of polyethylene resin C can comprise the IMW component, and an amount of from about 20 wt.% of polyethylene resin C can comprise the HMW component. Stated another way, the LMW component of polyethylene resin C can be present in an amount of from about 50 wt.%, the IMW component of polyethylene resin C can be present in an amount of from about 30 wt.%, and the HMW component of polyethylene resin C can be present in an amount of from about 20 wt.%. 
     In an aspect, polyethylene resin C can be a copolymer formed using a comonomer in at least one of the first reactor  100  and the MZCR  300 . The copolymer can have a comonomer content of from greater than about 0 wt.% to about 20 wt.%; alternatively, from greater than about 0 wt.% to about 6 wt.%; alternatively, from about 2 wt.% to about 6 wt.%; alternatively, from about 1 wt.% to about 5 wt.%; alternatively, from greater than about 6 wt.% to about 20 wt.%; alternatively, from greater than about 6 wt.% to about 15 wt.%; or alternatively, from greater than about 6 wt.% to about 10 wt.%. 
     In an aspect, the LMW component of polyethylene resin C can have a weight average molecular weight (M w ) of from about 25 kg/mol to about 65 kg/mol. 
     In an aspect, the IMW component of polyethylene resin C can have a weight average molecular weight (M w ) of from about 100 kg/mol to about 200 kg/mol. 
     In an aspect, the weight average molecular weight (M w ) of the HMW component of polyethylene resin C can be greater than the weight average molecular weight (M w ) of the IMW component of polyethylene resin C. 
     In an aspect, the HMW component of polyethylene resin C can have a weight average molecular weight (M w ) of from about 400 kg/mol to about 925 kg/mol. 
     In an aspect, the LMW component of polyethylene resin C can have a short chain branching content of from about 0 to about 2 short chain branches per 1,000 carbon atoms. 
     In an aspect, the IMW component of polyethylene resin C can have a short chain branching content of from about 0.1 to about 5 short chain branches per 1,000 carbon atoms. 
     In an aspect, the HMW component of polyethylene resin C can have a short chain branching content of from about 2 to about 12 short chain branches per 1,000 carbon atoms. 
     In an aspect, polyethylene resin C can have a slow crack growth, and a resistance to slow crack growth can be of equal to or greater than about 3,000 h, when tested in accordance with ASTM F1473, with the caveat that resistance to slow crack growth is defined as the polyethylene notch tensile test (PENT) failure time. 
     In an aspect, polyethylene resin C can be a trimodal polyethylene resin. 
     In an aspect, polyethylene resin C can have a resistance to slow crack growth of equal to or greater than about 8,760 h, when tested in accordance with ISO 16770 at 80° C. and 6 MPa, with the caveat that the resistance to slow crack growth is defined as the full notch creep test (FNCT) failure time. 
     In an aspect, polyethylene resin C can have a resistance to slow crack growth of equal to or greater than about 1,000 h, when tested in accordance with ISO 13479:2009(E) at 4.6 MPa, wherein the resistance to slow crack growth is defined as the notched pipe test (NPT) failure time. 
     In an aspect, polyethylene resin C can have a weight average molecular weight (M w ) of from about 200 kg/mol to about 400 kg/mol. 
     In an aspect, polyethylene resin C can have a number average molecular weight (M n ) of from about 7.5 kg/mol to about 20 kg/mol. 
     In an aspect, polyethylene resin C can have a z-average molecular weight (M z ) of from about 1,000 kg/mol to about 3,300 kg/mol. 
     In an aspect, polyethylene resin C can have an η 0  (eta_0) of equal to or greater than about 1.0×10 5  Pa-s. 
     In an aspect, polyethylene resin C can be formed into a pipe. Additionally, polyethylene resin C can be suitable for use as a film or an article formed by blow molding, small part blow molding, large part blow molding, extrusion molding, rotational molding, thermoforming, cast molding, and the like. 
     In an aspect, polyethylene resin C can have a gel count of less than about 750 gels/m 2 . Alternatively, polyethylene resin C can have a gel count of less than about 700 gels/m 2 ; alternatively, less than about 650 gels/m 2 ; alternatively, less than about 600 gels/m 2 . 
     In an aspect, polyethylene resin C can be made by an embodiment of the process having a combination of the aspects described herein. 
     In an aspect, an amount of from about 40 to about 60 wt.% of polyethylene resin D can comprise the first polyolefin, an amount of from about 5 to about 15 wt.% of polyethylene resin D can comprise the second polyolefin, and an amount of from about 30 to about 50 wt.% of polyethylene resin D can comprise the third polyolefin. Stated another way, an amount of from about 40 to about 60 wt.% of polyethylene resin D can comprise the LMW component, an amount of from about 5 to about 15 wt.% of polyethylene resin D can comprise the IMW component, and an amount of from about 30 to about 50 wt.% of polyethylene resin D can comprise the HMW component. Stated another way, the LMW component of polyethylene resin D can present in an amount of from about 40 wt.% to about 60 wt.%, the IMW component of polyethylene resin D can be present in an amount of from about 5 wt.% to about 15 wt.%, and the HMW component of polyethylene resin D can be present in an amount of from about 30 wt.% to about 50 wt.%. 
     In aspect, an amount of from about 40 to about 60 wt.% of polyethylene resin D can comprise the first polyolefin, an amount of from about 5 to about 35 wt.% of polyethylene resin D can comprise the second polyolefin, and an amount of from about 15 to about 50 wt.% of polyethylene resin D can comprise the third polyolefin. Stated another way, an amount of from about 40 to about 60 wt.% of polyethylene resin D can comprise the LMW component, an amount of from about 5 to about 35 wt.% of polyethylene resin D can comprise the IMW component, and an amount of from about 15 to about 50 wt.% of polyethylene resin D can comprise the HMW component. Stated another way, the LMW component of polyethylene resin D can be present in an amount of from about 40 wt.% to about 60 wt.%, the IMW component of polyethylene resin D can be present in an amount of from about 5 wt.% to about 35 wt.%, and the HMW component of polyethylene resin D can be present in an amount of from about 15 wt.% to about 50 wt.%. 
     In aspect, an amount of from about 50 wt.% of polyethylene resin D can comprise the first polyolefin, an amount of from about 30 wt.% of polyethylene resin D can comprise the second polyolefin, and an amount of from about 20 wt.% of polyethylene resin D can comprise the third polyolefin. Stated another way, an amount of from about 50 wt.% of polyethylene resin D can comprise the LMW component, an amount of from about 30 wt.% of polyethylene resin D can comprise the IMW component, and an amount of from about 20 wt.% of polyethylene resin D can comprise the HMW component. Stated another way, the LMW component of polyethylene resin D can be present in an amount of from about 50 wt.%, the IMW component of polyethylene resin D can be present in an amount of from about 30 wt.%, and the HMW component of polyethylene resin D can be present in an amount of from about 20 wt.%. 
     In an aspect, polyethylene resin D can be a copolymer formed using a comonomer in at least one of the first reactor  100  and the MZCR  300 . The copolymer can have a comonomer content of from greater than about 0 wt.% to about 20 wt.%; alternatively, from greater than about 0 wt.% to about 6 wt.%; alternatively, from about 2 wt.% to about 6 wt.%; alternatively, from about 1 wt.% to about 5 wt.%; alternatively, from greater than about 6 wt.% to about 20 wt.%; alternatively, from greater than about 6 wt.% to about 15 wt.%; or alternatively, from greater than about 6 wt.% to about 10 wt.%. 
     In an aspect, the LMW component of polyethylene resin D can have a weight average molecular weight (M w ) of from about 30 kg/mol to about 50 kg/mol. 
     In an aspect, the IMW component of polyethylene resin D can have a weight average molecular weight (M w ) of from about 90 kg/mol to about 150 kg/mol. 
     In an aspect, the HMW component of polyethylene resin D can have a weight average molecular weight (M w ) of from about 450 kg/mol to about 750 kg/mol. 
     In an aspect, the LMW component of polyethylene resin D can have a short chain branching content of from about 0.1 to about 2 short chain branches per 1,000 carbon atoms. 
     In an aspect, the IMW component of polyethylene resin D can have a short chain branching content of from about 0.1 to about 5 short chain branches per 1,000 carbon atoms. 
     In an aspect, the HMW component of polyethylene resin D can have a short chain branching content of from about 2 to about 10 short chain branches per 1,000 carbon atoms. 
     In an aspect, polyethylene resin D can have a tensile strength in the machine direction (MD) of greater than about 13,000 psi (about 89.6 MPa), when tested in accordance with ASTM D638 at 90 MPa. 
     In an aspect, polyethylene resin D can be a trimodal polyethylene resin. 
     In an aspect, polyethylene resin D can have a tensile strength in the transverse direction (TD) of greater than about 6,000 psi (about 41.4 MPa), when tested in accordance with ASTM D638 at 41 MPa. 
     In an aspect, polyethylene resin D can have an η 0  (eta_0) of equal to or greater than about 1.0×10 5  Pa-s. 
     In an aspect, polyethylene resin D can be formed into a film. Additionally, polyethylene resin D can be suitable for use as a pipe or an article formed by blow molding, small part blow molding, large part blow molding, extrusion molding, rotational molding, thermoforming, cast molding, and the like. 
     In an aspect, polyethylene resin D can be made by an embodiment of the process having a combination of the aspects described herein. 
     In an aspect, the multimodal polyolefin is a polyethylene resin E made by an embodiment of the process having a combination of the aspects described herein. 
     In an aspect, polyethylene resin E can be suitable for use as a pipe, film, or an article formed by blow molding, small part blow molding, large part blow molding, extrusion molding, rotational molding, thermoforming, cast molding, and the like. 
     In an aspect, polyethylene resin E can be a trimodal polyethylene resin. 
     In an aspect, polyethylene resin E can be a copolymer formed using a comonomer in at least one of the first reactor  100  and the MZCR  300 . The copolymer can have a comonomer content of from greater than about 0 wt.% to about 20 wt.%; alternatively, from greater than about 0 wt.% to about 6 wt.%; alternatively, from about 2 wt.% to about 6 wt.%; alternatively, from about 1 wt.% to about 5 wt.%; alternatively, from greater than about 6 wt.% to about 20 wt.%; alternatively, from greater than about 6 wt.% to about 15 wt.%; or alternatively, from greater than about 6 wt.% to about 10 wt.%. 
     In an aspect, the multimodal polyolefin that is a polyethylene resin A, B, C, D, or E can be produced using Ziegler-Natta catalyst in each of polymerization zones  112 ,  321 , and  341 . Stated another way, the multimodal polyolefin that is a polyethylene resin A, B, C, D, or E can be produced using Ziegler-Natta catalyst in each of the first reactor  100 , the riser  320  of the MZCR  300 , and the downcomer  340  of the MZCR  300 . Put yet another way, the multimodal polyolefin that is a polyethylene resin A, B, C, D, or E can be produced using Ziegler-Natta catalyst in each of the first reactor  100  and the MZCR  300 . 
     In an aspect, the LMW component of the multimodal polyolefin that is polyethylene resin A, B, C, D, or E can be produced in a polymerization zone  112  in the substantial absence of any comonomer described herein. Stated another way, the LMW component of the multimodal polyolefin that is polyethylene resin A, B, C, D, or E can be produced in the first reactor  100  in the substantial absence of any comonomer described herein. 
     In an aspect, the IMW component of the multimodal polyolefin that is polyethylene resin A, B, C, D, or E can be produced in polymerization zone  321  in the presence of a comonomer and hydrogen. Stated another way, the IMW component of the multimodal polyolefin that is polyethylene resin A, B, C, D, or E can be produced in the riser  320  of the MZCR  300  in the presence of a comonomer and hydrogen. 
     In an aspect, the HMW component of the multimodal polyolefin that is polyethylene resin A, B, C, D, or E can be produced in a polymerization zone  341  in the presence of a comonomer and hydrogen. Stated another way, the HMW component of the multimodal polyolefin that is polyethylene resin A, B, C, D, or E can be produced in the downcomer  340  of the MZCR  300  in the presence of a comonomer and hydrogen. 
     In an aspect, the amount of comonomer used in the polymerization zone  341  is greater than the amount of comonomer used in the polymerization zone  321 . Stated another way, the amount of comonomer used in the downcomer  340  of the MZCR  300  is greater than the amount of comonomer used in the riser  320  of the MZCR  300 . 
     In an aspect, the amount of hydrogen used in the polymerization zone  321  is greater than the amount of hydrogen used in the polymerization zone  341 . Stated another way, the amount of hydrogen used in the riser  320  of the MZCR  300  is greater than the amount of hydrogen used in the downcomer  340  of the MZCR  300 . 
     In an aspect, any of polyethylene resins A, B, C, D, or E can have an η 251  (eta_251) of less than about 1.5×10 3  Pa-s. 
     In an aspect, the first reactor  100  that produces the LMW component of any of polyethylene resins A, B, C, D, or E can be a gas phase reactor (also referred to as fluidized bed reactor). Stated another way, the polymerization zone  112  that produces the LMW component of any of polyethylene resins A, B, C, D, or E can be a gas phase reaction zone (also referred to as fluidized bed reaction zone). 
     In an aspect, the polymerization zone  321  of the MZCR  300  that produces the IMW component of any of polyethylene resins A, B, C, D, or E is a fast fluidization reaction zone. Stated another way, the polymerization zone  321  of the MZCR  300  that produces the IMW component of any of polyethylene resins A, B, C, D, or E operates under fast fluidization conditions. Stated another way, the riser  320  of the MZCR  300  that produces the IMW component of any of polyethylene resins A, B, C, D, or E operates under fast fluidization conditions. 
     In an aspect, the polymerization zone  341  of the MZCR  300  that produces the HMW component of any of polyethylene resins A, B, C, D, or E is a plug flow reaction zone. Stated another way, the polymerization zone  341  of the MZCR  300  that produces the HMW component of any of polyethylene resins A, B, C, D, or E operates under plug flow conditions. Stated another way, the downcomer  340  of the MZCR  300  that produces the HMW component of any of polyethylene resins A, B, C, D, or E operates under plug flow conditions. 
     ADDITIONAL ASPECTS 
     Apparatuses and processes for multiple reactor and multiple zone polyolefin polymerization have been described. Described below are process A, process B, process C, process D, apparatus A, apparatus B, apparatus C, apparatus D, polyethylene resin A, polyethylene resin B, polyethylene resin C, polyethylene resin D, polyethylene resin E and polyethylene resin F. 
     A first aspect of process A, which is a process for producing a multimodal polyolefin, is that process A comprises (a) polymerizing ethylene in a first reactor to produce a first polyolefin, (b) polymerizing ethylene in a first reaction mixture in a riser of a second reactor to produce a second polyolefin, (c) passing the first reaction mixture through an upper conduit from the riser to a separator, (d) recovering, in the separator, the second polyolefin from the first reaction mixture, (e) passing the second polyolefin from the separator into a downcomer of the second reactor, optionally via a liquid barrier, (f) polymerizing ethylene in a second reaction mixture in the downcomer to produce a third polyolefin, (g) passing the second reaction mixture through a lower conduit from the downcomer to the riser, and (h) one of (1) after step (a) and before steps (b)-(g), receiving the first polyolefin into the second reactor, or (2) before step (a) and after steps (b)-(g), receiving the second polyolefin and the third polyolefin into the first reactor. 
     In a second aspect of process A which can be used in combination with the first aspect of process A, the riser has a width-to-height ratio of less than about 0.1. 
     In a third aspect of process A which can be used in combination with any of the first to the second aspects of process A, the downcomer has a width-to-height ratio of less than about 0.1. 
     In a fourth aspect of process A which can be used in combination with any of the first to the third aspects of process A, the upper conduit has a length-to-diameter ratio of about 5 to about 20. 
     In a fifth aspect of process A which can be used in combination with any of the first to the fourth aspects of process A, the lower conduit has a length-to-diameter ratio of about 5 to about 20. 
     In a sixth aspect of process A which can be used in combination with any of the first to the fifth aspects of process A, process A further comprises adding or removing heat from the riser. 
     In a seventh aspect of process A which can be used in combination with any of the first to the sixth aspects of process A, process A further comprises adding or removing heat from the downcomer. 
     In an eighth aspect of process A which can be used in combination with any of the first to the seventh aspects of process A, the second reactor further comprises a transition conduit fluidly connected to the end of the lower conduit. 
     In a ninth aspect of process A which can be used in combination with the eighth aspect of process A, an angle of the transition conduit with respect to horizontal is less than about 90°. 
     In a tenth aspect of process A which can be used in combination with any of the eighth through the ninth aspects of process A, a length of the transition conduit is from about 6 feet to about 15 feet. 
     In an eleventh aspect of process A which can be used in combination with any of the eighth through the tenth aspects of process A, the second reactor further comprises a first elbow connector connected to a bottom portion of the riser and to an end of the lower conduit, and a second elbow connector connected to a top portion of the riser and to an end of the upper conduit, an a tee connector having a first connecting portion connected a bottom section of the downcomer, a second connecting portion connected to the lower conduit, and a third end connected to an end of the transition conduit, wherein a first angle between the first end and the second end is equal to or less than about 90° and a second angle between the second end and the third end is equal to or greater than 90°. 
     In a twelfth aspect of process A which can be used in combination with any of the first to the eleventh aspects of process A, the second reactor further comprises a first elbow connector connected to a bottom portion of the riser and to an end of the lower conduit, and a second elbow connector connected to a top portion of the riser and to an end of the upper conduit, and a third elbow connector connected to a bottom portion of the downcomer and to another end of the lower conduit. 
     In a thirteen aspect of process A which can be used in combination with the twelfth aspect of process A, at least one of the first, the second, or the third elbow connector has an inner diameter (d) and a radius (R c ) of an inner curvature, and process A further comprises maintaining, by at least one of the first, the second, or the third elbow, a Dean number (D n ) of the first or second reaction mixture flowing therein to be higher than 3,000,000, where D n =ρVd/µ*(d/2R c ) ½  and wherein ρ is a density of the first or second reaction mixture, V is a circulation velocity of the first or second reaction mixture, and µ is a dynamic viscosity of the first or second reaction mixture. 
     In a fourteenth aspect of process A which can be used in combination with any of the first to the thirteen aspects of process A, process A further comprises an elbow connector connected i) to the bottom portion of the riser and to the opposite end of the lower conduit, ii) to the top portion of the riser and to the end of the upper conduit, or iii) to the bottom portion of the downcomer and to the end of the lower conduit, wherein the elbow connector comprises a first tap on an outside radius of the elbow connector, a second tap on an inside radius of the elbow connector, a first sensing leg coupling the first tap to a differential pressure meter, and a second sensing leg coupling the second tap to the differential pressure meter. 
     In a fifteenth aspect of process A which can be used in combination with any of the first to the fourteenth aspects of process A, the second reactor has an internal surface which is polished to a root mean square of less than about 3.8 microns (150 microinches). 
     In a sixteenth aspect of process A which can be used in combination with any of the first to the fifteenth aspects of process A, an internal surface of the first reactor or an internal surface of the second reactor has a rust inhibitor coating. 
     In a seventeenth aspect of process A which can be used in combination with any of the first to the sixteenth aspects of process A, at least a portion of the first reactor or at least a portion of the second reactor is made of carbon steel, stainless steel, or a combination thereof. 
     In an eighteenth aspect of process A which can be used in combination with any of the first to the seventeenth aspects of process A, at least a portion of the first reactor or at least a portion of the second reactor is made of carbon steel, wherein the carbon steel is a low temperature carbon steel. 
     In a nineteenth aspect of process A which can be used in combination with any of the first to the eighteenth aspects of process A, one or more thermowells are located on the second reactor. 
     In a twentieth aspect of process A which can be used in combination with any of the first to the nineteenth aspects of process A, the second reactor further comprises an eductor or a standpipe coupled to the lower conduit or to a transition conduit fluidly connected to an end of the lower conduit. 
     In a twenty-first aspect of process A which can be used in combination with any of the first to the twentieth aspects of process A, the second reactor further comprises a gas density meter configured to measure a density of the first reaction mixture in the riser. 
     In a twenty-second aspect of process A which can be used in combination with any of the first to the twenty-first aspects of process A, the first polyolefin is a lower molecular weight polyethylene, the third polyolefin is a higher molecular weight polyethylene. 
     In a twenty-third aspect of process A which can be used in combination with the twenty-second aspect of process A, the second polyolefin has an average molecular weight greater (M w , M n , or M z ) than an average molecular weight (M w , M n , or M z ) of the first polyolefin and less than an average molecular weight of the third polyolefin. 
     In a twenty-fourth aspect of process A which can be used in combination with any of the first to the twenty-third aspects of process A, from about 20 to about 80 wt.% of the multimodal polyolefin comprises the first polyolefin and from about 80 to about 20 wt.% of the multimodal polyolefin comprises the second polyolefin and the third polyolefin. 
     In a twenty-fifth aspect of process A which can be used in combination with any of the first to the twenty-fourth aspects of process A, the multimodal polyolefin has a density in a range of from about 0.930 to about 0.970 g/ml when tested in accordance with ASTM D1505, a melt index in a range of from about 0.1 to about 30 g/10 min when tested in accordance with ASTM D1238 under a force of 2.16 kg and a temperature of 190° C., a comonomer content in a range of from 0 to about 6 wt.%, and a M w  in a range of from about 250 to about 1,500 kg/mol. 
     In a twenty-sixth aspect of process A which can be used in combination with the twenty-fifth aspect of process A, the multimodal polyolefin has a high load melt index of from about 1 to about 45 g/10 min when tested in accordance with ASTM D1238 under a force of 21.6 kg and a temperature of 190° C., a M z  in a range of from about 500 to about 5,000 kg/mol, a Mw/Mn in a range of from about 18 to about 52, a long chain branching index in a range of from 0 to about 0.96, and a shear induced crystallization (SIC) index in a range of from about 0.15 to about 8. 
     In a twenty-seventh aspect of process A which can be used in combination with any of the first to the twenty-sixth aspects of process A, the first reactor is a loop slurry reactor, a fluidized bed reactor, an autoclave reactor, a tubular reactor, a horizontal gas phase reactor, a continuous stirred-tank reactor, or a solution reactor. 
     A first aspect of process B, which is a process for producing a multimodal polyolefin, is that process B comprises (a) polymerizing ethylene in a first reactor to produce a first polyolefin, (b) polymerizing ethylene in a first reaction mixture in a riser of a second reactor to produce a second polyolefin contained in a riser product mixture, (c) passing the riser product mixture through an upper conduit from the riser to a separator, (d) recovering, in the separator, the second polyolefin from the riser product mixture, (e) passing the second polyolefin from the separator into a downcomer of the second reactor, optionally via a liquid barrier, (f) polymerizing ethylene in a second reaction mixture in the downcomer to produce a third polyolefin in a downcomer product mixture, (g) passing the downcomer product mixture through a lower conduit from the downcomer to the riser, and (h) one of (1) after step (a) and before steps (b)-(g), receiving the first polyolefin into the second reactor, or (2) before step (a) and after steps (b)-(g), receiving the second polyolefin and the third polyolefin into the first reactor. 
     In a second aspect of process B which can be used in combination with the first aspect of process B, process B further comprises discharging a portion of the downcomer product mixture containing the multimodal polyolefin from the downcomer of the second reactor. 
     In a third aspect of process B which can be used in combination with any of the first to the second aspects of process B, the downcomer product mixture is discharged through a product discharge conduit that is fluidly connected to the downcomer i) on a bottom half of the downcomer or ii) on or near a bottom tangent of the downcomer, wherein the product discharge conduit is fluidly connected to a continuous take-off valve or a discontinuous take-off valve. 
     In a fourth aspect of process B which can be used in combination with any of the first to the third aspects of process B, the product discharge conduit is connected to the downcomer such that an angle of the product discharge conduit with respect to horizontal is from about -60° to about 60°. 
     In a fifth aspect of process B which can be used in combination with any of the first to the fourth aspects of process B, process B further comprises passing the portion of the downcomer product mixture through a heater, wherein the heater is coupled to the product discharge conduit. 
     In a sixth aspect of process B which can be used in combination with the fifth aspect of process B, process B further comprises adding a catalyst or cocatalyst poison or deactivator to the downcomer product mixture in or upstream of the heater. 
     In a seventh aspect of process B which can be used in combination with any of the first to the sixth aspects of process B, process B further comprises discharging a polymer product in the downcomer product mixture from the heater at a temperature i) of from about 54.4° C. (130° F.) to about 104.4° C. (220° F.), or ii) below a melting point of the polymer product. 
     In an eighth aspect of process B which can be used in combination with any of the first to the seventh aspects of process B, process B further comprises receiving the downcomer product mixture from the heater into a separation vessel, and separating, in the separation vessel, the downcomer product mixture into a plurality of streams, each of the plurality of streams comprising a vapor, a polymer product, or both the vapor and the polymer product. 
     In a ninth aspect of process B which can be used in combination with the eighth aspect of process B, process B further comprises recovering one or more of an olefin monomer, an olefin comonomer, and a diluent from at least one of the plurality of streams comprising the vapor, and recycling one or more of the olefin monomer, the olefin comonomer, and the diluent to the first reactor, the second reactor, or both the first reactor and the second reactor. 
     In a tenth aspect of process B which can be used in combination with any of the first to the seventh aspects of process B, process B further comprises receiving the polymer product from the separation vessel into a degassing vessel, and removing, in the degassing vessel, at least a portion of a hydrocarbon entrained within the polymer product. 
     In an eleventh aspect of process B which can be used in combination with any of the first to the tenth aspects of process B, process B further comprises discharging a product mixture containing the multimodal polyolefin from the first reactor. 
     In a twelfth aspect of process B which can be used in combination with the eleventh aspect of process B, the product mixture is discharged through a product discharge conduit that is fluidly connected to the first reactor, wherein the product discharge conduit is fluidly connected to a continuous take-off valve or a discontinuous take-off valve. 
     In a thirteenth aspect of process B which can be used in combination with the twelfth aspect of process B, the product discharge conduit is connected to the first reactor such that an angle of the product discharge conduit with respect to horizontal is from about -600° to 60°. 
     In a fourteenth aspect of process B which can be used in combination with any of the first to the thirteenth aspects of process B, process B further comprises passing the product mixture through a heater, wherein the heater is coupled to the product discharge conduit. 
     In a fifteenth aspect of process B which can be used in combination with the fourteenth aspect of process B, process B further comprises adding a catalyst or cocatalyst poison or deactivator to the downcomer product mixture in or upstream of the heater. 
     In a sixteenth aspect of process B which can be used in combination with any of the first to the fifteenth aspects of process B, process B further comprises discharging a polymer product in the product mixture from the heater at a temperature i) of from about 54.4° C. (130° F.) to about 104.4° C. (220° F.), or ii) below a melting point of the polymer product. 
     In a seventeenth aspect of process B which can be used in combination with any of the first to the fifteenth aspects of process B, process B further comprises receiving the product mixture from the heater into a separation vessel, and separating, in the separation vessel, the product mixture into a plurality of streams, each of the plurality of streams comprising a vapor, a polymer product, or both the vapor and the polymer product. 
     In an eighteenth aspect of process B which can be used in combination with the seventeenth aspect of process B, process B further comprises recovering one or more of an olefin monomer, an olefin comonomer, and a diluent from at least one of the plurality of streams comprising the vapor, and recycling one or more of the olefin monomer, the olefin comonomer, and the diluent to the first reactor, the second reactor, or both the first reactor and the second reactor. 
     In a nineteenth aspect of process B which can be used in combination with any of the first to the eighteenth aspects of process B, process B further comprises receiving the polymer product from the separation vessel into a degassing vessel, and removing, in the degassing vessel, at least a portion of a hydrocarbon entrained within the polymer product. 
     In a twentieth aspect of process B which can be used in combination with any of the first to the nineteenth aspects of process B, the separator comprises a cyclone separator. 
     In a twenty-first aspect of process B which can be used in combination with the twentieth aspect of process B, the cyclone separator is a high efficiency cyclone separator, and process B further comprises separating, by the cyclone separator, 99 wt.% or more of solid particles in a riser product mixture from gas in the riser product mixture, wherein the solid particles have a size of about from about 2 µm to about 10 µm. 
     In a twenty-second aspect of process B which can be used in combination with any of the first to the twenty-first aspects of process B, the cyclone separator has a cone angle with respect to horizontal of from about 45° to about 80°. 
     In a twenty-third aspect of process B which can be used in combination with any of the first to the twenty-second aspects of process B, the cyclone separator has a tangential entrance angle of from 0° to about 15°. 
     In a twenty-fourth aspect of process B which can be used in combination with any of the first to the twenty-third aspects of process B, wherein the riser product mixture in step (c) is passed into a tangential entrance of the separator at a tangential entrance velocity of from about 15.24 m/s (50 ft/sec) to about 30.48 m/s (100 ft/sec). 
     In a twenty-fifth aspect of process B which can be used in combination with any of the first to the twenty-fourth aspects of process B, an angle with respect to horizontal of an opposite end of the upper conduit which fluidly connects to the cyclone separator is about 0° to about 15°. 
     In a twenty-sixth aspect of process B which can be used in combination with any of the first to the twenty-fifth aspects of process B, an opposite end of the upper conduit connects to the cyclone separator at a location of from about 0 m (0 ft) to about 6.10 m (20 ft) below a top of the cyclone separator. 
     In a twenty-seventh aspect of process B which can be used in combination with any of the first to the twenty-sixth aspects of process B, process B further comprises adding a reactor deactivation system to the second reactor, wherein the reactor deactivation system is configured to moderate or kill polymerization reactions in the riser, the downcomer, or both the riser and the downcomer. 
     In a twenty-eighth aspect of process B which can be used in combination with any of the first to the twenty-seventh aspects of process B, the separator comprises a flash tank or a flash chamber. 
     In a twenty-ninth aspect of process B which can be used in combination with any of the first to the twenty-eighth aspects of process B, the first polyolefin is a lower molecular weight polyethylene, the third polyolefin is a higher molecular weight polyethylene. 
     In a thirtieth aspect of process B which can be used in combination with the twenty-ninth aspect of process B, the second polyolefin has an average molecular weight (M w , M n , or M z ) greater than an average molecular weight (M w , M n , or M z ) of the first polyolefin and less than an average molecular weight of the third polyolefin. 
     In a thirty-first aspect of process B which can be used in combination with any of the first to the thirtieth aspects of process B, the first reactor is a loop slurry reactor, a fluidized bed reactor, an autoclave reactor, a tubular reactor, a horizontal gas phase reactor, a continuous stirred-tank reactor, or a solution reactor. 
     In a thirty-second aspect of process B which can be used in combination with any of the first to the thirty-first aspects of process B, wherein from about 20 to about 80 wt.% of the multimodal polyolefin comprises the first polyolefin and from about 80 to about 20 wt.% of the multimodal polyolefin comprises the second polyolefin and the third polyolefin. 
     In a thirty-third aspect of process B which can be used in combination with any of the first to the thirty-second aspects of process B, the multimodal polyolefin has a density in a range of from about 0.930 to about 0.970 g/ml, a melt index in a range of from about 0.1 to about 30 g/10 min when tested in accordance with ASTM D1238 under a force of 2.16 kg and a temperature of 190° C., a comonomer content in a range of from 0 to about 6 wt.%, and a M w  in a range of from about 250 to about 1,500 kg/mol. 
     In a thirty-fourth aspect of process B which can be used in combination with the thirty-third aspect of process B, the multimodal polyolefin has a high load melt index of from about 1 to about 45 g/10 min when tested in accordance with ASTM D1238 under a force of 21.6 kg and a temperature of 190° C., a M z  in a range of from about 500 to about 5,000 kg/mol, a M w /M n  in a range of from about 18 to about 52, a long chain branching index in a range of from 0 to about 0.96, and a shear induced crystallization (SIC) index in a range of from about 0.15 from about 8. 
     A first aspect of process C, which is a process for producing a multimodal polyolefin, performed with i) a first reactor having a first polymerization zone, and ii) a second reactor having a second polymerization zone in a riser and a third polymerization zone in a downcomer, is that process C comprises (a) polymerizing ethylene in the first polymerization zone to produce a first polyolefin, (b) passing a first reaction mixture upward through the second polymerization zone of the riser, wherein a second polyolefin is produced in the second polymerization zone, (c) receiving the first reaction mixture from the second polymerization zone in a separator, (d) separating, by the separator, a first polyolefin product from the received first reaction mixture, (e) passing the first polyolefin product through a barrier section of the second reactor and into the third polymerization zone, (f) adding, in the third polymerization zone, the first polyolefin product to a second reaction mixture, (g) passing the second reaction mixture downward through the third polymerization zone of the downcomer, wherein a third polyolefin is produced in the third polymerization zone, (h) repeating steps (b)-(g) n times, wherein n=1 to 100,000 and (i) one of 1) adding the first polyolefin to the second reactor at a location upstream of the second polymerization zone with respect to a direction of flow of the first reaction mixture in the second polymerization zone, and withdrawing the multimodal polyolefin from the downcomer, or 2) withdrawing a portion of a second polyolefin product from the second reactor, adding the portion of the second polyolefin product to the first polymerization zone of the first reactor, and withdrawing the multimodal polyolefin from the first reactor. 
     In a second aspect of process C which can be used in combination with the first aspect of process C, a gas composition of the second reaction mixture is different than a gas composition of the third reaction mixture. 
     In a third aspect of process C which can be used in combination with any of the first to the second aspects of process C, the gas composition of the second reaction mixture comprises at least two selected from monomer, diluent, and a catalyst. 
     In a fourth aspect of process C which can be used in combination with any of the first to the third aspects of process C, the gas composition of the third reaction mixture comprises at least two selected from hydrogen, monomer, comonomer, diluent, and a catalyst. 
     In a fifth aspect of process C which can be used in combination with any of the first to the fourth aspects of process C, wherein the barrier section is a liquid barrier comprising an inert liquid, wherein a concentration of the inert liquid in the liquid barrier is greater than a concentration of the inert liquid in the second polymerization zone and in the third polymerization zone. 
     In a sixth aspect of process C which can be used in combination with any of the first to the fifth aspects of process C, process C further comprises injecting comonomer into the third polymerization zone via one or more locations in the downcomer, wherein the third polyolefin is a copolymer. 
     In a seventh aspect of process C which can be used in combination with any of the first to the sixth aspects of process C, process C further comprises injecting an anti-static agent into one or more locations of the second reactor. 
     In an eighth aspect of process C which can be used in combination with the seventh aspect of process C, the step of injecting an anti-static agent comprises injecting a mixture comprising the anti-static agent and a carrier fluid into the one or more locations via one or more anti-static agent feed lines, wherein a concentration of the anti-static agent in each of the one or more anti-static agent feed lines is about 1 ppm to about 50 ppm based on weight of the carrier fluid in each of the one or more anti-static agent feed lines. 
     In a ninth aspect of process C which can be used in combination with any of the first to the eighth aspects of process C, a concentration of the anti-static agent in the second reactor is about 1 ppm to about 50 ppm based on weight of the carrier fluid in the second reactor. 
     In a tenth aspect of process C which can be used in combination with any of the first to the ninth aspects of process C, after passing the first reaction mixture upward through the second polymerization zone of the riser and before receiving the first reaction mixture in the separator, the process further comprises flowing the first reaction mixture through an upper conduit that fluidly connects the riser and the separator, wherein the first reaction mixture flows in the upper conduit at a velocity that is i) greater than a saltation velocity of the first reaction mixture and up to about 30.48 m/s (100 ft/sec), or ii) greater than 110% of the saltation velocity of the first reaction mixture. 
     In an eleventh aspect of process C which can be used in combination with any of the first to the tenth aspects of process C, after passing the second reaction mixture downward through the third polymerization zone of the downcomer, the process further comprises flowing the second reaction mixture through a lower conduit that fluidly connects the downcomer and the riser, wherein the second reaction mixture flows in the lower conduit at a velocity that is i) greater than a saltation velocity of the second reaction mixture and up to about 30.48 m/s (100 ft/sec), or ii) greater than 110% of the saltation velocity of the second reaction mixture. 
     In a twelfth aspect of process C which can be used in combination with any of the first to the eleventh aspects of process C, process C further comprises analyzing a sample of the first reaction mixture or the second reaction mixture at one or more locations in the second reactor to determine a concentration of gas, liquid, or solid in the first reaction mixture or the second reaction mixture, and to determine a concentration of monomer, comonomer, diluent, hydrogen, inert component, or polymer in the first reaction mixture or the second reaction mixture. 
     In a thirteenth aspect of process C which can be used in combination with any of the first to the twelfth aspects of process C, process C further comprises controlling a level of the first polyolefin product in the separator such that the first polyolefin product has a residence time of about 1 second to about 30 minutes in the separator. 
     In a fourteenth aspect of process C which can be used in combination with any of the first to the thirteenth aspects of process C, from about 20 to about 80 wt.% of the multimodal polyolefin comprises the first polyolefin and from about 80 to about 20 wt.% of the multimodal polyolefin comprises the second polyolefin and the third polyolefin. 
     In a fifteenth aspect of process C which can be used in combination with any of the first to the fourteenth aspects of process C, the multimodal polyolefin has a density in a range of from about 0.930 to about 0.970 g/ml when tested in accordance with ASTM D1505, a melt index in a range of from about 0.1 to about 30 g/10 min when tested in accordance with ASTM D1238 under a force of 2.16 kg and a temperature of 190° C., a comonomer content in a range of from about 0 to about 6 wt.%, and a M w  in a range of from about 250 to about 1,500 kg/mol. 
     In a sixteenth aspect of process C which can be used in combination with the fifteenth aspect of process C, the multimodal polyolefin has a high load melt index of from about 1 to about 45 g/10 min when tested in accordance with ASTM D1238 under a force of 21.6 kg and a temperature of 190° C., a M z  in a range of from about 500 to about 5.000 kg/mol, a Mw/Mn in a range of from about 18 to about 52, a long chain branching index in a range of from 0 to about 0.96, and a shear induced crystallization (SIC) index in a range of from about 0.15 to about 8. 
     In a seventeenth aspect of process C which can be used in combination with any of the first to the sixteenth aspects of process C, the first polymerization zone is in a loop slurry reactor, a fluidized bed reactor, an autoclave reactor, a tubular reactor, a horizontal gas phase reactor, a continuous stirred-tank reactor, or a solution reactor. 
     In an eighteenth aspect of process C which can be used in combination with any of the first to the seventeenth aspects of process C, the Mw of the first polyolefin and the Mw of the third polyolefin differ by an amount of greater than 10%, wherein step (b) comprises passing the first reaction mixture upward through the second polymerization zone of the riser such that an average residence time of the first reaction mixture in the second polymerization zone during a single pass is in a range of about 1 second to about 5 minutes. 
     In a nineteenth aspect of process C which can be used in combination with any of the fifteenth aspect or the eighteenth aspect of process C, the Mw of the first polyolefin and the Mw of the third polyolefin differ by an amount of greater than 10%, wherein step (g) comprises passing the second reaction mixture downward through the third polymerization zone of the downcomer such that an average residence time of the second reaction mixture in the third polymerization zone during a single pass is in a range of about 5 seconds to about 15 minutes. 
     In a twentieth aspect of process C which can be used in combination with any of the eighteenth aspect or the nineteenth aspect of process C, step (a) comprises polymerizing the first polyolefin in the first polymerization zone such that an average residence time of the first polyolefin in the first polymerization zone is in a range of about 1 second to about 14 hours; alternatively, about 1 second to about 12 hours; alternatively, about 1 second to about 10 hours; alternatively, about 1 second to about 8 hours; alternatively, about 2 hours to about 14 hours; alternatively, about 4 hours to about 14 hours; alternatively, about 4 hours to about 12 hours; alternatively, from about 1 hour to about 3 hours; alternatively, about 1 second to about 5 minutes; alternatively, less than 10 hours; alternatively, greater than 1 hour. 
     A first aspect of process D, which is a process for producing a multimodal polyolefin, is that process D comprises (a) polymerizing ethylene in a first reactor to produce a first polyolefin, (b) polymerizing ethylene in a first reaction mixture in a riser of a second reactor to produce a second polyolefin, (c) passing the first reaction mixture through an upper conduit from the riser to a separator, (d) recovering, in the separator, the second polyolefin from the first reaction mixture, (e) passing the second polyolefin from the separator into a downcomer of the second reactor, optionally via a liquid barrier, (f) polymerizing ethylene in a second reaction mixture in the downcomer to produce a third polyolefin, (g) passing the second reaction mixture through a lower conduit from the downcomer to the riser, and (h) one of (1) after step (a) and before steps (b)-(g), receiving the first polyolefin from the first reactor into the second reactor; or (2) before step (a) and after steps (b)-(g), receiving the second polyolefin and the third polyolefin from the second reactor into the first reactor. 
     In a second aspect of process D which can be used in combination with the first aspect of process D, the first reactor is a fluidized bed reactor, wherein receiving the first polyolefin from the first reactor into the second reactor comprises receiving the first polyolefin into a settling leg placed at least partially within a bottom portion of the fluidized bed reactor, wherein an end of the settling leg opens to the gas distributor and an opposite end extends outside the fluidized bed reactor. 
     In a third aspect of process D which can be used in combination with any of the first to the second aspects of process D, the settling leg has an inner diameter of from about 10.16 cm (4 inches) to about 30.48 cm (12 inches). 
     In a fourth aspect of process D which can be used in combination with any of the first to the third aspects of process D, process D further comprises receiving the first polyolefin and a gas mixture from the settling leg into a separation vessel, separating, by the separation vessel, the first polyolefin from a gas mixture, and treating the gas mixture, wherein the step of treating comprises a flaring a component of the gas mixture, capturing a component of the gas mixture in a pressure swing absorber, filtering a component of the gas mixture in a membrane, or a combination thereof. 
     In a fifth aspect of process D which can be used in combination with any of the first to the fourth aspects of process D, process D further comprises analyzing a sample of the first polyolefin obtain via a sample take-off conduit fluidly connected to the settling leg. 
     In a sixth aspect of process D which can be used in combination with any of the first to the fifth aspects of process D, the first reactor is a fluidized bed reactor, wherein receiving the first polyolefin from the first reactor into the second reactor comprises flowing the first polyolefin and a gas mixture from the fluidized bed reactor into a lock hopper via a product discharge conduit and a first cycling valve. 
     In a seventh aspect of process D which can be used in combination with the sixth aspect of process D, process D further comprises flowing the first polyolefin and the gas mixture from the lock hopper to a separation vessel via a second cycling valve, separating the first polyolefin from the gas mixture, and treating the gas mixture, wherein the step of treating comprises a flaring a component of the gas mixture, capturing a component of the gas mixture in a pressure swing absorber, filtering a component of the gas mixture in a membrane, or a combination thereof. 
     In an eighth aspect of process D which can be used in combination with any of the first to the seventh aspects of process D, process D further comprises analyzing a sample of the first polyolefin obtain via a sample take-off conduit fluidly connected to the product discharge conduit. 
     In a ninth aspect of process D which can be used in combination with any of the first to the eighth aspects of process D, the first reactor is a fluidized bed reactor, wherein receiving the first polyolefin from the first reactor into the second reactor comprises controlling a flow of the first polyolefin in a product discharge conduit fluidly connected to the fluidized bed reactor with a continuous take-off valve fluidly connected to the product discharge conduit. 
     In a tenth aspect of process D which can be used in combination with the ninth aspect of process D, process D further comprises receiving the first polyolefin and a gas mixture into a separation vessel coupled to the continuous take-off valve, separating, by the separation vessel, the first polyolefin from the gas mixture, and treating the gas mixture, wherein the step of treating comprises a flaring a component of the gas mixture, capturing a component of the gas mixture in a pressure swing absorber, filtering a component of the gas mixture in a membrane, or a combination thereof. 
     In an eleventh aspect of process D which can be used in combination with any of the first to the tenth aspects of process D, process D further comprises analyzing a sample of the first polyolefin obtain via a sample take-off conduit fluidly connected to the product discharge conduit. 
     In a twelfth aspect of process D which can be used in combination with any of the first to the eleventh aspects of process D, the first reactor is a fluidized bed reactor, wherein the second polyolefin and the third polyolefin from the second reactor are received into the first reactor, and process D further comprises receiving the multimodal polyolefin into a settling leg placed at least partially within a bottom portion of the fluidized bed reactor, wherein an end of the settling leg opens to the gas distributor and an opposite end extends outside the fluidized bed reactor. 
     In a thirteenth aspect of process D which can be used in combination with the twelfth aspect of process D, the settling leg has an inner diameter of from about 10.16 cm (4 inches) to about 30.48 cm (12 inches). 
     In a fourteenth aspect of process D which can be used in combination with any of the first to the thirteen aspects of process D, process D further comprises receiving the multimodal polyolefin and a gas mixture in a separation vessel coupled to the settling leg, separating, by the separation vessel, the multimodal polyolefin from the gas mixture, and treating the gas mixture, wherein the step of treating comprises a flaring a component of the gas mixture, capturing a component of the gas mixture in a pressure swing absorber, filtering a component of the gas mixture in a membrane, or a combination thereof. 
     In a fifteenth aspect of process D which can be used in combination with any of the first to the fourteenth aspects of process D, process D further comprises analyzing a sample of the multimodal polyolefin obtain via a sample take-off conduit fluidly connected to the product discharge conduit. 
     In a sixteenth aspect of process D which can be used in combination with any of the first to the fifteen aspects of process D, the first reactor is a fluidized bed reactor, wherein the second polyolefin and the third polyolefin from the second reactor are received into the first reactor, and process D further comprises flowing the multimodal polyolefin and a gas mixture from the fluidized bed reactor into a lock hopper via a product discharge conduit and a first cycling valve. 
     In a seventeenth aspect of process D which can be used in combination with the sixteenth aspect of process D, process D further comprises flowing the multimodal polyolefin and the gas mixture from the lock hopper to a separation vessel via a second cycling valve, separating the multimodal polyolefin from the gas mixture, and treating the gas mixture, wherein the step of treating comprises a flaring a component of the gas mixture, capturing a component of the gas mixture in a pressure swing absorber, filtering a component of the gas mixture in a membrane, or a combination thereof. 
     In an eighteenth aspect of process D which can be used in combination with any of the first to the seventeenth aspects of process D, process D further comprises analyzing a sample of the multimodal polyolefin obtain via a sample take-off conduit fluidly connected to the product discharge conduit. 
     In a nineteenth aspect of process D which can be used in combination with any of the first to the eighteenth aspects of process D, the first reactor is a fluidized bed reactor, wherein the second polyolefin and the third polyolefin from the second reactor are received into the first reactor, and process D further comprises controlling a flow of the multimodal polyolefin in a product discharge conduit fluidly connected to the fluidized bed reactor with a continuous take-off valve fluidly connected to the product discharge conduit. 
     In a twentieth aspect of process D which can be used in combination with the nineteenth aspect of process D, process D further comprises receiving the multimodal polyolefin and a gas mixture into a separation vessel coupled to the continuous take-off valve, separating, by the separation vessel, the multimodal polyolefin from the gas mixture, and treating the gas mixture, wherein the step of treating comprises a flaring a component of the gas mixture, capturing a component of the gas mixture in a pressure swing absorber, filtering a component of the gas mixture in a membrane, or a combination thereof. 
     In a twenty-first aspect of process D which can be used in combination with any of the first to the twentieth aspects of process D, process D further comprises analyzing a sample of the multimodal polyolefin obtain via a sample take-off conduit fluidly connected to the product discharge conduit. 
     In a twenty-second aspect of process D which can be used in combination with any of the first to the twenty-first aspects of process D, the first polyolefin is a lower molecular weight polyethylene, the third polyolefin is a higher molecular weight polyethylene. 
     In a twenty-third aspect of process D which can be used in combination with the twenty-second aspect of process D, the second polyolefin has an average molecular weight (M w , M n , or M z ) greater than an average molecular weight (M w , M n , or M z ) of the first polyolefin and less than an average molecular weight of the third polyolefin. 
     In a twenty-fourth aspect of process D which can be used in combination with any of the first to the twenty-third aspects of process D, from about 20 to about 80 wt.% of the multimodal polyolefin comprises the first polyolefin and from about 80 to about 20 wt.% of the multimodal polyolefin comprises the second polyolefin and the third polyolefin. 
     In a twenty-fifth aspect of process D which can be used in combination with any of the first to the twenty-fourth aspects of process D, the multimodal polyolefin has a density in a range of from about 0.930 to about 0.970 g/ml when tested in accordance with ASTM D1505, a melt index in a range of from about 0.1 to about 30 g/10 min when tested in accordance with ASTM D1238 under a force of 2.16 kg and a temperature of 190° C., a comonomer content in a range of from 0 to about 6 wt.%, and a M w  in a range of from about 250 to about 1,500 kg/mol. 
     In a twenty-sixth aspect of process D which can be used in combination with the twenty-fifth aspect of process D, the multimodal polyolefin has a high load melt index of from about 1 to about 45 g/10 min when tested in accordance with ASTM D1238 under a force of 21.6 kg and a temperature of 190° C., a M z  in a range of from about 500 to about 5,000 kg/mol, a Mw/Mn in a range of from about 18 to about 52, a long chain branching index in a range of from 0 to about 0.96, and a shear induced crystallization (SIC) index in a range of from about 0.15 to about 8. 
     In a twenty-seventh aspect of process D which can be used in combination with any of the first to the twenty-sixth aspects of process D, the first reactor is a loop slurry reactor, a fluidized bed reactor, an autoclave reactor, a tubular reactor, a horizontal gas phase reactor, a continuous stirred-tank reactor, or a solution reactor. 
     A first aspect of apparatus A which is an apparatus for producing a multimodal polyolefin, comprising a first reactor configured to produce a first polyolefin, a second reactor configured to produce a second polyolefin and a third polyolefin, where the second reactor comprises a riser configured to produce the second polyolefin, an upper conduit having an end fluidly connected to a top portion of the riser, a separator fluidly connected to an opposite end of the upper conduit, a downcomer configured to produce the third polyolefin, wherein a top portion of the downcomer is fluidly connected to the separator, optionally via a liquid barrier in the top portion of the downcomer, and a lower conduit having an end fluidly connected to a bottom portion of the downcomer and an opposite end fluidly connected to a bottom portion of the riser, wherein the second reactor is configured to receive the first polyolefin from the first reactor, or, the first reactor is configured to receive the second polyolefin and the third polyolefin from the second reactor. 
     In a second aspect of apparatus A which can be used in combination with the first aspect of apparatus A, the riser has a width-to-height ratio of less than about 0.1. 
     In a third aspect of apparatus A which can be used in combination with any of the first to the second aspects of apparatus A, the downcomer has a width-to-height ratio of less than about 0.1. 
     In a fourth aspect of apparatus A which can be used in combination with any of the first to the third aspects of apparatus A, the upper conduit has a length-to-diameter ratio of about 5 to about 20. 
     In a fifth aspect of apparatus A which can be used in combination with any of the first to the fourth aspects of apparatus A, the lower conduit has a length-to-diameter ratio of about 5 to about 20. 
     In a sixth aspect of apparatus A which can be used in combination with any of the first to the fifth aspects of apparatus A, apparatus A further comprises a heat apparatus configured to add or remove heat from the riser. 
     In a seventh aspect of apparatus A which can be used in combination with any of the first to the sixth aspects of apparatus A, apparatus A further comprises a heat apparatus configured to add or remove heat from the downcomer. 
     In an eighth aspect of apparatus A which can be used in combination with any of the first to the fourth aspects of apparatus A, the second reactor further comprises a transition conduit fluidly connected to the end of the lower conduit. 
     In a ninth aspect of apparatus A which can be used in combination with the eighth aspect of apparatus A, an angle of the transition conduit with respect to horizontal is less than about 90°. 
     In a tenth aspect of apparatus A which can be used in combination with any of the first to the ninth aspects of apparatus A, a length of the transition conduit is from about 6 feet to about 15 feet. 
     In an eleventh aspect of apparatus A which can be used in combination with any of the first to the tenth aspects of apparatus A, the second reactor further comprises a first elbow connector connected to the bottom portion of the riser and to the opposite end of the lower conduit, and a second elbow connector connected to the top portion of the riser and to the end of the upper conduit, and a tee connector having a first end connected to the bottom portion of the downcomer, a second end connected to the lower conduit, and a third end connected to an end of the transition conduit, wherein a first angle between the first end and the second end is equal to or less than about 90° and a second angle between the second end and the third end is equal to or greater than 90°. 
     In a twelfth aspect of apparatus A which can be used in combination with any of the first to the eleventh aspects of apparatus A, the second reactor further comprises a first elbow connector connected to the bottom portion of the riser and to the opposite end of the lower conduit, a second elbow connector connected to the top portion of the riser and to the end of the upper conduit, and a third elbow connector connected to the bottom portion of the downcomer and to the end of the lower conduit. 
     In a thirteenth aspect of apparatus A which can be used in combination with the twelfth aspect of apparatus A, at least one of the first, the second, or the third elbow connector has an inner diameter (d) and a radius (R c ) of an inner curvature and is configured to maintain a Dean number (D n ) of a reaction mixture flowing therein to be a value in a range of from about 1,000,000 to about 5,000,000, where Dn=ρVd/µ*(d/2R c ) ½  and where ρ is a density of the reaction mixture, V is a circulation velocity of the reaction mixture, and µ is a dynamic viscosity of the reaction mixture. 
     In a fourteenth aspect of apparatus A which can be used in combination with any of the first to the thirteenth aspects of apparatus A, apparatus A further comprises an elbow connector connected i) to the bottom portion of the riser and to the opposite end of the lower conduit, ii) to the top portion of the riser and to the end of the upper conduit, or iii) to the bottom portion of the downcomer and to the end of the lower conduit, wherein the elbow connector comprises a first tap on an outside radius of the elbow connector, a second tap on an inside radius of the elbow connector, a first sensing leg coupling the first tap to a differential pressure meter, and a second sensing leg coupling the second tap to the differential pressure meter. 
     In a fifteenth aspect of apparatus A which can be used in combination with any of the first to the fourteenth aspects of apparatus A, the second reactor has an internal surface which is polished to a root mean square of less than about 150 microinches. 
     In a sixteenth aspect of apparatus A which can be used in combination with any of the first to the fifteenth aspects of apparatus A, apparatus A further comprises a rust inhibitor coating on an internal surface of the first reactor or an internal surface of the second reactor. 
     In a seventeenth aspect of apparatus A which can be used in combination with any of the first to the sixteenth aspects of apparatus A, at least a portion of the first reactor or at least a portion of the second reactor is made of carbon steel, stainless steel, or a combination thereof. 
     In an eighteenth aspect of apparatus A which can be used in combination with any of the first to the seventeenth aspects of apparatus A, at least a portion of the first reactor or at least a portion of the second reactor is made of carbon steel, wherein the carbon steel is a low temperature carbon steel. 
     In a nineteenth aspect of apparatus A which can be used in combination with any of the first to the eighteenth aspects of apparatus A, apparatus A further comprises one or more thermowells located on the second reactor. 
     In a twentieth aspect of apparatus A which can be used in combination with any of the first to the nineteenth aspects of apparatus A, the second reactor further comprises an eductor or a standpipe coupled to the lower conduit or to a transition conduit that is fluidly connected to the end of the lower conduit. 
     In a twenty-first aspect of apparatus A which can be used in combination with any of the first to the twentieth aspects of apparatus A, the second reactor further comprises a gas density meter configured to measure a density of a reaction mixture in the riser. 
     In a twenty-second aspect of apparatus A which can be used in combination with any of the first to the twenty-first aspects of apparatus A, the first polyolefin is a lower molecular weight polyethylene, the third polyolefin is a higher molecular weight polyethylene. 
     In a twenty-third aspect of apparatus A which can be used in combination with the twenty-second aspect of apparatus A, the second polyolefin has an average molecular weight greater (M w , M n , or M z ) than an average molecular weight (M w , M n , or M z ) of the first polyolefin and less than an average molecular weight of the third polyolefin. 
     In a twenty-fourth aspect of apparatus A which can be used in combination with any of the first to the twenty-third aspects of apparatus A, from about 20 to about 80 wt.% of the multimodal polyolefin comprises the first polyolefin and fro about 8 to about 20 wt.% of the multimodal polyolefin comprises the second polyolefin and the third polyolefin. 
     In a twenty-fifth aspect of apparatus A which can be used in combination with any of the first to the twenty-fourth aspects of apparatus A, the multimodal polyolefin has a density in a range of from about 0.930 to about 0.970 g/ml when tested in accordance with ASTM D1505, a melt index in a range of from about 0.1 to about 30 g/10 min when tested in accordance with ASTM D1238 under a force of 2.16 kg and a temperature of 190° C., a comonomer content in a range of from 0 to about 6 wt.%, and a M w  in a range of from about 250 to about 1,500 kg/mol. 
     In a twenty-sixth aspect of apparatus A which can be used in combination with the twenty-fifth aspect of apparatus A, the multimodal polyolefin has a high load melt index of from about 1 to about 45 g/10 min when tested in accordance with ASTM D1238 under a force of 21.6 kg and a temperature of 190° C., a M z  in a range of from about 500 to about 5,000 kg/mol, a Mw/Mn in a range of from about 18 to about 52, a long chain branching index in a range of from 0 to about 0.96, and a shear induced crystallization (SIC) index in a range of from about 0.15 to about 8. 
     In a twenty-seventh aspect of apparatus A which can be used in combination with any of the first to the twenty-sixth aspects of apparatus A, wherein the first reactor is a loop slurry reactor, a fluidized bed reactor, an autoclave reactor, a tubular reactor, a horizontal gas phase reactor, a continuous stirred-tank reactor, or a solution reactor. 
     A first aspect of apparatus B which is an apparatus for producing a multimodal polyolefin, comprising a first reactor configured to produce a first polyolefin, a second reactor configured to produce a second polyolefin and a third polyolefin, where the second reactor comprises a riser configured to produce the second polyolefin, an upper conduit having an end fluidly connected to a top portion of the riser, a separator fluidly connected to an opposite end of the upper conduit, a downcomer configured to produce the third polyolefin, wherein a top portion of the downcomer is fluidly connected to the separator, optionally via a liquid barrier in the top portion of the downcomer, and a lower conduit having an end fluidly connected to a bottom portion of the downcomer and an opposite end fluidly connected to a bottom portion of the riser, wherein the second reactor is configured to receive the first polyolefin from the first reactor, or, the first reactor is configured to receive the second polyolefin and the third polyolefin from the second reactor. 
     In a second aspect of apparatus B which can be used in combination with the first aspect of apparatus B, apparatus B further comprises a first product discharge conduit fluidly connected to the first reactor, and a second product discharge conduit fluidly connected to the bottom portion of the downcomer. 
     In a third aspect of apparatus B which can be used in combination with any of the first to the second aspects of apparatus B, the first product discharge conduit or the second product discharge conduit is fluidly connected to a take-off valve, wherein the take-off valve is configured as a continuous take-off valve or a discontinuous take-off valve. 
     In a fourth aspect of apparatus B which can be used in combination with any of the first to the third aspects of apparatus B, the second product discharge conduit is connected to the downcomer such that an angle of the second product discharge conduit with respect to horizontal is 0° to 45°. 
     In a fifth aspect of apparatus B which can be used in combination with any of the first to the fourth aspects of apparatus B, apparatus B further comprises a heater coupled to the second product discharge conduit and configured to receive a product mixture and to add heat to the product mixture. 
     In a sixth aspect of apparatus B which can be used in combination with the fifth aspect of apparatus B, apparatus B further comprises a catalyst or cocatalyst poison or deactivator added to the product mixture in or upstream of the heater. 
     In a seventh aspect of apparatus B which can be used in combination with any of the first to the sixth aspects of apparatus B, the heater is further configured to discharge the multimodal polyolefin in the product mixture at a temperature i) of about 54.4° C. (130° F.) to about 104.4° C. (220° F.), or ii) below a melting point of the multimodal polyolefin. 
     In an eighth aspect of apparatus B which can be used in combination with any of the first to the seventh aspects of apparatus B, apparatus B further comprises a separation vessel fluidly connected to an opposite end of the heater, wherein the separation vessel is configured to separate the product mixture into a plurality of streams, each of the plurality of streams comprising a vapor, a polymer product, or both the vapor and the polymer product. 
     In a ninth aspect of apparatus B which can be used in combination with the eighth aspect of apparatus B, apparatus B further comprises a monomer recovery system configured to recover one or more of an olefin monomer, an olefin comonomer, and a diluent from at least one of the plurality of streams comprising the vapor and configured to recycle one or more of the olefin monomer, the olefin comonomer, and the diluent to the first reactor, the second reactor, or both the first reactor and the second reactor. 
     In a tenth aspect of apparatus B which can be used in combination with any of the first to the ninth aspects of apparatus B, apparatus B further comprises a degassing vessel configured to receive the polymer product from the separation vessel and to remove at least a portion of a hydrocarbon entrained within the polymer product. 
     In an eleventh aspect of apparatus B which can be used in combination with any of the first to the tenth aspects of apparatus B, the separator comprises a cyclone separator. 
     In a twelfth aspect of apparatus B which can be used in combination with the eleventh aspect of apparatus B, the riser is configured to produce a riser product mixture comprising solid particles and a gas mixture, wherein the cyclone separator is configured to receive the riser product mixture via the upper conduit, wherein the cyclone separator is a high efficiency cyclone separator configured to separate 99 wt.% or more of the solid particles which have a size of from about 2 µm to about 10 µm from the gas mixture. 
     In a thirteenth aspect of apparatus B which can be used in combination with any of the first to the twelfth aspects of apparatus B, the cyclone separator is configured to have a cone angle with respect to horizontal of about 45° to about 80°. 
     In a fourteenth aspect of apparatus B which can be used in combination with any of the first to the thirteenth aspects of apparatus B, the cyclone separator is configured to have an entrance angle of 0° to about 15° with respect to a tangent of the cyclone separator. 
     In a fifteenth aspect of apparatus B which can be used in combination with any of the first to the fourteenth aspects of apparatus B, the cyclone separator is configured to have a tangential entrance velocity of from about 15.24 m/s to about 30.48 m/s. 
     In a sixteenth aspect of apparatus B which can be used in combination with any of the first to the fifteenth aspects of apparatus B, an angle with respect to horizontal of the opposite end of the upper conduit which fluidly connects to the cyclone separator is about 0° to about 15°. 
     In a seventeenth aspect of apparatus B which can be used in combination with any of the first to the sixteenth aspects of apparatus B, a vertical distance between the opposite end of the upper conduit and a top of the cyclone separator is from about 0 m (0 ft) to about 6.10 m (20 ft). 
     In an eighteenth aspect of apparatus B which can be used in combination with any of the first to the seventeenth aspects of apparatus B, apparatus B further comprises a reactor deactivation system in the second reactor, wherein the reactor deactivation system is configured to moderate or kill polymerization reactions in the riser, the downcomer, or both the riser and the downcomer. 
     In a nineteenth aspect of apparatus B which can be used in combination with any of the first to the eighteenth aspects of apparatus B, the separator comprises a flash tank or a flash chamber. 
     In a twentieth aspect of apparatus B which can be used in combination with any of the first to the nineteenth aspects of apparatus B, the first polyolefin is a lower molecular weight polyethylene, the third polyolefin is a higher molecular weight polyethylene. 
     In a twenty-first aspect of apparatus B which can be used in combination with the twentieth aspect of apparatus B, the second polyolefin has an average molecular weight (M w , M n , or M z ) greater than an average molecular weight (M w , M n , or M z ) of the first polyolefin and less than an average molecular weight of the third polyolefin. 
     In a twenty-second aspect of apparatus B which can be used in combination with any of the first to the twenty-first aspects of apparatus B, the first reactor is a loop slurry reactor, a fluidized bed reactor, an autoclave reactor, a tubular reactor, a horizontal gas phase reactor, a continuous stirred-tank reactor, or a solution reactor. 
     In a twenty-third aspect of apparatus B which can be used in combination with any of the first to the twenty-second aspects of apparatus B, from about 20 to about 80 wt.% of the multimodal polyolefin comprises the first polyolefin and from about 80 to about 20 wt.% of the multimodal polyolefin comprises the second polyolefin and the third polyolefin. 
     In a twenty-fourth aspect of apparatus B which can be used in combination with any of the first to the twenty-third aspects of apparatus B, the multimodal polyolefin has a density in a range of from about 0.930 to about 0.970 g/ml, a melt index in a range of from about 0.1 to about 30 g/10 min when tested in accordance with ASTM D1238 under a force of 2.16 kg and a temperature of 190° C., a comonomer content in a range of from 0 to about 6 wt.%, and a M w  in a range of from about 250 to about 1,500 kg/mol. 
     In a twenty-fifth aspect of apparatus B which can be used in combination with the twenty-fourth aspect of apparatus B, the multimodal polyolefin has a high load melt index of from about 1 to about 45 g/10 min when tested in accordance with ASTM D1238 under a force of 21.6 kg and a temperature of 190° C., a M z  in a range of from about 500 to about 5,000 kg/mol, a Mw/Mn in a range of about 18 to about 52, a long chain branching index in a range of from about 0 to about 0.96, and a shear induced crystallization (SIC) index in a range of from about 0.15 to about 8. 
     A first aspect of apparatus C which is an apparatus for producing a multimodal polyolefin, comprising a first reactor configured to produce a first polyolefin, a second reactor configured to produce a second polyolefin and a third polyolefin, where the second reactor comprises a riser configured to produce the second polyolefin, an upper conduit having an end fluidly connected to a top portion of the riser, a separator fluidly connected to an opposite end of the upper conduit and configured to separate a polyolefin product from a first reaction mixture received from the upper conduit, a downcomer configured to produce the third polyolefin, wherein a top portion of the downcomer is fluidly connected to the separator, optionally via a liquid barrier in the top portion of the downcomer, and a lower conduit having an end fluidly connected to a bottom portion of the downcomer and an opposite end fluidly connected to a bottom portion of the riser, wherein the lower conduit is configured to pass a second reaction mixture from the downcomer to the riser, wherein the second reactor is configured to receive the first polyolefin from the first reactor, or, the first reactor is configured to receive the second polyolefin and the third polyolefin from the second reactor. 
     In a second aspect of apparatus C which can be used in combination with the first aspect of apparatus C, a gas composition of the second reaction mixture is different than a gas composition of the third reaction mixture. 
     In a third aspect of apparatus C which can be used in combination with any of the first to the second aspects of apparatus C, the gas composition of the second reaction mixture comprises at least two selected from monomer, diluent, and a catalyst. 
     In a fourth aspect of apparatus C which can be used in combination with the third aspect of apparatus C, the gas composition of the third reaction mixture comprises at least two selected from hydrogen, monomer, comonomer, diluent, and a catalyst. 
     In a fifth aspect of apparatus C which can be used in combination with any of the first to the fourth aspects of apparatus C, the liquid barrier comprises an inert liquid, wherein a concentration of the inert liquid in the liquid barrier is greater than a concentration of the inert liquid in the downcomer and in the riser. 
     In a sixth aspect of apparatus C which can be used in combination with any of the first to the fifth aspects of apparatus C, the second reactor further comprises one or more comonomer feed lines configured to inject comonomer into the downcomer, wherein the third polyolefin is a copolymer. 
     In a seventh aspect of apparatus C which can be used in combination with any of the first to the sixth aspects of apparatus C, apparatus C further comprises one or more anti-static agent feed lines configured to inject an anti-static agent into the second reactor. 
     In an eighth aspect of apparatus C which can be used in combination with the seventh aspect of apparatus C, the one or more anti-static agent lines are configured to inject a mixture comprising the anti-static agent and a carrier fluid, wherein a concentration of the anti-static agent in each of the one or more anti-static agent feed lines is about 1 ppm to about 50 ppm based on weight of the carrier fluid in each of the one or more anti-static agent feed lines. 
     In a ninth aspect of apparatus C which can be used in combination with any of the first to the eighth aspects of apparatus C, where a concentration of the anti-static agent in the second reactor is about 1 ppm to about 50 ppm based on weight of the carrier fluid in the second reactor. 
     In a tenth aspect of apparatus C which can be used in combination with any of the first to the ninth aspects of apparatus C, the upper conduit is configured to pass the first reaction mixture from the riser to the separator at a velocity that is i) greater than a saltation velocity of the first reaction mixture and up to about 30.48 m/s (100 ft/sec), or ii) greater than 110% of the saltation velocity of the first reaction mixture. 
     In an eleventh aspect of apparatus C which can be used in combination with any of the first to the tenth aspects of apparatus C, the lower conduit is further configured to pass the second reaction mixture from the downcomer to the riser at a velocity that is i) greater than a saltation velocity of the second reaction mixture and up to about 30.48 m/s (100 ft/sec), or ii) greater than 110% of the saltation velocity of the second reaction mixture. 
     In a twelfth aspect of apparatus C which can be used in combination with any of the first to the eleventh aspects of apparatus C, apparatus C further comprises a sample analyzer configured to: i) analyze a sample of the first reaction mixture or the second reaction mixture at one or more locations in the second reactor, ii) determine a concentration of gas, liquid, or solid in the first reaction mixture or the second reaction mixture, and iii) determine a concentration of monomer, comonomer, diluent, hydrogen, inert component, or polymer in the first reaction mixture or the second reaction mixture. 
     In a thirteenth aspect of apparatus C which can be used in combination with any of the first to the twelfth aspects of apparatus C, the separator comprises a level controller coupled to the separator and configured to control a level of the polyolefin product in the separator such that the polyolefin product has a residence time of about 1 minute to about 30 minutes in the separator. 
     In a fourteenth aspect of apparatus C which can be used in combination with any of the first to the thirteenth aspects of apparatus C, from about 20 to about 80 wt.% of the multimodal polyolefin comprises the first polyolefin and from about 80 to about 20 wt.% of the multimodal polyolefin comprises the second polyolefin and the third polyolefin. 
     In a fifteenth aspect of apparatus C which can be used in combination with any of the first to the fourteenth aspects of apparatus C, the multimodal polyolefin has a density in a range of from about 0.930 to about 0.970 g/ml when tested in accordance with ASTM D1505, a melt index in a range of from about 0.1 to about 30 g/10 min when tested in accordance with ASTM D1238 under a force of 2.16 kg and a temperature of 190° C., a comonomer content in a range of from 0 to about 6 wt.%, and a M w  in a range of from about 250 to about 1,500 kg/mol. 
     In a sixteenth aspect of apparatus C which can be used in combination with the fifteenth aspect of apparatus C, the multimodal polyolefin has a high load melt index of from about 1 to about 45 g/10 min when tested in accordance with ASTM D1238 under a force of 21.6 kg and a temperature of 190° C., a M z  in a range of from about 500 to about 5,000 kg/mol, a Mw/Mn in a range of from about 18 to about 52, a long chain branching index in a range of from about 0 to about 0.96, and a shear induced crystallization (SIC) index in a range of from about 0.15 to about 8. 
     In a seventeenth aspect of apparatus C which can be used in combination with any of the first to the sixteenth aspects of apparatus C, the first reactor is a loop slurry reactor, a fluidized bed reactor, an autoclave reactor, a tubular reactor, a horizontal gas phase reactor, a continuous stirred-tank reactor, or a solution reactor. 
     A first aspect of apparatus D which is an apparatus for producing a multimodal polyolefin, comprising a first reactor configured to produce a first polyolefin, a second reactor configured to produce a second polyolefin and a third polyolefin, where the second reactor comprises a riser configured to produce the second polyolefin, an upper conduit having an end fluidly connected to a top portion of the riser, a separator fluidly connected to an opposite end of the upper conduit, a downcomer configured to produce the third polyolefin, wherein a top portion of the downcomer is fluidly connected to the separator, optionally via a liquid barrier in the top portion of the downcomer, and a lower conduit having an end fluidly connected to a bottom portion of the downcomer and an opposite end fluidly connected to a bottom portion of the riser, wherein the second reactor is configured to receive the first polyolefin from the first reactor, or, the first reactor is configured to receive the second polyolefin and the third polyolefin from the second reactor. 
     In a second aspect of apparatus D which can be used in combination with the first aspect of apparatus D, the second reactor is configured to receive the first polyolefin from the first reactor, wherein the first reactor comprises a fluidized bed reactor, a gas distributor located inside the fluidized bed reactor in a bottom portion thereof, and a settling leg placed at least partially within the bottom portion of the fluidized bed reactor, wherein an end of the settling leg opens to the gas distributor and an opposite end extends outside the fluidized bed reactor. 
     In a third aspect of apparatus D which can be used in combination with any of the first to the second aspects of apparatus D, wherein the settling leg has an inner diameter of from about 10.16 cm (4 inches) to about 30.48 cm (12 inches). 
     In a fourth aspect of apparatus D which can be used in combination with any of the first to the third aspects of apparatus D, apparatus D further comprises a separation vessel coupled to the settling leg and configured to separate the first polyolefin from a gas mixture, and a treater configured to treat the gas mixture, wherein the treater comprises a flare stack or ground flare, a pressure swing absorber, a membrane, or a combination thereof. 
     In a fifth aspect of apparatus D which can be used in combination with any of the first to the fourth aspects of apparatus D, apparatus D further comprises a product discharge conduit fluidly connected to the settling leg, and a sampling system fluidly connected to the product discharge conduit and configured to analyze a sample of the first polyolefin. 
     In a sixth aspect of apparatus D which can be used in combination with any of the first to the fifth aspects of apparatus D, the second reactor is configured to receive the first polyolefin from the first reactor, wherein the first reactor comprises a fluidized bed reactor, a product discharge conduit fluidly connected to the fluidized bed reactor, a lock hopper coupled to the product discharge conduit, a first cycling valve coupled to the product discharge conduit and to the lock hopper, and a second cycling valve coupled to an outlet of the lock hopper. 
     In a seventh aspect of apparatus D which can be used in combination with the sixth aspect of apparatus D, apparatus D further comprises a separation vessel coupled to the second cycling valve and configured to separate the first polyolefin from a gas mixture, and a treater configured to treat the gas mixture, wherein the treater comprises a flare stack or ground flare, a pressure swing absorber, a membrane, or a combination thereof. 
     In an eighth aspect of apparatus D which can be used in combination with any of the first to the seventh aspects of apparatus D, apparatus D further comprises a sampling system fluidly connected to the product discharge conduit and configured to analyze a sample of the first polyolefin. 
     In a ninth aspect of apparatus D which can be used in combination with any of the first to the eighth aspects of apparatus D, the second reactor is configured to receive the first polyolefin from the first reactor, wherein the first reactor comprises a fluidized bed reactor, a product discharge conduit fluidly connected to the fluidized bed reactor, and a continuous take-off valve fluidly connected to the product discharge conduit. 
     In a tenth aspect of apparatus D which can be used in combination with the ninth aspect of apparatus D, apparatus D further comprises a separation vessel coupled to the continuous take-off valve and configured to separate the first polyolefin from a gas mixture, and a treater configured to treat the gas mixture, wherein the treater comprises a flare stack or ground flare, a pressure swing absorber, a membrane, or a combination thereof. 
     In an eleventh aspect of apparatus D which can be used in combination with any of the first to the tenth aspects of apparatus D, apparatus D further comprises a sampling system fluidly connected to the product discharge conduit and configured to analyze a sample of the first polyolefin. 
     In a twelfth aspect of apparatus D which can be used in combination with any of the first to the eleventh aspects of apparatus D, the first reactor is configured to receive the second polyolefin and the third polyolefin from the second reactor, wherein the first reactor comprises a fluidized bed reactor, a gas distributor located inside the fluidized bed reactor in a bottom portion thereof, and a settling leg placed at least partially within the bottom portion of the fluidized bed reactor, wherein an end of the settling leg opens to the gas distributor and an opposite end extends outside the fluidized bed reactor. 
     In a thirteenth aspect of apparatus D which can be used in combination with the twelfth aspect of apparatus D, the settling leg has an inner diameter of from about 10.16 cm (4 inches) to about 30.48 cm (12 inches). 
     In a fourteenth aspect of apparatus D which can be used in combination with any of the first to the thirteenth aspects of apparatus D, apparatus D further comprises a separation vessel coupled to the settling leg and configured to separate the multimodal polyolefin from a gas mixture, and a treater configured to treat the gas mixture, wherein the treater comprises a flare stack or ground flare, a pressure swing absorber, a membrane, or a combination thereof. 
     In a fifteen aspect of apparatus D which can be used in combination with any of the first to the fourteenth aspects of apparatus D, apparatus D further comprises a product discharge conduit fluidly connected to the settling leg, and a sampling system fluidly connected to the product discharge conduit and configured to analyze a sample of the multimodal polyolefin. 
     In a sixteenth aspect of apparatus D which can be used in combination with any of the first to the fifteenth aspects of apparatus D, the first reactor is configured to receive the second polyolefin and the third polyolefin from the second reactor, wherein the first reactor comprises a fluidized bed reactor, a product discharge conduit fluidly connected to the fluidized bed reactor, a lock hopper coupled to the product discharge conduit, a first cycling valve coupled to the product discharge conduit and to an inlet of the lock hopper, and a second cycling valve coupled to an outlet of the lock hopper. 
     In a seventeenth aspect of apparatus D which can be used in combination with the sixteenth aspect of apparatus D, apparatus D further comprises a separation vessel coupled to the second cycling valve and configured to separate the multimodal polyolefin from a gas mixture, and a treater configured to treat the gas mixture, wherein the treater comprises a flare stack or ground flare, a pressure swing absorber, a membrane, or a combination thereof. 
     In an eighteenth aspect of apparatus D which can be used in combination with any of the first to the seventeenth aspects of apparatus D, apparatus D further comprises a sampling system fluidly connected to the product discharge conduit and configured to analyze a sample of the multimodal polyolefin. 
     In a nineteenth aspect of apparatus D which can be used in combination with any of the first to the eighteenth aspects of apparatus D, the first reactor is configured to receive the second polyolefin and the third polyolefin from the second reactor, wherein the first reactor comprises a fluidized bed reactor, a product discharge conduit fluidly connected to the fluidized bed reactor, and a continuous take-off valve fluidly connected to the product discharge conduit. 
     In a twentieth aspect of apparatus D which can be used in combination with the nineteenth aspect of apparatus D, apparatus D further comprises a separation vessel coupled to the continuous take-off valve and configured to separate the multimodal polyolefin from a gas mixture, and a treater configured to treat the gas mixture, wherein the treater comprises a flare stack or ground flare, a pressure swing absorber, a membrane, or a combination thereof. 
     In a twenty-first aspect of apparatus D which can be used in combination with any of the first to the twentieth aspects of apparatus D, apparatus D further comprises a sampling system fluidly connected to the product discharge conduit and configured to analyze a sample of the multimodal polyolefin. 
     In a twenty-second aspect of apparatus D which can be used in combination with any of the first to the twenty-first aspects of apparatus D, the first polyolefin is a lower molecular weight polyethylene, the third polyolefin is a higher molecular weight polyethylene. 
     In a twenty-third aspect of apparatus D which can be used in combination with the twenty-second aspect of apparatus D, the second polyolefin has an average molecular weight (M w , M n , or M z ) greater than an average molecular weight (M w , M n , or M z ) of the first polyolefin and less than an average molecular weight of the third polyolefin. 
     In a twenty-fourth aspect of apparatus D which can be used in combination with any of the first to the twenty-third aspects of apparatus D, wherein from about 20 to about 80 wt.% of the multimodal polyolefin comprises the first polyolefin and from about 80 to about 20 wt.% of the multimodal polyolefin comprises the second polyolefin and the third polyolefin. 
     In a twenty-fifth aspect of apparatus D which can be used in combination with any of the first to the twenty-fourth aspects of apparatus D, the multimodal polyolefin has a density in a range of from about 0.930 to about 0.970 g/ml when tested in accordance with ASTM D1505, a melt index in a range of from about 0.1 to about 30 g/10 min when tested in accordance with ASTM D1238 under a force of 2.16 kg and a temperature of 190° C., a comonomer content in a range of from 0 to about 6 wt.%, and a M w  in a range of from about 250 to about 1,500 kg/mol. 
     In a twenty-sixth aspect of apparatus D which can be used in combination with the twenty-fifth aspect of apparatus D, the multimodal polyolefin has a high load melt index of from about 1 to about 45 g/10 min when tested in accordance with ASTM D1238 under a force of 21.6 kg and a temperature of 190° C., a M z  in a range of from about 500 to about 5,000 kg/mol, a Mw/Mn in a range of from about 18 to about 52, a long chain branching index in a range of from 0 to about 0.96, and a shear induced crystallization (SIC) index in a range of from about 0.15 to about 8. 
     In a twenty-seventh aspect of apparatus D which can be used in combination with any of the first to the twenty-sixth aspects of apparatus D, the first reactor is a loop slurry reactor, a fluidized bed reactor, an autoclave reactor, a tubular reactor, a horizontal gas phase reactor, a continuous stirred-tank reactor, or a solution reactor. 
     In a first aspect, polyethylene resin A can comprise the first polyolefin made in polymerization zone  112  of the first reactor  100 , the second polyolefin made in the polymerization zone  321  of the riser  320  of the MZCR  300 , and the third polyolefin made in the polymerization zone  341  of the downcomer  340  of the MZCR  300 . 
     In a second aspect that can be in combination with the first aspect, the first polyolefin in polyethylene resin A can be a low molecular weight (LMW) component of the multimodal polyolefin, the second polyolefin in polyethylene resin A can be an intermediate molecular weight (IMW) component of the multimodal polyolefin, and the third polyolefin in polyethylene resin A can be a high molecular weight component (HMW) of the multimodal polyolefin. 
     In a third aspect that can be in combination with the first and second aspects, the first polyolefin (e.g., the LMW component) in polyethylene resin A that is produced in the polymerization zone  112  of the first reactor  100  can be a lower molecular weight polyethylene, the second polyolefin (e.g., the IMW component) in polyethylene resin A that is produced in the polymerization zone  321  of the riser  320 , the third polyolefin (e.g., the HMW component) in polyethylene resin A that is produced in the polymerization zone  341  of the downcomer  340  can be a higher molecular weight polyethylene, or combinations thereof. 
     In a fourth aspect that can be in combination with any of the first to third aspects, an amount of from about 20 to about 80 wt.% of polyethylene resin A can comprise the first polyolefin and an amount of from about 80 to about 20 wt.% of polyethylene resin A can comprise the second polyolefin and the third polyolefin. 
     In a fifth aspect that can be in combination with any of the first to fourth aspects, an amount of from about 20 to about 80 wt.% of polyethylene resin A can comprise the LMW components and an amount of from about 80 to about 20 wt.% of polyethylene resin A can comprise the IMW component and the HMW component. 
     In a sixth aspect that can be in combination with any of the first to fifth aspects, the LMW component can be present in polyethylene resin A in an amount of from about 20 wt.% to about 75 wt.%, the IMW component can be present in polyethylene resin A in an amount of from about 5 wt.% to about 40 wt.%, and the HMW component can be present in polyethylene resin A in an amount of from about 10 wt.% to about 60 wt.%. 
     In a seventh aspect that can be in combination with any of the first to sixth aspects, polyethylene resin A can have a density in a range of about 0.930 to about 0.970 g/ml, when tested in accordance with ISO  1183  at 23° C. 
     In an eighth aspect that can be in combination with any of the first to seventh aspects, polyethylene resin A can have a melt index (MI 2 ) in a range of from about 0.1 to about 30 g/10 min, when tested in accordance with ISO  1133  at 190° C. under a force of 2.16 kg. 
     In a ninth aspect that can be in combination with any of the first to eighth aspects, polyethylene resin A can have a high load melt index (HLMI) of from about 1 to about 45 g/10 min, when tested in accordance with ISO  1133  at 190° C. under a force of 21.6 kg. 
     In a tenth aspect that can be in combination with any of the first to ninth aspects, polyethylene resin A can have a comonomer content in a range of from about 0 to about 6 wt.%. 
     In an eleventh aspect that can be in combination with any of the first to tenth aspects, polyethylene resin A can have a weight average molecular weight (M w ) in a range of from about 250 to about 1,500 kg/mol. 
     In a twelfth aspect that can be in combination with any of the first to eleventh aspects, polyethylene resin A can have a z-average molecular weight (M z ) in a range of from about 500 to about 5,000 kg/mol. 
     In a thirteenth aspect that can be in combination with any of the first to twelfth aspects, polyethylene resin A can have a polydispersity index (dispersity or PDI or M w /M n ) in a range of from about 18 to about 52. 
     In a fourteenth aspect that can be in combination with any of the first to thirteenth aspects, polyethylene resin A can have a long chain branching index in a range of from about 0 to about 0.96. 
     In a fifteenth aspect that can be in combination with any of the first to fourteenth aspects, polyethylene resin A can have a shear induced crystallization (SIC) index in a range of from about 0.15 to about 8. 
     In a sixteenth aspect that can be in combination with any of the first to fifteenth aspects, the second polyolefin (e.g., the IMW component) in polyethylene resin A that is produced in polymerization zone  321  of the riser  320  can have an average molecular weight (M w , M n , or M z ) greater than an average molecular weight (M w , M n , or M z ) of the first polyolefin (e.g., the LMW component) in polyethylene resin A that is produced in the polymerization zone  112  of the first reactor  100  and less than an average molecular weight (M w , M n , or M z ) of the third polyolefin (e.g., the HMW component) in polyethylene resin A that is produced in the polymerization zone  341  of the downcomer  340 . 
     In a seventeenth aspect that can be in combination with any of the first to sixteenth aspects, polyethylene resin A can have an environmental stress cracking resistance (ESCR) of equal to or greater than about 800 hours; alternatively, greater than about 900 hours; alternatively, greater than about 1,000 hours, when tested in accordance with ISO 16770. 
     In an eighteenth aspect that can be in combination with any of the first to seventeenth aspects, polyethylene resin A can have a value for rapid crack propagation (RCP) that is at least 100%; alternatively, at least 110%; alternatively, at least 120%; alternatively, at least 130%; alternatively, at least 140 % of the value for RCP of a bimodal polyethylene. 
     In a nineteenth aspect that can be in combination with any of the first to eighteenth aspects, polyethylene resin A can have a value for rapid crack propagation (RCP) that is at least 100%; alternatively, at least 110%; alternatively, at least 120%; alternatively, at least 130%; alternatively, at least 140 % of the value for RCP of a bimodal polyethylene. 
     In a twentieth aspect that can be in combination with any of the first to nineteenth aspects, polyethylene resin A can have a resistance to slow crack growth of at least 100%; alternatively, at least 110%; alternatively, at least 120%; alternatively, at least 130%; alternatively, at least 140 % of the value for resistance to slow crack growth of a bimodal polyethylene, when tested in accordance with ASTM F1473, with the caveat that the resistance to slow crack growth is defined as the polyethylene notch tensile test (PENT) failure time. 
     In a twenty-first aspect that can be in combination with any of the first to twentieth aspects, polyethylene resin A can have a tensile impact strength of from about 135 to about 165 kJ/m 2 . 
     In a twenty-second aspect that can be in combination with any of the first to twenty-first aspects, polyethylene resin A can be made by any embodiment of the process having any combination of the aspects described herein. 
     In a twenty-third aspect that can be in combination with any of the first to twenty-second aspects, polyethylene resin A can have a gel count of less than about 950 gels/m 2 ; alternatively, polyethylene resin A can have a gel count of less than about 900 gels/m 2 ; alternatively, less than about 850 gels/m 2 ; alternatively, less than about 800 gels/m 2 ; alternatively, less than about 750 gels/m 2 ; alternatively, a gel count of less than about 700 gels/m 2 ; alternatively, less than about 650 gels/m 2 ; alternatively, less than about 600 gels/m 2 . 
     In a first aspect, polyethylene resin B can comprise the first polyolefin made in polymerization zone  112  of the first reactor  100 , the second polyolefin made in the polymerization zone  321  of the riser  320  of the MZCR  300 , and the third polyolefin made in the polymerization zone  341  of the downcomer  340  of the MZCR  300 . 
     In a second aspect that can be in combination with the first aspect, the first polyolefin in polyethylene resin B can be a low molecular weight (LMW) component of the multimodal polyolefin, the second polyolefin in polyethylene resin B can be an intermediate molecular weight (IMW) component of the multimodal polyolefin, and the third polyolefin in polyethylene resin B can be a high molecular weight component (HMW) of the multimodal polyolefin. 
     In a third aspect that can be in combination with any of the first and the second aspects, the first polyolefin (e.g., the LMW component) in polyethylene resin B that is produced in the polymerization zone  112  of the first reactor  100  can be a lower molecular weight polyethylene, the second polyolefin (e.g., the IMW component) in polyethylene resin B that is produced in the polymerization zone  321  of the riser  320 , the third polyolefin (e.g., the HMW component) in polyethylene resin B that is produced in the polymerization zone  341  of the downcomer  340  can be a higher molecular weight polyethylene, or combinations thereof. 
     In a fourth aspect that can be in combination with any of the first to the third aspects, the LMW component is present in polyethylene resin B in an amount of from about 20 wt.% to about 75 wt.%. 
     In a fifth aspect that can be in combination with any of the first to the fourth aspects, the IMW component is present in polyethylene resin B in an amount of from about 5 wt.% to about 40 wt.%. 
     In a sixth aspect that can be in combination with any of the first to the fifth aspects, the HMW component is present in polyethylene resin B in an amount of from about 10 wt.% to about 60 wt.%. 
     In a seventh aspect that can be in combination with any of the first to the sixth aspects, the LMW component in polyethylene resin B has a weight average molecular weight of from about 20 kg/mol to about 150 kg/mol. 
     In an eighth aspect that can be in combination with any of the first to the seventh aspects, the IMW component in polyethylene resin B has a weight average molecular weight of from about 85 kg/mol to about 350 kg/mol. 
     In a ninth aspect that can be in combination with any of the first to the eighth aspects, the HMW component in polyethylene resin B has weight average molecular weight of greater than about 350 kg/mol. 
     In a tenth aspect that can be in combination with any of the first to the ninth aspects, the weight average molecular weight of the IMW component in polyethylene resin B is greater than the weight average molecular weight of the LMW component. 
     In an eleventh aspect that can be in combination with any of the first to the tenth aspects, the LMW component in polyethylene resin B has a short chain branching content of from about 0 to about 5 short chain branches per 1,000 carbon atoms. 
     In a twelfth aspect that can be in combination with any of the first to the eleventh aspects, the IMW component in polyethylene resin B has a short chain branching content of from about 0.1 to about 10 short chain branches per 1,000 carbon atoms. 
     In a thirteenth aspect that can be in combination with any of the first to the twelfth aspects, the HMW component in polyethylene resin B has a short chain branching content of from about 1 to about 15 short chain branches per 1,000 carbon atoms. 
     In a fourteenth aspect that can be in combination with any of the first to the thirteenth aspects, the polyethylene resin B has a magnitude of slip-stick of from about 300 psi to about 1,000 psi (about 2.07 MPa to about 6.89 MPa). 
     In a fifteenth aspect that can be in combination with any of the first to the fourteenth aspects, the polyethylene resin B is a trimodal polyethylene resin. 
     In a sixteenth aspect that can be in combination with any of the first to the fifteen aspects, polyethylene resin B can have a long chain branching content of less than about 0.01 long chain branches per 1,000 carbon atoms. 
     In a seventeenth aspect that can be in combination with any of the first to the sixteenth aspects, polyethylene B comprises a comonomer, the polyethylene resin B has a comonomer content of from greater than about 0 wt.% to about 20 wt.%. 
     In an eighteenth aspect that can be in combination with any of the first to the seventeenth aspects, the comonomer in the polyethylene resin B comprises 1-butene, 1-hexene, 1-octene, or combinations thereof. 
     In a nineteenth aspect that can be in combination with any of the first to the eighteenth aspects, the polyethylene resin B can have a comonomer content of from greater than about 0 wt.% to about 6 wt.%. 
     In a twentieth aspect that can be in combination with any of the first to the nineteenth aspects, the polyethylene resin B can have a comonomer content of from about 2 wt.% to about 6 wt.%. 
     In a twenty-first aspect that can be in combination with any of the first to the twentieth aspects, the polyethylene resin B can have a comonomer content of from about 1 wt.% to about 5 wt.%. 
     In a twenty-second aspect that can be in combination with any of the first to the twenty-first aspects, the polyethylene resin B can have a comonomer content of from greater than about 6 wt.% to about 20 wt.%; alternatively, from greater than about 6 wt.% to about 15 wt.%; alternatively, from greater than about 6 wt.% to about 10 wt.%. 
     In a twenty-third aspect that can be in combination with any of the first to the twenty-second aspects, the polyethylene resin B can have a density of from about 0.900 g/cc to about 0.980 g/cc, when tested in accordance with ASTM D1505. 
     In a twenty-fourth aspect that can be in combination with any of the first to the twenty-third aspects, the polyethylene resin B can have a density of less than about 0.960 g/cc, when tested in accordance with ASTM D1505. 
     In a twenty-fifth aspect that can be in combination with any of the first to the twenty-fourth aspects, the polyethylene resin B can have a density of from greater than about 0.940 g/cc to about 0.960 g/cc, when tested in accordance with ASTM D1505. 
     In a twenty-sixth aspect that can be in combination with any of the first to the twenty-fifth aspects, the polyethylene resin B can have a density of from about 0.920 g/cc to about 0.940 g/cc, when tested in accordance with ASTM D1505. 
     In a twenty-seventh aspect that can be in combination with any of the first to the twenty-sixth aspects, the polyethylene resin B can have a melt index of less than about 1 g/10 min, when tested in accordance with ASTM D1238 under a force of 2.16 kg. 
     In a twenty-eighth aspect that can be in combination with any of the first to the twenty-seventh aspects, the polyethylene resin B can have a high load melt index of from about 1 g/10 min to less than about 20 g/10 min, when tested in accordance with ASTM D1238 under a force of 21.6 kg. 
     In a twenty-ninth aspect that can be in combination with any of the first to the twenty-eighth aspects, the polyethylene resin B can have a weight average molecular weight (M w ) of from about 150 kg/mol to about 1,000 kg/mol. 
     In a thirtieth aspect that can be in combination with any of the first to the twenty-ninth aspects, the polyethylene resin B can have a number average molecular weight (M n ) of from about 7.5 kg/mol to about 30 kg/mol. 
     In a thirty-first aspect that can be in combination with any of the first to the thirtieth aspects, the polyethylene resin B can have a z-average molecular weight (M z ) of from about 1,000 kg/mol to about 5,000 kg/mol; alternatively from about 1,000 kg/mol to about 3,500 kg/mol. 
     In a thirty-second aspect that can be in combination with any of the first to the thirty-first aspects, the polyethylene resin B can have a (z+1)-average molecular weight (M z+1 ) of from about 2,000 kg/mol to about 9,000 kg/mol. 
     In a thirty-third aspect that can be in combination with any of the first to the thirty-second aspects, the polyethylene resin B can have a polydispersity index (PDI) of from about 5 to about 60. 
     In a thirty-fourth aspect that can be in combination with any of the first to the thirty-third aspects, the polyethylene resin B can have a polydispersity index (PDI) of less than about 18. 
     In a thirty-fifth aspect that can be in combination with any of the first to the thirty-fourth aspects, the LMW component of the polyethylene resin B is a homopolymer. 
     In a thirty-sixth aspect that can be in combination with any of the first to the thirty-fifth aspects, the LMW component of the polyethylene resin B has a density of less than about 0.960 g/cc, when tested in accordance with ASTM D1505. 
     In a thirty-seventh aspect that can be in combination with any of the first to the thirty-sixth aspects, the LMW component of the polyethylene resin B has a density of from equal to or greater than about 0.960 g/cc to about 0.985 g/cc, when tested in accordance with ASTM D1505. 
     In a thirty-eighth aspect that can be in combination with any of the first to the thirty-seventh aspects, the LMW component of the polyethylene resin B has a melt index of from about 3 g/10 min to about 400 g/10 min, when tested in accordance with ASTM D1238 under a force of 2.16 kg; and wherein the LMW component has a high load melt index of from about 160 g/10 min to about 41,000 g/10 min, when tested in accordance with ASTM D1238 under a force of 21.6 kg. 
     In a thirty-ninth aspect that can be in combination with any of the first to the thirty-eighth aspects, the LMW component of the polyethylene resin B has a number average molecular weight (M n ) of from about 5 kg/mol to about 25 kg/mol; alternatively, from about 5 kg/mol to about 15 kg/mol. 
     In a fortieth aspect that can be in combination with any of the first to the thirty-ninth aspects, the LMW component of the polyethylene resin B has a z-average molecular weight (M z ) of from about 100 kg/mol to about 340 kg/mol. 
     In a forty-first aspect that can be in combination with any of the first to the fortieth aspects, the LMW component of the polyethylene resin B has a polydispersity index (PDI) of from about 1 to about 30; alternatively, from about 1 to about 15. 
     In a forty-second aspect that can be in combination with any of the first to the forty-first aspects, the LMW component of the polyethylene resin B has a short chain branching content of from about 0 to about 4 short chain branches per 1,000 carbon atoms. 
     In a forty-third aspect that can be in combination with any of the first to the forty-second aspects, the LMW component of the polyethylene resin B has a short chain branching content of from about 0 to about 3 short chain branches per 1,000 carbon atoms. 
     In a forty-fourth aspect that can be in combination with any of the first to the forty-third aspects, the LMW component of the polyethylene resin B has a short chain branching content of from about 0 to about 2 short chain branches per 1,000 carbon atoms. 
     In a forty-fifth aspect that can be in combination with any of the first to the forty-fourth aspects, the LMW component of the polyethylene resin B has a short chain branching content of from about 0 to about 1 short chain branches per 1,000 carbon atoms. 
     In a forty-sixth aspect that can be in combination with any of the first to the forty-fifth aspects, the IMW component of the polyethylene resin B is a copolymer. 
     In a forty-seventh aspect that can be in combination with any of the first to the forty-sixth aspects, the IMW component of the polyethylene resin B has a first comonomer content of from greater than about 0 wt.% to about 10 wt.%; alternatively, from greater than about 0 wt.% to about 4 wt.%. 
     In a forty-eighth aspect that can be in combination with any of the first to the forty-seventh aspects, the IMW component of the polyethylene resin B has a density of from equal to or greater than about 0.915 g/cc to about 0.970 g/cc, when tested in accordance with ASTM D1505. 
     In a forty-ninth aspect that can be in combination with any of the first to the forty-eighth aspects, the IMW component of the polyethylene resin B has a melt index of from about 0.1 g/10 min to about 30 g/10 min, when tested in accordance with ASTM D1238 under a force of 2.16 kg. 
     In a fiftieth aspect that can be in combination with any of the first to the forty-ninth aspects, the IMW component of the polyethylene resin B has a high load melt index of from about 5 g/10 min to about 1,500 g/10 min, when tested in accordance with ASTM D1238 under a force of 21.6 kg. 
     In a fifty-first aspect that can be in combination with any of the first to the fiftieth aspects, the IMW component of the polyethylene resin B has a number average molecular weight (M n ) of from about 10 kg/mol to about 185 kg/mol; alternatively, from about 10 kg/mol to about 100 kg/mol; alternatively, from about 10 kg/mol to about 35 kg/mol. 
     In a fifty-second aspect that can be in combination with any of the first to the fifty-first aspects, the IMW component of the polyethylene resin B has a z-average molecular weight (M z ) of from about 215 kg/mol to about 2,300 kg/mol. 
     In a fifty-third aspect that can be in combination with any of the first to the fifty-second aspects, the IMW component of the polyethylene resin B has a polydispersity index (PDI) of from about 2.5 to about 35; alternatively from about 2.5 to about 25. 
     In a fifty-fourth aspect that can be in combination with any of the first to the fifty-third aspects, the IMW component of the polyethylene resin B has a short chain branching content of from about 0.1 to about 8 short chain branches per 1,000 carbon atoms. 
     In a fifty-fifth aspect that can be in combination with any of the first to the fifty-fourth aspects, the IMW component of the polyethylene resin B has a short chain branching content of from about 0.2 to about 7 short chain branches per 1,000 carbon atoms. 
     In a fifty-sixth aspect that can be in combination with any of the first to the fifty-fifth aspects, the IMW component of the polyethylene resin B has a short chain branching content of from about 0.3 to about 6 short chain branches per 1,000 carbon atoms. 
     In a fifty-seventh aspect that can be in combination with any of the first to the fifty-sixth aspects, the IMW component of the polyethylene resin B has a short chain branching content of from about 0.4 to about 5 short chain branches per 1,000 carbon atoms. 
     In a fifty-eighth aspect that can be in combination with any of the first to the fifty-seventh aspects, the HMW component of the polyethylene resin B is a copolymer. 
     In a fifty-ninth aspect that can be in combination with any of the first to the fifty-eighth aspects, the HMW component of the polyethylene resin B has a second comonomer content of greater than about 0 wt.%to about 10 wt.%; alternatively from about 1 wt.% to about 10 wt.%. 
     In a sixtieth aspect that can be in combination with any of the first to the fifty-ninth aspects, the second comonomer content of the polyethylene resin B is greater than the first comonomer content. 
     In a sixty-first aspect that can be in combination with any of the first to the sixtieth aspects, the HMW component of the polyethylene resin B has a density of from equal to or greater than about 0.900 g/cc to about 0.960 g/cc; alternatively from equal to or greater than about 0.900 g/cc to about 0.940 g/cc; alternatively, from equal to or greater than about 0.900 g/cc to about 0.930 g/cc, when tested in accordance with ASTM D1505. 
     In a sixty-second aspect that can be in combination with any of the first to the sixty-first aspects, the HMW component of the polyethylene resin B has a melt index of less than about 0.1 g/10 min, when tested in accordance with ASTM D1238 under a force of 2.16 kg. 
     In a sixty-third aspect that can be in combination with any of the first to the sixty-second aspects, the HMW component of the polyethylene resin B has a high load melt index of from about 0.005 g/10 min to about 2 g/10 min, when tested in accordance with ASTM D1238 under a force of 21.6 kg. 
     In a sixty-fourth aspect that can be in combination with any of the first to the sixty-third aspects, the HMW component of the polyethylene resin B has weight average molecular weight of from greater than about 350 kg/mol to about 1,500 kg/mol. 
     In a sixty-fifth aspect that can be in combination with any of the first to the sixty-fourth aspects, the HMW component of the polyethylene resin B has a number average molecular weight (M n ) of from about 75 kg/mol to about 200 kg/mol. 
     In a sixty-sixth aspect that can be in combination with any of the first to the sixty-fifth aspects, the HMW component of the polyethylene resin B has a z-average molecular weight (M z ) of from about 1,700 kg/mol to about 4,600 kg/mol. 
     In a sixty-seventh aspect that can be in combination with any of the first to the sixty-sixth aspects, the HMW component of the polyethylene resin B has a polydispersity index (PDI) of from about 2 to about 20; alternatively, from about 2 to about 15. 
     In a sixty-eighth aspect that can be in combination with any of the first to the sixty-seventh aspects, the HMW component of the polyethylene resin B has a short chain branching content of from about 2 to about 13 short chain branches per 1,000 carbon atoms. 
     In a sixty-ninth aspect that can be in combination with any of the first to the sixty-eighth aspects, the HMW component of the polyethylene resin B has a short chain branching content of from about 3 to about 12 short chain branches per 1,000 carbon atoms. 
     In a seventieth aspect that can be in combination with any of the first to the sixty-ninth aspects, the HMW component of the polyethylene resin B has a short chain branching content of from about 4 to about 11 short chain branches per 1,000 carbon atoms. 
     In a seventy-first aspect that can be in combination with any of the first to the seventieth aspects, the HMW component of the polyethylene resin B has a short chain branching content of from about 5 to about 10 short chain branches per 1,000 carbon atoms. 
     In a seventy-second aspect that can be in combination with any of the first to the seventy-first aspects, the polyethylene resin B can have a Young’s modulus (E) of equal to or greater than about 900 MPa; alternatively, from about 900 MPa to about 1350 MPa, when tested in accordance with ASTM D638. 
     In a seventy-third aspect that can be in combination with any of the first to the seventy-second aspects, the polyethylene resin B can have a tensile yield stress of equal to or greater than about 20 MPa; alternatively, from about 20 MPa to about 30 MPa, when tested in accordance with ASTM D638. 
     In a seventy-fourth aspect that can be in combination with any of the first to the seventy-third aspects, the polyethylene resin B can have a tensile yield strain of from about 5% to about 25%, when tested in accordance with ASTM D638. 
     In a seventy-fifth aspect that can be in combination with any of the first to the seventy-fourth aspects, the polyethylene resin B can have a tensile natural draw ratio at room temperature of from about 300% to about 600%, when tested in accordance with ASTM D638. 
     In a seventy-sixth aspect that can be in combination with any of the first to the seventy-fifth aspects, the polyethylene resin B can have a tensile natural draw ratio at 80° C. of less than 500%, when tested in accordance with ASTM D638. 
     In a seventy-seventh aspect that can be in combination with any of the first to the seventy-sixth aspects, the polyethylene resin B can have a tensile natural draw ratio at 80° C. of less than about 400%, when tested in accordance with ASTM D638. 
     In a seventy-eighth aspect that can be in combination with any of the first to the seventy-seventh aspects, the polyethylene resin B can have a tensile natural draw ratio at 80° C. of from about 250% to about 400%, when tested in accordance with ASTM D638. 
     In a seventy-ninth aspect that can be in combination with any of the first to the seventy-eighth aspects, the polyethylene resin B can have a tensile natural draw ratio at 80° C. of less than about 300%, when tested in accordance with ASTM D638. 
     In an eightieth aspect that can be in combination with any of the first to the seventy-ninth aspects, the polyethylene resin B can have a strain hardening modulus of from about 50 MPa to about 90 MPa, when tested in accordance with ISO 18488-2015(E). 
     In an eighty-first aspect that can be in combination with any of the first to the eightieth aspects, the polyethylene resin B can have an environmental stress cracking resistance (ESCR) of equal to or greater than about 1,000 hours, when tested in accordance with ASTM D1693 (condition A). 
     In an eighty-second aspect that can be in combination with any of the first to the eighty-first aspects, the polyethylene resin B can have a resistance to slow crack growth of equal to or greater than about 800 h; alternatively, equal to or greater than about 2,000 h; alternatively, equal to or greater than about 5,000 h; alternatively equal to or greater than about 10,000 h, when tested in accordance with ASTM F1473, wherein the resistance to slow crack growth is defined as the polyethylene notch tensile test (PENT) failure time. 
     In an eighty-third aspect that can be in combination with any of the first to the eighty-second aspects, the polyethylene resin B can have a resistance to slow crack growth of equal to or greater than about 8,760 h; alternatively, equal to or greater than about 10,000 h; alternatively, equal to or greater than about 15,000 h; alternatively, equal to or greater than about 25,000 h; alternatively, equal to or greater than about 50,000 h; alternatively, equal to or greater than about 100,000 h; alternatively, equal to or greater than about 500,000 h, when tested in accordance with ISO 16770 at 80° C. and 6 MPa, wherein the resistance to slow crack growth is defined as the full notch creep test (FNCT) failure time. 
     In an eighty-fourth aspect that can be in combination with any of the first to the eighty-third aspects, the polyethylene resin B can have a resistance to slow crack growth of equal to or greater than about 100 h; alternatively, equal to or greater than about 500 h; alternatively, equal to or greater than about 1,000 h; alternatively, equal to or greater than about 5,000 h; alternatively equal to or greater than about 10,000 h; alternatively equal to or greater than about 15,000 h, when tested in accordance with ISO 13479:2009(E) at 4.6 MPa, wherein the resistance to slow crack growth is defined as the notched pipe test (NPT) failure time. 
     In an eighty-fifth aspect that can be in combination with any of the first to the eighty-fourth aspects, the polyethylene resin B can have a viscous relaxation time of from about 0.5 s to about 7.5 s. 
     In an eighty-sixth aspect that can be in combination with any of the first to the eighty-fifth aspects, the polyethylene resin B can have an η 0  (eta_0) of equal to or greater than about 0.7× 10 5  Pa-s; alternatively, equal to or greater than about 1.0 × 10 5  Pa-s; alternatively, from about 0.7 × 10 5  Pa-s to about 2.0 × 10 6  Pa-s. 
     In an eighty-seventh aspect that can be in combination with any of the first to the eighty-sixth aspects, the polyethylene resin B can have an η 251  (eta_251) of less than about 1.5 × 10 3  Pa-s. 
     In an eighty-eighth aspect that can be in combination with any of the first to the eighty-seventh aspects, the polyethylene resin B can have a storage modulus (G′) of from about 225,000 Pa to about 325,000 Pa, wherein G′ is measured at 190° C. and 251 rad/s in accordance with ASTM D4440. 
     In an eighty-ninth aspect that can be in combination with any of the first to the eighty-eighth aspects, the polyethylene resin B can have a loss modulus (G″) of from about 100,000 Pa to about 200,00 Pa, wherein G″ is measured at 190° C. and 251 rad/s in accordance with ASTM D4440. 
     In a ninetieth aspect that can be in combination with any of the first to the eighty-ninth aspects, the polyethylene resin B can have a tanδ of from about 0.3 to about 0.7; wherein tanδ is the ratio of the loss modulus (G″) to storage modulus (G′), wherein G″ and G′ are measured at 190° C. and 251 rad/s in accordance with ASTM D4440. 
     In a ninety-first aspect that can be in combination with any of the first to the ninetieth aspects, the polyethylene resin B is made by a process described herein. 
     In a first aspect, polyethylene resin C can comprise the first polyolefin made in polymerization zone  112  of the first reactor  100 , the second polyolefin made in the polymerization zone  321  of the riser  320  of the MZCR  300 , and the third polyolefin made in the polymerization zone  341  of the downcomer  340  of the MZCR  300 . 
     In a second aspect that can be in combination with the first aspect, the first polyolefin in polyethylene resin C can be a low molecular weight (LMW) component of the multimodal polyolefin, the second polyolefin in polyethylene resin C can be an intermediate molecular weight (IMW) component of the multimodal polyolefin, and the third polyolefin in polyethylene resin C can be a high molecular weight component (HMW) of the multimodal polyolefin. 
     In a third aspect that can be in combination with any of the first and the second aspects, the first polyolefin (e.g., the LMW component) in polyethylene resin C that is produced in the polymerization zone  112  of the first reactor  100  can be a lower molecular weight polyethylene, the second polyolefin (e.g., the IMW component) in polyethylene resin C that is produced in the polymerization zone  321  of the riser  320 , the third polyolefin (e.g., the HMW component) in polyethylene resin C that is produced in the polymerization zone  341  of the downcomer  340  can be a higher molecular weight polyethylene, or combinations thereof. 
     In a fourth aspect that can be in combination with any of the first to the third aspects, the LMW component is present in polyethylene resin C in an amount of from about 40 wt.% to about 60 wt.%. 
     In a fifth aspect that can be in combination with any of the first to the fourth aspects, the IMW component is present in polyethylene resin C in an amount of from about 5 wt.% to about 15 wt.%. 
     In a sixth aspect that can be in combination with any of the first to the fifth aspects, the HMW component is present in polyethylene resin C in an amount of from about 30 wt.% to about 50 wt.%. 
     In a seventh aspect that can be in combination with any of the first to the sixth aspects, the LMW component in polyethylene resin C has a weight average molecular weight of from about 25 kg/mol to about 65 kg/mol. 
     In an eighth aspect that can be in combination with any of the first to the seventh aspects, the IMW component in polyethylene resin C has a weight average molecular weight of from about 100 kg/mol to about 200 kg/mol. 
     In a ninth aspect that can be in combination with any of the first to the eighth aspects, the HMW component in polyethylene resin C has weight average molecular weight of from about 400 kg/mol to about 925 kg/mol. 
     In a tenth aspect that can be in combination with any of the first to the ninth aspects, the LMW component in polyethylene resin C has a short chain branching content of from about 0 to about 2 short chain branches per 1,000 carbon atoms. 
     In an eleventh aspect that can be in combination with any of the first to the tenth aspects, the IMW component in polyethylene resin C has a short chain branching content of from about 0.1 to about 5 short chain branches per 1,000 carbon atoms. 
     In a twelfth aspect that can be in combination with any of the first to the eleventh aspects, the HMW component in polyethylene resin C has a short chain branching content of from about 2 to about 12 short chain branches per 1,000 carbon atoms. 
     In a thirteenth aspect that can be in combination with any of the first to the twelfth aspects, the polyethylene resin C has a resistance to slow crack growth of equal to or greater than about 3,000 h, when tested in accordance with ASTM F1473, wherein the resistance to slow crack growth is defined as the polyethylene notch tensile test (PENT) failure time. 
     In a fourteenth aspect that can be in combination with any of the first to the thirteenth aspects, the weight average molecular weight of the HMW in polyethylene resin C is greater than the weight average molecular weight of the IMW. 
     In a fifteenth aspect that can be in combination with any of the first to the fourteenth aspects, the polyethylene resin C is a trimodal polyethylene resin. 
     In a sixteenth aspect that can be in combination with any of the first to the fifteenth aspects, polyethylene resin C can have a resistance to slow crack growth of equal to or greater than about 8,760 h, when tested in accordance with ISO 16770 at 80° C. and 6 MPa, wherein the resistance to slow crack growth is defined as the full notch creep test (FNCT) failure time. 
     In a seventeenth aspect that can be in combination with any of the first to the sixteenth aspects, polyethylene resin C has a resistance to slow crack growth of equal to or greater than about 1,000 h, when tested in accordance with ISO 13479:2009(E) at 4.6 MPa, wherein the resistance to slow crack growth is defined as the notched pipe test (NPT) failure time. 
     In an eighteenth aspect that can be in combination with any of the first to the seventeenth aspects, polyethylene resin C has a weight average molecular weight (M w ) of from about 200 kg/mol to about 400 kg/mol. 
     In a nineteenth aspect that can be in combination with any of the first to the eighteenth aspects, polyethylene resin C has a number average molecular weight (M n ) of from about 7.5 kg/mol to about 20 kg/mol. 
     In a twentieth aspect that can be in combination with any of the first to the nineteenth aspects, polyethylene resin C has a z-average molecular weight (M z ) of from about 1,000 kg/mol to about 3,300 kg/mol. 
     In a twenty-first aspect that can be in combination with any of the first to the twentieth aspects, polyethylene resin C has an η 0  (eta_0) of equal to or greater than about 1.0 × 10 5  Pa-s. 
     In a twenty-second aspect that can be in combination with any of the first to the twenty-first aspects, polyethylene resin C is made by a process described herein. 
     In a first aspect, polyethylene resin D can comprise the first polyolefin made in polymerization zone  112  of the first reactor  100 , the second polyolefin made in the polymerization zone  321  of the riser  320  of the MZCR  300 , and the third polyolefin made in the polymerization zone  341  of the downcomer  340  of the MZCR  300 . 
     In a second aspect that can be in combination with the first aspect, the first polyolefin in polyethylene resin D can be a low molecular weight (LMW) component of the multimodal polyolefin, the second polyolefin in polyethylene resin D can be an intermediate molecular weight (IMW) component of the multimodal polyolefin, and the third polyolefin in polyethylene resin D can be a high molecular weight component (HMW) of the multimodal polyolefin. 
     In a third aspect that can be in combination with any of the first and the second aspects, the first polyolefin (e.g., the LMW component) in polyethylene resin D that is produced in the polymerization zone  112  of the first reactor  100  can be a lower molecular weight polyethylene, the second polyolefin (e.g., the IMW component) in polyethylene resin D that is produced in the polymerization zone  321  of the riser  320 , the third polyolefin (e.g., the HMW component) in polyethylene resin D that is produced in the polymerization zone  341  of the downcomer  340  can be a higher molecular weight polyethylene, or combinations thereof. 
     In a fourth aspect that can be in combination with any of the first to the third aspects, the LMW component is present in polyethylene resin D in an amount of from about 40 wt.% to about 60 wt.%. 
     In a fifth aspect that can be in combination with any of the first to the fourth aspects, the IMW component is present in polyethylene resin D in an amount of from about 5 wt.% to about 15 wt.%. 
     In a sixth aspect that can be in combination with any of the first to the fifth aspects, the HMW component is present in polyethylene resin D in an amount of from about 30 wt.% to about 50 wt.%. 
     In a seventh aspect that can be in combination with any of the first to the sixth aspects, the LMW component in polyethylene resin D has a weight average molecular weight of from about 30 kg/mol to about 50 kg/mol. 
     In an eighth aspect that can be in combination with any of the first to the seventh aspects, the IMW component in polyethylene resin D has a weight average molecular weight of from about 90 kg/mol to about 150 kg/mol. 
     In a ninth aspect that can be in combination with any of the first to the eighth aspects, the HMW component in polyethylene resin D has weight average molecular weight of from about 450 kg/mol to about 750 kg/mol. 
     In a tenth aspect that can be in combination with any of the first to the ninth aspects, the LMW component in polyethylene resin D has a short chain branching content of from about 0.1 to about 2 short chain branches per 1,000 carbon atoms. 
     In an eleventh aspect that can be in combination with any of the first to the tenth aspects, the IMW component in polyethylene resin D has a short chain branching content of from about 0.1 to about 5 short chain branches per 1,000 carbon atoms. 
     In a twelfth aspect that can be in combination with any of the first to the eleventh aspects, the HMW component in polyethylene resin D has a short chain branching content of from about 2 to about 10 short chain branches per 1,000 carbon atoms. 
     In a thirteenth aspect that can be in combination with any of the first to the twelfth aspects, the polyethylene resin D has a tensile strength in the machine direction (MD) of greater than about 13,000 psi (89.6 MPa), when tested in accordance with ASTM D638 at 90 MPa. 
     In a fourteenth aspect that can be in combination with any of the first to the thirteenth aspects, the polyethylene resin D is a trimodal polyethylene resin. 
     In a fifteenth aspect that can be in combination with any of the first to the fourteenth aspects, the polyethylene resin D has a tensile strength in the transverse direction (TD) of greater than about 6,000 psi (about 41.4 MPa), when tested in accordance with ASTM D638 at 41 MPa. 
     In a sixteenth aspect that can be in combination with any of the first to the fifteenth aspects, the polyethylene resin D an η 0  (eta_0) of equal to or greater than about 1.0 × 10 5  Pa-s. 
     In a seventeenth aspect that can be in combination with any of the first to the sixteenth aspects, polyethylene resin D is made by a process described herein. 
     In a first aspect, polyethylene resin E is a Ziegler Natta-catalyzed polyethylene resin. 
     In a second aspect that can be in combination with the first aspect, polyethylene resin E can comprise the first polyolefin made in polymerization zone  112  of the first reactor  100 , the second polyolefin made in the polymerization zone  321  of the riser  320  of the MZCR  300 , and the third polyolefin made in the polymerization zone  341  of the downcomer  340  of the MZCR  300 . 
     In a third aspect that can be in combination with any of the first and the second aspects, the first polyolefin in polyethylene resin E can be a low molecular weight (LMW) component of the multimodal polyolefin, the second polyolefin in polyethylene resin E can be an intermediate molecular weight (IMW) component of the multimodal polyolefin, and the third polyolefin in polyethylene resin E can be a high molecular weight component (HMW) of the multimodal polyolefin. 
     In a fourth aspect that can be in combination with any of the first to the third aspects, the first polyolefin (e.g., the LMW component) in polyethylene resin E that is produced in the polymerization zone  112  of the first reactor  100  can be a lower molecular weight polyethylene, the second polyolefin (e.g., the IMW component) in polyethylene resin E that is produced in the polymerization zone  321  of the riser  320 , the third polyolefin (e.g., the HMW component) in polyethylene resin E that is produced in the polymerization zone  341  of the downcomer  340  can be a higher molecular weight polyethylene, or combinations thereof. 
     In a fifth aspect that can be in combination with any of the first to the fourth aspects, the LMW component in polyethylene resin E is produced in a first reaction zone in the substantial absence of a comonomer, wherein the LMW component is present in an amount of from about 20 wt.% to about 75 wt.%. 
     In a sixth aspect that can be in combination with any of the first to the fifth aspects, the IMW component in polyethylene resin E is produced in a second reaction zone in the presence of a first amount of comonomer and a first amount of hydrogen. 
     In a seventh aspect that can be in combination with any of the first to the sixth aspects, the IMW component is present in polyethylene resin E in an amount of from about 5 wt.% to about 40 wt.%. 
     In an eighth aspect that can be in combination with any of the first to the seventh aspects, the HMW component in polyethylene resin E is produced in a third reaction zone in the presence of a second amount of comonomer and a second amount of hydrogen. 
     In a ninth aspect that can be in combination with any of the first to the eighth aspects, the second amount of comonomer in polyethylene resin E is greater than the first amount of comonomer. 
     In a tenth aspect that can be in combination with any of the first to the ninth aspects, first amount of hydrogen in polyethylene resin E is greater than the second amount of hydrogen. 
     In an eleventh aspect that can be in combination with any of the first to the tenth aspects, the HMW component is present in polyethylene resin E in an amount of from about 10 wt.% to about 60 wt.%. 
     In a twelfth aspect that can be in combination with any of the first to the eleventh aspects, the LMW component in polyethylene resin E has a weight average molecular weight of from about 20 kg/mol to about 150 kg/mol. 
     In a thirteenth aspect that can be in combination with any of the first to the twelfth aspects, the IMW component in polyethylene resin E has a weight average molecular weight of from about 85 kg/mol to about 350 kg/mol. 
     In a fourteenth aspect that can be in combination with any of the first to the thirteenth aspects, the HMW component in polyethylene resin E has weight average molecular weight of greater than about 350 kg/mol. 
     In a fifteenth aspect that can be in combination with any of the first to the fourteenth aspects, the weight average molecular weight of the IMW component in polyethylene resin E is greater than the weight average molecular weight of the LMW component. 
     In a sixteenth aspect that can be in combination with any of the first to the fifteenth aspects, the LMW component in polyethylene resin E has a short chain branching content of from about 0 to about 5 short chain branches per 1,000 carbon atoms. 
     In a seventeenth aspect that can be in combination with any of the first to the sixteenth aspects, the IMW component in polyethylene resin E has a short chain branching content of from about 0.1 to about 10 short chain branches per 1,000 carbon atoms. 
     In an eighteenth aspect that can be in combination with any of the first to the seventeenth aspects, the HMW component in polyethylene resin E has a short chain branching content of from about 1 to about 15 short chain branches per 1,000 carbon atoms. 
     In a nineteenth aspect that can be in combination with any of the first to the eighteenth aspects, the polyethylene resin E has an η 251  (eta_251) of less than about 1.5 × 10 3  Pa-s. 
     In a twentieth aspect that can be in combination with any of the first to the nineteenth aspects, the polyethylene resin E is a trimodal polyethylene resin. 
     In a twenty-first aspect that can be in combination with any of the first to the twentieth aspects, a first reactor in polyethylene resin E comprises the first reaction zone. 
     In a twenty-second aspect that can be in combination with any of the first to the twenty-first aspects, the first reaction zone in polyethylene resin E comprises a gas phase reaction zone. 
     In a twenty-third aspect that can be in combination with any of the first to the twenty-second aspects, a second reactor in polyethylene resin E comprises the second reaction zone and the third reaction zone. 
     In a twenty-fourth aspect that can be in combination with any of the first to the twenty-third aspects, the second reaction zone in polyethylene resin E comprises a riser. 
     In a twenty-fifth aspect that can be in combination with any of the first to the twenty-fourth aspects, the second reaction zone in polyethylene resin E comprises a fast fluidization reaction zone. 
     In a twenty-sixth aspect that can be in combination with any of the first to the twenty-fifth aspects, the third reaction zone in polyethylene resin E comprises a downcomer. 
     In a twenty-seventh aspect that can be in combination with any of the first to the twenty-sixth aspects, the third reaction zone in polyethylene resin E comprises a plug flow reaction zone. 
     In a first aspect, polyethylene resin F is a Ziegler Natta-catalyzed polyethylene resin. 
     In a second aspect that can be in combination with the first aspect, polyethylene resin F can comprise the first polyolefin made in polymerization zone  112  of the first reactor  100 , the second polyolefin made in the polymerization zone  321  of the riser  320  of the MZCR  300 , and the third polyolefin made in the polymerization zone  341  of the downcomer  340  of the MZCR  300 . 
     In a third aspect that can be in combination with any of the first and the second aspects, the first polyolefin in polyethylene resin F can be a low molecular weight (LMW) component of the multimodal polyolefin, the second polyolefin in polyethylene resin F can be an intermediate molecular weight (IMW) component of the multimodal polyolefin, and the third polyolefin in polyethylene resin F can be a high molecular weight component (HMW) of the multimodal polyolefin. 
     In a fourth aspect that can be in combination with any of the first to the third aspects, the first polyolefin (e.g., the LMW component) in polyethylene resin F that is produced in the polymerization zone  112  of the first reactor  100  can be a lower molecular weight polyethylene, the second polyolefin (e.g., the IMW component) in polyethylene resin F that is produced in the polymerization zone  321  of the riser  320 , the third polyolefin (e.g., the HMW component) in polyethylene resin F that is produced in the polymerization zone  341  of the downcomer  340  can be a higher molecular weight polyethylene, or combinations thereof. 
     In a fifth aspect that can be in combination with any of the first to the fourth aspects, the LMW component in polyethylene resin F is produced in a gas phase reaction zone in the substantial absence of a comonomer, 
     In a sixth aspect that can be in combination with any of the first to the fifth aspects, the LMW component is present in polyethylene resin F in an amount of from about 20 wt.% to about 75 wt.%. 
     In a seventh aspect that can be in combination with any of the first to the sixth aspects, the IMW component in polyethylene resin F is produced in a fast fluidization reaction zone in the presence of a first amount of comonomer and a first amount of hydrogen. 
     In an eighth aspect that can be in combination with any of the first to the seventh aspects, the IMW component is present in polyethylene resin F in an amount of from about 5 wt.% to about 40 wt.%. 
     In a ninth aspect that can be in combination with any of the first to the eighth aspects, the HMW component in polyethylene resin F is produced in a plug flow reaction zone in the presence of a second amount of comonomer and a second amount of hydrogen. 
     In a tenth aspect that can be in combination with any of the first to the ninth aspects, the second amount of comonomer in polyethylene resin F is greater than the first amount of comonomer. 
     In an eleventh aspect that can be in combination with any of the first to the tenth aspects, first amount of hydrogen in polyethylene resin F is greater than the second amount of hydrogen. 
     In a twelfth aspect that can be in combination with any of the first to the eleventh aspects, the HMW component is present in polyethylene resin F in an amount of from about 10 wt.% to about 60 wt.%. 
     In a thirteenth aspect that can be in combination with any of the first to the twelfth aspects, the LMW component in polyethylene resin F has a weight average molecular weight of from about 20 kg/mol to about 150 kg/mol. 
     In a fourteenth aspect that can be in combination with any of the first to the thirteenth aspects, the IMW component in polyethylene resin F has a weight average molecular weight of from about 85 kg/mol to about 350 kg/mol. 
     In a fifteenth aspect that can be in combination with any of the first to the fourteenth aspects, the HMW component in polyethylene resin F has weight average molecular weight of greater than about 350 kg/mol. 
     In a sixteenth aspect that can be in combination with any of the first to the fifteenth aspects, the weight average molecular weight of the IMW component in polyethylene resin F is greater than the weight average molecular weight of the LMW component. 
     In a seventeenth aspect that can be in combination with any of the first to the sixteenth aspects, the LMW component in polyethylene resin F has a short chain branching content of from about 0 to about 5 short chain branches per 1,000 carbon atoms. 
     In an eighteenth aspect that can be in combination with any of the first to the seventeenth aspects, the IMW component in polyethylene resin F has a short chain branching content of from about 0.1 to about 10 short chain branches per 1,000 carbon atoms. 
     In a nineteenth aspect that can be in combination with any of the first to the eighteenth aspects, the HMW component in polyethylene resin F has a short chain branching content of from about 1 to about 15 short chain branches per 1,000 carbon atoms. 
     In a twentieth aspect that can be in combination with any of the first to the nineteenth aspects, the polyethylene resin F has an η 251  (eta_251) of less than about 1.5 ×10 3  Pa-s. 
     In a twenty-first aspect that can be in combination with any of the first to the twentieth aspects, the polyethylene resin F is a trimodal polyethylene resin. 
     In a twenty-second aspect that can be in combination with any of the first to the twenty-first aspects, a first reactor in polyethylene resin F comprises the gas phase reaction zone. 
     In a twenty-third aspect that can be in combination with any of the first to the twenty-second aspects, a second reactor in polyethylene resin F comprises a riser and a downcomer. 
     In a twenty-fourth aspect that can be in combination with any of the first to the twenty-third aspects, the riser in polyethylene resin F comprises the fast fluidization reaction zone, and wherein the downcomer comprises the plug flow reaction zone. 
     At least one embodiment is disclosed and variations, combinations, and/or modifications of the embodiment(s) and/or features of the embodiment(s) made by a person having ordinary skill in the art are within the scope of the disclosure. Alternative embodiments that result from combining, integrating, and/or omitting features of the embodiment(s) are also within the scope of the disclosure. Where numerical ranges or limitations are expressly stated, such express ranges or limitations should be understood to include iterative ranges or limitations of like magnitude falling within the expressly stated ranges or limitations (e.g., from about 1 to about 10 includes, 2, 3, 4, etc.; greater than 0.10 includes 0.11, 0.12, 0.13, etc.). For example, whenever a numerical range with a lower limit, R 1 , and an upper limit, R u , is disclosed, any number falling within the range is specifically disclosed. In particular, the following numbers within the range are specifically disclosed: R=R 1  +k* (R u -R 1 ), wherein k is a variable ranging from 1 percent to 100 percent with a 1 percent increment, i.e., k is 1 percent, 2 percent, 3 percent, 4 percent, 5 percent, ..... 50 percent, 51 percent, 52 percent... 95 percent, 96 percent, 97 percent, 98 percent, 99 percent, or 100 percent. Moreover, any numerical range defined by two R numbers as defined in the above is also specifically disclosed. Use of the term “optionally” with respect to any element of a claim means that the element is required, or alternatively, the element is not required, both alternatives being within the scope of the claim. Use of broader terms such as comprises, includes, and having should be understood to provide support for narrower terms such as consisting of, consisting essentially of, and comprised substantially of. Accordingly, the scope of protection is not limited by the description set out above but is defined by the claims that follow, that scope including all equivalents of the subject matter of the claims. Each and every claim is incorporated as further disclosure into the specification and the claims are embodiment(s) of the disclosed inventive subject matter. The discussion of a reference in the disclosure is not an admission that it is prior art, especially any reference that has a publication date after the priority date of this application. The disclosure of all patents, patent applications, and publications cited in the disclosure are hereby incorporated by reference, to the extent that they provide exemplary, procedural or other details supplementary to the disclosure.