Abstract:
A process and apparatus uses a flash drum to separate light hydrocarbons from heavy oligomerate from an oligomerization zone. The heavy oligomerate can bypass a fractionation column in the oligomerate recovery section and be recycled to the oligomerization zone or other zones. Costs are saved by avoiding repeatedly transporting and processing the heavier recycled oligomerate.

Description:
BACKGROUND 
     When oligomerizing light olefins within a refinery, there is frequently a desire to have the flexibility to make high octane gasoline, high cetane diesel, or combination of both. However, catalysts that make high octane gasoline typically make product that is highly branched and within the gasoline boiling point range. This product is very undesirable for diesel. In addition, catalysts that make high cetane diesel typically make product that is more linear and in the distillate boiling point range. This results in less and poorer quality gasoline due to the more linear nature of the product which has a lower octane value. 
     The oligomerization of butenes is often associated with a desire to make a high yield of high quality gasoline product. There is typically a limit as to what can be achieved when oligomerizing butenes. When oligomerizing butenes, dimerization is desired to obtain gasoline range material. However, trimerization and higher oligomerization can occur which can produce material heavier than gasoline such as diesel. Efforts to produce diesel by oligomerization have failed to provide high yields except through multiple passes. 
     When oligomerizing olefins from a fluid catalytic cracking (FCC) unit, there is often a desire to maintain a liquid phase within the oligomerization reactors. A liquid phase helps with catalyst stability by acting as a solvent to wash the catalyst of heavier species produced. In addition, the liquid phase provides a higher concentration of olefins to the catalyst surface to achieve a higher catalyst activity. This liquid phase in the reactor may be maintained by recycling heavy oligomerate to the oligomerization reactor. 
     To maximize propylene produced by the FCC unit, refiners may contemplate oligomerizing FCC olefins to make heavy oligomerate and recycling heavy oligomers to the FCC unit for cracking down to propylene. 
     Recycling heavy oligomers to the oligomerization unit or the FCC unit requires the heavy oligomers to be separated from lighter hydrocarbons in the oligomerate effluent typically in a fractionation column. A recycle ratio of oligomerate to feed can exceed 1. Transporting and separating heavy oligomerate recycled to the fractionation column exacts high utility costs. 
     Efficient processes and apparatuses are desired to recycle heavy oligomerate. 
     SUMMARY 
     We have discovered a process and apparatus that uses a flash drum to initially separate heavy oligomerate from light oligomerate, so the light oligomerate can bypass a fractionation column in an oligomerate recovery section. Operational expenses for separating heavy oligomerate from light oligomerate are reduced because the heavy oligomerate which is more utility intensive to transport and separate is decreased. 
     An embodiment is a process for making oligomers comprising passing an oligomerization feed stream to an oligomerization zone to oligomerize olefins in the oligomerization feed stream to produce an oligomerate stream; separating the oligomerate stream from the oligomerization zone in a flash drum to provide a light flash oligomerate stream and a heavy flash oligomerate stream; fractionating the light flash oligomerate stream in a recovery zone; and recycling at least a portion of the heavy flash oligomerate stream to the oligomerization zone. 
     An embodiment is an apparatus for making oligomers comprising an oligomerization zone for oligomerizing olefins in the oligomerization feed stream to produce an oligomerate stream; a flash drum for separating the oligomerate stream in communication with the oligomerization zone. a light flash line from the flash drum and a heavy flash line from the flash drum with an inlet to the light flash line above an inlet to the heavy flash line; a fractionation column in communication with the light flash line for fractionating the light flash oligomerate stream; and the oligomerization zone in downstream communication with the heavy flash line. 
     An object is to recycle heavy oligomerate to oligomerization or fluid catalytic cracking at lower expense. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic drawing of the present invention. 
         FIG. 2  is a plot of C 8 -C 11  olefin selectivity versus normal butene conversion. 
         FIG. 3  is a plot of C 12 + olefin selectivity versus normal butene conversion. 
         FIG. 4  is a plot of reactant conversion versus total butene conversion. 
         FIG. 5  is a plot of normal butene conversion versus reactor temperature. 
         FIGS. 6 and 7  are plots of butene conversion versus total butene conversion. 
         FIG. 8  is a plot of selectivity versus maximum reactor bed temperature. 
         FIGS. 9-11  are bar graphs of conversion and yield for three different catalysts. 
         FIG. 12  is a plot of C 3  olefin yield versus VGO conversion. 
     
    
    
     DEFINITIONS 
     As used herein, the term “stream” can include various hydrocarbon molecules and other substances. Moreover, the term “stream comprising C x  hydrocarbons” or “stream comprising C x  olefins” can include a stream comprising hydrocarbon or olefin molecules, respectively, with “x” number of carbon atoms, suitably a stream with a majority of hydrocarbons or olefins, respectively, with “x” number of carbon atoms and preferably a stream with at least 75 wt % hydrocarbons or olefin molecules, respectively, with “x” number of carbon atoms. Moreover, the term “stream comprising C x + hydrocarbons” or “stream comprising C x + olefins” can include a stream comprising a majority of hydrocarbon or olefin molecules, respectively, with more than or equal to “x” carbon atoms and suitably less than 10 wt % and preferably less than 1 wt % hydrocarbon or olefin molecules, respectively, with x−1 carbon atoms. Lastly, the term “C x − stream” can include a stream comprising a majority of hydrocarbon or olefin molecules, respectively, with less than or equal to “x” carbon atoms and suitably less than 10 wt % and preferably less than 1 wt % hydrocarbon or olefin molecules, respectively, with x+1 carbon atoms. 
     As used herein, the term “zone” can refer to an area including one or more equipment items and/or one or more sub-zones. Equipment items can include one or more reactors or reactor vessels, heaters, exchangers, pipes, pumps, compressors, controllers and columns. Additionally, an equipment item, such as a reactor, dryer, or vessel, can further include one or more zones or sub-zones. 
     As used herein, the term “substantially” can mean an amount of at least generally about 70%, preferably about 80%, and optimally about 90%, by weight, of a compound or class of compounds in a stream. 
     As used herein, the term “gasoline” can include hydrocarbons having a boiling point temperature in the range of about 25° to about 200° C. at atmospheric pressure. 
     As used herein, the term “diesel” or “distillate” can include hydrocarbons having a boiling point temperature in the range of about 150° to about 400° C. and preferably about 200° to about 400° C. 
     As used herein, the term “vacuum gas oil” (VGO) can include hydrocarbons having a boiling temperature in the range of from 343° to 552° C. 
     As used herein, the term “vapor” can mean a gas or a dispersion that may include or consist of one or more hydrocarbons. 
     As used herein, the term “overhead stream” can mean a stream withdrawn at or near a top of a vessel, such as a column. 
     As used herein, the term “bottom stream” can mean a stream withdrawn at or near a bottom of a vessel, such as a column. 
     As depicted, process flow lines in the figures can be referred to interchangeably as, e.g., lines, pipes, feeds, gases, products, discharges, parts, portions, or streams. 
     As used herein, “bypassing” with respect to a vessel or zone means that a stream does not pass through the zone or vessel bypassed although it may pass through a vessel or zone that is not designated as bypassed. 
     The term “communication” means that material flow is operatively permitted between enumerated components. 
     The term “downstream communication” means that at least a portion of material flowing to the subject in downstream communication may operatively flow from the object with which it communicates. 
     The term “upstream communication” means that at least a portion of the material flowing from the subject in upstream communication may operatively flow to the object with which it communicates. 
     The term “direct communication” means that flow from the upstream component enters the downstream component without undergoing a compositional change due to physical fractionation or chemical conversion. 
     The term “column” means a distillation column or columns for separating one or more components of different volatilities. Unless otherwise indicated, each column includes a condenser on an overhead of the column to condense and reflux a portion of an overhead stream back to the top of the column and a reboiler at a bottom of the column to vaporize and send a portion of a bottom stream back to the bottom of the column. Feeds to the columns may be preheated. The top pressure is the pressure of the overhead vapor at the outlet of the column. The bottom temperature is the liquid bottom outlet temperature. Overhead lines and bottom lines refer to the net lines from the column downstream of the reflux or reboil to the column. 
     As used herein, the term “boiling point temperature” means atmospheric equivalent boiling point (AEBP) as calculated from the observed boiling temperature and the distillation pressure, as calculated using the equations furnished in ASTM D1160 appendix A7 entitled “Practice for Converting Observed Vapor Temperatures to Atmospheric Equivalent Temperatures”. 
     As used herein, “taking a stream from” means that some or all of the original stream is taken. 
     DETAILED DESCRIPTION 
     The present invention is an apparatus and process that can be used to make gasoline, diesel and propylene. The apparatus and process may be described with reference to five components shown in  FIG. 1 : a fluid catalytic cracking (FCC) zone  20 , an FCC recovery zone  100 , a purification zone  110 , an oligomerization zone  130 , and an oligomerization recovery zone  200 . Many configurations of the present invention are possible, but specific embodiments are presented herein by way of example. All other possible embodiments for carrying out the present invention are considered within the scope of the present invention. 
     The FCC zone  20  may comprise a first FCC reactor  22 , a regenerator vessel  30 , and an optional second FCC reactor  70 . 
     A conventional FCC feedstock and higher boiling hydrocarbon feedstock are a suitable FCC hydrocarbon feed  24  to the first FCC reactor. The most common of such conventional feedstocks is a VGO. Higher boiling hydrocarbon feedstocks to which this invention may be applied include heavy bottom from crude oil, heavy bitumen crude oil, shale oil, tar sand extract, deasphalted residue, products from coal liquefaction, atmospheric and vacuum reduced crudes and mixtures thereof. The FCC feed  24  may include an FCC recycle stream from FCC recycle line  280  to be described later. 
     The first FCC reactor  22  may include a first reactor riser  26  and a first reactor vessel  28 . A regenerator catalyst pipe  32  delivers regenerated catalyst from the regenerator vessel  30  to the reactor riser  26 . A fluidization medium such as steam from a distributor  34  urges a stream of regenerated catalyst upwardly through the first reactor riser  26 . At least one feed distributor injects the first hydrocarbon feed in a first hydrocarbon feed line  24 , preferably with an inert atomizing gas such as steam, across the flowing stream of catalyst particles to distribute hydrocarbon feed to the first reactor riser  26 . Upon contacting the hydrocarbon feed with catalyst in the first reactor riser  26  the heavier hydrocarbon feed cracks to produce lighter gaseous cracked products while coke is deposited on the catalyst particles to produce spent catalyst. 
     The resulting mixture of gaseous product hydrocarbons and spent catalyst continues upwardly through the first reactor riser  26  and are received in the first reactor vessel  28  in which the spent catalyst and gaseous product are separated. Disengaging arms discharge the mixture of gas and catalyst from a top of the first reactor riser  26  through outlet ports  36  into a disengaging vessel  38  that effects partial separation of gases from the catalyst. A transport conduit carries the hydrocarbon vapors, stripping media and entrained catalyst to one or more cyclones  42  in the first reactor vessel  28  which separates spent catalyst from the hydrocarbon gaseous product stream. Gas conduits deliver separated hydrocarbon cracked gaseous streams from the cyclones  42  to a collection plenum  44  for passage of a cracked product stream to a first cracked product line  46  via an outlet nozzle and eventually into the FCC recovery zone  100  for product recovery. 
     Diplegs discharge catalyst from the cyclones  42  into a lower bed in the first reactor vessel  28 . The catalyst with adsorbed or entrained hydrocarbons may eventually pass from the lower bed into a stripping section  48  across ports defined in a wall of the disengaging vessel  38 . Catalyst separated in the disengaging vessel  38  may pass directly into the stripping section  48  via a bed. A fluidizing distributor delivers inert fluidizing gas, typically steam, to the stripping section  48 . The stripping section  48  contains baffles or other equipment to promote contacting between a stripping gas and the catalyst. The stripped spent catalyst leaves the stripping section  48  of the disengaging vessel  38  of the first reactor vessel  28  stripped of hydrocarbons. A first portion of the spent catalyst, preferably stripped, leaves the disengaging vessel  38  of the first reactor vessel  28  through a spent catalyst conduit  50  and passes into the regenerator vessel  30 . A second portion of the spent catalyst may be recirculated in recycle conduit  52  from the disengaging vessel  38  back to a base of the first riser  26  at a rate regulated by a slide valve to recontact the feed without undergoing regeneration. 
     The first riser  26  can operate at any suitable temperature, and typically operates at a temperature of about 150° to about 580° C. at the riser outlet  36 . The pressure of the first riser is from about 69 to about 517 kPa (gauge) (10 to 75 psig) but typically less than about 275 kPa (gauge) (40 psig). The catalyst-to-oil ratio, based on the weight of catalyst and feed hydrocarbons entering the riser, may range up to 30:1 but is typically between about 4:1 and about 25:1. Steam may be passed into the first reactor riser  26  and first reactor vessel  28  at a rate between about 2 and about 7 wt % for maximum gasoline production and about 10 to about 30 wt % for maximum light olefin production. The average residence time of catalyst in the riser may be less than about 5 seconds. 
     The catalyst in the first reactor  22  can be a single catalyst or a mixture of different catalysts. Usually, the catalyst includes two catalysts, namely a first FCC catalyst, and a second FCC catalyst. Such a catalyst mixture is disclosed in, e.g., U.S. Pat. No. 7,312,370 B2. Generally, the first FCC catalyst may include any of the well-known catalysts that are used in the art of FCC. Preferably, the first FCC catalyst includes a large pore zeolite, such as a Y-type zeolite, an active alumina material, a binder material, including either silica or alumina, and an inert filler such as kaolin. 
     Typically, the zeolites appropriate for the first FCC catalyst have a large average pore size, usually with openings of greater than about 0.7 nm in effective diameter defined by greater than about 10, and typically about 12, member rings. Suitable large pore zeolite components may include synthetic zeolites such as X and Y zeolites, mordenite and faujasite. A portion of the first FCC catalyst, such as the zeolite portion, can have any suitable amount of a rare earth metal or rare earth metal oxide. 
     The second FCC catalyst may include a medium or smaller pore zeolite catalyst, such as exemplified by at least one of ZSM-5, ZSM-11, ZSM-12, ZSM-23, ZSM-35, ZSM-38, ZSM-48, and other similar materials. Other suitable medium or smaller pore zeolites include ferrierite, and erionite. Preferably, the second component has the medium or smaller pore zeolite dispersed on a matrix including a binder material such as silica or alumina and an inert filler material such as kaolin. These catalysts may have a crystalline zeolite content of about 10 to about 50 wt % or more, and a matrix material content of about 50 to about 90 wt %. Catalysts containing at least about 40 wt % crystalline zeolite material are typical, and those with greater crystalline zeolite content may be used. Generally, medium and smaller pore zeolites are characterized by having an effective pore opening diameter of less than or equal to about 0.7 nm and rings of about 10 or fewer members. Preferably, the second FCC catalyst component is an MFI zeolite having a silicon-to-aluminum ratio greater than about 15. In one exemplary embodiment, the silicon-to-aluminum ratio can be about 15 to about 35. 
     The total catalyst mixture in the first reactor  22  may contain about 1 to about 25 wt % of the second FCC catalyst, including a medium to small pore crystalline zeolite, with greater than or equal to about 7 wt % of the second FCC catalyst being preferred. When the second FCC catalyst contains about 40 wt % crystalline zeolite with the balance being a binder material, an inert filler, such as kaolin, and optionally an active alumina component, the catalyst mixture may contain about 0.4 to about 10 wt % of the medium to small pore crystalline zeolite with a preferred content of at least about 2.8 wt %. The first FCC catalyst may comprise the balance of the catalyst composition. The high concentration of the medium or smaller pore zeolite as the second FCC catalyst of the catalyst mixture can improve selectivity to light olefins. In one exemplary embodiment, the second FCC catalyst can be a ZSM-5 zeolite and the catalyst mixture can include about 0.4 to about 10 wt % ZSM-5 zeolite excluding any other components, such as binder and/or filler. 
     The regenerator vessel  30  is in downstream communication with the first reactor vessel  28 . In the regenerator vessel  30 , coke is combusted from the portion of spent catalyst delivered to the regenerator vessel  30  by contact with an oxygen-containing gas such as air to regenerate the catalyst. The spent catalyst conduit  50  feeds spent catalyst to the regenerator vessel  30 . The spent catalyst from the first reactor vessel  28  usually contains carbon in an amount of from 0.2 to 7 wt %, which is present in the form of coke. An oxygen-containing combustion gas, typically air, enters the lower chamber  54  of the regenerator vessel  30  through a conduit and is distributed by a distributor  56 . As the combustion gas enters the lower chamber  54 , it contacts spent catalyst entering from spent catalyst conduit  50  and lifts the catalyst at a superficial velocity of combustion gas in the lower chamber  54  of perhaps at least 1.1 m/s (3.5 ft/s) under fast fluidized flow conditions. In an embodiment, the lower chamber  54  may have a catalyst density of from 48 to 320 kg/m 3  (3 to 20 lb/ft 3 ) and a superficial gas velocity of 1.1 to 2.2 m/s (3.5 to 7 ft/s). The oxygen in the combustion gas contacts the spent catalyst and combusts carbonaceous deposits from the catalyst to at least partially regenerate the catalyst and generate flue gas. 
     The mixture of catalyst and combustion gas in the lower chamber  54  ascends through a frustoconical transition section to the transport, riser section of the lower chamber  54 . The mixture of catalyst particles and flue gas is discharged from an upper portion of the riser section into the upper chamber  60 . Substantially completely or partially regenerated catalyst may exit the top of the transport, riser section. Discharge is effected through a disengaging device  58  that separates a majority of the regenerated catalyst from the flue gas. The catalyst and gas exit downwardly from the disengaging device  58 . The sudden loss of momentum and downward flow reversal cause a majority of the heavier catalyst to fall to the dense catalyst bed and the lighter flue gas and a minor portion of the catalyst still entrained therein to ascend upwardly in the upper chamber  60 . Cyclones  62  further separate catalyst from ascending gas and deposits catalyst through dip legs into a dense catalyst bed. Flue gas exits the cyclones  62  through a gas conduit and collects in a plenum  64  for passage to an outlet nozzle of regenerator vessel  30 . Catalyst densities in the dense catalyst bed are typically kept within a range of from about 640 to about 960 kg/m 3  (40 to 60 lb/ft 3 ). 
     The regenerator vessel  30  typically has a temperature of about 594° to about 704° C. (1100° to 1300° F.) in the lower chamber  54  and about 649° to about 760° C. (1200° to 1400° F.) in the upper chamber  60 . Regenerated catalyst from dense catalyst bed is transported through regenerated catalyst pipe  32  from the regenerator vessel  30  back to the first reactor riser  26  through the control valve where it again contacts the first feed in line  24  as the FCC process continues. The first cracked product stream in the first cracked product line  46  from the first reactor  22 , relatively free of catalyst particles and including the stripping fluid, exit the first reactor vessel  28  through an outlet nozzle. The first cracked products stream in the line  46  may be subjected to additional treatment to remove fine catalyst particles or to further prepare the stream prior to fractionation. The line  46  transfers the first cracked products stream to the FCC recovery zone  100 , which is in downstream communication with the FCC zone  20 . 
     The FCC recovery zone  100  typically includes a main fractionation column and a gas recovery section. The FCC recovery zone can include many fractionation columns and other separation equipment. The FCC recovery zone  100  can recover a propylene product stream in propylene line  102 , a gasoline stream in gasoline line  104 , a light olefin stream in light olefin line  106  and an LCO stream in LCO line  107  among others from the cracked product stream in first cracked product line  46 . The light olefin stream in light olefin line  106  comprises an oligomerization feed stream having C 4  hydrocarbons including C 4  olefins and perhaps having C 5  hydrocarbons including C 5  olefins. 
     An FCC recycle line  280  delivers an FCC recycle stream to the FCC zone  20 . The FCC recycle stream is directed into a first FCC recycle line  202  with the control valve  202 ′ thereon opened. In an aspect, the FCC recycle stream may be directed into an optional second FCC recycle line  204  with the control valve  204 ′ thereon opened. The first FCC recycle line  202  delivers the first FCC recycle stream to the first FCC reactor  22  in an aspect to the riser  26  at an elevation above the first hydrocarbon feed in line  24 . The second FCC recycle line  204  delivers the second FCC recycle stream to the second FCC reactor  70 . Typically, both control valves  202 ′ and  204 ′ will not be opened at the same time, so the FCC recycle stream goes through only one of the first FCC recycle line  202  and the second FCC recycle line  204 . However, feed through both is contemplated. 
     The second FCC recycle stream may be fed to the second FCC reactor  70  in the second FCC recycle line  204  via feed distributor  72 . The second FCC reactor  70  may include a second riser  74 . The second FCC recycle stream is contacted with catalyst delivered to the second riser  74  by a catalyst return pipe  76  to produce cracked upgraded products. The catalyst may be fluidized by inert gas such as steam from distributor  78 . Generally, the second FCC reactor  70  may operate under conditions to convert the second FCC recycle stream to second cracked products such as ethylene and propylene. A second reactor vessel  80  is in downstream communication with the second riser  74  for receiving second cracked products and catalyst from the second riser. The mixture of gaseous, second cracked product hydrocarbons and catalyst continues upwardly through the second reactor riser  74  and is received in the second reactor vessel  80  in which the catalyst and gaseous, second cracked products are separated. A pair of disengaging arms may tangentially and horizontally discharge the mixture of gas and catalyst from a top of the second reactor riser  74  through one or more outlet ports  82  (only one is shown) into the second reactor vessel  80  that effects partial separation of gases from the catalyst. The catalyst can drop to a dense catalyst bed within the second reactor vessel  80 . Cyclones  84  in the second reactor vessel  80  may further separate catalyst from second cracked products. Afterwards, a second cracked product stream can be removed from the second FCC reactor  70  through an outlet in a second cracked product line  86  in downstream communication with the second reactor riser  74 . The second cracked product stream in line  86  is fed to the FCC recovery zone  100 , preferably separately from the first cracked products to undergo separation and recovery of ethylene and propylene. Separated catalyst may be recycled via a recycle catalyst pipe  76  from the second reactor vessel  80  regulated by a control valve back to the second reactor riser  74  to be contacted with the second FCC recycle stream. 
     In some embodiments, the second FCC reactor  70  can contain a mixture of the first and second FCC catalysts as described above for the first FCC reactor  22 . In one preferred embodiment, the second FCC reactor  70  can contain less than about 20 wt %, preferably less than about 5 wt % of the first FCC catalyst and at least 20 wt % of the second FCC catalyst. In another preferred embodiment, the second FCC reactor  70  can contain only the second FCC catalyst, preferably a ZSM-5 zeolite. 
     The second FCC reactor  70  is in downstream communication with the regenerator vessel  30  and receives regenerated catalyst therefrom in line  88 . In an embodiment, the first FCC reactor  22  and the second FCC reactor  70  both share the same regenerator vessel  30 . Line  90  carries spent catalyst from the second reactor vessel  80  to the lower chamber  54  of the regenerator vessel  30 . The catalyst regenerator is in downstream communication with the second FCC reactor  70  via line  90 . 
     The same catalyst composition may be used in both reactors  22 ,  70 . However, if a higher proportion of the second FCC catalyst of small to medium pore zeolite is desired in the second FCC reactor  70  than the first FCC catalyst of large pore zeolite, replacement catalyst added to the second FCC reactor  70  may comprise a higher proportion of the second FCC catalyst. Because the second FCC catalyst does not lose activity as quickly as the first FCC catalyst, less of the second catalyst inventory must be forwarded to the catalyst regenerator  30  in line  90  from the second reactor vessel  80 , but more catalyst inventory may be recycled to the riser  74  in return conduit  76  without regeneration to maintain a high level of the second FCC catalyst in the second reactor  70 . 
     The second reactor riser  74  can operate in any suitable condition, such as a temperature of about 425° to about 705° C., preferably a temperature of about 550° to about 600° C., and a pressure of about 140 to about 400 kPa, preferably a pressure of about 170 to about 250 kPa. Typically, the residence time of the second reactor riser  74  can be less than about 3 seconds and preferably is less than about 1 second. Exemplary risers and operating conditions are disclosed in, e.g., US 2008/0035527 A1 and U.S. Pat. No. 7,261,807 B2. 
     Before cracked products can be fed to the oligomerization zone  130 , the light olefin stream in light olefin line  106  may require purification. Many impurities in the light olefin stream in light olefin line  106  can poison an oligomerization catalyst. Carbon dioxide and ammonia can attack acid sites on the catalyst. Sulfur containing compounds, oxygenates, and nitriles can harm oligomerization catalyst. Acetylenes and diolefins can polymerize and produce gums on the catalyst or equipment. Consequently, the light olefin stream which comprises the oligomerization feed stream in light olefin line  106  may be purified in an optional purification zone  110 . 
     The light olefin stream in light olefin line  106  may be introduced into an optional mercaptan extraction unit  112  to remove mercaptans to lower concentrations. In the mercaptan extraction unit  112 , the light olefin feed may be prewashed in an optional prewash vessel containing aqueous alkali to convert any hydrogen sulfide to sulfide salt which is soluble in the aqueous alkaline stream. The light olefin stream, now depleted of any hydrogen sulfide, is contacted with a more concentrated aqueous alkali stream in an extractor vessel. Mercaptans in the light olefin stream react with the alkali to yield mercaptides. An extracted light olefin stream lean in mercaptans passes overhead from the extraction column and may be mixed with a solvent that removes COS in route to an optional COS solvent settler. COS may be removed with the solvent from the bottom of the settler, while the overhead light olefin stream may be fed to an optional water wash vessel to remove remaining alkali and produce a sulfur depleted light olefin stream in line  114 . The mercaptide rich alkali from the extractor vessel receives an injection of air and a catalyst such as phthalocyanine as it passes from the extractor vessel to an oxidation vessel for regeneration. Oxidizing the mercaptides to disulfides using a catalyst regenerates the alkaline solution. A disulfide separator receives the disulfide rich alkaline from the oxidation vessel. The disulfide separator vents excess air and decants disulfides from the alkaline solution before the regenerated alkaline is drained, washed with oil to remove remaining disulfides and returned to the extractor vessel. Further removal of disulfides from the regenerated alkaline stream is also contemplated. The disulfides may be run through a sand filter and removed from the process. For more information on mercaptan extraction, reference may be made to U.S. Pat. No. 7,326,333 B2. 
     In order to prevent polymerization and gumming in the oligomerization reactor that can inhibit equipment and catalyst performance, it is desired to minimize diolefins and acetylenes in the light olefin feed in line  114 . Diolefin conversion to monoolefin hydrocarbons may be accomplished by selectively hydrogenating the sulfur depleted stream with a conventional selective hydrogenation reactor  116 . Hydrogen may be added to the purified light olefin stream in line  118 . 
     The selective hydrogenation catalyst can comprise an alumina support material preferably having a total surface area greater than 150 m 2 /g, with most of the total pore volume of the catalyst provided by pores with average diameters of greater than 600 angstroms, and containing surface deposits of about 1.0 to 25.0 wt % nickel and about 0.1 to 1.0 wt % sulfur such as disclosed in U.S. Pat. No. 4,695,560. Spheres having a diameter between about 0.4 and 6.4 mm ( 1/64 and ¼ inch) can be made by oil dropping a gelled alumina sol. The alumina sol may be formed by digesting aluminum metal with an aqueous solution of approximately 12 wt % hydrogen chloride to produce an aluminum chloride sol. The nickel component may be added to the catalyst during the sphere formation or by immersing calcined alumina spheres in an aqueous solution of a nickel compound followed by drying, calcining, purging and reducing. The nickel containing alumina spheres may then be sulfided. A palladium catalyst may also be used as the selective hydrogenation catalyst. 
     The selective hydrogenation process is normally performed at relatively mild hydrogenation conditions. These conditions will normally result in the hydrocarbons being present as liquid phase materials. The reactants will normally be maintained under the minimum pressure sufficient to maintain the reactants as liquid phase hydrocarbons which allow the hydrogen to dissolve into the light olefin feed. A broad range of suitable operating pressures therefore extends from about 276 (40 psig) to about 5516 kPa gauge (800 psig). A relatively moderate temperature between about 25° C. (77° F.) and about 350° C. (662° F.) should be employed. The liquid hourly space velocity of the reactants through the selective hydrogenation catalyst should be above 1.0 hr −1 . Preferably, it is between 5.0 and 35.0 hr −1 . The molar ratio of hydrogen to diolefinic hydrocarbons may be maintained between 1.5:1 and 2:1. The hydrogenation reactor is preferably a cylindrical fixed bed of catalyst through which the reactants move in a vertical direction. 
     A purified light olefin stream depleted of sulfur containing compounds, diolefins and acetylenes exits the selective hydrogenation reactor  116  in line  120 . The optionally sulfur and diolefin depleted light olefin stream in line  120  may be introduced into an optional nitrile removal unit (NRU) such as a water wash unit  122  to reduce the concentration of oxygenates and nitriles in the light olefin stream in line  120 . Water is introduced to the water wash unit in line  124 . An oxygenate and nitrile-rich aqueous stream in line  126  leaves the water wash unit  122  and may be further processed. A drier may follow the water wash unit  122 . Other NRU&#39;s may be used in place of the water wash unit. A NRU can consist of a group of regenerable beds that adsorb the nitriles and other nitrogen components from the diolefin depleted light olefin stream. Examples of NRU&#39;s can be found in U.S. Pat. No. 4,831,206, U.S. Pat. No. 5,120,881 and U.S. Pat. No. 5,271,835. 
     A purified light olefin oligomerization feed stream perhaps depleted of sulfur containing compounds, diolefins and/or oxygenates and nitriles is provided in oligomerization feed stream line  128 . The light olefin oligomerization feed stream in line  128  may be obtained from the cracked product stream in lines  46  and/or  86 , so it may be in downstream communication with the FCC zone  20  and/or the FCC recovery zone  100 . The oligomerization feed stream need not be obtained from a cracked FCC product stream but may come from another source such as from a paraffin dehydrogenation unit or a unit that converts oxygenates to olefins. The selective hydrogenation reactor  116  is in upstream communication with the oligomerization feed stream line  128 . The oligomerization feed stream may comprise C 4  hydrocarbons such as butenes, i.e., C 4  olefins, and butanes. Butenes include normal butenes and isobutene. The oligomerization feed stream in oligomerization feed stream line  128  may comprise C 5  hydrocarbons such as pentenes, i.e., C 5  olefins, and pentanes. Pentenes include normal pentenes and isopentenes. Typically, the oligomerization feed stream will comprise about 20 to about 80 wt % olefins and suitably about 40 to about 75 wt % olefins. In an aspect, about 55 to about 75 wt % of the olefins may be butenes and about 25 to about 45 wt % of the olefins may be pentenes. Up to as much as 10 wt %, suitably 20 wt %, typically 25 wt % and most typically 30 wt % of the oligomerization feed may be C 5  olefins. 
     The oligomerization feed line  128  feeds the oligomerization feed stream to an oligomerization zone  130  which may be in downstream communication with the FCC recovery zone  100 . The oligomerization feed stream in oligomerization feed line  128  may be mixed with recycle streams from line  225 ,  226  or  230  prior to entering the oligomerization zone  130  to provide a mixed oligomerization feed stream in a mixed oligomerization feed conduit  132 . An oligomerization zone  130  is in downstream communication with the mixed oligomerization feed conduit  132 . The ratio of recycle oligomerate from lines  225 ,  226  and  230  to the oligomerization feed from line  128  in the mixed oligomerization feed conduit  132  is about 1:1 to about 5:1. 
     In an aspect, an oligomerate recycle stream in oligomerate recycle line  230  to be described hereinafter may be mixed with the oligomerization feed stream in the oligomerization feed conduit line  128 . The oligomerization feed stream in the oligomerization feed conduit  132  may comprise about 10 to about 50 wt % olefins and suitably about 25 to about 40 wt % olefins if the oligomerate recycle stream from oligomerate return line  230  is mixed with the oligomerization feed stream. Accordingly, the oligomerization feed stream may comprise no more than about 38 wt % butene and in another aspect, the oligomerization feed stream may comprise no more than about 23 wt % pentene. The oligomerization feed stream to the oligomerization zone  130  in mixed oligomerization feed conduit  132  may comprise at least about 10 wt % butene, at least about 5 wt % pentene and preferably no more than about 1 wt % hexene. In a further aspect, the oligomerization feed stream may comprise no more than about 0.1 wt % hexene and no more than about 0.1 wt % propylene. At least about 40 wt % of the butene in the oligomerization feed stream may be normal butene. In an aspect, it may be that no more than about 70 wt % of the oligomerization feed stream is normal butene. At least about 40 wt % of the pentene in the oligomerization feed stream may be normal pentene. In an aspect, no more than about 70 wt % of the oligomerization feed stream in the mixed oligomerization feed conduit  132  may be normal pentene. 
     The oligomerization zone  130  comprises a first oligomerization reactor  138 . The first oligomerization reactor may be preceded by an optional guard bed for removing catalyst poisons that is not shown. The first oligomerization reactor  138  contains the oligomerization catalyst. An oligomerization feed stream may be preheated before entering the first oligomerization reactor  138  in an oligomerization zone  130 . The first oligomerization reactor  138  may contain a first catalyst bed  142  of oligomerization catalyst. The first oligomerization reactor  138  may be an upflow reactor to provide a uniform feed front through the catalyst bed, but other flow arrangements are contemplated. In an aspect, the first oligomerization reactor  138  may contain an additional bed or beds  144  of oligomerization catalyst. C 4  olefins in the oligomerization feed stream oligomerize over the oligomerization catalyst to provide an oligomerate comprising C 4  olefin dimers and trimers. C 5  olefins that may be present in the oligomerization feed stream oligomerize over the oligomerization catalyst to provide an oligomerate comprising C 5  olefin dimers and trimers and co-oligomerize with C 4  olefins to make C 9  olefins. The oligomerization produces other oligomers with additional carbon numbers. 
     Oligomerization effluent from the first bed  142  may optionally be quenched with a liquid such as recycled oligomerate before entering the additional bed  144 , and/or oligomerization effluent from the additional bed  144  of oligomerization catalyst may also be quenched with a liquid such as recycled oligomerate to avoid excessive temperature rise. The liquid oligomerate may also comprise oligomerized olefins that can react with the C 4  olefins and C 5  olefins in the feed and other oligomerized olefins if present to make diesel range olefins. Oligomerized product, also known as oligomerate, exits the first oligomerization reactor  138  in line  146 . 
     In an aspect, the oligomerization reactor zone may include one or more additional oligomerization reactors  150 . The oligomerization effluent may be heated and fed to the optional additional oligomerization reactor  150 . It is contemplated that the first oligomerization reactor  138  and the additional oligomerization reactor  150  may be operated in a swing bed fashion to take one reactor offline for maintenance or catalyst regeneration or replacement while the other reactor stays online. In an aspect, the additional oligomerization reactor  150  may contain a first bed  152  of oligomerization catalyst. The additional oligomerization reactor  150  may also be an upflow reactor to provide a uniform feed front through the catalyst bed, but other flow arrangements are contemplated. In an aspect, the additional oligomerization reactor  150  may contain an additional bed or beds  154  of oligomerization catalyst. Remaining C 4  olefins in the oligomerization feed stream oligomerize over the oligomerization catalyst to provide an oligomerate comprising C 4  olefin dimers and trimers. Remaining C 5  olefins, if present in the oligomerization feed stream, oligomerize over the oligomerization catalyst to provide an oligomerate comprising C 5  olefin dimers and trimers and co-oligomerize with C 4  olefins to make C 9  olefins. Over 90 wt % of the C 4  olefins in the oligomerization feed stream can oligomerize in the oligomerization zone  130 . Over 90 wt % of the C 5  olefins in the oligomerization feed stream can oligomerize in the oligomerization zone  130 . If more than one oligomerization reactor is used, conversion is achieved over all of the oligomerization reactors  138 ,  150  in the oligomerization zone  130 . 
     Oligomerization effluent from the first bed  152  may be quenched with a liquid such as recycled oligomerate before entering the additional bed  154 , and/or oligomerization effluent from the additional bed  154  of oligomerization catalyst may also be quenched with a liquid such as recycled oligomerate to avoid excessive temperature rise. The recycled oligomerate may also comprise oligomerized olefins that can react with the C 4  olefins and C 5  olefins in the feed and other oligomerized olefins to increase production of diesel range olefins. 
     An oligomerate conduit  156 , in downstream communication with the oligomerization zone  130 , withdraws an oligomerate stream from the oligomerization zone  130 . The oligomerate conduit  156  may be in downstream communication with the first oligomerization reactor  138  and the additional oligomerization reactor  150 . 
     The oligomerization zone  130  may contain an oligomerization catalyst. The oligomerization catalyst may comprise a zeolitic catalyst. The zeolite may comprise between 5 and 95 wt % of the catalyst. Suitable zeolites include zeolites having a structure from one of the following classes: MFI, MEL, SFV, SVR, ITH, IMF, TUN, FER, EUO, BEA, FAU, BPH, MEI, MSE, MWW, UZM-8, MOR, OFF, MTW, TON, MTT, AFO, ATO, and AEL. These three-letter codes for structure types are assigned and maintained by the International Zeolite Association Structure Commission in the  Atlas of Zeolite Framework Types , which is at http://www.iza-structure.org/databases/. In a preferred aspect, the oligomerization catalyst may comprise a zeolite with a framework having a ten-ring pore structure. Examples of suitable zeolites having a ten-ring pore structure include those comprising TON, MTT, MFI, MEL, AFO, AEL, EUO and FER. In a further preferred aspect, the oligomerization catalyst comprising a zeolite having a ten-ring pore structure may comprise a uni-dimensional pore structure. A uni-dimensional pore structure indicates zeolites containing non-intersecting pores that are substantially parallel to one of the axes of the crystal. The pores preferably extend through the zeolite crystal. Suitable examples of zeolites having a ten-ring uni-dimensional pore structure may include MTT. In a further aspect, the oligomerization catalyst comprises an MTT zeolite. 
     The oligomerization catalyst may be formed by combining the zeolite with a binder, and then forming the catalyst into pellets. The pellets may optionally be treated with a phosphoric reagent to create a zeolite having a phosphorous component between 0.5 and 15 wt % of the treated catalyst. The binder is used to confer hardness and strength on the catalyst. Binders include alumina, aluminum phosphate, silica, silica-alumina, zirconia, titania and combinations of these metal oxides, and other refractory oxides, and clays such as montmorillonite, kaolin, palygorskite, smectite and attapulgite. A preferred binder is an aluminum-based binder, such as alumina, aluminum phosphate, silica-alumina and clays. 
     One of the components of the catalyst binder utilized in the present invention is alumina. The alumina source may be any of the various hydrous aluminum oxides or alumina gels such as alpha-alumina monohydrate of the boehmite or pseudo-boehmite structure, alpha-alumina trihydrate of the gibbsite structure, beta-alumina trihydrate of the bayerite structure, and the like. A suitable alumina is available from UOP LLC under the trademark Versal. A preferred alumina is available from Sasol North America Alumina Product Group under the trademark Catapal. This material is an extremely high purity alpha-alumina monohydrate (pseudo-boehmite) which after calcination at a high temperature has been shown to yield a high purity gamma-alumina. 
     A suitable oligomerization catalyst is prepared by mixing proportionate volumes of zeolite and alumina to achieve the desired zeolite-to-alumina ratio. In an embodiment, about 5 to about 80, typically about 10 to about 60, suitably about 15 to about 40 and preferably about 20 to about 30 wt % MTT zeolite and the balance alumina powder will provide a suitably supported catalyst. A silica support is also contemplated. 
     Monoprotic acid such as nitric acid or formic acid may be added to the mixture in aqueous solution to peptize the alumina in the binder. Additional water may be added to the mixture to provide sufficient wetness to constitute a dough with sufficient consistency to be extruded or spray dried. Extrusion aids such as cellulose ether powders can also be added. A preferred extrusion aid is available from The Dow Chemical Company under the trademark Methocel. 
     The paste or dough may be prepared in the form of shaped particulates, with the preferred method being to extrude the dough through a die having openings therein of desired size and shape, after which the extruded matter is broken into extrudates of desired length and dried. A further step of calcination may be employed to give added strength to the extrudate. Generally, calcination is conducted in a stream of air at a temperature from about 260° C. (500° F.) to about 815° C. (1500° F.). The MTT catalyst is not selectivated to neutralize surface acid sites such as with an amine. 
     The extruded particles may have any suitable cross-sectional shape, i.e., symmetrical or asymmetrical, but most often have a symmetrical cross-sectional shape, preferably a spherical, cylindrical or polylobal shape. The cross-sectional diameter of the particles may be as small as 40 μm; however, it is usually about 0.635 mm (0.25 inch) to about 12.7 mm (0.5 inch), preferably about 0.79 mm ( 1/32 inch) to about 6.35 mm (0.25 inch), and most preferably about 0.06 mm ( 1/24 inch) to about 4.23 mm (⅙ inch). 
     In an embodiment, the oligomerization catalyst may be a solid phosphoric acid catalyst (SPA). The SPA catalyst refers to a solid catalyst that contains as a principal ingredient an acid of phosphorous such as ortho-, pyro- or tetraphosphoric acid. SPA catalyst is normally formed by mixing the acid of phosphorous with a siliceous solid carrier to form a wet paste. This paste may be calcined and then crushed to yield catalyst particles or the paste may be extruded or pelleted prior to calcining to produce more uniform catalyst particles. The carrier is preferably a naturally occurring porous silica-containing material such as kieselguhr, kaolin, infusorial earth and diatomaceous earth. A minor amount of various additives such as mineral talc, fuller&#39;s earth and iron compounds including iron oxide may be added to the carrier to increase its strength and hardness. The combination of the carrier and the additives preferably comprises about 15-30 wt % of the catalyst, with the remainder being the phosphoric acid. The additive may comprise about 3-20 wt % of the total carrier material. Variations from this composition such as a lower phosphoric acid content are possible. Further details as to the composition and production of SPA catalysts may be obtained from U.S. Pat. No. 3,050,472, U.S. Pat. No. 3,050,473 and U.S. Pat. No. 3,132,109. Feed to the oligomerization zone  130  containing SPA catalyst should be kept dry except in an initial start-up phase. 
     The oligomerization reaction conditions in the oligomerization reactors  138 ,  150  in the oligomerization zone  130  are set to keep the reactant fluids in the liquid phase. With liquid oligomerate recycle, lower pressures are necessary to maintain liquid phase. Operating pressures include between about 2.1 MPa (300 psia) and about 10.5 MPa (1520 psia), suitably at a pressure between about 2.1 MPa (300 psia) and about 6.9 MPa (1000 psia) and preferably at a pressure between about 2.8 MPa (400 psia) and about 4.1 MPa (600 psia). Lower pressures may be suitable if the reaction is kept in the liquid phase. 
     For the zeolite catalyst, the temperature of the oligomerization zone  130  expressed in terms of a maximum bed temperature is in a range between about 150° and about 300° C. If diesel oligomerate is desired, the bed temperature should between about 200° and about 250° C. and preferably between about 215° and about 245° C. or between about 220° and about 240° C. The weight hourly space velocity should be between about 0.5 and about 5 hr −1 . 
     For the SPA catalyst, the oligomerization temperature in the oligomerization zone  130  should be in a range between about 100° and about 250° C. and suitably between about 150° and about 200° C. The weight hourly space velocity (LHSV) should be between about 0.5 and about 5 hr −1 . 
     Across a single bed of oligomerization catalyst, the exothermic reaction will cause the temperature to rise. Consequently, the oligomerization reactor should be operated to allow the temperature at the outlet to be over about 25° C. greater than the temperature at the inlet. 
     The oligomerization zone  130  with the oligomerization catalyst can be run in high conversion mode of greater than 95% conversion of feed olefins to produce a high quality diesel product and gasoline product. Normal butene conversion can exceed about 80%. Additionally, normal pentene conversion can exceed about 80%. 
     We have found that when C 5  olefins are present in the oligomerization feed stream, they dimerize or co-dimerize with other olefins, but tend to mitigate further oligomerization over the zeolite with a 10-ring uni-dimensional pore structure. Best mitigation of further oligomerization occurs when the C 5  olefins comprise between about 15 and about 50 wt % and preferably between 20 or 40 of the olefins in the oligomerization feed. Consequently, the oligomerate stream in oligomerate conduit  156  may comprise less than about 80 wt % C 9 + hydrocarbons when C 5  olefins are present in the oligomerization feed at these proportions. Moreover, said oligomerate may comprise less than about 60 wt % C 12 + hydrocarbons when C 5  olefins are present in the oligomerization feed at these proportions. Furthermore, the net gasoline yield may be at least about 40 wt % when C 5  olefins are present in the oligomerization feed. 
     If diesel is desired, however, the oligomerization zone with the oligomerization catalyst can be operated to oligomerize light olefins; i.e., C 4  olefins, to distillate-range material by over 70 wt % yield per pass through the oligomerization zone  130 . In an aspect, at least about 70 wt % of the olefins in the oligomerization feed convert to C 9 + product oligomers boiling above about 150° C. (302° F.) cut point in a single pass through the oligomerization zone. The C 12 + oligomer from the oligomerization zone boiling above about 200° C. (392° F.) may have a cetane of at least 30 and preferably at least 40. 
     An oligomerization recovery zone  200  is in downstream communication with the oligomerization zone  130  and the oligomerate conduit  156 . The oligomerate conduit  156  removes the oligomerate stream from the oligomerization zone  130 . 
     In order to conduct an initial rough separation of a light stream comprising unreacted olefins from a heavy oligomerate stream comprising a C 6 + olefins, the oligomerate stream in the oligomerate conduit  156  may be heat exchanged and then flashed in a flash drum  180  to provide a light flash stream in a flash overhead line  182  comprising C 4  and perhaps C 5  hydrocarbons and a heavy flash stream in a flash bottoms line  184  comprising C 6 + olefinic hydrocarbons. The flash drum  180  is in downstream communication with the oligomerization zone  130 . The light flash line  182  from the flash drum  180  has an inlet  183  above an inlet  185  to the heavy flash line  184 . The light flash stream may be fractionated in the oligomerization recovery zone  200  to provide a product stream while the heavy flash stream bypasses a debutanizer column  210  and/or a depentanizer column  220  in the oligomerization recovery zone  200 . The temperature in the flash drum  180  may be between about 138° C. (280° F.) and about 250° C. (482° F.) and the pressure may be between about 2.8 MPa (gauge) (400 psig) and about 6.2 MPa (gauge) (900 psig). 
     The oligomerization recovery zone  200  may include a debutanizer column  210  which is a fractionation column in downstream communication with the light flash line  182 . The debutanizer column  210  fractionates the light flash oligomerate stream between vapor and liquid into a first vaporous oligomerate overhead light stream comprising C 4  olefins and hydrocarbons in a first overhead line  212  and a first liquid oligomerate product stream comprising C 5 + olefins and hydrocarbons in a first product line  214 . The first product line  214  may come from the bottom of the debutanizer column  210  and be a bottom line. When maximum production of distillate is desired, either to obtain diesel product or to recrack the diesel in the FCC zone  20  to make more propylene, the overhead pressure in the debutanizer column  210  may be between about 300 and about 700 kPa (gauge) and the bottom temperature may be between about 225° and about 300° C. When maximum production of gasoline is desired, the overhead pressure in the debutanizer column  210  may be between about 300 and about 700 kPa (gauge) and the bottom temperature may be between about 175° and about 225° C. 
     The first liquid oligomerate product stream in the first product line  214  may enter a surge drum via a route line  216  and a surge inlet line  234 . Some, all or none of the first liquid oligomerate product stream in the first product line  214  may be routed through the route line  216  as regulated by a control valve  216 ′. If the oligomerization feed in the oligomerization feed line  128  does not include substantial C 5  olefins, the control valve  216 ′ may be fully open and a control valve  218 ′ on a depentanizer feed line  218  may be completely shut, so all of the first liquid oligomerate product stream in the first product line  214  is routed in the rout line  216 . Consequently, the surge drum may be in downstream communication with the first product line  214 . 
     If substantial C 5  olefins are in the oligomerization feed in the oligomerization feed line  128 , the oligomerization recovery zone  200  may include a depentanizer column  220 . The depentanizer column  220  is a fractionation column in downstream communication with the light flash line  182  and the first product line  214 . The first liquid oligomerate product stream comprising C 5 + hydrocarbons may be fed in the first product line  214  and the depentanizer feed line  218  to the depentanizer column  220 . In such case, the control valve  218 ′ may be completely open and control valve  216 ′ may be completely shut, so all of the first liquid oligomerate product stream in the first product line  214  is fed to the depentanizer column  220  in the depentanizer feed line  218 . However, flow through both valves  216 ′ and  218 ′ is envisioned. 
     The depentanizer column  220  may be in downstream communication with the first product line  214  from said debutanizer column  210 . The depentanizer column  220  may fractionate the first liquid oligomerate product stream in the first product line  214  between vapor and liquid into an intermediate stream comprising C 5  olefins and hydrocarbons in an intermediate line  222  and a second liquid oligomerate product stream comprising C 6 + olefins in a second product line  224 . The second product line  224  may come from a bottom of the depentanizer column  220  and be a bottom line. When maximum production of distillate is desired, either to obtain diesel product or to recrack the diesel in the FCC zone  20  to make more propylene, the overhead pressure in the depentanizer column  220  may be between about 50 and about 100 kPa (gauge) and the bottom temperature may be between about 200° and about 275° C. When maximum production of gasoline is desired, the overhead pressure in the depentanizer column  220  may be between about 100 and about 500 kPa (gauge) and the bottom temperature may be between about 150° and about 225° C. 
     It is desired to maintain liquid phase in the oligomerization reactors. This can be achieved by saturating product olefins and recycling them to the oligomerization reactor as a liquid. However, if olefinic product is being recycled to either the FCC zone  20  or the oligomerization zone  130 , saturating olefins would inactivate the recycle feed. The oligomerization zone  130  can only further oligomerize olefinic recycle and the FCC zone  20  prefers olefinic feed to be further cracked to form propylene. Liquid phase may be maintained in the first oligomerization zone  130  by incorporating into the feed a C 4  stream and/or a C 5  stream from the oligomerization recovery zone  200 . 
     The light stream in overhead line  212  may comprise at least 70 wt % and suitably at least 90 wt % C 4  hydrocarbons which can be recycled if increased conversion of the light olefins is required. The overhead intermediate stream comprising C 4  hydrocarbons may have less than 10 wt % C 3  or C 5  hydrocarbons and preferably less than 1 wt % C 3  or C 5  hydrocarbons. 
     The light stream in the overhead line  212  may be condensed and recycled to the first oligomerization zone  130  as a first light recycle stream in a light recycle line  225  at a rate governed by control valve  225 ′. The light stream may comprise C 4  olefins that can oligomerize in the first oligomerization zone  130 . The butanes are easily separated from the heavier olefinic product such as in the debutanizer column  210 . The butane recycled to the oligomerization zone also dilutes the feed olefins to help limit the temperature rise within the oligomerization reactor due to the exothermicity of the reaction. 
     In an aspect, the light stream in the overhead line  212  comprising C 4  hydrocarbons may be split into a purge stream in purge line  229  and the light recycle stream comprising C 4  hydrocarbons in the light recycle line  225 . In an aspect, the light recycle stream in the light recycle line  225  taken from the light stream in the light line  212  is recycled to the first oligomerization zone  130  downstream of the selective hydrogenation reactor  116 . The light stream in the light line  212  and the light recycle stream in the light recycle line  225  should be understood to be condensed overhead streams. The recycle rate may be adjusted as necessary to maximize selectivity to gasoline range oligomer products. 
     The purge stream comprising C 4  hydrocarbons taken from the light stream may be purged from the process in line  229  to avoid C 4  build up in the process. The purge stream comprising C 4  hydrocarbons in line  229  may be subjected to further processing to recover useful components or be blended in the gasoline pool. 
     The intermediate stream in intermediate line  222  may comprise at least 70 wt % and suitably at least 90 wt % C 5  hydrocarbons which can then act as a solvent in the first oligomerization reactor zone  140  to maintain liquid phase therein. The overhead intermediate stream comprising C 5  hydrocarbons should have less than 10 wt % C 4  or C 6  hydrocarbons and preferably less than 1 wt % C 4  or C 6  hydrocarbons. 
     The intermediate stream may be condensed and recycled to the first oligomerization reactor zone  140  as a first intermediate recycle stream in an intermediate recycle line  226  at a rate governed by control valve  226 ′ to maintain the liquid phase in the oligomerization reactors  138 ,  150  operating in the first oligomerization zone  130 . The intermediate stream may comprise C 5  olefins that can oligomerize in the oligomerization zone. The C 5  hydrocarbon presence in the oligomerization zone maintains the oligomerization reactors at liquid phase conditions. The pentanes are easily separated from the heavier olefinic product such as in the depentanizer column  220 . The pentane recycled to the oligomerization zone also dilutes the feed olefins to help limit the temperature rise within the reactor due to the exothermicity of the reaction. 
     In an aspect, the intermediate stream in the intermediate line  222  comprising C 5  hydrocarbons may be split into a purge stream in purge line  228  and the first intermediate recycle stream comprising C 5  hydrocarbons in the first intermediate recycle line  226 . In an aspect, the first intermediate recycle stream in first intermediate recycle line  226  taken from the intermediate stream in the intermediate line  222  is recycled to the first oligomerization zone  130  downstream of the selective hydrogenation reactor  116 . The intermediate stream in intermediate line  222  and the first intermediate recycle stream in intermediate recycle line  226  should be understood to be condensed overhead streams. The recycle rate may be adjusted as necessary to maintain liquid phase in the oligomerization reactors and to control temperature rise, and/or to maximize selectivity to gasoline range oligomer products. 
     The purge stream comprising C 5  hydrocarbons taken from the intermediate stream may be purged from the process in line  228  to avoid C 5  paraffin build up in the process. The purge stream comprising C 5  hydrocarbons in line  228  may be subjected to further processing to recover useful components or be blended in the gasoline pool. 
     We have found that dimethyl sulfide boils with the C 5  hydrocarbons and deactivates the unidimensional, 10-ring pore structured zeolite which may be the oligomerization catalyst. The mercaptan extraction unit  112  may not remove sufficient dimethyl sulfide to avoid deactivating the oligomerization catalyst. Consequently, recycle of C 5  hydrocarbons to the oligomerization zone  130  with oligomerization catalyst may be avoided by keeping valve  226 ′ shut unless sufficient dimethyl sulfide can be successfully removed from the oligomerate stream or the oligomerization catalyst is not a unidimensional, 10-ring pore structured zeolite. However, the dimethyl sulfide does not substantially harm the solid phosphoric acid catalyst, so recycle of C 5  hydrocarbons to the oligomerization zone  130  is suitable if SPA is the oligomerization catalyst. 
     Bypassing heavy oligomerate around the debutanizer column  210  and the optional depentanizer column  220  enables the bottoms temperature to be diminished because relatively lighter material must be reboiled which can be achieved at a lower temperature and smaller heater duty in the debutanizer column  210  and the optional depentanizer column  220 . 
     At least a first portion of the heavy oligomerate flash stream in the heavy flash line  184  may be recycled to the oligomerization zone  130 . The heavy oligomerate flash stream comprising C 6 + olefins in heavy flash line  184  may enter a process line  192  via a heavy inlet line  186 . At least a first portion of the heavy flash oligomerate stream in a process line  192  may be taken as a recycle oligomerate stream in recycle oligomerate line  230  to the oligomerization zone  130 . Consequently, the oligomerization zone  130  is in downstream communication with the heavy flash line  184  of the flash drum  180 . Moreover, the process line  192  may be in downstream communication with the heavy flash line  184 . The heavy flash oligomerate stream in the process line  192  may have greater than 10 wt % C 10  isoolefins. Flow through recycle oligomerate line  230  can be regulated by control valve  230 ′. Recycle of the heavy oligomerate from the flash drum  180  to the oligomerization zone  130  lowers utility expenses and lowers the required capacity of the debutanizer column  210  and the depentanizer column  220  because the heavy oligomerate bypasses the debutanizer column  210  and the depentanizer column  220 . Flow of the heavy oligomerate flash stream from the heavy inlet line  186  to the process line  192  may be through an optional surge drum  190 . 
     In an aspect, the process line  192  may be in downstream communication with the first product line  214  via route line  216  and a product inlet line  234 . The process line  192  may also be in downstream communication with the second product line  224  via the product inlet line  234 . At least a first portion of the first liquid oligomerate product stream and/or the second liquid oligomerate product stream may be recycled in the process line  192  and the recycle oligomerate line  230  to the oligomerization zone  130 . Flow of at least a portion of the first liquid oligomerate product stream from the first product line  214  via route line  216  and a product inlet line  234  and/or the second liquid oligomerate product stream from the second product line  224  via the product inlet line  234  to the process line  192  may be through an optional surge drum  190 . 
     In an aspect, the first liquid oligomerate product stream and/or the second liquid oligomerate product stream may be mixed with the heavy oligomerate flash stream to provide a mixed stream in the process line  192 . At least a first portion of this resulting mixed stream in the process line  192  may be recycled to the oligomerization feed line  132  of the oligomerization zone  130  through the recycle oligomerate line  230 . Consequently, the oligomerization zone  130  is in downstream communication with the heavy flash line  184  of the flash drum  180  and/or the first liquid oligomerate product stream in the first product line  214  from the debutanizer column  210  and/or the second liquid oligomerate product stream in the second product line  224  from the depentanizer column  220 . 
     In an aspect, the first liquid oligomerate product stream and/or the second liquid oligomerate product stream may be mixed with the heavy oligomerate flash stream in the optional surge drum  190  and exit the surge drum in the process line  192 . Additionally, the oligomerization zone  130  may be in downstream communication with the surge drum  190 . It is contemplated that a surge drum  190  need not be used to mix these streams, but that mixing may be achieved in the heavy inlet line  186 , the product inlet line  234  and the process line  192 . 
     The recycle oligomerate product stream comprising C 6 + olefins serves to maintain liquid phase in the oligomerization zone  130  and provides olefins that can oligomerize to heavier diesel range olefins. In this embodiment, the oligomerization zone  130  is in downstream communication with the first product line  214  of the debutanizer column  210  and perhaps the second product line  224  of the depentanizer column  220 . In a further aspect, the recycle oligomerate product line  230  is in downstream communication with the oligomerization zone  130 . Consequently, the oligomerization zone  130  is in upstream and downstream communication with the first product line  214 , the second product line  224  and the recycle oligomerate line  230 . 
     A second portion of the heavy oligomerate flash stream from heavy flash line  184  may be processed as a heavy product stream in a heavy product line  196 . In an aspect, a second portion of the first liquid oligomerate product stream from the first product line  214  and/or the second liquid oligomerate product stream from the second product line  224  may be processed as a heavy product stream in the heavy product line  196 . In a further aspect, when the heavy oligomerate flash stream and the liquid oligomerate product stream are mixed together to provide a mixed stream in process line  192 , a second portion of the mixed stream may be processed as the heavy product stream in the heavy product line  196 . 
     By recycling the recycle oligomerate product stream in the recycle oligomerate product line  230  from the first portion of the process stream in the process line  192  from which a second portion can be taken in heavy product line  196 , an accumulation of heavy material in the recycle oligomerate product line  230  is avoided. Heavy material can be taken downstream in the heavy product line  196  to avoid accumulation in the recycle oligomerate product stream. Recycle of the recycle oligomerate product stream directly from heavy flash line  184  would not prevent accumulation of heavy material in the recycle oligomerate product line  230 . If a refiner desires to make additional propylene in the FCC unit  20 , a portion of the heavy product stream or the mixed stream in the heavy product line  196  comprising  C6 + olefins may be recycled to the FCC unit  20  in the FCC recycle line  280  as an FCC recycle oligomerate stream. The FCC recycle oligomerate stream may be taken from the heavy product stream or the mixed stream in the heavy product line  196 . A control valve  280 ′ on the FCC recycle line  280  may be open if recycle of the heavy product stream or the mixed stream to the FCC zone  20  is desired. In an aspect, the FCC recycle stream in the FCC recycle line  280  is in downstream communication with the FCC recovery zone  200 . In a further aspect, the FCC recycle line  280  is in downstream communication with the oligomerization zone  130 . Hence, in an aspect, the FCC zone  20  is in upstream and downstream communication with oligomerization zone  130  and/or the FCC recovery zone  100 . In a still further aspect, FCC recycle line  280  is in upstream communication with the FCC zone  20  to recycle heavy oligomerate for fluid catalytic cracking down to propylene or other light olefins. Lastly, the FCC zone  20  may be in downstream communication with the heavy flash line  184  and/or the first product line  214  and/or the second product line  224  and the process line  192 . 
     If the FCC zone  20  comprises a single reactor riser  26 , the first reactor riser  26  may be in downstream communication with the hydrocarbon feed line  24  and the FCC recycle line  280 . If the FCC zone  20  comprises the first reactor riser  26  and a second reactor riser  74 , the first reactor riser  26  may be in downstream communication with the hydrocarbon feed line  24  and the second reactor riser  74  may be in downstream communication with the FCC recycle line  280 . 
     We have found that C 6 + oligomerate and distillate-range oligomerate subjected to FCC is converted best over a blend of medium or smaller pore zeolite blended with a large pore zeolite such as Y zeolite as explained previously with respect to the FCC zone  20 . Additionally, oligomerate produced over the oligomerization catalyst in the oligomerization zone  130  provides an excellent feed to the FCC zone that can be cracked to yield greater quantities of propylene. 
     In an embodiment in which the oligomerization catalyst is SPA in the oligomerization zone  130  for oligomerizing C 4  olefins or a mixed C 4  and C 5  olefin stream, we have found that a gasoline product stream can be provided in the heavy product line  196 . The SPA catalyst minimizes the formation of C 12 + species with either a C 4  olefin or C 4  and C 5  olefin feed. Consequently, even when heavier olefins than C 4  olefins are present in the oligomerization feed stream, the SPA catalyst manages to keep C 12 + olefins present in the liquid oligomerate bottom product stream in the second product line  224  below less than about 20 wt % even when over 85 wt % of feed olefins are converted and particularly when over 90 wt % of C 4  olefins are converted to oligomerate. 
     Consequently, a gasoline oligomerate product stream may be collected from the heavy product stream in a gasoline oligomerate product line  250  and blended in the gasoline pool. The gasoline oligomerate product line  250  may be in upstream communication with a gasoline tank  252  or a gasoline blending line of a gasoline pool. However, further treatment such as partial or full hydrogenation to reduce olefinicity may be contemplated. In such a case, a control valve  250 ′ may be all or partially opened to allow C 6 + gasoline product to be sent to the gasoline tank  252  or the gasoline blending line. 
     In another aspect, a distillate separator feed stream may be taken in a distillate feed line  232  from the second portion of the heavy oligomerate flash stream from heavy flash line  184  in heavy product line  196 . In an additional aspect, a distillate separator feed stream may be taken in a distillate feed line  232  from the second portion of the first liquid oligomerate product stream from the first product line  214  and/or the second liquid oligomerate product stream from the second product line  224  in the heavy product line  196 . In a further aspect, when the heavy oligomerate flash stream and the liquid oligomerate product stream are mixed together to provide a mixed stream in process line  192 , a distillate separator feed stream may be taken in a distillate feed line  232  from the second portion of the mixed stream in the heavy product line  196 . Flow through the distillate feed line  232  can be regulated by control valve  232 ′. 
     The oligomerization recovery zone  200  may also include a distillate separator column  240  to which the heavy product stream comprising oligomerate C 6 + hydrocarbons may be fed in distillate feed line  232  taken from the heavy product line  196  for further separation. The distillate separator column  240  is in downstream communication with the first product line  214  of the debutanizer column  210 , the second product line  224  of the depentanizer column  220 , the heavy flash line  184  and/or the process line  192 . 
     The distillate separator column  240  separates the distillate separator oligomerate feed stream into an gasoline overhead stream in an overhead line  242  comprising C 6 , C 7 , C 8 , C 9 , C 10  and/or C 11  olefins and a bottom distillate stream comprising C 8 +, C 9 +, C 10 +, C 11 +, or C 12 + olefins in a diesel bottom line  244 . When maximum production of distillate is desired, the overhead pressure in the distillate separator column  240  may be between about 10 and about 60 kPa (gauge) and the bottom temperature may be between about 225° and about 275° C. When maximum production of gasoline is desired, the overhead pressure in the distillate separator column  240  may be between about 10 and about 60 kPa (gauge) and the bottom temperature may be between about 190° and about 250° C. The bottom temperature can be adjusted between about 175° and about 275° C. to adjust the bottom product between a C 9 + olefin cut and a C 12 + olefin cut based on the heaviness of the diesel cut desired by the refiner. The diesel bottoms stream in diesel bottoms line  244  may have greater than 30 wt % C 9 + isoolefins. 
     In an aspect, the gasoline overhead stream in gasoline overhead line  242  may be recovered as product in product gasoline line  248  in downstream communication with the recovery zone  200 . The gasoline product stream may be subjected to further processing to recover useful components or blended in the gasoline pool. The gasoline product line  248  may be in upstream communication with a gasoline tank  252  or a gasoline blending line of a gasoline pool. In this aspect, the overhead line  242  of the distillate separator column  240  may be in upstream communication with the gasoline tank  252  or the gasoline blending line. 
     In an aspect, the diesel product stream may be recovered as product in a diesel bottom line  244  in downstream communication with the oligomerization recovery zone  200 . The diesel product stream may be subjected to further processing to recover useful components or blended in the diesel pool. The diesel bottom line  244  may be in upstream communication with a diesel tank  264  or a diesel blending line of a diesel pool. Additionally, LCO from LCO line  107  may also be blended with diesel in diesel bottom line  244 . 
     Flow through the recycle oligomerate line  230 , the FCC recycle line  280 , the distillate feed line  232  and the gasoline oligomerate product line  250  can be regulated by control valves  230 ′,  280 ′,  232 ′ and  250 ′, respectively, such that flow through each line can be shut off or allowed irrespective of the other lines. 
     In an aspect, a bypass line  194  may be in downstream communication with the heavy flash line  184 . Flow of the heavy flash stream through the bypass line is regulated by a control valve  194 ′. At least a portion of the heavy flash oligomerate stream may be bypassed around the process line  192  and the surge drum  190  to avoid recycling at least some of the heavy flash oligomerate to the oligomerization zone  130  and mixing the heavy flash oligomerate with the first liquid oligomerate product stream from first product line  214  and/or the second oligomerate product stream in the second product line  224  before the first portion of the first liquid oligomerate product stream and the second oligomerate product stream is recycled to the oligomerization zone  130 . The heavy flash oligomerate will have a larger molecular weight than the first oligomerate product stream and/or the second oligomerate product stream. Hence, bypass of the heavy flash oligomerate stream in bypass line  194  will decrease the molecular weight of the recycle oligomerate stream in recycle oligomerate line  230  to the oligomerization zone  130 . Consequently, the oligomerization to heavy oligomer in the oligomerization zone  130  is minimized because lighter oligomerate is present in the oligomerate recycle stream in recycle line  230 . The bypass line  194  may be out of upstream communication with the oligomerate recycle line  230  but may be in upstream communication with the FCC recycle line  280 , the distillate feed line  232  and the gasoline oligomerate product line  250 . Accordingly, they bypass line  194  may feed the bypassed portion of the heavy flash oligomerate as FCC recycle stream to the FCC zone  20  and/or as the distillate separator feed stream to the distillate separator column  240  and/or as to the gasoline tank  252  or a gasoline blending line of a gasoline pool. 
     The invention will now be further illustrated by the following non-limiting examples. 
     EXAMPLES 
     Example 1 
     Feed 1 in Table 2 was contacted with four catalysts to determine their effectiveness in oligomerizing butenes. 
     
       
         
               
               
               
             
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Component 
                 Fraction, wt % 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 propylene 
                 0.1 
               
               
                   
                 Iso-C 4 &#39;s 
                 70.04 
               
               
                   
                 isobutylene 
                 7.7 
               
               
                   
                 1-butene 
                 5.7 
               
               
                   
                 2-butene (cis and trans) 
                 16.28 
               
               
                   
                 3-methyl-1-butene 
                 0.16 
               
               
                   
                 acetone 
                 0.02 
               
               
                   
                 Total 
                 100 
               
               
                   
                   
               
             
          
         
       
     
     Catalyst A is an MTT catalyst purchased from Zeolyst having a product code Z2K019E and extruded with alumina to be 25 wt % zeolite. Of MTT zeolite powder, 53.7 grams was combined with 2.0 grams Methocel and 208.3 grams Catapal B boehmite. These powders were mixed in a muller before a mixture of 18.2 g HNO 3  and 133 grams distilled water was added to the powders. The composition was blended thoroughly in the muller to effect an extrudable dough of about 52% LOI. The dough then was extruded through a die plate to form cylindrical extrudates having a diameter of about 3.18 mm. The extrudates then were air dried, and calcined at a temperature of about 550° C. The MTT catalyst was not selectivated to neutralize surface acid sites such as with an amine. 
     Catalyst B is a SPA catalyst commercially available from UOP LLC. 
     Catalyst C is an MTW catalyst with a silica-to-alumina ratio of 36:1. Of MTW zeolite powder made in accordance with the teaching of U.S. Pat. No. 7,525,008 B2, 26.4 grams was combined with and 135.1 grams Versal 251 boehmite. These powders were mixed in a muller before a mixture of 15.2 grams of nitric acid and 65 grams of distilled water were added to the powders. The composition was blended thoroughly in the muller to effect an extrudable dough of about 48% LOI. The dough then was extruded through a die plate to form cylindrical extrudates having a diameter of about 1/32″. The extrudates then were air dried and calcined at a temperature of about 550° C. 
     Catalyst D is an MFI catalyst purchased from Zeolyst having a product code of CBV-8014 having a silica-to-alumina ratio of 80:1 and extruded with alumina at 25 wt % zeolite. Of MFI-80 zeolite powder, 53.8 grams was combined with 205.5 grams Catapal B boehmite and 2 grams of Methocel. These powders were mixed in a muller before a mixture of 12.1 grams nitric acid and 115.7 grams distilled water were added to the powders. The composition was blended thoroughly in the muller, then an additional 40 grams of water was added to effect an extrudable dough of about 53% LOI. The dough then was extruded through a die plate to form cylindrical extrudates having a diameter of about 3.18 mm. The extrudates then were air dried, and calcined at a temperature of about 550° C. 
     The experiments were operated at 6.2 MPa and inlet temperatures at intervals between 160° and 240° C. to obtain different normal butene conversions. Results are shown in  FIGS. 2 and 3 . In  FIG. 2 , C 8  to C 11 olefin selectivity is plotted against normal butene conversion to provide profiles for each catalyst. 
     Table 3 compares the RONC±3 for each product by catalyst and provides a key to  FIG. 3 . The SPA catalyst B is superior, but the MTT catalyst A is the least effective in producing gasoline range olefins. 
     
       
         
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 Catalyst 
                 RONC 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 A 
                 MTT 
                 circles 
                 92 
               
               
                   
                 B 
                 SPA 
                 diamonds 
                 96 
               
               
                   
                 C 
                 MTW 
                 triangles 
                 97 
               
               
                   
                 D 
                 MFI-80 
                 asterisks 
                 95 
               
               
                   
                   
               
             
          
         
       
     
     The SPA catalyst was able to achieve over 95 wt % yield of gasoline having a RONC of &gt;95 and with an Engler T90 value of 185° C. for the entire product. The T-90 gasoline specification is less than 193° C. 
     In  FIG. 3 , C 12 + olefin selectivity is plotted against normal butene conversion to provide profiles for each catalyst. Table 4 compares the derived cetane number±2 for each product by catalyst and provides a key to  FIG. 3 . 
     
       
         
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                 Catalyst 
                 Cetane 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 A 
                 MTT 
                 circles 
                 41 
               
               
                   
                 B 
                 SPA 
                 diamonds 
                 &lt;14 
               
               
                   
                 C 
                 MTW 
                 triangles 
                 28 
               
               
                   
                 D 
                 MFI-80 
                 asterisks 
                 36 
               
               
                   
                   
               
             
          
         
       
     
       FIG. 3  shows that the MTT catalyst provides the highest C 12 + olefin selectivity which reaches over 70 wt %. These selectivities are from a single pass of the feed stream through the oligomerization reactor. Additionally, the MTT catalyst provided C 12 + oligomerate with the highest derived cetane. Cetane was derived using ASTM D6890 on the C 12 + fraction at the 204° C. (400° F.) cut point. Conversely to gasoline selectivity, the MTT catalyst A is superior, but the SPA catalyst B is the least effective in producing diesel range olefins. 
     The MTT catalyst was able to produce diesel with a cetane rating of greater than 40. The diesel cloud point was determined by ASTM D2500 to be −66° C. and the T90 was 319° C. using ASTM D86 Method. The T90 specification for diesel in the United States is between 282 and 338° C., so the diesel product meets the U.S. diesel standard. 
     Example 2 
     Two types of feed were oligomerized over oligomerization catalyst A of Example 1, MTT zeolite. Feeds 1 and 2 contacted with catalyst A are shown in Table 4. Feed 1 is from Example 1. 
     
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 4 
               
               
                   
                   
               
               
                   
                   
                 Feed 1 
                 Feed 2 
               
               
                   
                 Component 
                 Fraction, wt % 
                 Fraction, wt % 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 propylene 
                 0.1 
                 0.1 
               
               
                   
                 isobutane 
                 70.04 
                 9.73 
               
               
                   
                 isobutylene 
                 7.7 
                 6.3 
               
               
                   
                 1-butene 
                 5.7 
                 4.9 
               
               
                   
                 2-methyl-2-butene 
                 0 
                 9.0 
               
               
                   
                 2-butene (cis &amp; trans) 
                 16.28 
                 9.8 
               
               
                   
                 3-met-1-butene 
                 0.16 
                 0.16 
               
               
                   
                 n-hexane 
                 0 
                 60 
               
               
                   
                 acetone 
                 0.02 
                 0.01 
               
               
                   
                 Total 
                 100 
                 100 
               
               
                   
                   
               
             
          
         
       
     
     In Feed 2, C 5  olefin is made up of 2-methyl-2-butene and 3-methyl-1-butene which comprises 9.16 wt % of the reaction mixture representing about a third of the olefins in the feed. 3-methyl-1-butene is present in both feeds in small amounts. Propylene was present at less than 0.1 wt % in both feeds. 
     The reaction conditions were 6.2 MPa and a 1.5 WHSV. The maximum catalyst bed temperature was 220° C. Oligomerization achievements are shown in Table 5. 
     
       
         
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 5 
               
               
                   
                   
               
               
                   
                 Feed 1 
                 Feed 2 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Inlet Temperature, ° C. 
                 192 
                 198 
               
               
                   
                 C 4  olefin conversion, % 
                 98 
                 99 
               
               
                   
                 nC 4  olefin conversion, % 
                 97 
                 99 
               
               
                   
                 C 5  olefin conversion, % 
                 n/a 
                 95 
               
               
                   
                 C 5 -C 7  selectivity, wt % 
                 3 
                 5 
               
               
                   
                 C 8 -C 11  selectivity, wt % 
                 26 
                 40 
               
               
                   
                 C 12 -C 15  selectivity, wt % 
                 48 
                 40 
               
               
                   
                 C 16 + selectivity, wt % 
                 23 
                 16 
               
               
                   
                 Total C 9 + selectivity, wt % 
                 78 
                 79 
               
               
                   
                 Total C 12 + selectivity, wt % 
                 71 
                 56 
               
               
                   
                 Net gasoline yield, wt % 
                 35 
                 44 
               
               
                   
                 Net distillate yield, wt % 
                 76 
                 77 
               
               
                   
                   
               
             
          
         
       
     
     Normal C 4  olefin conversion reached 99% with C 5  olefins in Feed 2 and was 97 wt % without C 5  olefins in Feed 1. C 5  olefin conversion reached 95%. With C 5  olefins in Feed 2, it was expected that a greater proportion of heavier, distillate range olefins would be made. However, the Feed 2 with C 5  olefins oligomerized to a greater selectivity of lighter, gasoline range product in the C 5 -C 7  and C 8 -C 11  range and a smaller selectivity to heavier distillate range product in the C 12 -C 15  and C 16 + range. 
     This surprising result indicates that by adding C 5  olefins to the feed, a greater yield of gasoline can be made over Catalyst A, MTT. This is confirmed by the greater net yield of gasoline and the lower selectivity to C 12 + fraction for Feed 2 than for Feed 1. Also, but not to the same degree, by adding C 5  olefins to the feed, a greater yield of distillate range material can be made. This is confirmed by the greater net yield of distillate for Feed 2 than for Feed 1 on a single pass basis. Gasoline yield was classified by product meeting the Engler T90 requirement and distillate yield was classified by product boiling over 150° C. (300° F.). 
     Example 3 
     Three types of feed were oligomerized over oligomerization catalyst B of Example 1, SPA. The feeds contacted with catalyst B are shown in Table 6. Feed 2 is the same as Feed 2 in Example 2. Normal hexane and isooctane were used as heavy paraffin solvents with Feeds 2 and 3, respectively. All feeds had similar C 4  olefin levels and C 4  olefin species distributions. Feed 4 is similar to Feed 2 but has the pentenes evenly split between iso- and normal pentenes, which is roughly expected to be found in an FCC product, and Feed 4 was diluted with isobutane instead of n-hexane. 
     
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 6 
               
               
                   
               
               
                   
                 Feed 2 
                 Feed 3 
                 Feed 4 
               
               
                 Component 
                 Fraction, wt % 
                 Fraction, wt % 
                 Fraction, wt % 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 propylene 
                 0.1 
                 0.08 
                 0.1 
               
               
                 1,3-butadiene 
                 0 
                 0.28 
                 0 
               
               
                 isobutane 
                 9.73 
                 6.45 
                 69.72 
               
               
                 isobutylene 
                 6.3 
                 7.30 
                 6.3 
               
               
                 1-butene 
                 4.9 
                 5.07 
                 4.9 
               
               
                 2-methyl-2-butene 
                 9.0 
                 0 
                 4.5 
               
               
                 2-butene (cis &amp; trans) 
                 9.8 
                 11.33 
                 9.8 
               
               
                 3-met-1-butene 
                 0.16 
                 0.16 
                 0.16 
               
               
                 2-pentene 
                 0 
                 0 
                 4.5 
               
               
                 cyclopentane 
                 0 
                 0.28 
                 0 
               
               
                 n-hexane 
                 60 
                 0 
                 0 
               
               
                 isooctane 
                 0 
                 60.01 
                 0 
               
               
                 acetone 
                 0.01 
                 0.01 
                 0.02 
               
               
                 Total 
                 100 
                 100 
                 100 
               
               
                   
               
             
          
         
       
     
     The reaction pressure was 3.5 MPa. Oligomerization process conditions and testing results are shown in Table 7. 
     
       
         
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 7 
               
               
                   
                   
               
               
                   
                 Feed 2 
                 Feed 3 
                 Feed 4 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 WHSV, hr −1   
                 .75 
                 1.5 
                 .75 
               
               
                   
                 Pressure, MPa 
                 3.5 
                 3.5 
                 6.2 
               
               
                   
                 Inlet Temperature, ° C. 
                 190 
                 170 
                 178 
               
               
                   
                 Maximum Temperature, ° C. 
                 198 
                 192 
                 198 
               
               
                   
                 Total C 4  olefin conversion, % 
                 95 
                 92 
                 93 
               
               
                   
                 n-butene conversion, % 
                 95 
                 90 
                 93 
               
               
                   
                 Total C 5  olefin conversion, % 
                 90 
                 n/a 
                 86 
               
               
                   
                 C 5 -C 7  selectivity, wt % 
                 8 
                 5 
                 8 
               
               
                   
                 C 8 -C 11  selectivity, wt % 
                 77 
                 79 
                 77 
               
               
                   
                 C 12 -C 15  selectivity, wt % 
                 15 
                 16 
                 15 
               
               
                   
                 C 16 + selectivity, wt % 
                 0.3 
                 0.1 
                 .01 
               
               
                   
                 Total C 9 + selectivity, wt % 
                 35 
                 20 
                 25 
               
               
                   
                 Total C 12 + selectivity, wt % 
                 17 
                 16 
                 15 
               
               
                   
                 Net gasoline yield, wt % 
                 94 
                 92 
                 91 
               
               
                   
                 Net distillate yield, wt % 
                 32 
                 18 
                 23 
               
               
                   
                 RONC (±3) 
                 97 
                 96 
                 96 
               
               
                   
                 Engler T-90, ° C. 
                 182 
                 164 
                 182 
               
               
                   
                   
               
             
          
         
       
     
     Net gasoline yield goes up to C 12 − hydrocarbons and net distillate yield goes down to C 9 + hydrocarbons to account for different cut points that may be selected by a refiner. Olefin conversion was at least 90% and normal butene conversion was over 90%. Normal butene conversion reached 95% with C 5  olefins in Feed 2 and was 90% without C 5  olefins in Feed 3. C 5  olefin conversion reached 90% but was less when both iso- and normal C 5  olefins were in Feed 4. 
     It can be seen that the SPA catalyst minimized the formation of C 12 + species to below 20 wt %, specifically, at 16 and 17 wt %, respectively, for feeds containing C 4  olefins or mixtures of C 4  and C 5  olefins in the oligomerization feed stream. When normal C 5  olefins were added, C 12 + formation reduced to 15 wt %. The C 6 + oligomerate produced by all three feeds met the gasoline T-90 spec indicating that 90 wt % boiled at temperatures under 193° C. (380° F.). The Research Octane Number for all three products was high, over 95, with and without substantial C 5  olefins present. 
     Example 4 
     Feed 2 with C 5  olefins present was subjected to oligomerization with Catalyst B, SPA, at different conditions to obtain different butene conversions. C 5  olefin is made up of 2-methyl-2-butene and 3-methyl-1-butene which comprises 9.16 wt % of the reaction mixture representing about a third of the olefins in the feed. Propylene was present at less than 0.1 wt %. Table 8 shows the legend of component olefins illustrated in  FIG. 4 . 
     
       
         
               
               
               
             
           
               
                   
                 TABLE 8 
               
               
                   
                   
               
               
                   
                 Component 
                 Symbols in FIG. 4 
               
               
                   
                   
               
             
             
               
                   
                 isobutylene 
                 Circle 
               
               
                   
                 1-butene 
                 Triangle 
               
               
                   
                 2-methyl-2-butene and 
                 Diamond 
               
               
                   
                 3-met-1-butene 
               
               
                   
                 2-butene (cis &amp; trans) 
                 Asterisk 
               
               
                   
                   
               
             
          
         
       
     
       FIG. 4  shows conversions for each of the olefins in Feed 2 over Catalyst B, SPA. Over 95% conversion of normal C 4  olefins was achieved at over 90% total butene conversion. Pentene conversion reached 90% at over 90% total butene conversion. Normal butene conversion actually exceeded isobutene conversion at high butene conversion over about 95%. 
     Example 5 
     Three feeds were oligomerized to demonstrate the ability of Catalyst A, MTT, to produce diesel range oligomerate by recycling gasoline range oligomerate to the oligomerization zone. Feed 1 from Example 1 with an isobutane diluent was tested along with Feed 5 which had a normal hexane diluent and Feed 6 which had an isobutane diluent but spiked with diisobutene to simulate the recycle of gasoline range oligomers to the reactor feed. The feeds are shown in Table 9. The symbols in  FIG. 5  correspond to those indicated in the last row of Table 9. 
     
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 9 
               
               
                   
               
               
                   
                 Feed 1 
                 Feed 5 
                 Feed 6 
               
               
                 Component 
                 Fraction, wt % 
                 Fraction, wt % 
                 Fraction, wt % 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 propylene 
                 0.1 
                 0.08 
                 0.08 
               
               
                 isobutane 
                 70.04 
                 15.75 
                 15.75 
               
               
                 isobutylene 
                 7.7 
                 7.3 
                 7.3 
               
               
                 1-butene 
                 5.7 
                 5.1 
                 5.1 
               
               
                 2-butene (cis &amp; trans) 
                 16.28 
                 11.6 
                 11.6 
               
               
                 3-met-1-butene 
                 0.16 
                 0.16 
                 0.16 
               
               
                 n-hexane 
                 0 
                 60 
                 0 
               
               
                 acetone 
                 0.02 
                 0.01 
                 0.01 
               
               
                 tert-butyl alcohol 
                 0 
                 0.0008 
                 0.0008 
               
               
                 diisobutene 
                 0 
                 0 
                 60 
               
               
                 Total 
                 100 
                 100 
                 100 
               
               
                 FIG. 5 symbol 
                 square 
                 diamond 
                 asterisk 
               
               
                   
               
             
          
         
       
     
     The oligomerization conditions included 6.2 MPa pressure, 0.75 WHSV over Catalyst A, MTT. Normal butene conversion as a function of temperature is graphed in  FIG. 5  for the three feeds. 
       FIG. 5  demonstrates that Feed 6 with the diisobutene oligomer has greater normal butene conversion at equivalent temperatures between 180° and 240° C. Consequently, gasoline oligomerate recycle to the oligomerization zone will improve normal butene conversion. Butene conversion for Feed 5 is shown in  FIG. 6  and for Feed 6 is shown in  FIG. 7 . The key for  FIGS. 6 and 7  is shown in Table 10. 
     
       
         
               
               
               
             
           
               
                   
                 TABLE 10 
               
               
                   
                   
               
               
                   
                 Component 
                 Symbols in FIGS. 6 &amp; 7 
               
               
                   
                   
               
             
             
               
                   
                 isobutylene 
                 Circle 
               
               
                   
                 1-butene 
                 Triangle 
               
               
                   
                 2-butene (cis &amp; trans) 
                 Asterisk 
               
               
                   
                   
               
             
          
         
       
     
     At higher butene conversions and with diisobutene recycle, isobutene has the lowest conversion with both 1-butene and 2-butene having greater oligomerization to oligomers. This result is probably due to back-cracking of diisobutene back to isobutene. However, without diisobutene recycle, isobutene undergoes the greatest conversion, but with 1-butene conversion apparently surpassing isobutene conversion at over 94% total butene conversion. This trend may be showing that isobutene is more reactive and reaches a back-cracking limit faster, after which isobutene conversion is limited. We expect the same performance for Feed 1 with isobutane diluent. 
     Table 11 gives feed performance for the three feeds at conditions selected to achieve high butene conversion and high C 12 + yield including 6.2 MPa of pressure. 
     
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 11 
               
               
                   
               
               
                 Run 
                 Feed 1 
                 Feed 5 
                 Feed 6 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 WHSV, hr −1   
                 0.9 
                 0.6 
                 0.7 
               
               
                 Maximum Bed Temperature, ° C. 
                 240 
                 236 
                 239 
               
               
                 Total C 4  olefin conversion, % 
                 95 
                 96 
                 95 
               
               
                 n-butene conversion, % 
                 95 
                 95 
                 97 
               
               
                 isobutene conversion, % 
                 96 
                 97 
                 91 
               
               
                 1-butene conversion, % 
                 97 
                 98 
                 97 
               
               
                 2-butene conversion, % 
                 94 
                 94 
                 97 
               
               
                 C 5 -C 7  selectivity, wt % 
                 3 
                 3 
                 0.8 
               
               
                 C 8 -C 11  selectivity, wt % 
                 27 
                 27 
                 26 
               
               
                 C 12 -C 15  selectivity, wt % 
                 49 
                 52 
                 39 
               
               
                 C 16 + selectivity, wt % 
                 20 
                 19 
                 34 
               
               
                 Total C 9 + selectivity, wt % 
                 76 
                 77 
                 77 
               
               
                 Total C 12 + selectivity, wt % 
                 70 
                 71 
                 73 
               
               
                 Diesel Yield, wt % 
                 72 
                 74 
                 73 
               
               
                   
               
             
          
         
       
     
     C 12 + selectivity increased and C 16 + increased substantially with feeds containing diisobutene compared with the feeds without diisobutene. Yield calculated by multiplying C 4  olefin conversion by total C 9 + selectivity taken at the 150° C. (300° F.) cut point was over 70% for all feeds based on a single pass through the oligomerization reactor. 
     Example 6 
     Feed 1 and Feed 5 were reacted over Catalyst A, MTT, at 6.2 MPa and 0.75 WHSV. A graph of selectivity as a function of maximum catalyst bed temperature in  FIG. 8  shows optimal maximum bed temperature between about 220° and about 240° C. has an apex that corresponds with maximal C 12 + olefin selectivity and to a minimum C 8 -C 11  olefin selectivity and a C 5 -C 7  olefin selectivity. Table 12 provides a key for  FIG. 8 . In  FIG. 8 , solid points and lines represent Feed 1; whereas; hollow points and dashed lines represent Feed 5. 
     
       
         
               
               
               
               
             
               
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 12 
               
               
                   
                   
               
               
                   
                 Symbol 
                 Solid - Feed 1 
                 Hollow - Feed 5 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 C 12 + olefin selectivity 
                 Triangles 
                   
               
               
                   
                 C 8 -C 11  olefin selectivity 
                 Circles 
               
             
          
           
               
                   
                 C 5 -C 7  olefin selectivity 
                 Greek Crosses 
                 Asterisks 
               
               
                   
                   
               
             
          
         
       
     
     Example 7 
     Three different feeds representing product oligomerate were subjected to micro reactor cracking testing over three different catalysts. The three feeds were 2,4,4-trimethyl-1-pentene, 1-octene and mixed C 12  and larger olefins which contained linear molecules. The three catalysts included a ZSM-5 additive with 40 wt % ZSM-5 crystals, Zeolite Y and a blend of 25 wt % of the ZSM-5 additive and 75 wt % Zeolite Y such that 10 wt % of the blend was ZSM-5 crystals. The test conditions included 565° C., 10.3 kPa (gauge) and a residence time of 0.05 seconds at standard feed conditions of 25° C. and atmospheric pressure. The feeds were a mixture of 10 mol-% hydrocarbon, 5 mol-% steam, and the balance nitrogen. Table 13 provides the key for  FIGS. 9-11 . 
     
       
         
               
               
               
             
           
               
                   
                 TABLE 13 
               
               
                   
                   
               
               
                   
                 Component 
                 Key 
               
               
                   
                   
               
             
             
               
                   
                 Conversion, % 
                 Diagonal lines 
               
               
                   
                 C 3  olefin yield, wt % 
                 Dotted fill 
               
               
                   
                 C 4  olefin yield, wt % 
                 Cross Hatch 
               
               
                   
                 C 5  olefin yield, wt % 
                 Diagonal Cross Hatch 
               
               
                   
                 ZSM-5 
                 Left 
               
               
                   
                 Zeolite Y 
                 Middle 
               
               
                   
                 Blend of ZSM-5 and Zeolite Y 
                 Right 
               
               
                   
                 Trimethyl pentene feed 
                 FIG. 9 
               
               
                   
                 1-Octene feed 
                 FIG. 10 
               
               
                   
                 Mixed C 12  olefins 
                 FIG. 11 
               
               
                   
                   
               
             
          
         
       
     
       FIG. 9  reveals that achieving high conversion of 2,4,4,-trimethyl-1-pentene over ZSM-5 alone was very difficult. The same feed over Zeolite Y or the blend of ZSM-5 and Zeolite Y reached high conversion easily. The blend of ZSM-5 and Y zeolite had the highest propylene yield.  FIG. 10  shows that the conversion of 1-octene was very high over all three catalysts. We saw a similar pattern for methyl heptene in a separate test. Again, the blend of ZSM-5 and Y zeolite had the highest propylene yield.  FIG. 11  shows that conversion of C 12  and larger olefins, propylene tetramer, over the blend of ZSM-5 and Y zeolite had the highest propylene yield of all the feeds tested. ZSM-5 alone was not able to achieve much conversion of the C 12  and larger olefin feed. 
     This example establishes that feeding oligomerate produced over Catalyst A of Example 1, MTT, which produces less of the trimethyl pentene but more of the linear and less-branched C 8  olefins and C 12  olefins to an FCC unit will provide the best FCC feed to crack into the most propylene. 
     Example 8 
     Three feeds were reacted over FCC equilibrium catalyst comprising 8 wt % ZSM-5. Feed 7 comprised hydrotreated VGO with a hydrogen content of 13.0 wt %. Feed 8 comprised the same VGO mixed with 25 wt % oligomerate product catalyzed by Catalyst A of Example 1. Feed 9 comprised the same VGO mixed with 25 wt % oligomerate product catalyzed by Catalyst B of Example 1. The feeds were heated to 260-287° C. and contacted with the FCC catalyst in a riser apparatus to achieve 2.5-3.0 seconds of residence time.  FIG. 12  plots C 3  olefin yield versus VGO conversion. The key for  FIG. 13  is in Table 14. 
     
       
         
               
               
               
               
             
           
               
                   
                 TABLE 14 
               
               
                   
                   
               
               
                   
                 Feed 
                 Composition 
                 Key 
               
               
                   
                   
               
             
             
               
                   
                 Feed 7 
                 VGO 
                 Solid diamond 
               
               
                   
                 Feed 8 
                 VGO/MTT oligomerate 
                 Square 
               
               
                   
                 Feed 9 
                 VGO/SPA oligomerate 
                 Triangle 
               
               
                   
                   
               
             
          
         
       
     
       FIG. 12  shows that recycle of oligomerate product to the FCC zone can boost propylene production. At the apex of the propylene yield curve of VGO alone, the feed comprising VGO and oligomerate provided 3.2 wt % more propylene yield from the FCC zone. 
     Specific Embodiments 
     While the following is described in conjunction with specific embodiments, it will be understood that this description is intended to illustrate and not limit the scope of the preceding description and the appended claims. 
     A first embodiment of the invention is a process for making oligomers comprising passing an oligomerization feed stream to an oligomerization zone to oligomerize olefins in the oligomerization feed stream to produce an oligomerate stream; separating the oligomerate stream from the oligomerization zone in a flash drum to provide a light flash oligomerate stream and a heavy flash oligomerate stream; fractionating the light flash oligomerate stream in a recovery zone; and recycling at least a portion of the heavy flash oligomerate stream to the oligomerization zone. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph further comprising fractionating the light flash oligomerate stream to provide a product stream; mixing the product stream with the heavy flash oligomerate stream to provide a mixed stream and recycling at least a portion of the mixed stream to the oligomerization zone. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph further comprising feeding a portion of the mixed stream to an FCC zone. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph further comprising taking a distillate separator feed stream from the mixed stream and separating the distillate separator feed stream into a gasoline stream and a distillate stream. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the fractionation comprises fractionating the light flash oligomerate stream to provide a light stream comprising C 4  hydrocarbons and a first oligomerate stream comprising C 5  hydrocarbons. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph further comprising fractionating the first oligomerate stream to provide an intermediate stream and a product stream; mixing the product stream with the heavy flash oligomerate stream to provide a mixed stream and recycling at least a portion of the mixed stream to the oligomerization zone. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph further comprising feeding a portion of the mixed stream to an FCC zone or taking a distillate separator feed stream from the mixed stream and separating the distillate separator feed stream into a gasoline stream and a distillate stream. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph further comprising debutanizing the light flash oligomerate stream to additionally provide a product stream; mixing the product stream with the heavy flash oligomerate stream to provide a mixed stream and recycling at least a portion of the mixed stream to the oligomerization zone. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph further comprising feeding a portion of the mixed stream to an FCC zone or taking a distillate separator feed stream from the mixed stream and separating the distillate separator feed stream into a gasoline stream and a distillate stream. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph further comprising bypassing a portion of the heavy flash oligomerate stream to avoid recycling to the oligomerization zone and feeding the portion to the FCC zone or feeding the portion as a distillate separator feed stream and separating the distillate separator feed stream into a gasoline stream and a distillate stream. 
     A second embodiment of the invention is a process for making oligomers comprising passing an oligomerization feed stream to an oligomerization zone to oligomerize C 4  olefins in the oligomerization feed stream to produce an oligomerate stream; separating the oligomerate stream from the oligomerization zone in a flash drum to provide a light flash oligomerate stream and a heavy flash oligomerate stream; fractionating the light flash oligomerate stream in a recovery zone; recycling at least a portion of the heavy flash oligomerate stream to the oligomerization zone; and bypassing a bypass portion of the heavy flash oligomerate stream to avoid recycling to the oligomerization zone. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph further comprising feeding the bypass portion to the FCC zone or feeding the portion as a distillate separator feed stream and separating the distillate separator feed stream into a gasoline stream and a distillate stream. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph further comprising fractionating the light flash oligomerate stream to provide a product stream and recycling a portion of the product stream to the oligomerization zone. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph wherein the fractionation comprises debutanizing the light flash oligomerate stream to provide a light stream comprising C 4  hydrocarbons and a first oligomerate stream comprising C 5  hydrocarbons. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph further comprising depentanizing the first oligomerate stream to provide an intermediate stream and a product stream and recycling at least a portion of the product stream to the oligomerization zone. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph further comprising feeding a portion of the bypass portion to an FCC zone or taking a distillate separator feed stream from the mixed stream and separating the distillate separator feed stream into a gasoline stream and a distillate stream. 
     A third embodiment of the invention is a process for making oligomers comprising passing an oligomerization feed stream to an oligomerization zone to oligomerize olefins in the oligomerization feed stream to produce an oligomerate stream; separating the oligomerate stream from the oligomerization zone in a flash drum to provide a light flash oligomerate stream and a heavy flash oligomerate stream; fractionating the light flash oligomerate stream in a recovery zone to provide a product stream; mixing the product stream with the heavy flash oligomerate stream to provide a mixed stream; and recycling at least a portion of the mixed stream to the oligomerization zone. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the third embodiment in this paragraph further comprising feeding a portion of the mixed stream to an FCC zone or taking a distillate separator feed stream from the mixed stream and separating the distillate separator feed stream into a gasoline stream and a distillate stream. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the third embodiment in this paragraph wherein the fractionation comprises debutanizing the light flash oligomerate stream to provide a light stream comprising C 4  hydrocarbons and a first oligomerate stream comprising C 5  hydrocarbons. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the third embodiment in this paragraph further comprising depentanizing the first oligomerate stream to provide an intermediate stream and the product stream or further debutanizing the light flash oligomerate stream to additionally provide the product stream. 
     A fourth embodiment of the invention is an apparatus for making oligomers comprising an oligomerization zone for oligomerizing olefins in the oligomerization feed stream to produce an oligomerate stream; a flash drum for separating the oligomerate stream in communication with the oligomerization zone; a light flash line from the flash drum and a heavy flash line from the flash drum with an inlet to the light flash line above an inlet to the heavy flash line; a fractionation column in communication with the light flash line for fractionating the light flash oligomerate stream; and the oligomerization zone in downstream communication with the heavy flash line. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the fourth embodiment in this paragraph further comprising a product line in downstream communication with the fractionation column and a recycle line in downstream communication with the heavy flash line and the product line. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the fourth embodiment in this paragraph further comprising a process line in downstream communication with the product line and the heavy flash line and the oligomerization zone is in downstream communication with the process line via the recycle line. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the fourth embodiment in this paragraph further comprising an FCC zone in downstream communication with the heavy flash line and the product line. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the fourth embodiment in this paragraph further comprising a distillate separator in downstream communication with the heavy flash line and the product line. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the fourth embodiment in this paragraph wherein the fractionation column is a debutanizer column. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the fourth embodiment in this paragraph further comprising the debutanizer column in a recovery zone and a depentanizer column in the recovery zone; the depentanizer column in downstream communication with a bottoms line from the debutanizer; and the product line comes from the bottom of the depentanizer column. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the fourth embodiment in this paragraph further comprising the product line comes from the bottom of the debutanizer column. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the fourth embodiment in this paragraph further comprising a bypass line in downstream communication with the heavy flash line and a process line in downstream communication with the heavy flash line; the bypass line being out of communication with the recycle line. 
     A fifth embodiment of the invention is an apparatus for making oligomers comprising an oligomerization zone for oligomerizing olefins in the oligomerization feed stream to produce an oligomerate stream; a flash drum for separating the oligomerate stream in communication with the oligomerization zone; a light flash line from the flash drum and a heavy flash line from the flash drum with an inlet to the light flash line above an inlet to the heavy flash line; a fractionation column in communication with the light flash line for fractionating the light flash oligomerate stream; a product line in downstream communication with the fractionation column; a recycle line in downstream communication with the heavy flash line and the product line; the oligomerization zone in downstream communication with the recycle line. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the fifth embodiment in this paragraph further comprising a surge drum in downstream communication with the product line and the heavy flash line and the oligomerization zone is in downstream communication with the surge drum via the recycle line. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the fifth embodiment in this paragraph further comprising a process line in downstream communication with the product line and the heavy flash line and the recycle line is in downstream communication with the process line. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the fifth embodiment in this paragraph further comprising an FCC zone in downstream communication with the process line. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the fifth embodiment in this paragraph further comprising a distillate separator in downstream communication with the process line. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the fifth embodiment in this paragraph wherein the fractionation column is a debutanizer column. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the fifth embodiment in this paragraph further comprising the debutanizer column in a recovery zone and a depentanizer column in the recovery zone; the depentanizer column in downstream communication with a bottoms line from the debutanizer; and the product line comes from the bottom of the depentanizer column. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the fifth embodiment in this paragraph further comprising the product line comes from the bottom of the debutanizer column. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the fifth embodiment in this paragraph further comprising a bypass line in downstream communication with the heavy flash line and a process line in downstream communication with the heavy flash line; the bypass line being out of communication with the recycle line. 
     A sixth embodiment of the invention is an apparatus for making oligomers comprising an oligomerization zone for oligomerizing olefins in the oligomerization feed stream to produce an oligomerate stream; a flash drum for separating the oligomerate stream in communication with the oligomerization zone; a light flash line from the flash drum and a heavy flash line from the flash drum with an inlet to the light flash line above an inlet to the heavy flash line; a recovery zone in communication with the light flash line for fractionating the light flash oligomerate stream; and the oligomerization zone in downstream communication with the heavy flash line. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the sixth embodiment in this paragraph further comprising a process line in downstream communication with the product line and the heavy flash line and a recycle line is in downstream communication with the process line; the oligomerization zone being in downstream communication with the recycle line and an FCC zone or an distillate separator is in downstream communication with the process line. 
     Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. The preceding preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever. 
     In the foregoing, all temperatures are set forth in degrees Celsius and, all parts and percentages are by weight, unless otherwise indicated. Pressures are given at the vessel outlet and particularly at the vapor outlet in vessels with multiple outlets. Control valves should be opened or closed as consistent with the intent of the disclosure. 
     From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions.