Patent Publication Number: US-7914754-B2

Title: Integrated production of FCC-produced C2 and ethyl benzene

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a Division of prior U.S. application Ser. No. 11/924,809, which is filed Oct. 26, 2007 and is now U.S. Pat. No. 7,795,485, the contents of which are incorporated herein by reference thereto. 
    
    
     TECHNICAL FIELD 
     This disclosure relates generally to hydrocarbon processing. More specifically, this disclosure relates to the initial processing of hydrocarbon-containing materials into an intermediate stream of ethane and ethylene, produced by the cracking of a heavy hydrocarbon feedstock. This disclosure also relates to the subsequent use of said intermediate stream in the making of valuable aromatics, such as ethyl benzene. 
     BACKGROUND OF THE RELATED ART 
     Light olefins serve as feed materials for the production of numerous chemicals. Light olefins have traditionally been produced through the processes of steam or catalytic cracking of hydrocarbons derived from petroleum sources. Fluidized catalytic cracking (FCC) of heavy hydrocarbon streams is commonly carried out by contacting relatively high boiling hydrocarbons with a catalyst composed of finely divided or particulate solid material. The catalyst is transported in a fluid-like manner by transmitting a gas or vapor through the catalyst at sufficient velocity to produce a desired regime of fluid transport. Contact of the oil with the fluidized catalyst results in the cracking reaction. 
     FCC processing is more fully described in U.S. Pat. Nos. 5,360,533, 5,584,985, 5,858,206 and 6,843,906. Specific details of the various contact zones, regeneration zones, and stripping zones along with arrangements for conveying the catalyst between the various zones are well known to those skilled in the art. 
     The FCC reactor serves to crack gas oil or heavier feeds into a broad range of products. Cracked vapors from an FCC unit enter a separation zone, typically in the form of a main column, that provides a gas stream, a gasoline cut, light cycle oil (LCO) and clarified oil (CO) which includes heavy cycle oil (HCO) components. The gas stream may include hydrogen and C 1  and C 2  hydrocarbons, and liquefied petroleum gas (“LPG”), i.e., C 3  and C 4  hydrocarbons. 
     There is an increasing need for light olefins such as ethylene for the production of polyethylene, ethyl benzene and the like as opposed to heavier olefins. Research efforts have led to the development of an FCC process that produces or results in greater relative yields of light olefins, e.g., ethylene. Such processing is more fully described in U.S. Pat. No. 6,538,169. 
     Ethyl benzene is an important intermediate compound for the production of styrene. Although often present in small amounts in crude oil, ethyl benzene is produced in bulk quantities by combining the petrochemicals benzene and ethylene in an acid or zeolite catalyzed chemical reaction. Catalytic dehydrogenation of the ethyl benzene then gives hydrogen gas and styrene. 
     A conventional FCC process produces a combined ethylene/ethane stream. The ethylene/ethane stream is typically run through a splitter or distillation column to separate the ethylene from the ethane. The operation of such a splitter is energy intensive in addition to construction and maintenance costs. 
     In view of the increasing need and demand for light olefins such as ethylene and the use thereof in producing ethyl benzene, there is a need and a demand for improved processing and arrangements for the separation and recovery of light olefins, such as ethylene, from such FCC process effluent and the efficient conversion of those olefins into useful aromatic intermediates, such as ethyl benzene. 
     SUMMARY OF THE INVENTION 
     An integrated process is disclosed for (i) catalytically cracking (FCC) a heavy hydrocarbon feedstock, (ii) obtaining a combined ethylene/ethane stream, and (iii) reacting the ethylene of the combined ethane/ethylene stream with benzene to produce an ethyl benzene product stream. The integrated process comprises contacting a heavy hydrocarbon feedstock with a hydrocarbon cracking catalyst in a fluidized reaction zone to produce a hydrocarbon effluent stream that includes ethane and ethylene. The process then further comprises separating the combined ethane/ethylene stream from the hydrocarbon effluent stream, passing the combined ethane/ethylene stream to an alkylation reactor, and reacting at least some of the ethylene of the combined ethane/ethylene stream with benzene in the alkylation reactor to produce ethyl benzene. 
     By linking the FCC process directly to the ethyl benzene alkylation process, substantial capital and energy costs savings are achieved. First, the need for an ethylene/ethane splitter column is eliminated as ethane is inert to the ethyl benzene alkylation process and does not hinder the process in an appreciable way. Second, along with the energy savings achieved by eliminating the ethylene/ethane splitter, additional energy savings are achieved by linking the intercoolers used to cool the alkylation reactor to one of the splitter columns of the FCC process. Further, additional savings may achieved by using the bottoms stream from the ethyl benzene column of the alkylation zone in one of two ways. First the EB column bottoms may be used as a solvent in the primary absorber of the absorption zone, thereby reducing the dependence upon debutanized gasoline recycle as a solvent for the primary absorber. Second, the EB column bottoms may be used as a co-feed with the effluent stream to the main column of the separation zone. Employing either of these strategies can reduce the debutanized gasoline recycle demand by 5 to 10%. 
     The ethane is preferably not stripped from the combined ethane/ethylene stream prior to the combined ethane/ethylene stream entering the alkylation reactor. The ethane content of the combined ethane/ethylene stream may be up to or about 30 wt %. 
     Further, the combined ethane/ethylene stream entering the alkylation reactor is cold as it preferably has just passed through a demethanizer. The combined ethane/ethylene stream has a temperature of less than 0° C. (32° F.) which further reduces the duty of the intercoolers used to cool the alkylation reactor. 
     The alkylation reactor preferably includes six catalyst beds, six feed inlets, and two intercoolers disposed between the second and fourth catalyst beds. 
     As noted above, the hydrocarbon effluent generated in the FCC process passes through a separation zone to form a separator liquid stream and a separator vapor stream. C 2 − hydrocarbon materials are stripped from the separator liquid stream in a stripper column to form a C 3 + hydrocarbon process stream substantially free of C 2 − hydrocarbons. This stripper column may be advantageously heated with heat generated in the alkylation reactor. Thus, heat may be transferred from the intercoolers used to cool the alkylation reactor to the stripper column to lessen the cooling duty of the intercoolers. 
     Further, in generating the ethane/ethylene combined stream, the separator vapor stream is contacted with an absorption solvent in an absorption zone to remove C 3 + hydrocarbons therefrom to form the combined ethane/ethylene stream. More specifically, the separator vapor stream is contacted with the first absorption solvent comprising debutanized gasoline recycle in a primary absorber to form a first primary absorber process stream comprising ethane and ethylene and residual amounts of C 3 + hydrocarbons. In one embodiment, the first absorption solvent used in the primary absorber also comprises a bottoms stream from an ethyl benzene (EB) column of the ethyl benzene process. Employing this option eliminates the need for a transalkylation section as well as a polyethyl benzenes (PEB) column in the alkylation process. The EB bottoms stream supplements some of the debutanized gasoline recycle that is also used as the solvent in the primary absorber, thereby reducing the amount of recycle that is required. Any diethyl benzene (DEB) and polyethyl benzene (PEB) would ultimately end up as a high octane component in the gasoline product of the FCC process. 
     Another alternative is to send the EB column bottoms to the FCC main separation zone column, where the heavier species would be removed in a heavier fraction such as the heavy naphtha draw. The lighter species in this stream would still act to reduce the required debutanized gasoline recycle for use as the primary absorber solvent and will exit in the unstabilized gasoline that is recovered from the main column overhead. 
     Treatments to remove carbon dioxide, hydrogen sulfide, acetylene and methane from the combined ethane/ethylene stream may be carried out prior to passing of the ethane/ethylene stream to the alkylation reactor. 
     An integrated system for (i) catalytically cracking a hydrocarbon feedstock, (ii) obtaining selected hydrocarbon fractions including a combined ethane/ethylene stream and (iii) reacting the ethylene of the combined ethane/ethylene stream with benzene to produce an ethyl benzene product stream is provided. The integrated system includes a fluidized reactor zone wherein the hydrocarbon feedstock contacts a catalyst to produce a cracked effluent stream including ethane and ethylene. The system also includes a separation zone for separating the cracked effluent stream into at least one separator liquid stream and a separator vapor stream. The at least one separator liquid stream includes C 3 + hydrocarbons; the separator vapor stream includes ethane and ethylene. The system also includes an absorption zone to absorb C 3 + hydrocarbons from the separator vapor stream to form an absorption zone effluent stream comprising ethane and ethylene and a treatment zone to remove impurities other than ethane and ethylene from the absorption zone effluent stream to provide a combined ethane/ethylene stream. The combined ethane/ethylene stream is fed through a process line to an alkylation reactor for reacting at least some of the ethylene in the combined ethane/ethylene stream with benzene to form ethyl benzene. 
     Intercoolers used to cool the alkylation reactor can be used to drive one or more reboilers of a splitter column. The bottoms stream from an ethyl benzene column can be used as an absorber solvent or can be added to the cracked effluent stream. 
     Other advantages will be apparent to those skilled in the art from the following detailed description taken in conjunction with the appended claims and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a simplified schematic diagram of a system for catalytic cracking a heavy hydrocarbon feedstock and obtaining selected hydrocarbon fractions, including C2 light olefins via an absorption-based product recovery; 
         FIG. 2  is a simplified schematic diagram of a system for converting ethylene and benzene to ethyl benzene that is integrated with the system of  FIG. 1 ; and 
         FIG. 3  is a simplified schematic diagram of another system for converting ethylene and benzene to ethyl benzene that is also integrated with the system of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS 
       FIG. 1  schematically illustrates a system  10   a  for catalytic cracking a heavy hydrocarbon feedstock and obtaining light olefins via absorption-based product recovery and  FIGS. 2 and 3  schematically illustrate systems  10   b ,  10   c  for efficiently converting the light olefins from the system  10   a  into one or more useful intermediates. Those skilled in the art and guided by the teachings herein provided will recognize and appreciate that the illustrated systems  10   a ,  10   b ,  10   c  have been simplified by eliminating some usual or customary pieces of process equipment including some heat exchangers, process control systems, pumps, fractionation systems, and the like. It may also be discerned that the process flows depicted in  FIGS. 1-3  may be modified in many aspects without departing from the basic overall concepts disclosed herein. 
     In the cracking system  10   a , a suitable heavy hydrocarbon feedstock stream is introduced via a line  12  into a fluidized reactor zone  14  wherein the heavy hydrocarbon feedstock contacts a hydrocarbon cracking catalyst zone to produce a hydrocarbon effluent comprising a range of hydrocarbon products, including light olefins such as ethylene and light hydrocarbons such as ethane. 
     Suitable fluidized catalytic cracking reactor zones for use in the practice of such an embodiment may, as is described in above-identified U.S. Pat. No. 6,538,169, include a separator vessel, a regenerator, a blending vessel, and a vertical riser that provides a pneumatic conveyance zone in which conversion takes place. The arrangement circulates catalyst and contacts the catalyst with the feed. 
     More specifically and as described therein, the FCC catalyst typically comprises two components that may or may not be on the same matrix. The two components are circulated throughout the reactor  14 . The first component may include any of the well-known catalysts that are used in the art of fluidized catalytic cracking, such as an active amorphous clay-type catalyst and/or a high activity, crystalline molecular sieve. Molecular sieve catalysts are preferred over amorphous catalysts because of their much-improved selectivity to desired products. Zeolites are the most commonly used molecular sieves in FCC processes. Preferably, the first catalyst component comprises a large pore zeolite, such as a Y-type zeolite, an active alumina material, a binder material, comprising either silica or alumina and an inert filler such as kaolin. 
     The zeolitic molecular sieves appropriate for the first catalyst component should have a large average pore size. Typically, molecular sieves with a large pore size have pores with openings of greater than 0.7 nm in effective diameter defined by greater than 10 and typically 12 membered rings. Pore Size Indices of large pores are above about 31. Suitable large pore zeolite components include synthetic zeolites such as X-type and Y-type zeolites, mordenite and faujasite. It has been found that Y zeolites with low rare earth content are preferred in the first catalyst component. Low rare earth content denotes less than or equal to about 1.0 wt % rare earth oxide on the zeolite portion of the catalyst. Octacat™ catalyst made by W. R. Grace &amp; Co. is a suitable low rare earth Y-zeolite catalyst. 
     The second catalyst component comprises a catalyst containing, medium or smaller pore zeolite catalyst exemplified by ZSM-5, ZSM-11, ZSM-12, ZSM-23, ZSM-35, ZSM-38, ZSM-48, and other similar materials. U.S. Pat. No. 3,702,886 describes ZSM-5. Other suitable medium or smaller pore zeolites include ferrierite, erionite, and ST-5, developed by Petroleos de Venezuela, S. A. The second catalyst component preferably disperses the medium or smaller pore zeolite on a matrix comprising a binder material such as silica or alumina and an inert filer material such as kaolin. The second component may also comprise some other active material such as Beta zeolite. These catalyst compositions have a crystalline zeolite content of 10-25 wt % or more and a matrix material content of 75-90 wt %. Catalysts containing 25 wt % crystalline zeolite material are preferred. Catalysts with greater crystalline zeolite content may be used, provided they have satisfactory attrition resistance. Medium and smaller pore zeolites are characterized by having an effective pore opening diameter of less than or equal to 0.7 nm, rings of 10 or fewer members and a Pore Size Index of less than 31. 
     The total catalyst composition should contain 1-10 wt % of a medium to small pore zeolite with greater than or equal to 1.75 wt % being preferred. When the second catalyst component contains 25 wt % crystalline zeolite, the composition contains 4-40 wt % of the second catalyst component with a preferred content of greater than or equal to 7 wt %. ZSM-5 and ST-5 type zeolites are particularly preferred since their high coke resistivity will tend to preserve active cracking sites as the catalyst composition makes multiple passes through the riser, thereby maintaining overall activity. The first catalyst component will comprise the balance of the catalyst composition. The relative proportions of the first and second components in the catalyst composition will not substantially vary throughout the FCC unit  14 . 
     The high concentration of the medium or smaller pore zeolite in the second component of the catalyst composition improves selectivity to light olefins by further cracking the lighter naphtha range molecules. But at the same time, the resulting smaller concentration of the first catalyst component still exhibits sufficient activity to maintain conversion of the heavier feed molecules to a reasonably high level. 
     The relatively heavier feeds suitable for processing in accordance herewith include conventional FCC feedstocks or higher boiling or residual feeds. A common conventional feedstock is vacuum gas oil which is typically a hydrocarbon material prepared by vacuum fractionation of atmospheric residue and which has a broad boiling range of from 315-622° C. (600-1150° F.) and, more typically, which has a narrower boiling point range of from 343-551° C. (650-1025° F.). Heavy or residual feeds, i.e., hydrocarbon fractions boiling above 499° C. (930° F.), are also suitable. The fluidized catalytic cracking processing the invention is typically best suited for feedstocks that are heavier than naptha range hydrocarbons boiling above about 177° C. (350° F.). 
     The effluent or at least a selected portion thereof is passed from the fluidized reactor zone  14  through a line  16  into a hydrocarbon separation system  20 , which may include a main column section  22  and a staged compression section  24 . The main column section  22  may desirably include a main column separator and associated overhead receiver where the fluidized reactor zone effluent can be separated into desired fractions including a main column vapor stream that is passed through line  26  to the two stage compressor  24 , and a main column liquid stream, which is passed through line  30  to the absorber  40 . To facilitate illustration and discussion, other fraction lines such as including a heavy gasoline stream, a light cycle oil (“LCO”) stream, a heavy cycle oil (“HCO”) stream and a clarified oil (“CO”) stream, for example, may not be shown or specifically described. 
     The main column vapor stream line  26  is introduced into the staged compression section  24 . The staged compression section  24  results in the formation of a high pressure separator liquid stream in a line  32  and a high pressure separator vapor stream in a line  34 . While the pressure of such high pressure liquid and high pressure vapor can vary, in practice such streams are typically at a pressure ranging from about 1375 kPag to about 2100 kPag (about 200 psig to about 300 psig). The compression section  24  may also result in the formation of a stream of spill back materials largely composed of heavier hydrocarbon materials and such as can be returned to the main column section  22  via the line  35 . 
     The high pressure separator liquid stream  32  includes C 3 + hydrocarbons and is substantially free of carbon dioxide and hydrogen sulfide. The high pressure separator vapor stream  34  includes C 3 − hydrocarbons and typically includes some carbon dioxide and hydrogen sulfide. 
     The separator vapor stream line  34  is introduced into an absorption zone  36 , which includes the primary absorber  40 , where the separator vapor stream  34  is contacted with a debutanized gasoline material provided by the line  42  and the main column overhead liquid stream  30  to absorb C 3 + materials and separate C 2  and lower boiling fractions from the separator vapor stream. In general, the absorption zone  36  includes the primary absorber  40  that suitably includes a plurality of stages with at least one and preferably two or more intercoolers interspaced therebetween to assist in achieving desired absorption. In practice, such a primary absorber  40  includes about five absorber stages between each pair of intercoolers. The primary absorber  40  may include at least about 15 to 25 ideal stages with 2 to 4 intercoolers appropriately spaced therebetween. 
     C 3 + hydrocarbons absorbed in or by the debutanized gasoline stream  42  and main column liquid stream  30  in the absorber  40  can be passed via the line  43  back to the two-stage compressor  24  for further processing. The off gas from the primary absorber  40  passes via a line  44  to a secondary or sponge absorber  46 . The secondary absorber  46  contacts the off gas with light cycle oil from a line  50 . Light cycle oil absorbs most of the remaining C 4  and higher hydrocarbons and returns to the main fractionators via a line  52 . A stream of C 2 − hydrocarbons is withdrawn as off gas from the secondary or sponge absorber  46  in the line  54  for further treatment as later described herein. 
     The high pressure liquid stream  32  from the compressor  24  is passed through to the stripper  62  which removes most of the C 2  and lighter gases through the line  64  and passes them back to the compressor  24 . In practice, the stripper  62  can be operated at a pressure ranging from about 1375 kPag to about 2100 kPag (about 200 psig to about 300 psig) with a C 2 /C 3  molar ratio in the stripper bottoms of less than 0.001 and preferably with a C 2 /C 3  molar ratio in the stripper bottoms of less than about 0.0002 to about 0.0004. 
     As discussed in greater detail below, the reboiler heat exchanger  63  may be heated by the alkylation reactor  164  shown in  FIGS. 2 and 3 . Specifically, one or more inter-coolers  63   a ,  63   b  ( FIGS. 2-3 ) may be combined with the reboiler heat exchanger  63  ( FIG. 1 ) associated with the stripper  62 . 
     As shown, the C 2  and lighter gases in the line  64  are combined in the compressor  24  with the main column vapor stream  26  to form with high pressure separator vapor stream  34  that is fed into the primary absorber  40 . The stripper  62  supplies a liquid C 3 + stream  66  to the debutanizer  70 . A suitable debutanizer  70  includes a condenser (not shown) that desirably operates at a pressure ranging from about 965 kPag to about 1105 kPag (about 140 psig to about 160 psig), with no more than about 5 mol % C 5  hydrocarbons in the overhead and no more than about 5 mol % C 4  hydrocarbons in the bottoms. More preferably, the relative amount of C 5  hydrocarbons in the overhead is less than about 1-3 mol % and the relative amount of C 4  hydrocarbons in the bottoms is less than about 1-3 mol %. 
     A stream of C 3  and C 4  hydrocarbons from the debutanizer  70  is taken as overhead through the line  72  for further treatment as described below and the bottoms stream  76  from the debutanizer  70  comprises gasoline, part of which forms the stream  42  which is fed to the top of the primary absorber  40  where it serves as the primary first absorption solvent. Another portion of the stream of debutanized gasoline is passed in the line  77  to a naphtha splitter (not shown), which may be a dividing wall separation column. 
     The C 2 − hydrocarbon stream  54  withdrawn from the secondary or sponge absorber  46  is passed through a further compression section  90  to form a compressed vapor stream  92  that is passed into a compression or discharge vessel  94 . The discharge vessel  94  forms a liquid knockout stream generally composed of heavy components (e.g., C 3 + hydrocarbons that liquefy in the discharge vessel  94 ) and are withdrawn in the line  96 . The discharge vessel  94  also forms an overhead vapor stream  100 , primarily comprising C 2 − hydrocarbons, with typically no more than trace amounts (e.g., less than 1 wt %) of C 3 + hydrocarbons. 
     The overhead stream  100  is passed to an amine treatment section  102  to remove CO 2  and H 2 S. The utilization of amine treatment system  102  for carbon dioxide and/or hydrogen sulfide removal is well known in the art. Conventional such amine treatment systems typically employ an amine solvent such as methyl diethanol amine (MDEA) to absorb or otherwise separate CO 2  and H 2 S from hydrocarbon stream materials. A stripper or regenerator is typically subsequently used to strip the absorbed CO 2  and H 2 S from the amine solvent, permitting the reuse of the amine solvent. 
     While such amine treatment has proven generally effective for removal of carbon dioxide from various hydrocarbon-containing streams, the application of such amine treatment to ethylene-rich hydrocarbon and carbon dioxide-containing streams, such as being processed at this point of the subject system, may experience some undesired complications as some of the olefin material may be co-absorbed with the CO 2  and H 2 S in or by the amine solvent. Such co-absorption of olefin material undesirably reduces the amounts of light olefins available for recovery from such processing. Moreover, during such subsequent stripper processing of the amine solvent, the presence of such olefin materials can lead to polymerization. Such polymerization can lead to degradation of the amine solvent and require expensive off-site reclamation processing. 
     In view thereof, it may be desirable to utilize an amine treatment system such as includes or incorporates a pre-stripper interposed between the amine system absorber and the amine system stripper/regenerator. Such an interposed pre-stripper, can desirably serve to separate hydrocarbon materials, including light olefins such as ethylene, from the carbon dioxide and amine solvent prior to subsequent processing through the regenerator/stripper. A CO 2 /H 2 S outlet is shown at  103 . 
     A stream  104  containing C 2 − hydrocarbons substantially free of carbon dioxide and hydrogen sulfide passes to a dryer section  106  with a water outlet line  107 . A stream containing dried C 2 − hydrocarbons substantially free of carbon dioxide and hydrogen sulfide passes via a line  108  to an acetylene conversion section or unit  110 . As is known in the art, acetylene conversion sections or units are effective to convert acetylene to form ethylene. Thus, an additionally ethylene-enriched process stream  112  is withdrawn from the acetylene conversion section or unit  110  and passed to the optional dryer  114  or to the CO 2 , carbonyl sulfide (“COS”), arsine and/or phosphine treater  116  as is known in the art to effect removal of CO 2 , COS, arsine and/or phosphine. 
     Water is withdrawn from the dryer  114  through the line  117 . CO 2 , COS, Arsine and/or Phosphine are withdrawn through the line  118 , and the treated stream  120  is introduced into a demethanizer  122 . A suitable demethanizer  122  may include a condenser (not specifically shown) that desirably operates at a temperature of no greater than about −90° C. (−130° F.), more preferably operates at a temperature ranging from about −90° C. to about −102° C., preferably about −96° C. (−130° to about −150° F., preferably at about −140° F.). In addition, the demethanizer  122  may operate with a methane to ethylene molar ratio in the bottoms of no greater than about 0.0005 and, more preferably at a methane to ethylene molar ratio in the bottoms of no greater than about 0.0003 to about 0.0002. 
     The overhead stream  124  of methane and hydrogen gas from the demethanizer  122  may be used as a fuel or, if desired, taken for further processing or treatment such as to a pressure swing absorption unit (not shown) for H 2  recovery. The demethanizer outlet stream  126  is passed directly to an ethyl benzene unit  10   b  of  FIG. 2  or  10   c  of  FIG. 3  without the need for heating or a splitter to separate the ethane from the ethylene. By avoiding the use of a C 2 /C 2 =splitter, which would operate at a pressure ranging from about 1930 kPag to about 2105 kPag (about 280 psig to about 305 psig), substantial savings in terms of operating coast and capital costs are achieved. 
     Still referring to  FIG. 1 , the stream  72  containing C 3  and C 4  hydrocarbons taken overhead from the debutanizer  70  may contain some significant relative amounts of hydrogen sulfide and is therefore preferably passed to a hydrogen sulfide removal treatment unit  128 , such as an amine treatment section, where hydrogen sulfide is removed through the line  129  and the treated stream  130  is passed to an optional extraction unit  132  to catalytically oxidize mercaptans present to disulfides via a caustic wash, which are removed through the line  134 . 
     The resulting stream  136  is passed to the C 3 /C 4  splitter  138 . A suitable C 3 /C 4  splitter includes a condenser (not specifically shown) that desirably operates at a pressure ranging from about 1650 kPag to about 1800 kPag (about 240 psig to about 260 psig), preferably at a pressure of about 1724 kPa (about 250 psig) and desirably operates such that there is no more than about 5 mol % C 4 s in the overhead product stream, preferably less than about 1 mol % C 4 s in the overhead product stream and no more than about 5 mol % C 3 s in the bottoms stream, preferably less than about 1 mol % C 3 s in the bottoms stream. 
     The C 3 /C 4  splitter  138  forms a bottoms stream  140  of C 4 + hydrocarbons for use as either for product recovery or further desired processing, as is known in the art. The C 3 /C 4  splitter  138  also forms a stream  142  composed primarily of C 3  hydrocarbons which is passed to a propylene/propane splitter  144 . A suitable such propane/propylene splitter  144  may operate such that at least 98 wt % and, preferably, at least about 99 wt % of the propylene is recovered in the overhead stream and the propylene in the overhead stream is at least about 99.5% pure. 
     The propylene/propane splitter  144  forms a propylene stream  146  and a propane stream  148 . The propylene stream  146  may be passed to dryer  150  for the removal of water through the line  152  before being passed on to a regenerative COS treater  154  to remove COS through the line  156  before being passed through the arsine and/or phosphine treater  158  to effect removal of trace amounts of arsine and/or phosphine through the line  160  and producing an propylene product stream  162 . 
     Turning to  FIG. 2 , the combined ethane/ethylene stream  126  is introduced at various stages  165   a - 165   f  of the alkylation reactor  164 , without pre-heating and without separating the ethane, where the ethylene reacts catalytically with benzene provided in the form of fresh benzene through the line  166  and recycled benzene through the line  168 . Because ethane is essentially inert to the ethyl benzene process system  170 , the need for an upstream ethane/ethylene splitter is not required. Further, pre-heating the cool stream  126  from the demethanizer  122  is not required as the low temperatures have been surprisingly found to improve selectivity in the alkylation reactor  164  as explained below. As the material in the combined ethane/ethylene stream  126  is liquid, it may be delivered at pressures ranging from about 2900 to about 4000 kPa (˜421 to ˜580 psi) using a conventional pump  125  instead of a more expensive compressor that would be required to deliver polymer grade ethylene gas to the alkylation reactor  164 . 
     Ethylene in the stream  126  reacts with the benzene in the alkylation reactor  164  to produce a combined product stream  172  that will include ethyl benzene, diethyl benzene (DEB), triethyl benzene (TEB) and unreacted ethane, ethylene and benzene. 
     The combined alkylation product stream  172  is passed to a benzene column  174  where it is combined with a transalkylation product stream  176  from the transalkylation reactor  178 . The transalkylation reactor  178  converts the polyethyl benzenes (PEBs) such as DEB and TEB to EB and DEB respectively. Hence, the feed for the transalkylation reactor  178  may include a PEB stream  182  from the PEB column  180  coupled with benzene from the line  168   a  taken from the feed line  168  to the alkylation reactor  164 . The combined benzene/PEB stream  184  enters the transalkylation reactor  178  after being heated by the boiler or heater  186 . The transalkylation product stream  176  will include lower amounts of PEBs. 
     The benzene column  174  removes benzene and lighter components through the overhead stream  188  which passes through condenser  190  and into the receiver  192 . Condensed benzene is recycled through the lines  168  and  168   a  to the alkylation reactor  164  and transalkylation reactor  178  respectively. The vapor stream  194  from the condenser  192  is passed to the lights removal column  196  where off gases are removed through the line  198  and cooling water is provided through the line  200 . Heavier components are drawn out the bottom of the column  196  through the line  202  before passing into a collector  204  and through the line  206  to be recycled back to the receiver  192 . 
     The bottoms stream  208  from the benzene column  174  contains ethyl benzene and heavier materials and is passed on to the ethyl benzene column  210 . The lighter ethyl benzene passes as overhead through the line  212 , condenser  214 , and a receiver  216  to the ethyl benzene product outlet  218 . The bottoms stream  220  from the ethyl benzene column  210  is passed on to the PEB column  180  where PEBs are separated from heavier components to produce a PEB product stream  220  and bottoms stream  222  which is essentially a flux oil discharge stream. The PEB stream  220  passes through the condenser  224  and receiver  226  before being recycled through the line  184  to the transalkylation reactor  178 . 
     The intercoolers  63   a ,  63   b  in the alkylation section  164  typically require a cooling water utility. In accordance with this disclosure, integrating the alkylation intercoolers  63   a ,  63   b  ( FIGS. 2-3 ) with the C 2 − stripper  62  saves about 24 MM kcal/hr of additional heating by LP steam which would be required by the reboiler  63  ( FIG. 1 ). All of the heat for the reboiler  63  can be provided by the two intercoolers  63   a ,  63   b , each of which typically require about −16.5 MM kcal/hr for the case described here. Additional cooling water duty will be required to remove the additional 9 MM kcal/hr of heat in the intercoolers  63   a ,  63   b , but overall the process is more efficient by reducing the steam requirement for the stripper  62 , as well as much of the cooling water requirement in the alkylation section  164 . 
     Injecting the cold, liquid combined ethane/ethylene steam  136  provides a direct heat exchange benefit in the alkylation reactor  164 . First, the hotter catalyst beds  165   b ,  165   d  and  165   f  have a lower inlet temperature. This may result in better EB selectivity as some EB alkylation catalysts (such as UZM-8) have a slightly better EB selectivity at lower temperatures. Further, the lower inlet temperatures to the alkylation reactor  164  provide reduced formation of heavies, such as diphenyethane (DPE) and ethyldiphenylethane (EDPE). The outlet temperature of the hot catalyst beds  165   b ,  165   d  and  165   f  is also somewhat lower. Therefore, the two intercoolers  63   a ,  63   b  have a smaller duty requirement, and even with the transfer of heat to the splitter column  62 , a savings results in terms of equipment cost (smaller heat exchanger area requirement), and utilities as cooling water costs are reduced. A small portion of this advantage is offset by the need to heat the recycle benzene in the line  168  to a slightly hotter temperature in order to achieve the desired alkylation inlet temperature. 
     An overall summary of the disclosed process and integrated is shown in following tables with the date in the middle column being generated using a cool liquid combined ethane/ethylene stream and the data in right column using a conventional gaseous ethylene feed. 
     
       
         
           
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Mixed C2 
                 Polymer Grade 
               
               
                 C2 Feed Properties 
                 (Ethane/Ethylene) 
                 Ethylene (Prior Art) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 Ethylene Content (wt %) 
                      87% 
                 99.5% 
               
               
                 Temperature, ° C. 
                   12.2 
                 89.5 
               
               
                 Pressure (kPa) 
                 4,520 
                 4,520 
               
               
                 Phase 
                 Liquid 
                 Gas 
               
               
                 Ethylene Process Rate kg/hr 
                 65,435  
                 65,434 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                   
                 Mixed C2 
                 Polymer Grade 
               
               
                 Alkylation Chemistry 
                 (Ethane/Ethylene) 
                 Ethylene (Prior Art) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 Ethyl Benzene Selectivity 
                 87.87% 
                 87.69% 
               
               
                 Diethyl Benzene Selectivity 
                 11.34% 
                 11.45% 
               
               
                 Triethyl Benzene Selectivity 
                 0.70% 
                 0.75% 
               
               
                 Others 
                 0.09% 
                 0.11% 
               
               
                 Total 
                 100.00% 
                 100.00% 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                   
                 Mixed C2 
                 Polymer Grade 
               
               
                   
                 Heavy Byproducts 
                 (Ethane/Ethylene) 
                 Ethylene (Prior Art) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Diphenylethane 
                 0.045% 
                 0.052% 
               
               
                   
                 Ethyldiphenylethane 
                 0.015% 
                 0.018% 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
               
             
               
                   
                 TABLE 4 
               
             
            
               
                   
                   
               
               
                   
                 Alkylation Reactor Inlet Temperatures 
               
               
                   
                 (° C.) for Six Bed Reactor 
               
            
           
           
               
               
               
            
               
                   
                 Mixed C2 
                 Polymer Grade 
               
               
                   
                 (Ethane/Ethylene) 
                 Ethylene (Prior Art) 
               
               
                   
                   
               
            
           
           
               
               
               
            
               
                 Bed 1 (Bottom; see bed 
                 200.00 
                 200.00 
               
               
                 165a in FIG. 2) In 
               
               
                 Bed 1 Out 
                 228.32 
                 228.40 
               
               
                 Bed 2 In 
                 222.24 
                 227.13 
               
               
                 Bed 2 Out 
                 248.80 
                 252.88 
               
               
                 Bed 3 In 
                 200.00 
                 200.00 
               
               
                 Bed 3 Out 
                 227.51 
                 227.73 
               
               
                 Bed 4 In 
                 222.01 
                 226.50 
               
               
                 Bed 4 Out 
                 247.38 
                 251.79 
               
               
                 Bed 5 In 
                 200.00 
                 200.00 
               
               
                 Bed 5 Out 
                 226.69 
                 227.06 
               
               
                 Bed 6 (Top) In 
                 221.17 
                 225.81 
               
               
                 Bed 6 Out 
                 246.02 
                 250.79 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
             
               
                   
                 TABLE 5 
               
             
            
               
                   
                   
               
               
                   
                 Alkylation Intercooler Duties (MM kcal/hr) 
               
            
           
           
               
               
               
            
               
                   
                 Mixed C2 
                 Polymer Grade 
               
               
                   
                 (Ethane/Ethylene) 
                 Ethylene (Prior Art) 
               
               
                   
                   
               
            
           
           
               
               
               
            
               
                 Lower Intercooler (see 
                 −16.5 
                 −19.4 
               
               
                 intercooler 63b in FIG. 2) 
               
               
                 Upper Intercooler (see 
                 −16.5 
                 −19.4 
               
               
                 intercooler 63a in FIG. 2) 
                   
                   
               
               
                 Total 
                 −33 
                 −38.8 
               
               
                   
               
            
           
         
       
     
     One additional integration option is illustrated in  FIG. 3  and involves eliminating the transalkylation section  178  and the polyethyl benzenes (PEB) column  180 . The ethyl benzene (EB) column bottoms  220  is passed to the primary absorber  40  by combining the ethyl benzenes bottoms stream  220  with the debutanized gasoline recycle stream  42  ( FIG. 1 ) to supplement some of the debutanized gasoline recycle, reducing the amount of recycle that is required. If all of the ethylene produced by the FCC process  10   a  is used in the EB process  10   c , the EB column bottoms  220  would reduce the required debutanized gasoline recycle stream  42  by an amount ranging from about 5 to about 10%. The polyethyl benzenes including DEB and PEB would ultimately end up as a high octane component in the gasoline product stream  76 . Because the EB column bottoms  220  contains a small fraction of heavy components (e.g., diphenylethane, ethyldiphenylethane) that may be slightly too heavy for the gasoline pool, another alternative shown in  FIG. 3  is to send the EB column bottoms  220  to the FCC main column  22 , where the heavier species in this stream would be removed in a heavier fraction such as the heavy naphtha draw. The lighter species in this stream will still act to reduce the required debutanized gasoline recycle stream  42 , as they will exit in the unstabilized gasoline stream  76  that is recovered from the main column overhead stream  26 . 
     Thus, improved processing schemes and arrangements are provided for obtaining ethylene and ethane via the catalytic cracking of a heavy hydrocarbon feedstock and converting the ethylene into ethyl benzene without separating the ethane from the feed stream. More particularly, processing schemes and arrangements are provided that advantageously eliminate any separation of ethylene from ethane produced by a FCC process prior to using the combined ethylene/ethane stream as a feed for an ethyl benzene process. 
     The disclosed processes and schemes may be practiced in the absence of any element, part, step, component, or ingredient which is not specifically disclosed herein.