Abstract:
An integrated process for treating pyrolysis gasolines, including: feeding the pyrolysis gasoline to a first stage wherein the pyrolysis gasoline is substantially depentanized and acetylene and diolefins are reacted with hydrogen to produce an effluent having a reduced acetylene and diolefin content; and feeding the effluent to a second stage, wherein the second stage comprises a catalytic distillation hydrotreating process. The second stage may include a first catalytic distillation reactor system comprising a first distillation reaction zone containing a first hydrogenation catalyst, and the process may further include treating a C 6 -boiling material in the first distillation reaction zone to react sulfur compounds with hydrogen to produce hydrogen sulfide, the treated C 6  material being concurrently separated as a second overheads from C 7  and heavier material by fractional distillation, the C 7  and heavier material being removed from the first distillation reaction zone as a first bottoms.

Description:
BACKGROUND OF INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    Embodiments disclosed herein relate to a process for the processing of pyrolysis gasoline. More particularly, embodiments disclosed relate to a separation of the pyrolysis gasoline into commercially attractive fractions and treating the fractions to remove or convert unwanted contaminants in an integrated process wherein some separations are carried out concurrently with a specific treatment in distillation column reactors containing the appropriate catalysts. 
         [0003]    2. Background Art 
         [0004]    Pyrolysis gasoline (also referred to as “pygas”) is a liquid by-product of the steam cracking process to make ethylene and propylene. Pyrolysis gasoline is a highly unsaturated hydrocarbon mixture (carbon range of about C 5 -C 14 ) that is rich in dienes, olefin and aromatics, especially benzene. In addition, pyrolysis gasoline includes undesirable heteroatom-containing hydrocarbons, such as sulfur- and nitrogen-containing compounds. 
         [0005]    To allow for its use as a gasoline blendstock, pyrolysis gasoline must be at least partially hydrogenated or hydrotreated to reduce the levels of unsaturation and heteroatom-containing hydrocarbons. Left untreated, pyrolysis gasoline typically degrades to form gums and varnishes in fuel systems. 
         [0006]    Pygas is not stable, and, in one prior art process, is treated in a two-stage reactor configuration, as illustrated in  FIG. 1 . The first column DP depentanizes the pygas feed, and the second column HR removes components that boil higher than the desired gasoline end point. The remaining pygas is then treated in a two-stage reactor configuration. 
         [0007]    The first stage reactor FSR is commonly loaded with a Pd or Ni catalyst and operated at moderate temperatures (150-375° F.) and at pressures of 20-70 bar in order to cyclodienes, styrene and styrenic (alkenyl benzene) compounds. Typically styrene and styrenic levels in the gasoline to the first stage reactor FSR are in the 2 to 8 wt. % range, more typically 2 to 4 wt. %. Sulfur levels are typically in the 50 to 1000 wt. ppm, more typically 100 to 400 ppm. 
         [0008]    Although the pyrolysis gasoline produced from a first stage reactor FSR is sufficiently stable for gasoline blending, the material often cannot be used because of the low sulfur concentration now required in the gasoline pool. This has increased the importance of having a good second-stage reactor SSR. To meet sulfur regulations, the product from the first stage reactor FSR is sent to a second stage reactor SSR having CoMo and/or NiMo catalysts to remove sulfur, where the second stage reactor SSR is typically operated at pressures of 20-70 bar and temperatures of 450-700° F. 
         [0009]    Following the second stage, it is fairly common that there is further distillation (C6D, C7D) of the pygas to isolate a C 6  fraction for benzene extraction, or perhaps even a C 7 -C 9  faction for toluene/xylenes extraction. For downstream extraction, olefins and sulfur are typically removed to very low levels while aromatics saturation is minimized. 
         [0010]    The C 5 s are recovered and may be used in gasoline, or in isomerization, etherification and alkylation processes, among others. As noted above, isoprene may be recovered as a useful product. Normally, however, the diolefins are removed along with acetylenes by selective hydrogenation. If desired, the C 5 s may be completely hydrogenated and returned to the naphtha cracker ethylene plant as recycle. 
         [0011]    The C 6  and heavier fractions contain sulfur compounds which are usually removed by hydrodesulfurization. The aromatic compounds are often removed and purified by distillation to produce benzene, toluene, and xylenes. The aromatic containing fraction is often treated with clay material to remove trace olefinic and diolefinic material. 
         [0012]    A common problem with prior second-stage pygas reactors is short run life due to the highly reactive nature of the species in the pygas (even after first stage treatment). Unconverted styrenic compounds and dienes tend to lead to polymer formation and fouling when exposed to the higher temperatures of the second stage. This causes fouling in heaters and high pressure drop across the catalyst bed. 
         [0013]    What is still needed therefore is improved catalyst stability and reduced fouling and plugging problems and improved run length in pygas units without a major revamp of the first-stage reactor to increase conversion of styrenics and dienes. It is also desired that such improved processes result in reduced capital or operating costs. 
       SUMMARY OF INVENTION 
       [0014]    In one aspect, embodiments disclosed herein relate to an integrated process for treating pyrolysis gasolines. The process may include: feeding the pyrolysis gasoline to a first stage wherein the pyrolysis gasoline is substantially depentanized and acetylene and diolefins are reacted with hydrogen to produce an effluent having a reduced acetylene and diolefin content; and feeding the effluent to a second stage, wherein the second stage comprises a catalytic distillation hydrotreating process. 
         [0015]    In some embodiments, the second stage may include a first catalytic distillation reactor system comprising a first distillation reaction zone containing a first hydrogenation catalyst, and the process may further include treating a C 6 -boiling material in the first distillation reaction zone to react sulfur compounds with hydrogen to produce hydrogen sulfide, the treated C 6  material being concurrently separated as a second overheads from C 7  and heavier material by fractional distillation, the C 7  and heavier material being removed from the first distillation reaction zone as a first bottoms. 
         [0016]    Other aspects and advantages of the invention will be apparent from the following description and the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0017]      FIG. 1  is a simplified flow diagram of a prior art two-stage reactor pygas treating system. 
           [0018]      FIG. 2  is a flow diagram in schematic form of a first embodiment of the process for treating pygas according to the present disclosure. 
           [0019]      FIG. 3  is a flow diagram in schematic form of a second embodiment of the process for treating pygas according to the present disclosure. 
           [0020]      FIG. 4  is a flow diagram in schematic form of a third embodiment of the process for treating pygas according to the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    The concurrent reaction and separation of products has been referred to as catalytic distillation or reactive distillation. Within the scope of this application, the expression “catalytic distillation reactor system” denotes an apparatus in which the reaction and the separation of the products take place at least partially simultaneously. The apparatus may comprise a conventional catalytic distillation column reactor, where the reaction and distillation are concurrently taking place at boiling point conditions, or a distillation column combined with at least one side reactor, where the side reactor may be operated as a liquid phase reactor or a boiling point reactor. While both catalytic distillation processes may be preferred over conventional liquid phase reaction followed by separations, a catalytic distillation column reactor may have the advantages of decreased piece count, efficient heat removal (heat of reaction may be absorbed into the heat of vaporization of the mixture), and a potential for shifting equilibrium. 
         [0022]    Embodiments disclosed herein use catalytic distillation hydrotreating processes (carried out in a distillation column reactor system) to achieve a number of improvements in pygas treating. Specifically, the present inventors have discovered that catalytic distillation may offer superior catalyst stability and may avoid fouling and plugging problems due to the washing action of the reflux in the column, especially for embodiments in which the second stage hydrotreating is performed in catalytic distillation reactor systems. 
         [0023]    As defined herein, hydrotreating is considered to be a process wherein hydrogen is utilized to remove unwanted contaminants by 1) selective hydrogenation, or 2) destructive hydrodesulfarization. 
         [0024]    The operation of the distillation column reactor results in both a liquid and vapor phase within the distillation reaction zone. A considerable portion of the vapor is hydrogen while a portion is vaporous hydrocarbon from the petroleum fraction. Within the distillation reaction zone (the zone where a bed of catalyst, usually associated with or prepared as distillation structures, is positioned) there is an internal reflux and liquid from an external reflux which cools the rising vaporous hydrocarbon condensing a portion within the bed. 
         [0025]    Without limiting the scope of the invention it is proposed that the mechanism that produces the effectiveness of the present hydrotreating is the condensation of a portion of the vapors in the reaction system which occludes sufficient hydrogen in the condensed liquid to obtain the requisite intimate contact between the hydrogen and the sulfur compounds, olefins, diolefins and the like, in the presence of the catalyst to result in their hydrogenation. In addition, the downward flow of the internal reflux continuously washes the catalyst, which may reduce the build up of coke, coke precursors, and reaction by products, thus increasing catalyst life between regenerations. 
         [0026]    The result of the operation of the process in the catalytic distillation mode is that lower hydrogen partial pressures (and thus lower total pressures) may be used to achieve results comparable to the prior art high hydrogen pressure operations. As in any distillation there is a temperature gradient within the distillation column reactor. The temperature at the lower end of the column contains higher boiling material and thus is at a higher temperature than the upper end of the column. 
         [0027]    The catalytic material is preferably a component of a distillation system functioning as both a catalyst and distillation packing, i.e., a packing for a distillation column having both a distillation function and a catalytic function, however, the present integrated refinery may also use such systems as described in U.S. Pat. Nos. 5,133,942; 5,368,691; 5,308,592; 5,523,061; and European Patent Application No. EP 0 755 706 A1. 
         [0028]    The reaction system can be described as heterogeneous, since the catalyst remains a distinct entity. A preferred catalyst structure for the present hydrogenation reaction comprises flexible, semi-rigid open mesh tubular material, such as stainless steel wire mesh, filled with a particulate catalytic material in one of several embodiments recently developed in conjunction with the present process. 
         [0029]    Of particular interest is the structured packing disclosed and claimed in U.S. Pat. No. 5,730,843 which is incorporated. Other catalyst structures useful in the present refinery scheme are described in U.S. Pat. Nos. 5,266,546; 4,242,530; 4,443,559; 5,348,710; 4,731,229 and 5,073,236 which are also incorporated by reference. 
         [0030]    The particulate catalyst material may be a powder, small irregular chunks or fragments, small beads and the like. The particular form of the catalytic material in the structure is not critical so long as sufficient surface area is provided to allow a reasonable reaction rate. The sizing of catalyst particles can be best determined for each catalytic material (since the porosity or available internal surface area will vary for different material and, of course, affect the activity of the catalytic material). 
         [0031]    Catalysts which are useful in all the reactions described herein include metals of Group VII of the Periodic Table of Elements. Catalysts preferred for the selective hydrogenation of acetylenes and diolefins are alumina supported palladium and nickel catalysts. Catalysts preferred for the hydrodesulfurization reactions include Group VIII metals such as cobalt, nickel, palladium, alone or in combination with other metals such as molybdenum or tungsten on a suitable support which may be alumina, silica-alumina, titania-zirconia or the like. 
         [0032]    Generally, the metals are deposited as the oxides on extrudates or spheres, typically alumina. The catalyst may then be prepared as the structures described above, and may be fully or partially sulfided prior to use. 
         [0033]    Referring now to  FIG. 2 , a simplified flow diagram of a pygas treating process according to an embodiment of the present disclosure is illustrated. The feed comprises pyrolysis gasoline which is a complex mixture of predominately hydrocarbon paraffins, naphthenics, acetylenes, dienes, cyclodienes and styrenic compounds (alkynyl benzenes) and other aromatics boiling in the range of 10 to 450° F. Typical pyrolysis gasolines may contain: 4-30% aromatics (2-8% styrene and styrenics), 10-30% olefins, 35-72% paraffins and 1-20% unsaturated containing trace amounts of sulfur (from 100 to 100 wppm), oxygen and/or nitrogen organic compounds. The hydrocarbons are principally C 4 -C 8  alkanes, olefins, diolefins, acetylenes, benzene, toluene and xylenes and some heavier residuum. 
         [0034]    The pyrolysis gasoline is fed to the depentanizer  10  via flow line  101 . In the depentanizer, the C 5 s and lighter material are taken as overheads via flow line  102  and sent for further treatment. The C 6  and heavier material is taken as bottoms via flow line  103  and fed to a second distillation column  20 , where the end point of gasoline is adjusted by removing unwanted heavy material as bottoms via flow line  104 . The pyrolysis gasoline now containing the C 6  to 450° F. boiling material is taken as overheads via flow line  105  and combined with make up hydrogen from flow line  106  and fed via flow line  108  to the first stage hydrogenation reactor  30  containing a bed  32  of hydrogenation catalyst, which is typically nickel or palladium. 
         [0035]    The reactor, as shown, is a standard fixed bed trickle flow reactor. The effluent from the reactor  30 , including unreacted hydrogen, is taken via flow line  109  and split into two streams. The first, the recycle stream, is recycled to the top of the reactor via flow line  107 . The second stream, in flow line  110 , is fed to the second stage hydrogenation reactor in the dehexanizer  50  and final splitter column  60 . A bed  52  of NiMo or CoMo is placed in the upper end or rectification section of the dehexanizer to treat the C 6  material to prepare it for benzene extraction. C 6 s are recovered as an overheads fraction from dehexanizer  50  via flow line  114 . 
         [0036]    In particular, the sulfur may be removed down to about 50 ppm by weight levels and olefins are reduced. Two beds  62  and  64  of catalyst are placed in the rectification and stripping sections of the final splitter  60  to treat material going to both overhead and bottoms streams,  117  and  118 , respectively. 
         [0037]    Hydrogen may be supplied via flow lines  120 ,  122  to column  50  and flow line  121  to column  60 . Preferably, the hydrogen is fed below beds  52  and  64 . Because the streams are useful for aromatics extraction it is not important to preserve olefins in the second stage hydrogenation, but rather to minimize aromatic saturation. 
         [0038]    In  FIG. 3  there is shown another embodiment in accordance with the present disclosure. Specifically, the embodiments may include a first stage depentanizing step DP coupled with a catalytic distillation hydrotreating step HT. 
         [0039]    In the embodiment illustrated in  FIG. 3 , the pyrolysis gasoline, along with hydrogen, is fed to the first stage reactors via flow lines  301 ,  301 A and  302 . The first stage reactor may include one or two downflow trickle bed reactor vessels  210  and  220  containing beds  212  and  222  of nickel or palladium catalyst, respectively. Effluent from the first vessel  210  is taken via flow line  303  and a portion may be recycled back to vessel  210  via flow lines  307  and  302  with the remainder being fed to the second vessel  220  via flow line  306 . 
         [0040]    The effluent from the second vessel  220  is taken via flow line  304  with a portion being recycled to the top of the first vessel  210  via flow line  305 ,  307  and  302 . The highly reactive materials, such as acetylenes and dienes are saturated in the first stage. Although described above with respect to two down flow reactors  210 ,  220 , processes described herein may include one or more down flow reactors, where, in general, at least a portion of the effluent from the last first-stage reactor may be recycled. The remainder of the effluent is fed via flow line  308  to a first distillation column  230 , which acts as a depentanizer to remove the C 5  and lighter material as overheads via flow line  309 . Because the highly reactive materials have been removed or converted, fouling in the depentanizer may be reduced or eliminated. 
         [0041]    The bottoms from the depentanizer  230  are fed via flow line  310  to a second distillation column  250  which contains a bed  252  of hydrogenation catalyst, particularly Ni—Mo or Co—Mo as oxides supported on an alumina base, in the rectification section to remove sulfur compounds and saturate olefins and any diolefins from the C 6  fraction which is considered benzene concentrate. Hydrogen is fed to the column  250  via flow lines  320  and  322 . C 6 s are recovered as an overheads fraction from column  250  via flow line  314 . The bottoms from the second distillation column are fed via flow line  316  to a third distillation column  260  which contains two beds  262  and  264  in the rectification and stripping sections respectively, treating material going to both overhead and bottoms streams,  317  and  318 , respectively. Hydrogen is fed to column  260  via flow lines  320  and  321 . The distillation column  250 , which treats the C 6  material, is operated as milder conditions than the column  260  which treats the heavier material. 
       EXAMPLE 
       [0042]    An embodiment of the invention is described in the following example. Feed to the process is 20,000 bbl/day of a typical pygas feed. The stream numbers refer to those in TABLE 1, below, and  FIG. 4 . 
         [0043]    The first step in the process removes most of the styrenic components in the feed stream  401  by reaction with excess H 2  fed via flow line  401 A in selective hydrogenation unit (SHU) reactor  415 . The SHU reactor is a conventional fixed bed reactor that contains a bed  422  of palladium or nickel catalyst. The vapor stream  424  withdrawn from the cold drum  420 , consisting mostly of the excess H 2 , may be cascaded downstream to a hydrogenation system which treats the benzene concentrate (described below). The liquid stream  413  withdrawn from the cold drum  420  goes to the depentanizer column  430 . 
         [0044]    Distillate product from the depentanizer column  430  is a vapor stream  410  comprising C 5  and lighter components. Bottoms product  462  comprising the C 6 /C 7+  components is sent to a benzene concentrate/C 7+  splitter column  440 . The column  440  recovers 99% of the benzene in the feed in the overhead product stream  469 . 
         [0045]    Bottoms product from the benzene concentrate/C 7+  splitter column  440  is fed via flow line  467  to a C 7+  catalytic distillation (CD) hydrotreating system comprising a distillation column reactor  450  (reboiler, heat exchangers, drums, H 2  recycle compressor, and reflux pump are conventional components and not shown). 
         [0046]    The distillation column reactor  450  is configured with reaction zones comprised of structured packing containing a Co—Mo catalyst and with trays above and below the reaction zones  451  and  452 . The reaction zones are configured above and below the liquid feed point while hydrogen is fed directly into the column below the reaction zones via flow line  453 . 
         [0047]    Reaction conditions with respect to the temperature and hydrogen partial pressure profiles across the reaction zone needed to achieve desired desulfurization performance with minimal aromatics and olefin loss are feedstock and catalyst dependent. These profiles are in turn dependent on the system pressure and reflux ratio. For this example, the pressure is 250 psig and the reflux ratio is 1.7. Under these conditions, the temperature profile across the reaction zone is essentially flat at 560° F. and the hydrogen partial pressure is 93.7 psi at the bottom of the reaction zone and 84.5 psi at the top of the reaction zone. 
         [0048]    The hot vapor distillate stream  464  from the distillation column reactor  450  may provide the heat duty for the depentanizer column  430  and the benzene concentrate/C 7+  splitter column  440  while being partially condensed and the resulting vapor/liquid mixtures are combined and separated. The liquid fraction may be split to reflux to the distillation column reactor  450 , fed via flow line  485 , while the remainder is withdrawn via flow line  489  as a hot feed to a C 7+  stripper-stabilizer column  460 . Additional heat may be recovered from the vapor fraction by using it to supply the heat duty for the benzene stripper column  490 . The final C 7+  product stream  431  is obtained after cooling in heat exchangers, for example, heat may be recovered from the hot C 7+  product  431  by heat exchange with the feed  462  to the benzene concentrate/C 7+  splitter column  440 . 
         [0049]    The benzene hydrotreat reactor  470  is a fixed bed-vapor phase-adiabatic reactor. Distillate product stream  469  from the benzene concentrate/C 7+  splitter  440  is vaporized and combined with H 2  (e.g., recycle and cascaded vapor stream  424 ) and heated to reaction temperature. Effluent product stream  468  from reactor  470  is partially condensed and vapor/liquid separated via condensers and drums  480 . The resulting condensates are fed via flow line  478  to the benzene concentrate/C 7+  stripper column  490 . The H 2  rich vapor fraction  479  may be recycled within the system after removal of a purge. 
         [0050]    Benzene concentrate product stream  446  is recovered from the bottom of the stripper column  490  after cooling. 
         [0000]    
       
         
               
               
               
               
               
               
               
               
             
           
               
                 TABLE I 
               
               
                   
               
             
             
               
                 Stream No. 
                 401 
                 413 
                 469 
                 464 
                 431 
                 468 
                 446 
               
               
                 Temp. ° F. 
                 122 
                 221 
                 232 
                 485 
                 105 
                 298 
                 105 
               
               
                 Press. PSI 
                 384 
                 368 
                 40 
                 250 
                 97 
                 351 
                 102 
               
               
                 Tot. Mass Flow lb/hr 
                 260000 
                 259766 
                 86500 
                 467676 
                 168192 
                 99716 
                 86725 
               
               
                 Component, 
               
               
                 Mass Flow lb/hr 
               
               
                 H2 
                 0 
                 65 
                 0 
                 4858 
                 0 
                 5982 
                 0 
               
               
                 CH4 
                 0 
                 166 
                 0 
                 3857 
                 0 
                 3360 
                 0 
               
               
                 H2S 
                 0 
                 0 
                 0 
                 101 
                 0 
                 52 
                 0 
               
               
                 N-BUTANE 
                 0 
                 0 
                 0 
                 2 
                 0 
                 63 
                 32 
               
               
                 ISOPRENE 
                 104 
                 8 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 2M2B 
                 26 
                 111 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 I-PENTANE 
                 104 
                 97 
                 0 
                 0 
                 0 
                 87 
                 64 
               
               
                 CPD 
                 338 
                 24 
                 1 
                 0 
                 0 
                 0 
                 0 
               
               
                 CPENTENE 
                 260 
                 239 
                 22 
                 0 
                 0 
                 37 
                 32 
               
               
                 CPENTANE 
                 234 
                 552 
                 138 
                 0 
                 0 
                 174 
                 155 
               
               
                 1,4PD 
                 598 
                 48 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 PENTENE 
                 338 
                 481 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 N-PENTENE 
                 130 
                 463 
                 678 
                 0 
                 0 
                 59 
                 45 
               
               
                 2,3DMBD 
                 7847 
                 682 
                 10891 
                 0 
                 0 
                 713 
                 675 
               
               
                 2MPENTENE 
                 7795 
                 11040 
                 8748 
                 0 
                 0 
                 107 
                 100 
               
               
                 N-HEXANE 
                 5196 
                 8920 
                 61413 
                 0 
                 0 
                 21157 
                 19631 
               
               
                 BENZENE 
                 68277 
                 62068 
                 1364 
                 1121 
                 616 
                 62530 
                 60691 
               
               
                 CHEXANE 
                 1299 
                 1513 
                 787 
                 278 
                 149 
                 2023 
                 1974 
               
               
                 HEPTENE 
                 7795 
                 6023 
                 2389 
                 1981 
                 988 
                 0 
                 0 
               
               
                 N-HEPTANE 
                 5196 
                 6947 
                 0 
                 17308 
                 8870 
                 3277 
                 3233 
               
               
                 TOLUENE 
                 48847 
                 48615 
                 0 
                 108207 
                 48391 
                 66 
                 66 
               
               
                 MCHEXANE 
                 2650 
                 2821 
                 0 
                 6410 
                 3014 
                 7 
                 7 
               
               
                 STYRENE 
                 11692 
                 2104 
                 0 
                 7 
                 2 
                 0 
                 0 
               
               
                 EBENZENE 
                 5093 
                 14861 
                 0 
                 46237 
                 17082 
                 4 
                 4 
               
               
                 ′XYLENE 
                 22709 
                 22704 
                 0 
                 62265 
                 22574 
                 5 
                 5 
               
               
                 2,5DMHEXD 
                 156 
                 13 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 OCTENE 
                 4489 
                 3974 
                 0 
                 1882 
                 818 
                 4 
                 3 
               
               
                 OCTANE 
                 5794 
                 6965 
                 0 
                 24071 
                 10187 
                 6 
                 6 
               
               
                 INDENE 
                 4807 
                 1485 
                 0 
                 247 
                 63 
                 0 
                 0 
               
               
                 INDANE 
                 364 
                 3743 
                 0 
                 19342 
                 5178 
                 0 
                 0 
               
               
                 MSTYRENE 
                 9717 
                 4133 
                 0 
                 2007 
                 554 
                 0 
                 0 
               
               
                 IPBENZENE 
                 19123 
                 24800 
                 0 
                 88056 
                 28255 
                 2 
                 2 
               
               
                 DCPD 
                 11666 
                 1644 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 UNDECANE 
                 1039 
                 1039 
                 0 
                 4278 
                 1034 
                 0 
                 0 
               
               
                 C10NAPH 
                 4105 
                 5726 
                 0 
                 51005 
                 15239 
                 0 
                 0 
               
               
                 DHDCPD 
                 3040 
                 11618 
                 0 
                 8900 
                 1822 
                 0 
                 0 
               
               
                 DMCHEXANE 
                 0 
                 0 
                 0 
                 320 
                 132 
                 0 
                 0 
               
               
                 IPCHEXANE 
                 0 
                 0 
                 0 
                 578 
                 132 
                 0 
                 0 
               
               
                 DODECANE 
                 2598 
                 2598 
                 0 
                 9631 
                 2016 
                 0 
                 0 
               
               
                 BENZOTHIO 
                 109 
                 109 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 THIOPHENE 
                 68 
                 68 
                 66 
                 0 
                 0 
                 0 
                 0 
               
               
                 MEINDENE 
                 1299 
                 1299 
                 0 
                 769 
                 175 
                 0 
                 0 
               
               
                 MEINDANE 
                 0 
                 0 
                 0 
                 3959 
                 852 
                 0 
                 0 
               
               
                   
               
             
          
         
       
     
         [0051]    In addition to the above described embodiments, other flow and reaction configurations may be possible. Flow configurations in some embodiments may result in the first stage reactor treating all or a portion of the pygas feed (e.g., the depentanizer location may be varied). In other embodiments, the second stage catalytic distillation reactors may include additional reaction zones, such as catalyst in the lower portion of the de-C 6  column to treat the heavier gasoline. Other embodiments may also be envisaged where the second stage treatment is conducted in catalytic distillation reactor systems, depending on various heat integration issues and other site-specific factors. 
         [0052]    Thus, by employing catalytic distillation hydrotreating techniques and apparatuses, the present inventors advantageously may improve run length in pygas units without a major revamp of the first-stage reactor to increase conversion of styrenics and dienes. This represents a significant benefit. A further capital cost advantage can be gained through the combination of two unit operations. Namely, the second stage hydrotreating step can be conducted in the same column(s) that isolate the C 6  fraction for benzene extraction, or any other suitable downstream column. 
         [0053]    Improved stability of the catalyst through use of catalytic distillation may also allow for reduced temperatures and pressures (reduced severity) in the first stage reactor, thus improving cycle length in the first stage reactor. Further, embodiments disclosed herein may advantageously allow the distillation columns fractionating untreated pyrolysis gasoline to be operated at much lower pressure as compared to typical operating conditions, which reduces the likelihood of fouling of the reboilers. 
         [0054]    Additionally, embodiments disclosed herein may perform, in a single multifunctional distillation column, many of the separate steps and processes as described above with respect to the prior art. Processes disclosed herein may also allow for energy savings as compared to prior art processes. 
         [0055]    While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.