WO2012173755A2

WO2012173755A2 - Heavy aromatics processing

Info

Publication number: WO2012173755A2
Application number: PCT/US2012/039136
Authority: WO
Inventors: Timothy P. Bender; John R. Porter
Original assignee: Exxonmobil Chemical Patents Inc.
Priority date: 2011-06-13
Filing date: 2012-05-23
Publication date: 2012-12-20
Also published as: WO2012173755A3

Abstract

In a process for converting C₉+ aromatic hydrocarbons to lighter aromatic products, a C₈+ aromatic hydrocarbon feed is passed through a xylenes fractionation column to separate the feed into a C₈ rich vapor overhead fraction and a C₁₀+ rich liquid bottoms fraction. In addition, a vapor side-stream is removed from adjacent the bottom of the xylenes fractionation column and at least part of the vapor side-stream is passed through a condenser to condense a heavy liquid stream rich in C₁₀ and higher aromatics and leave a lighter vapor stream rich in C₉ and C₁₀ aromatics. The lighter vapor stream rich in C₉ and C₁₀ aromatics is then contacted with toluene or benzene in the presence of a trans alky lation catalyst system under transalkylation reaction conditions to produce a transalkylation reaction product comprising (i) benzene or toluene and (ii) xylene.

Description

HEAVY AROMATICS PROCESSING

PRIORITY CLAIM

[0001] This application claims the benefit of Provisional Application No. 61/496,262, filed June 13, 201 1 , the disclosure of which is incorporated by reference in its entirety.

FIELD

[0002] This invention relates to heavy aromatics processing and in particular to a process for transalkylating a C9+ aromatics feed to produce lighter aromatic products. BACKGROUND

[0003] Benzene, toluene, and xylenes (BTX) are important petrochemical materials, for which the worldwide demand is steadily increasing. The demand for xylenes, particularly para-xylene, has increased in proportion to the increase in demand for polyester fibers and film. Benzene is a highly valuable product for use as a chemical raw material. Toluene is also a valuable petrochemical for use as a solvent and an intermediate in chemical manufacturing processes and as a high octane gasoline component.

[0004] A major source of benzene, toluene, and xylenes (BTX) is catalytic reformate, which is produced by contacting petroleum naphtha with a strong hydrogenation/dehydrogenation catalyst, such as platinum, on a moderately acidic support, such as a halogen-treated alumina. The resulting reformate is a complex mixture of paraffins, the desired Ce to Cs aromatics, in addition to a significant quantity of heavier aromatic hydrocarbons. Usually, a Ce to Cs fraction is separated from the reformate, extracted with a solvent selective for aromatics or aliphatics to produce a mixture of aromatic compounds that is relatively free of aliphatics. This mixture of aromatic compounds is composed of benzene, toluene and xylenes (BTX), along with ethyl benzene.

[0005] Other valuable sources of BTX are the C₉+ heavy aromatics streams available in refineries as the by-products from catalytic reforming units and xylene isomerization units. Thus, for example, U.S. Pat. No. 5,942,651 discloses a process for converting C₉+ aromatic hydrocarbons to lighter aromatic products, comprising the step of reacting (i) the C₉+ aromatic hydrocarbons and (ii) toluene or benzene under trans alky lation reaction conditions, over a first catalyst composition comprising a zeolite having a constraint index ranging from 0.5 to 3 and a hydrogenation component and a second catalyst composition comprising an intermediate pore size zeolite having a constraint index ranging from 3 to 12 and a silica to alumina ratio of at least about 5, to produce a trans alky lation reaction product comprising (i) benzene or toluene and (ii) xylene.

[0006] One problem with producing BTX by catalytic transalkylation of C9+ aromatic feeds is that the life of the catalyst is found to decrease as the amount of very heavy aromatic compounds, namely C₁₀ and higher aromatics, in the feed increases. The conventional approach for dealing with this problem involves either using a liquid side-stream, rather than the bottoms stream, from the Cs distillation column as the feed to the transalkylation process or fractionating the bottoms stream in a separate heavy aromatics tailing column before feeding the overhead from the tailing column to the transalkylation process. Although the liquid side-stream option has the lower capital investment and energy cost, it only partially removes the heavy components in the feed and so leads to increased catalyst regeneration and replacement costs. The heavy aromatics tailing column removes most of the heavy components in the feed but requires the highest capital and energy expenditure.

[0007] According to the present invention, it has now been found that, by integrating separation of the very heavy aromatic components into the xylenes fractionation process, the capital investment and energy costs associated with removal of these heavy components can be reduced. This can be achieved by removing a vapor side-stream from near the bottom of the xylenes fractionation column and passing the side-stream through a separate condenser to condense heavy aromatic components from the side stream before the side stream is passed to the transalkylation catalyst.

SUMMARY

[0008] The invention resides in a process for converting C₉+ aromatic hydrocarbons to lighter aromatic products, the process comprising:

(a) passing a Cs+ aromatic hydrocarbon feed through a xylenes fractionation column to separate said feed into a Cs rich vapor overhead fraction and a C1₀+ rich liquid bottoms fraction;

(b) removing a vapor side-stream from adjacent the bottom of said xylenes fractionation column;

(c) passing at least part of said vapor side-stream through a rectifier to condense a stream rich in C₉ and a stream rich in C₁₀ and higher aromatics; and (d) contacting said stream rich in C9 aromatics with toluene and/or benzene in the presence of a transalkylation catalyst system under transalkylation reaction conditions to produce a transalkylation reaction product comprising (i) benzene and/or toluene and (ii) xylene.

[0009] In one embodiment, the vapor side-stream is removed from an internal C9+ aromatics rectification section of said xylenes fractionation column and the heavy liquid stream is conveniently recycled to the internal C9+ aromatics rectification section as a reflux stream.

[00010] In another embodiment, the vapor side-stream is fed to a C9+ aromatics rectifier separate from and external to said xylenes fractionation column and the overhead from the rectifier is passed through said condenser. Conveniently, a portion of the condensate is recycled to the rectifier as a reflux stream.

[00011] Conveniently, the transalkylation catalyst system comprises a first catalyst bed comprising a first molecular sieve having a constraint index less than 3 and a first hydrogenation component. Generally, the transalkylation catalyst system also comprises a second catalyst bed upstream of the first catalyst bed and comprising a second molecular sieve having a constraint index the range of about 3 to about 12 and a second hydrogenation component. Typically, the transalkylation catalyst system further comprises a third catalyst bed downstream of the first catalyst bed and comprising a third catalyst composition comprising a third molecular sieve having a Constraint Index in the range of about 1 to about 12.

BRIEF DESCRIPTION OF THE DRAWINGS

[00012] Figure 1 is a flow diagram of part of a conventional process for converting C9+ aromatic hydrocarbons to lighter aromatic products.

[00013] Figure 2 is a flow diagram of part of a further conventional process for converting C9+ aromatic hydrocarbons to lighter aromatic products.

[00014] Figures 3A and 3B are flow diagrams showing schematically part of an apparatus for converting C9+ aromatic hydrocarbons to lighter aromatic products according to embodiments of the invention. [00015] Figure 4A and 4B are flow diagrams showing schematically part of an apparatus for converting C9+ aromatic hydrocarbons to lighter aromatic products according to other embodiments of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[00016] As used herein, the numbering scheme for the Periodic Table Groups is as described in Chemical and Engineering News, 63(5), 27 (1985).

[00017] The term "aromatic" is used herein in accordance with its art-recognized scope which includes alkyl substituted and unsubstituted mono- and polynuclear compounds.

[00018] The term "C_n" hydrocarbon or aromatic as used herein means a hydrocarbon or aromatic compound having n number of carbon atom(s) per molecule. The term "C_n+" hydrocarbon or aromatic means hydrocarbon or aromatic compound having n or more than n carbon atom(s) per molecule. The term "Cn-" hydrocarbon or aromatic means a hydrocarbon or aromatic compound having less than n carbon atom(s) per molecule.

[00019] Described herein is an improved method for reducing the level of heavy aromatic compounds, namely C1₀+ aromatic compounds, in the feed to a process for converting C₉+ aromatic hydrocarbons to lighter aromatic products by trans alky lation with benzene and/or toluene.

[00020] The feed to the present process is any conventional Cs+ hydrocarbon feed available in a petroleum or petrochemical refinery, such as a catalytic reformate, FCC or TCC naphtha, or a xylene isomerizate from which heptanes and lighter components have been removed. The feed is initially passed through a xylenes fractionation column to remove the C8 components from the feed and leave a C₉+ rich fraction which can then be fed to a trans alky lation reactor for reaction with benzene or toluene in the presence of a trans alky lation catalyst system to produce lighter aromatic products, primarily BTX. However, to avoid rapid aging of the trans alky lation catalyst it is normal to adjust the composition of the C₉+ rich fraction to reduce the level of very heavy aromatic compounds, namely C₁₀ and higher aromatics, that contribute to catalyst deactivation.

[00021] One known method of adjustment of the composition of the C₉+ rich fraction is shown in Figure 1, in which a Cs+ hydrocarbon feed is fed by line 1 1 to a xylenes fractionation column 12, where the feed is fractionated into Cs rich vapor overhead fraction 13 and a C₉+ rich liquid bottoms fraction 14. However, rather than feed the C₉+ rich liquid bottoms fraction 14 to the transalkylation unit (not shown), a liquid side stream 15 is removed from adjacent to the bottom of the tower and used as the transalkylation feed. Although this option minimizes capital investment and energy cost, it only partially removes the deleterious heavy components in the feed and so leads to increased catalyst regeneration and replacement costs.

[00022] Another known method of adjustment of the composition of the C9+ rich fraction is shown in Figure 2, in which a Cs+ hydrocarbon feed is again fed by line 11 to a xylenes fractionation column 12, where the feed is fractionated into Cs rich vapor overhead fraction 13 and a C9+ rich liquid bottoms fraction 14. In this case, however, the C9+ rich liquid bottoms fraction 14 is vaporized and fed to in a separate heavy aromatics tailing column 16, where the fraction 14 is separated into an overhead stream 17, which is used as the feed to the transalkylation process, and a bottoms stream 18, which is purged. A heating means (not shown) for stream 14 is advantageous but optional as column 12 is generally operated at a higher pressure than column 16. While the heavy aromatics tailing column 16 is effective in removing most of the deleterious heavy components in the feed, it requires significant capital and energy expenditure.

[00023] A first example of the present improved treatment process is shown in Figure 3A, in which a Cs+ hydrocarbon feed is fed by line 21 to a xylenes fractionation column 22, where the feed is fractionated into Cs rich vapor overhead fraction 23 and a C₁₀+ rich liquid bottoms fraction 24. In addition, a vapor side-stream 25 is removed from an internal C₉+ aromatics rectification section 26 of the xylenes fractionation column 22 adjacent the base of the column 22. The vapor side-stream 25 is then passed through a condenser 27, advantageously assisted by pump(s) shown symbolically and unnumbered in the figure, to condense a liquid stream rich in C₉ aromatics, a portion 28 of which is typically recycled as reflux to the rectifier section 26, and a portion 29 of which is advantageously used as the feed to the transalkylation process. In an alternative shown in Figure 3B, relux to the divided wall section 26 in the xylene rerun column could be a fresh benzene, toluene, or another C9+ aromatic stream. The other features in Figure 3B are identical to those described above for Figure 3A. Other possibilities not shown explicated in Figure 3A and 3B will immediately suggest themselves to one of ordinary skill in the art in possession of this discourse, such as an apparatus having appropriate plumbing so as to combine the options of reflux to rectifier 26 as shown in Figures 3A and 3B. [00024] A second example of the present improved treatment process is shown in Figure 4A, in which a Cs+ hydrocarbon feed is again fed by line 21 to a xylenes fractionation column 22, where the feed is fractionated into Cs rich vapor overhead fraction 23 and a Cio+ rich liquid bottoms fraction 24. A vapor side-stream 25 is again removed from the xylenes fractionation column 22 adjacent the base of the column 22, but in this case the side-stream 25 is fed to a C9+ aromatics rectifier 31 separate from and external to said xylenes fractionation column 22. In embodiments, the rectifier 31 employs smaller distillation column than tailing column 16 of Figure 2 and does not have an external reboiler and therefore has lower capital and operating cost than the Figure 2 embodiment. The stream 25 is fractioned in the rectifier 31 into a liquid bottoms stream 32, which is returned to the column 22, and an overhead 33, which is passed through a condenser 34. Similar to Figures 3A and 3B, the condenser 34 in Figure 4A condenses a liquid stream rich in C9, aromatics from the overhead 33 (assisted by pump illustrated symbolically and unnumbered in the figure), a portion 35 of which is advantageously recycled as reflux to rectifier 31, and a portion 36 of which is advantageously used as the feed to the transalkylation process. In an alternative shown in Figure 4B, relux to the tailing column 31 could be a benzene, toluene, or another C9+ aromatic stream as shown in Figure 4B. The other features in Figure 4B are identical to those described above for Figure 4A. Other possibilities not shown explicated in Figure 4A and 4B will immediately suggest themselves to one of ordinary skill in the art in possession of this discourse, such as an apparatus having appropriate plumbing so as to combine the options of reflux to tailing colum 31 as shown in Figures 4A and 4B.

[00025] The configuration of Figure 3 is preferred for a new grass roots transalkylation plant, whereas the configuration of Figure 4 is preferred for a revamp to an existing transalkylation plant. Both configurations provide an effective and inexpensive method of minimizing the level of heavy aromatic species that contribute to catalyst deactivation and/or cause increased gas yields while maximizing the C1₀+ aromatic species that increase xylene and liquid yield. The unnumbered arrow into column 22 in both Figures 3 and 4 represents another possible feed point, which could be, by way of example, isomerate.

[00026] After removal of the deleterious heavy aromatics according to the method of Figure 3 or Figure 4, the C9+ aromatic hydrocarbon feed is supplied to one or more reactors housing a transalkylation catalyst system, which includes a first catalyst bed and desirably includes first, second and third catalyst beds mounted in series. [00027] The first catalyst bed is effective to transalkylate the C9+ aromatic hydrocarbons in the feed and comprises a first catalyst composition comprising a first molecular sieve having a constraint index less than 3 and a first hydrogenation component. The first hydrogenation component generally comprises at least one metal or compound thereof of Groups 6 to 12 of the Periodic Table of the Elements and is present in an amount from about 0.01 to about 10 wt. % of the first catalyst composition. Suitable metals for the first hydrogenation component include at least one of Pt, Pd, Ir, and Re.

[00028] Constraint Index is a convenient measure of the extent to which an aluminosilicate or other molecular sieve provides controlled access to molecules of varying sizes to its internal structure. For example, molecular sieves which provide a highly restricted access to and egress from its internal structure have a high value for the Constraint Index. Molecular sieves of this kind usually have pores of small diameter, e.g., less than 5 Angstroms. On the other hand, molecular sieves which provide relatively free access to their internal pore structure have a low value for the constraint index, and usually pores of large size. The method by which constraint index is determined is described fully in U.S. Pat. No. 4,016,218, which is incorporated herein by reference for the details of the method.

[00029] The first molecular sieve typically comprises at least one of a M41 S family molecular sieve, a MCM-22 family molecular sieve, ETS-10, ETAS-10, ETGS-10, UZM-5, UZM-8, UZM-14 and a molecular sieve having a zeolite framework type comprising at least one of ABW, AET, AFG, AFI, AFX, ANA, AST, ASV, BCT, *BEA, BEC, BIK, BOG, BPH, BRE, CAN, CAS, CDO, CFI, CGS, CHA, CHI, CON, DAC, DDR, DFT, DOH, DON, EAB, EDI, EMT, EON, EPI, ERI, ESV, ETR, EUO, EZT, FAR, FAU, FER, FRA, GIS, GIU, GME, GON, GOO, HEU, IFR, IHW, IMF, ISV, ITE, ITH, ITW, IWR, IWV, IWW, JBW, KFI, LAU, LEV, LIO, LIT, LOS, LOV, LTA, LTL, LTN, MAR, MAZ, MEI, MEL, MEP, MER, MFI, MFS, MON, MOR, MOZ, MSE, MSO, MTF, MTN, MTT, MTW, MWW, NAB, NAT, NES, NON, NPO, NSI, OBW, OFF, OSO, OWE, PAR, PAU, PHI, PON, RHO, RON, RRO, RSN, RTE, RTH, RUT, RWR, RWY, SFE, SFF, SFG, SFH, SFN, SFO, SGT, SIV, SOD, SOS, SSY, STF, STI, STT, SZR, TER, THO, TOL, TON, TSC, TUN, UEI, UFI, UOZ, USI, UTL, VET, VNI, VSV, WEN, and YUG.

[00030] The M41 S family mesoporous molecular sieve is described in J. Amer. Chem. Soc, 1992, 114, 10834. Members of the M41 S family mesoporous molecular sieve include MCM-41, MCM-48 and MCM-50. A member of this class is MCM-41 whose preparation is described in U.S. Pat. No. 5,098,684. MCM-41 is characterized by having a hexagonal structure with a unidimensional arrangement of pores having a cell diameter greater than 13 Angstroms. The physical structure of MCM-41 is like a bundle of straws wherein the opening of the straws (the cell diameters of the pores) ranges from 13 to 200 Angstroms. MCM-48 has a cubic symmetry and is described for example in U.S. Pat. No. 5, 198,203. MCM-50 has a layered or lamellar structure and is described in U.S. Pat. No. 5,246,689.

[00031] The term "MCM-22 family material" (or "material of the MCM-22 family" or "molecular sieve of the MCM-22 family"), as used herein, includes one or more of:

(i) molecular sieves made from a common first degree crystalline building block unit cell, which unit cell has the MWW framework topology. (A unit cell is a spatial arrangement of atoms which if tiled in three-dimensional space describes the crystal structure. Such crystal structures are discussed in the "Atlas of Zeolite Framework Types", Fifth edition, 2001);

(ii) molecular sieves made from a common second degree building block, being a 2- dimensional tiling of such MWW framework topology unit cells, forming a monolayer of one unit cell thickness, preferably one c-unit cell thickness;

(iii) molecular sieves made from common second degree building blocks, being layers of one or more than one unit cell thickness, wherein the layer of more than one unit cell thickness is made from stacking, packing, or binding at least two monolayers of one unit cell thickness. The stacking of such second degree building blocks can be in a regular fashion, an irregular fashion, a random fashion, or any combination thereof; and

(iv) molecular sieves made by any regular or random 2-dimensional or 3-dimensional combination of unit cells having the MWW framework topology.

[00032] The MCM-22 family materials are characterized by having an X-ray diffraction pattern including d-spacing maxima at 12.4+0.25, 3.57+0.07 and 3.42+0.07 Angstroms (either calcined or as-synthesized). The MCM-22 family materials may also be characterized by having an X-ray diffraction pattern including d-spacing maxima at 12.4+0.25, 6.9+0.15, 3.57+0.07 and 3.42+0.07 Angstroms (either calcined or as-synthesized). The X-ray diffraction data used to characterize the molecular sieve are obtained by standard techniques using the K-alpha doublet of copper as the incident radiation and a diffractometer equipped with a scintillation counter and associated computer as the collection system. Materials belong to the MCM-22 family include MCM-22 (described in U.S. Pat. No. 4,954,325 and U.S. Patent Application Ser. No. 11/823,722); PSH-3 (described in U.S. Pat. No. 4,439,409); SSZ-25 (described in U.S. Pat. No. 4,826,667); ERB-1 (described in European Patent No. 0293032); ITQ-1 (described in U.S. Pat. No. 6,077,498); ITQ-2 (described in International Patent Publication No. WO97/17290); ITQ-30 (described in International Patent Publication No. WO20051 18476); MCM-36 (described in U.S. Pat. No. 5,250,277); MCM-49 (described in U.S. Pat. No. 5,236,575); UZM-8 (described in U.S. Pat. No. 6,756,030); MCM-56 (described in U.S. Pat. No. 5,362,697); EMM-10-P (described in U.S. Patent Application Ser. No. 1 1/823, 129); and EMM-10 (described in U.S. Patent Application Ser. Nos. 1 1/824,742 and 1 1/827,953).

[00033] It is to be appreciated the MCM-22 family molecular sieves described above are distinguished from conventional large pore zeolite alky lation catalysts, such as mordenite, in that the MCM-22 materials have 12-ring surface pockets which do not communicate with the 10-ring internal pore system of the molecular sieve.

[00034] The zeolitic materials designated by the IZA-SC as being of the MWW topology are multi-layered materials which have two pore systems arising from the presence of both 10 and 12 membered rings. The Atlas of Zeolite Framework Types classes five differently named materials as having this same topology: MCM-22, ERB-1, ITQ-1, PSH-3, and SSZ- 25.

[00035] The MCM-22 family molecular sieves have been found to be useful in a variety of hydrocarbon conversion processes. Examples of MCM-22 family molecular sieve are MCM- 22, MCM-49, MCM-56, ITQ-1, PSH-3, SSZ-25, and ERB-1. Such molecular sieves are useful for alkylation of aromatic compounds. For example, U.S. Pat. No. 6,936,744 discloses a process for producing a monoalkylated aromatic compound, particularly cumene, comprising the step of contacting a polyalkylated aromatic compound with an alkylatable aromatic compound under at least partial liquid phase conditions and in the presence of a trans alkylation catalyst to produce the monoalkylated aromatic compound, wherein the trans alkylation catalyst comprises a mixture of at least two different crystalline molecular sieves, wherein each of said molecular sieves is selected from zeolite beta, zeolite Y, mordenite and a material having an X-ray diffraction pattern including d-spacing maxima at 12.4±0.25, 6.9±0.15, 3.57±0.07 and 3.42±0.07 Angstrom. [00036] The MCM-22 family molecular sieves including MCM-22, MCM-49, and MCM- 56 have various applications in hydrocarbon conversion processes. Unfortunately, industrial applications of zeolite catalysts have been hindered due to some major disadvantages associated with the current synthesis techniques that make large scale production of these catalysts complicated and therefore expensive. At present, crystalline zeolite catalysts are synthesized mainly by conventional liquid-phase hydrothermal treatment, including in-situ crystallization and seeding method, and the liquid phase transport method.

[00037] Preferred molecular sieves for use in the first catalyst composition include at least one molecular sieve having a zeolite framework type comprising BEA, BOG, CAN, CHA, CON, EMT, EUO, FAU, FER, LEV, LTA, LTL, MAR, MAZ, MEI, MEL, MFI, MFS, MOR, MTW, MWW, RHO, SOD, and/or TON.

[00038] In one preferred embodiment, the first molecular sieve comprises ZSM-12 and especially ZSM-12 having an average crystal size of less than 0.1 micron, such as about 0.05 micron.

[00039] Conveniently, the first molecular sieve has an alpha value of at least 20, such as from about 20 to about 500, for example from about 30 to about 100.

[00040] Generally, the first molecular sieve is an aluminosilicate having a silica to alumina molar ratio of less than 500, typically from about 50 to about 300.

[00041] Typically, the first catalyst composition typically comprises at least 1 wt. %, preferably at least 10 wt. %, more preferably at least 50 wt. %, and most preferably at least 65 wt. %, of the second molecular sieve.

[00042] Generally, the first catalyst composition also contains a binder or matrix material, which can be any of the materials listed as being suitable for the first catalyst and can be present in an amount ranging from 5 to 95 wt. %, and typically from 10 to 60 wt. %, of the second catalyst composition.

[00043] In addition to the first catalyst bed, it may be desirable to include in the or one trans alky lation reactor a second catalyst bed which is effective to dealkylate ethyl and propyl groups in the feed and which is located upstream of the first catalyst bed. The second catalyst bed typically comprises a second catalyst composition comprising a second molecular sieve having a Constraint Index in the range of about 3 to about 12 and at least one second hydrogenation component, which generally comprises at least one metal or compound thereof of Groups 6 to 12 of the Periodic Table of the Elements. The second hydrogenation component is generally present in an amount from about 0.01 to about 10 wt. % of the second catalyst composition and typically is at least one of Pt, Pd, Ir, and Re.

[00044] Conveniently, the weight ratio of the first catalyst composition to the second catalyst composition is in the range of 5:95 to 75:25.

[00045] In addition to the first and second catalyst beds, it may be desirable to include in the or one transalkylation reactor a third catalyst bed downstream of the second catalyst bed and effective to crack non-aromatic cyclic hydrocarbons in the effluent from the first and second catalyst beds. The third catalyst bed accommodates a third catalyst composition comprising a third molecular sieve having a Constraint Index from about 1 to 12. Suitable molecular sieves for use in the third catalyst comprise at least one of ZSM-5, ZSM-1 1, ZSM- 12, zeolite beta, ZSM-22, ZSM-23, ZSM-35, ZSM-48, ZSM-57 and ZSM-58, with ZSM-5 being preferred.

[00046] The first, second and third catalyst beds may be located in separate reactors but are conveniently located in a single reactor, typically separated from another by spacers or by inert materials, such as, alumina balls or sand. Alternatively, the first and second catalyst beds could be located in one reactor and the third catalyst bed located in a different reactor. As a further alternative, the first catalyst bed could be located in one reactor and the second and third catalyst beds located in a different reactor. In all situations, the first catalyst is not mixed with the second catalyst and the hydrocarbon feedstocks and hydrogen are arranged to contact the first catalyst bed prior to contacting the second catalyst bed. Similarly, if the third catalyst bed is present, the hydrocarbon feedstocks and hydrogen are arranged to contact the second catalyst bed prior to contacting the third catalyst bed.

[00047] In operation, the first catalyst bed is maintained under conditions effective to dealkylate aromatic hydrocarbons containing C2+ alkyl groups in the heavy aromatic feedstock and to saturate the resulting C2+ olefins. Suitable conditions for operation of the first catalyst bed comprise a temperature in the range of about 100 to about 800°C, preferably about 300 to about 500°C, a pressure in the range of about 790 to about 7000 kPa-a, preferably about 2170 to 3000 kPa-a, a ]¾:ΗΌ molar ratio in the range of about 0.01 to about 20, preferably about 1 to about 10, and a WHSV in the range of about 0.01 to about 100 hr ¹, preferably about 2 to about 20 hr^"1.

[00048] The second catalyst bed is maintained under conditions effective to transalkylate C9+ aromatic hydrocarbons with said at least one C6-C7 aromatic hydrocarbon. Suitable conditions for operation of the second catalyst bed comprise a temperature in the range of about 100 to about 800°C, preferably about 300 to about 500°C, a pressure in the range of about 790 to about 7000 kPa-a, preferably about 2170 to 3000 kPa-a, a I¾:HC molar ratio in the range of about 0.01 to about 20, preferably about 1 to about 10, and a WHSV in the range of about 0.01 to about 100 hr^"1, preferably about 1 to about 10 hr^"1.

[00049] Where present, the third catalyst bed is maintained under conditions effective to crack non-aromatic cyclic hydrocarbons in the effluent from the second catalyst bed. Suitable conditions for operation of the third catalyst bed comprise a temperature in the range of about 100 to about 800°C, preferably about 300 to about 500°C, a pressure in the range of about 790 to about 7000 kPa-a, preferably about 2170 to 3000 kPa-a, a H₂:HC molar ratio in the range of about 0.01 to about 20, preferably about 1 to about 10, and a WHSV in the range of about 0.01 to about 100 hr^"1, preferably about 1 to about 50 hr^"1.

[00050] Obviously, where the first, second and optional third catalyst beds are located in a single reactor, the operating conditions in each bed are substantially the same.

[00051] While the present invention has been described and illustrated by reference to particular embodiments, those of ordinary skill in the art will appreciate that the invention lends itself to variations not necessarily illustrated herein. For this reason, then, reference should be made solely to the appended claims for purposes of determining the true scope of the present invention.

Claims

1. A process for converting C₉+ aromatic hydrocarbons to lighter aromatic products, the process comprising:

(a) passing a Cs+ aromatic hydrocarbon feed through a xylenes fractionation column to separate said feed into a Cs rich vapor overhead fraction and a C₁₀+ rich liquid bottoms fraction;

(c) passing at least part of said vapor side-stream through a rectifier to separate said side stream into a stream rich in C₁₀ and higher aromatics and a stream rich in C₉ aromatics; and

(d) contacting said stream rich in C9 aromatics with toluene and/or benzene in the presence of a transalkylation catalyst system under trans alky lation reaction conditions to produce a transalkylation reaction product comprising (i) benzene and/or toluene and (ii) xylene.

2. The process of Claim 1, wherein said vapor side-stream is removed from an internal C₉+ aromatics rectification section of said xylenes fractionation column.

3. The process of Claim 2, further comprising at least one of the following: (i) wherein at least a portion said heavy liquid stream is recycled to said internal C9+ aromatics rectification section as a reflux stream; (ii) wherein a stream comprising at least one of benzene, toluene, and C9+ aromatics different than said heavy liquid stream, is provided to said rectifier as a reflux stream.

4. The process of Claim 1, wherein said vapor side-stream is fed to a C₉+ aromatics rectifier separate from and external to said xylenes fractionation column and the overhead from said rectifier is passed through said condenser to provide a stream rich in C₉ aromatics..

5. The process of Claim 4, further comprising at least one of the following: (i) a portion of said stream rich in C₉ aromatics is recycled to said rectifier as a reflux stream; (ii) a stream comprising at least one of benzene, toluene, and C9+ aromatics different than said stream rich in C9 aromatics, is provided to said rectifier as a reflux stream.

6. The process of Claim 1, wherein the trans alky lation catalyst system comprises a first catalyst bed comprising a first molecular sieve having a constraint index less than 3 and a first hydrogenation component.

7. The process of Claim 6, wherein the first molecular sieve comprises at least one of a M41S family molecular sieve, a MCM-22 family molecular sieve, ETS-10, ETAS-10, ETGS- 10, UZM-5, UZM-8, UZM-14 and a molecular sieve having a zeolite framework type comprising at least one of ABW, AET, AFG, AFI, AFX, ANA, AST, ASV, BCT, *BEA, BEC, BIK, BOG, BPH, BRE, CAN, CAS, CDO, CFI, CGS, CHA, CHI, CON, DAC, DDR, DFT, DOH, DON, EAB, EDI, EMT, EON, EPI, ERI, ESV, ETR, EUO, EZT, FAR, FAU, FER, FRA, GIS, GIU, GME, GON, GOO, HEU, IFR, IHW, IMF, ISV, ITE, ITH, ITW, IWR, IWV, IWW, JBW, KFI, LAU, LEV, LIO, LIT, LOS, LOV, LTA, LTL, LTN, MAR, MAZ, MEI, MEL, MEP, MER, MFI, MFS, MON, MOR, MOZ, MSE, MSO, MTF, MTN, MTT, MTW, MWW, NAB, NAT, NES, NON, NPO, NSI, OBW, OFF, OSO, OWE, PAR, PAU, PHI, PON, RHO, RON, RRO, RSN, RTE, RTH, RUT, RWR, RWY, SFE, SFF, SFG, SFH, SFN, SFO, SGT, SIV, SOD, SOS, SSY, STF, STI, STT, SZR, TER, THO, TOL, TON, TSC, TUN, UEI, UFI, UOZ, USI, UTL, VET, VNI, VSV, WEN, and YUG.

8. The process of Claim 6, wherein the first molecular sieve comprises at least one molecular sieve having a zeolite framework type comprising BEA, BOG, CAN, CHA, CON, EMT, EUO, FAU, FER, LEV, LTA, LTL, MAR, MAZ, MEI, MEL, MFI, MFS, MOR, MTW, MWW, RHO, SOD, and/or TON.

9. The process of Claim 6, wherein the first hydrogenation component comprises a metal or compound thereof from Groups 6 to 10 of the Periodic Table of the Elements.

10. The process of Claim 6, wherein the transalkylation catalyst system comprises a second catalyst bed upstream of the first catalyst bed and comprising a second molecular sieve having a constraint index the range of about 3 to about 12 and a second hydrogenation component.

11. The process of Claim 10, wherein said second molecular sieve comprises at least one of ZSM-5, ZSM-1 1, ZSM-22, ZSM-23, ZSM-35, and ZSM-48.

12. The process of Claim 10, wherein the second hydrogenation component comprises a metal or compound thereof from Groups 6 to 10 of the Periodic Table of the Elements.

13. The process of Claim 10, wherein the transalkylation catalyst system comprises a third catalyst bed downstream of the first catalyst bed and comprising a third catalyst composition comprising a third molecular sieve having a Constraint Index in the range of about 1 to about 12.

14. The process of Claim 12, wherein said third molecular sieve comprises at least one of ZSM-5, ZSM-11, ZSM-12, zeolite beta, ZSM-22, ZSM-23, ZSM-35, ZSM-48, ZSM-57 and ZSM-58.

15. An apparatus for converting C9+ aromatic hydrocarbons to lighter aromatic products substantially according to any one of Figure 3A, 3B, 4A, and 4B.