CN110790625B

CN110790625B - Process for producing aromatic hydrocarbons

Info

Publication number: CN110790625B
Application number: CN201911115819.1A
Authority: CN
Inventors: M·莫立尼尔; K·J·诺布; D·J·斯坦利; T·S·万德博尔; 曹春社; 郑晓波; T·勒卢尔; J·拉乌尔; S·克劳德尔; I·普雷沃; J·皮古瑞尔; C·费尔南德斯
Original assignee: ExxonMobil Chemical Patents Inc
Current assignee: ExxonMobil Chemical Patents Inc
Priority date: 2014-08-15
Filing date: 2015-06-18
Publication date: 2022-09-06
Anticipated expiration: 2035-06-18
Also published as: KR101920578B1; CN106573855A; KR20170031729A; CN110790625A; CN106573855B; WO2016025077A1; JP2017524039A; JP6615888B2

Abstract

In the method for preparing paraxylene, at least one catalyst containing C ₆₊ The raw material of aromatic hydrocarbon is supplied to a dividing wall distillation column to separate the raw material into C _7‑ Stream of aromatic hydrocarbons, containing C ₈ Stream of aromatic hydrocarbons and containing C ₉₊ A stream of aromatic hydrocarbons. Then at least a part of the water containing C ₈ A stream of aromatic hydrocarbons is supplied to a para-xylene recovery unit to recover a C-containing stream from the para-xylene recovery unit ₈ Para-xylene is recovered from the stream of aromatic hydrocarbons and a para-xylene depleted stream is produced. The para-xylene depleted stream is contacted in a xylene isomerization zone under conditions effective to isomerize xylenes in the para-xylene depleted stream and produce an isomerized stream, at least a portion of which is then recycled to the para-xylene recovery unit.

Description

Process for producing aromatic hydrocarbons

The inventor:Michel Molinier、Kevin J.Knob、Dennis J. Stanley、Terri Vander Pol、Chunshe James Cao、Xiaobo Zheng、 Thierry Leflour、Jacques Rault、Stephane Claudel、Isabelle Prevost、Jerome Pigourier、Celia Fernandez

cross Reference to Related Applications

The present application is a divisional application of the chinese patent application 201580034836.6. This application claims priority and benefit from U.S. provisional application 62/037645 filed on 8, 15, 2014, which is incorporated herein by reference in its entirety.

Technical Field

The present invention relates to a process for producing aromatic hydrocarbons, in particular for producing para-xylene.

Background

Benzene, toluene and xylene (BTX) are important aromatic hydrocarbons, and their worldwide demand is increasing. The demand for xylene, particularly xylene, increases proportionally with the demand for polyester fibers and films, and generally increases at a rate of 5-7% per year. Benzene is a very valuable product as a chemical feedstock. Toluene is also a valuable petrochemical used as a solvent and intermediate in chemical production processes and as a high octane gasoline component. However, in many modern aromatics complex, some or all of the benzene and/or toluene is converted to more xylenes by transalkylation or methylation, or a combination thereof.

The main sources of benzene, toluene and xylene (BTX) are catalytic reformate produced by reacting naphtha with a carrierHydrogenation/dehydrogenation catalyst contact. The resulting reformate is a paraffinic hydrocarbon and the desired C ₆ To C ₈ A complex mixture of aromatic compounds, and also significant amounts of heavy aromatic hydrocarbons. In the removal of light (C) _5- ) After the paraffinic hydrocarbon component, the remaining reformate is typically separated into fractions containing C using multiple distillation steps _7- 、C ₈ And C ₉₊ The fraction (c) of (a). Can then be obtained from a compound containing C _7- The fraction(s) is/are recovered from benzene, leaving a toluene-rich fraction, usually by methylation or with a portion of the C-containing fraction ₉₊ The transalkylation of the fractions of (A) produces additional C ₈ An aromatic compound. Containing C ₈ Is fed to a xylene production circuit, where the para-xylene is recovered, typically by adsorption or crystallization, and the resulting para-xylene depleted stream is catalytically converted to isomerize the xylenes back to equilibrium distribution and reduce the level of ethylbenzene that would otherwise accumulate in the xylene production circuit.

Although catalytic technology becomes more efficient in achieving the desired chemical reaction to maximize para-xylene production while reducing the loss of valuable aromatic molecules, there is a continuing need to achieve savings in hardware costs and energy consumption in order to reduce the overall production cost of para-xylene.

Summary of The Invention

In accordance with the present invention, it has now been found that a dividing wall distillation column provides for the separation of hydrocarbon streams, particularly C-containing streams encountered in certain integrated para-xylene production plants _7- 、C ₈ And C ₉₊ Efficient and energy efficient measures of the fraction of (a).

In a first embodiment, at least one compound comprising C ₆₊ Feeding a feedstock of aromatic hydrocarbons to a dividing wall distillation column to separate the feed into fractions containing C _7- Stream of aromatic hydrocarbons, containing C ₈ Stream of aromatic hydrocarbons and containing C ₉₊ A stream of aromatic hydrocarbons. Then, at least a part of the solution containing C ₈ A stream of aromatic hydrocarbons is supplied to a para-xylene recovery unit to recover a C-containing stream from the para-xylene recovery unit ₈ A stream of aromatic hydrocarbons recovers para-xylene and produces a para-xylene depleted stream, which is mixed with xyleneThe isomerization catalyst is contacted in a xylene isomerization zone under conditions to isomerize xylenes in the para-xylene depleted stream and produce an isomerized stream. At least a portion of the isomerized stream is then recycled to the para-xylene recovery unit.

In another embodiment, the method further comprises converting a compound containing C _7- Removing at least a portion of the aliphatic hydrocarbons from the hydrocarbon stream to produce C _7- An aromatic-hydrocarbon-enriched stream, which is supplied to a separation unit to separate C _7- The aromatic-rich stream is separated into a benzene-containing stream and a toluene-containing stream. At least a portion of the toluene-containing stream and at least a portion of the C-containing stream ₉₊ A stream of hydrocarbons is contacted with a transalkylation catalyst under conditions effective to produce a transalkylation product comprising xylene, which is passed to a para-xylene recovery unit.

Desirably, the method further comprises combining C-containing compounds from (a1 or a2 or a3) ₈ At least a portion of the stream of aromatic hydrocarbons is supplied to an ethylbenzene removal unit located upstream of the para-xylene recovery unit and effective to remove C-containing hydrocarbons ₈ Operating under conditions of ethylbenzene in the stream of aromatic hydrocarbons. Ideally, the conditions in the ethylbenzene removal unit are effective to remove C-containing compounds ₈ The stream of aromatic hydrocarbons is maintained substantially in the vapor phase and the conditions in the xylene isomerization zone are effective to maintain the para-xylene depleted stream substantially in the liquid phase.

In a third embodiment, will comprise C ₆₊ Feeding a feedstock of a mixture of aliphatic and aromatic hydrocarbons to a distillation column to separate the feedstock into C-containing _7- Hydrocarbon stream and C ₈₊ A stream of hydrocarbons. From C _7- The hydrocarbon stream is depleted of at least a portion of the aliphatic hydrocarbons to produce C _7- An aromatic hydrocarbon-enriched stream, C _7- The aromatic-rich stream is supplied to a separation unit to recover benzene therefrom to produce a toluene-containing stream. At least a part of which contains C ₈₊ Hydrocarbon streams effective in rendering C-containing ₈₊ Dealkylation of ethylbenzene in a stream of hydrocarbons and producing a stream comprising benzene and C ₈₊ The dealkylation effluent of the hydrocarbon is contacted with ethylbenzene dealkylation catalyst under the condition of that it is separated into C-containing component in the partition wall distillation column _7- Stream of aromatic hydrocarbons, containing C ₈ Stream of aromatic hydrocarbons and containing C ₉₊ A stream of aromatic hydrocarbons. Then will contain C ₈ The stream of aromatic hydrocarbons is sent to a para-xylene recovery unit to recover a C-containing stream ₈ Para-xylene is recovered from the stream of aromatic hydrocarbons to produce a para-xylene depleted stream, which is contacted with a xylene isomerization catalyst under conditions effective to isomerize xylenes in the para-xylene depleted stream and produce an isomerized stream, which is recycled to the dividing wall distillation column. At least part of the toluene-containing stream and at least part of the C-containing stream ₉₊ The hydrocarbon stream is contacted with a transalkylation catalyst under conditions effective to produce a transalkylation product comprising xylene, which is passed to a separation unit.

The present application also relates to the following embodiments:

1. a process for producing para-xylene, the process comprising:

(a1) will contain C ₆₊ At least one feed of aromatic hydrocarbons is supplied to a dividing wall distillation column to separate the feed into C-containing _7- Stream of aromatic hydrocarbons, containing C ₈ Stream of aromatic hydrocarbons and containing C ₉₊ A stream of aromatic hydrocarbons;

(b1) adding said C ₈ At least a portion of the stream of aromatic hydrocarbons is supplied to a para-xylene recovery unit to recover a C-containing stream from the C-containing stream ₈ Recovering para-xylene from the stream of aromatic hydrocarbons to produce a para-xylene depleted stream;

(c1) contacting at least a portion of the para-xylene depleted stream with a xylene isomerization catalyst in a xylene isomerization zone under conditions effective to isomerize xylenes in the para-xylene depleted stream and produce an isomerized stream; and

(d1) recycling at least a portion of the isomerized stream to the para-xylene recovery unit.

2. The process of embodiment 1, wherein the at least one feedstock to (a1) comprises a reformate stream produced by removing C from the reformate stream _5- C of hydrocarbon production ₆₊ A mixture of aromatic and aliphatic hydrocarbons.

3. The method of embodiment 2, further comprising:

(e1) from said group containing C _7- Removal of at least a portion of aliphatic hydrocarbons from a stream of aromatic hydrocarbons to produce C _7- An aromatic hydrocarbon-enriched stream.

4. The method of embodiment 3, further comprising:

(f1) subjecting said C to _7- Supplying at least a portion of the aromatic-rich stream to a separation unit to recover benzene therefrom to produce a toluene-containing stream;

(g1) contacting at least a portion of the toluene-containing stream and the C-containing stream under conditions effective to produce a xylene-containing transalkylation product ₉₊ Contacting at least a portion of the stream of aromatic hydrocarbons with a transalkylation catalyst; and

(h1) supplying at least a portion of the transalkylation product to the separation unit in (f 1).

5. The process of embodiment 4, wherein the separation unit in (f1) comprises an additional dividing wall distillation column.

6. The method of any one of embodiments 1-5, further comprising:

(i1) adding said C ₈ At least a portion of the stream of aromatic hydrocarbons is supplied to an ethylbenzene removal zone; and

(j1) in the effective removal of said C-containing compounds ₈ Subjecting said stream containing C to conditions such that at least a portion of the ethylbenzene in said stream contains aromatic hydrocarbons ₈ A stream of aromatic hydrocarbons is contacted with a first catalyst in the ethylbenzene removal zone.

7. The process of embodiment 6 wherein the conditions in the ethylbenzene removal zone are effective to remove the C-containing compounds ₈ The stream of aromatic hydrocarbons is kept essentially in the gas phase.

8. The process of embodiment 7, wherein the ethylbenzene removal zone is located upstream of the para-xylene recovery unit.

9. The process of embodiment 7, wherein the ethylbenzene removal zone is located downstream of the para-xylene recovery unit.

10. The process of embodiment 8 or 9 wherein said ethylbenzene removal zone further comprises conditions effective to cause said C-containing stream to be produced under said conditions ₈ Stream of aromatic hydrocarbonsA second catalyst for xylene isomerization in (b).

11. The process of any of embodiments 1-10, wherein the conditions in the xylene isomerization zone are effective to maintain the para-xylene depleted stream substantially in the liquid phase.

12. The process of any of embodiments 1-10, wherein the conditions in the xylene isomerization zone are effective to maintain the para-xylene-depleted stream substantially in the vapor phase.

13. A process for producing para-xylene and benzene, the process comprising:

(a2) will contain C ₆₊ A feed of a mixture of aliphatic and aromatic hydrocarbons is supplied to a dividing wall distillation column to separate the feed into fractions containing C _7- Stream of hydrocarbons, containing C ₈ Stream of hydrocarbons and containing C ₉₊ A stream of hydrocarbons;

(b2) from said group containing C _7- Removing at least a portion of the aliphatic hydrocarbons from the hydrocarbon stream to produce C _7- An aromatic-rich stream;

(c2) subjecting said C to _7- At least a portion of the aromatic-rich stream is supplied to a separation unit to supply the C _7- Separating the aromatic-rich stream into a benzene-containing stream and a toluene-containing stream;

(d2) adding said C ₈ At least a portion of the hydrocarbon stream is supplied to a para-xylene recovery unit to recover a C-containing stream from the C-containing stream ₈ Recovering the para-xylene from the hydrocarbon stream to produce a para-xylene depleted stream;

(e2) contacting at least a portion of the para-xylene depleted stream with a xylene isomerization catalyst in a xylene isomerization zone under conditions effective to isomerize xylenes in the para-xylene depleted stream and produce an isomerized stream;

(f2) recycling at least a portion of the isomerized stream to a para-xylene recovery unit;

(g2) contacting at least a portion of the toluene-containing stream and the C-containing stream under conditions effective to produce a xylene-containing transalkylation product ₉₊ Contacting at least a portion of the stream of hydrocarbons with a transalkylation catalyst; and

(h2) at least a portion of the xylenes in the transalkylation product are supplied to a para-xylene recovery unit.

14. The process of embodiment 13, wherein said feedstock to (a2) is produced by removing C from a reformate stream _5- Hydrocarbons are produced.

15. The method of

embodiment

13 or 14, further comprising:

(i2) subjecting said C-containing fraction from (a2) ₈ At least a portion of the stream of aromatic hydrocarbons is supplied to an ethylbenzene removal zone located upstream of the para-xylene recovery unit; and

(j2) prior to (d2) in effecting removal of said C-containing ₈ Subjecting said C-containing stream to ethylbenzene removal in said ethylbenzene removal zone under conditions such that at least a portion of the ethylbenzene in said stream of aromatic hydrocarbons ₈ A stream of aromatic hydrocarbons is contacted with a first catalyst.

16. The process of embodiment 15, wherein the ethylbenzene removal zone further comprises conditions effective to cause the C-containing stream to be removed under said conditions ₈ A second catalyst for xylene isomerization in a stream of aromatic hydrocarbons.

17. The process of

embodiment

15 or 16, wherein the conditions in the ethylbenzene removal zone are effective to convert the C-containing stream to ₈ The stream of aromatic hydrocarbons is kept essentially in the gas phase.

18. The method of any one of embodiments 13-17, further comprising:

(k2) supplying at least a portion of the para-xylene depleted stream from (d2) to an ethylbenzene removal zone located upstream of the xylene isomerization zone; and

(l2) contacting the para-xylene depleted stream with a first catalyst in the ethylbenzene removal zone under conditions effective to remove at least a portion of the ethylbenzene from the para-xylene depleted stream prior to (e 2).

19. The process of embodiment 18, wherein the conditions in the ethylbenzene removal zone are effective to maintain the para-xylene depleted stream substantially in the vapor phase.

20. The process of any of embodiments 13-19, wherein the conditions in the xylene isomerization zone are effective to maintain the para-xylene depleted stream substantially in the liquid phase.

21. The process of any one of embodiments 13-20, wherein at least a portion of the transalkylation product from (g2) is supplied to the separation unit in (C2) and the separation unit is effective to separate xylenes from the transalkylation product, and the C _7- The aromatic-rich stream is separated into a benzene-containing stream and a toluene-containing stream.

22. The process of any one of embodiments 13-21, wherein the separation unit in (c2) comprises an additional dividing wall distillation column.

23. The method of embodiment 22, further comprising:

(m2) removing C from the additional dividing wall distillation column ₈₊ A hydrocarbon residue stream; and

(n2) adding said C ₈₊ At least a portion of the hydrocarbon residue stream is supplied to a para-xylene recovery unit.

24. A process for producing para-xylene and benzene, the process comprising:

(a3) will contain C ₆₊ A feed of a mixture of aliphatic and aromatic hydrocarbons is supplied to a distillation column to separate the feed into C-containing _7- Hydrocarbon stream and C ₈₊ A stream of hydrocarbons;

(b3) from said group containing C _7- Removal of at least a portion of the aliphatic hydrocarbons from the hydrocarbon stream to produce C _7- An aromatic-rich stream;

(c3) subjecting said C to _7- At least a portion of the aromatic-hydrocarbon-enriched stream is supplied to a separation system to recover benzene therefrom to produce a toluene-containing stream;

(d3) in a state effective to make said C-containing ₈₊ Dealkylation of ethylbenzene in a stream of hydrocarbons and producing a stream comprising benzene and C ₈₊ Subjecting said C-containing effluent to hydrocarbon dealkylation conditions ₈₊ Contacting at least a portion of the stream of hydrocarbons with an ethylbenzene dealkylation catalyst;

(e3) supplying the dealkylation effluent to a dividing wall distillation column to separate the dealkylation effluent into C-containing _7- Stream of aromatic hydrocarbons, containing C ₈ Stream of aromatic hydrocarbons and C ₉₊ A stream of aromatic hydrocarbons;

(f3) adding said C ₈ At least a portion of the stream of aromatic hydrocarbons is supplied to a para-xylene recovery unit to recover a C-containing stream from the C-containing stream ₈ Recovering para-xylene from the stream of aromatic hydrocarbons to produce a para-xylene depleted stream;

(g3) contacting at least a portion of the para-xylene depleted stream with a xylene isomerization catalyst under conditions effective to isomerize xylenes in the para-xylene depleted stream and produce an isomerized stream;

(h3) recycling at least a portion of the isomerized stream to the dividing wall distillation column;

(i3) contacting at least a portion of the toluene-containing stream and the C-containing stream under conditions effective to produce a xylene-containing transalkylation product ₉₊ Contacting at least a portion of the stream of hydrocarbons with a transalkylation catalyst; and

(j3) supplying at least a portion of the transalkylation product to the separation system in (c3), wherein the separation system is also effective to separate xylenes from the transalkylation product from (i 3).

25. The process of embodiment 24, wherein the separation system in (c3) comprises an additional dividing wall distillation column.

Drawings

Fig. 1 is a flow diagram of a process for producing para-xylene from a catalytic reformate according to a first embodiment of the invention.

Fig. 2 is a flow diagram of a process for producing para-xylene from a catalytic reformate according to a second embodiment of the invention.

Fig. 3 is a flow diagram of a process for improving the production of para-xylene from a catalytic reformate according to a second embodiment of the invention.

Fig. 4 is a flow diagram of a process for producing para-xylene from a catalytic reformate according to a third embodiment of the invention.

FIG. 5 depicts a process for separating C in an aromatics complex _7- /C ₈ /C ₉₊ A dividing wall column fractionation system for a stream.

FIG. 6 depicts a process for separating C in an aromatics complex _7- /C ₈ /C ₉₊ Conventional 2-column fractionation system for streams.

FIG. 7 depicts the separation of C in an aromatic complex _7- /C ₈ /C ₉₊ A 3-fraction splitter fractionation system for a stream.

Detailed description of the embodiments

The production of para-xylene from catalytic reformate requires a number of costly fractionation steps. In order to reduce the investment and operating costs, the invention uses one or more dividing-wall distillation columns for dividing the various C ₆₊ Separating the hydrocarbon fraction into at least C _7- Stream of aromatic hydrocarbons, containing C ₈ Stream of aromatic hydrocarbons and containing C ₉₊ A stream of aromatic hydrocarbons. May then be selected from the group consisting of C _7- Benzene is recovered from a stream of aromatic hydrocarbons, and toluene can be used to recover benzene by using at least a portion of the C-containing stream ₉₊ A stream of aromatic hydrocarbons is transalkylated to produce additional xylenes. Then will contain C ₈ A stream of aromatic hydrocarbons and additional xylenes produced by the transalkylation reaction are fed to a para-xylene production loop comprising a para-xylene recovery unit and a xylene isomerization unit. At least a portion of the ethylbenzene contained in the reformate feedstock may be removed upstream or downstream of the para-xylene recovery unit by dealkylation to benzene or by isomerization to xylenes.

As the name implies, the term "dividing wall distillation column" refers to a particular known form of distillation column comprising a dividing wall. The dividing wall vertically bisects a portion of the interior of the distillation column, but does not extend to the top or bottom of the column, thus enabling the column to reflux and reboil similar to a conventional column. The partition walls provide fluid impermeable barriers to separate the interior of the column. The inlet to the column is located on one side of the partition, while the side draw or side draws are located on the opposite side. The partition wall enables the side of the column not having the inlet to operate in a more stable manner, minimizing the effect on fluctuations in inlet flow, conditions or composition. The increase in stability can allow the column to be designed and operated with a process that removes one or more side draw streams from the column, the side draw stream having a different composition than either the overhead stream or the bottoms stream.

The ability to produce three or more product streams from a single column enables component separation with fewer distillation columns and potentially reduces capital and operating costs. The dividing wall distillation column may be used as a single distillation column or a plurality of dividing wall distillation columns may be used, and may be used in series or in parallel. The dividing wall distillation column may also be used in combination with one or more conventional distillation columns. Embodiments of the present invention are particularly useful when the optimum feed position to the column is higher than the optimum sidedraw position. If the feed position is higher than the sidedraw position in a conventional distillation column, the downward flow of the liquid feed in the column has a significant effect on the sidedraw composition. Variations in feed fluidity, conditions or composition of the feed stream alter the sidedraw composition and make the production of a stable sidedraw stream difficult to achieve.

In some embodiments, as shown in fig. 1, 2, 3, and 5, a dividing wall distillation column is used instead of a conventional reformate splitter to fractionate the removal of C from the catalytic reformate stream _5- C remaining after aliphatic hydrocarbons ₆₊ A hydrocarbon stream.

In some embodiments, as shown in FIG. 4, the feed to the dividing wall distillation column is partially fed from C ₆₊ The aromatic hydrocarbon stream constitutes and partly consists of the effluent from the xylene isomerization unit when passing from C ₈₊ The C is produced when the aromatic fraction is dealkylated to remove ethylbenzene ₆₊ An aromatic hydrocarbon stream, C ₈₊ The aromatic fraction comes from a conventional reformate splitter.

It can thus be seen that the dividing wall distillation column provides a cost effective separation system for the various feed and product streams encountered in modern para-xylene production complexes.

The present invention will now be described in more detail with reference to the accompanying drawings.

FIG. 1 shows a process for producing para-xylene according to a first embodiment of the present invention in which a catalytic reformate feed stream containing aromatic compounds is supplied via line 11 to a depentanizer zone 12 for C removal _5- And (6) cutting. Pentane and lighter hydrocarbons are removed via line 13, and C ₆₊ The bottom fraction is passed through a pipeLine 14 is fed to a dividing wall distillation column 15 for separating the bottom fraction into C-containing fraction _7- 、C ₈ And C ₉₊ A stream of aromatic hydrocarbons. The fuel gas separated in the dividing wall distillation column 15 is collected via a line 20.

C-containing gas from dividing wall distillation column 15 _7- Is sent via line 16 to an extractive distillation or liquid-liquid extraction unit 17 wherein aliphatic hydrocarbons are removed via line 18 leaving a benzene and toluene rich stream which is fed via line 19 to an olefin saturation zone 21. The olefin saturation zone 21 may be a clay treater or any other device effective to remove olefin contaminants from the aromatic stream, including catalytic processes, with optional hydrogen addition. The effluent from the olefin saturation zone 21 is fed via line 22 to another dividing wall distillation column 23 from which benzene is collected via line 24, toluene is fed via line 25 to a transalkylation unit 26, and C ₈₊ The distillate is fed via line 27 to a xylene distillation column 28.

C-containing recovered from reformate dividing wall column 15 ₈ A stream of aromatic hydrocarbons is supplied from line 29 to the olefin saturation zone 37. The olefin saturation zone 37 can be a clay treater or any other device effective to remove olefin contaminants from aromatic streams, including catalytic processes, with optional hydrogen addition. The effluent from the olefin saturation zone 37 is fed via line 38 to the xylene distillation column 28. Preferably, the effluent from the olefin saturation zone 37 is contacted with C in line 27 ₈₊ The supply point for the distillate is split and supplied to column 28 above it, since the stream in line 38 is much lighter than the stream in line 27.

The xylene distillation column 28 will be lean in C overhead ₉₊ Is separated from the feed to distillation column 28. The overhead stream is then supplied via line 39 to a para-xylene separation zone 41 wherein para-xylene is separated in a conventional manner by adsorption or crystallization separation or a combination of both and is recovered via line 42. Residual toluene in the overhead stream is removed from the para-xylene separation section 41 and passed via line 43 to the transalkylation section 26, while the remaining para-xylene depleted stream is fed via line 40 to the ethylbenzene removal and xylene isomerization zone 44. When p-xylene is separated by adsorption, the adsorbent used preferably containsA zeolite. Typical adsorbents used include natural or synthetic crystalline aluminosilicate zeolites such as zeolite X or Y or mixtures thereof. These zeolites are preferably exchanged with cations such as alkali or alkaline earth metal or rare earth cations. The adsorption column is preferably a simulated moving bed column (SMB) and uses a desorbent, for example p-diethylbenzene, p-difluorobenzene, diethylbenzene or toluene or a mixture thereof.

In the ethylbenzene removal and xylene isomerization zone 44, the removal of ethylbenzene is preferably carried out in the vapor phase and is carried out by dealkylation to benzene or by isomerization to xylenes. When the preferred process is dealkylation to benzene, any conventional catalytic process for dealkylation of ethylbenzene can be used. However, in a preferred embodiment, the dealkylation is carried out in the presence of a catalyst comprising a medium pore size zeolite having a constraint index of 1 to 12 as defined in U.S. Pat. No. 4,016,218 and a hydrogenation component, optionally in combination with a non-acidic binder such as silica. Examples of suitable intermediate pore size zeolites include ZSM-5 (U.S. Pat. Nos. 3,702,886 and Re.29,948); ZSM-11 (U.S. Pat. No. 3,709,979); ZSM-12 (U.S. Pat. No. 3,832,449); ZSM-21 (U.S. Pat. No. 4,046,859); ZSM-22 (U.S. Pat. No. 4,556,477); ZSM-23 (U.S. Pat. No. 4,076,842); ZSM-35 (U.S. Pat. No. 4,016,245); ZSM-38 (U.S. Pat. No. 4,406,859); ZSM-48 (U.S. Pat. No. 4,397,827); ZSM-57 (U.S. Pat. No. 4,046,685) and ZSM-58 (U.S. Pat. No. 4,417,780). Examples of suitable hydrogenation components include oxides, hydroxides, sulfides or free metal forms (i.e., zero valent) of group 8-10 metals (i.e., Pt, Pd, Ir, Rh, Os, Ru, Ni, Co, and Fe), group 14 metals (i.e., Sn and Pb), group 15 metals (i.e., Sb and Bi), and group 7 metals (i.e., Mn, Tc, and Re). Noble metals (i.e., Pt, Pd, Ir, and Rh) or Re are preferred hydrogenation components. Combinations of catalytic forms of such noble or non-noble metals, such as Pt in combination with Sn, may be used. As used herein, the numbering scheme for groups of the periodic Table of the elements is as disclosed in Chemical and Engineering News,63(5),27 (1985).

In a preferred embodiment, the dealkylation catalyst is selectively deactivated prior to introduction into the dealkylation reactor or in situ in the reactor by: the catalyst is contacted with a selectivating agent, such as at least one organosilicon in a liquid carrier and the selectivated catalyst is then calcined at a temperature of 350-. The process of selectivation changes the diffusion characteristics of the catalyst such that the catalyst requires at least 50 minutes to adsorb 30% of the equilibrium capacity of ortho-xylene at 120 ℃ and at an ortho-xylene partial pressure of 4.5 ± 0.8mm hg. One example of a selectivated ethylbenzene dealkylation catalyst is described in U.S. Pat. No. 5,516,956, which is incorporated herein by reference in its entirety.

Suitable conditions for the vapor phase dealkylation of ethylbenzene using the above-described catalyst include a temperature of from about 400F to about 1000F (204 to 538℃), a pressure of from about 0 to about 1000psig (100 to 7000kPa), and a Weight Hourly Space Velocity (WHSV) of from about 0.1 to about 200hr ^-1 The molar ratio of hydrogen to hydrocarbon is from about 0.5 to about 10. Preferably, these conversion conditions include a temperature of about 660 ° F to about 900 ° F (350 ℃ to 480 ℃), a pressure of about 50 to about 400psig (446 to 2860kPa), about 3 to about 50hr ^-1 The molar ratio of hydrogen to hydrocarbon of about 0.7 to about 5. WHSV is based on the weight of the catalyst composition, i.e., the total weight of active catalyst and binder, if used. The transformation conditions are selected to contain C ₈ The aromatic hydrocarbon feed is in a substantially vapor phase in the ethylbenzene removal zone 44.

In the ethylbenzene removal and xylene isomerization zone 44, xylene isomerization is also preferably effected in the vapor phase. Any gas phase catalytic isomerization process known to those skilled in the art can be used to effect xylene isomerization in zone 44, but one preferred catalytic system employs a medium pore size zeolite having different ortho-xylene diffusion properties than the ethylbenzene removal catalyst. Thus, in one embodiment, the xylene isomerization catalyst requires less than 50 minutes to absorb 30% of the equilibrium capacity of ortho-xylene at 120 ℃ and at an ortho-xylene partial pressure of 4.5 ± 0.8mm hg.

The conditions of xylene isomerization employed in the ethylbenzene removal and xylene isomerization zone 44 are selected to isomerize xylenes in the para-xylene depleted stream to produce a stream having a specific para-xylene depleted contentA stream of toluene with a higher concentration of an isomerized stream of para-xylene. Suitable conditions include a temperature of about 660 ° F to about 900 ° F (350 ℃ to 480 ℃), a pressure of about 50 to about 400psig (446 to 2860kPa), about 3 to about 50hr ^-1 The molar ratio of hydrogen to hydrocarbon of about 0.7 to about 5. WHSV is based on the weight of the catalyst composition, i.e., the total weight of active catalyst and binder, if used.

A preferred method for operating the ethylbenzene removal and xylene isomerization zone 44 is described in U.S. patent No. 5,516,956.

The effluent from the ethylbenzene removal and xylene isomerization zone 44 is supplied via line 45 to dividing wall distillation column 15 for separation of the effluent into C-containing streams _7- 、C ₈ And C ₉₊ A stream of aromatic hydrocarbons.

C-containing fraction recovered from the reformate dividing wall distillation column 15 ₉₊ A stream of aromatic hydrocarbons is supplied via line 48 to a heavy aromatic hydrocarbons distillation column 49 which also receives a bottoms stream from the xylene distillation column 28 via line 51. Heavy aromatic distillation column 49 will have C supplied from

lines

48 and 51 ₉₊ Separation of aromatic hydrocarbons into C-containing stream removed in line 52 ₉ /C ₁₀ Light C ₁₁ And contains C ₁₁ + fraction which is supplied via line 53 to the gasoline pool, fuel pool or topping tower. Then will contain C ₉ /C ₁₀ Light C ₁₁ Is fed to the transalkylation unit 26 along with the toluene-rich stream supplied via

lines

25 and 43, optionally after passing through an olefin saturation zone such as clay treatment or any other means of removing olefin contaminants, including catalytic processes, with optional hydrogen addition. In fig. 1, the olefin saturation zone and the transalkylation zone are shown combined in a single unit 26, but the purpose of this schematic is not limiting. Those skilled in the art will appreciate that olefin saturation may be carried out in a unit located upstream of and separate from the transalkylation unit. In addition, olefin saturation is only carried out when needed, so if, for example, stream 52 requires olefin removal, and the olefin content in stream 25 makes olefin removal unnecessary, only stream 52 will pass through the olefin saturation zone.

Any transalkylation process known to those skilled in the art can be used, but one preferred process employs a multi-stage catalytic system described in U.S. Pat. No. 7,663,010, which is incorporated herein by reference in its entirety. Such systems include (i) a first catalyst comprising a first molecular sieve having a constraint index in the range of from 3 to 12 and containing from 0.01 to 5 wt.% of at least one source of at least one first metallic element of groups 6 to 10 of the periodic table of elements and (i i) a second catalyst comprising a second molecular sieve having a constraint index of less than 3 and containing from 0 to 5 wt.% of at least one source of at least one second metallic element of groups 6 to 10 of the periodic table of elements, wherein the first catalyst or the second catalyst is in the range of from 5:95 to 75:25, and wherein the first catalyst is located upstream of the second catalyst.

Examples of suitable molecular sieves having a constraint index of 3 to 12 for the first catalyst include ZSM-5, ZSM-11, ZSM-22, ZSM-23, ZSM-35, ZSM-48, ZSM-57 and ZSM-58, with ZSM-5 being preferred. Examples of suitable molecular sieves having a constraint index of less than 3 for the second catalyst include zeolite beta, zeolite Y, ultrastable Y (USY), dealuminated Y (deal Y), mordenite, ZSM-3, ZSM-4, ZSM-12, ZSM-18, NU-87 and ZSM-20, with ZSM-12 being preferred. Specific examples of useful metals in the first and second catalysts include iron, ruthenium, osmium, nickel, cobalt, rhenium, molybdenum, tin, and noble metals such as platinum, rhodium, iridium, or palladium.

The transalkylation process may be carried out in any suitable reactor, including a radial flow, fixed bed, continuous downflow, or fluidized bed reactor. The conditions in the first and second catalyst beds may be the same or different but typically comprise a temperature of 100-; a pressure of 790 to 7000kPa-a (kilopascals absolute), preferably in the range of 2170 and 3000kPa-a, and a molar ratio of hydrogen to hydrocarbon of 0.01 to 20, preferably 1 to 10; and 0.01 to 100hr ^-1 Preferably in the range of 1-20hr ^-1 Within the range of (1).

The effluent from transalkylation unit 26 is fed via line 54 to stabilizer 55 where light gases are collected and removed via line 56. A side stream from stabilizer 55 is recycled via line 57 to depentanizer 12 and the stabilizer bottoms are fed via line 58, optionally through olefin saturation zone 21, to benzene/toluene/C8 + dividing column 23.

One advantage of the embodiment shown in FIG. 1, as compared to prior art aromatics complex that use a conventional distillation unit instead of the dividing wall column section 15, is the ability to feed reformate C to the paraxylene loop ₈ Major part of fraction C ₉₊ The contents were removed. To a lesser extent, the same advantages apply to the isomer C ₈ Fraction which also has reduced C ₉₊ Fractions, if any, will also be removed. Due to C from both the reformer section and from the isomerization section ₈ The aromatic hydrocarbon fractions are all C-lean ₉₊ So that they may be located at the C receiving the effluent from the transalkylation unit ₈ The aromatic fraction is sent to the xylene column 28 at a feed column above the feed tray. This is illustrated in fig. 1 by the flow in line 38 being above the flow in line 27. Further, if C is in the stream in line 38 ₉₊ With the material content within the specifications of separation zone 41, then this portion or all of the stream can bypass xylene column 28 and be fed directly to separation zone 41, as shown by dashed line 70. Severity and separation zone 41 for C according to the fractionation effected in the dividing wall column section 15 ₉₊ The tolerance of the compound may be considered to be either choice or a combination of the two. These options will reduce the overall energy consumption of the xylene column 28 compared to prior art aromatic complexes without a dividing wall column.

In a modification (not shown) of the process shown in fig. 1, the ethylbenzene removal and xylene isomerization zone 44 is divided into two separate reactors, both of which are located downstream of the para-xylene separation section 41. The two reactors may be arranged in parallel or in series, in which case the ethylbenzene removal reactor is typically located upstream of the xylene isomerization reactor. In this modification, the ethylbenzene removal reactor may be operated at conditions significantly different from the xylene isomerization reactor. For example, the ethylbenzene removal reactor may be operated substantially in the vapor phase, while the xylene isomerization reactor may be operated substantially in the liquid phase to reduce xylene losses during isomerization.

FIG. 2 shows a process for producing paraxylene according to a second embodiment of the present invention, in which a dividing wall distillation column is again used in place of a conventional reformate splitter to fractionate in the removal of C from a catalytic reformate stream _5- C remaining after aliphatic hydrocarbons ₆₊ A hydrocarbon stream. Thus in the second embodiment, a catalytic reformate feed stream containing aromatics is supplied from line 111 to depentanizer zone 112 for removal of C _5- And (6) cutting. Pentanes and lighter hydrocarbons are removed via line 113, and C ₆₊ The bottom fraction enters dividing wall distillation column 115 through line 114 to separate the bottom fraction into C _7- 、C ₈ And C ₉₊ A stream of aromatic hydrocarbons.

Will C _7- The stream is passed via line 116 to an extractive distillation or liquid-liquid extraction unit 117 wherein aliphatic hydrocarbons are removed via line 118 to leave a benzene and toluene rich stream which is fed via line 119 to an olefin saturation zone 121. The olefin saturation zone 121 may be a clay treater or any other device effective to remove olefin contaminants from aromatic streams, including catalytic processes, with optional hydrogen addition. The effluent from the olefin saturation zone 121 effluent is fed via line 122 to another dividing wall distillation column 123 from which benzene is collected via line 124, toluene is fed via line 125 to transalkylation unit 126, and C ₈₊ The fraction is connected to a xylene distillation column 128 via line 127, preferably towards the bottom of said xylene distillation column 128.

Unlike the embodiment shown in FIG. 1, in the second embodiment shown in FIG. 2, C-containing is recovered from the reformate dividing wall column 115 ₈ A stream of aromatic hydrocarbons is supplied by line 129 to an ethylbenzene removal reaction zone 131 which is located upstream of the xylene distillation column 128 and separate from the xylene isomerization section. Optionally, C-containing in line 129 ₈ A stream of aromatic hydrocarbons may be supplied to the ethylbenzene removal reaction zone 131 via an olefin saturation zone, such as clay treatment or any other means of removing olefin contaminants, including catalytic processes, with optional hydrogen addition.

As in the embodiment of fig. 1, the removal of ethylbenzene may be carried out in the vapor or liquid phase, but is preferably carried out in the vapor phase and is carried out by dealkylation to benzene or by isomerization to xylene. When the preferred process is dealkylation to benzene, suitable and preferred catalysts and conditions for dealkylation are described with reference to the embodiment of figure 1.

The effluent from the ethylbenzene removal section 131 is supplied via line 132 to a deheptanizer 133 from which fuel gas is removed via line 134, C ₆ /C ₇ The stream is redirected to the depentanizer zone 112 via line 135, and the xylene-rich effluent is fed via line 136 to an olefin saturation zone 137, typically a clay treater or any other means to remove olefin contaminants, including catalytic processes, with optional hydrogen addition. The effluent from the olefin saturation zone 137 is fed via line 138 to the xylene distillation column 128, preferably with the heavies C in line 127 ₈₊ The fractions were split and above.

The overhead of the xylene distillation column 128 is supplied via line 139 to a para-xylene separation zone 141 wherein para-xylene is separated, typically by adsorption or crystallization or a combination of both, and recovered via line 142. Residual toluene is removed by para-xylene separation zone 141 and fed to transalkylation stage 126 via line 143, while the remaining para-xylene depleted stream is fed via line 140 to xylene isomerization zone 144. The para-xylene separation zone 141 is substantially similar to the para-xylene separation zone 41 described above.

Xylene isomerization zone 144 can operate in the vapor phase or the liquid phase, but preferably operates in the liquid phase. Any liquid phase catalytic isomerization process known to those skilled in the art can be used in xylene isomerization zone 144, but one preferred catalytic system is described in U.S. patent application publication nos. 2011/0263918 and 2011/0319688, both of which are incorporated herein by reference in their entirety.

The conditions in the xylene isomerization section 144 are selected to isomerize xylenes in the para-xylene depleted stream while maintaining the para-xylene depleted stream substantially in the liquid phase, thereby producing an isomerization having a higher concentration of para-xylene than the para-xylene depleted streamAnd (3) feeding. Suitable conditions include a temperature of about 230 ℃ to about 300 ℃, a pressure of about 1300 to about 2100kPa and about 0.5 to about 10hr ^-1 Weight Hourly Space Velocity (WHSV).

The effluent from xylene isomerization zone 144 is supplied via line 145 to split between: recycled to the xylene column 128 via line 161, recycled to the deheptanizer 133 via line 146 or redirected to the ethylbenzene removal reaction zone 131 via line 147. The redirection of the xylene isomerization zone effluent in line 145 between line 161, line 146 and line 147 can be optimized for the ethylbenzene content and overall composition of the effluent.

C-containing fraction recovered from the reformate dividing wall distillation column 115 ₉₊ A stream of aromatic hydrocarbons is supplied via line 148 to a heavy aromatic hydrocarbons distillation column 149, which also receives a bottoms stream from the xylene distillation column 128 via line 151. Heavy aromatic hydrocarbon distillation column 149 will have C supplied from

lines

148 and 151 ₉₊ Separation of aromatic hydrocarbons into C-containing stream removed in line 152 ₉ /C ₁₀ Light C ₁₁ And contains C ₁₁ + fraction which is supplied by line 153 to the gasoline pool, fuel pool or topping column. Then will contain C ₉ /C ₁₀ Light C ₁₁ Is fed to the transalkylation unit 126 in combination with the toluene-rich stream supplied via

lines

125 and 143, optionally after passing through an olefin saturation zone such as a clay treater or any other process capable of removing olefin contaminants, including catalytic processes, with optional hydrogen addition. In fig. 2, the olefin saturation zone and the transalkylation zone are combined in a single unit 126, but the purpose of this schematic is not limiting. Those skilled in the art will appreciate that olefin saturation may be carried out in a unit located upstream of and separate from the transalkylation unit. In addition, olefin saturation is only carried out when needed, so if, for example, stream 152 requires olefin removal, and the olefin content in stream 125 makes olefin removal unnecessary, only stream 152 will pass through the olefin saturation zone. Suitable transalkylation processes are described with reference to the embodiment of FIG. 1 above.

Any transalkylation process known to those skilled in the art may be used, but one preferred process employs a multi-stage catalytic system as described in U.S. Pat. No. 7,663,010, which is incorporated herein by reference in its entirety. Such systems include (i) a first catalyst comprising a first molecular sieve having a constraint index in the range of 3-12 and containing from 0.01 to 5 wt.% of at least one source of a first metallic element from groups 6-10 of the periodic table of elements and (i i) a second catalyst comprising a second molecular sieve having a constraint index less than 3 and containing from 0 to 5 wt.% of at least one source of a second metallic element from groups 6-10 of the periodic table of elements, wherein the weight ratio of the first catalyst or the second catalyst is in the range of 5:95 to 75:25, and wherein the first catalyst is located upstream of the second catalyst.

Examples of suitable molecular sieves having a constraint index of 3 to 12 for the first catalyst include ZSM-5, ZSM-11, ZSM-22, ZSM-23, ZSM-35, ZSM-48, ZSM-57 and ZSM-58, with ZSM-5 being preferred. Examples of suitable molecular sieves having a constraint index less than 3 for the second catalyst include zeolite beta, zeolite Y, ultrastable Y (USY), dealuminated Y (deal Y), mordenite, ZSM-3, ZSM-4, ZSM-12, ZSM-18, NU-87 and ZSM-20, with ZSM-12 being preferred. Specific examples of useful metals in the first and second catalysts include iron, ruthenium, osmium, nickel, cobalt, rhenium, molybdenum, tin, and noble metals such as platinum, rhodium, iridium, or palladium.

The transalkylation process may be carried out in any suitable reactor, including a radial flow, fixed bed, continuous downflow or fluidized bed reactor. The conditions in the first and second catalyst beds may be the same or different but typically comprise a temperature of 100-1000 ℃, preferably 300-500 ℃; 790 kPa-a (kilopascals absolute) preferably within the range of 2170 kPa-a, and hydrogen to hydrocarbon molar ratio of 0.01 to 20, preferably 1 to 10; and 0.01 to 100hr ^-1 Preferably in the range of 1-20hr ^-1 In the presence of a surfactant.

The effluent from the transalkylation unit 126 is fed via line 154 to a stabilizer 155 where light gases are collected and removed via line 156. The side stream from the stabilizer 155 is recycled via line 157 to the depentanizer 112 for stabilizationThe bottoms of the fractionator are fed via line 158 to the benzene/toluene/C, optionally via olefin saturation zone 121 ₈ + dividing wall column 123.

As shown in the embodiment of fig. 1, if C is in the stream in line 138 ₉₊ With material content within the specification of the separation zone 141, some or all of this stream can bypass the xylene column 128 and be fed directly to the separation zone 141, as shown by dashed line 170.

FIG. 3 shows various possible improvements to the process shown in FIG. 2, and like reference numerals are used to refer to like components. In such a modification, isomerization C to region 131 (see FIG. 2) ₈ Aromatic hydrocarbon recycle stream 147 substituted for para-xylene depleted C ₈ An aromatic hydrocarbon recycle stream 163 (see fig. 3) taken upstream of isomerization unit 144, while recycle stream 147 is taken downstream of isomerization unit 144. When the catalyst used in the ethylbenzene removal zone 131 is selectivated as described above, xylene loss tends to increase with the para-xylene concentration in the feed due to the similar molecular size of ethylbenzene and para-xylene. Thus, although diffusion of ortho-xylene and meta-xylene into the catalyst pores is limited, para-xylene-like ethylbenzene-will readily react on catalytically active sites, thereby increasing xylene loss. However, since the effluent from the separation zone 141 is depleted in para-xylene, its addition to the feed to the ethylbenzene removal zone 131 via line 163 will dilute the para-xylene content of the feed and thus the xylene loss through the ethylbenzene removal zone 131 will be reduced.

Another modification shown in figure 3 of the second embodiment is to recycle a portion of the effluent from the isomerization section 144 directly to the para-xylene separation zone 141 via line 162. When the liquid phase isomerization zone 144 is operated at conditions that produce less to no benzene, or when this benzene yield does not affect the performance of the para-xylene separation section 141, as already shown in fig. 2, it may be advantageous to recycle a portion of the effluent from the isomerization section 144 directly to the xylene column 128 via line 161. In addition, when liquid phase isomerization section 144 is producing less to no benzene and less C ₉₊ Aromatic compounds to free of C ₉₊ When operating at aromatic conditions, or when this yield does not affect the performance of the para-xylene separation section 141, as shown in fig. 3, it may be advantageous to recycle a portion of the effluent from the isomerization section 144 directly to the para-xylene separation section 141 via line 162. Benzene yield and C from liquid phase isomerization ₉₊ The aromatics yield is generally related to the operating temperature of the unit and also to the ethylbenzene content of the unit feed. Thus, depending on the efficiency of the catalyst in the ethylbenzene removal zone 131 and depending on the state of the catalyst in the liquid phase isomerization unit 144 (the liquid phase isomerization catalyst is typically operated at low temperatures early in the cycle and at high temperatures late in the cycle), and depending on the type of adsorbent and desorbent used in the para-xylene separation zone 141, the distribution of the liquid phase isomerization feed effluent through

lines

146, 161 and 162 can be optimized.

Such recycling

162 and 161 may also be practiced in other process embodiments contemplated herein.

In a further modification shown in fig. 3, the vapor phase ethylbenzene removal reaction zone 131, optionally fed through an olefin saturation zone such as clay treatment or any other means to remove olefin contaminants, including catalytic processes, with optional hydrogen addition, is replaced with a vapor phase ethylbenzene removal and xylene isomerization zone. Thus, in addition to ethylbenzene removal by dealkylation to benzene or isomerization to xylenes by ethylbenzene, xylene isomerization will also occur in zone 131. An example of a suitable combined ethylbenzene removal/xylene isomerization system is disclosed in the above-mentioned U.S. Pat. No. 5,516,956. The effluent of zone 131, which is supplied via line 132 to deheptanizer 133 and then further to separation section 141 via

lines

136, 138 and 139, by some xylene isomerization in zone 131, has a higher para-xylene concentration than the process described in fig. 2. This means that the ratio of para-xylene to xylene is higher than the scheme depicted in fig. 2, so a smaller separation unit 141 would be required. It should be noted that the concept of adding a xylene isomerization function to the ethylbenzene removal section is also applicable to other process schemes contemplated herein.

Another modification of the process shown in figure 2, as shown in figure 3, is the addition of stream 138 to optional bypass 164 of liquid phase isomerization zone 144. When stream 138 contains little or no para-xylene, it is advantageous to isomerize the xylenes in stream 138, which is then recycled via line 161 to xylene column 128 and separation zone 141 to reduce the flow in these portions, thereby reducing the associated operating costs. This alternative is more particularly suitable when the isomerization efficiency in zone 131 is low, because little or no xylene isomerization catalyst is added in zone 131, and thus the primary function of zone 131 is ethylbenzene removal, and further, if stream 129 is heavily diluted by stream 163.

Another modification of the process shown in fig. 2, as shown in fig. 3, is the optional addition of stream 165 from the xylene column 128 to the effluent line 140 of the separation zone 141. This recycle to the liquid phase isomerization zone 144 allows a stream with a low para-xylene content to be isomerized to nearly equilibrium xylenes without recycling through the separation 141 zone when the stream 165 is collected at a location in the xylene column 128 rich in ortho-xylene, thus reducing the flow through the separation section and associated operating costs. This improvement is also applicable to the other process schemes contemplated herein.

Another modification of the process shown in fig. 2, as shown in fig. 3, is the addition of an optional bypass stream 166 from stream 148 to the olefin saturation and transalkylation zone 126. When C of stream 148 ₁₁ When the + content is low, which may occur when the reformate fraction stream 111 has a low endpoint, at least a portion of the stream 148 may bypass the heavy aromatic column 149 and be directed to the olefin saturation and transalkylation zone 126 via line 166, thereby reducing the flow through the heavy aromatic column 149 and associated operating costs. This modification is also applicable to the arrangements shown in figures 1, 2 and 4. As previously mentioned, in FIG. 3, the olefin saturation zone and the transalkylation zone are shown combined in a single unit 126, but the purpose of this schematic is not limiting. It is known to those skilled in the art that olefin saturation may be carried out in a unit located upstream of and separate from the transalkylation unit. In addition, olefin saturation is only carried out when needed, thus if, for example, streams 152 and 166 are neededOlefins are removed and the olefin content in stream 125 is such that olefin removal is not required, then only streams 152 and 166 will pass through the olefin saturation zone.

Another optional modification to the scheme shown in fig. 3 is the separation of the isomerized recycle stream from two isomerization sections, a vapor phase isomerization zone 131 and a liquid phase isomerization zone 144. These recycle streams may then be recycled according to their C ₉ The aromatic hydrocarbon content is provided at different feed points to the xylene column 128 (see line 138 for feeding the vapor phase isomerization feed effluent to the xylene column 128 and line 161 for feeding the liquid phase isomerization feed effluent to the xylene column 128 in fig. 3), thus reducing column size and energy consumption.

FIG. 4 illustrates a process for producing para-xylene according to a third embodiment of the present invention in which C is removed from a catalytic reformate stream using conventional reformate splitter fractionation _5- C remaining after aliphatic hydrocarbons ₆₊ A hydrocarbon stream. Thus, in the third embodiment, a reformate feed stream containing aromatic hydrocarbons is supplied from line 201 to the depentanizer zone 202 for C removal _5- And (6) cutting. Pentane and lighter hydrocarbons are removed via line 203, while C ₆₊ The bottoms fraction is fed via line 204 to a conventional reformate splitter 205 to separate the bottoms fraction into C-containing _7- And C ₈₊ A stream of aromatic hydrocarbons.

C from reformate splitter 205 _7- The stream is passed via line 206 to an extractive distillation or liquid-liquid extraction unit 207 wherein aliphatic hydrocarbons are removed via line 208 to leave a benzene and toluene rich stream which is passed via line 209 to an olefin saturation zone 211. The olefin saturation zone 211 may be a clay treater or any other device effective to remove olefin contaminants from the aromatic stream, including catalytic processes, with optional hydrogen addition. The effluent from the olefin saturation zone 211 is fed via line 212 to dividing wall distillation column 213 from which benzene is collected via line 214 and toluene is fed via line 215 to transalkylation unit 216, C ₈₊ The distillate is fed to a xylene distillation column 218 via line 217.

C containing recovered from reformate splitter 205 ₈₊ A stream of aromatic hydrocarbons is supplied via line 219 to the ethylbenzene removal zone 221, orA zone of olefin saturation is gated, such as clay treatment or any other means to remove olefin contaminants, including catalytic processes, with optional hydrogen addition. The ethylbenzene removal in zone 221 is preferably by deethylation to benzene and light (C) as described above ₂ ) The gas, preferably in the gas phase. Alternatively, ethylbenzene removal may be carried out by isomerizing it to xylenes.

The effluent from the ethylbenzene removal section 221 is supplied via line 222 to a further dividing wall distillation column 223 from which fuel gas, C, is removed via line 224 ₆ /C ₇ The stream is redirected to the depentanizer section 202, C via line 225 ₉₊ The stream is fed via line 227 to the heavy aromatic column 226 and is enriched in C of xylenes ₈ The stream is fed via line 228 to an olefin saturation zone 229, typically any process capable of removing olefin contaminants, including catalytic processes, with optional hydrogen addition. The effluent from the olefin saturation zone 229 is fed via line 231 to a para-xylene separation zone 232 which also receives an overhead from the xylene distillation column 218 via line 233. Para-xylene is typically separated in a para-xylene separation zone 232 by adsorption or crystallization, or a combination thereof, and recovered via line 234. Residual toluene is separated from the para-xylene separation zone 232 and passed via line 235 to the transalkylation zone 216, while the remaining para-xylene depleted stream is fed via line 237 to the xylene isomerization zone 236.

Any xylene isomerization process known to those skilled in the art can be used in the xylene isomerization zone 236, but one preferred process is carried out in the liquid phase and uses a catalytic system, as described in U.S. patent application publication nos. 2011/0263918 and 2011/0319688, both of which are incorporated herein by reference in their entirety.

The effluent from xylene isomerization zone 236 is supplied via line 238 to be split between recycle to dividing wall distillation column 223 via line 239 or reintroduction to ethylbenzene removal zone 221 via line 241. When the ethylbenzene removal zone 221 is operated at very high conversion (about 50% or greater), the slip stream reintroduced into the ethylbenzene removal zone via line 241 will be very small and the majority of the isomerization section effluent will be redirected to dividing wall distillation column 223 via line 239.

C from dividing wall distillation column 223 ₉₊ The stream is supplied via line 227 to the heavy aromatic distillation column 226, which also receives a bottoms stream from the xylene distillation column 218 via line 242. Heavy aromatic hydrocarbon distillation column 226 feeds C from

lines

227 and 242 ₉₊ Separation of aromatic hydrocarbons into C-containing stream removed in line 243 ₉ /C ₁₀ And a fraction containing C ₁₁ Via line 244 to the gasoline pool. Then optionally after passing through an olefin saturation zone such as clay treatment or any other means of removing olefin contaminants, including catalytic processes, with optional hydrogen addition, will contain C ₉ /C ₁₀ Is sent to the transalkylation unit 216 along with the toluene-rich stream provided via line 215. In fig. 4, the olefin saturation zone and the transalkylation zone are shown combined in a single unit 216, but the purpose of this schematic is not limiting. It is known to those skilled in the art that olefin saturation may be carried out in a unit located upstream of and separate from the transalkylation unit. In addition, olefin saturation is only carried out when needed, so if, for example, stream 243 requires olefin removal, while the olefin content in stream 215 is such that olefin removal is not required, only stream 243 will pass through the olefin saturation zone.

Any transalkylation process known to those skilled in the art may be used in transalkylation unit 216, but one preferred process employs a multi-stage catalytic system as described in U.S. patent No. 7,663,010, described above with respect to the embodiment of fig. 1.

The effluent from the transalkylation unit 216 is fed via line 245 to a stabilizer 246 where light gases are collected and removed via line 247. A side stream from stabilizer 246 is recycled to depentanizer 202 via line 249 and the stabilizer bottoms is fed to dividing wall distillation column 213 via line 248, optionally through olefin saturation zone 211.

It can be seen that in the second and third embodiments shown in figures 2 to 4, the EB-rich C recovered from the fractionation of the reformate effluent is addressed ₈ Aromatic compound mixture in region 131, 2Ethylbenzene removal is performed in 21 and xylene isomerization is performed in

dedicated sections

144, 236 for the para-xylene depleted stream. This arrangement decouples ethylbenzene removal from xylene isomerization, so that isomerization of a large para-xylene-depleted stream is carried out in the liquid phase (isomerization unit without addition of a gas phase), while EB removal is carried out in the gas phase for a small EB-rich stream. This reduces the costs associated with reboiling of the liquid effluent from the

para-xylene separation zone

141, 232, which is required for isomerization of para-depleted xylenes in a vapor phase isomerization unit, when both catalytic reactions are carried out in the same unit 44, as shown in fig. 1. In addition, separating xylene isomerization from ethylbenzene removal reduces catalyst cost since liquid phase isomerization catalysts are generally metal free and vapor phase isomerization catalysts include precious or non-precious expensive metals such as rhenium. Further overall xylene loop efficiency can be increased because the conditions of each process can be set independently to maximize its yield and efficiency over the life of the plant.

According to a fourth embodiment (illustrated in fig. 7 described below), the scheme shown in fig. 1 to 3 can be modified by replacing the first

dividing wall column

15, 115 with a conventional distillation column, which allows the separation of three fractions: i.e. C _7- Fraction as the top fraction, C ₈ Fraction as side-cut and C ₉₊ Fractions were taken as bottom fractions. When mixing C ₈ When the fraction is sent to the EB removal zone 131 (FIG. 2 or 3) or 211 (FIG. 4), this solution results in the introduction of C ₈ More C in the fraction ₉ Sent to an ethylbenzene removal unit, compared to the case where a dividing wall column is used. Some C ₉ The components will be dealkylated to toluene, thus transalkylation toluene/C in the feed ₉₊ The ratio will increase and the benzene/PX ratio in the aromatics complex will also increase, which is of interest when more benzene production is targeted, provided that the catalytic system in the EB removal unit can handle heavier feedstocks without significantly affecting the EB removal efficiency of the EB removal unit. In this case, C ₉₊ The fraction may contain some residual C ₈ Aromatic compounds, and should be directed to heavy aromaticsThe hydrocarbon distillation column or to a xylene distillation column.

Some configuration options are not described herein, but are within the scope of the present disclosure, namely: (a) dividing wall column 23 in FIG. 1, dividing wall column 123 in FIGS. 2&3 and dividing wall column 213 in FIG. 4 can be replaced by conventional apparatuses for benzene and toluene columns; (b) the dividing wall column 15 in fig. 1 and the dividing wall column 115 in fig. 2&3 can be replaced by a conventional arrangement of light reformate splitter and heavy reformate splitter columns as shown in fig. 6; (c) in the schemes shown in fig. 2&3, EB removal unit 131 (fig. 2) or EB removal and xylene isomerization unit 131 (fig. 3) may optionally be located between depentanizer 112 and dividing wall column 115 on stream 114, rather than downstream of dividing wall column 115 on stream 129; and (d) similarly, in the scheme shown in fig. 4, EB removal unit 221 may optionally be located between depentanizer 202 and reformate splitter 205 on stream 204, rather than downstream of reformate splitter 205 on stream 219.

The present invention will now be described in more detail with reference to the following non-limiting examples.

Example 1

This example illustrates the benefit of using a divided wall column (fig. 5) as compared to conventional light and heavy reformate splitters (fig. 6) in the configurations depicted in fig. 1-3.

This example is based on 85 wt% of a C rich feedstock obtained from the reforming of a naphtha feedstock having the following carbon number distribution ₆₊ Stream of aromatic hydrocarbons:

C7-	17％
		C7	31％
C8	32％
		C9+	20％

referring to FIG. 5, 220t/h of C-rich ₆₊ The feed of aromatic hydrocarbons (stream 301) is fed to dividing wall column 302, which is operated at a pressure of 1.4kPa, a condenser temperature of 83 ℃, and a reboiler temperature of 209 ℃. The Divided Wall Column (DWC)302 contains 58 theoretical stages, including a condenser (plate N ° 1) and a reboiler (plate N ° 58). DWC technology involves a vertical separation between the feed or prefractionator, and the product side of three product columns. The separation of the low-boiling fraction and the high-boiling fraction takes place on the feed side and the separation of the medium-boiling fraction takes place on the product side. The pre-fractionator side of the DWC distributes the intermediate key between the top and bottom allowing great flexibility to match the composition of the top and bottom of the main column.

In the embodiment shown in FIG. 5, the vertical wall 303 in the divided wall column 302 extends downward from tray N11 to tray N37 and allows each of these trays to be divided into 2 zones: a feed zone and a withdrawal zone located on each side of the wall. The C6+ rich aromatic hydrocarbon feed stream 301 is placed on the wall

The fractionation performance of the dividing wall column 302 is summarized as follows:

toluene recovery (defined as C) _7- The toluene in the fraction (stream 304) divided by the toluene in the feed (stream 301) was 99.9 wt%.

C ₈ Aromatic hydrocarbon recovery (defined as C) ₈ EB + PX + MX + OX in the fraction (stream 305) divided by EB + PX + MX + OX in the feed (stream 301) was 99 wt%.

C ₈ C in the fraction (stream 305) ₉ The aromatic hydrocarbon content was 5% by weight.

To achieve the above separation performance, conventional fractionation would require the use of 2 distillation columns implemented in series as shown in fig. 6. Thus, referring to FIG. 6, a C enrichment of 220t/h ₆₊ Aromatic hydrocarbon feedstock(stream 401) is fed to first distillation column 402 on tray N ° 15. The first distillation column 402 contains 29 theoretical plates and operates at a pressure of 1.4kPa, a condenser temperature of 83 ℃ and a reboiler temperature of 175 ℃. Condensation was carried out using an air cooler, removing 26.7MW, ensuring reboiling by a heating medium, providing 29.6MW of heat at a minimum temperature of 180 ℃, preferably a temperature 15 ℃ above the bottom temperature of the first column. First distillation column 402 allows recovery of C as a liquid distillate on panel N1 _7- Fraction (stream 403) and C as bottom product ₈₊ Fraction (stream 404).

The fractionation performance of the first distillation column 402 is summarized as follows:

toluene recovery (defined as C) _7- Toluene in the fraction (stream 403) divided by toluene in the feed (stream 401) was 99.9 wt%.

C ₈ Aromatic hydrocarbon recovery (defined as C) ₈₊ The EB + PX + MX + OX in the fraction (stream 404) divided by EB + PX + MX + OX in the feed (stream 401) was 99.5 wt%.

The bottom product of the first distillation column 402 (stream 404) is fed to a second distillation column 405 containing 29 theoretical plates operating at a pressure of 1.4kPa, a condenser temperature of 144 c, a reboiler temperature of 197 c. Condensation was carried out using an air cooler, removing 13.7MW, ensuring reboiling by the heating medium, providing 19.5MW of heat at a minimum temperature of 202 ℃, preferably a temperature 15 ℃ above the bottom temperature of the second column. Second distillation column 405 allows recovery of C as a liquid distillate on panel N ° 1 ₈ Fraction (stream 406) and C as bottom product ₉₊ Fraction (stream 407).

The fractionation performance of the second distillation column 405 is summarized as follows:

C ₈ aromatic hydrocarbon recovery (defined as C) ₈ The EB + PX + MX + OX in the fraction (stream 406) divided by EB + PX + MX + OX in the feed (stream 404) was 99.5 wt%.

C ₈ C in the fraction (stream 406) ₉ The aromatic hydrocarbon content was 5% by weight.

Thus, the fractionation performance of a system consisting of 2 fractionation columns in series (fig. 6) is similar to that of a dividing wall column (fig. 5). However, the dividing wall column shown in FIG. 5 is more energy efficient than the conventional apparatus shown in FIG. 6 because the heat requirement to perform the same fractionation performance has been reduced from 49.1MW to 33.3 MW. Another advantage of the dividing wall column over conventional units is that it reduces half of the fractionation system hardware (number of columns, reboilers, etc.) required to obtain the desired fractionation performance.

Example 2

Referring now to fig. 7, this example illustrates the effect of implementing a 3-stage distillation column as the

reformate splitter

15, 115 rather than a dividing wall column in the configurations shown in fig. 1-3.

In the embodiment of FIG. 7, 220t/h of C-rich is fed over N20 of the tray of a 3-stage distillation column 502 containing 58 theoretical plates and operating at 1.4kPa, a condenser temperature of 83 ℃ and a reboiler temperature of 202 ℃ ₆₊ An aromatic hydrocarbon feed (stream 501). The 3-stage distillation column 502 produces C as a liquid distillate on a tray N ° 1 _7- Fraction (stream 503) C as a side draw from column N40 ₈ Fractions (stream 504) and C ₉₊ The fraction (stream 505) is taken as bottom product. Condensation was carried out using an air cooler with 31MW removal, reboiling was ensured by the heating medium, providing 33.7MW of heat at a minimum temperature of 207 ℃, preferably 15 ℃ above the bottom temperature of the distillation column.

The fractionation performance of the 3-fraction distillation column 502 was reduced compared to the dividing wall column in example 1, and is summarized as follows:

toluene recovery (defined as C) ₇ Toluene in the fraction (stream 503) divided by toluene in the feed (stream 501) was 99.9 wt%.

C ₈ Aromatic hydrocarbon recovery (defined as C) ₈ The fraction (stream 504) of EB + PX + MX + OX divided by the feed (stream 501) of EB + PX + MX + OX) was 87 wt%.

C ₈ C in the fraction (stream 504) ₉ The aromatic hydrocarbon content was 15% by weight.

However, ethylbenzene recovery (defined as C) was achieved with a 3-stage distillation column (98 wt.%) ₈ EB in the fraction divided by EB in the feed) was similar to the partition in example 1Column (98.5 wt%).

The performance of the distillation schemes of example 1 and example 2 are summarized in table 1 below, where Qr represents the heat requirement.

TABLE 1 Performance of the distillation schemes of example 1 and example 2

All patents, test procedures, and other documents (including priority documents) cited herein are fully incorporated by reference to the extent such disclosure is not inconsistent and for all jurisdictions in which such incorporation is permitted

While the illustrative forms disclosed herein have been described with particularity, various other modifications will be apparent to and can be readily made by those skilled in the art without departing from the spirit and scope of the disclosure. Accordingly, it is not intended that the scope of the claims appended hereto be limited to the examples and descriptions set forth herein but rather that the claims be construed as encompassing all the features of patentable novelty which reside herein, including all features which would be treated as equivalents thereof by those skilled in the art to which the disclosure pertains.

When numerical lower limits and numerical upper limits are listed herein, ranges from any lower limit to any upper limit are contemplated and are expressly within the scope of the invention. The term "comprising" is synonymous with the term "including". Likewise, when a composition, element, or component group is preceded by the transitional phrase "comprising," it is to be understood that we also contemplate the transitional phrase "consisting essentially of," consisting of, "" selected from "consisting of," or "being," before the listing of the composition, element, or component, and vice versa.

Claims

1. A process for producing para-xylene, the process comprising:

(d1) recycling at least a portion of the isomerized stream to the para-xylene recovery unit,

(e1) from said group containing C _7- Removal of at least a portion of aliphatic hydrocarbons from a stream of aromatic hydrocarbons to produce C _7- An aromatic hydrocarbon-rich stream, which stream,

(f1) will C _7- Supplying at least a portion of the aromatic-rich stream to a separation unit to recover benzene therefrom to produce a toluene-containing stream;

(h1) supplying at least a portion of the transalkylation product to the separation unit in (f1),

wherein the separation unit in (f1) comprises an additional dividing wall distillation column.

2. The process of claim 1, wherein the at least one feedstock to (a1) comprises a reformate stream obtained by removing C from the reformate stream _5- C of hydrocarbon production ₆₊ A mixture of aromatic and aliphatic hydrocarbons.

3. The method of any one of claims 1-2, further comprising:

(j1) in the effective removal ofSaid C is ₈ Subjecting said stream containing C to conditions such that at least a portion of the ethylbenzene in said stream contains aromatic hydrocarbons ₈ A stream of aromatic hydrocarbons is contacted with a first catalyst in the ethylbenzene removal zone.

4. The process of claim 3 wherein the conditions in the ethylbenzene removal zone are effective to remove the C-containing compounds ₈ The stream of aromatic hydrocarbons is maintained in the gas phase.

5. The process of claim 4, wherein the ethylbenzene removal zone is located upstream of the para-xylene recovery unit.

6. The process of claim 4, wherein the ethylbenzene removal zone is located downstream of the paraxylene recovery unit.

7. The process of claim 5 or 6 wherein the ethylbenzene removal zone further comprises conditions effective to cause the C-containing stream to be produced under said conditions ₈ A second catalyst for xylene isomerization in a stream of aromatic hydrocarbons.

8. The process of any one of claims 1-2, wherein the conditions in the xylene isomerization zone are effective to maintain the para-xylene depleted stream in the liquid phase.

9. The process of any one of claims 1-2, wherein the conditions in the xylene isomerization zone are effective to maintain the para-xylene depleted stream in the vapor phase.