Production of paraxylene by liquid phase isomerization and separation thereof

Abstract

A feed mixture comprising one or more xylene isomers may be separated in a p-xylene recovery unit using simulated moving bed chromatography with toluene as a desorbent to yield a p-xylene enriched product stream and a p-xylene depleted raffinate stream. Optionally, an intermediate stream may also be obtained. At least a portion of the raffinate stream or isomerized raffinate stream may be separated in a distillation column to produce an overhead stream comprising toluene, which may be sent to a paraxylene recovery unit as at least a portion of a desorbent. If present, the intermediate stream may be isomerized under liquid phase isomerization conditions and sent to a paraxylene recovery unit. At least a portion of the raffinate stream or one or more lower streams obtained from the distillation column may be isomerized under liquid phase isomerization conditions and passed to a paraxylene recovery unit.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to and the benefit of U.S. Provisional Application No. 63 / 351,898, filed on June 14, 2022, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0003] The present disclosure relates to the isomerization of C8+ aromatic hydrocarbons and more particularly, to the isomerization of C8+ aromatic hydrocarbons and the separation of para-xylene therefrom under liquid phase isomerization conditions. Background Art

[0004] The worldwide production capacity of paraxylene from various industrial sources is about 40 million tons per year. Paraxylene is a valuable chemical raw material that can be obtained from a mixture of C8+ aromatic hydrocarbons. Paraxylene is mainly used for conversion into 1,4-benzenedicarboxylic acid (terephthalic acid) which can be used in synthetic textiles, bottles and plastic materials and other industrial applications. The demand for other xylene isomers is much lower, but also considerable. For example, metaxylene can be used as a blending component for aviation gasoline.

[0005] C8+ aromatic hydrocarbon mixtures (e.g., ortho-, meta- and / or para-xylene isomers, as well as ethylbenzene and heavier aromatic hydrocarbons) can be produced by various methods, such as alkylation of lower aromatic hydrocarbons (e.g., benzene and / or toluene), transalkylation, toluene disproportionation, catalytic reforming, isomerization, cracking, etc. Alkylation of lower aromatic hydrocarbons using methanol and / or dimethyl ether promoted by a zeolite catalyst can be a particularly effective and advantageous route to produce para-xylene with relatively high selectivity relative to ortho- and para-xylene, as described, for example, in U.S. Patent Application Publication No. 20200308085 and International Patent Application Publication No. WO / 2020 / 197888, each of which is incorporated herein by reference.

[0006] After at least partially separating the para-xylene from the other C8+ aromatics, a raffinate stream depleted in para-xylene is obtained. Such a raffinate stream can be isomerized to form additional para-xylene and then undergo further separation to separate the additional para-xylene that has been produced. Conventionally, such isomerization processes have been performed using vapor phase isomerization, which is a very energy intensive process. Recently, progress has been made in the isomerization of xylene isomers by liquid phase isomerization, which is generally a much less energy intensive process.

[0007] Although generally less energy intensive, the presence of toluene, ethylbenzene and / or C9+ aromatics during liquid phase isomerization can produce unwanted by-products and result in the loss of para-xylene or complicate its separation. Summary of the invention

[0008] In some aspects, the present disclosure provides a method comprising: (I) providing a feed mixture comprising one or more xylene isomers and optionally ethylbenzene; (II) separating the feed mixture in a para-xylene recovery unit using simulated moving bed chromatography with toluene as a desorbent to obtain a product stream rich in para-xylene, a raffinate stream depleted in para-xylene, and optionally an intermediate stream comprising para-xylene at a concentration higher than that in the raffinate stream and lower than that in the product stream, the raffinate stream comprising toluene, optionally ethylbenzene, and o-xylene, m-xylene, or any combination thereof; (III) optionally, liquid phase isomerizing at least a portion of the raffinate stream under liquid phase isomerization conditions in the presence of a liquid phase isomerization catalyst to obtain an isomerized raffinate stream; (IV) separating at least a portion of the raffinate stream and / or the isomerized raffinate stream, if any, in a distillation column; at least a portion thereof to obtain an overhead stream comprising at least a majority of the toluene in the raffinate stream and one or more lower streams, each of which comprises one or more xylene isomers; (V) sending at least a portion of the overhead stream to a para-xylene recovery unit as at least a portion of the desorbent; (VI) conducting liquid phase isomerization under liquid phase isomerization conditions in the presence of a liquid phase isomerization catalyst and obtaining one or more isomerized recycle streams after conducting liquid phase isomerization, the liquid phase isomerization being performed on at least one of: (a) at least a portion of the one or more lower streams; and / or (b) at least a portion of the intermediate stream, if any; and / or (c) conducting liquid phase isomerization of at least a portion of the raffinate stream in (III); and (VII) sending at least a portion of the one or more isomerized recycle streams to a para-xylene recovery unit.

[0009] In some aspects, the present disclosure provides a method comprising: (i) providing a feed mixture comprising one or more xylene isomers and optionally ethylbenzene; (ii) separating the feed mixture in a para-xylene recovery unit using simulated moving bed chromatography with toluene as a desorbent to obtain a para-xylene-rich product stream and a para-xylene-depleted raffinate stream, the raffinate stream comprising toluene, optionally ethylbenzene, and o-xylene, m-xylene, or any combination thereof; (iii) liquid phase isomerizing at least a portion of the raffinate stream in the presence of a liquid phase isomerization catalyst under liquid phase isomerization conditions to obtain an isomerized raffinate stream; and (iv) separating the isomerized raffinate stream. (v) sending a portion of the raffinate stream to a first side of a dividing wall distillation column; (v) sending a portion of the raffinate stream to a second side of the dividing wall distillation column; (vi) obtaining a first lower stream rich in paraxylene from the first side of the dividing wall distillation column, obtaining a second lower stream depleted in paraxylene from the second side of the dividing wall distillation column, and obtaining a top stream rich in toluene from the dividing wall distillation column; (vii) sending at least a portion of the top stream to a paraxylene recovery unit as at least a portion of the desorbent; and (viii) sending one or more isomerized recycle streams to a paraxylene recovery unit, the one or more isomerized recycle streams being obtained as at least a portion of the first lower stream.

[0010] In still other aspects, the present disclosure provides a process comprising: (A) providing a feed mixture comprising one or more xylene isomers and optionally ethylbenzene; (B) separating the feed mixture in a para-xylene recovery unit using simulated moving bed chromatography with toluene as a desorbent to obtain a product stream rich in para-xylene, a raffinate stream depleted in para-xylene, and optionally an intermediate stream comprising para-xylene at a concentration higher than that in the raffinate stream and lower than that in the product stream, the raffinate stream comprising toluene, optionally ethylbenzene, and o-xylene, m-xylene, or any combination thereof; and (C) separating at least a portion of the raffinate stream in a distillation column to obtain an overhead stream comprising at least a majority of the toluene in the raffinate stream. and one or more lower streams, each of which comprises one or more xylene isomers; (D) sending at least a portion of the overhead stream to a para-xylene recovery unit as at least a portion of the desorbent; (E) conducting a liquid phase isomerization under liquid phase isomerization conditions in the presence of a liquid phase isomerization catalyst to produce one or more isomerized recycle streams, the liquid phase isomerization being conducted on at least one of: (a) at least a portion of the one or more lower streams; and / or (b) at least a portion of the intermediate stream, if present; and / or (c) at least a portion of the raffinate stream; and (F) sending at least a portion of the one or more isomerized recycle streams to a para-xylene recovery unit.

[0011] These and other features and properties of the disclosed methods and compositions of the present disclosure, as well as their advantageous applications and / or uses, will be apparent from the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The following figures are included to illustrate certain aspects of the present disclosure and should not be construed as exclusive embodiments. The disclosed subject matter is capable of considerable modification, alteration, combination, and equivalence in form and function as will occur to those of ordinary skill in the art having the benefit of this disclosure.

[0013] In order to assist persons of ordinary skill in the relevant art in making and using the subject matter of this document, reference is made to the accompanying drawings, in which:

[0014] Figure 1 is a block diagram of a system and process for xylene separation and liquid phase isomerization according to a first embodiment of the present disclosure.

[0015] Figure 2 is a block diagram of a system and process for xylene separation and liquid phase isomerization according to a second embodiment of the present disclosure.

[0016] Figure 3 is a block diagram of a system and process for xylene separation and liquid phase isomerization according to a third embodiment of the present disclosure.

[0017] Figure 4 is a block diagram of a system and process for xylene separation and liquid phase isomerization according to a fourth embodiment of the present disclosure.

[0018] Figure 5 is a block diagram of a system and process for xylene separation and liquid phase isomerization according to a fifth embodiment of the present disclosure.

[0019] Figure 6 is a block diagram of a system and process for xylene separation and liquid phase isomerization according to a sixth embodiment of the present disclosure. DETAILED DESCRIPTION

[0020] The present disclosure relates to the isomerization of C8+ aromatic hydrocarbons and more particularly, to the isomerization of C8+ aromatic hydrocarbons and the separation of para-xylene therefrom under liquid phase isomerization conditions.

[0021] definition

[0022] Various specific embodiments, versions and examples of the invention will now be described, including preferred embodiments and definitions adopted herein for the purpose of understanding the claimed invention. Although the following detailed description provides specific preferred embodiments, those skilled in the art will understand that these embodiments are exemplary only, and that the invention may be implemented in other ways. For the purpose of determining infringement, the scope of the invention will refer to any one or more of the appended claims, including their equivalents, and elements or limitations equivalent to those recorded. Any reference to the "present invention" may refer to one or more of the inventions defined by the claims, but not necessarily all.

[0023] In the present disclosure, a method may be described as comprising at least one "step". It is understood that each step is an action or operation that may be performed one or more times in a method in a continuous or non-continuous manner. Unless otherwise indicated or the context clearly indicates otherwise, multiple steps in a method may be performed in the order in which they are listed, overlapping or non-overlapping with one or more other steps, or in any other order, as the case may be. In addition, one or more or all steps may be performed simultaneously for the same or different batches of materials. For example, in a continuous method, while the first step in the method is being performed on the starting raw material that has just been fed into the method, the second step may be performed simultaneously on the intermediate product produced by processing the raw material fed into the method at an earlier time in the first step. Preferably, the steps are performed in the order described. However, the various steps may occur out of sequence and / or simultaneously, rather than clearly in the order listed.

[0024] Unless otherwise indicated, all numbers indicating quantities in this disclosure are to be understood as being modified in all cases by the term "about". It is also to be understood that the precise numerical values ​​used in the specification and claims constitute specific embodiments. Efforts have been made to ensure the accuracy of the data in the examples. However, it is to be understood that any measured data inherently contain a certain degree of error due to the limitations of the techniques and equipment used to make the measurements.

[0025] As used herein, the indefinite article "a" or "an" shall mean "at least one", unless specified to the contrary or the context clearly indicates otherwise. Thus, for example, embodiments using "a fractionation column" include embodiments in which one, two, or more fractionation columns are used, unless specified to the contrary or the context clearly indicates that only one fractionation column is used.

[0026] As used herein, the term "essentially consisting of" means that the composition, feed, stream or effluent contains a given component or group of components in a concentration of at least about 60 weight %, preferably at least about 70 weight %, more preferably at least about 80 weight %, more preferably at least about 90 weight %, or still more preferably at least about 95 weight %, based on the total weight of the composition, feed, stream or effluent.

[0027] For the sake of brevity, the following abbreviations are used herein: RT is room temperature (and is 23° C. unless otherwise indicated), kPag is kilopascals (gauge), psig is pounds-force per square inch (gauge), psia is pounds-force per square inch (absolute), and WHSV is weight hourly space velocity.

[0028] As used herein, "wt%" means percent by weight, "vol%" means percent by volume, "mole%" means percent by mole, "ppm" means parts per million, and "ppm wt" and "wppm" are used interchangeably to mean parts per million on a weight basis. All concentrations herein are expressed on the basis of the total amount of the composition in question. All ranges expressed herein shall include both endpoints as two specific embodiments unless otherwise indicated or indicated.

[0029] The nomenclature of elements and their groups used herein follows the periodic table used by the International Union of Pure and Applied Chemistry after 1988. An example of a periodic table is shown inside the front cover of Advanced Inorganic Chemistry, 6th edition, by F. Albert Cotton et al. (John Wiley & Sons, Inc., 1999).

[0030] As used herein, the term "hydrocarbon" means (i) any compound consisting of hydrogen and carbon atoms or (ii) any mixture of two or more such compounds of (i). The term "Cn hydrocarbon", where n is a positive integer, means (i) any hydrocarbon compound containing a total of n carbon atoms (one or more) in its molecule or (ii) any mixture of two or more such hydrocarbon compounds of (i). Thus, C2 hydrocarbons can be ethane, ethylene, acetylene or any mixture of at least two of them in any proportion. "Cm to Cn hydrocarbons" or "Cm-Cn hydrocarbons", where m and n are positive integers and m < n, means any of Cm, Cm+1, Cm+2, …… Cn-1, Cn hydrocarbons, or any mixture of two or more of them. Thus, "C2 to C3 hydrocarbons" or "C2-C3 hydrocarbons" can be any of ethane, ethylene, acetylene, propane, propylene, propyne, allene, cyclopropane and any mixture of two or more of them in any proportion between the components. "Saturated C2-C3 hydrocarbons" can be ethane, propane, cyclopropane or any mixture of two or more of them in any proportion. "Cn+ hydrocarbons" means (i) any hydrocarbon compound containing a total of at least n carbon atoms (one or more) in its molecule or (ii) any mixture of two or more such hydrocarbon compounds of (i). "Cn- hydrocarbons" means (i) any hydrocarbon compound containing a total of at most n carbon atoms in its molecule or (ii) any mixture of two or more such hydrocarbon compounds of (i). "Cm hydrocarbon stream" means a hydrocarbon stream consisting essentially of Cm hydrocarbon(s). "Cm-Cn hydrocarbon stream" means a hydrocarbon stream consisting essentially of Cm-Cn hydrocarbon(s).

[0031] As used herein, an "aromatic hydrocarbon" is a hydrocarbon that contains an aromatic ring in its molecular structure. An aromatic compound may have a cyclic cloud of π electrons that complies with Hückel's rule. "Non-aromatic hydrocarbon" means a hydrocarbon other than an aromatic hydrocarbon.

[0032] As used herein, the term "lower aromatic hydrocarbon" refers to benzene, toluene or a mixture of benzene and toluene.

[0033] An "effluent" or "feed" is sometimes also referred to as a "stream" in the present disclosure. In cases where it is shown that two or more streams form a combined stream and then it is supplied to a container, it should be construed to include alternatives where the streams are supplied to the container separately, where appropriate. Similarly, in cases where two or more streams are supplied to a container separately, it should be construed to include alternatives where the streams are combined into a combined stream(s) before entering the container, where appropriate. Additionally, a single stream can be divided into two or more separate streams and provided to different locations.

[0034] As used herein, the term "liquid phase" means a reaction condition in which the aromatic hydrocarbons present in the reactor are substantially in a liquid state. "Substantially in a liquid phase" means ≥ about 90 wt%, preferably ≥ about 95 wt%, preferably ≥ about 99 wt%, and preferably all of the aromatic hydrocarbons are in a liquid phase.

[0035] As used herein, the term "gas phase" means reaction conditions in which the aromatic hydrocarbons present in the reactor are substantially in a gaseous state. "Substantially in the gas phase" means ≥ about 90 wt%, preferably ≥ about 95 wt%, preferably ≥ about 99 wt%, and preferably all of the aromatic hydrocarbons are in the gas phase.

[0036] As used herein, the term "alkylation" means a chemical reaction in which an alkyl group is transferred from an alkyl group source compound, such as an alkylating agent, to an aromatic ring as a substituent thereon. "Methylation" means an alkylation in which the transferred alkyl group is a methyl group. Thus, methylation of benzene can produce toluene, xylene, trimethylbenzene, etc.; and methylation of toluene can produce xylene, trimethylbenzene, etc.

[0037] As used herein, the term "methylated aromatic hydrocarbon" means an aromatic hydrocarbon containing at least one methyl group and containing only methyl groups (one or more) attached to aromatic rings (one or more) therein. Examples of methylated aromatic hydrocarbons include toluene, xylene, trimethylbenzene, tetramethylbenzene, pentamethylbenzene, hexamethylbenzene, methylnaphthalene, dimethylnaphthalene, trimethylnaphthalene, tetramethylnaphthalene, etc.

[0038] As used herein, the term "molecular sieve" means a crystalline or semi-crystalline material, such as a zeolite, having pores of a molecular size that allow molecules below a certain critical size to pass therethrough.

[0039] "Crystallite" means a grain of a material. Crystallites having micrometer or nanometer size can be observed using a microscope such as a transmission electron microscope ("TEM"), a scanning electron microscope ("SEM"), a reflection electron microscope ("REM"), a scanning transmission electron microscope ("STEM"), etc. Crystallites can aggregate to form a polycrystalline material. Agglomerated particles comprising a plurality of crystallites may be present in the material in some cases.

[0040] As used herein, the term "enriched" or "enriched" when describing a component in a stream or feed means that the stream or feed contains a higher concentration of the component than the source material from which the stream is derived. As used herein, the term "depleted" or "depleted" when describing a component in a stream or feed means that the stream or feed contains a lower concentration of the component than the source material from which the stream is derived.

[0041] Unless otherwise indicated herein, any stream or feed "enriched" in a particular component may "consist of" or "consist essentially of" that component. A feed or stream "enriched" in a component may constitute the majority component of the feed or stream as compared to other components.

[0042] As used herein, the term "overhead stream" refers to a vapor stream withdrawn from the top portion of a distillation column.

[0043] As used herein, the term "lower stream" refers to a vapor or liquid stream that is not an overhead stream and is withdrawn from a location other than the top portion of a distillation column. A "lower stream" may be a side stream or a bottoms stream.

[0044] Unless otherwise indicated herein, any stream or feed that is "depleted" in a particular component may be "free" or "substantially free" of that component. "Substantially free" and "substantially free" are used interchangeably herein to mean that a composition, feed, stream, or effluent contains a given component in a concentration of at most about 10% by weight, preferably at most about 8% by weight, more preferably at most about 5% by weight, more preferably at most about 3% by weight, and still more preferably at most about 1% by weight, based on the total mass of the composition, feed, stream, or effluent in question.

[0045] In the present disclosure, o-xylene means 1,2-dimethylbenzene, m-xylene means 1,3-dimethylbenzene, and p-xylene means 1,4-dimethylbenzene. Herein, the general term "xylene(s) or xylene isomer(s)" in the singular or plural form, collectively means any mixture or one of two to four of p-xylene, m-xylene and o-xylene, and / or ethylbenzene in any proportion thereof. In the disclosure herein, ethylbenzene shall be considered a xylene isomer. Thus, a mixture of xylene isomers may comprise one or more of or consist essentially of one or more of: o-xylene, m-xylene, p-xylene and ethylbenzene. A stream containing xylene isomers may be depleted in p-xylene or enriched in p-xylene, depending on the location from which the stream is withdrawn and the process conditions, as further explained herein.

[0046] A stream or feed that is depleted in one component may be enriched in another component. For example, a stream that is depleted in para-xylene may be enriched in ortho-xylene and / or meta-xylene.

[0047] Liquid phase isomerization after separation of para-xylene from feed mixture

[0048] As discussed above, it may be desirable to perform isomerization after separating para-xylene from a feed mixture containing C8+ aromatics. Isomerization may form additional para-xylene from other C8 aromatics and promote more efficient utilization of the feed mixture. Although liquid phase isomerization may provide benefits over vapor phase isomerization, such as reduced energy input requirements, the presence of toluene and / or ethylbenzene during liquid phase isomerization may produce unwanted byproducts and result in para-xylene losses and / or complex separation thereof. Descriptions of exemplary methods, conditions, and catalysts for liquid phase isomerization may be found, for example, in U.S. Patent Application Publications 2011 / 0319688; 2012 / 0108867; 2013 / 0274532; 2014 / 0023563; and 2015 / 0051430, the relevant contents of which are incorporated herein by reference. Additional details regarding methods, conditions, and catalysts for liquid phase isomerization are provided herein.

[0049] Toluene often coexists in the feed mixture comprising C8+ aromatics. Catalysts effective for isomerizing xylene isomers can also often work on toluene and cause the formation of by-products. Advantageously, the liquid phase isomerization catalyst comprising the zeolite with MEL framework can easily promote the isomerization of xylene isomers under liquid phase isomerization conditions, to produce an equilibrium mixture of xylenes by the raffinate stream poor in p-xylene, optionally after it is further separated. Unexpectedly, the zeolite catalyst with MEL framework is essentially inert to toluene, so that even in the presence of high concentrations of toluene, liquid phase isomerization can also occur, and solve the significant difficulties associated with liquid phase isomerization in addition. Although the zeolite catalyst with MFI framework is slightly more active in converting toluene, it can also be used in the favorable liquid phase isomerization disclosed herein and in further processing operations.

[0050] Advantageous methods for separating para-xylene in the context of this disclosure may use simulated moving bed chromatography, the details of which will be familiar to those of ordinary skill in the art. A commercially available simulated moving bed chromatography method is available from the French company Axens as ELUXYL ® The invention relates to a method for isomerizing paraxylene, wherein the toluene is separated from the isomerization product by a raffinate stream obtained after separation of the paraxylene, and the toluene is separated from the isomerization product by a raffinate stream obtained after separation of the paraxylene, and the raffinate stream is separated from the isomerization product by a raffinate stream obtained after separation of the paraxylene, and the raffinate stream is sent to the paraxylene recovery unit, wherein the toluene can advantageously act as a desorbent for the simulated moving bed chromatography used therein. Therefore, the liquid phase isomerization and separation methods disclosed herein provide considerable synergy when used to produce paraxylene.

[0051] Further advantages of the present disclosure include considerable flexibility in when to perform liquid phase isomerization on the raffinate stream. In some cases, at least a portion of the raffinate stream can be isomerized and recycled to the para-xylene recovery unit without further separation in a distillation column. Thus, the present disclosure can reduce distillation throughput requirements, thereby reducing energy input requirements, and potentially reduce capital equipment costs by facilitating the use of smaller distillation columns.

[0052] In addition, the liquid phase isomerization catalyst and liquid phase isomerization conditions of the present disclosure also do not result in the large-scale production of ethylbenzene and other byproducts that may otherwise complicate further separation operations. In order to address the ethylbenzene or other byproducts formed under liquid phase isomerization conditions, the method disclosed herein can be further incorporated into gas phase isomerization to continuously or as needed remove problematic byproducts from a portion of the raffinate stream. By combining gas phase isomerization with the liquid phase isomerization method according to the present disclosure, the energy input requirement of gas phase isomerization can be reduced compared to the energy input requirement of treating the entire raffinate stream by gas phase isomerization. Additional details and further advantages are discussed in the following description.

[0053] Before further discussing more specific aspects and advantages of the present disclosure, the method of the present disclosure will be described according to the accompanying drawings. For the sake of brevity, common reference numerals are used in the drawings to describe elements with similar structures and functions in various system and method configurations.

[0054] Figure 1 is a block diagram of a system and method for xylene separation and liquid phase isomerization according to a first embodiment of the present disclosure. In the system and method 100, a feed mixture 102 comprising at least toluene, mixed xylenes, and optionally ethylbenzene is received in a para-xylene recovery unit 104. Preferably, the amount of ethylbenzene is below a specified critical amount and / or the feed mixture 102 is treated to remove excess ethylbenzene therefrom. The para-xylene recovery unit 104 uses simulated moving bed chromatography with toluene as a desorbent to produce a para-xylene product stream 106 that is enriched in para-xylene and may consist essentially of para-xylene, and a raffinate stream 108 that is depleted in para-xylene. The raffinate stream 108 may be enriched in at least one of ortho-xylene and meta-xylene and contain toluene and optionally at least some ethylbenzene.

[0055] In the system and process 100, a raffinate stream 108 is provided to a distillation column 110 and is separated into an overhead stream 112 and a bottom stream 114. A majority of the overhead stream 112 comprises toluene, and preferably, the overhead stream 112 comprises at least a majority of the toluene in the raffinate stream 108 and / or preferably, the overhead stream 112 consists essentially of toluene. The overhead stream 112 is sent (recycled) to the para-xylene recovery unit 104 as at least a portion of the desorbent used therein. Additional toluene desorbent may be sent to the para-xylene recovery unit 104 from an external source (not shown). Figure 1 middle).

[0056] At least a portion of the lower stream 114 is subjected to liquid phase isomerization and is then sent to the paraxylene recovery unit 104. Figure 1 As described in , the lower stream 114 is divided into a first stream 120 and a second stream 122. However, the division of the lower stream 114 into the first stream 120 and the second stream 122 is optional, depending on factors such as whether byproducts such as ethylbenzene have increased to a level that indicates the need for removal by vapor phase isomerization or transalkylation. If the second stream 122 is produced, it can be sent to a vapor phase isomerization unit 130, which performs vapor phase isomerization of xylene isomers under vapor phase isomerization conditions in the presence of a vapor phase isomerization catalyst to convert one or more xylene isomers into additional para-xylene. Although the energy input is higher, such vapor phase isomerization can more effectively convert ethylbenzene into other xylene isomers compared to liquid phase isomerization. The vapor phase isomerization unit 130 may form part of a xylene isomerization loop (not shown) which may further include a distillation column for separating xylene isomers from other aromatic hydrocarbons, and a paraxylene recovery unit which may use simulated moving bed chromatography or crystallization recovery techniques.

[0057] The first stream 120 is sent to a liquid phase isomerization unit 140, which performs liquid phase isomerization of xylene isomers in the presence of a suitable liquid phase isomerization catalyst under liquid phase isomerization conditions. The first stream 120 may be depleted in para-xylene but contain other xylene isomers (including ethylbenzene) and residual toluene that is not separated in the overhead stream 112. Under the liquid phase isomerization conditions in the liquid phase isomerization unit 140, additional para-xylene is produced from the xylene isomers to provide an isomerized recycle stream 142 that is enriched in para-xylene compared to the first stream 120. The isomerized recycle stream 142 is then sent to the para-xylene recycle unit 104. Figure 1As described in , the isomerized recycle stream 142 is returned to the para-xylene recovery unit 104 at a location different from where the feed mixture 102 is introduced into the para-xylene recovery unit 104. However, it should be understood that at least a portion of the isomerized recycle stream 142 can be combined with the feed mixture 102 and / or returned to the para-xylene recovery unit 104 at the same location as where the feed mixture 102 is introduced.

[0058] Figure 2 is a block diagram of a system and method for xylene separation and liquid phase isomerization according to a second embodiment of the present disclosure. In the system and method 200, a feed mixture 102 is received in a para-xylene recovery unit 104 and is prepared in the same manner as described above for Figure 1 The feed mixture is separated into a para-xylene product stream 106 and a raffinate stream 108 in a manner similar to that described in the system and method 100 of FIG.

[0059] In the system and method 200, the raffinate stream 108 is separated into a first stream 210 and a second stream 212. The second stream 212 containing at least a portion of the raffinate stream 108 is provided to a distillation column 110 and separated into an overhead stream 112 and a lower stream 114. A majority of the overhead stream 112 comprises toluene, and preferably, the overhead stream 112 comprises at least a majority of the toluene present in the portion of the raffinate stream 108 within the second stream 212, and / or preferably, the overhead stream 112 consists essentially of toluene. The overhead stream 112 is sent to the paraxylene recovery unit 104 as at least a portion of the desorbent used therein. The lower stream 114 is sent to a vapor phase isomerization unit 130, which performs vapor phase isomerization of xylene isomers in the presence of a vapor phase isomerization catalyst under vapor phase isomerization conditions, as described above with respect to Figure 1 The system and method 100 are discussed in more detail.

[0060] The first stream 210 containing at least a portion of the raffinate stream 108 is sent to the liquid phase isomerization unit 140, which performs liquid phase isomerization of xylene isomers in the presence of a liquid phase isomerization catalyst under liquid phase isomerization conditions. Under the liquid phase isomerization conditions in the liquid phase isomerization unit 140, additional para-xylene is produced from the xylene isomers to provide an isomerized recycle stream 142 that is enriched in para-xylene compared to the first stream 210. The isomerized recycle stream 142 is then sent to the para-xylene recovery unit 104. Figure 2As described in , the isomerized recycle stream 142 is returned to the para-xylene recovery unit 104 at a location different from where the feed mixture 102 is provided to the para-xylene recovery unit 104. However, it should be understood that at least a portion of the isomerized recycle stream 142 can be combined with the feed mixture 102 and / or returned to the para-xylene recovery unit 104 at the same location as where the feed mixture 102 is introduced.

[0061] Figure 3 is a block diagram of a system and method for xylene separation and liquid phase isomerization according to a third embodiment of the present disclosure. In the system and method 300, a feed mixture 102 is received in a para-xylene recovery unit 104 and is prepared in the same manner as described above for Figure 1 The feed mixture is separated into a para-xylene product stream 106 and a raffinate stream 108 in a manner similar to that described for the system and method 100 in . The raffinate stream 108 is provided to a distillation column 110 and separated into an overhead stream 112 and a bottom stream 114. A majority of the overhead stream 112 comprises toluene, and preferably, the overhead stream 112 comprises at least a majority of the toluene present in the raffinate stream 108, and / or preferably, the overhead stream 112 consists essentially of toluene. The overhead stream 112 is sent to the para-xylene recovery unit 104 as at least a portion of the desorbent used therein. The bottom stream 114 is sent to a vapor phase isomerization unit 130, which performs vapor phase isomerization of xylene isomers in the presence of a vapor phase isomerization catalyst under vapor phase isomerization conditions, as described above with respect to FIG. Figure 1 The system and method 100 are discussed in more detail.

[0062] In the system and method 300, an intermediate stream 302 is obtained from the paraxylene recovery unit 104 and is recycled in the unit after undergoing liquid phase isomerization. The intermediate stream 302 contains paraxylene at a concentration higher than that in the raffinate stream 108 and lower than that in the paraxylene product stream 106. The paraxylene concentration in the intermediate stream 302 may be further lower than the paraxylene concentration in the feed mixture 102. Figure 3 As described in the above, the intermediate stream 302 is sent to the liquid phase isomerization unit 140, which performs liquid phase isomerization of xylene isomers in the presence of a liquid phase isomerization catalyst under liquid phase isomerization conditions. Under the liquid phase isomerization conditions in the liquid phase isomerization unit 140, additional para-xylene is produced from the xylene isomers to provide an isomerized recycle stream 142, which is enriched in para-xylene compared to the intermediate stream 302. The isomerized recycle stream 142 is then sent to the para-xylene recovery unit 104. Figure 3As described in , the isomerized recycle stream 142 is returned to the para-xylene recovery unit 104 at a location different from where the feed mixture 102 is provided to the para-xylene recovery unit 104. However, it should be understood that at least a portion of the isomerized recycle stream 142 can be combined with the feed mixture 102 and / or returned to the para-xylene recovery unit 104 at the same location as where the feed mixture 102 is introduced.

[0063] Figure 4 is a block diagram of a system and method for xylene separation and liquid phase isomerization according to a fourth embodiment of the present disclosure. In the system and method 400, a feed mixture 102 is received in a para-xylene recovery unit 104 and is prepared in the same manner as described above for Figure 1 The feed mixture is separated into a para-xylene product stream 106 and a raffinate stream 108 in a manner similar to that described in the system and method 100 of FIG.

[0064] In the system and method 400, the raffinate stream 108 is divided into a first stream 410 and a second stream 412. The first stream 410 is sent to the liquid phase isomerization unit 140, which performs liquid phase isomerization of xylene isomers under liquid phase isomerization conditions in the presence of a liquid phase isomerization catalyst. Under the liquid phase isomerization conditions in the liquid phase isomerization unit 140, additional para-xylene is produced from the xylene isomers to provide an isomerized raffinate stream 420 that is enriched in para-xylene compared to the portion of the raffinate stream 108 in the first stream 410.

[0065] The isomerized raffinate stream 420 and the second stream 412 (containing the non-isomerized portion of the raffinate stream 412) are sent to a distillation column 110 containing a wall 430. The wall 430 extends upward from the bottom surface of the distillation column 110 but does not reach the top surface thereof, thereby dividing the distillation column 110 into a first side 431 and a second side 432 that are in vapor communication with each other. The isomerized raffinate stream 420 is sent to the first side 431 of the distillation column 110, and the second stream 412 is sent to the second side 432 of the distillation column 110. An overhead stream 112 is obtained from the distillation column 110, and a majority of the overhead stream 112 comprises toluene. The overhead stream 112 represents a combined vapor stream received from the first side 431 and the second side 432 of the distillation column 110. Preferably, overhead stream 112 comprises a portion of raffinate stream 108 in second stream 412 and at least a majority of the toluene in isomerized raffinate stream 420, and / or preferably, overhead stream 112 consists essentially of toluene. Overhead stream 112 is sent to para-xylene recovery unit 104 as at least a portion of the desorbent used therein.

[0066] At least two lower streams are obtained from the distillation column 110. Specifically, a first lower stream 450 is obtained from the first side 431, and a second lower stream 452 is obtained from the second side 432. Since the second lower stream 452 is directly generated from a portion of the raffinate stream 108 within the second stream 412, the second lower stream 452 is still depleted in para-xylene. Therefore, the second lower stream 452 is sent to the gas phase isomerization unit 130, which performs gas phase isomerization of xylene isomers under gas phase isomerization conditions in the presence of a gas phase isomerization catalyst to convert one or more xylene isomers into additional para-xylene, as described above with respect to Figure 1 The system and method 100 are discussed in more detail.

[0067] Since the first lower stream 450 is generated from the isomerized raffinate stream 420 at the first side 431 of the distillation column 110, the first stream 450 is enriched in paraxylene compared to the portion of the raffinate stream 108 in the first stream 410. Therefore, at least a portion of the first lower stream 450 is sent to the paraxylene recovery unit 104 as the isomerized recycle stream 142 to recover additional paraxylene therefrom. Figure 4 As described in , the isomerized recycle stream 142 is returned to the para-xylene recovery unit 104 at a location different from where the feed mixture 102 is provided to the para-xylene recovery unit 104. However, it should be understood that at least a portion of the isomerized recycle stream 142 can be combined with the feed mixture 102 and / or returned to the para-xylene recovery unit 104 at the same location as where the feed mixture 102 is introduced.

[0068] The distillation column 110 containing the wall 430 (i.e., a dividing wall column) is capable of separating multiple streams (e.g., an overhead stream 112 and a first lower stream 450) that can be sent directly to the para-xylene recovery unit 104 to effect further para-xylene separation. It should be understood that multiple streams of similar nature can be similarly produced using two distillation columns connected in series with each other, but without separating the raffinate stream 108, such as Figure 5 Displayed in.

[0069] Figure 5 is a block diagram of a system and method for xylene separation and liquid phase isomerization according to a fifth embodiment of the present disclosure. In the system and method 500, a feed mixture 102 is received in a para-xylene recovery unit 104 and is prepared in the same manner as described above for Figure 1The feed mixture is separated into a para-xylene product stream 106 and a raffinate stream 108 in a manner similar to that described in the system and method 100 of . The raffinate stream 108 is sent to a liquid phase isomerization unit 140, which performs liquid phase isomerization of the xylene isomers in the raffinate stream under liquid phase isomerization conditions in the presence of a liquid phase isomerization catalyst. Under the liquid phase isomerization conditions in the liquid phase isomerization unit 140, additional para-xylene is produced from the xylene isomers to provide an isomerized raffinate stream 520, which is enriched in para-xylene compared to the raffinate stream 108.

[0070] The isomerized raffinate stream 520 is sent to a distillation column 110a, and an overhead stream 112 is obtained, most of which comprises toluene. Preferably, the overhead stream 112 comprises at least most of the toluene in the isomerized raffinate stream 520, and / or preferably, the overhead stream 112 consists essentially of toluene. The overhead stream 112 is sent to the paraxylene recovery unit 104 as at least a portion of the desorbent used therein.

[0071] A lower stream 111 is also obtained from the distillation column 110a and sent to the distillation column 110b. The lower stream 111 contains xylene isomers and is enriched in paraxylene compared to the raffinate stream 108. When undergoing further separation in the distillation column 110b, an overhead stream 542 and a lower stream 544 are obtained. The overhead stream 542 is enriched in paraxylene compared to the lower stream 111 and the raffinate stream 108. At least a portion of the overhead stream 542 is sent to the paraxylene recovery unit 104 as an isomerized recycle stream 142. Figure 5 As described in , the isomerized recycle stream 142 is returned to the para-xylene recovery unit 104 at a location different from where the feed mixture 102 is provided to the para-xylene recovery unit 104. However, it should be understood that at least a portion of the isomerized recycle stream 142 can be combined with the feed mixture 102 and / or returned to the para-xylene recovery unit 104 at the same location as where the feed mixture 102 is introduced. Optionally, if an excess of ethylbenzene is present in the overhead stream 542, a partial distillation can be performed to limit the introduction of ethylbenzene to the overhead stream 542, in which case the amount of ethylbenzene and other xylene isomers present in the lower stream 544 can be greater.

[0072] The lower stream 544 comprises C9+ aromatics and possibly remaining xylene isomers and this stream may be sent to a vapor phase isomerization unit 130 which performs vapor phase isomerization of the xylene isomers in the presence of a vapor phase isomerization catalyst under vapor phase isomerization conditions to convert one or more xylene isomers into additional para-xylene. Figure 1As an alternative to gas phase isomerization, or in addition to gas phase isomerization, transalkylation may be performed to convert C9+ aromatics to additional xylene isomers. If performed, such transalkylation may preferably be performed prior to performing gas phase isomerization in gas phase isomerization unit 130.

[0073] Figure 6 is a block diagram of a system and method for xylene separation and liquid phase isomerization according to a sixth embodiment of the present disclosure. In the system and method 600, a feed mixture 102 comprising at least toluene, mixed xylenes, and optionally ethylbenzene is received in a para-xylene recovery unit 104. Preferably, the amount of ethylbenzene is below a specified critical amount and / or the feed mixture 102 is treated to remove excess ethylbenzene therefrom. The para-xylene recovery unit 104 uses simulated moving bed chromatography with toluene as a desorbent to produce a para-xylene product stream 106 that is enriched in para-xylene and may be substantially composed of para-xylene, and a raffinate stream 108 that is depleted in para-xylene. The raffinate stream 108 may be enriched in at least one of ortho-xylene and meta-xylene and contain toluene and optionally at least some ethylbenzene.

[0074] In the system and method 600, the raffinate stream 108 undergoes liquid phase isomerization in the liquid phase isomerization unit 140. Under liquid phase isomerization conditions in the liquid phase isomerization unit 140, additional para-xylene is produced from the xylene isomers to provide an isomerized raffinate stream 620 that is enriched in para-xylene relative to the raffinate stream 108.

[0075] The isomerized raffinate stream 620 is provided to a distillation column 110 and separated into an overhead stream 112 and a bottoms stream 114. A majority of the overhead stream 112 comprises toluene, and preferably, the overhead stream 112 comprises at least a majority of the toluene in the raffinate stream 108 and / or preferably, the overhead stream 112 consists essentially of toluene. The overhead stream 112 is sent (recycled) to the para-xylene recovery unit 104 as at least a portion of the desorbent used therein. Additional toluene desorbent may be sent to the para-xylene recovery unit 104 from an external source (not shown). Figure 6 middle).

[0076] like Figure 1As described above, the lower stream 114 is divided into the first stream 120 and the second stream 122. However, the division of the lower stream 114 into the first stream 120 and the second stream 122 is optional, depending on factors such as whether byproducts such as ethylbenzene have increased to a level that indicates the need for removal by vapor phase isomerization or transalkylation. If the second stream 122 is produced, it can be sent to a vapor phase isomerization unit 130, which performs vapor phase isomerization of the xylene isomers in the presence of a vapor phase isomerization catalyst under vapor phase isomerization conditions to convert one or more xylene isomers into additional para-xylene. As described above with respect to Figure 1 The system and method 100 are discussed in more detail.

[0077] The first stream 120 is sent to the para-xylene recovery unit 104 to effect separation of additional para-xylene in the para-xylene product stream 106. Figure 1 As described in the foregoing, the first stream 120 is returned to the para-xylene recovery unit 104 at a location different from where the feed mixture 102 is provided to the para-xylene recovery unit 104. However, it should be understood that the first stream 120 can be combined with the feed mixture 102 and / or returned to the para-xylene recovery unit 104 at the same location as where the feed mixture 102 is introduced.

[0078] Liquid Phase Isomerization of C8+ Aromatics in Feed Mixtures

[0079] Liquid phase isomerization can be expected to be used to produce para-xylene from various feed streams poor in para-xylene. Preferably, since ethylbenzene undergoes relatively slow isomerization under liquid phase isomerization conditions and can be gradually accumulated in the isomerized recycle stream produced under liquid phase isomerization conditions, a feed stream with low levels of ethylbenzene can be used in such a liquid phase isomerization process or a feed stream with ethylbenzene levels below a specified critical level can be refined. In addition, the liquid phase isomerization catalyst and liquid phase isomerization conditions described herein are further not inclined to produce a large amount of ethylbenzene. Since ethylbenzene and other by-products that are not easily isomerized under liquid phase isomerization conditions can undergo easy conversion to para-xylene and other valuable components under vapor phase isomerization conditions, once it becomes necessary to remove ethylbenzene or other by-products, vapor phase isomerization can be further used in combination with liquid phase isomerization to further process the stream poor in para-xylene. Such a vapor phase isomerization method can occur continuously or as needed. By using the liquid phase isomerization and separation processes disclosed herein, lower energy separation of para-xylene from a feed mixture can be achieved.

[0080] In the advantageous separation methods disclosed herein, simulated moving bed chromatography can be used to facilitate the separation of para-xylene from a feed mixture containing C7+ aromatics and optionally C6+ aromatics. When separating para-xylene from a feed mixture containing toluene, a raffinate stream depleted in para-xylene and further containing toluene can be produced. Toluene can be separated from the raffinate stream before or after liquid phase isomerization thereof, and toluene is provided as a desorbent for simulated moving bed chromatography, thereby providing synergy for the combined isomerization and separation methods disclosed herein.

[0081] To support the above process, a liquid phase isomerization catalyst having selectivity for promoting isomerization of C8 aromatics over C7 aromatics (toluene) and / or C9+ aromatics may be used. This type of catalyst preference allows isomerization of the p-xylene-depleted raffinate stream or various streams derived therefrom under liquid phase isomerization conditions to produce additional p-xylene for separation (e.g., by simulated moving bed chromatography), even when large amounts of toluene and / or C9+ aromatics are present. Various process configurations for conducting liquid phase isomerization in accordance with the above may be suitable, such as those described above with respect to Figure 1-6 Discussed in more detail. For example, C8 aromatics can be isomerized by liquid phase isomerization before at least a portion of toluene is separated from at least a portion of the raffinate stream, and / or at least a portion of toluene can be separated before at least a portion of the raffinate stream is subjected to liquid phase isomerization. In addition, although it is desirable to have a liquid phase isomerization catalyst with high selectivity for isomerization of C8 aromatics, the separation and isomerization methods disclosed herein are flexible enough to accommodate liquid phase isomerization catalysts that do not fully selectively promote the isomerization of C8 aromatic compounds. Therefore, a range of suitable liquid phase isomerization catalysts may also be applicable to the methods disclosed herein. Additional details about suitable liquid phase isomerization catalysts are provided below.

[0082] Thus, the present disclosure provides an isomerization and separation process comprising: (I) providing a feed mixture comprising one or more xylenes and optionally ethylbenzene; (II) separating the feed mixture in a para-xylene recovery unit using simulated moving bed chromatography with toluene as a desorbent to obtain a product stream rich in para-xylene, a raffinate stream depleted in para-xylene, and optionally an intermediate stream comprising para-xylene at a concentration higher than that in the raffinate stream and lower than that in the product stream, the raffinate stream comprising toluene, optionally ethylbenzene, and o-xylene, m-xylene, or any combination thereof; (III) optionally, liquid phase isomerizing at least a portion of the raffinate stream under liquid phase isomerization conditions in the presence of a liquid phase isomerization catalyst to obtain an isomerized raffinate stream; and (IV) separating at least a portion of the raffinate stream in a distillation column. and / or if present, at least a portion of the raffinate stream to obtain an overhead stream comprising at least a majority of the toluene in the raffinate stream and one or more lower streams, each of which comprises one or more xylene isomers; (V) sending at least a portion of the overhead stream to a para-xylene recovery unit as at least a portion of the desorbent; (VI) conducting a liquid phase isomerization under liquid phase isomerization conditions in the presence of a liquid phase isomerization catalyst and obtaining one or more isomerized recycle streams after conducting the liquid phase isomerization, wherein the liquid phase isomerization is conducted on at least one of: (a) at least a portion of the one or more lower streams; and / or (b) if present, at least a portion of the intermediate stream; and / or (c) conducting the liquid phase isomerization of at least a portion of the raffinate stream in (III); and

[0083] (VII) sending at least a portion of the one or more isomerized recycle streams to a para-xylene recovery unit.

[0084] When produced by simulated moving bed chromatography, the para-xylene-enriched product stream can comprise para-xylene in a concentration ≥ about 95%, ≥ about 97%, ≥ about 98%, ≥ about 99%, or even ≥ about 99.5%, based on total mass.

[0085] Suitable feed mixtures for use in the present disclosure may include, but are not limited to, those obtained from catalytic reforming processes, benzene or toluene alkylation processes, xylene isomerization processes, toluene disproportionation processes, transalkylation processes, cracking, petroleum sources, bioproduction sources, or any combination thereof. In addition to one or more xylene isomers, the feed mixture may also contain up to about 30 wt% or up to about 20 wt% of ethylbenzene, based on the total feed mixture. Preferably, the feed mixture may contain an amount of ethylbenzene below a specified critical amount or the feed stream mixture may be pretreated / refined in a suitable manner to reduce the amount of ethylbenzene below the specified critical amount. More preferably, the feed mixture may be produced or obtained with a low level of ethylbenzene such that the feed mixture can be used directly without further refining the feed mixture to remove at least a portion of the ethylbenzene, which is time-consuming, energy-consuming, and / or costly. Starting with a low level of ethylbenzene can further reduce the load or frequency of the gas-phase isomerization conducted herein. For example, a suitable feed mixture may preferably contain 2000 ppm or less, or about 1500 ppm or less, or about 1000 ppm or less of ethylbenzene, based on the total mass, or the feed mixture may be further processed to provide an ethylbenzene concentration below these values. Particularly advantageous feed mixtures can be produced by alkylating toluene with methanol and / or dimethyl ether as the alkylating agent, which can provide significantly more para-xylene than the equilibrium amount relative to the other xylene isomers (especially ortho-xylene), as well as limited production of ethylbenzene (e.g., <2000 ppm by weight) and other problematic by-products. Descriptions of exemplary methylation catalysts, methylation reagents, and methylation conditions for lower aromatic hydrocarbons can be found, for example, in U.S. Pat. Nos. 6,423,879; 6,504,072; 6,642,426; and 9,440,893, the relevant content of which is incorporated herein by reference.

[0086] The feed mixture may contain para-xylene and other C8 aromatic hydrocarbons at various xylene concentrations. The feed mixture may contain an equilibrium or non-equilibrium distribution of xylene isomers. In non-limiting examples, based on the total weight of the feed mixture, the total concentration of xylene isomers (including ethylbenzene) may be in the range of c(xylene)1 to c(xylene)2 wt%, where c(xylene)1 and c(xylene)2 may independently be 30, 40, 50, 55, 60, 65, 70, 75, 80, 85, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, or even 100, provided that c(xylene)1 < c(xylene)2. Preferably, c(xylene)1 is 70 wt% or higher. More preferably, c(xylene)1 is 80 wt% or higher. Even more preferably, the feed mixture may consist essentially of xylene isomers.

[0087] In a non-limiting example, based on the total weight of the feed mixture, the total concentration of p-xylene in the feed mixture can be in the range of c(pX)1 to c(pX)2 wt%, where c(pX)1 and c(pX)2 can independently be 10, 20, 30, 40, 50, 55, 60, 65, 70, 75, 80, 85, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, or even 100, provided that c(pX)1 < c(pX)2. Preferably, c(pX)1 is 30 wt% or higher, more preferably, c(pX)1 is 50 wt% or higher.

[0088] The feed mixture can contain ethylbenzene at various concentrations. In a non-limiting example, based on the total weight of the feed mixture, the feed mixture can contain ethylbenzene at a concentration in the range of c(EB)1 to c(EB)2 wt%, where c(EB)1 and c(EB)2 can independently be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, provided that c(EB)1 < c(EB)2. Preferably, c(EB)2 is 20 wt% or lower. More preferably, c(EB)2 is 10 wt% or lower. More preferably, c(EB)2 is 5 wt% or lower. Even more preferably, c(EB)2 is 2 wt% or lower, or 1 wt% or lower, more preferably about 2000 ppm or lower, or about 1500 ppm or lower, or about 1000 ppm or lower. Optionally, the feed mixture with a higher ethylbenzene content can be further processed to achieve the ethylbenzene concentration within the aforementioned range. The recycle stream returned to the p-xylene separation unit can contain any of the aforementioned amounts of ethylbenzene, but preferably the amount of ethylbenzene returned is kept as small as possible.

[0089] Although a feed mixture or a recycle stream containing a small amount of ethylbenzene may be desirable for the disclosure herein, it should also be understood that ethylbenzene and other by-products can be effectively addressed in the disclosure herein through gas-phase isomerization. Additional details regarding suitable gas-phase isomerization catalysts and gas-phase isomerization conditions are provided further below.

[0090] The feed mixture can contain benzene, toluene, and C9+ hydrocarbons in various amounts. In non-limiting examples, based on the total weight of the feed mixture, the feed mixture can contain benzene and toluene in a combined amount in the range of c(BT)1 to c(BT)2 weight %, where c(BT)1 and c(BT)2 can independently be 0.01, 0.1, 1.0, 2.0, 3.0, 5.0, 8.0, 10.0, 15.0, 20.0, 30.0, 40.0, or 50.0, provided that c(BT)1 < c(BT)2. Preferably, c(BT)2 is 10.0 or less. More preferably, c(BT)2 is 5.0 or less. Even more preferably, c(BT)2 is 3.0 or less. In various embodiments, toluene can be the major component of benzene and toluene, and in some embodiments, the combined benzene and toluene can consist essentially of toluene. That is, in some embodiments, the feed mixture can be substantially free of benzene. In some or other non-limiting examples, based on the total weight of the feed mixture, the feed mixture can contain C9+ hydrocarbons in a total amount in the range of c(C9+)1 to c(C9+)2 weight %, where c(C9+)1 and c(C9+)2 can independently be 0.01, 0.1, 1.0, 5.0, 10.0, 20.0, provided that c(C9+)1 < c(C9+)2.

[0091] The raffinate stream or one or more streams derived therefrom may contain an unbalanced distribution of xylene isomers and / or para-xylene at a lower concentration than present in the feed mixture. In a non-limiting example, based on the mass of total xylene isomers in the raffinate stream, the total amount of para-xylene in the raffinate stream or one or more streams derived therefrom may have a para-xylene concentration in the range of c(pX)1 to c(pX)2 weight %, where c(pX)1 and c(pX)2 may independently be 0, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, or 30, provided that c(pX)1 < c(pX)2. Preferably, c(pX)2 is 20 or less, 15 or less, 12 or less, 10 or less, 8 or less, 6 or less, 5 or less, 4 or less, 2 or less or 1 or less. In a non-limiting example, based on the mass of total xylene isomers in the raffinate stream, the total amount of meta-xylene in the raffinate stream or one or more streams derived therefrom may have a meta-xylene concentration in the range of c(mX)1 to c(mX)2 weight %, where c(mX)1 and c(mX)2 may independently be 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, provided that c(mX)1 < c(mX)2. Preferably, c(mX)1 is 30 or higher and / or c(mX)2 is 80 or less. Preferably, c(mX)1 is 40 or higher and / or c(mX)2 is 80 or less. In a non-limiting example, based on the mass of total xylene isomers in the raffinate stream, the total amount of ortho-xylene in the raffinate stream or one or more streams derived therefrom may have an ortho-xylene concentration in the range of c(oX)1 to c(oX)2 weight %, where c(oX)1 and c(oX)2 may independently be 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, provided that c(oX)1 < c(oX)2. Preferably, c(oX)1 is 10 or higher and / or c(oX)2 is 80 or less. Preferably, c(oX)1 is 10 or higher and / or c(oX)2 is 60 or less. Preferably, c(oX)1 is 10 or higher and / or c(oX)2 is 50 or less.

[0092] One or more isomerized recycle streams sent to the paraxylene recovery unit may contain a balanced distribution of xylene isomers and / or a higher concentration of paraxylene than present in the raffinate stream. In a non-limiting example, based on the mass of the total xylene isomers in one or more isomerized recycle streams, the total amount of paraxylene in one or more isomerized recycle streams may have a paraxylene concentration in the range of c(pX)1 to c(pX)2 wt%, where c(pX)1 and c(pX)2 can independently be 0, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, or 30, provided that c(pX)1 < c(pX)2. Preferably, c(pX)2 is 20 or less, 15 or less, 12 or less, 10 or less, 8 or less, 6 or less, 5 or less, 4 or less, 2 or less, or 1 or less. In a non-limiting example, based on the mass of the total xylene isomers in one or more isomerized recycle streams, the total amount of m-xylene in one or more isomerized recycle streams may have a m-xylene concentration in the range of c(mX)1 to c(mX)2 wt%, where c(mX)1 and c(mX)2 can independently be 0, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, or 30, provided that c(mX)1 < c(mX)2. Preferably, c(mX)2 is 20 or less, 15 or less, 12 or less, 10 or less, 8 or less, 6 or less, 5 or less, 4 or less, 2 or less, or 1 or less. In a non-limiting example, based on the mass of the total xylene isomers in one or more isomerized recycle streams, the total amount of o-xylene in one or more isomerized recycle streams may have an o-xylene concentration in the range of c(oX)1 to c(oX)2 wt%, where c(oX)1 and c(oX)2 can independently be 0, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, or 30, provided that c(oX)1 < c(oX)2. Preferably, c(oX)2 is 20 or less, 15 or less, 12 or less, 10 or less, 8 or less, 6 or less, 5 or less, 4 or less, 2 or less, or 1 or less.

[0093] In various embodiments of the methods disclosed herein, 80 weight percent or more, preferably 85 weight percent or more, more preferably 90 weight percent or more, more preferably 95 weight percent or more, more preferably 98 weight percent or more, more preferably 99 weight percent or more, or even more preferably about 100% of the feed mixture may be in the liquid phase at the inlet of the isomerization reaction where liquid phase isomerization can occur. The feed mixture may have an inlet temperature in the range of T1 to T2 °C, where T1 and T2 can independently be 200, 210, 220, 230, 240, 250, 255, 260, 265, 270, 275, 280, 285, 290, 295, or 300, provided that T1 < T2. The relatively low inlet temperature of the feed mixture in combination with other liquid phase isomerization conditions described below may facilitate the liquid phase isomerization of C8 aromatics to para-xylene for recycle to a para-xylene recovery unit.

[0094] The liquid phase isomerization in the present disclosure may be carried out using a fixed bed reactor, a fluidized bed reactor, or a moving bed reactor. The feed provided to the liquid phase isomerization conditions may be poor in para-xylene, such as a raffinate stream, an intermediate stream, or one or more lower streams after separating the raffinate in a distillation column, obtained after separating para-xylene from a C8-containing feed mixture. The feed provided to the liquid phase isomerization conditions may flow upward, downward, or radially within the isomerization reactor. Alternatively, in some cases, the liquid phase isomerization may be carried out batchwise.

[0095] Suitable liquid phase isomerization conditions may include a reaction gauge pressure in the range of p1 to p2 kPa in the isomerization reactor, where p1 and p2 can independently be 1700, 1800, 1900, 2000, 2100, 2200, 2300, 2400, 2500, 2600, 2700, 2800, 2900, 3000, 3100, 3200, 3300, 3400, or 3500, provided that p1 < p2. Preferably, p2 is 3000 kPa or lower. Preferably, p2 is 2500 kPa or lower. The relatively high reaction gauge pressure may facilitate the dissolution of molecular hydrogen in the liquid phase in the isomerization reaction, where molecular hydrogen is provided in the form of a co-feed combined with the feed mixture to promote the liquid phase isomerization reaction.

[0096] Suitable liquid phase isomerization conditions may include a reaction temperature in the range of T1 to T2 °C, where T1 and T2 can independently be 200, 210, 220, 230, 240, 250, 255, 260, 265, 270, 275, 280, 285, 290, 295, or 300, provided that T1 < T2. The relatively low reaction temperature during liquid phase isomerization may improve the energy efficiency by requiring less energy to heat the feed undergoing isomerization and by not having to condense a large amount of high-temperature gas phase after gas phase isomerization.

[0097] Suitable liquid-phase isomerization conditions can include a high WHSV in the range of w1 to w2 hours -1 where w1 and w2 can be 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0, 9.5, 10, 11, 12, 12.5, 13, 14, 15, 16, 17, 17.5, 18, 19, or 20, provided that w1 < w2. The high WHSV value can be promoted by co-feeding molecular hydrogen at a suitable rate.

[0098] Molecular hydrogen can optionally be provided as a co-feed to the liquid-phase isomerization conditions. In certain embodiments, molecular hydrogen or a portion thereof that is co-fed to the isomerization reactor can be introduced as a pressurized gas through an inlet on the isomerization reactor. Additionally or alternatively, molecular hydrogen or a portion thereof can be fed into a feed line, vessel, or storage tank associated with the feed provided to the liquid-phase isomerization conditions, which can facilitate the mixing of molecular hydrogen with the feed and feed the molecular hydrogen together with the feed to the liquid-phase isomerization conditions. Most of the molecular hydrogen (e.g., ≥50%, ≥60%, ≥70%, ≥80%, ≥90%, ≥95%, ≥98%), more preferably substantially all (≥99%) can be dissolved in the liquid phase under the liquid-phase isomerization conditions. To achieve a higher concentration of dissolved molecular hydrogen in the liquid phase, a suitable high pressure can be maintained in the isomerization reactor.

[0099] In a non-limiting example, based on the total weight of the feed, molecular hydrogen can be fed into the isomerization reactor at a feed rate of r(H2)1 to r(H2)2 ppm by weight, where r(H2)1 and r(H2)2 can independently be 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 950, 1000, 1500, 2000, 2500, 3000, 3500, 4000, 4500, or 5000, provided that r(H2)1 < r(H2)2. Preferably, r(H2)2 is 3000 or less, 2000 or less, 1000 or less, 800 or less, 600 or less, or 500 or less.

[0100] Suitable liquid-phase isomerization catalysts can comprise zeolites having a MEL framework structure (e.g., ZSM-11), an MFI framework structure (e.g., ZSM-5), or any combination thereof. Other suitable examples of zeolites effective for liquid-phase isomerization can include, for example, those having an MWW framework, a MOR framework, etc. Examples can include MWW-22, MWW-49, MWW-54, and combinations thereof.

[0101] In certain embodiments, the liquid phase isomerization catalyst can comprise a first metal element selected from Fe, Co, Ni, Ru, Rh, Pd, Re, Os, Ir, Pt, and combinations thereof, and a second metal selected from Sn, Zn, Ag, and combinations thereof. The first metal element can catalyze the hydrogenation of olefins (such as those produced by the dealkylation of ethylbenzene) that can be produced under liquid phase isomerization. The second metal element can promote or enhance the catalytic action of the first metal element. In other embodiments, the liquid phase isomerization catalyst can be free of noble metals (i.e., Ru, Rh, Pd, Os, Ir, and Pt). In other embodiments, the liquid phase isomerization catalyst can be free of any Group 7-10 metals. In still other embodiments, the liquid phase isomerization catalyst can be free of any Group 7-15 metals other than aluminum.

[0102] Zeolites having an MFI framework (e.g., ZSM-5) suitable for use in the present disclosure can have one or more of the following characteristics: being in the hydrogen form (HZSM-5); having a crystal size ≤ 0.1 micrometer; having a mesoporous surface area (MSA) ≥ 45 m 2 / g; having a ratio of total surface area to mesoporous surface area ≤ 9; and having a silica to alumina molar ratio in the range of 20 to 50.

[0103] Suitable zeolites having a MEL framework (e.g., ZSM-11) can comprise a plurality of primary microcrystals, wherein at least 75% (e.g., ≥ 80%, ≥ 85%, ≥ 90%, or even ≥ 95%) of the microcrystals have a microcrystal size less than or equal to 200 nanometers (e.g., ≤ 150, ≤ 100, ≤ 80, ≤ 50, ≤ 30 nanometers). Thus, at least 75% (e.g., ≥ 80%, ≥ 85%, ≥ 90%, or even ≥ 95%) of the microcrystals can have a microcrystal size in the range of cs1 to cs2 nanometers (nm), where cs1 and cs2 can be independently 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 120, 140, 150, 160, 180, or 200, provided that cs1 < cs2. Preferably, cs1 is 10 or greater and cs2 is 150 or less. More preferably, cs1 is 10 or greater and cs2 is 50 or less. In the present disclosure, the microcrystal size can be defined as the maximum size of the microcrystals observed under a transmission electron microscope ("TEM"). To determine the microcrystal size, a sample of the zeolite material is placed in the TEM and an image of the sample is taken. The image is then analyzed to determine the microcrystal size and its distribution. The small microcrystal size of the MEL framework type zeolite material of the present disclosure results in surprising high catalytic activity and other advantages in addition to surprising tolerance to p-xylene reactivity under liquid phase isomerization conditions.

[0104] Optionally, by X-ray diffraction measurement, the primary crystallites of the zeolite with a MEL framework may have an average primary crystallite size of less than 80 nm, preferably less than 70 nm, and in some cases less than 60 nm, on each of the a, b, c crystal vectors. By X-ray diffraction measurement, the primary crystallites may optionally have an average primary crystallite size greater than 20 nm, optionally greater than 30 nm, on each of the a, b, c crystal vectors.

[0105] The primary crystallite size may have a narrow particle size distribution such that at least 90% by number of the primary crystallites have a primary crystallite size in the range of 10 to 80 nm, preferably in the range of 20 to 50 nm, as determined by analyzing images of the primary crystallites taken by TEM.

[0106] The crystallites of the zeolite with a MEL framework may have various shapes, such as substantially spherical, rod-like, etc. Alternatively or additionally, the crystallites may have an irregular shape in the TEM image. Thus, the crystallites may exhibit the longest dimension (“major dimension”) in a first direction and a width (“minor dimension”) in another direction perpendicular to the first direction, where the width is defined as the dimension at the middle of the major dimension determined by TEM image analysis. The ratio of the major dimension to the width is referred to as the aspect ratio of the crystallite. In certain embodiments, the crystallites may have an average aspect ratio in the range of ar1 to ar2 determined by TEM image analysis, where ar1 and ar2 may independently be 1, 1.2, 1.4, 1.5, 1.6, 1.8, 2.0, 2.2, 2.4, 2.5, 2.6, 2.8, 3.0, 3.2, 3.4, 3.5, 3.6, 3.8, 4.0, 4.2, 4.4, 4.5, 4.6, 4.7, 4.8, or 5.0, provided that ar1 < ar2. Preferably, ar1 is 1 or greater and ar2 is 3 or less, or ar1 is 1 or greater and ar2 is 2 or less.

[0107] The small crystallites of the zeolite with a MEL framework may aggregate to form an agglomerate. The agglomerate is a polycrystalline material having void spaces at the boundaries of the crystallites. The agglomerate may be formed from such primary crystallites that have an average primary crystallite size of less than 80 nm, preferably less than 70 nm and more preferably less than 60 nm, or even less than 50 nm, as determined by TEM image analysis.

[0108] Suitable zeolites with a MEL framework may comprise a mixture of agglomerates of primary microcrystals and some unagglomerated primary microcrystals. Most of the zeolites with a MEL framework, e.g., more than 50 wt% or more than 80 wt% thereof, may comprise agglomerates of primary microcrystals. The agglomerates may be in regular or irregular form. For more information on agglomerates, see Walter, D. (2013) Primary Particles—Agglomerates—Aggregates, Nanomaterials (ed Deutsche Forschungsgemeinschaft (DFG)), Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim, Germany. doi: 10.1002 / 9783527673919, pp. 1-24.

[0109] Preferably, the zeolite with a MEL framework may comprise less than 10 wt% of primary microcrystals having a size >200 nm as determined by TEM image analysis, or less than 10 wt% of primary microcrystals having a size >150 nm as determined by TEM image analysis, or less than 10 wt% of primary microcrystals having a size >100 nm as determined by TEM image analysis, or less than 10 wt% of primary microcrystals having a size >80 nm as determined by TEM image analysis.

[0110] Suitable zeolites with a MEL framework may have a silica to alumina ratio of R(s / a) that can vary from r1 to r2, where r1 and r2 can independently be 10, 12, 14, 15, 16, 18, 20, 22, 24, 25, 26, 28, 30, 32, 34, 35, 36, 38, 40, 42, 44, 45, 46, 48, 50, 52, 54, 55, 56, 58, or 60, provided that r1 < r2. Preferably, r1 is 20 or greater and r2 is 50 or less. Preferably, r1 is 20 or greater and r2 is 40 or less. Preferably, r1 is 20 or greater and r2 is 30 or less. The ratio R(s / a) can be determined by ICP-MS (Inductively Coupled Plasma Mass Spectrometry) or XRF (X-ray Fluorescence).

[0111] Suitable zeolites with a MEL framework may have a BET total specific surface area of A(st), where A(st) can be from a1 to a2 m 2 / g changes, where a1 and a2 can independently be 300, 320, 340, 350, 360, 380, 400, 420, 440, 450, 460, 480, 500, 520, 540, 550, 560, 580, or 600, provided that a1 < a2. Preferably, a1 is 400 or greater and a2 is 500 or less. Preferably, a1 is 400 or greater and a2 is 475 or less. A(st) can be determined by the BET method (Brunauer - Emmet - Teller method, nitrogen adsorption method). The high total surface area A(st) of the zeolite material of the present disclosure is another reason for its high catalytic activity for the conversion of aromatic hydrocarbons. The BET method can obtain the total specific surface area of the measured material, including the micropore specific surface area part and the mesopore specific surface area part. The mesopore specific surface area can be referred to as the mesopore area, mesopore area, or external area in the present disclosure. The total specific surface area can be referred to as the total surface area or total area in the present disclosure.

[0112] A suitable zeolite having a MEL framework can have a mesopore area of A(mp) that is ≥ 15% (e.g., ≥ 16%, ≥ 18%, ≥ 20%, ≥ 22%, ≥ 24%, ≥ 25%) of the total surface area A(st) discussed above. In certain embodiments, it is preferred that A(mp) ≥ 20% * A(st). In certain embodiments, it is preferred that A(mp) ≤ 40% * A(st). In certain embodiments, it is preferred that A(mp) ≤ 30% * A(st). The high mesopore area A(mp) of the zeolite material of the present disclosure is another reason for its high catalytic activity for the conversion of aromatic hydrocarbons. Without intending to be bound by a particular theory, it is believed that there are more catalytic sites present on the mesopore region of the zeolite material of the present disclosure due to the high mesopore area, and these catalytic sites tend to contribute more to the catalytic activity than the catalytic sites located in the deep channels inside the zeolite material. The time required for reactant molecules to reach the catalytic sites on the mesopore surface and for product molecules to leave them is relatively short. Conversely, it takes a significantly longer time for reactant molecules to diffuse into the deep channels and for product molecules to diffuse out of them.

[0113] A suitable zeolite having a MEL framework can have a hexane adsorption value of v(hs) that changes from v1 to v2 mg / g, where v1 and v2 can independently be 90, 92, 94, 95, 96, 98, 100, 102, 104, 105, 106, 108, or 110, provided that v1 < v2. The hexane adsorption value can be determined by the industrially conventional TGA (thermogravimetric analysis).

[0114] Suitable zeolites with a MEL framework may have an α value that varies from a1 to a2, where a1 and a2 can independently be 500, 600, 700, 800, 900, 1000, 1200, 1400, 1500, 1600, 1800, 2000, 2200, 2400, 2500, 2600, 2800, or 3000, provided that a1 < a2. The α value can be determined by the methods described in U.S. Patent No. 3,354,078 and Journal of Catalysis, Volume 4, page 527 (1965); Volume 6, page 278 (1966) and Volume 61, page 395 (1980).

[0115] Optionally, suitable zeolites with a MEL framework can be calcined and subjected to post-treatment such as steam treatment and / or pickling. The steam treatment can be carried out continuously for a period of 1 to 20 hours, preferably 2 to 10 hours, at a temperature of at least 200°C, preferably at least 350°C, more preferably at least 400°C, and in some cases at least 500°C. Pickling can be carried out with an aqueous solution of an acid (preferably an organic acid, such as a carboxylic acid, preferably oxalic acid). Optionally, the steam-treated zeolite can be treated with an aqueous solution of an acid at a temperature of at least 50°C, preferably at least 60°C, for a period of at least 1 hour, preferably at least 4 hours, for example, in the range of 5 to 20 hours. Preferably, the treated zeolite with a MEL framework can have a chemical composition with a molar ratio of nSiO2:Al2O3, where n is at least 20, more preferably at least 50, and in some cases at least 100.

[0116] The liquid-phase isomerization catalysts suitable for use in the present disclosure may be formulated with a binder or exist in the form of non-bonded free powder. The binder may comprise a binder material that is tolerant to temperature and other liquid-phase isomerization conditions. Examples of suitable binder materials include clays, alumina, silica, silica-alumina, silica-magnesia, silica-zirconia, silica-thoria, silica-beryllia, silica-titania, and ternary compositions such as silica-alumina-thoria, silica-alumina-zirconia, silica-alumina-magnesia, and silica-magnesia-zirconia. In a non-limiting example, based on the total weight of the catalyst, the binder material may be included with the liquid-phase isomerization catalyst at a concentration of c1 to c2 wt%, where c1 and c2 may independently be 1, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 98, 99, provided that c1 < c2. The inclusion of a binder in the isomerization catalyst can improve its mechanical strength and other factors. Zeolites capable of promoting liquid-phase isomerization may also be blended with a second zeolite as the binder material, thereby forming zeolite-bonded zeolites as described in U.S. Pat. Nos. 5,993,642 and 5,994,603, each of which is incorporated herein by reference. The relative proportions of the zeolite and the binder material may range from about 1:99 to about 99:1 on a mass basis. In an illustrative example, the zeolite capable of promoting liquid-phase isomerization may be present in an amount of 10% to about 70% by mass of the zeolite-bonded zeolite, or about 20% to about 50% by mass of the zeolite-bonded zeolite.

[0117] The liquid-phase isomerization catalyst may be a fresh catalyst, a regenerated catalyst, or a mixture thereof. The regeneration of the catalyst may be carried out in the isomerization reactor after the catalyst activity has decreased to a critical level at the end of the catalyst cycle, for example, by exposing the catalyst to a gas stream containing molecular hydrogen. Alternatively, non-in-situ regeneration of the catalyst may be carried out, where the used catalyst is removed from the isomerization reactor and heated and / or exposed to a gas stream containing molecular hydrogen in an oxygen-rich environment to reduce the coke on its surface.

[0118] As discussed above, the present disclosure can adapt to converting a p-xylene-poor stream into a p-xylene-rich recycle stream for liquid phase isomerization of various streams separated in a p-xylene recovery unit. In a non-limiting example, at least a portion of a raffinate stream, at least a portion of an intermediate stream, or at least a portion of a lower stream obtained from distillation can undergo liquid phase isomerization in the disclosure herein. The raffinate stream and / or the intermediate stream (when produced) may include up to 50% by volume of toluene. Similarly, one or more isomerized recycle streams may include up to 50% by volume of toluene, depending on the amount of toluene present in the stream that produces the isomerized recycle stream (one or more).

[0119] In some embodiments, at least a portion of the raffinate stream may be subjected to the liquid phase isomerization in (III) above to obtain an isomerized raffinate stream. Carried out in (III) above. In some embodiments, at least a portion of the isomerized raffinate stream may be sent to a distillation tower that provides an overhead stream and one or more lower streams. In other embodiments, at least a portion of the isomerized raffinate stream is not sent to a distillation tower, in which case at least a portion of the isomerized raffinate stream may be sent to a para-xylene recovery unit as at least a portion of one or more isomerized recycle streams.

[0120] In some embodiments, the isomerized raffinate stream may be sent to the distillation tower in (IV), and the one or more lower streams may be obtained as at least a portion of the one or more lower streams produced when the isomerized raffinate stream is separated in the distillation tower. Preferably, the distillation tower may include a dividing wall distillation tower, and a first lower stream rich in paraxylene may be obtained from the first side of the dividing wall distillation tower and a second lower stream depleted in paraxylene may be obtained from the second side of the dividing wall distillation tower. One or more isomerized recycle streams may be obtained as at least a portion of the first lower stream. When a dividing wall distillation tower is used, the method of the present disclosure may include sending the isomerized raffinate stream to the first side of the dividing wall distillation tower, and sending at least a portion of the raffinate stream to the second side of the dividing wall distillation tower. As an alternative to the dividing wall distillation tower, the distillation tower may include a first distillation tower and a second distillation tower connected in series, wherein the isomerized raffinate stream is sent to the first distillation tower. In such a two-tower process, an overhead stream comprising at least a majority of toluene can be obtained from a first distillation column, a first lower stream can be obtained from the first distillation column and sent to a second distillation column, an overhead stream rich in paraxylene can be obtained from the second distillation column and sent to a paraxylene recovery unit as at least a portion of one or more isomerized recycle streams, and a second lower stream depleted in paraxylene can be obtained from the second distillation column.

[0121] In some embodiments, at least a portion of the one or more lower streams may be subjected to liquid phase isomerization in (VI) to produce one or more isomerized recycle streams. When the one or more lower streams are subjected to liquid phase isomerization, liquid phase isomerization of the raffinate stream in (III) may not be performed and / or the intermediate stream in (II) may not be produced. Preferably, when liquid phase isomerization of the one or more lower streams is performed, the distillation column may produce a lower stream.

[0122] In some embodiments, an intermediate stream is obtained in (II), at least a portion of the intermediate stream is subjected to liquid phase isomerization in (VI), and at least a portion of the one or more isomerized recycle streams in (VII) is obtained from the intermediate stream after liquid phase isomerization thereof. Preferably, when the intermediate stream is produced, liquid phase isomerization is not performed on the raffinate stream or one or more bottom streams obtained from the distillation column. When the intermediate stream is produced, it may contain up to about 50% by volume of toluene.

[0123] Thus, in various embodiments, the liquid phase isomerization disclosed herein may be performed on one of the following: an intermediate stream, a raffinate stream, or one or more lower streams.

[0124] In a more specific embodiment, a process of the present disclosure using liquid phase isomerization of a portion of a raffinate stream may include: (i) providing a feed mixture comprising one or more xylene isomers and optionally ethylbenzene; (ii) separating the feed mixture in a para-xylene recovery unit using simulated moving bed chromatography with toluene as a desorbent to obtain a para-xylene-enriched product stream and a para-xylene-depleted raffinate stream, the raffinate stream comprising toluene, optionally ethylbenzene, and o-xylene, m-xylene, or any combination thereof; (iii) subjecting at least a portion of the raffinate stream to liquid phase isomerization conditions in the presence of a liquid phase isomerization catalyst to obtain an isomerized raffinate stream; and (iv) separating the feed mixture in a para-xylene recovery unit using simulated moving bed chromatography with toluene as a desorbent to obtain a para-xylene-enriched product stream and a para-xylene-depleted raffinate stream. ) sending the isomerized raffinate stream to a first side of a dividing wall distillation column; (v) sending a portion of the raffinate stream to a second side of a dividing wall distillation column; (vi) obtaining a first lower stream rich in paraxylene from the first side of the dividing wall distillation column, obtaining a second lower stream depleted in paraxylene from the second side of the dividing wall distillation column, and obtaining a top stream rich in toluene from the dividing wall distillation column; (vii) sending at least a portion of the top stream to a paraxylene recovery unit as at least a portion of the desorbent; and (viii) sending one or more isomerized recycle streams to a paraxylene recovery unit to obtain the one or more isomerized recycle streams as at least a portion of the first lower stream.

[0125] In other more specific embodiments, the process of the present disclosure using liquid phase isomerization of a portion of one or more bottom streams, intermediate streams or raffinate streams may include: (A) providing a feed mixture comprising one or more xylene isomers and optionally ethylbenzene; (B) separating the feed mixture in a para-xylene recovery unit using simulated moving bed chromatography with toluene as a desorbent to obtain a product stream rich in para-xylene, a raffinate stream depleted in para-xylene, and optionally an intermediate stream comprising para-xylene at a concentration higher than that in the raffinate stream and lower than that in the product stream, the raffinate stream comprising toluene, optionally ethylbenzene, and o-xylene, m-xylene or any combination thereof; (C) separating at least a portion of the raffinate stream in a distillation column to obtain a product stream comprising an overhead stream of at least a majority of the toluene in the raffinate stream and one or more lower streams, each of which comprises one or more xylene isomers; (D) passing at least a portion of the overhead stream to a para-xylene recovery unit as at least a portion of the desorbent; (E) conducting a liquid phase isomerization under liquid phase isomerization conditions in the presence of a liquid phase isomerization catalyst to produce one or more isomerized recycle streams, the liquid phase isomerization being conducted on at least one of: (a) at least a portion of the one or more lower streams; and / or (b) at least a portion of the intermediate stream, if present; and / or (c) at least a portion of the raffinate stream; and (F) passing at least a portion of the one or more isomerized recycle streams to a para-xylene recovery unit.

[0126] In one or more embodiments, at least a portion of the one or more lower streams can be subjected to liquid phase isomerization, and at least a portion of the one or more isomerized recycle streams can be derived from the one or more lower streams after liquid phase isomerization thereof.

[0127] In one or more embodiments, at least a portion of the raffinate stream can be subjected to liquid phase isomerization to produce an isomerized raffinate stream, and at least a portion of one or more isomerized recycle streams can be derived from the isomerized raffinate stream.

[0128] In one or more embodiments, an intermediate stream can be obtained, at least a portion of the intermediate stream can be subjected to liquid phase isomerization, and at least a portion of one or more isomerized recycle streams can be obtained from the intermediate stream after liquid phase isomerization thereof.

[0129] Gas phase isomerization

[0130] In any of the foregoing embodiments, the lower stream depleted in paraxylene may be further treated by vapor phase isomerization, for example to isomerize ethylbenzene or other byproducts present therein. When ethylbenzene is present in high concentrations, for example, when ethylbenzene is present in an amount greater than or equal to about 10 wt % based on the total mass, vapor phase isomerization may be preferred over liquid phase isomerization. Such vapor phase isomerization may be carried out under vapor phase isomerization conditions in the presence of a suitable vapor phase isomerization catalyst, as described in further detail below.

[0131] Suitable gas phase isomerization conditions may include temperature and pressure such that a majority of the xylenes are in the gas phase. Descriptions of exemplary gas phase isomerization processes, conditions, and catalysts may be found, for example, in U.S. Patent Application Publications 2011 / 03196881; 2012 / 0108867; 2012 / 0108868; 2014 / 0023563; 2015 / 0051430; and 2017 / 0081259, the relevant contents of which are incorporated herein by reference.

[0132] In one example, a suitable gas phase isomerization catalyst may include a zeolite having an MWW framework. Such a zeolite may have a constraint index of ≤5 and include a molecular sieve having one or more of the following properties:

[0133] a) molecular sieves made of common first degree crystalline building block unit cells, whose unit cells have a MWW framework topology. (A unit cell is the spatial arrangement of atoms, which if stacked in three dimensions describes the crystal structure. Such crystal structures are discussed in "Atlas of Zeolite Framework Types", Fifth Edition, 2001, which is incorporated herein by reference);

[0134] b) a molecular sieve made of second degree building blocks, which is a two-dimensional stacking of such MWW framework topology unit cells, forming a monolayer with a thickness of one unit cell, and in the embodiment, forming a monolayer with a thickness of one c-unit cell;

[0135] c) A molecular sieve made of common second-degree building blocks, which is one or more than one unit cell thick layer, wherein the layer of more than one unit cell thick is made by stacking, piling or bonding at least two monolayers of MWW framework topology unit cells. Such secondary building blocks can be stacked in a regular manner, irregular manner, random manner or any combination thereof; and

[0136] d) Molecular sieves made of any regular or random two-dimensional or three-dimensional combination of unit cells having the MWW framework topology.

[0137] Example zeolites having an MWW framework include MCM-22 (U.S. Pat. No. 4,954,325), PSH-3 (U.S. Pat. No. 4,439,409), SSZ-25 (U.S. Pat. No. 4,826,667), ERB-1 (European Patent No. 0293032), ITQ-1 (U.S. Pat. No. 6,077,498), ITQ-2 (International Publication No. WO97 / 17290), MCM-36 (U.S. Pat. No. 5,250,277), MCM-49 (U.S. Pat. No. 5,236,575) and MCM-50 (U.S. Pat. No. 5,236,575). ), MCM-56 (U.S. Patent No. 5,362,697), UZM-8 (U.S. Patent No. 6,756,030), UZM-8HS (U.S. Patent No. 7,713,513), UZM-37 (U.S. Patent No. 7,982,084), EMM-10 (U.S. Patent No. 7,842,277), EMM-12 (U.S. Patent No. 8,704,025), EMM-13 (U.S. Patent No. 8,704,023), UCB-3 (U.S. Patent No. 9,790,143B2) and mixtures thereof.

[0138] In some embodiments, the zeolite having an MWW framework may be contaminated with other microcrystalline materials, such as ferrierite or quartz, which may be present in an amount of ≤ 10 wt % or ≤ 5 wt %.

[0139] The present disclosure may further include the following non-limiting aspects and / or embodiments:

[0140] A1. Methods, including:

[0141] (I) providing a feed mixture comprising one or more xylene isomers and optionally ethylbenzene;

[0142] (II) separating the feed mixture in a para-xylene recovery unit using simulated moving bed chromatography with toluene as a desorbent to obtain a product stream rich in para-xylene, a raffinate stream depleted in para-xylene, and optionally an intermediate stream comprising para-xylene at a concentration higher than that in the raffinate stream and lower than that in the product stream, the raffinate stream comprising toluene, optionally ethylbenzene, and o-xylene, m-xylene, or any combination thereof;

[0143] (III) optionally, subjecting at least a portion of the raffinate stream to liquid phase isomerization under liquid phase isomerization conditions in the presence of a liquid phase isomerization catalyst to obtain an isomerized raffinate stream;

[0144] (IV) separating at least a portion of the raffinate stream and / or, if present, at least a portion of the isomerized raffinate stream in a distillation column to provide an overhead stream comprising at least a majority of the toluene in the raffinate stream and one or more bottoms streams, each of which comprises one or more xylene isomers;

[0145] (V) sending at least a portion of the overhead stream to a para-xylene recovery unit as at least a portion of the desorbent;

[0146] (VI) conducting liquid phase isomerization under liquid phase isomerization conditions in the presence of a liquid phase isomerization catalyst and obtaining one or more isomerized recycle streams after conducting the liquid phase isomerization, wherein the liquid phase isomerization is conducted on at least one of:

[0147] (a) at least a portion of one or more lower streams; and / or

[0148] (b) at least a portion of an intermediate stream, if any; and / or

[0149] (c) liquid phase isomerization of at least a portion of the raffinate stream in (III); and

[0150] (VII) sending at least a portion of the one or more isomerized recycle streams to a para-xylene recovery unit.

[0151] A2. The method as described in A1 further comprises:

[0152] (VIII) vapor phase isomerizing at least a portion of the one or more lower streams in the presence of a vapor phase isomerization catalyst under vapor phase isomerization conditions.

[0153] A3. The method as described in A1 or A2, wherein the liquid phase isomerization catalyst comprises a zeolite having a MEL framework structure, a zeolite having an MFI framework structure or any combination thereof.

[0154] A4. The process as described in any one of A1 to A3, wherein at least a portion of the raffinate stream is subjected to the liquid phase isomerization in (III) to obtain an isomerized raffinate stream.

[0155] A5. The process as described in A4, wherein the one or more isomerized recycle streams are obtained as at least a part of the one or more bottom streams produced when the isomerized raffinate stream is separated in the distillation column in (IV).

[0156] A6. The method as described in A4 or A5, wherein the distillation column comprises a dividing wall distillation column, and a first lower stream rich in paraxylene is obtained from a first side of the dividing wall distillation column, and a second lower stream depleted in paraxylene is obtained from a second side of the dividing wall distillation column;

[0157] One or more isomerized recycle streams are obtained as at least a portion of the first lower stream.

[0158] A7. The method as described in A6 further comprises:

[0159] passing the isomerized raffinate stream to a first side of a dividing wall distillation column; and

[0160] At least a portion of the raffinate stream is sent to a second side of the dividing wall distillation column.

[0161] A8. The method as described in A4, wherein the distillation column comprises a first distillation column and a second distillation column connected in series, and the isomerized raffinate stream is sent to the first distillation column;

[0162] A top stream comprising at least most of the toluene in the raffinate stream is obtained from the first distillation column, a first lower stream is obtained from the first distillation column and sent to a second distillation column, a top stream rich in paraxylene is obtained from the second distillation column and sent to a paraxylene recovery unit as at least a part of one or more isomerized recycle streams, and a second lower stream depleted in paraxylene is obtained from the second distillation column.

[0163] A9. A process as described in A4, wherein at least a portion of the isomerized raffinate stream is sent to a para-xylene recovery unit as at least a portion of one or more isomerized recycle streams.

[0164] A10. The method as described in A4 or A9, wherein at least a portion of the isomerized raffinate stream is not sent to the distillation column.

[0165] A11. The process of any one of A1-A3, wherein at least a portion of the one or more lower streams is subjected to the liquid phase isomerization in (VI) to produce one or more isomerized recycle streams.

[0166] A12. The process as described in A11, wherein the liquid phase isomerization in (III) is not carried out and / or the distillation column provides a lower stream.

[0167] A13. A method as described in any one of A1-A3, wherein an intermediate feed stream is obtained in (II), at least a portion of the intermediate feed stream is subjected to liquid phase isomerization in (VI), and at least a portion of one or more isomerized recycle streams in (VII) is obtained from the intermediate feed stream after liquid phase isomerization.

[0168] A14. A process as described in A13, wherein the intermediate stream comprises up to about 50 volume % toluene.

[0169] A15. A method as described in any of A1-A14, wherein the feed mixture is obtained from a catalytic reforming process, a benzene or toluene alkylation process, a xylene isomerization process, a toluene disproportionation process, a transalkylation process, cracking, a petroleum source, a biological production process or any combination thereof.

[0170] A16. The process of any one of A1 to A15, wherein the feed mixture and / or the isomerized recycle stream comprises 20 wt% ethylbenzene or less.

[0171] A17. The process of any one of A1-A16, wherein the raffinate stream comprises up to about 50% by volume of toluene.

[0172] A18. The process of any one of A1-A17, wherein liquid phase isomerization is performed on one of the following: an intermediate stream, a raffinate stream, or one or more lower streams.

[0173] A19. The process of any one of A1-A18, wherein one or more isomerized recycle streams are returned to the para-xylene recovery unit at the same location as or a different location from where the feed is introduced into the para-xylene recovery unit.

[0174] A20. The process of any one of A1-A19, wherein the one or more isomerized recycle streams comprises up to about 50% by volume of toluene.

[0175] B1. Methods, including:

[0176] (i) providing a feed mixture comprising one or more xylene isomers and optionally ethylbenzene;

[0177] (ii) separating the feed mixture in a para-xylene recovery unit using simulated moving bed chromatography with toluene as a desorbent to obtain a para-xylene-enriched product stream and a para-xylene-depleted raffinate stream comprising toluene, optionally ethylbenzene, and o-xylene, m-xylene or any combination thereof;

[0178] (iii) liquid phase isomerizing at least a portion of the raffinate stream under liquid phase isomerization conditions in the presence of a liquid phase isomerization catalyst to produce an isomerized raffinate stream;

[0179] (iv) passing the isomerized raffinate stream to a first side of a dividing wall distillation column;

[0180] (v) passing a portion of the raffinate stream to a second side of the dividing wall distillation column;

[0181] (vi) obtaining a first lower stream rich in paraxylene from the first side of the dividing wall distillation column, a second lower stream depleted in paraxylene from the second side of the dividing wall distillation column, and a top stream rich in toluene from the dividing wall distillation column;

[0182] (vii) sending at least a portion of the overhead stream to a paraxylene recovery unit as at least a portion of the desorbent; and

[0183] (viii) sending one or more isomerized recycle streams to a para-xylene recovery unit, the one or more isomerized recycle streams being obtained as at least a portion of the first lower stream.

[0184] B2. The process of B1, wherein the overhead stream comprises at least a majority of the toluene in the raffinate stream.

[0185] B3. The method as described in B1 or B2, wherein the liquid phase isomerization catalyst comprises a zeolite having a MEL framework structure, a zeolite having an MFI framework structure, or any combination thereof.

[0186] B4. The method as described in any one of B1-B3, further comprising:

[0187] (ix) vapor phase isomerizing at least a portion of the second lower stream in the presence of a vapor phase isomerization catalyst under vapor phase isomerization conditions.

[0188] C1. Methods, including:

[0189] (A) providing a feed mixture comprising one or more xylene isomers and optionally ethylbenzene;

[0190] (B) separating the feed mixture in a para-xylene recovery unit using simulated moving bed chromatography with toluene as a desorbent to obtain a product stream rich in para-xylene, a raffinate stream depleted in para-xylene, and optionally an intermediate stream comprising para-xylene at a concentration higher than that in the raffinate stream and lower than that in the product stream, the raffinate stream comprising toluene, optionally ethylbenzene, and o-xylene, m-xylene, or any combination thereof;

[0191] (C) separating at least a portion of the raffinate stream in a distillation column to provide an overhead stream comprising at least a majority of the toluene in the raffinate stream and one or more bottoms streams, each of which comprises one or more xylene isomers;

[0192] (D) sending at least a portion of the overhead stream to a paraxylene recovery unit as at least a portion of a desorbent;

[0193] (E) conducting liquid phase isomerization in the presence of a liquid phase isomerization catalyst under liquid phase isomerization conditions to produce one or more isomerized recycle streams, the liquid phase isomerization being conducted on at least one of:

[0194] (a) at least a portion of one or more lower streams; and / or

[0195] (b) at least a portion of an intermediate stream, if any; and / or

[0196] (c) at least a portion of the raffinate stream; and

[0197] (F) sending at least a portion of the one or more isomerized recycle streams to a para-xylene recovery unit.

[0198] C2. The process as described in C1, wherein at least a portion of the one or more lower streams is subjected to liquid phase isomerization, and at least a portion of the one or more isomerized recycle streams is obtained from the one or more lower streams after liquid phase isomerization.

[0199] C3. The process of C1, wherein at least a portion of the raffinate stream is subjected to liquid phase isomerization to produce an isomerized raffinate stream, and at least a portion of the one or more isomerized recycle streams are obtained from the isomerized raffinate stream.

[0200] C4. A process as described in C1, wherein an intermediate stream is obtained, at least a portion of the intermediate stream is subjected to liquid phase isomerization, and at least a portion of one or more isomerized recycle streams is obtained from the intermediate stream after liquid phase isomerization thereof.

[0201] C5. The method as described in any one of C1-C4, wherein the liquid phase isomerization catalyst comprises a zeolite having a MEL framework structure, a zeolite having an MFI framework structure, or any combination thereof.

[0202] C6. The method as described in any one of C1-C5, further comprising:

[0203] (G) vapor phase isomerizing at least a portion of the one or more lower streams in the presence of a vapor phase isomerization catalyst under vapor phase isomerization conditions.

[0204] In order to facilitate a better understanding of the embodiments of the present disclosure, the following examples of preferred or representative embodiments are provided.The following examples should in no way be construed as limiting or defining the scope of the present invention. Example

[0205] Catalyst 1. A catalyst that is substantially inert to toluene conversion under liquid phase isomerization conditions was prepared as described in U.S. Patent Application Publication No. 2022 / 0134318. The catalyst had a ZSM-11 zeolite framework having a Si:Al2 ratio of 25:1. The catalyst was used to obtain the data shown in Tables 1A and 1B below.

[0206] Catalyst 2. A catalyst effective for liquid phase isomerization but not completely inert to toluene conversion was prepared as described in U.S. Pat. No. 4,526,879. The catalyst had a ZSM-5 zeolite framework with a Si / Al2 molar ratio of about 26 and a crystallite size of about 100 nanometers. The catalyst was used to obtain the data shown in Table 2 below. Briefly, the zeolite was synthesized from a mixture of n-propylamine sol, silica, aluminum sulfate sol, and aqueous NaOH. Uncalcined zeolite (80 parts) was mixed with HSA alumina (20 parts) and water in a grinder. The resulting mixture was extruded and then dried at 121° C. overnight. The dried extrudates were calcined at 538° C. in nitrogen for 3 hours to decompose and remove the n-propylamine template. Thereafter, the calcined extrudates were humidified with saturated air and exchanged with 1 N ammonium nitrate to reduce the sodium level to <500 wppm. The extrudates were then washed with deionized water to remove remaining nitrate ions and subsequently dried. The extrudates were then dried at 121°C overnight and calcined at 538°C in air for 3 hours to obtain alumina bound hydrogen ZSM-5. The catalyst extrudates had a 450 m 2 / g total surface area, 90 mg / g hexane adsorption value, and α value of 900.

[0207] Liquid Phase Isomerization. A commercially available raffinate stream depleted in paraxylene (obtained by separating paraxylene from mixed xylenes by simulated moving bed chromatography) was mixed with toluene in various ratios and treated with Catalyst 1 under the liquid phase isomerization conditions specified in Tables 1A and 1B below. Table 1A shows the results using 100% raffinate, and Table 1B shows the results using 1:1 weight / weight toluene / raffinate and 3:1 weight / weight toluene / raffinate. The following were obtained using Catalyst 2: Figure 2 The data displayed in .

[0208] As shown, the liquid phase isomerization catalyst that is inert to toluene (Catalyst 1, Tables 1A and 1B) provides less xylene loss and higher para-xylene yield than the catalyst that is less inert to toluene (Catalyst 2, Table 2).

[0209] Many changes, modifications and variations will be apparent to those of ordinary skill in the art in view of the above description without departing from the spirit or scope of the present disclosure, and when numerical lower limits and numerical upper limits are listed herein, ranges from any lower limit to any upper limit are contemplated.

[0210] Table 1A

[0211] Table 1B

[0212] Table 2

[0213] For the purpose of all jurisdictions that allow such practice, all documents described herein, including any priority documents and / or test procedures that are not contradictory to this article, are incorporated herein by reference. As is apparent from the above general description and specific embodiments, although the form of the present disclosure has been illustrated and described, various modifications can be made without departing from the spirit and scope of the present disclosure. Therefore, it is not intended to limit the disclosure thereby. For example, the composition described herein may not contain any component or composition that is not clearly recorded or disclosed herein. Any method may lack any step that is not recorded or disclosed herein. Similarly, the term "comprising" is considered to be synonymous with the term "including". When a method, composition, element or element group is preceded by the transition phrase "comprising", it should be understood that we also consider the same composition or element group with the transition phrase "substantially ... consisting of", "consisting of ... consisting of", "selected from" or "for" before the recording of the composition, one element or multiple elements.

[0214] One or more illustrative embodiments incorporating one or more inventive elements are shown herein. For the purpose of brevity, all features of entity implementations are not described or shown in this application. It should be understood that in the development of entity implementations incorporating one or more elements of the present invention, many implementation-specific decisions must be made to reach the developer's goals, such as subjecting system-related, business-related, government-related and other restrictions, which change from implementation to time. Although the developer's work may be time-consuming, such work will be a routine task for those skilled in the art who benefit from the present disclosure.

[0215] Unless otherwise indicated, all numbers used in this specification and the appended claims expressing quantities of ingredients, properties such as molecular weight, reaction conditions, etc. should be understood as being modified in all instances by the term "about". Therefore, unless indicated to the contrary, the numerical parameters listed in the following specification and the appended claims are approximate values ​​that may vary depending on the desired properties sought to be achieved by embodiments of the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the present claims, each numerical parameter should at least be construed based on the number of reported significant digits and by applying ordinary rounding techniques.

[0216] Whenever a numerical range with a lower limit and an upper limit is disclosed, any number and any included range falling within the range, including the lower limit and the upper limit, is specifically disclosed. In particular, each range of values ​​disclosed herein ("about a to about b" or equivalently "about a to b" or equivalently "about ab" in the form) should be understood to set forth each number and range covered within the wider range of values. In addition, unless otherwise clearly and unambiguously defined by the patentee, the terms in the claims have their plain, ordinary meanings. In addition, the indefinite article "a" or "an", as used in the claims, is defined herein to mean one or more than one of the elements it introduces.

[0217] Therefore, the present disclosure is well adapted to achieve the objects and advantages mentioned, as well as those inherent therein. The specific embodiments disclosed above are illustrative only, as the present disclosure may be modified and implemented in different but equivalent manners apparent to one of ordinary skill in the art having the benefit of the teachings herein. In addition, except as described in the claims below, it is not intended to limit the details of construction or design shown herein. It is therefore apparent that the specific illustrative embodiments disclosed above may be altered, combined or modified, and all such changes are considered to be within the scope and spirit of the present disclosure. The embodiments disclosed illustratively herein may be suitably implemented in the absence of any element not specifically disclosed herein and / or any optional element disclosed herein.

Claims

1. Methods, including: (I) providing a feed mixture comprising one or more xylene isomers and optionally ethylbenzene; (II) separating the feed mixture in a para-xylene recovery unit using simulated moving bed chromatography with toluene as a desorbent to obtain a product stream rich in para-xylene, a raffinate stream depleted in para-xylene, and optionally an intermediate stream containing para-xylene at a concentration higher than that in the raffinate stream and lower than that in the product stream, the raffinate stream comprising toluene, optionally ethylbenzene, and o-xylene, m-xylene, or any combination thereof; (III) optionally, subjecting at least a portion of the raffinate stream to liquid phase isomerization under liquid phase isomerization conditions in the presence of a liquid phase isomerization catalyst to obtain an isomerized raffinate stream; (IV) separating at least a portion of the raffinate stream and / or, if present, at least a portion of the isomerized raffinate stream in a distillation column to provide an overhead stream comprising at least a majority of the toluene in the raffinate stream and one or more bottoms streams, each of which comprises one or more xylene isomers; (V) sending at least a portion of the overhead stream to a para-xylene recovery unit as at least a portion of the desorbent; (VI) conducting liquid phase isomerization under liquid phase isomerization conditions in the presence of a liquid phase isomerization catalyst and obtaining one or more isomerized recycle streams after conducting the liquid phase isomerization, wherein the liquid phase isomerization is conducted on at least one of: (a) at least a portion of one or more lower streams; and / or (b) at least a portion of an intermediate stream, if any; and / or (c) liquid phase isomerization of at least a portion of the raffinate stream in (III); and (VII) sending at least a portion of the one or more isomerized recycle streams to a para-xylene recovery unit.

2. The method according to claim 1, further comprising: (VIII) vapor phase isomerizing at least a portion of the one or more lower streams in the presence of a vapor phase isomerization catalyst under vapor phase isomerization conditions.

3. The process according to claim 1 or claim 2, wherein the liquid phase isomerization catalyst comprises a zeolite having a MEL framework structure, a zeolite having an MFI framework structure or any combination thereof.

4. The process according to any one of the preceding claims, wherein at least a portion of the raffinate stream is subjected to the liquid phase isomerization in (III) to obtain an isomerized raffinate stream.

5. The process according to claim 4, wherein the one or more isomerized recycle streams are obtained as at least part of the one or more bottom streams produced when separating the isomerized raffinate stream in a distillation column in (IV).

6. The process according to claim 4 or claim 5, wherein the distillation column comprises a dividing wall distillation column, and a first lower stream rich in paraxylene is obtained from a first side of the dividing wall distillation column, and a second lower stream depleted in paraxylene is obtained from a second side of the dividing wall distillation column; One or more isomerized recycle streams are obtained as at least a portion of the first lower stream.

7. The method according to claim 6, further comprising: passing the isomerized raffinate stream to a first side of a dividing wall distillation column; and At least a portion of the raffinate stream is sent to a second side of the dividing wall distillation column.

8. The process of any one of claims 4 to 7, wherein at least a portion of the isomerized raffinate stream is sent to a para-xylene recovery unit as at least a portion of one or more isomerized recycle streams.

9. The process according to any one of claims 4 to 8, wherein at least a portion of the isomerized raffinate stream is not sent to a distillation column.

10. A process according to any one of the preceding claims, wherein at least a portion of the one or more lower streams is subjected to the liquid phase isomerization in (VI) to produce one or more isomerized recycle streams.

11. The process according to claim 10, wherein the liquid phase isomerization in (III) is not carried out and / or the distillation column provides a bottom stream.

12. The process according to any one of the preceding claims, wherein an intermediate stream is obtained in (II), at least a portion of the intermediate stream is subjected to liquid phase isomerization in (VI), and at least a portion of the one or more isomerized recycle streams in (VII) is obtained from the intermediate stream after liquid phase isomerization thereof.

13. The process of claim 12, wherein the intermediate stream comprises up to about 50 volume percent toluene.

14. A process according to any one of the preceding claims, wherein the feed mixture and / or the isomerized recycle stream comprises 20 wt% ethylbenzene or less.

15. The process of any one of the preceding claims, wherein the raffinate stream comprises up to about 50% by volume toluene.

16. A process according to any one of the preceding claims, wherein the liquid phase isomerisation is carried out on one of the following: an intermediate stream, a raffinate stream, or one or more bottoms streams.

17. A method comprising: (i) providing a feed mixture comprising one or more xylene isomers and optionally ethylbenzene; (ii) separating the feed mixture in a para-xylene recovery unit using simulated moving bed chromatography with toluene as a desorbent to obtain a para-xylene-enriched product stream and a para-xylene-depleted raffinate stream comprising toluene, optionally ethylbenzene, and o-xylene, m-xylene or any combination thereof; (iii) liquid phase isomerizing at least a portion of the raffinate stream under liquid phase isomerization conditions in the presence of a liquid phase isomerization catalyst to produce an isomerized raffinate stream; (iv) passing the isomerized raffinate stream to a first side of a dividing wall distillation column; (v) passing a portion of the raffinate stream to a second side of the dividing wall distillation column; (vi) obtaining a first lower stream rich in paraxylene from the first side of the dividing wall distillation column, a second lower stream depleted in paraxylene from the second side of the dividing wall distillation column, and a top stream rich in toluene from the dividing wall distillation column; (vii) sending at least a portion of the overhead stream to a para-xylene recovery unit as at least a portion of the desorbent; and (viii) sending one or more isomerized recycle streams to a para-xylene recovery unit, the one or more isomerized recycle streams being obtained as at least a portion of the first lower stream.

18. The process of claim 17, wherein the overhead stream comprises at least a majority of the toluene in the raffinate stream.

19. The process according to claim 17 or claim 18, wherein the liquid phase isomerization catalyst comprises a zeolite having a MEL framework structure, a zeolite having an MFI framework structure, or any combination thereof.

20. The method according to any one of claims 17 to 19, further comprising: (ix) vapor phase isomerizing at least a portion of the second lower stream in the presence of a vapor phase isomerization catalyst under vapor phase isomerization conditions.

21. A method comprising: (A) providing a feed mixture comprising one or more xylene isomers and optionally ethylbenzene; (B) separating the feed mixture in a para-xylene recovery unit using simulated moving bed chromatography with toluene as a desorbent to obtain a product stream rich in para-xylene, a raffinate stream depleted in para-xylene, and optionally an intermediate stream comprising para-xylene at a concentration higher than that in the raffinate stream and lower than that in the product stream, the raffinate stream comprising toluene, optionally ethylbenzene, and o-xylene, m-xylene, or any combination thereof; (C) separating at least a portion of the raffinate stream in a distillation column to provide an overhead stream comprising at least a majority of the toluene in the raffinate stream and one or more bottoms streams, each of which comprises one or more xylene isomers; (D) sending at least a portion of the overhead stream to a paraxylene recovery unit as at least a portion of a desorbent; (E) conducting liquid phase isomerization in the presence of a liquid phase isomerization catalyst under liquid phase isomerization conditions to produce one or more isomerized recycle streams, the liquid phase isomerization being conducted on at least one of: (a) at least a portion of one or more lower streams; and / or (b) at least a portion of an intermediate stream, if any; and / or (c) at least a portion of a raffinate stream; and (F) sending at least a portion of the one or more isomerized recycle streams to a para-xylene recovery unit.

22. The process of claim 21, wherein at least a portion of the one or more lower streams is subjected to liquid phase isomerization and at least a portion of the one or more isomerized recycle streams is obtained from the one or more lower streams after liquid phase isomerization thereof.

23. A process according to claim 21 or claim 22, wherein at least a portion of the raffinate stream is subjected to liquid phase isomerization to produce an isomerized raffinate stream, and at least a portion of one or more isomerized recycle streams is obtained from the isomerized raffinate stream.

24. The process according to any one of claims 21 to 23, wherein an intermediate stream is obtained, at least a portion of the intermediate stream is subjected to liquid phase isomerization, and at least a portion of one or more isomerized recycle streams is obtained from the intermediate stream after subjecting it to liquid phase isomerization.

25. The process according to any one of claims 21 to 24, wherein the liquid phase isomerization catalyst comprises a zeolite having a MEL framework structure, a zeolite having an MFI framework structure, or any combination thereof.

26. The method according to any one of claims 21 to 25, further comprising: (G) vapor phase isomerizing at least a portion of the one or more lower streams in the presence of a vapor phase isomerization catalyst under vapor phase isomerization conditions.

Images