Production of paraxylene by liquid phase isomerization and separation thereof in presence of C9 + aromatic hydrocarbons

Abstract

A feed mixture comprising one or more xylene isomers and C9 + aromatic hydrocarbons may be separated in a first distillation column to obtain a first overhead stream comprising m-xylene and / or p-xylene and a first bottoms stream comprising o-xylene and C9 + aromatic hydrocarbons. The first bottoms stream may optionally be isomerized by liquid phase isomerization and added to a second distillation column to obtain a second overhead stream comprising at least ortho-xylene and a second bottoms stream comprising C9 + aromatic hydrocarbons. The second overhead stream may optionally be isomerized by liquid phase isomerization. Liquid phase isomerization may occur over at least one of the first bottoms stream, the second overhead stream, an optional side stream obtained from the first or second distillation column, or within the first and second distillation columns, such that the second overhead stream or the isomerized second overhead stream is rich in p-xylene.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to and the benefit of U.S. Provisional Application No. 63 / 351,905, filed on June 14, 2022, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0003] The disclosure of this application relates to the isomerization of C8 aromatic hydrocarbons, and more particularly to the isomerization of C8 aromatic hydrocarbons in the presence of C9+ aromatic hydrocarbons under liquid phase isomerization conditions and the separation of para-xylene therefrom. Background Art

[0004] The worldwide production capacity of paraxylene from various industrial sources is about 40 million tons / year. Paraxylene is a valuable chemical feedstock that can be obtained from C8+ aromatic hydrocarbon mixtures and is primarily used for conversion into 1,4-benzenedicarboxylic acid (terephthalic acid), which can be used in the synthesis of textiles, bottles and plastic materials, as well as other industrial applications. The other xylene isomers experience considerably lower, though still significant, demand. For example, metaxylene can be used as an aviation gas blending component.

[0005] C8+ aromatic hydrocarbon mixtures (e.g., ortho-, meta- and / or para-xylene isomers, as well as ethylbenzene and heavier aromatic hydrocarbons) can be prepared by various methods, such as alkylation of lower aromatic hydrocarbons (e.g., benzene and / or toluene), transalkylation, toluene disproportionation, catalytic reforming, isomerization, cracking (e.g., steam or catalytic cracking), etc. Alkylation of lower aromatic hydrocarbons with methanol and / or dimethyl ether promoted by zeolite catalysts can be a particularly effective and advantageous route for producing para-xylene with relatively high selectivity relative to ortho- and meta-xylene, such as described 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 p-xylene from other C8+ aromatic hydrocarbons, a residual oil liquid stream lean in p-xylene can be obtained. Such residual oil liquid stream can be isomerized to form additional p-xylene, and then further separated to separate the additional p-xylene that has been produced. Conventionally, such isomerization methods are carried out using vapor phase isomerization, which is a very energy-consuming method. Recently, progress has been made in the isomerization of xylene isomers by liquid phase isomerization, which usually consumes much less energy. Although usually less energy-consuming, the presence of ethylbenzene and / or C9+ aromatic hydrocarbons in the liquid phase isomerization process can produce unwanted by-products and cause p-xylene losses or their complicated separation. SUMMARY OF THE INVENTION

[0007] In some aspects, the disclosure of the present application provides a method comprising: (I) introducing a feed mixture comprising one or more xylene isomers and C9+ aromatic hydrocarbons into a first distillation column at a feed position on the first distillation column, the first distillation column optionally containing a liquid phase isomerization catalyst loaded therein; (II) optionally, contacting a portion of the feed mixture with a liquid phase isomerization catalyst under liquid phase isomerization conditions in the first distillation column; (III) obtaining a first overhead stream comprising meta-xylene, para-xylene or any combination thereof, a first bottoms stream comprising ortho-xylene and C9+ aromatic hydrocarbons from the first distillation column, and optionally a first side stream; (IV) optionally, a) obtaining the first side stream from the first distillation column, b) performing liquid phase isomerization of the first side stream outside the first distillation column under liquid phase isomerization conditions in the presence of a liquid phase isomerization catalyst to produce an isomerized first side stream, and c) returning at least a portion of the isomerized first side stream to the first distillation column; (V) optionally, performing liquid phase isomerization on at least a portion of the first bottoms stream outside the first distillation column under liquid phase isomerization conditions in the presence of a liquid phase isomerization catalyst to produce an isomerized first bottoms stream; (VI) returning at least a portion of the first The bottoms stream and / or at least a portion of the isomerized first bottoms stream are fed to a second distillation column optionally containing a liquid phase isomerization catalyst loaded therein; (VII) optionally, contacting a portion of the first bottoms stream with a liquid phase isomerization catalyst in the second distillation column under liquid phase isomerization conditions; (VIII) obtaining a second overhead stream comprising at least o-xylene, a second bottoms stream comprising C9+ aromatic hydrocarbons, and an optional second side stream from the second distillation column; (IX) optionally, a) obtaining a second side stream from the second distillation column, b) contacting a second bottoms stream outside the second distillation column under liquid phase isomerization conditions in the presence of a liquid phase isomerization catalyst (X) optionally, conducting liquid phase isomerization on at least a portion of the second overhead stream outside the second distillation column under liquid phase isomerization conditions in the presence of a liquid phase isomerization catalyst to produce an isomerized second overhead stream; wherein the liquid phase isomerization is carried out in at least one of (II), (IV), (V), (VII), (IX) or (X) and the second overhead stream and / or the isomerized second overhead stream is enriched in para-xylene.

[0008] In some aspects, the disclosure of the present application provides a method comprising: (A) providing a feed mixture comprising one or more xylene isomers and C9+ aromatic hydrocarbons, wherein o-xylene constitutes at least a majority of the one or more xylene isomers, and the feed mixture is depleted in ethylbenzene; (B) optionally, conducting liquid phase isomerization on at least a portion of the feed mixture in the presence of a liquid phase isomerization catalyst under liquid phase isomerization conditions to produce an isomerized feed mixture; (C) introducing the feed mixture and / or at least a portion of the isomerized feed mixture into a distillation column at a feed position on the distillation column, the distillation column optionally containing a liquid phase isomerization catalyst loaded therein; (D) optionally, contacting a portion of the feed mixture with a liquid phase isomerization catalyst under liquid phase isomerization conditions in the distillation column. (E) obtaining from a distillation column an ​​overhead stream comprising at least ortho-xylene, a bottoms stream comprising C9+ aromatic hydrocarbons, and optionally a side stream; (F) optionally, a) obtaining the side stream from the distillation column, b) performing liquid phase isomerization of the side stream outside the distillation column under liquid phase isomerization conditions in the presence of a liquid phase isomerization catalyst to produce an isomerized side stream, and c) returning at least a portion of the isomerized side stream to the distillation column; (G) optionally, performing liquid phase isomerization on at least a portion of the overhead stream outside the distillation column under liquid phase isomerization conditions in the presence of a liquid phase isomerization catalyst to produce an isomerized overhead stream; wherein liquid phase isomerization is performed in at least one of (B), (D), (F) or (G), and the overhead stream and / or the isomerized overhead stream is enriched in para-xylene.

[0009] Disclosure of the Present Application These and other features and properties of the disclosed methods and compositions and their advantageous applications and / or uses will be apparent from the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The following drawings are included to illustrate certain aspects of the present disclosure and should not be considered as exclusive embodiments. The disclosed subject matter is capable of significant modifications, alterations, combinations, and equivalences in form and function as will occur to those of ordinary skill in the art having the benefit of the present disclosure.

[0011] To assist persons of ordinary skill in the relevant art in making and using the subject matter herein, reference is made to the accompanying drawings, wherein:

[0012] Figure 1 is a block diagram of a system and process for xylene separation and liquid phase isomerization according to the disclosure of the present application, wherein a feed mixture containing C9+ aromatic hydrocarbons and optionally ethylbenzene can be processed.

[0013] Figure 2-5 Shown with Figure 1 A block diagram of a system and process configuration similar to system and process 100 is shown in FIG. 1 , wherein liquid phase isomerization occurs at one location.

[0014] Figure 6 is a block diagram of a system and process for xylene separation and liquid phase isomerization according to the disclosure of the present application, wherein a feed mixture depleted in ethylbenzene and containing C9+ aromatics can be further processed.

[0015] Figure 7-9 Shown with Figure 6 A block diagram of a system and process configuration similar to system and process 600 is shown in FIG. 6A , in which liquid phase isomerization occurs at one location.

[0016] Detailed Description

[0017] The disclosure of this application relates to the isomerization of C8 aromatic hydrocarbons, and more particularly to the isomerization of C8 aromatic hydrocarbons in the presence of C9+ aromatic hydrocarbons under liquid phase isomerization conditions and the separation of para-xylene therefrom.

[0018] definition

[0019] Various specific embodiments, variants and examples of the present 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 gives specific preferred embodiments, it will be appreciated by those skilled in the art that these embodiments are exemplary only, and the present invention may be implemented in other ways. For the purpose of determining infringement, the scope of the present invention will refer to any one or more of the appended claims, including its equivalents and elements or limitations equivalent to those recorded. Any reference to the "invention" may refer to one or more of the present invention defined by the claims, but not necessarily all.

[0020] In the disclosure of the present application, a method may be described as comprising at least one "step". It should be understood that each step is an action or operation that can be performed one or more times in a continuous or discontinuous manner in the method. Unless otherwise specified or the context clearly indicates otherwise, multiple steps in the method may be performed in the order in which they are listed, overlapping or not overlapping with one or more other steps, or in any other order as the case may be. In addition, with respect to the same or different batches of materials, one or more or even all steps may be performed simultaneously. For example, in a continuous method, when the first step in the method is performed with respect to the raw material just fed to the beginning of the method, the second step may be performed simultaneously with respect to the intermediate material, which is produced by processing the raw material fed to the method at an earlier time in the first step. Preferably, the steps are performed in the order described. However, the steps may occur out of order and / or simultaneously rather than in the order listed.

[0021] Unless otherwise indicated, all numbers indicating quantities in the disclosure of this application should be understood to be modified by the term "about" in all cases. It should also 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 should be understood that due to the limitations of the technology and equipment used to make the measurements, any measured data inherently contain a certain level of error.

[0022] As used herein, the indefinite article "a" or "an" should 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 using one, two, or more fractionation columns, unless specified to the contrary or the context clearly indicates that only one fractionation column is used.

[0023] As used herein, the term "consisting essentially of" means a composition, feed, stream, or effluent that includes a given component or group of components at a concentration of at least about 60 weight percent, preferably at least about 70 weight percent, more preferably at least about 80 weight percent, more preferably at least about 90 weight percent, or still more preferably at least about 95 weight percent, based on the total weight of the composition, feed, stream, or effluent.

[0024] For brevity, the following abbreviations may be 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.

[0025] As used herein, "wt%" means percent by weight, "vol%" means percent by volume, "mol%" means percent by mole, "ppm" means parts per million and "wt ppm" and "wppm" are used interchangeably to mean parts per million on a weight basis. All concentrations herein are expressed based on the total amount of the composition. Unless otherwise specified or indicated, all ranges expressed herein shall include both endpoints as two specific embodiments.

[0026] The nomenclature of elements and their groups used herein is based on the periodic table used by the International Union of Pure and Applied Chemistry after 1988. An example of a periodic table is shown on the inside cover of Advanced Inorganic Chemistry, 6th edition, by F. Albert Cotton et al. (John Wiley & Sons, Inc., 1999).

[0027] As used herein, the term "hydrocarbon" means (i) any compound composed 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 carbon atoms (one or more) in a total number of n 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 one 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 one 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 carbon atoms (one or more) in a total number of at least n in its molecule, or (ii) any mixture of two or more such hydrocarbon compounds of (i). "Cn- hydrocarbons" means (i) any hydrocarbon compound containing carbon atoms in a total number of at most n 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).

[0028] As used herein, an "aromatic hydrocarbon" is a hydrocarbon that contains an aromatic ring in its molecular structure. An aromatic compound can have a cyclic cloud of π electrons that satisfies Hückel's rule. A "non-aromatic hydrocarbon" means a hydrocarbon other than an aromatic hydrocarbon.

[0029] As used herein, the term "lower aromatic hydrocarbon" refers to benzene, toluene, or a mixture of benzene and toluene.

[0030] In the disclosure of this application, an "effluent" or a "feed" is sometimes also referred to as a "stream". When it is shown that two or more streams form a combined stream and are then supplied to a container, it should be interpreted to include, where appropriate, the alternative of supplying the streams separately to the container. Similarly, when two or more streams are supplied separately to a container, it should be interpreted to include, where appropriate, the alternative of combining the streams before entering the container as a combined stream(s). In addition, a single stream can be split into two or more separate streams and provided to different locations.

[0031] As used herein, the term "liquid phase" means reaction conditions in which the aromatic hydrocarbons present in the reactor are essentially in a liquid state. "Essentially in the liquid phase" means that > ​​about 90 wt%, preferably > about 95 wt%, preferably > about 99 wt%, and preferably the entirety of the aromatic hydrocarbons are in the liquid phase.

[0032] As used herein, the term "gas phase" means reaction conditions in which the aromatic hydrocarbons present in the reactor are essentially in a gaseous state. "Essentially in the gas phase" means that > ​​about 90 wt%, preferably > about 95 wt%, preferably > about 99 wt%, and preferably the entirety of the aromatic hydrocarbons are in the gas phase.

[0033] As used herein, the term "alkylation" means a chemical reaction in which an alkyl group is converted 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 alkyl group converted is a methyl group. Thus, methylation of benzene can produce toluene, xylenes, trimethylbenzenes, etc.; and methylation of toluene can produce xylenes, trimethylbenzenes, etc.

[0034] As used herein, the term "methylated aromatic hydrocarbon" means an aromatic hydrocarbon containing at least one methyl group and only methyl groups (one or more) attached to the aromatic ring (one or more). Examples of methylated aromatic hydrocarbons include toluene, xylene, trimethylbenzene, tetramethylbenzene, pentamethylbenzene, hexamethylbenzene, methylnaphthalene, dimethylnaphthalene, trimethylnaphthalene, tetramethylnaphthalene, etc.

[0035] As used herein, the term "molecular sieve" means a crystalline or semi-crystalline material, such as a zeolite, having molecular-sized pores that allow molecules below a certain critical size to pass through.

[0036] "Crystallite" means a crystallized grain of a material. Crystallites having micrometer or nanometer dimensions 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 polycrystalline materials. In some cases, agglomerated particles comprising multiple crystallites may be present in the material.

[0037] As used herein, the terms "enriched" or "rich" when describing a component in a stream or feed mean that the stream or feed comprises a higher concentration of the component than the source material from which the stream is derived. As used herein, the terms "depleted" or "lean" when describing a component in a stream or feed mean that the stream or feed comprises a lower concentration of the component than the source material from which the stream is derived.

[0038] Unless otherwise indicated herein, any stream or feed that is "enriched" in a particular component may "consist of" or "consist essentially of" that component. A feed or stream that is "enriched" in a component may constitute the majority component of the feed or stream compared to other components.

[0039] As used herein, the term "overhead stream" refers to the vapor stream removed from the top of a distillation column.

[0040] As used herein, the term "bottoms stream" refers to the liquid stream removed from the lower portion of a distillation column.

[0041] As used herein, the term "bottom stream" refers to a vapor or liquid stream that is not an overhead stream and is removed from a location other than the top of a distillation column. A "bottom stream" can be a side stream or a bottom stream. Depending on the vertical location from which it is removed, a side stream can be a vapor stream, a liquid stream, or a combination thereof.

[0042] 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," as used interchangeably herein, mean that the composition, feed, stream, or effluent contains the given component at a concentration of at most about 10 wt%, preferably at most about 8 wt%, more preferably at most about 5 wt%, more preferably at most about 3 wt%, and still more preferably at most about 1 wt%, based on the total mass of the composition, feed, stream, or effluent.

[0043] In the disclosure of the present application, o-xylene means 1,2-dimethylbenzene, m-xylene means 1,3-dimethylbenzene and p-xylene means 1,4-dimethylbenzene. Herein, the general term "xylene (one or more) or xylene isomer (one or more)" means either in the singular or in the plural together any mixture of one or two to four of p-xylene, m-xylene and o-xylene in any proportion and / or ethylbenzene. In the disclosure of this article, ethylbenzene is considered to be a xylene isomer. Therefore, a mixture of xylene isomers may contain one or more of o-xylene, m-xylene, p-xylene and ethylbenzene 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 of the withdrawal stream and the processing conditions, as further explained herein.

[0044] A stream or feed that is depleted in one component may be enriched in another component. For example, a stream that is depleted in paraxylene may be enriched in ortho-xylene and / or meta-xylene and / or C9+ aromatics.

[0045] Liquid Phase Isomerization of Feed Mixtures Containing C9+ Aromatics

[0046] As discussed above, it is desirable to carry out isomerization of the residual oil liquid stream obtained after separating para-xylene from a feed mixture containing C8+ aromatic hydrocarbons. Isomerization can form additional para-xylene from other C8 aromatic hydrocarbons and promote more efficient utilization of the feed mixture. This type of isomerization is usually carried out using a vapor phase isomerization that is a very energy-consuming method. The progress of the liquid phase isomerization of C8 aromatic hydrocarbons can provide benefits that are superior to vapor phase isomerization, such as reducing energy input requirements and minimizing the formation of by-products. However, the presence of C9+ aromatic hydrocarbons in the mixed aromatic hydrocarbon feed mixture can produce unwanted by-products and cause para-xylene losses and / or their complex separation. The description of exemplary liquid phase isomerization processes, conditions and catalysts can be found in, for example, 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 on liquid phase isomerization processes, conditions and catalysts are provided herein.

[0047] Catalysts effective for isomerizing xylene isomers under liquid phase conditions to produce additional p-xylene can also often act on C9+ aromatic hydrocarbons and cause by-product formation. The disclosure of the present application provides a favorable process for producing and separating p-xylene from a feed mixture also containing C9+ aromatic hydrocarbons, wherein liquid phase isomerization can be effectively carried out using a suitable liquid phase isomerization catalyst in the presence of C9+ aromatic hydrocarbons. Advantageously, a liquid phase isomerization catalyst comprising a zeolite (such as ZSM-11) with a MEL framework can easily promote the isomerization of xylene isomers under liquid phase isomerization conditions to produce an equilibrium mixture of xylenes from a stream poor in p-xylene. Surprisingly, the zeolite catalyst with a MEL framework exhibits a relatively low reactivity to C9+ aromatic hydrocarbons and causes minimal by-product formation when contacted therewith. This benefit solves the significant difficulties associated with carrying out liquid phase isomerization of a feed mixture containing a large amount of C9+ aromatic hydrocarbons. In addition, various favorable process configurations disclosed herein allow considerable flexibility to be achieved at the location where liquid phase isomerization occurs. In this case, the advantageous process configuration disclosed herein can even facilitate the use of zeolite catalysts that are less tolerant to the presence of C9+ aromatic hydrocarbons, provided that liquid phase isomerization is carried out at a suitable process location. For example, in some cases, zeolite catalysts having an MFI framework can also be used in the process disclosed herein during liquid phase isomerization.

[0048] Additional advantages of the disclosure of the present application may include reducing the separation burden (tower specifications) in the distillation tower for separating para-xylene from C9+ aromatics and other xylene isomers. By reducing the separation burden, additional energy efficiencies can be achieved in addition to those produced by liquid phase isomerization (as opposed to vapor phase isomerization) on the resulting residual oil liquid stream depleted in para-xylene. More specifically, because liquid phase isomerization can be effectively performed in the presence of C9+ aromatics in the disclosure of the present application, it is not necessary to completely remove xylene isomers from the residual oil liquid stream because the xylene isomers can be subsequently isomerized to produce additional para-xylene. In addition, the reduced separation burden can potentially reduce capital equipment costs by promoting the use of smaller distillation towers. C9+ aromatics can be separated from the process stream in the disclosure of the present application and further converted into one or more value-added products (if desired).

[0049] The advantageous separation process disclosed herein can also allow for feed mixtures containing a large amount of ethylbenzene by performing an initial separation of ethylbenzene from a residual oil liquid stream. In addition, when further processing the residual oil liquid stream to produce additional p-xylene, the liquid phase isomerization catalyst and liquid phase isomerization conditions disclosed herein do not result in a large amount of ethylbenzene and other byproducts, which otherwise complicate the further separation of p-xylene in the p-xylene recovery unit. In order to address ethylbenzene and other byproducts that can accumulate in concentration during operation, the method disclosed herein can also include vapor phase isomerization to mitigate components that may not be effectively converted using liquid phase isomerization, which can provide additional amounts of p-xylene. By combining vapor phase isomerization with a liquid phase isomerization process according to the disclosure herein, the overall energy input requirement can be reduced compared to processing by vapor phase isomerization alone through a residual oil liquid stream. Additional details and additional process advantages are discussed in the following description.

[0050] Before discussing more specific aspects and advantages of the present disclosure in further detail, the process of the present disclosure will be described with reference to the accompanying drawings. For simplicity, common reference numerals are used in the drawings to describe elements with similar structures and functions in various systems and process configurations.

[0051] Figure 11 is a block diagram of a system and process for xylene separation and liquid phase isomerization according to the disclosure of the present application, wherein a feed mixture containing C9+ aromatic hydrocarbons and optionally ethylbenzene can be processed. In the system and process 100, a feed mixture 102 containing one or more xylene isomers, C9+ aromatic hydrocarbons, and optionally ethylbenzene is introduced into a distillation column 104. The feed mixture 102 can be enriched in para-xylene or depleted in para-xylene, depending on the source of the received feed mixture 102 and how it has been previously processed. When the feed mixture 102 is separated in the distillation column 104, an overhead stream 106 and a bottoms stream 108 can be produced. The separation of the overhead stream 106 and the bottoms stream 108 can be facilitated by the different boiling points of the xylene isomers (ortho-xylene, meta-xylene, and para-xylene have normal boiling points of 144° C., 139° C., and 138° C., respectively; and ethylbenzene has a normal boiling point of 136° C.). Facilitated by the different boiling points, overhead stream 104 may comprise or consist essentially of the lower boiling components (meta-xylene, para-xylene, and ethylbenzene (if present)) in feed mixture 102, and at least a majority of the higher boiling components (ortho-xylene and C9+ aromatics) in feed mixture 102 may be located in bottoms stream 108. As further described below, these components may also be formed within or adjacent to distillation column 104. While bottoms stream 108 may comprise primarily ortho-xylene and C9+ aromatics, it is not required that complete resolution (separation) of meta-xylene and / or para-xylene from ortho-xylene and C9+ aromatics occur, as subsequent separation of para-xylene may occur after subsequent processing of bottoms stream 108 by liquid phase isomerization in accordance with the present disclosure. Preferably, bottoms stream 108 may be substantially free of ethylbenzene to facilitate liquid phase isomerization and subsequent separation of para-xylene.Additional details regarding suitable locations where liquid phase isomerization may be performed and the composition of each stream obtained after liquid phase isomerization are provided below.

[0052] Liquid phase isomerization in the system and process 100 can occur at one or more locations in the presence of a liquid phase isomerization catalyst under liquid phase isomerization conditions. In one example, the distillation column 104 can contain a liquid phase isomerization catalyst loaded therein, and the liquid phase isomerization can occur when at least a portion of the feed mixture 104 in the distillation column 104 contacts the liquid phase isomerization catalyst. In another alternative, the side stream 180a can be removed from the distillation column 102, and the liquid phase isomerization can occur in the liquid phase isomerization unit 190 outside the distillation column 104. The isomerized side stream 180b can then be returned to the distillation column 104, wherein the isomerized side stream 180b can be returned to the same location or a different location from which the side stream 180a was withdrawn. When returned to a different location, the isomerized side stream 180b can be returned to a location above or below the vertical location from which the side stream 180a was withdrawn. Likewise, the isomerized side stream 180b may be returned to a location above or below the feed point where the feed mixture 102 is introduced into the distillation column 104. Optionally, liquid phase isomerization does not occur in the distillation column 104, and the side stream 180a is not withdrawn and isomerized, in which case liquid phase isomerization occurs further downstream, as discussed further below. Thus, depending on various process considerations, the liquid phase isomerization catalyst may not be present in the distillation column 104 and / or the liquid phase isomerization unit 190 may not be fluidly connected to the distillation column 104.

[0053] Depending on the content of the feed mixture 102 and / or whether liquid phase isomerization is performed in the distillation column 104 or outside the distillation column 104, the composition of the overhead stream 106 can vary greatly. If the feed mixture 102 is rich in para-xylene, or if liquid phase isomerization is performed in the distillation column 104 or outside the distillation column 104, the overhead stream 106 can be correspondingly rich in para-xylene. However, if the feed mixture 102 is depleted in para-xylene, or if liquid phase isomerization is not performed in the distillation column 104 or outside the distillation column 104, the overhead stream 106 can be depleted in para-xylene, or para-xylene may even be essentially absent from the overhead stream 106. If liquid phase isomerization is performed in the distillation column 104 or outside the distillation column 104, the liquid phase isomerization can be performed in such a way that the bottoms stream 108 contains a balanced or unbalanced distribution of xylene isomers. Preferably, liquid phase isomerization (if performed in distillation column 104 or external to distillation column 104) can produce a balanced distribution of xylene isomers in bottoms stream 108, thereby eliminating the need for additional liquid phase isomerization further downstream, as discussed below. In addition to meta-xylene and / or para-xylene, overhead stream 106 can also include ethylbenzene, if present in feed mixture 102.

[0054] You can Figure 1The overhead stream 106 in the tower is provided to a para-xylene recovery unit 110, which can utilize absorption chromatography, crystallization, or any combination thereof to provide a first stream 112 rich in para-xylene and a second stream 114 depleted in para-xylene. The second stream 114 can include or consist essentially of meta-xylene and ethylbenzene. If desired, the second stream 114 can be further processed by vapor phase isomerization under vapor phase isomerization conditions in the presence of a vapor phase isomerization catalyst to form additional para-xylene in the equilibrium mixture of xylene isomers, as further described below.

[0055] If the bottoms stream 108 does not contain an equilibrium mixture of xylene isomers, liquid phase isomerization can be performed downstream of the distillation column 104. Thus, in another example showing that liquid phase isomerization can be performed in the system and process 100, the bottoms stream 108 can be fed to a liquid phase isomerization unit 191 to be subjected to liquid phase isomerization therein in the presence of a suitable liquid phase isomerization catalyst under liquid phase isomerization conditions, thereby forming an isomerized bottoms stream that is fed to the distillation column 140. The liquid phase isomerization in the liquid phase isomerization unit 191 can occur in the presence of C9+ aromatic hydrocarbons. If liquid phase isomerization of the bottoms stream 108 is not desired or is not considered necessary, the liquid phase isomerization unit 191 can be absent, or alternatively, at least a portion of the bottoms stream 108 can be diverted as a bypass stream 130 before being provided to the distillation column 140.

[0056] Bottoms stream 108, or the isomerized bottoms stream produced therefrom, is fed to distillation column 140 and separated into overhead stream 144 and bottoms stream 142. Bottoms stream 142 comprises or consists essentially of C9+ aromatic hydrocarbons, which are removed from the process stream and optionally further processed (not shown), for example by transalkylation or disproportionation to produce additional paraxylene.

[0057] The overhead stream 144 obtained from the distillation column 140 may contain at least ortho-xylene, which may be derived from the bottoms stream 108 or an isomerized bottoms stream produced therefrom. If liquid phase isomerization is performed upstream of the distillation column 140 and / or if the distillation column 104 does not completely separate meta-xylene and / or para-xylene from the feed mixture 102 into the overhead stream 106, other xylene isomers (e.g., meta-xylene and / or ortho-xylene) derived from the bottoms stream 108 may be present in the overhead stream 144.

[0058] In still another example, the distillation column 140 may contain a liquid phase isomerization catalyst loaded therein, and liquid phase isomerization may occur when at least a portion of the bottoms stream 108 within the distillation column 140 contacts the liquid phase isomerization catalyst. In another alternative, the side stream 190a may be removed from the distillation column 140, and the liquid phase isomerization may occur outside the distillation column 140 in a liquid phase isomerization unit 192. The isomerized side stream 190b may then be returned to the distillation column 140, wherein the isomerized side stream 190b may be returned to the same location or a different location from where the side stream 190a was withdrawn. When returned to a different location, the isomerized side stream 190b may be returned to a location above or below the vertical location from which the side stream 190a was withdrawn. Likewise, the isomerized side stream 190b may be returned to a location above or below the feed location where the bottoms stream 108 is introduced into the distillation column 140. Optionally, liquid phase isomerization does not occur in the distillation column 140 and the side stream 190a is not withdrawn and isomerized. If liquid phase isomerization occurs upstream of the distillation column 140, as described above, the liquid phase isomerization within the distillation column 140 and / or the withdrawal and liquid phase isomerization of the side stream 190a may be omitted. Alternatively, if liquid phase isomerization and / or the withdrawal and liquid phase isomerization of the side stream 190a do not occur in the distillation column 140, the liquid phase isomerization may occur further downstream, as discussed further below. Thus, depending on various process considerations, the liquid phase isomerization catalyst may not be present in the distillation column 140 and / or the liquid phase isomerization unit 192 may not be fluidly connected to the distillation column 140.

[0059] Thus, similar to the discussion above, if liquid phase isomerization is not performed upstream of distillation column 140, within distillation column 140, or within liquid phase isomerization unit 192, overhead stream 144 may be depleted in para-xylene. In such cases, overhead stream 144 may comprise primarily or consist essentially of ortho-xylene. However, if liquid phase isomerization is performed at any of these locations, overhead stream 144 may be enriched in para-xylene and preferably comprise a mixture of xylene isomers. Preferably, overhead stream 144 may remain depleted in ethylbenzene because the production rate of ethylbenzene may remain low under liquid phase isomerization conditions.

[0060] If the overhead stream 144 does not contain an equilibrium mixture of xylene isomers or if liquid phase isomerization is not performed at an upstream location, liquid phase isomerization can be performed downstream of the distillation column 140. Thus, in another example showing that liquid phase isomerization can be performed in the system and process 100, the overhead stream 144 can be fed to a liquid phase isomerization unit 193 to be liquid phase isomerized therein in the presence of a suitable liquid phase isomerization catalyst, thereby forming an isomerized overhead stream that can be subsequently processed. Optionally, if liquid phase isomerization of the overhead stream 144 is not desired or is not considered necessary, the liquid phase isomerization unit 193 can be absent, or at least a portion of the overhead stream 144 can be diverted as a bypass stream 150.

[0061] The overhead stream 144 or the isomerized overhead stream produced thereby may be fed to a para-xylene recovery unit 160. The para-xylene recovery unit 160 may utilize a separation technique such as absorption chromatography, crystallization, or any combination thereof to facilitate separation of the overhead stream 144 or the isomerized overhead stream produced thereby into a first stream 162 that is enriched in para-xylene and may consist essentially of para-xylene and a second stream 164 that may be depleted in para-xylene or contain para-xylene and other xylene isomers. For example, if the separation in the para-xylene recovery unit 160 occurs by absorption chromatography, such as simulated moving bed chromatography, the second stream 164 may contain primarily other xylene isomers. Conversely, if the separation occurs in the para-xylene recovery unit 160 by crystallization, the second stream 164 may contain para-xylene and one or more other xylene isomers (e.g., a mixture of para-xylene with ortho-xylene and meta-xylene). A commercially available simulated moving bed chromatography process suitable for use in the para-xylene recovery unit 160 is available from Axens (a French company) as ELUXYL® technology, although any other simulated moving bed process may also be effectively utilized. The second stream 164 may be subsequently vapor isomerized in the presence of a vapor isomerization catalyst under vapor isomerization conditions in the vapor isomerization unit 170 to promote the additional formation of xylenes thereby. Optionally, the second stream 114 may also be introduced into the vapor isomerization unit. The vapor isomerization unit 170 may include a portion of a xylene isomerization loop (not shown), which may also include a distillation column (for separating xylene isomers from other aromatic hydrocarbons) and a para-xylene recovery unit, which may utilize simulated moving bed chromatography or crystallization recovery technology. Additional details on suitable vapor isomerization conditions and vapor isomerization catalysts are provided below.

[0062] Preferably, liquid phase isomerization performed at any of the various locations within the system and process 100 can provide an equilibrium mixture of xylene isomers. Once an equilibrium mixture of xylene isomers is formed, the concentration of para-xylene can be increased by additional isomerization until the equilibrium position is changed, such as by withdrawing para-xylene from the process stream. Therefore, a more specific process configuration can be characterized as liquid phase isomerization performed at one of the aforementioned locations, such as within the distillation column 100, outside the distillation column 104 in the liquid phase isomerization unit 190, on the bottom material stream 108 in the liquid phase isomerization unit 191, within the distillation column 140, outside the distillation column 140 in the liquid phase isomerization unit 192, or on the overhead stream 144 in the liquid phase isomerization unit 193. Figure 2-5 Shown with Figure 1 A block diagram of a system and process configuration similar to system and process 100 is shown in , where liquid phase isomerization occurs at one location, except that the latter can be performed in the presence of C9+ aromatic hydrocarbons. Figure 2 A block diagram of a system and process configuration 200 is shown in which liquid phase isomerization occurs on side stream 180a within a liquid phase isomerization unit 190 . Figure 3 A block diagram of a system and process configuration 300 is shown in which liquid phase isomerization occurs on a bottoms stream 108 within a liquid phase isomerization unit 191 . Figure 4 A block diagram of a system and process configuration 400 is shown in which liquid phase isomerization occurs on side stream 190a within a liquid phase isomerization unit 192 . Figure 5 A block diagram of a system and process configuration 500 is shown in which liquid phase isomerization occurs on overhead stream 144 within liquid phase isomerization unit 193 .

[0063] and Figure 1-5 System and process configurations similar to those described in but omitting distillation column 104 are also possible provided that a feed mixture containing ethylbenzene below a critical concentration that does not interfere with downstream separations is used. Figure 6 is a block diagram of a system and process for xylene separation and liquid phase isomerization according to the disclosure of the present application, wherein a feed mixture depleted in ethylbenzene and containing C9+ aromatics can be further processed. Figure 6 The system and process 600 shown in Figure 1 The system and process 100 in FIG. 6 has similarities to the portion downstream of the distillation column 104 and thus may be better understood by reference thereto. Therefore, only the features of the system and process 600 are briefly discussed below.

[0064] refer to Figure 6, the system and process 600 contains a distillation column 640 that receives a feed mixture 608 and facilitates its separation into a bottoms stream 642 and an overhead stream 644. The feed mixture 608 can be depleted in ethylbenzene (e.g., containing less than a specified amount of ethylbenzene that can be effective for further separation) and contain one or more xylene isomers and C9+ aromatic hydrocarbons. The feed mixture 608 can be enriched in para-xylene and also contain at least one of meta-xylene and para-xylene, or the feed mixture 608 can be depleted in para-xylene and contain at least one of meta-xylene and ortho-xylene. For example, the feed mixture 608 can be depleted in ethylbenzene and in some cases contain primarily ortho-xylene and C9+ aromatic hydrocarbons.

[0065] Optionally, at least a portion of the feed mixture 608 may be subjected to liquid phase isomerization prior to introduction into the distillation column 640. Figure 6 , at least a portion of the feed mixture 608 can be diverted to a bypass stream 630, which provides a portion of the feed mixture 608 to a liquid phase isomerization unit 691. The isomerized feed stream can be produced in the liquid phase isomerization unit 691 under liquid phase isomerization conditions in the presence of a liquid phase isomerization catalyst and subsequently fed to a distillation column 640.

[0066] As mentioned above, bottoms stream 642 and overhead stream 644 are both obtained from distillation column 640. Bottom stream 642 is rich in C9+ aromatics and may consist essentially of C9+ aromatics. The C9+ aromatics within bottoms stream 642 may be removed from the process stream and further manipulated if desired.

[0067] Optionally, the distillation column 640 may contain a liquid phase isomerization catalyst loaded therein, and liquid phase isomerization may occur when at least a portion of the feed mixture 640 within the distillation column 608 contacts the liquid phase isomerization catalyst. In another alternative, the side stream 690a may be removed from the distillation column 640, and the liquid phase isomerization may occur outside the distillation column 640 in the liquid phase isomerization unit 692 under liquid phase isomerization conditions in the presence of a liquid phase isomerization catalyst. The isomerized side stream 690b may then be returned to the distillation column 640, wherein the isomerized side stream 690b may be returned to the same location or a different location from which the side stream 690a was withdrawn. When returned to a different location, the isomerized side stream 690b may be returned to a location above or below the vertical location from which the side stream 690a was withdrawn. Optionally, liquid phase isomerization does not occur in the distillation column 640 and the side stream 690a is not withdrawn and isomerized. If liquid phase isomerization occurs upstream of distillation column 640 (e.g., in liquid phase isomerization unit 691, as described above), then liquid phase isomerization and / or withdrawal and liquid phase isomerization of side stream 690a in distillation column 640 may be omitted. Alternatively, if liquid phase isomerization and / or withdrawal and liquid phase isomerization of side stream 690a do not occur in distillation column 640, then liquid phase isomerization may occur further downstream (e.g., on overhead stream 644), as discussed further below. Thus, depending on various process considerations, a liquid phase isomerization catalyst may not be present in distillation column 640 and / or liquid phase isomerization unit 692 may not be fluidly connected to distillation column 640.

[0068] If the overhead stream 644 does not contain an equilibrium mixture of xylene isomers or if liquid phase isomerization is not performed at an upstream location, liquid phase isomerization may be performed downstream of the distillation column 640. Thus, in another example showing that liquid phase isomerization may be performed in the system and process 600, the overhead stream 644 may be fed to a liquid phase isomerization unit 693 to be subjected to liquid phase isomerization therein in the presence of a suitable liquid phase isomerization catalyst under liquid phase isomerization conditions, thereby forming an isomerized overhead stream that may be subsequently processed. Optionally, if liquid phase isomerization of the overhead stream 644 is not desired or is not considered necessary, the liquid phase isomerization unit 693 may not be present, or at least a portion of the overhead stream 644 may be diverted as a bypass stream 650 without being isomerized in the liquid phase isomerization unit 693.

[0069] Thus, overhead stream 644 can be enriched or depleted in para-xylene, depending on whether feed mixture 608 is enriched or depleted in para-xylene and / or whether liquid phase isomerization is performed prior to separation of overhead stream 644. For example, in some examples overhead stream 644 can comprise primarily or consist essentially of ortho-xylene.

[0070] The para-xylene-rich overhead stream 644 or the isomerized overhead stream produced thereby may be fed to a para-xylene recovery unit 660. The para-xylene recovery unit 660 may utilize separation techniques such as absorption chromatography, crystallization, or any combination thereof to facilitate separation of the overhead stream 644 or the isomerized overhead stream produced thereby into a first stream 662 that is rich in para-xylene and may be substantially composed of para-xylene and a second stream 664 that may be depleted in para-xylene or contain para-xylene and other xylene isomers. For example, if the separation in the para-xylene recovery unit 660 occurs by absorption chromatography, such as simulated moving bed chromatography, the second stream 664 may primarily contain other xylene isomers. Conversely, if the separation occurs in the para-xylene recovery unit 660 by crystallization, the second stream 664 may contain para-xylene and one or more other xylene isomers (e.g., a mixture of para-xylene with ortho-xylene and meta-xylene). The second stream 664 may be subsequently subjected to vapor phase isomerization in a vapor phase isomerization unit 670 under vapor phase isomerization conditions in the presence of a vapor phase isomerization catalyst to promote the additional formation of para-xylene therefrom. The vapor phase isomerization unit may include a portion of a xylene loop (not shown), as described above with reference to Figure 1 Further discussion.

[0071] Preferably, liquid phase isomerization performed at any of the various locations within the system and process 600 can provide an equilibrium mixture of xylene isomers, and various configurations of the system and process 600 can be characterized as liquid phase isomerization occurring at one location, such as on the feed mixture 608 within the liquid phase isomerization unit 691, within the distillation column 640, outside the distillation column 640 within the liquid phase isomerization unit 692, or on the overhead stream 644 within the liquid phase isomerization unit 693. Figure 7-9 Shown with Figure 6 A block diagram of a system and process configuration similar to system and process 600 is shown in FIG. 6A , in which liquid phase isomerization occurs at one location. Figure 7 A block diagram of a system and process configuration 700 is shown in which liquid phase isomerization occurs on a feed mixture 608 within a liquid phase isomerization unit 691 . Figure 8 A block diagram of a system and process configuration 800 is shown in which liquid phase isomerization occurs on side stream 690a within a liquid phase isomerization unit 692 . Fig. 9 A block diagram of a system and process configuration 900 is shown in which liquid phase isomerization occurs on an overhead stream 644 within a liquid phase isomerization unit 693. In the system and process 900, the liquid phase isomerization occurs in the presence of C9+ aromatic hydrocarbons.

[0072] Liquid phase isomerization can be desirable for producing p-xylene from various feed mixtures poor in p-xylene. The system and process configuration disclosed herein can advantageously adapt to feed mixtures that are either rich in or poor in p-xylene and optionally contain different amounts of ethylbenzene, and the presence of ethylbenzene can complicate the downstream separation of p-xylene (if present in excess). For example, in a system and process similar to system and process 100, a feed mixture containing high levels of ethylbenzene can be effectively used because ethylbenzene can be discharged into overhead stream 106 before liquid phase isomerization and subsequent separation of p-xylene. In a system and process similar to system and process 600, a feed mixture with low levels of ethylbenzene can be effectively utilized or a feed mixture with ethylbenzene levels that can be refined to provide ethylbenzene levels below a specified critical value can be provided without a separate distillation tower to promote the separation of ethylbenzene into the overhead stream. In either case, a suitable feed mixture can contain an equilibrium distribution less than p-xylene relative to other xylene isomers, so that the production of p-xylene can be increased by liquid phase isomerization according to the disclosure herein. Any ethylbenzene collected or accumulated in the systems and processes disclosed herein can be subjected to subsequent vapor phase isomerization to convert ethylbenzene into other xylene isomers, because ethylbenzene undergoes relatively slow isomerization under liquid phase isomerization conditions, but can be easily isomerized under vapor phase isomerization conditions. In contrast, the liquid phase isomerization catalyst and liquid phase isomerization conditions described herein do not further tend to produce a large amount of ethylbenzene, thereby promoting its use in the methods disclosed herein. By utilizing liquid phase isomerization and separation methods disclosed herein, less energy separation of p-xylene from the feed mixture can be achieved. More efficient utilization of the feed mixture can also be achieved.

[0073] Advantageously and surprisingly, isomerization of xylene isomers under liquid phase isomerization conditions can occur effectively in the presence of C9+ aromatics, typically after separation of ethylbenzene from the feed mixture. Surprisingly, the liquid phase isomerization catalysts specified herein can exhibit selectivity for isomerizing C8 aromatics over C9+ aromatics, which can limit the formation of by-products resulting from exposure of C9+ aromatics to liquid phase isomerization conditions. In addition, because liquid phase isomerization of C8 aromatics can occur effectively in the presence of C9+ aromatics, it is not necessary to achieve complete separation of C8 aromatics from C9+ aromatics when separating ethylbenzene from the feed mixture. This reduced separation burden can reduce the energy input requirements required to separate and isomerize xylene isomers to form para-xylene in accordance with the disclosure herein, as well as potentially reduce capital equipment costs by reducing the size of the distillation towers used during processing. Various systems and process configurations suitable for liquid phase isomerization as described above are possible, such as those described in the above references. Figure 1-9Detailed discussion. In addition, while a liquid phase isomerization catalyst having high selectivity for isomerization of C8 aromatics over C9+ aromatics may be desirable, the system and process configurations disclosed herein are also flexible enough to accommodate liquid phase isomerization catalysts that are less tolerant to byproduct formation when contacting C9+ aromatics. As such, a range of suitable liquid phase isomerization catalysts may also be accommodated in the methods disclosed herein. Additional details regarding suitable liquid phase isomerization catalysts and liquid phase isomerization conditions are provided below.

[0074] Therefore, the disclosure of the present application provides an isomerization and separation process, comprising: (I) introducing a feed mixture comprising one or more xylene isomers and C9+ aromatic hydrocarbons into a first distillation column at a feed position on the first distillation column, the first distillation column optionally containing a liquid phase isomerization catalyst loaded therein; (II) optionally, contacting a portion of the feed mixture with a liquid phase isomerization catalyst under liquid phase isomerization conditions in the first distillation column; (III) obtaining a first overhead stream comprising meta-xylene, para-xylene or any combination thereof, a first bottoms stream comprising ortho-xylene and C9+ aromatic hydrocarbons from the first distillation column, and optionally a first side stream; (IV) optionally, a) obtaining the first side stream from the first distillation column, b) performing liquid phase isomerization of the first side stream outside the first distillation column under liquid phase isomerization conditions in the presence of a liquid phase isomerization catalyst to produce an isomerized first side stream, and c) returning at least a portion of the isomerized first side stream to the first distillation column; (V) optionally, performing liquid phase isomerization on at least a portion of the first bottoms stream outside the first distillation column under liquid phase isomerization conditions in the presence of a liquid phase isomerization catalyst to produce an isomerized first bottoms stream; (VI) returning at least a portion of the first (VII) optionally, contacting a portion of the first bottoms stream with a liquid phase isomerization catalyst in the second distillation column under liquid phase isomerization conditions; (VIII) obtaining a second overhead stream comprising at least o-xylene, a second bottoms stream comprising C9+ aromatic hydrocarbons, and an optional second side stream from the second distillation column; and (IX) optionally, a) obtaining a second side stream from the second distillation column, b) contacting a portion of the first bottoms stream with a liquid phase isomerization catalyst under liquid phase isomerization conditions outside the second distillation column in the presence of a liquid phase isomerization catalyst. (II), (IV), (V), (VII), (IX), or (X) wherein the liquid phase isomerization is carried out in at least one of (II), (IV), (V), (VII), (IX), or (X) and the second overhead stream and / or the isomerized second overhead stream are enriched in paraxylene. The liquid phase isomerization at any of (II), (IV), (V), (VII), or (IX) may occur in the presence of C9+ aromatic hydrocarbons.

[0075] The feed mixture processed according to the foregoing may contain any amount of ethylbenzene, and at least a majority of the ethylbenzene may be obtained after distillation in the first overhead stream.Additional details regarding suitable feed mixtures and their sources are provided below.

[0076] Alternatively, a feed mixture having ethylbenzene present in less than a specified amount, preferably a feed mixture depleted in ethylbenzene or lacking ethylbenzene, can be isomerized under liquid phase isomerization conditions and further separated without first separating the feed mixture using a first distillation column. Such a method may include: (A) providing a feed mixture depleted in ethylbenzene comprising one or more xylene isomers and C9+ aromatic hydrocarbons, with ortho-xylene constituting at least a majority of the one or more xylene isomers; (B) optionally, conducting liquid phase isomerization of the feed mixture under liquid phase isomerization conditions in the presence of a liquid phase isomerization catalyst to produce an isomerized feed mixture; (C) introducing the feed mixture or the isomerized feed mixture into a distillation column at a feed position on the distillation column, the distillation column optionally containing a liquid phase isomerization catalyst loaded therein; (D) optionally, contacting a portion of the feed mixture with a liquid phase isomerization catalyst in the distillation column under liquid phase isomerization conditions; (E) obtaining from the distillation column a feed mixture comprising at least ortho-xylene. (B), (D), (F), or (G), wherein the liquid phase isomerization is performed on at least a portion of the overhead stream in the presence of a liquid phase isomerization catalyst under liquid phase isomerization conditions to produce an isomerized overhead stream; wherein the liquid phase isomerization is performed in at least one of (B), (D), (F), or (G), and the overhead stream and / or the isomerized overhead stream is enriched in paraxylene. The liquid phase isomerization at any of (B), (D), or (F) may occur in the presence of C9+ aromatic hydrocarbons.

[0077] Suitable feed mixtures for use in the disclosure herein may include, but are not limited to, those obtained by catalytic reforming processes, benzene or toluene alkylation processes, xylene isomerization processes, toluene disproportionation processes, transalkylation processes, cracking (e.g., steam or catalytic cracking), petroleum sources, biological production sources, or any combination thereof. The feed mixture may include ethylbenzene in an amount lower than a specified critical amount or the feed mixture may be preprocessed / refined in a suitable manner to reduce the amount of ethylbenzene to a specified critical amount lower than the amount required to support a specific process configuration. In addition to one or more xylene isomers, the feed mixture may include ethylbenzene in an amount of up to about 30% by weight or up to about 20% by weight of the total feed mixture. Preferably, the feed mixture may be produced or obtained by low levels of ethylbenzene to minimize the fraction of the feed mixture processed by gas phase isomerization. For example, a suitable feed mixture may include ethylbenzene in an amount of about 2000 ppm or less, or about 1500 ppm or less, or about 1000 ppm or less based on total mass, or may be further processed to provide ethylbenzene concentrations lower than these values. A particularly advantageous feed mixture can be produced via toluene alkylation using methanol and / or dimethyl ether as alkylating agents, which can provide significantly greater than balanced amounts of p-xylene relative to other xylene isomers (particularly o-xylene), as well as limiting the production of ethylbenzene (e.g., <2000 ppm by weight) and other problematic byproducts. Descriptions of exemplary methylation catalysts, methylating agents, and methylation conditions for lower aromatic hydrocarbons can be found in, for example, U.S. Patents 6,423,879, 6,504,072, 6,642,426, and 9,440,893, the relevant contents of which are incorporated herein by reference. In one example, a suitable feed mixture can include a raffinate stream rich in o-xylene obtained after separation of p-xylene produced with methanol and / or dimethyl ether in a toluene alkylation process.

[0078] The feed mixture suitable for use in the present disclosure may include one or more xylene isomers, optionally ethylbenzene and C9+ aromatics. One or more xylene isomers may include an equilibrium or non-equilibrium distribution of o-xylene, m-xylene and p-xylene. Relative to total xylene isomers, the feed mixture may be enriched in any one of o-xylene, m-xylene or p-xylene, provided that enough o-xylene and C9+ aromatics are present in the bottoms stream obtained from the first distillation tower (or may be formed in the bottoms stream by liquid phase isomerization) to promote separation in the second distillation tower. In some embodiments, the feed mixture may mainly include o-xylene, C9+ aromatics and optionally ethylbenzene.

[0079] In a non-limiting example, the total concentration of xylene isomers (including ethylbenzene) can range from c(xylene)1 to c(xylene)2 wt%, based on the total weight of the feed mixture, where c(xylene)1 and c(xylene)2 can independently be 30, 40, 50, 55, 60, 65, 70, 75, 80, 85, or 90, provided that c(xylene)1 < c(xylene)2.

[0080] In a non-limiting example, the total concentration of p-xylene in the feed mixture can range from c(pX)1 to c(pX)2 wt%, based on the total weight of the feed mixture, where c(pX)1 and c(pX)2 can independently be 10, 20, 30, 40, 50, 55, 60, 65, 70, 75, 80, 85, or 90, provided that c(pX)1 < c(pX)2.

[0081] In a non-limiting example, the total concentration of m-xylene in the feed mixture can range from c(mX)1 to c(mX)2 wt%, based on the total weight of the feed mixture, where c(mX)1 and c(mX)2 can independently be 10, 20, 30, 40, 50, 55, 60, 65, 70, 75, 80, 85, or 90, provided that c(mX)1 < c(mX)2.

[0082] In a non-limiting example, the total concentration of o-xylene in the feed mixture can range from c(oX)1 to c(oX)2 wt%, based on the total weight of the feed mixture, where c(oX)1 and c(oX)2 can independently be 10, 20, 30, 40, 50, 55, 60, 65, 70, 75, 80, 85, or 90, provided that c(oX)1 < c(oX)2.

[0083] In a non-limiting example, the feed mixture can contain C9+ hydrocarbons, in total in the range from c(C9+)1 to c(C9+)2 wt%, based on the total weight of the feed mixture, where c(C9+)1 and c(C9+)2 can independently be 0.01, 0.1, 1.0, 5.0, 10.0, 15.0, 20.0, 25.0, or 30.0, provided that c(C9+)1 < c(C9+)2.

[0084] In a non-limiting example, the feed mixture can contain ethylbenzene in a concentration range from c(EB)1 to c(EB)2 wt%, based on the total weight of the feed mixture, 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 less. More preferably, c(EB)2 is 10 wt% or less. More preferably, c(EB)2 is 5 wt% or less. Even more preferably, c(EB)2 is 2 wt% or less, or 1 wt% or less, more preferably about 2000 ppm or less, or about 1500 ppm or less, or about 1000 ppm or less. Optionally, the feed mixture having a higher ethylbenzene content can be further processed to achieve an ethylbenzene concentration within any of the foregoing ranges.

[0085] If the feed mixture is processed without first separating it into an overhead stream and a bottoms stream in a first distillation column, the feed mixture preferably has a low ethylbenzene concentration within the foregoing ranges. When the feed mixture is processed in this manner, the ethylbenzene content can be 2 wt% or less, or 1 wt% or less, more preferably about 2000 ppm or less, or about 1500 ppm or less, or about 1000 ppm or less.

[0086] The feed mixture can optionally contain benzene and / or toluene. In a non-limiting example, the feed mixture can contain benzene and toluene combined in a range from c(BT)1 to c(BT)2 wt%, based on the total weight of the feed mixture, 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 between benzene and toluene, and in some embodiments, the combination of benzene and toluene can consist essentially of toluene. That is, in some embodiments, the feed mixture can be essentially free of benzene. In some embodiments, the feed mixture can also be essentially free of toluene.

[0087] Thus, in some embodiments, the feed mixture can be rich in ortho-xylene and also contain C9+ aromatic hydrocarbons and optionally ethylbenzene. Optionally, such a feed mixture can also contain meta-xylene and / or para-xylene, in separate amounts less than the amount of ortho-xylene or in total amounts less than the amount of ortho-xylene. In other embodiments, a suitable feed mixture can be rich in para-xylene or meta-xylene and also contain ortho-xylene, C9+ aromatic hydrocarbons and optionally ethylbenzene. When ethylbenzene is not initially separated in the first distillation column, ethylbenzene can still be present, although in a low enough amount that still promotes para-xylene separation in the para-xylene recovery unit, as discussed above. A suitable small amount of ethylbenzene is provided above.

[0088] Provided that no liquid-phase isomerization is carried out in the first distillation column or on a side stream removed from the first distillation column, the amount of para-xylene in the bottoms stream can range from 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, or 10, provided that c(pX)1 < c(pX)2. The total amount of meta-xylene in the bottoms stream obtained from the first distillation column can similarly range from 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, or 10, provided that c(mX)1 < c(mX)2. The total amount of ortho-xylene in the bottoms stream can range from c(oX)1 to c(oX)2 wt%, where c(oX)1 and c(oX)2 can independently be 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, or 70, provided that c(oX)1 < c(oX)2.

[0089] In various embodiments of the processes disclosed herein, 80 wt% or greater, preferably 85 wt% or greater, more preferably 90 wt% or greater, more preferably 95 wt% or greater, more preferably 98 wt% or greater, more preferably 99 wt% or greater, or even more preferably about 100 wt% of the feed mixture can be in the liquid phase at the inlet of the liquid-phase isomerization unit where liquid-phase isomerization occurs. The feed mixture can have an inlet temperature in the range from 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, along with the other liquid-phase isomerization conditions described below, can promote the liquid-phase isomerization of C8 aromatic hydrocarbons to form additional para-xylene.

[0090] Unless carried out in a distillation column, a liquid-phase isomerization unit characterized by a fixed-bed reactor, a fluidized-bed reactor, or a moving-bed reactor can be used to carry out the liquid-phase isomerization in the disclosure of the present application. The feed provided to the liquid-phase isomerization conditions can be poor in p-xylene. In accordance with the above disclosure, and after liquid-phase isomerization, an equilibrium distribution of xylene isomers can preferably be obtained. If the equilibrium distribution of xylene isomers is not obtained, the liquid-phase isomerization conditions can be adjusted and / or the liquid-phase isomerization can be repeated at different positions. The feed exposed to the liquid-phase isomerization conditions can flow upward, downward, or in a radial manner within the liquid-phase isomerization unit. Alternatively, in some cases, the liquid-phase isomerization can be carried out batchwise in the liquid-phase isomerization unit.

[0091] Suitable liquid-phase isomerization conditions can include a reaction gauge pressure in the isomerization unit ranging from p1 to p2 kPa, 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. A higher reaction gauge pressure can promote the dissolution of molecular hydrogen in the liquid phase during the isomerization reaction, where molecular hydrogen is provided as a co-feed together with the feed mixture to facilitate the liquid-phase isomerization reaction.

[0092] Suitable liquid-phase isomerization conditions can include a reaction temperature ranging from 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. A relatively low reaction temperature during liquid-phase isomerization can improve energy efficiency by requiring less energy to heat the feed undergoing isomerization and by not requiring the condensation of a large amount of high-temperature gas phase after gas-phase isomerization.

[0093] Suitable liquid-phase isomerization conditions can include a high WHSV ranging from 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 an appropriate rate.

[0094] Molecular hydrogen can optionally be provided as a co-feed to the liquid-phase isomerization conditions. In some embodiments, molecular hydrogen or a portion thereof co-fed to the isomerization unit can be introduced via an inlet on the isomerization unit as a pressurized gas. Additionally or alternatively, molecular hydrogen or a portion thereof can be introduced into a feed line, vessel, or storage tank associated with the feed provided to the liquid-phase isomerization conditions, which can facilitate admixture of the molecular hydrogen with the feed and convey the molecular hydrogen along with the feed to the liquid-phase isomerization conditions. Most (e.g., ≥50%, ≥60%, ≥70%, ≥80%, ≥90%, ≥95%, ≥98%), and more preferably substantially all (≥99%) of the molecular hydrogen can be dissolved in the liquid phase under the liquid-phase isomerization conditions. To achieve a relatively high concentration of molecular hydrogen dissolved in the liquid phase, an appropriately high pressure can be maintained in the isomerization unit.

[0095] In a non-limiting example, molecular hydrogen can be added to the isomerization unit at a feed rate of r(H2)1 to r(H2)2 ppm by weight, based on the total weight of the feed, 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.

[0096] Suitable liquid-phase isomerization catalysts can comprise zeolites having a MEL framework structure (e.g., ZSM-11), a MFI framework structure (e.g., ZSM-5), or any combination thereof. Other suitable examples of zeolites that can effectuate 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.

[0097] In some 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 optionally a second metal selected from Sn, Zn, Ag, and combinations thereof. The first metal element can catalyze the hydrogenation of olefins that can be produced in the liquid-phase isomerization, such as those produced by the dealkylation of ethylbenzene. The second metal element can promote or enhance the catalytic effect 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, except for aluminum.

[0098] Zeolites having an MFI framework (such as ZSM-5) suitable for use in the disclosure of the present application can have one or more of the following characteristics: in the hydrogen form (HZSM-5); crystal size ≤ 0.1 micrometer; mesoporous surface area (MSA) ≥ 45 m 2 / g; total surface area to mesoporous surface area ratio ≤ 9; and silica to alumina molar ratio in the range of 20 to 50.

[0099] Suitable zeolites having a MEL framework (such as ZSM-11) can comprise a plurality of primary microcrystals, wherein at least 75% (such as ≥ 80%, ≥ 85%, ≥ 90%, or even ≥ 95%) of the microcrystals have a microcrystal size less than or equal to 200 nanometers (such as ≤ 150, ≤ 100, ≤ 80, ≤ 50, ≤ 30 nanometers). Thus, at least 75% (such as ≥ 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 disclosure of the present application, 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 zeolite material sample 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 disclosed in the present application results in surprisingly high catalytic activity and other advantages, complementing the surprisingly high tolerance to the limited reactivity of C9+ aromatic hydrocarbons under liquid-phase isomerization conditions.

[0100] Optionally, 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, in each of the a, b, and c crystal vectors, as measured by X-ray. The primary crystallites may optionally have an average primary crystallite size of greater than 20 nm, optionally greater than 30 nm, in each of the a, b, and c crystal vectors, as measured by X-ray.

[0101] The primary crystallites 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 - 80 nm, preferably in the range of 20 - 50 nm, as determined by analysis of an image of the primary crystallites taken by TEM.

[0102] The crystallites of the zeolite with a MEL framework may exhibit 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 a longest dimension in a first direction (“major direction”) and a width in another direction perpendicular to the first direction (“minor direction”), where the width is defined as the dimension midway between the major dimensions, as 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 some embodiments, the crystallites may have an average aspect ratio determined by TEM image analysis in the range from ar1 to ar2, 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.

[0103] The small crystallites of the zeolite with a MEL framework may aggregate to form agglomerates. An agglomerate is a polycrystalline material having void spaces at the interfaces of the crystallites. The agglomerates may be formed from primary crystallites having an average primary crystallite size determined by TEM image analysis of less than 80 nm, preferably less than 70 nm, more preferably less than 60 nm, or even less than 50 nm.

[0104] Suitable zeolites having a MEL framework may comprise a mixture of agglomerates of primary microcrystals together with some unaggregated primary microcrystals. Most of the zeolites having a MEL framework may comprise, for example, greater than 50 wt% or greater than 80 wt% 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 in Nanomaterials (edited by Deutsche Forschungsgemeinschaft (DFG)), Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim, Germany. doi: 10.1002 / 9783527673919, pp. 1-24.

[0105] Preferably, the zeolite having 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.

[0106] Suitable zeolites having a MEL framework may have a silica to alumina ratio of R(s / a), which may vary from r1 to r2, where r1 and r2 may 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) may be determined by ICP-MS (inductively coupled plasma mass spectrometry) or XRF (X-ray fluorescence).

[0107] Suitable zeolites having a MEL framework may have a BET total specific surface area of A(st), which may range from a1 to a2 m 2Variation of / g, 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 application disclosure is another reason why it exhibits high catalytic activity for the conversion of C8 aromatic hydrocarbons. The BET method can produce the total specific area of the measured material, including the micropore specific area component and the mesopore specific area component. In the disclosure of the present application, the mesopore specific area can be referred to as the mesopore area, the area of the mesopores, or the external area. In the disclosure of the present application, the total specific area can be referred to as the total surface area or the total area.

[0108] Suitable zeolites having a MEL framework can have a mesopore area A(mp) that is ≥ 15% (e.g., ≥ 16%, ≥ 18%, ≥ 20%, ≥ 22%, ≥ 24%, ≥ 25%) of the above - discussed total surface area A(st). In some embodiments, preferably A(mp) ≥ 20% * A(st). In some embodiments, preferably A(mp) ≤ 40% * A(st). In some embodiments, preferably A(mp) ≤ 30% * A(st). The high mesopore area A(mp) of the zeolite material of the present application disclosure is another reason why it exhibits high catalytic activity for the conversion of aromatic hydrocarbons. Without intending to be bound by a particular theory, it is believed that there are a greater number of catalytic sites present on the mesopore area of the zeolite material of the present application disclosure due to the high mesopore area, which 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. In contrast, it will take significantly longer for reactant molecules to diffuse into the deep channels and for product molecules to diffuse out of the deep channels.

[0109] Suitable zeolites having a MEL framework can have a hexane adsorption value v(hs) that can vary 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 typical TGA (thermogravimetric analysis) in the industry.

[0110] Suitable zeolites with a MEL framework can have an α value that can vary 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).

[0111] Optionally, suitable zeolites with a MEL framework can be calcined and subjected to post-treatment such as steaming and / or pickling. Steaming can be carried out 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 for a period of 1 - 20 hours, preferably 2 - 10 hours. Pickling can be carried out using an acid, preferably an organic acid such as a carboxylic acid, preferably an aqueous solution of oxalic acid. Optionally, the steamed 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 at least 1 hour, preferably at least 4 hours, for example, for a period within the range of 5 - 20 hours. Preferably, the treated zeolite with a MEL framework can have a chemical composition having a molar ratio of nSiO2:Al2O3, where n is at least 20, more preferably at least 50, and in some cases at least 100.

[0112] The liquid-phase isomerization catalysts suitable for use in the present disclosure can be formulated with a binder or exist as an unbound free powder. The binder can include binder materials resistant 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, and silica-titania, as well as ternary compositions such as silica-alumina-thoria, silica-alumina-zirconia, silica-alumina-magnesia, and silica-magnesia-zirconia. In a non-limiting example, the binder material can be included in the liquid-phase isomerization catalyst at a concentration from c1 to c2 wt%, based on the total weight of the catalyst, where c1 and c2 can 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. Inclusion of a binder in the isomerization catalyst can enhance its mechanical strength among other factors. A zeolite capable of promoting liquid-phase isomerization can also be blended with a second zeolite as the binder material, thereby forming zeolite-bound zeolite, 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 can 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 can be present in an amount of 10 wt% to about 70 wt% of the zeolite-bound zeolite, or about 20 wt% to about 50 wt% of the zeolite-bound zeolite.

[0113] The liquid-phase isomerization catalyst can be a newly prepared catalyst, a regenerated catalyst, or a mixture thereof. Catalyst regeneration can be carried out in the isomerization unit, for example, by exposing the catalyst to a gas stream containing molecular hydrogen after the catalyst activity has decreased to a critical level at the end of the catalyst cycle. Alternatively, non-in situ regeneration of the catalyst can be achieved, where the spent catalyst is removed from the isomerization unit and heated and / or exposed to a gas stream containing molecular hydrogen in an oxygen-rich environment to reduce the coke on its surface.

[0114] After liquid phase isomerization is performed according to the above disclosure, the method disclosed in the present application may also include separating at least a portion of the para-xylene using a para-xylene recovery unit. More specifically, when two distillation towers are used to process the feed mixture, the method disclosed in the present application may also include: (XI) adding at least a portion of the second overhead stream and / or the isomerized second overhead stream to a para-xylene recovery unit; and (XII) obtaining a first stream rich in para-xylene and a second stream poor in para-xylene from the para-xylene recovery unit. Similarly, when one distillation tower is used to process a feed mixture poor in ethylbenzene, the method may also include: (H) adding at least a portion of the overhead stream and / or the isomerized overhead stream to a para-xylene recovery unit; and (I) obtaining a first stream rich in para-xylene and a second stream poor in para-xylene from the para-xylene recovery unit. The para-xylene recovery unit may utilize any technology suitable for separating a first stream sufficiently rich in para-xylene. Suitable separation techniques may include adsorption chromatography (eg, simulated moving bed chromatography), crystallization (eg, fractional crystallization), or any combination thereof.

[0115] Gas phase isomerization

[0116] In any of the foregoing embodiments, the second stream depleted in para-xylene obtained from the para-xylene recovery unit can be further processed by vapor phase isomerization to produce additional para-xylene. Optionally, the first overhead stream (when obtained) can be combined with the second stream depleted in para-xylene and also undergo vapor phase isomerization, which can isomerize ethylbenzene or other byproducts present therein and also form additional para-xylene. Such vapor phase isomerization can be carried out under vapor phase isomerization conditions in the presence of a suitable vapor phase isomerization catalyst, as described in further detail below.

[0117] 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.

[0118] 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 ≤ 5 and include a molecular sieve having one or more of the following properties:

[0119] 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 a spatial arrangement of atoms that, if packed in three dimensions, describes a crystal structure. Such crystal structures are discussed in "Atlas of Zeolite Framework Types", Fifth Edition, 2001, incorporated herein by reference);

[0120] b) molecular sieves made of second degree building blocks, being two-dimensional stacking of such MWW framework topology unit cells, thereby forming a monolayer of one unit cell thickness, in one embodiment one c-unit cell thickness;

[0121] c) a molecular sieve made of common second-order building blocks, which is a layer of one or more than one unit cell thickness, wherein the layer of more than one unit cell thickness is made of a monolayer of at least two MWW framework topology unit cells stacked, piled or combined. Such stacking of second-order building blocks can be in a regular form, an irregular form, a random form or any combination thereof; and

[0122] d) Molecular sieves made from any regular or random two-dimensional or three-dimensional combination of unit cells having the MWW framework topology.

[0123] 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) , 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.

[0124] In some embodiments, the zeolite having an MWW framework may be contaminated with other crystalline materials such as ferrierite or quartz, which may be present in an amount of ≤ 10 wt % or ≤ 5 wt %.

[0125] The disclosure of the present application also relates to the following non-limiting aspects and / or embodiments:

[0126] A1. A method comprising:

[0127] (I) introducing a feed mixture comprising one or more xylene isomers and C9+ aromatic hydrocarbons into a first distillation column at a feed position on the first distillation column, the first distillation column optionally containing a liquid phase isomerization catalyst loaded therein;

[0128] (II) optionally, contacting a portion of the feed mixture with a liquid phase isomerization catalyst under liquid phase isomerization conditions in a first distillation column;

[0129] (III) obtaining from a first distillation column a first overhead stream comprising meta-xylene, para-xylene, or any combination thereof, a first bottoms stream comprising ortho-xylene and C9+ aromatic hydrocarbons, and optionally a first side stream;

[0130] (IV) optionally, a) obtaining a first side stream from the first distillation column, b) liquid phase isomerization of the first side stream outside the first distillation column under liquid phase isomerization conditions in the presence of a liquid phase isomerization catalyst to produce an isomerized first side stream, and c) returning at least a portion of the isomerized first side stream to the first distillation column;

[0131] (V) optionally, conducting liquid phase isomerization on at least a portion of the first bottoms stream external to the first distillation column under liquid phase isomerization conditions in the presence of a liquid phase isomerization catalyst to produce an isomerized first bottoms stream;

[0132] (VI) feeding at least a portion of the first bottoms stream and / or at least a portion of the isomerized first bottoms stream to a second distillation column optionally containing a liquid phase isomerization catalyst loaded therein;

[0133] (VII) optionally, contacting a portion of the first bottoms stream with a liquid phase isomerization catalyst in a second distillation column under liquid phase isomerization conditions; (VIII) obtaining from the second distillation column a second overhead stream comprising at least ortho-xylene, a second bottoms stream comprising C9+ aromatic hydrocarbons, and optionally a second side stream;

[0134] (IX) optionally, a) obtaining a second side stream from the second distillation column, b) performing liquid phase isomerization of the second side stream outside the second distillation column under liquid phase isomerization conditions in the presence of a liquid phase isomerization catalyst to produce an isomerized second side stream, and c) returning at least a portion of the isomerized second side stream to the second distillation column; and

[0135] (X) optionally, conducting liquid phase isomerization on at least a portion of the second overhead stream external to the second distillation column under liquid phase isomerization conditions in the presence of a liquid phase isomerization catalyst to produce an isomerized second overhead stream;

[0136] wherein liquid phase isomerization is carried out in at least one of (II), (IV), (V), (VII), (IX) or (X) and the second overhead stream and / or the isomerized second overhead stream is enriched in para-xylene.

[0137] A2. The method according to A1, further comprising:

[0138] (XI) feeding at least a portion of the second overhead stream and / or the isomerized second overhead stream to a para-xylene recovery unit; and

[0139] (XII) obtaining a first stream rich in paraxylene and a second stream depleted in paraxylene from a paraxylene recovery unit.

[0140] A3. A method according to A2, wherein the paraxylene recovery unit separates the first stream from the second stream by absorption chromatography, crystallization, or any combination thereof.

[0141] A4. The method according to any one of A1 to A3, 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.

[0142] A5. The process according to any one of A1 to A4, wherein liquid phase isomerization is carried out in (II).

[0143] A6. The process according to any one of A1 to A4, wherein liquid phase isomerization is carried out in (IV).

[0144] A7. The process according to any one of A1 to A4, wherein liquid phase isomerization is carried out in (V).

[0145] A8. The process according to any one of A1 to A4, wherein liquid phase isomerization is carried out in (VII).

[0146] A9. The process according to any one of A1 to A4, wherein liquid phase isomerization is carried out in (IX).

[0147] A10. The process according to any one of A1 to A4, wherein liquid phase isomerization is carried out in (X).

[0148] A11. The process according to any one of A1 to A10, wherein liquid phase isomerization is carried out in one of (II), (IV), (V), (VII), (IX) or (X).

[0149] A12. The process according to any one of A1 to A4, wherein in at least one of (IV), (V), (IX) or (X) liquid phase isomerization is carried out in at least one liquid phase isomerization unit.

[0150] A13. The process according to A12, wherein liquid phase isomerization is carried out in one of (IV), (V), (IX) or (X).

[0151] A14. The method according to A12 or A13, further comprising:

[0152] At least one liquid phase isomerization unit is at least temporarily bypassed.

[0153] A15. A process according to any one of A1 to A4, wherein the liquid phase isomerization is carried out in the presence of C9+ aromatic hydrocarbons in at least one of (II), (IV), (V), (VII) or (IX).

[0154] A16. A process according to A15, wherein the liquid phase isomerization is carried out in the presence of C9+ aromatic hydrocarbons in one of (II), (IV), (V), (VII) or (IX).

[0155] A17. The method according to any one of A2-A16, further comprising:

[0156] Vapor phase isomerization is carried out on at least a portion of the second stream in the presence of a vapor phase isomerization catalyst under vapor phase isomerization conditions, optionally wherein the first overhead stream and the second stream are combined with one another prior to carrying out the vapor phase isomerization.

[0157] A18. The process according to any one of A1 to A17, wherein the feed mixture comprises ethylbenzene and at least a majority of the ethylbenzene is obtained in the first overhead stream.

[0158] A19. A process according to any one of A1 to A18, wherein o-xylene constitutes at least a majority of the one or more xylene isomers in the feed mixture.

[0159] B1. A method comprising:

[0160] (A) providing a feed mixture comprising one or more xylene isomers and C9+ aromatic hydrocarbons, wherein ortho-xylene constitutes at least a majority of the one or more xylene isomers, and the feed mixture is depleted in ethylbenzene;

[0161] (B) optionally, conducting liquid phase isomerization on at least a portion of the feed mixture in the presence of a liquid phase isomerization catalyst under liquid phase isomerization conditions to produce an isomerized feed mixture;

[0162] (C) introducing the feed mixture and / or at least a portion of the isomerized feed mixture into a distillation column at a feed point on the distillation column, the distillation column optionally having a liquid phase isomerization catalyst loaded therein;

[0163] (D) optionally, contacting a portion of the feed mixture with a liquid phase isomerization catalyst in a distillation column under liquid phase isomerization conditions;

[0164] (E) obtaining from the distillation column an ​​overhead stream comprising at least o-xylene, a bottoms stream comprising C9+ aromatic hydrocarbons, and optionally a side stream;

[0165] (F) optionally, a) obtaining a side stream from the distillation column, b) subjecting the side stream to liquid phase isomerization external to the distillation column under liquid phase isomerization conditions in the presence of a liquid phase isomerization catalyst to produce an isomerized side stream, and c) returning at least a portion of the isomerized side stream to the distillation column;

[0166] (G) optionally, conducting liquid phase isomerization on at least a portion of the overhead stream external to the distillation column under liquid phase isomerization conditions in the presence of a liquid phase isomerization catalyst to produce an isomerized overhead stream;

[0167] wherein liquid phase isomerization is carried out in at least one of (B), (D), (F) or (G), and the overhead stream and / or the isomerized overhead stream is enriched in para-xylene.

[0168] B2. The method according to B1, further comprising:

[0169] (H) feeding at least a portion of the overhead stream and / or the isomerized overhead stream to a para-xylene recovery unit; and

[0170] (I) A first stream rich in paraxylene and a second stream poor in paraxylene are obtained from a paraxylene recovery unit.

[0171] B3. The method according to B2, wherein the para-xylene recovery unit separates the first stream from the second stream by absorption chromatography, crystallization, or any combination thereof.

[0172] B4. The method according to any one of B1 to B3, 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.

[0173] B5. The process according to any one of B1 to B4, wherein liquid phase isomerization is carried out in one of (B), (D), (F) or (G).

[0174] B6. A process according to any one of B1 to B4, wherein the liquid phase isomerization is carried out in the presence of C9+ aromatic hydrocarbons in one of (B), (D) or (F).

[0175] B7. The method according to any one of B1-B6, further comprising:

[0176] Vapor phase isomerization is carried out on at least a portion of the second stream in the presence of a vapor phase isomerization catalyst under vapor phase isomerization conditions and / or at least a portion of the second stream is fed to a distillation column.

[0177] In order to facilitate a better understanding of the embodiments of the present disclosure, the following examples of preferred or representative embodiments are given. The following examples should in no way be construed as limiting or defining the scope of the present invention. Example

[0178] A catalyst that is essentially inert to toluene conversion under liquid phase isomerization conditions was prepared as described in U.S. Patent Application Publication No. 2022 / 0134318. The catalyst has a ZSM-11 zeolite framework with a Si:Al2 ratio of 25:1.

[0179] A commercial C9+ heavy aromatics stream was mixed with ortho-xylene to provide a 1:1 wt / wt mixture. The mixture was reacted under various liquid phase isomerization conditions specified in Table 1 below using the above catalyst.

[0180] Table 1

[0181] Under all conditions shown above, the reaction is essentially maintained in the liquid phase because gasification begins at about 300° C. As shown, under liquid phase isomerization reaction conditions, the conversion of C9+ aromatics or xylene loss is minimal, while the conversion of ortho-xylene remains high.

[0182] From the foregoing description, many changes, modifications and variations will be apparent to those of ordinary skill in the art without departing from the spirit or scope of the disclosure of this application, and when numerical limits and numerical upper limits are listed herein, ranges from any lower limit to any upper limit are encompassed.

[0183] For the purpose of all jurisdictions that allow such practice, all documents described herein are incorporated herein by reference, including any priority documents and / or test procedures, as long as they do not contradict this article. As is apparent from the general description and specific embodiments above, although the form of the disclosure has been set forth and described, various changes can be made without departing from the spirit and scope of the 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". Whenever, the method, composition, element or group of elements is preceded by the conjunction "comprising", it should be understood that we also consider the same composition or element group with the conjunction "substantially consisting of...", "consisting of...", "selected from the group consisting of..." or "is" in front of the recording of the composition, one or more elements, and vice versa.

[0184] One or more illustrative embodiments including one or more inventive elements are proposed herein. For the sake of clarity, all features of physical implementation are not described or shown in this application. It should be understood that in the development of the physical implementation scheme including one or more elements of the present invention, in order to achieve the developer's goal, many specific decisions of implementation must be made, such as complying with system-related, business-related, government-related and other constraints, which change from time to time with implementation. Although the developer's efforts may be time-consuming, such efforts are routine tasks for those of ordinary skill in the art who benefit from the disclosure of the application.

[0185] Unless otherwise indicated, all numerical values ​​used in this specification and the related claims to express the amount of ingredients, properties such as molecular weight, reaction conditions, etc. should be understood as being modified in all cases by the term "about". Therefore, unless otherwise indicated, the numerical parameters listed in the following specification and the attached claims are approximate values, which may vary depending on the desired properties sought to be obtained by the 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 claims, each numerical parameter should at least be interpreted in light of the number of reported significant digits and by applying ordinary rounding techniques.

[0186] Whenever a numerical range with a lower limit and an upper limit is disclosed, any value and any included range falling within the range, including the lower limit and the upper limit, is specifically disclosed. In particular, each value range disclosed herein (having the following form "from about a to about b", or equivalently "from about a to b", or equivalently "from about ab") should be understood to enumerate each value and range included in the wider range of values. In addition, the terms in the claims have their ordinary, general meaning unless otherwise explicitly and clearly defined by the patentee. 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.

[0187] Therefore, the present disclosure is well suited to obtain the results and advantages mentioned and inherent therein. The specific embodiments disclosed above are merely illustrative, as it is apparent that different but equivalent ways can be adopted to modify and practice the disclosure of the present application for those of ordinary skill in the art who benefit from the teachings herein. In addition, except as described in the following claims, it is not intended to limit the details of the construction or design shown herein. It is therefore apparent that the specific illustrative embodiments disclosed above can be changed, combined or modified, and all such changes are considered to be within the scope and spirit of the disclosure of the present application. In the absence of any elements not specifically disclosed herein and / or any optional elements disclosed herein, the embodiments disclosed illustratively herein can be appropriately implemented.

Claims

1. A method comprising: (I) introducing a feed mixture comprising one or more xylene isomers and C9+ aromatic hydrocarbons into a first distillation column at a feed position on the first distillation column, the first distillation column optionally containing a liquid phase isomerization catalyst loaded therein; (II) optionally, contacting a portion of the feed mixture with a liquid phase isomerization catalyst under liquid phase isomerization conditions in a first distillation column; (III) obtaining from a first distillation column a first overhead stream comprising meta-xylene, para-xylene, or any combination thereof, a first bottoms stream comprising ortho-xylene and C9+ aromatic hydrocarbons, and optionally a first side stream; (IV) optionally, a) obtaining a first side stream from the first distillation column, b) liquid phase isomerization of the first side stream outside the first distillation column under liquid phase isomerization conditions in the presence of a liquid phase isomerization catalyst to produce an isomerized first side stream, and c) returning at least a portion of the isomerized first side stream to the first distillation column; (V) optionally, conducting liquid phase isomerization on at least a portion of the first bottoms stream external to the first distillation column under liquid phase isomerization conditions in the presence of a liquid phase isomerization catalyst to produce an isomerized first bottoms stream; (VI) feeding at least a portion of the first bottoms stream and / or at least a portion of the isomerized first bottoms stream to a second distillation column optionally containing a liquid phase isomerization catalyst loaded therein; (VII) optionally, contacting a portion of the first bottoms stream with a liquid phase isomerization catalyst in a second distillation column under liquid phase isomerization conditions; (VIII) obtaining from the second distillation column a second overhead stream comprising at least o-xylene, a second bottoms stream comprising C9+ aromatic hydrocarbons, and optionally a second side stream; (IX) optionally, a) obtaining a second side stream from the second distillation column, b) liquid phase isomerization of the second side stream outside the second distillation column under liquid phase isomerization conditions in the presence of a liquid phase isomerization catalyst to produce an isomerized second side stream, and c) returning at least a portion of the isomerized second side stream to the second distillation column; and (X) optionally, conducting liquid phase isomerization on at least a portion of the second overhead stream external to the second distillation column under liquid phase isomerization conditions in the presence of a liquid phase isomerization catalyst to produce an isomerized second overhead stream; wherein liquid phase isomerization is carried out in at least one of (II), (IV), (V), (VII), (IX) and (X), and the second overhead stream and / or the isomerized second overhead stream is enriched in paraxylene.

2. The method according to claim 1, further comprising: (XI) feeding at least a portion of the second overhead stream and / or the isomerized second overhead stream to a para-xylene recovery unit; and (XII) obtaining a first stream rich in paraxylene and a second stream depleted in paraxylene from a paraxylene recovery unit.

3. The process of claim 2, wherein the para-xylene recovery unit separates the first stream from the second stream by absorption chromatography, crystallization, or any combination thereof.

4. The method according to claim 2 or claim 3, further comprising: Vapor phase isomerization is carried out on at least a portion of the second stream in the presence of a vapor phase isomerization catalyst under vapor phase isomerization conditions, optionally wherein the first overhead stream and the second stream are combined with one another prior to carrying out the vapor phase isomerization.

5. The process according to any one of the preceding claims, 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.

6. The process according to any one of the preceding claims, wherein in (II) a liquid phase isomerization is carried out.

7. The process according to any one of the preceding claims, wherein in (IV) a liquid phase isomerization is carried out.

8. The process according to any one of the preceding claims, wherein in (V) a liquid phase isomerization is carried out.

9. The process according to any one of the preceding claims, wherein in (VII) a liquid phase isomerization is carried out.

10. The process according to any one of the preceding claims, wherein in (IX) a liquid phase isomerization is carried out.

11. The process according to any one of the preceding claims, wherein in (X) a liquid phase isomerization is carried out.

12. The process according to any one of the preceding claims, wherein liquid phase isomerization is carried out in one of (II), (IV), (V), (VII), (IX) or (X).

13. The process according to any one of the preceding claims, wherein the liquid phase isomerization in at least one of (IV), (V), (IX) or (X) is carried out in at least one liquid phase isomerization unit.

14. The process according to claim 13, wherein liquid phase isomerization is carried out in one of (IV), (V), (IX) or (X).

15. The method according to claim 13 or claim 14, further comprising: At least one liquid phase isomerization unit is at least temporarily bypassed.

16. A process according to any one of the preceding claims, wherein the liquid phase isomerization is carried out in the presence of C9+ aromatic hydrocarbons in at least one of (II), (IV), (V), (VII) or (IX).

17. The process of claim 16, wherein the liquid phase isomerization is carried out in the presence of C9+ aromatic hydrocarbons in one of (II), (IV), (V), (VII) or (IX).

18. The process according to any one of the preceding claims, wherein the feed mixture comprises ethylbenzene and at least a major portion of the ethylbenzene is obtained in the first overhead stream.

19. A process according to any one of the preceding claims, wherein ortho-xylene constitutes at least a majority of the one or more xylene isomers in the feed mixture.

20. A method comprising: (A) providing a feed mixture comprising one or more xylene isomers and C9+ aromatic hydrocarbons, wherein ortho-xylene constitutes at least a majority of the one or more xylene isomers, and the feed mixture is depleted in ethylbenzene; (B) optionally, conducting liquid phase isomerization on at least a portion of the feed mixture in the presence of a liquid phase isomerization catalyst under liquid phase isomerization conditions to produce an isomerized feed mixture; (C) introducing the feed mixture and / or at least a portion of the isomerized feed mixture into a distillation column at a feed point on the distillation column, the distillation column optionally containing a liquid phase isomerization catalyst loaded therein; (D) optionally, contacting a portion of the feed mixture with a liquid phase isomerization catalyst in a distillation column under liquid phase isomerization conditions; (E) obtaining from the distillation column an ​​overhead stream comprising at least o-xylene, a bottoms stream comprising C9+ aromatic hydrocarbons, and optionally a side stream; (F) optionally, a) obtaining a side stream from the distillation column, b) subjecting the side stream to liquid phase isomerization external to the distillation column under liquid phase isomerization conditions in the presence of a liquid phase isomerization catalyst to produce an isomerized side stream, and c) returning at least a portion of the isomerized side stream to the distillation column; (G) optionally, conducting a liquid phase isomerization on at least a portion of the overhead stream external to the distillation column under liquid phase isomerization conditions in the presence of a liquid phase isomerization catalyst to produce an isomerized overhead stream; wherein liquid phase isomerization is carried out in at least one of (B), (D), (F) or (G), and the overhead stream and / or the isomerized overhead stream is enriched in para-xylene.

21. The method according to claim 20, further comprising: (H) feeding at least a portion of the overhead stream and / or the isomerized overhead stream to a para-xylene recovery unit; and (I) A first stream rich in paraxylene and a second stream poor in paraxylene are obtained from a paraxylene recovery unit.

22. The process of claim 21, wherein the para-xylene recovery unit separates the first stream from the second stream by absorption chromatography, crystallization, or any combination thereof.

23. The process of any one of claims 20 to 22, 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.

24. The process according to any one of claims 20 to 23, wherein liquid phase isomerization is carried out in one of (B), (D), (F) or (G).

25. The process according to any one of claims 20 to 24, wherein the liquid phase isomerization is carried out in the presence of C9+ aromatic hydrocarbons in one of (B), (D) or (F).

26. The method according to any one of claims 20 to 25, further comprising: Vapor phase isomerization is carried out on at least a portion of the second stream in the presence of a vapor phase isomerization catalyst under vapor phase isomerization conditions and / or at least a portion of the second stream is fed to a distillation column.

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