Alkylbenzene-containing desorbent and use thereof for adsorptive separation of meta-aromatic hydrocarbons

Abstract

Relates to a desorption agent containing alkylbenzene and its use for the adsorptive separation of meta-aromatic hydrocarbons, said desorption agent containing or consisting of 20-100 wt% of an alkylbenzene compound of general formula (I) wherein R1, R2 and R3 are independently selected from C1-4 alkyl groups, R4, R5 and R6 are independently selected from hydrogen, C1-4 saturated hydrocarbon groups, C1-4 alkoxy groups and halogens, and 0-80 wt% of C5-C14 saturated aliphatic hydrocarbons. The desorption agent is wide in source, has adsorption selectivity more similar to that of a target product, and is beneficial to improving the yield and purity of the product.

Description

Alkylbenzene-containing desorbent and its use for adsorption separation of meta-aromatic hydrocarbons Technical Field

[0001] The present application relates to the separation and purification of meta-aromatic hydrocarbons, and in particular to an alkylbenzene-containing desorbent and its use in the adsorption separation of meta-aromatic hydrocarbons. Background Art

[0002] Meta-xylene (m-Xylene, MX) is an important basic organic chemical raw material, widely used in many fields such as synthetic resins, pesticides, pharmaceuticals, coatings, and dyes. High-purity meta-xylene is usually separated from a mixed C8 aromatic hydrocarbon containing ethylbenzene, para-xylene, meta-xylene, and o-xylene. Due to the similar boiling points of the four C8 aromatic isomers, they are difficult to separate using conventional distillation methods. Therefore, the main processes for separating meta-xylene include sulfonation and hydrolysis, complexation separation, extractive distillation, and adsorption separation. Among them, adsorption separation has the advantages of being environmentally friendly, pollution-free, corrosion-free, low equipment cost, high product purity and yield, and long adsorbent service life. It is the main development direction of meta-xylene separation technology.

[0003] CN101745364A discloses an adsorbent for adsorbing and separating meta-xylene and a preparation method thereof. The adsorbent comprises Y zeolite exchanged with Group IA metal ions and copper or silver ions and a binder. Toluene is used as a desorbent, with a fast mass transfer rate and a small amount of use.

[0004] CN101772478A discloses a method for separating meta-xylene with a purity of at least 99 wt% by adsorption using a simulated moving bed. The number of moving bed layers can be configured as 12, 13 or 15, and the desorbent is toluene or a mixture of toluene and tetralin.

[0005] CN1939883A discloses a method for separating meta-xylene using a faujasite-type zeolite adsorbent, using tetralin and its alkylated derivatives as desorbents, thereby reducing the cost of recovering and reusing the desorbent.

[0006] CN1379007A discloses a method for co-producing p-xylene and m-xylene including two-stage separation. The method utilizes two separation steps, respectively selecting barium-exchanged X zeolite and potassium-exchanged Y zeolite as adsorbent components, p-diethylbenzene or p-difluorobenzene (first separation step) and toluene, indane or p-methylethylbenzene (second separation step) as desorbents, to produce qualified p-xylene and m-xylene.

[0007] US5900523A discloses the use of sodium-exchanged Y zeolite as an active adsorbent component and indane as a desorbent, thereby recovering meta-xylene in a single extraction raffinate without the need for an expensive fractionation process to remove o-xylene.

[0008] However, using toluene as a desorbent, with its mass fraction in both the extract and raffinate being 80%-90%, requires a high heat load and consumes a lot of energy. Using aromatic hydrocarbons (such as indan or tetralin) and their derivatives, which are scarce, low in content, and difficult to obtain, and have significantly different selective adsorption properties from the target product, as desorbents results in high material and energy consumption, high operating costs, and low target product yields.

[0009] Therefore, it is necessary to find a desorbent with a boiling point significantly different from that of the target product, a wide source, low cost, and the ability to improve the separation effect of the target product, so as to effectively reduce production costs and improve the economic benefits of the device.

[0010] Summary of the Invention

[0011] The purpose of the present application is to provide an alkylbenzene-containing desorbent and its use for the adsorption separation of meta-aromatic hydrocarbons, wherein the desorbent can effectively desorb the target product from the adsorbent, and its boiling point is significantly different from that of the target product, thereby facilitating subsequent separation from the target product by distillation for recycling.

[0012] To achieve the above objectives, the present application provides, on the one hand, a method for using a liquid material comprising 20-100 wt% of an alkylbenzene compound of the following general formula (I) and 0-80 wt% of a C5-C14 saturated aliphatic hydrocarbon or a liquid material consisting thereof as a desorbent for the adsorption separation of meta-aromatic hydrocarbons.

[0013] in:

[0014] R1, R2 and R3, which may be the same or different, are independently selected from C 1-4 of chain alkyl;

[0015] R4, R5 and R6, which may be the same or different, are independently selected from hydrogen, C 1-4 Saturated hydrocarbon group, C 1-4 Alkoxy and halogen.

[0016] On the other hand, the present application provides a method for separating meta-aromatic hydrocarbons from a mixed aromatic hydrocarbon feedstock comprising meta-aromatic hydrocarbons and isomers thereof, the method comprising the following steps:

[0017] 1) contacting the mixed aromatic hydrocarbon feedstock with an adsorbent to adsorb meta-aromatic hydrocarbons, thereby obtaining an adsorbent adsorbed with the meta-aromatic hydrocarbons and a raffinate containing unadsorbed components;

[0018] 2) contacting the adsorbent adsorbed with meta-aromatic hydrocarbons obtained in step 1) with a desorbent to desorb the meta-aromatic hydrocarbons, thereby obtaining an extract containing the meta-aromatic hydrocarbons and the desorbent; and

[0019] 3) performing rectification and separation on the extract obtained in step 2) to obtain the meta-aromatic hydrocarbons and the desorbent,

[0020] Wherein, based on the total amount of the desorbent, the desorbent comprises or consists of 20-100 wt% of the alkylbenzene compound of the above general formula (I) and 0-80 wt% of C5-C14 saturated aliphatic hydrocarbon.

[0021] On the other hand, the present application provides an adsorption-desorbent kit comprising a solid adsorbent and a liquid desorbent, wherein the solid adsorbent comprises at least 90 wt% of a Y-type molecular sieve as an active component, the Y-type molecular sieve having a silica / alumina molar ratio of 4.0-6.0, and the liquid desorbent comprises 20-100 wt% of an alkylbenzene compound having the above-mentioned general formula (I) and 0-80 wt% of a C5-C14 saturated aliphatic hydrocarbon or consists of them.

[0022] The alkylbenzene-containing desorbent of the present application has a wide source. Compared with the toluene desorbent, it has a closer selective adsorption property to meta-aromatics, which can effectively improve the yield of the meta-aromatic target product; and its boiling point is quite different from that of the target product, which is conducive to subsequent separation from the target product by distillation for recycling. For example, when used for the separation of meta-xylene, the boiling point of the desorbent is significantly higher than that of C8 aromatics (for example, it can be more than 30 ° C higher), which is conducive to recycling after recovery from the tower bottom by distillation treatment, greatly reducing the energy consumption required for the current device using low-boiling point desorbents such as toluene to distill a large amount of low-boiling point desorbents to the top of the tower for recovery, effectively saving production costs. The desorbent of the present application is used to separate meta-aromatics from mixed aromatics raw materials by adsorption-desorption, which has strong adaptability to raw materials, and the entire separation operation process can accurately control the process parameters to obtain meta-aromatic products with high purity and yield with high efficiency, which is environmentally friendly and can significantly improve the economic benefits of the comprehensive utilization of C9+ heavy aromatics.

[0023] Other features and advantages of the present application will be described in detail in the subsequent detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The accompanying drawings are used to provide a further understanding of the present application and constitute a part of the specification. Together with the following detailed description, they are used to explain the present application but do not constitute a limitation of the present application. In the accompanying drawings:

[0025] FIG1 is an X-ray diffraction spectrum of the molecular sieve of Adsorbent Preparation Example 1;

[0026] FIG2 is a pulse spectrum diagram of Example 1;

[0027] FIG3 is a pulse spectrum diagram of Example 6;

[0028] FIG4 is a pulse spectrum diagram of Example 9;

[0029] FIG5 is a pulse spectrum diagram of Example 10;

[0030] FIG6 is a pulse spectrum diagram of Comparative Example 1;

[0031] FIG7 is a pulse spectrum diagram of Comparative Example 2;

[0032] FIG8 is a pulse spectrum diagram of Comparative Example 3; and

[0033] FIG9 is a schematic diagram of the simulated moving bed adsorption separation of the present application. DETAILED DESCRIPTION

[0034] The following describes the specific embodiments of the present application in detail with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present application and are not intended to limit the present application.

[0035] The word "exemplary" is used exclusively herein to mean "serving as an example, example, or illustration." Any embodiment described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments. Although various aspects of the embodiments are shown in the drawings, the drawings are not necessarily drawn to scale unless otherwise indicated.

[0036] Any specific numerical value disclosed herein (including the endpoints of a numerical range) is not limited to the exact value of the numerical value, but should be understood to also include values ​​close to the exact value, such as all possible values ​​within ±5% of the exact value. Moreover, for a disclosed numerical range, any combination of the endpoints of the range, between the endpoints and the specific points in the range, and between the specific points can be used to generate one or more new numerical ranges, and these new numerical ranges should also be considered to be specifically disclosed herein.

[0037] Unless otherwise specified, the terms used herein have the same meaning as commonly understood by those skilled in the art. If a term is defined herein and its definition is different from the commonly understood meaning in the art, the definition herein shall prevail.

[0038] In this application, the term "meta-aromatic hydrocarbon" is also referred to as "meta-substituted aromatic hydrocarbon", which refers to an aromatic hydrocarbon compound having only two substituents on the aromatic ring, one of which is in the meta position relative to the other substituent. According to the present application, the substituents on the meta-aromatic hydrocarbon do not contain Group VIA heteroatoms and Group VIIA heteroatoms, and may include, but are not limited to, hydrocarbon groups, amine groups, etc., preferably hydrocarbon groups. Further preferably, the meta-aromatic hydrocarbon is a meta-alkyl aromatic hydrocarbon, that is, a meta-aromatic hydrocarbon in which both substituents are alkyl groups. Particularly preferably, the meta-aromatic hydrocarbon is a C8-C12 meta-aromatic hydrocarbon, more preferably a C8-C12 meta-alkyl aromatic hydrocarbon, such as meta-xylene or 2,7-dimethylnaphthalene.

[0039] In the present application, the term "saturated aliphatic hydrocarbon" has the meaning generally understood in the art, including paraffins and cycloalkanes.

[0040] In the present application, the term "paraffin" has the meaning generally understood in the art, including normal paraffins (also known as straight-chain paraffins) and isoparaffins (also known as branched-chain paraffins).

[0041] In the present application, the term "saturated hydrocarbon group" has the meaning generally understood in the art, including chain alkyl groups and cycloalkyl groups.

[0042] In the present application, the term "chain alkyl" has the meaning generally understood in the art, including straight-chain alkyl and branched-chain alkyl.

[0043] In this application, the term "C8" refers to an aromatic hydrocarbon having 8 carbon atoms, and the term "C8 aromatic hydrocarbon" refers to an aromatic hydrocarbon having 8 carbon atoms.

[0044] In this application, the term "C9" refers to aromatic hydrocarbons having 9 carbon atoms, and the term "C9+ aromatic hydrocarbons" refers to aromatic hydrocarbons having more than 9 carbon atoms, also referred to herein as "heavy aromatic hydrocarbons".

[0045] In this application, unless otherwise indicated, all pressures given are gauge pressures.

[0046] In this application, except for the contents explicitly stated, any matters or issues not mentioned are directly applicable to those known in the art without any changes. Moreover, any embodiment described herein can be freely combined with one or more other embodiments described herein, and the technical solutions or technical ideas formed thereby are deemed to be part of the original disclosure or original record of this application, and should not be regarded as new content not disclosed or anticipated herein, unless a person skilled in the art considers that the combination is obviously unreasonable.

[0047] All patent and non-patent literature, including but not limited to textbooks and journal articles, mentioned herein are incorporated by reference in their entirety.

[0048] In the adsorption system, the metal ions in the molecular sieve crystals of the active component of the adsorbent are located above the aromatic ring of the meta-aromatic hydrocarbon and are biased towards the side of the aromatic ring with substituents. Therefore, the area with a stronger positive electrostatic potential is biased towards the side of the aromatic ring, and the positive extreme value is located on one side of the aromatic ring. The two substituents of the meta-aromatic hydrocarbon are located on one side, and the angle is about 120 degrees. The negative electrostatic potential of the aromatic ring is distributed on one side of the aromatic ring, and the dispersion is good, and the negative extreme value site is relatively not centered. Therefore, the area on one side of the aromatic ring is the position where the electrostatic attraction between the adsorbent and the adsorbate is the strongest. The adsorbent can preferentially adsorb meta-aromatic hydrocarbons relative to other impurities. After other impurities are removed from this system, the target component needs to be desorbed from the adsorbent to produce a high-purity component for processing and utilization. At this time, whether high-efficiency, high-recycle rate and high-purity desorption can be carried out depends on the properties of the desorbent. There is a certain interaction with the adsorbent, and this force cannot be too strong or too weak. If it is too strong, the target component will be quickly desorbed and cannot be effectively distinguished from other impurities, and the product purity cannot be guaranteed. If it is too weak, the desorption process will be very slow, the consumption will be very large, the timeliness and economy will be too poor, and the target component will be difficult to desorb, which will occupy the effective pore volume of the adsorbent and affect the next processing volume. At the same time, the negative electrostatic potential distribution area of ​​the desorbent must match the positive electrostatic potential distribution area of ​​the metal ion, the target component and the action area of ​​the impurity molecules. Only when the interaction between the desorbent, the adsorbent and the target component is appropriate, can the target component be replaced from the adsorbent, and the adsorption and desorption process can be repeated quickly and efficiently to obtain a high-purity product. Therefore, finding a desorbent with a suitable negative electrostatic potential distribution area and suitable interaction forces with the adsorbent and the adsorbate can improve the adsorption and separation effect. In addition, in the adsorbent-desorbent system, there are intermolecular interactions between the target product and other impurity components and desorbent molecules, such as dispersion force, induction force, and mutual repulsion force, which will affect the diffusion coefficient of each component molecule within and between adsorbent crystals, thereby affecting the preferential adsorption selectivity of each component in this adsorption-desorption system. Therefore, different raw material compositions and different adsorption-desorption systems will produce different adsorption effects.

[0049] As described above, in a first aspect, the present application provides a method for using a liquid material comprising 20-100 wt% of an alkylbenzene compound of the following general formula (I) and 0-80 wt% of a C5-C14 saturated aliphatic hydrocarbon or consisting thereof as a desorbent for the adsorptive separation of meta-aromatic hydrocarbons.

[0050] According to the present application, in the general formula (I), R1, R2 and R3, which may be the same or different, are independently selected from C 1-4chain alkyl, such as methyl, ethyl, propyl, butyl, including their various isomers; preferably at least one of R1, R2 and R3 is methyl, more preferably at least two are methyl, and further preferably all are methyl.

[0051] According to the present application, in the general formula (I), R4, R5 and R6, which may be the same or different, are independently selected from hydrogen, C 1-4 Saturated hydrocarbon group, C 1-4 Alkoxy and halogen, wherein the C 1-4 Saturated hydrocarbon groups include, but are not limited to, methyl, ethyl, propyl, butyl, isopropyl, isobutyl, tert-butyl, cyclopropyl, cyclobutyl, and various isomers thereof, preferably methyl; the C 1-4 Alkoxy includes but is not limited to methoxy, ethoxy, propoxy, butoxy, cyclopropyloxy, cyclobutyloxy, including their various isomers, and the halogen includes but is not limited to fluorine, chlorine and bromine. Preferably, at least one of R4, R5 and R6 is hydrogen or C 1-4 Saturated hydrocarbon group, such as R4 or R6 is C 1-4 Saturated hydrocarbon groups, more preferably at least two of which are independently hydrogen or C 1-4 Saturated hydrocarbon group, for example, R4 and R6 are C 1-4 Saturated hydrocarbon group, further preferably three are independently hydrogen or C 1-4 The saturated hydrocarbon groups are particularly preferably all three of which are hydrogen.

[0052] In certain preferred embodiments, in formula (I), at least one of R1, R2 and R3 is a methyl group, and R4, R5 and R6 are independently hydrogen or C 1-4 Saturated hydrocarbon group.

[0053] In a further preferred embodiment, in formula (I), at least two of R1, R2 and R3 are methyl, and R4, R5 and R6 are independently hydrogen or C 1-4 Saturated hydrocarbon groups, at least one of which is hydrogen.

[0054] In a further preferred embodiment, in formula (I), at least two of R1, R2 and R3 are methyl, and R5 and R6 are independently hydrogen or C 1-4 A saturated hydrocarbon group, at least two of which are hydrogen, preferably all three are hydrogen.

[0055] According to the present application, the liquid material as the desorbent can be a C9+ heavy aromatic hydrocarbon, a C9+ heavy aromatic hydrocarbon derivative or a mixture thereof with an alkane having a specific structure. Preferably, the C9+ heavy aromatic hydrocarbon is selected from one or more of the following: 1,2,3-trisubstituted C9+ alkylbenzene or its derivatives, 1,2,3,4-tetrasubstituted C9+ alkylbenzene or its derivatives, 1,2,3,4,5-pentasubstituted C9+ alkylbenzene or its derivatives. In a particularly preferred embodiment, the alkylbenzene compound of formula (I) is selected from 1,2,3-trimethylbenzene (also referred to as trimethylbenzene herein), 1,2,3,4-tetramethylbenzene (also referred to as trimethylbenzene herein), 1,2,3,4,5-pentamethylbenzene (also referred to as trimethylbenzene herein) and 3-ethyl o-xylene, more preferably 1,2,3-trimethylbenzene or 1,2,3,4-tetramethylbenzene.

[0056] In recent years, with the commissioning of large-scale integrated naphtha reforming, ethylene, and aromatics complexes in my country, heavy aromatics production has continued to increase. The C9+ heavy aromatics in catalytic reforming products typically reach a mass fraction of 20%-50%, with low heteroatom and olefin content and excellent stability, making them high-quality raw materials for further processing and utilization. The mass fraction of trimethylbenzenes in reformed C9+ heavy aromatics ranges from 15%-30%, and the mass fraction of tetramethylbenzenes is 3%-8%. Currently, the unsatisfactory and mesitylene components of these trimethylbenzenes and tetramethylbenzenes are separated through mature industrial processes and used to produce trimesic anhydride and trimesic acid. However, the utilization of trimethylbenzenes and tetramethylbenzenes is relatively limited, with most of them being sold as high-boiling-point aromatic solvent oils with lower added value. This application utilizes C9+ heavy aromatics, such as 1,2,3-trimethylbenzene, as a desorbent for separating meta-aromatics, which can not only achieve high-value utilization of C9+ heavy aromatics resources, but also help reduce the energy consumption and material consumption of meta-aromatic adsorption separation equipment, which can not only bring considerable economic benefits to production enterprises, but also help enterprises save energy and reduce consumption.

[0057] In a preferred embodiment, the adsorptive separation comprises separating the meta-aromatic hydrocarbon from a mixed aromatic hydrocarbon feedstock comprising the meta-aromatic hydrocarbon and at least one isomer thereof by adsorption and desorption.

[0058] In a further preferred embodiment, the meta-aromatic hydrocarbon is a C8-C12 meta-aromatic hydrocarbon, more preferably a C8-C12 meta-alkyl aromatic hydrocarbon, such as meta-xylene or 2,7-dimethylnaphthalene.

[0059] In certain further preferred embodiments, the meta-aromatic hydrocarbon is meta-xylene, and the mixed aromatic hydrocarbon feedstock is a C8 aromatic hydrocarbon mixed feedstock comprising meta-xylene and at least one other C8 aromatic hydrocarbon selected from para-xylene, o-xylene and ethylbenzene. Further preferably, the C8 aromatic hydrocarbon mixed feedstock comprises 5-95wt% of meta-xylene. Particularly preferably, the mixed aromatic hydrocarbon feedstock comprises 5-94wt% of meta-xylene and 6-95wt% of para-xylene, more preferably 5-90wt% of meta-xylene and 10-95wt% of para-xylene. For example, the content of meta-xylene in the mixed aromatic hydrocarbon feedstock may be 10-90wt%, 20-80wt%, 30-70wt% or 40-60wt%; the content of para-xylene in the mixed aromatic hydrocarbon feedstock may be 6-50wt%, 7-40wt%, 8-30wt% or 10-25wt%.

[0060] In certain particularly preferred embodiments, the meta-aromatic hydrocarbon is meta-xylene, and the mixed aromatic hydrocarbon feedstock contains 20-60 wt% of meta-xylene, 10-30 wt% of para-xylene, 10-30 wt% of o-xylene and 5-20 wt% of ethylbenzene, for example, contains 40-55 wt% of meta-xylene, 15-25 wt% of para-xylene, 15-25 wt% of o-xylene and 5-15 wt% of ethylbenzene.

[0061] In some further preferred embodiments, the meta-aromatic hydrocarbon is 2,7-dimethylnaphthalene, and the mixed aromatic hydrocarbon feedstock is a C12 aromatic hydrocarbon mixed feedstock comprising 2,7-dimethylnaphthalene (meta-position) and at least one other C12 aromatic hydrocarbon selected from 1,6-dimethylnaphthalene (non-para-non-ortho-position), 2,6-dimethylnaphthalene (para-position) and 1,8-dimethylnaphthalene (ortho-position), 1,2-dimethylnaphthalene, 1,3-dimethylnaphthalene, 1,4-dimethylnaphthalene, 1,5-dimethylnaphthalene, 1,7-dimethylnaphthalene, and 2,3-dimethylnaphthalene. Still more preferably, the C12 aromatic hydrocarbon mixed feedstock comprises 5-95 wt% of 2,7-dimethylnaphthalene.

[0062] In a preferred embodiment, the adsorbent used in the adsorptive separation comprises at least 90 wt% of a Y-type molecular sieve as an active component, wherein the Y-type molecular sieve has a silica to alumina molar ratio of 4.0 to 6.0, preferably 4.3 to 5.7. Other features of the adsorbent are as described in the second aspect of the application below.

[0063] In a preferred embodiment, based on the total amount of the liquid material, the liquid material comprises 30-95wt%, preferably 30-80wt%, more preferably 30-50wt% of the alkylbenzene compound, and 5-70wt%, preferably 20-70wt%, more preferably 50-70wt% of an alkane selected from C5-C14 normal alkanes, preferably C6-C10 normal alkanes, more preferably C6-C8 normal alkanes, or consists of the same. The inventors of the present application have found that including a certain amount of C5-C14 normal alkanes in the liquid material as a desorbent is beneficial to alleviating the strong desorption performance of the aromatic desorbent and is beneficial to reducing the half-width of the separation peak, thereby improving the separation degree between the target component and other components, reducing the total amount of desorbent required, and reducing material consumption and energy consumption.

[0064] In a particularly preferred embodiment, the meta-aromatic hydrocarbon is meta-xylene, the mixed aromatic hydrocarbon feedstock comprises 20-60 wt% of meta-xylene, 10-30 wt% of para-xylene, 10-30 wt% of o-xylene and 5-20 wt% of ethylbenzene, the alkylbenzene compound of formula (I) is selected from 1,2,3-trimethylbenzene, 1,2,3,4-tetramethylbenzene, 1,2,3,4,5-pentamethylbenzene and 3-ethyl-o-xylene; based on the total amount of the liquid material, the liquid material comprises 30-70 wt% of the alkylbenzene compound and 30-70 wt% of an alkane selected from C5-C14 normal alkanes; and the charge-balancing cation of the adsorbent is selected from Na + 、Sr 2+ 、Ba 2+ and Ag + , and the adsorbent contains 0.05-0.8 wt%, preferably 0.1-0.5 wt% of adsorbed water.

[0065] In a second aspect, the present application provides a method for separating meta-aromatic hydrocarbons from a mixed aromatic hydrocarbon feedstock comprising meta-aromatic hydrocarbons and isomers thereof, the method comprising the following steps:

[0066] 1) contacting the mixed aromatic hydrocarbon feedstock with an adsorbent to adsorb meta-aromatic hydrocarbons, thereby obtaining an adsorbent adsorbed with the meta-aromatic hydrocarbons and a raffinate containing unadsorbed components;

[0067] 2) contacting the adsorbent adsorbed with meta-aromatic hydrocarbons obtained in step 1) with a desorbent to desorb the meta-aromatic hydrocarbons, thereby obtaining an extract containing the meta-aromatic hydrocarbons and the desorbent; and

[0068] 3) performing rectification and separation on the extract obtained in step 2) to obtain the meta-aromatic hydrocarbons and the desorbent,

[0069] Wherein, based on the total amount of the desorbent, the desorbent comprises or consists of 20-100 wt% of an alkylbenzene compound having the following general formula (I) and 0-80 wt% of a C5-C14 saturated aliphatic hydrocarbon,

[0070] wherein R1, R2, R3, R4, R5 and R6 are as defined above.

[0071] In certain preferred embodiments, in formula (I), at least one of R1, R2 and R3 is a methyl group, and R4, R5 and R6 are independently hydrogen or C 1-4 Saturated hydrocarbon group.

[0072] In a further preferred embodiment, in formula (I), at least two of R1, R2 and R3 are methyl, and R4, R5 and R6 are independently hydrogen or C 1-4 Saturated hydrocarbon groups, at least one of which is hydrogen.

[0073] In a further preferred embodiment, in formula (I), at least two of R1, R2 and R3 are methyl, and R5 and R6 are independently hydrogen or C 1-4 A saturated hydrocarbon group, at least two of which are hydrogen, preferably all three are hydrogen.

[0074] In a particularly preferred embodiment, the alkylbenzene compound of formula (I) is selected from 1,2,3-trimethylbenzene, 1,2,3,4-tetramethylbenzene, 1,2,3,4,5-pentamethylbenzene and 3-ethyl-o-xylene, preferably 1,2,3-trimethylbenzene or 1,2,3,4-tetramethylbenzene.

[0075] In a preferred embodiment, the meta-aromatic hydrocarbon is a C8-C12 meta-aromatic hydrocarbon, preferably a C8-C12 meta-alkyl aromatic hydrocarbon, such as meta-xylene or 2,7-dimethylnaphthalene.

[0076] In certain further preferred embodiments, the meta-aromatic hydrocarbon is meta-xylene, and the mixed aromatic hydrocarbon feedstock is a C8 aromatic hydrocarbon mixed feedstock comprising meta-xylene and at least one other C8 aromatic hydrocarbon selected from para-xylene, o-xylene and ethylbenzene. Further preferably, the C8 aromatic hydrocarbon mixed feedstock comprises 5-95wt% of meta-xylene. Particularly preferably, the mixed aromatic hydrocarbon feedstock comprises 5-94wt% of meta-xylene and 6-95wt% of para-xylene, more preferably 5-90wt% of meta-xylene and 10-95wt% of para-xylene. For example, the content of meta-xylene in the mixed aromatic hydrocarbon feedstock may be 10-90wt%, 20-80wt%, 30-70wt% or 40-60wt%; the content of para-xylene in the mixed aromatic hydrocarbon feedstock may be 6-50wt%, 7-40wt%, 8-30wt% or 10-25wt%.

[0077] In some further preferred embodiments, the meta-aromatic hydrocarbon is 2,7-dimethylnaphthalene, and the mixed aromatic hydrocarbon feedstock is a C12 aromatic hydrocarbon mixed feedstock comprising 2,7-dimethylnaphthalene (meta-position) and at least one other C12 aromatic hydrocarbon selected from 1,6-dimethylnaphthalene (non-para-non-ortho-position), 2,6-dimethylnaphthalene (para-position), and 1,8-dimethylnaphthalene (ortho-position). Even more preferably, the C12 aromatic hydrocarbon mixed feedstock comprises 5-95 wt% of 2,7-dimethylnaphthalene.

[0078] The present application has no strict restrictions on the source of the mixed aromatic feedstock. In certain exemplary embodiments, the mixed aromatic feedstock, especially the C8 aromatic mixed feedstock, can come from a catalytic reforming unit, a disproportionation and transalkylation unit, a toluene selective disproportionation unit, an isomerization unit and / or a paraxylene adsorption separation unit.

[0079] In a preferred embodiment, based on the total amount of the desorbent, the desorbent comprises 30-95 wt%, preferably 30-80 wt%, more preferably 30-50 wt% of the alkylbenzene compound, and 5-70 wt%, preferably 20-70 wt%, more preferably 50-70 wt% of an alkane selected from C5-C14 normal alkanes, preferably C6-C10 normal alkanes, more preferably C6-C8 normal alkanes, or consists of the same.

[0080] In a preferred embodiment, the adsorbent used in step 1) comprises at least 90 wt% of a Y-type molecular sieve as an active component, and the silicon oxide / aluminum oxide molar ratio of the Y-type molecular sieve is 4.0-6.0, preferably 4.3-5.7. Further preferably, the crystallite size of the Y-type molecular sieve is 0.5-2.0 μm, preferably 0.8-1.2 μm. In certain exemplary embodiments, the finished spheres of the adsorbent have a toluene adsorption capacity of 155-220 mg / g, a calcined bulk density of 0.645-0.867 g / mL, and a 130N crushing rate of 0.3-5.0 wt%.

[0081] In a further preferred embodiment, the adsorbent contains 0.05-2wt%, preferably 0.05-1wt%, more preferably 0.05-0.8wt%, and further preferably 0.1-0.5wt% of adsorbed water. The inventors of the present application have found that the water molecules in the adsorbent have the function of regulating the adsorption capacity and adsorption performance. The water content in the adsorbent is different, and the preferential selectivity of the adsorbent to the target component is different. Due to the polarization effect of water molecules, the polarization strength of the cations outside the adsorbent molecular sieve crystal framework will be affected by the water molecules, and the interaction between the adsorbent and the adsorbate, especially the electrostatic interaction between the adsorbent and the target component will change. Therefore, the selectivity of the adsorbent and the mass transfer efficiency of the adsorbate in the adsorption system will change. In addition, if the mass fraction of water molecules is high, a large amount of water molecules occupy part of the effective pore volume in the adsorbent molecular sieve crystal framework, which reduces the adsorption capacity of the target component. When the water content exceeds a certain range, the molecular sieve crystal structure of the adsorbent will undergo irreversible hydrothermal damage, resulting in a significant reduction in adsorption capacity and adsorption selectivity. Therefore, a suitable water content in the adsorbent is conducive to the adsorbent to stably exert the optimal adsorption performance for a long time.

[0082] This application does not have strict requirements for the preparation method of the adsorbent. In certain exemplary embodiments, the adsorbent is prepared by a rolling ball mixing method, and the raw material composition is 90-99wt% of Y-type molecular sieve, 0.5-9wt% of binder and 0.5-1wt% of molding aid. Preferably, the binder is kaolin, bentonite and / or attapulgite, and the molding aid is lignin, sesbania powder, dry starch, carboxymethyl cellulose and / or activated carbon. After preparation, the adsorbent is composed of 91-99.5wt% of Y-type molecular sieve and 0.5-9wt% of binder.

[0083] In a further preferred embodiment, the adsorbent further comprises one or more, for example one or two, of Group IA, IIA and IB metal ions as charge-balancing cations, wherein the Group IA metal ions are preferably selected from Li+ and Na + , the Group IIA metal ion is preferably selected from Mg 2+ 、Sr 2+ and Ba 2+ , the IB group metal ion is preferably Ag + Preferably, the total amount of Group IA, IIA and IB metals in the adsorbent is 10-45% calculated as metal oxides and based on the total weight of the adsorbent.

[0084] In a particularly preferred embodiment, the adsorbent comprises at least 90 wt% of NaY molecular sieve as an active component, and the adsorbent is preferably treated with metal ion exchange, i.e., Na in the molecular sieve is exchanged with other metal ions. +ions, so that the metal ion exchange degree is 78.0-99.9%. Particularly preferably, the molar concentration of the metal salt during the ion exchange process is 0.05-0.65 mol / L, preferably 0.15-0.50 mol / L.

[0085] All features of the adsorbent disclosed in the second aspect of the present application are also applicable to the adsorbents described in the first and third aspects of the present application, and therefore will not be described in detail in the first and third aspects of the present application.

[0086] In a particularly preferred embodiment, the meta-aromatic hydrocarbon is meta-xylene, the mixed aromatic hydrocarbon feedstock comprises 20-60 wt% of meta-xylene, 10-30 wt% of para-xylene, 10-30 wt% of o-xylene and 5-20 wt% of ethylbenzene, the alkylbenzene compound of formula (I) is selected from 1,2,3-trimethylbenzene, 1,2,3,4-tetramethylbenzene, 1,2,3,4,5-pentamethylbenzene and 3-ethyl o-xylene; based on the total amount of the desorbent, the desorbent comprises 30-70 wt% of the alkylbenzene compound and 30-70 wt% of an alkane selected from C5-C14 normal alkanes; and the charge-balancing cation of the adsorbent is selected from Na + 、Sr 2+ 、Ba 2+ and Ag + , and the adsorbent contains 0.05-0.8 wt%, preferably 0.1-0.5 wt% of adsorbed water.

[0087] In a preferred embodiment, the operating conditions of the adsorption in step 1) and the desorption in step 2) each independently include:

[0088] The temperature is 100-190°C, preferably 110-180°C, more preferably 120-160°C; and / or

[0089] The pressure is 0.6-1.6 MPa, preferably 0.8-1.0 MPa.

[0090] According to the application, the method for separating meta-aromatics can be adopted but is not limited to simulated moving bed to implement. Usually, simulated moving bed can comprise one or more adsorption towers, contains the bed of multiple loading adsorbent in each tower, each bed all has its own material inlet and outlet pipeline, material flows from top to bottom in the adsorption tower, and material between towers is transported by circulating pump, and material flows through the adsorption bed of different adsorption towers to form a closed loop connected end to end. The material entering and exiting the adsorption bed at least comprises raw material (F), desorbent (D), extract (E) and raffinate (R). The material entering and exiting the simulated moving bed is divided into desorption zone, purification zone, adsorption zone and isolation zone by the adsorption bed therein, the adsorption bed between desorbent injection and extract extraction is desorption zone, the adsorption bed between extract extraction and raw material injection is purification zone, the adsorption bed between raw material injection and raffinate extraction is adsorption zone, the adsorption bed temperature is described adsorption temperature, and the adsorption bed between raffinate extraction and desorbent injection is isolation zone. During simulated moving bed operation, the positions at which each stream enters and exits the adsorption tower bed change periodically. Multi-way rotary valves or programmable on / off valves can be used to control the entry and exit of each stream into a specific bed. At a given moment, each stream is connected to a specific bed. At intervals of a certain time, known as a step time, the entry and exit positions of each stream move down one adsorption bed. The time required for a stream to enter an adsorption bed (or exit an adsorption bed) and return to its starting position after passing through all adsorption beds is considered a cycle.

[0091] In certain preferred embodiments, steps 1) and 2) are performed using a simulated moving bed, comprising multiple adsorption beds loaded with adsorbent, each bed being provided with a corresponding material inlet and outlet pipeline, and the material entering and exiting the simulated moving bed divides the adsorption beds into a desorption zone, a purification zone, an adsorption zone, and an isolation zone. Preferably, the ratio of the number of beds in the simulated moving bed, the adsorption zone, the purification zone, the desorption zone, and the isolation zone is 25±10%:38±15%:25±5%:12±4%.

[0092] In a further preferred embodiment, the mass flow rate ratio of the desorbent entering the simulated moving bed to the mixed aromatic feedstock is 0.01-6.0, preferably 0.01-5.5, more preferably 0.01-5.0.

[0093] In a further preferred embodiment, the flow rate of the mixed aromatic hydrocarbon feedstock entering the simulated moving bed relative to the unit mass of adsorbent is in the range of 0.1-8 kg / (h·kg adsorbent), preferably 0.15-8 kg / (h·kg adsorbent), and more preferably 0.17-8 kg / (h·kg adsorbent).

[0094] In a further preferred embodiment, the step time of the simulated moving bed is 60-160 seconds, preferably 70-120 seconds.

[0095] In a further preferred embodiment, one cycle of the simulated moving bed is 12-70 minutes, preferably 20-40 minutes.

[0096] In the method of the present application, by selecting a suitable desorbent and corresponding operating conditions, the separation effect can be improved when a simulated moving bed is used to carry out the separation of step 1) and step 2), including purity and yield, and the raw material processing capacity can be increased, and material consumption and energy consumption can be reduced, including the pipeline flow rate and circulation flow rate of each logistics, as well as the energy consumption for recycling and reuse.

[0097] According to the present application, the extract obtained in step 2) comprises meta-aromatics and part of the desorbent, and the difference in boiling points between the two can be utilized to separate and recover the two by the distillation in step 3). For example, when the meta-aromatics is meta-xylene, a rectifying tower can be utilized to reclaim the desorbent in the extract in the tower kettle in step 3), and the overhead stream obtains a high-purity meta-xylene product through a subsequent product tower. In addition, when a simulated moving bed is employed, the main component of the raffinate obtained in step 1) is the desorbent and other components in the raw material except meta-xylene, and a rectifying tower can be utilized to reclaim the desorbent in the raffinate in the tower kettle. The raffinate oil obtained from the tower top can then be subjected to corresponding subsequent processing and separation, or can be used as an isomerization feed for an aromatics unit.

[0098] In a third aspect, the present application provides an adsorption-desorbent kit comprising a solid adsorbent and a liquid desorbent, wherein the solid adsorbent comprises at least 90 wt% of a Y-type molecular sieve as an active component, and the Y-type molecular sieve has a silicon oxide / aluminum oxide molar ratio of 4.0-6.0, preferably 4.3-5.7, and the liquid desorbent comprises 20-100 wt% of an alkylbenzene compound having the following general formula (I) and 0-80 wt% of a C5-C14 saturated aliphatic hydrocarbon or consists thereof,

[0099] wherein R1, R2, R3, R4, R5 and R6 are as defined above.

[0100] In certain preferred embodiments, in formula (I), at least one of R1, R2 and R3 is a methyl group, and R4, R5 and R6 are independently hydrogen or C 1-4 Saturated hydrocarbon group.

[0101] In a further preferred embodiment, in formula (I), at least two of R1, R2 and R3 are methyl, and R4, R5 and R6 are independently hydrogen or C 1-4 Saturated hydrocarbon groups, at least one of which is hydrogen.

[0102] In a further preferred embodiment, in formula (I), at least two of R1, R2 and R3 are methyl, and R5 and R6 are independently hydrogen or C 1-4 A saturated hydrocarbon group, at least two of which are hydrogen, preferably all three are hydrogen.

[0103] In a particularly preferred embodiment, the alkylbenzene compound of formula (I) is selected from 1,2,3-trimethylbenzene, 1,2,3,4-tetramethylbenzene, 1,2,3,4,5-pentamethylbenzene and 3-ethyl-o-xylene, preferably 1,2,3-trimethylbenzene or 1,2,3,4-tetramethylbenzene.

[0104] In a preferred embodiment, based on the total amount of the liquid desorbent, the desorbent comprises 30-95 wt%, preferably 30-80 wt%, more preferably 30-50 wt% of the alkylbenzene compound, and 5-70 wt%, preferably 20-70 wt%, more preferably 50-70 wt% of an alkane selected from C5-C14 normal alkanes, preferably C6-C10 normal alkanes, more preferably C6-C8 normal alkanes, or consists of the same.

[0105] In a preferred embodiment, the solid adsorbent contains 0.05-2 wt%, preferably 0.05-1 wt%, more preferably 0.05-0.8 wt%, further preferably 0.1-0.5 wt% of adsorbed water.

[0106] In a particularly preferred embodiment, the liquid desorbent comprises 30-70 wt% of the alkylbenzene compound and 30-70 wt% of an alkane selected from C5-C14 normal alkanes, based on the total amount of the liquid desorbent; and the charge-balancing cation of the solid adsorbent is selected from Na + 、Sr 2+ 、Ba 2+ and Ag + , and the adsorbent contains 0.05-0.8 wt%, preferably 0.1-0.5 wt% of adsorbed water.

[0107] Other features of the adsorbent used in the third aspect of the present application are as described in the second aspect of the present application and will not be repeated here.

[0108] In certain preferred embodiments, the present application provides the following technical solutions:

[0109] 1. A method for separating high-purity meta-xylene by adsorption using a heavy desorbent, comprising: introducing a C8 aromatic hydrocarbon mixed feedstock into an adsorbent, wherein the meta-xylene in the feedstock is adsorbed by the adsorbent, and the non-adsorbed components are discharged as a raffinate; introducing a heavy desorbent into the adsorbent to desorb the adsorbed meta-xylene to obtain an extract; subjecting the extract containing the desorbent and the raffinate to separate distillation, respectively, to obtain meta-xylene and other C8 aromatic hydrocarbon components at the top of a distillation tower; and recovering the desorbent in the bottom of the distillation tower.

[0110] 2. The method as described in item 1 is characterized in that the heavy desorbent is one or more selected from the following: 1,2,3-trisubstituted C9+ alkylbenzene or its derivatives, 1,2,3,4-tetrasubstituted C9+ alkylbenzene or its derivatives, 1,2,3,4,5-pentasubstituted C9+ alkylbenzene or its derivatives.

[0111] 3. The method according to item 1, characterized in that the heavy desorbent is a mixture of one or more selected from the following and alkanes, wherein the alkanes are preferably C5-C8 normal alkanes, and the content is not higher than 80 wt%: 1,2,3-trisubstituted C9+ alkylbenzene or its derivatives, 1,2,3,4-tetrasubstituted C9+ alkylbenzene or its derivatives, 1,2,3,4,5-pentasubstituted C9+ alkylbenzene or its derivatives.

[0112] 4. The method as described in item 2 or 3, characterized in that the 1,2,3-trisubstituted C9+ alkylbenzene is 1,2,3-trimethylbenzene and 3-ethyl o-xylene, the 1,2,3,4-tetrasubstituted C9+ alkylbenzene is 1,2,3,4-tetramethylbenzene, and the 1,2,3,4,5-pentasubstituted C9+ alkylbenzene is 1,2,3,4,5-pentamethylbenzene.

[0113] 5. The method according to any one of items 1 to 4, characterized in that the active component of the adsorbent is a Y-type molecular sieve, and its silicon oxide / aluminum oxide molar ratio is 4.0-6.0, preferably 4.3-5.7.

[0114] 6. The method as described in item 5 is characterized in that the particle size of the Y-type molecular sieve is 0.5-2.0 μm, preferably 0.8-1.2 μm.

[0115] 7. The method according to any one of items 1 to 4, characterized in that the adsorbent contains no more than 2 wt%, preferably no more than 1 wt%, more preferably no more than 0.8 wt% of adsorbed water.

[0116] 8. The method according to items 1 to 4, characterized in that the active component of the adsorbent is a Y-type molecular sieve, and the charge-balancing cations of the adsorbent are one or two metal ions from groups IA, IIA and IB, preferably the metal ions from group IA are Li+ and Na+.+ One or two of the metal ions in Group IIA are Mg 2+ 、Sr 2+ and Ba 2+ One or two of the metal ions in group IB are Ag. + .

[0117] 9. The method according to items 1 to 4, characterized in that metal ion exchange is performed on the adsorbent whose active component is NaY molecular sieve, and the molar concentration of the metal salt during the ion exchange process is 0.05-0.65 mol / L, preferably 0.15-0.50 mol / L.

[0118] 10. The method according to any one of items 1 to 9, characterized in that the adsorption temperature is 100-190°C, preferably 110-180°C, and more preferably 120-160°C.

[0119] 11. The method according to any one of items 1 to 10, characterized in that the adsorption pressure is 0.6-1.6 MPa, preferably 0.8-1.0 MPa.

[0120] 12. The method according to any one of items 1 to 11, characterized in that the raw materials come from a catalytic reforming unit, a disproportionation and transalkylation unit, a toluene shape-selective disproportionation unit, an isomerization unit and / or a paraxylene adsorption separation unit.

[0121] 13. The method according to any one of items 1 to 12 is characterized in that the rolling ball mixture used in the adsorbent preparation process is composed of: 90-99wt% Y-type molecular sieve, 0.5-9wt% binder and 0.5-1wt% molding aid, and the adsorbent is composed of: 91.0-99.5wt% Y-type molecular sieve and 0.5-9wt% binder.

[0122] 14. The method according to item 13, characterized in that the binder is kaolin, bentonite and / or attapulgite.

[0123] 15. The method according to item 13, wherein the molding aid is lignin, sesbania powder, dry starch, carboxymethyl cellulose and / or activated carbon.

[0124] 16. The method according to any one of items 1 to 15, characterized in that the adsorption separation adopts a simulated moving bed process.

[0125] 17. The method described in Item 16 is characterized in that the simulated moving bed comprises a plurality of adsorption beds filled with adsorbents, each bed having its own material inlet and outlet pipelines, and the materials entering and leaving the simulated moving bed divide the adsorption beds therein into a desorption zone, a purification zone, an adsorption zone and an isolation zone, the adsorption bed between desorbent injection and extract production is the desorption zone, the adsorption bed between extract production and raw material injection is the purification zone, the adsorption bed between raw material injection and residual liquid production is the adsorption zone, and the adsorption bed between residual liquid production and desorbent injection is the isolation zone.

[0126] 18. The method as described in item 16 is characterized in that the ratio of the number of bed layers in the adsorption zone, purification zone, desorption zone and isolation zone in the simulated moving bed is 25+10%:38±15%:25+5%:12±4%.

[0127] 19. The method of item 16 is characterized in that the mass flow rate ratio of the desorbent to the raw material entering the simulated moving bed is not greater than 6.0, preferably not greater than 5.5, and more preferably not greater than 5.0.

[0128] 20. The method as described in Item 16 is characterized in that the flow rate of raw materials entering the simulated moving bed relative to the unit mass of adsorbent is not less than 0.1 kg / (h·kg adsorbent), preferably not less than 0.15 kg / (h·kg adsorbent), and more preferably not less than 0.17 kg / (h·kg adsorbent).

[0129] 21. The method according to item 16, wherein a cycle of the simulated moving bed is 12-70 minutes, preferably 20-40 minutes.

[0130] 22. A desorbent composition comprising an alkylbenzene selected from the following and one or more alkanes selected from C5-C8 normal alkanes, wherein the alkylbenzene is one or more selected from the following: 1,2,3-trisubstituted C9+ alkylbenzene or its derivatives, 1,2,3,4-tetrasubstituted C9+ alkylbenzene or its derivatives, 1,2,3,4,5-pentasubstituted C9+ alkylbenzene or its derivatives, and the content of the alkane is not higher than 80 wt% based on the weight of the desorbent composition.

[0131] 23. The composition of item 22, wherein the 1,2,3-trisubstituted C9+ alkylbenzene is 1,2,3-trimethylbenzene and 3-ethyl-o-xylene, the 1,2,3,4-tetrasubstituted C9+ alkylbenzene is 1,2,3,4-tetramethylbenzene, and the 1,2,3,4,5-pentasubstituted C9+ alkylbenzene is 1,2,3,4,5-pentamethylbenzene.

[0132] 24. Use of an alkylbenzene selected from the following as a desorbent for the adsorptive separation of high-purity meta-xylene, wherein the alkylbenzene is one or more selected from the following: 1,2,3-trisubstituted C9+ alkylbenzene or its derivatives, 1,2,3,4-tetrasubstituted C9+ alkylbenzene or its derivatives, 1,2,3,4,5-pentasubstituted C9+ alkylbenzene or its derivatives, and the content of the alkane is not higher than 80 wt% based on the weight of the desorbent composition.

[0133] 25. The use according to item 22, wherein the alkylbenzene is combined with one or more alkanes selected from C5-C8 normal alkanes as the desorbent, wherein the content of the alkanes is not higher than 80 wt% based on the weight of the desorbent.

[0134] 26. The use according to item 24 or 25, characterized in that the 1,2,3-trisubstituted C9+ alkylbenzene is 1,2,3-trimethylbenzene and 3-ethyl-o-xylene, the 1,2,3,4-tetrasubstituted C9+ alkylbenzene is 1,2,3,4-tetramethylbenzene, and the 1,2,3,4,5-pentasubstituted C9+ alkylbenzene is 1,2,3,4,5-pentamethylbenzene.

[0135] Example

[0136] The present application is further described in detail below through examples, but the present application is not limited thereto.

[0137] Test Method

[0138] Adsorbent performance evaluation

[0139] The adsorption capacity of an adsorbent is measured through a toluene vapor-phase adsorption experiment. The specific procedure is to allow nitrogen gas laden with toluene (toluene partial pressure of 0.05 MPa) to contact a predetermined mass of adsorbent at 35°C until toluene adsorption equilibrium is reached. The adsorption capacity of the adsorbent is calculated using the following formula based on the difference in adsorbent mass before and after toluene adsorption.

[0140] Wherein, C is the adsorption capacity, in mg / g; m1 is the mass of the adsorbent before adsorption of toluene, in g; m2 is the mass of the adsorbent after adsorption of toluene, in g.

[0141] The calcined bulk density of the adsorbent is determined by the following method: 50 mL of adsorbent is added to a 100 mL graduated cylinder, and the mixture is vibrated on a tap density meter (produced by Liaoning Instrument Research Institute Co., Ltd.) for 5 minutes. Then 50 mL of adsorbent is added and vibrated for 5 minutes. The ratio of the mass to the volume of the adsorbent in the graduated cylinder is the adsorbent bulk density. A certain mass of adsorbent is calcined at 600°C for 2 hours and placed in a desiccator to cool to room temperature. The ratio of the mass of the adsorbent after calcination to that before calcination is the calcined bulk density, and the product of the calcined bulk density and the adsorbent bulk density is the calcined bulk density.

[0142] The compressive strength of an adsorbent is measured by the breakage rate of the pellets under a given pressure. The lower the breakage rate, the higher the compressive strength. Adsorbent compressive strength is determined using a DL-II Particle Strength Tester (manufactured by the Dalian Chemical Industry Research and Design Institute). After passing the pellets through a 300-micron sieve, approximately 1.5 mL of adsorbent is placed in a stainless steel cylinder. During the test, a pin with an interference fit within the cylinder is installed. The pellets are pressed once under a pre-set pressure, then poured out and passed through a 300-micron sieve and weighed. The mass loss of the adsorbent before and after the pressure test represents the breakage rate at the set pressure.

[0143] The metal ion exchange degree of the adsorbent is determined by the following method: After the ion exchange test, the mass fraction of the metal oxide in the adsorbent is measured by X-ray fluorescence spectrometry, and the molar fraction of the metal ion is calculated based on this. The metal ion exchange degree of the adsorbent is further calculated by the following formula.

[0144] Wherein, η is the degree of ion exchange, m1 is the mass fraction of Na2O in the adsorbent after ion exchange, m2 is the mass fraction of the target metal (exchanged metal) oxide in the adsorbent after ion exchange, M1 is the molar mass of Na2O, and M2 is the molar mass of the target metal oxide.

[0145] Performance evaluation of adsorption-desorption system

[0146] In the following examples and comparative examples, a dynamic pulse test apparatus was used to evaluate the performance of the adsorption-desorption system, including the adsorption selectivity of the adsorbent and the adsorption and desorption rates of the target product. The apparatus consists of a feed system, an adsorption column, a heating furnace, and a pressure control valve. The adsorption column is a Φ6 x 940 mm stainless steel tube. The lower inlet of the column is connected to the feed and nitrogen system, while the upper outlet is connected to a pressure control valve and then to an effluent collector.

[0147] For a specific adsorbent and adsorbate, performing a pulse test under the same process conditions and changing the type or composition of the desorbent may produce different separation effects. This is because the desorbent, adsorbate, and target component will interact synergistically, promoting and restricting each other. Changing the desorbent will change the selectivity difference between the target component and impurities in the adsorbate, and will also change the adsorbent's selectivity for the target component. Therefore, when using different desorbents in pulse tests, the peak elution time, peak shape, interval, and extreme value position of the target component and impurity may vary, and the degree of separation may also vary. The specific parameters manifested as separation coefficient and resolution will be significantly different.

[0148] The method for determining the adsorption selectivity of the adsorption-desorption system is as follows: weigh the adsorbent particles with a particle size of 500-1000 μm and place them in the adsorption column to shake them solid. Then, nitrogen is introduced at room temperature to remove the remaining air in the system. Then, desorbent is introduced to remove the gas in the system. The system pressure and temperature are raised to the set values, and the introduction of desorbent is stopped. -1 5-10mL of pulse feed liquid is introduced at a volumetric space velocity, and the feed liquid contains a non-adsorbed tracer. Then, the desorbent is introduced at the same volumetric space velocity, and 3 drops of desorbent sample are taken every 2mL, and analyzed by gas chromatography. The desorption curve of each component of the pulse feed liquid is drawn with the volume of the desorbent for desorption as the horizontal coordinate and the concentration of each component of the pulse feed liquid as the vertical coordinate. Among them, the non-adsorbed tracer can be used to obtain the dead volume of the adsorption system. The midpoint of the half-peak width of the tracer is taken as the zero point, and the net retention volume from the midpoint of the half-peak width to the zero point of each component is measured. The net retention volume of any component is proportional to the distribution coefficient at adsorption equilibrium, which reflects the interaction force between each component and the adsorption material. The ratio of the net retention volume of the two components is the separation coefficient β. For example, the ratio of the net retention volume of meta-xylene to the net retention volume of ethylbenzene is the ratio of the adsorption performance of the adsorbent for the two in the adsorption-desorption system, which is the separation coefficient of meta-xylene relative to ethylbenzene, recorded as β MX / EB The larger the β value, the greater the difference in the adsorption capacity of the adsorbent for MX and ethylbenzene (EB) in the adsorption-desorption system. MX is more easily adsorbed and EB is less likely to be adsorbed, so the two components are easier to separate.

[0149] The half-width at half maximum of the pulse peak envelope provides information about the mass transfer rate between adsorbent particles, between molecular sieve grains, and within the molecular sieve crystals. The narrower the half-width at half maximum of a component, the smaller the half-width value, indicating that the adsorbent in the adsorption-desorption system has a faster adsorption and desorption rate for that component, and the faster the mass transfer of that component within the adsorbent. Increased adsorption and desorption rates improve adsorbent efficiency, which helps reduce adsorbent loading and investment. Increased adsorption and desorption rates also reduce the amount of desorbent used for desorption, which helps reduce energy consumption.

[0150] Separation is usually one of the indicators of separation efficiency of adsorption-desorption system, especially when evaluating the effect of different adsorbents or desorbents on adsorption separation under the same operating parameters. Separation is equal to the ratio of the difference between the net retention volume of two pulse peaks to the average half-peak width of the two pulse peaks. For example, the ratio of the difference between the net retention volume of m-xylene and the net retention volume of ethylbenzene to the average half-peak width of the pulse peaks of the two is the separation between the two components, which is recorded as R MX / EB According to the definition and calculation method of separation, the separation of a strongly adsorbed component from a weakly adsorbed component is proportional to the difference in net retention volume between the two and inversely proportional to the mean half-peak width. Therefore, the separation R comprehensively considers the effects of the difference in adsorption strength and mass transfer rate on adsorption separation. MX / EB The larger the value, the greater the difference in net retention volume between the MX and EB components or the smaller the half-peak width average, the greater the difference in adsorption selectivity or the faster the adsorption and desorption rate. Compared with the EB component, MX is more easily adsorbed on the adsorbent in the adsorption-desorption system or the adsorption and desorption rate in the adsorption-desorption system is faster, and the overall separation effect is better.

[0151] In the following examples and comparative examples, unless otherwise specified, all reagents and raw materials used are commercially available products and are chemically pure.

[0152] Adsorbent Preparation Example 1

[0153] NaY molecular sieve with a silica / alumina molar ratio of 5.0 and a crystal particle size of 0.8 μm was uniformly mixed with kaolin mineral and sesbania powder in a mass ratio of 95:4:1, rolled into balls, dried, and calcined at 540°C for 8 hours. The calcined balls were washed with deionized water, with a liquid-to-solid ratio of 10, and dried at 100°C for 4 hours to obtain adsorbent A.

[0154] The mass ratio of molecular sieve to kaolin mineral in the adsorbent pellets is 96:4, and its X-ray diffraction (XRD) spectrum is shown in Figure 1. Analysis of adsorbent A revealed a toluene adsorption capacity of 213 mg / g, a basic bulk density of 0.651 g / mL, a 130N crushing efficiency of 0.9 wt%, and a mass fraction of balancing cations, calculated as metal oxide, of 12.8%.

[0155] Adsorbent Preparation Example 2

[0156] A NaY molecular sieve with a silica / alumina molar ratio of 4.3 and a grain size of 0.9 μm was uniformly mixed with kaolin mineral and sesbania powder in a mass ratio of 95:4:1, rolled into balls, dried, and calcined at 540°C for 8 hours. The calcined balls were washed with deionized water, with a liquid-to-solid ratio of 10, and dried at 100°C for 4 hours to obtain adsorbent B.

[0157] The mass ratio of molecular sieve to kaolin mineral in the adsorbent pellets is 96:4. The toluene adsorption capacity of adsorbent B is analyzed to be 212 mg / g, the basic bulk density is 0.652 g / mL, the 130N crushing rate is 1.0 wt%, and the mass fraction of the balanced charge cation based on the metal oxide is 13.6%.

[0158] Adsorbent Preparation Example 3

[0159] NaY molecular sieve with a silicon oxide / aluminum oxide molar ratio of 5.0 and a crystal particle size of 1.1 μm was mixed with kaolin mineral and sesbania powder at a mass ratio of 92:7:1, rolled into balls, dried, and calcined at 540°C for 6 hours. The calcined balls were subjected to column ion exchange with 0.25 mol / L silver nitrate solution for 8 hours at a temperature of 85°C, a liquid-to-solid ratio of 45, and a space velocity of 5 h. -1 The ion exchange degree calculated according to the formula is 89.5%. After exchange, the beads are dried at 100°C for 3 hours to obtain adsorbent C.

[0160] The mass ratio of molecular sieve to kaolin mineral in the adsorbent pellets was 93:7. Analysis of adsorbent C revealed a toluene adsorption capacity of 183 mg / g, a basic bulk density of 0.823 g / mL, a 130 N crushing efficiency of 2.5 wt%, and a mass fraction of balancing cations, calculated as metal oxide, of 37.6%.

[0161] Adsorbent Preparation Example 4

[0162] NaY molecular sieve with a silicon oxide / aluminum oxide molar ratio of 5.0 and a crystal particle size of 1.0 μm was mixed with kaolin mineral and sesbania powder in a mass ratio of 94:5.5:0.5, rolled into balls, dried, and calcined at 550°C for 9 hours. The calcined balls were subjected to column ion exchange with 0.40 mol / L strontium chloride hexahydrate solution for 8 hours at a temperature of 90°C, a liquid-to-solid ratio of solution to adsorbent of 40, and a space velocity of 5 h. -1 The ion exchange degree calculated according to the formula is 99.5%. After exchange, the beads are dried at 100°C for 4 hours to obtain adsorbent D.

[0163] The mass ratio of molecular sieve to kaolin mineral in the adsorbent pellets was 94.5:5. Analysis of adsorbent D revealed a toluene adsorption capacity of 185 mg / g, a basic bulk density of 0.785 g / mL, a 130 N crushing efficiency of 3.0 wt%, and a mass fraction of balancing cations, calculated as metal oxide, of 36.9%.

[0164] Adsorbent Preparation Example 5

[0165] NaY molecular sieve with a silicon oxide / aluminum oxide molar ratio of 5.0 and a crystal particle size of 0.8 μm was mixed with kaolin mineral and sesbania powder at a mass ratio of 95:4:1, rolled into balls, dried, and calcined at 550°C for 9 hours. The calcined balls were subjected to column ion exchange with 0.20 mol / L barium chloride solution for 8 hours at a temperature of 90°C, a liquid-to-solid ratio of 40, and a space velocity of 5 h. -1 The ion exchange degree calculated according to the formula is 99.8%. After exchange, the beads are dried at 100°C for 4 hours to obtain adsorbent E.

[0166] The mass ratio of molecular sieve to kaolin mineral in the adsorbent pellets was 95.5:4.5. Analysis of adsorbent E revealed a toluene adsorption capacity of 179 mg / g, a basic bulk density of 0.845 g / mL, a 130 N crushing efficiency of 3.0 wt%, and a mass fraction of cations balancing the charge, calculated as metal oxide, of 39.8%.

[0167] Example 1

[0168] An appropriate amount of adsorbent A was heated to 180°C in a muffle furnace and subjected to fluidized dehydration for 2 hours. The mass fraction of adsorbed water was determined to be 1.84%. A 26-ml sample of this adsorbent was used in a liquid pulse experiment to determine its adsorption selectivity, separation, and the adsorption and desorption rates of m-xylene. The liquid pulse experiment was conducted at a pressure of 0.8 MPa and a temperature of 145°C. The desorbents used were 30 wt% trimethylol and 70 wt% n-heptane. The pulse feed liquid consisted of 5 wt% each of p-xylene, m-xylene, o-xylene, ethylbenzene, and n-nonane, with 75 wt% of the desorbent, where n-nonane served as a tracer.

[0169] The separation coefficient and resolution (β MX / EB and R MX / EB , β MX / PX and R MX / PX , β MX / OX and R MX / OX ) are shown in Table 1, and the pulse spectrum is shown in Figure 2.

[0170] Example 2

[0171] Meta-xylene was separated from mixed C8 aromatics according to the method of Example 1, except that adsorbent A was programmed to heat to 220° C. in a muffle furnace and subjected to fluidized dehydration for 2 hours. The mass fraction of adsorbed water was determined to be 1.03%.

[0172] The results of separation coefficient and resolution between m-xylene and ethylbenzene, p-xylene and o-xylene are shown in Table 1.

[0173] Example 3

[0174] Meta-xylene in mixed C8 aromatics was separated according to the method of Example 1, except that the desorbent used in the experiment was 50 wt% of trimethylol and 50 wt% of n-heptane.

[0175] The results of separation coefficient and resolution between m-xylene and ethylbenzene, p-xylene and o-xylene are shown in Table 1.

[0176] Example 4

[0177] Meta-xylene in mixed C8 aromatics was separated according to the method of Example 1, except that the desorbent used in the experiment was 80 wt% of trimethylol and 20 wt% of n-heptane.

[0178] The results of separation coefficient and resolution between m-xylene and ethylbenzene, p-xylene and o-xylene are shown in Table 1.

[0179] Example 5

[0180] The m-xylene in the mixed C8 aromatics was separated according to the method of Example 2, except that the desorbent was trimethylol.

[0181] The results of separation coefficient and resolution between m-xylene and ethylbenzene, p-xylene and o-xylene are shown in Table 1.

[0182] Example 6

[0183] Meta-xylene was separated from mixed C8 aromatics according to the method of Example 1, except that adsorbent A was programmed to heat to 230° C. in a muffle furnace and subjected to fluidized dehydration for 2 hours. The mass fraction of adsorbed water was determined to be 0.82%.

[0184] The results of the separation coefficient and resolution between m-xylene and ethylbenzene, p-xylene and o-xylene are shown in Table 1, and the pulse spectrum is shown in Figure 3.

[0185] Example 7

[0186] Meta-xylene was separated from mixed C8 aromatics according to the method of Example 1, except that adsorbent A was programmed to heat to 250° C. in a muffle furnace and subjected to fluidized dehydration for 2 hours. The mass fraction of adsorbed water was determined to be 0.55%.

[0187] The results of separation coefficient and resolution between m-xylene and ethylbenzene, p-xylene and o-xylene are shown in Table 1.

[0188] Example 8

[0189] Meta-xylene was separated from mixed C8 aromatics according to the method of Example 1, except that adsorbent A was heated to 280° C. in a muffle furnace and subjected to fluidized dehydration for 2 hours. The mass fraction of adsorbed water was determined to be 0.10%.

[0190] The results of separation coefficient and resolution between m-xylene and ethylbenzene, p-xylene and o-xylene are shown in Table 1.

[0191] Example 9

[0192] Meta-xylene was separated from mixed C8 aromatics according to the method of Example 1, except that adsorbent A was heated to 260° C. in a muffle furnace and subjected to fluidized dehydration for 2 hours. The mass fraction of adsorbed water was determined to be 0.26%.

[0193] The results of the separation coefficient and resolution between m-xylene and ethylbenzene, p-xylene and o-xylene are shown in Table 1, and the pulse spectrum is shown in Figure 4.

[0194] Example 10

[0195] The method of Example 9 was used to separate m-xylene from mixed C8 aromatics, except that the temperature of the liquid phase pulse experiment was 130°C.

[0196] The results of the separation coefficient and resolution between m-xylene and ethylbenzene, p-xylene and o-xylene are shown in Table 1, and the pulse spectrum is shown in Figure 5.

[0197] Example 11

[0198] The m-xylene in the mixed C8 aromatics was separated according to the method of Example 1, except that the adsorbent was adsorbent B.

[0199] The results of separation coefficient and resolution between m-xylene and ethylbenzene, p-xylene and o-xylene are shown in Table 1.

[0200] Example 12

[0201] The m-xylene in the mixed C8 aromatics was separated according to the method of Example 1, except that the adsorbent was adsorbent C.

[0202] The results of separation coefficient and resolution between m-xylene and ethylbenzene, p-xylene and o-xylene are shown in Table 1.

[0203] Example 13

[0204] The m-xylene in the mixed C8 aromatic hydrocarbons was separated according to the method of Example 1, except that the adsorbent was adsorbent D.

[0205] The results of separation coefficient and resolution between m-xylene and ethylbenzene, p-xylene and o-xylene are shown in Table 1.

[0206] Example 14

[0207] Meta-xylene in mixed C8 aromatics was separated according to the method of Example 9, except that the desorbent was 20% tetramethylbenzene and 80% n-octane.

[0208] The results of separation coefficient and resolution between m-xylene and ethylbenzene, p-xylene and o-xylene are shown in Table 1.

[0209] Example 15

[0210] The m-xylene in the mixed C8 aromatics was separated according to the method of Example 9, except that 50% of pentachlorobenzene and 50% of n-decane were present.

[0211] The results of separation coefficient and resolution between m-xylene and ethylbenzene, p-xylene and o-xylene are shown in Table 1.

[0212] Example 16

[0213] The m-xylene in the mixed C8 aromatics was separated according to the method of Example 9, except that 50% of 3-ethyl-o-xylene and 50% of n-undecane were present.

[0214] The results of separation coefficient and resolution between m-xylene and ethylbenzene, p-xylene and o-xylene are shown in Table 1.

[0215] Example 17

[0216] The m-dimethylnaphthalene in the mixed C12 aromatic hydrocarbons was separated according to the method of Example 1, except that the adsorbent was E, and the pulse feed liquid was composed of 5 wt% each of 2,7-dimethylnaphthalene, 1,6-dimethylnaphthalene, 2,6-dimethylnaphthalene, 1,8-dimethylnaphthalene, n-nonane and 75 wt% of desorbent, wherein n-nonane was used as a tracer.

[0217] The results of the separation coefficients and resolutions between 2,7-dimethylnaphthalene and 1,6-dimethylnaphthalene, 2,6-dimethylnaphthalene and 1,8-dimethylnaphthalene are shown in Table 1.

[0218] Example 18

[0219] The m-dimethylnaphthalene in the mixed C12 aromatic hydrocarbons was separated according to the method of Example 17, except that when the adsorbent was subjected to the ion exchange experiment, the exchange liquid concentration was 0.15 mol / L, and the exchange degree of the obtained adsorbent E was 78.5%.

[0220] The results of the separation coefficients and resolutions between 2,7-dimethylnaphthalene and 1,6-dimethylnaphthalene, 2,6-dimethylnaphthalene and 1,8-dimethylnaphthalene are shown in Table 1.

[0221] Example 19

[0222] Meta-xylene in mixed C8 aromatics was separated according to the method of Example 9, except that the pulse feed liquid consisted of 10 wt% each of meta-xylene, ethylbenzene, and n-nonane, and 70 wt% of a desorbent, wherein n-nonane was used as a tracer.

[0223] The results of the separation coefficient and resolution between m-xylene and ethylbenzene are shown in Table 1.

[0224] Comparative Example 1

[0225] Meta-xylene in mixed C8 aromatics was separated according to the method of Example 9, except that the desorbent was 30 wt% toluene and 70 wt% n-heptane.

[0226] The results of the separation coefficient and resolution between m-xylene and ethylbenzene, p-xylene and o-xylene are shown in Table 1, and the pulse spectrum is shown in Figure 6.

[0227] Comparative Example 2

[0228] Meta-xylene was separated from mixed C8 aromatic hydrocarbons according to the method of Example 9, except that the desorbent was 30 wt% tetralin and 70 wt% n-heptane.

[0229] The results of the separation coefficient and resolution between m-xylene and ethylbenzene, p-xylene and o-xylene are shown in Table 1, and the pulse spectrum is shown in Figure 7.

[0230] Comparative Example 3

[0231] Meta-xylene in mixed C8 aromatics was separated according to the method of Example 9, except that the desorbent was 30 wt% of trimethylol and 70 wt% of n-heptane.

[0232] The results of the separation coefficient and resolution between m-xylene and ethylbenzene, p-xylene and o-xylene are shown in Table 1, and the pulse spectrum is shown in Figure 8.

[0233] Comparative Example 4

[0234] Meta-xylene was separated from mixed C8 aromatics according to the method of Example 1, except that adsorbent A was heated to 600° C. in a muffle furnace and dehydrated for 24 hours. The mass fraction of adsorbed water was determined to be 0.005%.

[0235] The results of separation coefficient and resolution between m-xylene and ethylbenzene, p-xylene and o-xylene are shown in Table 1.

[0236] Comparative Example 5

[0237] The m-xylene in the mixed C8 aromatics was separated according to the method of Example 9, except that the adsorption temperature was 95°C.

[0238] The results of separation coefficient and resolution between m-xylene and ethylbenzene, p-xylene and o-xylene are shown in Table 1.

[0239] Comparative Example 6

[0240] Meta-xylene in mixed C8 aromatics was separated according to the method of Example 9, except that the desorbent was 10 wt% of trimethylol and 90 wt% of n-heptane.

[0241] The results of separation coefficient and resolution between m-xylene and ethylbenzene, p-xylene and o-xylene are shown in Table 1.

[0242] It can be seen from the test results in Table 1 that in Examples 1-13 of the present application, when trimethylbenzene or its mixture with alkanes is used as a desorbent for the adsorption separation of MX, the separation effect is improved compared with when toluene is used as a desorbent (Example 1 vs. Comparative Example 1). Ethylbenzene (EB), paraxylene (PX), and o-xylene (OX) components other than MX can be separated from MX at the same time. The net retention volumes corresponding to the pulse peaks of the three are relatively similar, and the separation coefficients and separation degrees of the three with MX are slightly different, indicating that the interaction forces between the three impurities and the adsorbent are similar, which is significantly different from the interaction forces between the target components and the adsorbent. Therefore, the three impurities can be removed in the same time period and the same process interval by process parameter design. However, when toluene is used as a desorbent, the three impurities cannot be removed in the same time range and the same process interval. If they are forcibly removed at the same time, the process parameter control range is very small, and the precision requirements of the process equipment are high. Therefore, when toluene is used as a desorbent, the efficiency of the entire separation process is low, the material consumption is large, and the energy consumption for recycling is also high. In addition, in this adsorption separation system, the components that are more difficult to separate from MX are PX and OX, and the component that is easier to separate is EB. Therefore, the key factor in whether a high-purity MX product can be obtained is the complete removal of the most difficult impurities PX and OX, that is, it is necessary to compare the separation coefficient and separation degree of these two components with MX, rather than focusing on the removal of easily separated impurities. Compared with toluene as a desorbent, the net retention volume corresponding to the pulse peak of PX and OX is significantly reduced, indicating that in the presence of trimethylbenzene desorbent, the adsorbent's adsorption capacity for PX and OX is significantly weakened, and the separation of PX, OX and MX is easier than when toluene is used as a desorbent. The separation coefficient and separation degree are larger, the separation effect is better, the entire separation process is faster, the logistics usage is smaller, and the energy consumption for recycling is lower.

[0243] The test results of Examples 14-18 show that the present application can also be used for the separation of other meta-aromatic hydrocarbons, such as meta-dimethylnaphthalene, and other alkylbenzene compounds that conform to the general formula (I), such as tetramethylbenzene, pentamethylbenzene and 3-ethyl-o-xylene can also be used in the present application.

[0244] Example 20

[0245] Using 2116g of adsorbent A and a water content of 0.26%, a simulated moving bed adsorption separation apparatus was used to separate m-xylene from mixed C8 aromatics. The mixed C8 aromatics feedstock contained 1.5wt% non-aromatics, 0.5wt% benzene, 0.9wt% toluene, 48.1wt% m-xylene, 20.2wt% p-xylene, 18.9wt% o-xylene, 9.8wt% ethylbenzene, and 0.1wt% C9+ aromatics.

[0246] The simulated moving bed apparatus consists of 24 columns connected in series. The internal cavities for holding the adsorbent are 200 mm high and 40 mm in diameter. The 24th column is connected to the first column via a pump, circulating the fluid within the columns. Material can be introduced or removed at the junctions between the columns. Seven columns form the adsorption zone between the raffinate outlet and the feed inlet; nine columns form the purification zone between the feed inlet and the extract outlet; five columns form the desorption zone between the extract outlet and the desorbent inlet; and three columns form the isolation zone between the desorbent inlet and the raffinate outlet. The positions of the various inlet and outlet streams are shown in Figure 9. The inlet and outlet positions change according to a stepping time. Each stepping time causes the inlet and outlet to advance one column, moving from the position indicated by the solid arrow in the figure to the position indicated by the dashed arrow. The inlet and outlet are then advanced in the predetermined direction at the next stepping time, and the positions of the inlet and outlet are repeated in this manner until the inlet and outlet return to their starting positions, forming one cycle. One step time is 80 seconds and one cycle is 32 minutes. After the simulated moving bed runs stably, mixed samples of the extract and raffinate are taken from each cycle and their compositions are analyzed. Based on the analysis results, the purity and yield of meta-xylene are calculated as follows:

[0247] Where X is the mass fraction of each component in the extract;

[0248] where X 间二甲苯，抽出液 Q is the mass fraction of xylene in the extract, 抽出液 is the mass flow rate of the extracted liquid, X 间二甲苯，抽余液 Q is the mass fraction of xylene in the raffinate, 抽余液 is the mass flow rate of the raffinate.

[0249] The adsorption bed temperature was controlled at 145°C and the operating pressure was 0.90 MPa. The desorbent was 93 wt% trimethylbenzene (purchased from Xilong Chemical Reagent Company, CAS: 526-73-8). The raw material feed rate was 0.36 kg / h, the desorbent injection rate was 1.79 kg / h, the extracted liquid volume was 0.84 kg / h, the raffinate volume was 1.31 kg / h, and the purification zone flow rate was 2.85 kg / h. The ratio of the mass flow rate of the desorbent to the C8 aromatic feed entering the simulated moving bed was 4.97, and the C8 aromatic feed flow rate per unit mass of adsorbent was 0.17 kg / (h·kg adsorbent). The simulated moving bed adsorption separation unit had 24 adsorption beds, with 7, 9, 5, and 3 beds in the adsorption zone, purification zone, desorption zone, and isolation zone, respectively. The step time was 80 seconds, and one cycle was 32 minutes. After adsorption separation, the yield of meta-xylene was 96.25% by weight, with a purity of 99.65% by weight. The desorbent accounted for 81.11% by weight of the extract and 84.23% by weight of the raffinate. Based on the extract and raffinate compositions, the RadFrac module in Aspen Plus software was used to calculate the theoretical plate number, overhead condensing load, and bottom heating load of the distillation column. Simulation results show that with an extract flow rate of 124 t / h and a raffinate flow rate of 202 t / h, the recovered desorbent mass fraction after separation can reach 99.995%. The mass fraction of desorbent in the overhead meta-xylene product or other C8 aromatics is 0.01%. The heat loads in the extract and raffinate distillation columns are 11.8 Gcal / h and 18.2 Gcal / h, respectively.

[0250] Comparative Example 7

[0251] Meta-xylene was separated from mixed C8 aromatics using the method of Example 20, except that the desorbent was 99 wt% toluene (purchased from Inokai Technology Co., Ltd., CAS: 108-88-3). Under the same operating conditions, the regional flow rate in the purification zone was 2.90 kg / h, and the yield of meta-xylene was 95.55 wt% with a purity of 99.50 wt%. The desorbent toluene was recovered at the top of the extract and raffinate distillation towers, respectively. Simulation results showed that the heat loads in the extract and raffinate distillation towers were 27.6 Gcal / h and 35.8 Gcal / h, respectively.

[0252] Comparing the separation purity and yield results of Example 20 with Comparative Example 7, it can be seen that when trimethylbenzene is used as the desorbent, the separation of the more difficult-to-separate components PX and OX from the target component MX is easier than when toluene is used as the desorbent, which is beneficial for the purification of MX in the simulated moving bed purification zone. At the same time, the required purification zone regional flow rate is reduced to a certain extent, by about 10%, that is, the reduction in material consumption, saving the cost of purchasing materials and recycling costs. The purity and yield of the final target component MX are correspondingly improved, with the purity increased by 0.1 percentage points and the yield increased by 0.75 percentage points. This will lead to an increase in the separation efficiency of MX in the industrial device, an increase in the amount of processed raw materials, and a reduction in operating costs. Trimethylbenzene has a higher boiling point than the target component MX. When used as a desorbent, it is recycled and reused in the extract and raffinate distillation tower reactors. Therefore, compared with toluene as the desorbent and recycled at the tower top, the required tower reactor heat load is significantly reduced. The extract distillation tower heat load is reduced by 57%, and the raffinate distillation tower heat load is reduced by 49%, and the device energy consumption is significantly reduced.

[0253] The preferred embodiments of the present application are described in detail above. However, the present application is not limited to the specific details of the above embodiments. Within the technical concept of the present application, various simple modifications can be made to the technical solution of the present application, and these simple modifications all fall within the scope of protection of the present application.

[0254] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner unless there is any contradiction. In order to avoid unnecessary repetition, this application will not further describe various possible combinations.

[0255] In addition, the various implementation methods of the present application can be arbitrarily combined, as long as they do not violate the concept of the present application, they should also be regarded as the content of the invention of the present application.

Claims

1. Use of a liquid material comprising 20-100 wt % of an alkylbenzene compound of the following general formula (I) and 0-80 wt % of a C5-C14 saturated aliphatic hydrocarbon or consisting thereof as a desorbent for the adsorptive separation of meta-aromatic hydrocarbons, in: R1, R2 and R3, which may be the same or different, are independently selected from C 1-4 chain alkyl, preferably at least one of R1, R2 and R3 is a methyl group, more preferably at least two are methyl groups, and further preferably all are methyl groups; R4, R5 and R6, which may be the same or different, are independently selected from hydrogen, C 1-4 Saturated hydrocarbon group, C 1-4 Alkoxy and halogen, preferably at least one of R4, R5 and R6 is hydrogen or C 1-4 Saturated hydrocarbon group, such as R4 or R6 is C 1-4 Saturated hydrocarbon groups, more preferably at least two of which are independently hydrogen or C 1-4 Saturated hydrocarbon group, for example, R4 and R6 are C 1-4 Saturated hydrocarbon group, further preferably three are independently hydrogen or C 1-4 Saturated hydrocarbon group, particularly preferably all three are hydrogen, wherein the C 1-4 The saturated hydrocarbon group is preferably a methyl group.

2. The use according to claim 1, wherein the adsorptive separation comprises separating the meta-aromatic hydrocarbon from a mixed aromatic hydrocarbon feedstock comprising the meta-aromatic hydrocarbon and at least one isomer thereof by adsorption and desorption, wherein the meta-aromatic hydrocarbon is preferably a C8-C12 meta-aromatic hydrocarbon, more preferably a C8-C12 meta-alkyl aromatic hydrocarbon, such as meta-xylene or 2,7-dimethylnaphthalene, Further preferably, the mixed aromatic hydrocarbon feedstock is a C8 aromatic hydrocarbon mixed feedstock comprising m-xylene and at least one other C8 aromatic hydrocarbon selected from p-xylene, o-xylene and ethylbenzene, More preferably, the C8 aromatic mixed feedstock contains 5-95 wt% of meta-xylene.

3. The method according to claim 2, wherein the meta-aromatic hydrocarbon is meta-xylene, and the mixed aromatic hydrocarbon feedstock comprises 5-94 wt% of meta-xylene and 6-95 wt% of para-xylene, preferably 5-90 wt% of meta-xylene and 10-95 wt% of para-xylene.

4. The method according to claim 2, wherein the adsorbent used in the adsorptive separation comprises at least 90 wt% of a Y-type molecular sieve as an active component, wherein the Y-type molecular sieve has a silicon oxide / aluminum oxide molar ratio of 4.0-6.0, preferably 4.3-5.

7. Further preferably, the adsorbent comprises one or more, for example one or two, of Group IA, IIA and IB metal ions as charge-balancing cations, wherein the Group IA metal ions are preferably selected from Li + and Na + , the Group IIA metal ion is preferably selected from Mg 2+ 、Sr 2+ and Ba 2+ , the IB group metal ion is preferably Ag + Preferably, the total amount of Group IA, IIA and IB metals in the adsorbent is 10-45%, preferably 10-40%, calculated as metal oxide and based on the total weight of the adsorbent. More preferably, the adsorbent contains 0.05-2 wt%, preferably 0.05-1 wt%, more preferably 0.05-0.8 wt%, and further preferably 0.1-0.5 wt% of adsorbed water. Particularly preferably, the adsorbent comprises at least 90 wt% of NaY molecular sieve as an active component, and is preferably subjected to a metal ion exchange treatment so that the metal ion exchange degree thereof is 78.0-99.9%.

5. The use according to any one of claims 2 to 4, wherein Based on the total amount of the liquid material, the liquid material contains 30-95wt%, preferably 30-80wt%, more preferably 30-50% of the alkylbenzene compound, and 5-70wt%, preferably 20-70wt%, more preferably 50-70% of alkanes selected from C5-C14 normal alkanes, preferably selected from C6-C10 normal alkanes, or consists of them.

6. The use according to any one of claims 2 to 5, wherein in formula (I), at least two of R1, R2 and R3 are methyl, and R4, R5 and R6 are independently hydrogen or C 1-4 Saturated hydrocarbon group, and at least one of which is hydrogen; preferably at least two of R4, R5 and R6 are hydrogen, and the C 1-4 The saturated hydrocarbon group is methyl; More preferably, the alkylbenzene compound is selected from 1,2,3-trimethylbenzene, 1,2,3,4-tetramethylbenzene, 1,2,3,4,5-pentamethylbenzene and 3-ethyl-o-xylene, preferably 1,2,3-trimethylbenzene or 1,2,3,4-tetramethylbenzene.

7. The use according to claim 4, wherein the meta-aromatic hydrocarbon is meta-xylene, the mixed aromatic hydrocarbon feedstock comprises 20-60 wt% of meta-xylene, 10-30 wt% of para-xylene, 10-30 wt% of o-xylene and 5-20 wt% of ethylbenzene, and the alkylbenzene compound is selected from 1,2,3-trimethylbenzene, 1,2,3,4-tetramethylbenzene, 1,2,3,4,5-pentamethylbenzene and 3-ethyl o-xylene; Based on the total amount of the liquid material, the liquid material comprises 30-70 wt% of the alkylbenzene compound and 30-70 wt% of an alkane selected from C5-C14 normal alkanes; and The charge-balancing cation of the adsorbent is selected from Na + 、Sr 2+ 、Ba 2+ and Ag + , and the adsorbent contains 0.05-0.8 wt%, preferably 0.1-0.5 wt% of adsorbed water.

8. A method for separating meta-aromatic hydrocarbons from a mixed aromatic hydrocarbon feedstock comprising meta-aromatic hydrocarbons and isomers thereof, the method comprising the steps of: 1) contacting the mixed aromatic hydrocarbon feedstock with an adsorbent to adsorb meta-aromatic hydrocarbons, thereby obtaining an adsorbent adsorbed with the meta-aromatic hydrocarbons and a raffinate containing unadsorbed components; 2) contacting the adsorbent adsorbed with meta-aromatic hydrocarbons obtained in step 1) with a desorbent to desorb the meta-aromatic hydrocarbons, thereby obtaining an extract containing the meta-aromatic hydrocarbons and the desorbent; and 3) performing rectification and separation on the extract obtained in step 2) to obtain the meta-aromatic hydrocarbons and the desorbent, in, Based on the total amount of the desorbent, the desorbent comprises or consists of 20-100 wt% of an alkylbenzene compound having the following general formula (I) and 0-80 wt% of a C5-C14 saturated aliphatic hydrocarbon, in: R1, R2 and R3, which may be the same or different, are independently selected from C 1-4 chain alkyl, preferably at least one of R1, R2 and R3 is a methyl group, more preferably at least two are methyl groups, and further preferably all are methyl groups; R4, R5 and R6, which may be the same or different, are independently selected from hydrogen, C 1-4 Saturated hydrocarbon group, C 1-4 Alkoxy and halogen, preferably at least one of R4, R5 and R6 is hydrogen or C 1-4 Saturated hydrocarbon group, such as R4 or R6 is C 1-4 Saturated hydrocarbon groups, more preferably at least two of which are independently hydrogen or C 1-4 Saturated hydrocarbon group, for example, R4 and R6 are C 1-4 Saturated hydrocarbon group, further preferably three are independently hydrogen or C 1-4 Saturated hydrocarbon groups, particularly preferably all three are hydrogen, wherein the alkyl group is preferably methyl.

9. The method according to claim 8, wherein the meta-aromatic hydrocarbon is a C8-C12 meta-aromatic hydrocarbon, preferably a C8-C12 meta-alkyl aromatic hydrocarbon, such as meta-xylene or 2,7-dimethylnaphthalene, Preferably, the mixed aromatic feedstock is a C8 aromatic mixed feedstock comprising meta-xylene and at least one other C8 aromatic selected from p-xylene, o-xylene and ethylbenzene. Further preferably, the C8 aromatic mixed feedstock comprises 5-95 wt% of meta-xylene.

10. The method according to claim 9, wherein the meta-aromatic hydrocarbon is meta-xylene, and the mixed aromatic hydrocarbon feedstock comprises 5-94 wt% of meta-xylene and 6-95 wt% of para-xylene, preferably 5-90 wt% of meta-xylene and 10-95 wt% of para-xylene.

11. The method according to any one of claims 8 to 10, wherein: Based on the total amount of the desorbent, the desorbent comprises 30-95 wt%, preferably 30-80 wt%, more preferably 30-50 wt% of the alkylbenzene compound, and 5-70 wt%, preferably 20-70 wt%, more preferably 50-70 wt% of an alkane selected from C5-C14 normal alkanes, preferably selected from C6-C10 normal alkanes, or consists of them.

12. The method according to any one of claims 8 to 11, wherein in formula (I), at least two of R1, R2 and R3 are methyl, and R4, R5 and R6 are independently hydrogen or C 1-4 Saturated hydrocarbon group, and at least one of which is hydrogen; preferably at least two of R4, R5 and R6 are hydrogen, and the C 1-4 The saturated hydrocarbon group is methyl; More preferably, the alkylbenzene compound is selected from 1,2,3-trimethylbenzene, 1,2,3,4-tetramethylbenzene, 1,2,3,4,5-pentamethylbenzene and 3-ethyl-o-xylene, preferably 1,2,3-trimethylbenzene or 1,2,3,4-tetramethylbenzene.

13. The method according to any one of claims 8 to 12, wherein the adsorbent used in step 1) comprises at least 90 wt% of a Y-type molecular sieve as an active component, wherein the Y-type molecular sieve has a silicon oxide / aluminum oxide molar ratio of 4.0 to 6.0, preferably 4.3 to 5.7, Preferably, the adsorbent comprises one or more, for example one or two, of Group IA, IIA and IB metal ions as charge-balancing cations, wherein the Group IA metal ions are preferably selected from Li + and Na + , the Group IIA metal ion is preferably selected from Mg 2+ 、Sr 2+ and Ba 2+ , the IB group metal ion is preferably Ag + Preferably, the total amount of Group IA, IIA and IB metals in the adsorbent is 10-45% calculated as metal oxides and based on the total amount of the adsorbent, More preferably, the particle size of the Y-type molecular sieve is 0.5-2.0 μm, preferably 0.8-1.2 μm. More preferably, the adsorbent comprises at least 90 wt% of NaY molecular sieve as an active component, and is preferably treated with metal ion exchange to achieve a metal ion exchange degree of 78.0-99.9%.

14. The method according to claim 13, wherein the adsorbent contains 0.05-2 wt%, preferably 0.05-1 wt%, more preferably 0.05-0.8 wt%, further preferably 0.1-0.5 wt% of adsorbed water.

15. The method according to claim 13, wherein the meta-aromatic hydrocarbon is meta-xylene, the mixed aromatic hydrocarbon feedstock comprises 20-60 wt% of meta-xylene, 10-30 wt% of para-xylene, 10-30 wt% of o-xylene and 5-20 wt% of ethylbenzene, and the alkylbenzene compound is selected from 1,2,3-trimethylbenzene, 1,2,3,4-tetramethylbenzene, 1,2,3,4,5-pentamethylbenzene and 3-ethyl-o-xylene; Based on the total amount of the liquid material, the liquid material comprises 30-70 wt% of the alkylbenzene compound and 30-70 wt% of an alkane selected from C5-C14 normal alkanes; and The charge-balancing cation of the adsorbent is selected from Na + 、Sr 2+ 、Ba 2+ and Ag + , and the adsorbent contains 0.05-0.8 wt%, preferably 0.1-0.5 wt% of adsorbed water.

16. The method according to any one of claims 8 to 15, wherein the operating conditions of the adsorption in step 1) and the desorption in step 2) each independently comprise: The temperature is 100-190°C, preferably 110-180°C, more preferably 120-160°C; and / or The pressure is 0.6-1.6 MPa, preferably 0.8-1.0 MPa.

17. The method according to any one of claims 8 to 16, wherein step 1) and step 2) are performed using a simulated moving bed, the simulated moving bed comprising a plurality of adsorption beds filled with adsorbent, each bed being provided with a corresponding material inlet and outlet pipeline, the material entering and exiting the simulated moving bed dividing the adsorption beds therein into a desorption zone, a purification zone, an adsorption zone and an isolation zone, wherein the adsorption bed between the desorbent injection position and the extract withdrawal position is the desorption zone, the adsorption bed between the extract withdrawal position and the raw material injection position is the purification zone, the adsorption bed between the raw material injection position and the raffinate withdrawal position is the adsorption zone, and the adsorption bed between the raffinate withdrawal position and the desorbent injection position is the isolation zone. Preferably, the ratio of the number of bed layers of the adsorption zone, purification zone, desorption zone and isolation zone in the simulated moving bed is 25±10%: 38±15%: 25±5%: 12±4%. Further preferably, the mass flow rate ratio of the desorbent to the raw material entering the simulated moving bed is 0.01-6.0, preferably 0.01-5.5, more preferably 0.01-5.0, More preferably, the flow rate of the raw material entering the simulated moving bed relative to the unit mass of the adsorbent is in the range of 0.1-8 kg / (h·kg adsorbent), preferably 0.15-8 kg / (h·kg adsorbent), more preferably 0.17-8 kg / (h·kg adsorbent), Particularly preferably, one cycle of the simulated moving bed is 12-70 minutes, preferably 20-40 minutes.

18. An adsorption-desorbent kit comprising a solid adsorbent and a liquid desorbent, wherein the solid adsorbent comprises at least 90 wt% of a Y-type molecular sieve as an active component, the Y-type molecular sieve having a silica / alumina molar ratio of 4.0-6.0, preferably 4.3-5.7, and the liquid desorbent comprises or consists of 20-100 wt% of an alkylbenzene compound having the following general formula (I) and 0-80 wt% of a C5-C14 saturated aliphatic hydrocarbon, in: R1, R2 and R3, which may be the same or different, are independently selected from C 1-4 chain alkyl, preferably at least one of R1, R2 and R3 is a methyl group, more preferably at least two are methyl groups, and further preferably all are methyl groups; R4, R5 and R6, which may be the same or different, are independently selected from hydrogen, C 1-4 Saturated hydrocarbon group, C 1-4 Alkoxy and halogen, preferably at least one of R4, R5 and R6 is hydrogen or C 1-4 Saturated hydrocarbon group, such as R4 or R6 is C 1-4 Saturated hydrocarbon groups, more preferably at least two of which are independently hydrogen or C 1-4 Saturated hydrocarbon group, for example, R4 and R6 are C 1-4 Saturated hydrocarbon group, further preferably three are independently hydrogen or C 1-4 Saturated hydrocarbon groups, particularly preferably all three are hydrogen, wherein the alkyl group is preferably methyl.

19. The kit of claim 18, wherein: Based on the total amount of the liquid desorbent, the desorbent comprises 30-95 wt%, preferably 30-80 wt%, more preferably 30-50% of the alkylbenzene compound, and 5-70 wt%, preferably 20-70 wt%, more preferably 50-70 wt% of an alkane selected from C5-C14 normal alkanes, preferably selected from C6-C10 normal alkanes, or consists of the same.

20. The kit according to claim 18 or 19, wherein in formula (I), at least two of R1, R2 and R3 are methyl, and R4, R5 and R6 are independently hydrogen or C 1-4 Saturated hydrocarbon group, and at least one of which is hydrogen; preferably at least two of R4, R5 and R6 are hydrogen, and the C 1-4 The saturated hydrocarbon group is methyl; More preferably, the alkylbenzene compound is selected from 1,2,3-trimethylbenzene, 1,2,3,4-tetramethylbenzene, 1,2,3,4,5-pentamethylbenzene and 3-ethyl-o-xylene, preferably 1,2,3-trimethylbenzene or 1,2,3,4-tetramethylbenzene.

21. The kit according to any one of claims 18 to 20, wherein the adsorbent comprises one or more, preferably one or two, of Group IA, IIA and IB metal ions as charge-balancing cations, wherein the Group IA metal ions are preferably selected from Li + and Na + , the Group IIA metal ion is preferably selected from Mg 2+ 、Sr 2+ and Ba 2+ , the IB group metal ion is preferably Ag + Preferably, the total amount of Group IA, IIA and IB metals in the adsorbent is 10-45% calculated as metal oxides and based on the total amount of the adsorbent, Preferably, the particle size of the Y-type molecular sieve in the solid adsorbent is 0.5-2.0 μm, preferably 0.8-1.2 μm. More preferably, the adsorbent contains 0.05-2 wt%, preferably 0.05-1 wt%, more preferably 0.05-0.8 wt%, and further preferably 0.1-0.5 wt% of adsorbed water. More preferably, the adsorbent comprises at least 90 wt% of NaY molecular sieve as an active component, and is preferably subjected to metal ion exchange treatment to achieve a metal ion exchange degree of 78.0-99.9%.

22. The kit according to claim 21, wherein the liquid desorbent comprises 30-50 wt% of the alkylbenzene compound and 50-70 wt% of an alkane selected from C5-C14 normal alkanes, based on the total amount of the liquid desorbent; and the charge-balancing cation of the solid adsorbent is selected from Na + 、Sr 2+ 、Ba 2+ and Ag + , and the adsorbent contains 0.05-0.8 wt%, preferably 0.1-0.5 wt% of adsorbed water.

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