Modified X-type molecular sieve, adsorbent containing the modified X-type molecular sieve, and method for preparing and using the same

Abstract

The present invention relates to a modified X-type molecular sieve, the surface area of ​​which is 9.5-19 m 2 / g, with the sum of the mesopore volume and macropore volume accounting for 6-18% of the total pore volume. The present invention also relates to an adsorbent for aromatic hydrocarbon isomers containing a modified X-type molecular sieve, a preparation method thereof, and use thereof. The modified X-type molecular sieve and the adsorbent are used for the adsorption and separation of p-xylene from mixed C8 aromatic hydrocarbons.

Description

[Technical Field]

[0001] The present invention relates to the technical field of adsorptive separation of organic substances, more particularly to a modified X-type molecular sieve, an adsorbent containing the modified X-type molecular sieve as an active ingredient, and methods for preparing and using the same. [Background technology]

[0002] Aromatic monomers are important petrochemical base materials with high added value and are widely used in the production of polyesters, pesticides, pharmaceuticals, and other products. In industrial production processes, aromatic hydrocarbon isomers with multiple substituents are typically produced as mixtures, which require further separation to obtain high-value-added monomers. Because these aromatic hydrocarbon isomers have very similar boiling points, they cannot be separated and purified using conventional distillation processes. Therefore, selective adsorption is now widely used in industry to separate these aromatic hydrocarbon isomers. The most widely used application of this technology is the separation of p-xylene from mixed C8 aromatic hydrocarbons.

[0003] X-type molecular sieve adsorbents exchanged with barium ions or barium ions and potassium ions have the property of selectively adsorbing p-xylene. In the simulated moving bed process, mixed C8 aromatic hydrocarbons and the adsorbent are repeatedly adsorbed and desorbed, enriching the adsorbent with p-xylene. High-purity p-xylene is then obtained through desorption and distillation. The key to obtaining high-purity p-xylene is the preparation of a high-performance adsorbent.

[0004] The active ingredient used as an adsorbent for industrial p-xylene separation is primarily type X molecular sieve. Type X molecular sieve is uniformly mixed with clay as a binder at a certain ratio, then rolled into balls, dried, calcined, and subjected to cation exchange to obtain adsorbent pellets. Adsorption capacity and mass transfer performance are important indices for evaluating adsorbents. Higher adsorption capacity and excellent mass transfer performance are advantageous for obtaining high-purity p-xylene products.

[0005] Both U.S. Pat. No. 3,960,774 and Chinese Patent Publication No. 1,565,718 report methods for increasing the adsorption capacity of adsorbents by treating the adsorbent with an aqueous solution containing sodium hydroxide to convert the binder therein into X-type zeolite.

[0006] CN1275926 discloses an agglomerated zeolite adsorbent made from X zeolite with a Si / Al atomic ratio of 1-1.15, which is exchanged with barium and potassium ions. The exchangeable sites in the adsorbent contain at least 70% barium ions and up to 30% potassium ions. This adsorbent uses kaolin as a binder and increases its adsorption capacity by in-situ crystallization of X zeolite through alkaline solution treatment.

[0007] The selectivity of an adsorbent is primarily determined by the type of exchanged ions and the properties of the zeolite. U.S. Patent No. 3,997,620 demonstrates higher p-xylene selectivity by using an X zeolite adsorbent exchanged with bimetallic ions of strontium and barium.

[0008] The prior art also discloses steaming Y molecular sieves to form mesopores and macropores, which aims to improve the catalytic performance of the molecular sieves, but does not guarantee the adsorption capacity of the molecular sieves.

[0009] Therefore, the adsorption capacity and mass transfer performance of the adsorbents obtained by the prior art are still not completely satisfactory. Therefore, the technical problem to be solved by the present invention is to generate mesopores and macropores while maintaining a high micropore volume, that is, to improve the mass transfer efficiency of adsorption separation while maintaining the high adsorption capacity of X-type molecular sieves. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] U.S. Patent No. 3,960,774 [Patent Document 2] Chinese Patent Application Publication No. 1565718 [Patent Document 3] Chinese Patent Application Publication No. 1275926 [Patent Document 4] U.S. Patent No. 3,997,620 Summary of the Invention [Problem to be solved by the invention]

[0011] The first object of the present invention is to provide a modified X-type molecular sieve having mesopore and macropore channels, a preparation method thereof, and its use, which exhibits excellent mass transfer performance, adsorption capacity, and separation performance for p-xylene in the adsorptive separation of p-xylene.

[0012] A second object of the present invention is to provide an adsorbent, particularly an adsorbent for aromatic hydrocarbon isomers, containing a modified X-type molecular sieve having mesopore and macropore channels as an active ingredient, as well as a preparation method and use thereof. This adsorbent exhibits excellent mass transfer performance, adsorption capacity, and p-xylene separation performance in the adsorptive separation of p-xylene. [Means for solving the problem]

[0013] To achieve the first object of the present invention, in a first aspect, the present invention provides a carbon nanotube having a surface area of ​​9.5 to 19 m2 measured by a nitrogen physical adsorption method. 2 / g, and the sum of the mesopore volume and macropore volume accounts for 6 to 18% of the total pore volume, wherein the mesopores have a pore diameter of 10 nm to 50 nm, and the macropores have a pore diameter of more than 50 nm and less than 80 nm.

[0014] In a second aspect, the present invention provides a method for preparing a modified X-type molecular sieve, the method comprising the following steps: (1) placing the X-type molecular sieve under a water vapor atmosphere to carry out a hydrothermal treatment at a temperature of preferably 250-550°C for at least 0.5 hours, and then washing and drying to obtain a first product; (2) placing the first product obtained at the end of step (1) in an aqueous solution containing NaOH, SiO and an organic ammonium salt at a temperature of preferably 60-120°C for at least 0.5 hours, and then washing, drying and calcining the resulting modified X-type molecular sieve; The present invention is characterized by comprising:

[0015] In a third aspect, the present invention relates to the use of a modified X-type molecular sieve for adsorptive separation of aromatic hydrocarbon isomers, particularly p-xylene, characterized in that the modified X-type molecular sieve or a modified X-type molecular sieve prepared by the method for preparing the modified X-type molecular sieve is used as an adsorbent.

[0016] To achieve the second object of the present invention, in a fourth aspect, the present invention provides an adsorbent for aromatic hydrocarbon isomers, particularly p-xylene, characterized in that the adsorbent contains the modified X-type molecular sieve according to the first aspect, and the surface area of ​​the modified X-type molecular sieve is 9.5 to 19 m. 2 / g, the sum of the mesopore volume and macropore volume accounts for 6% to 18% of the total pore volume, the mesopores are pores with a pore diameter of 10 nm to 50 nm, and the macropores are pores with a pore diameter of more than 50 nm and less than 80 nm. According to a preferred embodiment, the adsorbent for aromatic hydrocarbon isomers contains 88 to 95 mass %, preferably 90 to 94 mass %, of a modified X-type molecular sieve. Preferably, the adsorbent for aromatic hydrocarbon isomers further contains 4 to 11 mass % of a transformed crystalline X-type molecular sieve and 1 to 3 mass % of a matrix.

[0017] In a fifth aspect, the present invention provides a method for preparing the adsorbent for aromatic hydrocarbon isomers as described above, the method comprising the steps of: (1) placing the X-type molecular sieve in a water vapor atmosphere to perform hydrothermal treatment, and then washing and drying to obtain a first product; (2) treating the first product obtained in step (1) in an aqueous solution containing NaOH, SiO2 and an organic ammonium salt, followed by washing, drying and calcining to obtain a modified X-type molecular sieve; (3) mixing the modified X-type molecular sieve obtained in step (2) with a binder to form a molded body, and then calcining the molded body; (4) treating the compact obtained in step (3) with an alkaline solution to crystallize the binder in situ, and then drying; (5) barium ion-exchanging the product obtained in step (4), optionally potassium ion-exchanging it, and then drying it to obtain an adsorbent for aromatic isomers; Includes.

[0018] According to one preferred embodiment, the present invention provides a method for preparing the adsorbent for aromatic hydrocarbon isomers, comprising the following steps: (1) placing the X-type molecular sieve in a water vapor atmosphere to perform hydrothermal treatment at a temperature of 250-550°C for at least 0.5 hours, and then washing and drying to obtain a first product; (2) placing the first product obtained in step (1) in an aqueous solution containing NaOH, SiO2 and an organic ammonium salt, treating at a temperature of 60-120°C for at least 0.5 hours, and then washing, drying and calcining to obtain a modified X-type molecular sieve; (3) molding the modified X-type molecular sieve obtained in step (2) with a binder, drying, and calcining to obtain a molded body, wherein the shape of the molded body is preferably small spheres; (4) treating the molded body obtained at the end of step (3) with a mixed solution of sodium hydroxide and potassium hydroxide to crystallize the binder therein in situ, and then drying; (5) subjecting the dried compact obtained in step (4) to cation exchange with a soluble barium salt solution or a solution of a soluble barium salt and a soluble potassium salt, followed by drying and activation; The present invention is characterized by comprising:

[0019] In a sixth aspect, the present invention also relates to the use of the adsorbent for the adsorptive separation of aromatic hydrocarbon isomers, in particular p-xylene.

[0020] The modified X-type molecular sieve and the adsorbent containing the modified X-type molecular sieve provided by the present invention maintain a relatively high adsorption capacity, and at the same time, have mesopore channels and macropore channels, which significantly improve the mass transfer performance, thereby improving the separation performance of aromatic hydrocarbon isomers (especially p-xylene).

[0021] The following drawings, together with the following specific embodiments, are used to explain the present invention, but are not intended to limit the protection scope of the present invention. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a pore size distribution curve of mesopores and macropores of the X-type molecular sieve used in step (1) of Example 1. [Figure 2] 1 is a pore size distribution curve of mesopores and macropores of the modified X-type molecular sieve A obtained in step (2) of Example 1. [Figure 3] FIG. 1 is a schematic diagram of the small-scale simulated moving bed adsorptive separation carried out in Example 13. DETAILED DESCRIPTION OF THE INVENTION

[0023] (Detailed Description of the Invention) Specific embodiments of the present application are described in detail below, but it should be noted that the scope of protection of the present application is not limited to these specific embodiments, but is determined by the appended claims.

[0024] Specific numerical values ​​(including the endpoints of numerical ranges) disclosed herein are not limited to the exact value, but should be understood to encompass values ​​near that exact value, such as all possible values ​​within a range of ±5% of the exact value. Furthermore, by combining any of the endpoints of the disclosed numerical ranges, or any combination of endpoints with specific range values, one or more new numerical ranges can be obtained, and these new numerical ranges should also be considered to be specifically disclosed herein.

[0025] Unless otherwise specified, terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. If a term is defined herein and that definition differs from the meaning commonly understood in the art, the definition herein shall prevail.

[0026] In this application, the pore volume and surface area of ​​the molecular sieve are measured by nitrogen physisorption.

[0027] In this application, except for the contents explicitly described, any unmentioned matter or item can be directly applied to the aspects known in the art without any modifications. Furthermore, 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 shall be considered as part of the original disclosure or original record of this application, unless a person skilled in the art finds such combination to be obviously unreasonable, and shall not be considered as new content not disclosed or anticipated herein.

[0028] All patent and non-patent literature (including but not limited to textbooks and journal articles) cited herein is hereby incorporated by reference in its entirety.

[0029] The present inventors believe that adsorption capacity and mesopore channels are essential for maintaining the high separation performance of type X molecular sieves. Without being limited to a particular theory, the present inventors surprisingly found that treating type X molecular sieves in a high-temperature steam atmosphere slightly damages their framework structure. Furthermore, placing the slightly damaged type X molecular sieve in an alkaline solution containing NaOH, SiO2, and an organic ammonium salt for treatment repairs the partially damaged type X molecular sieve. At the same time, the organic amines generated by the organic ammonium salt penetrate into the mesopore channels, occupying these sites and inhibiting crystal growth at these sites, thereby forming mesopore and macropore channels while maintaining a high micropore volume. The formation of such mesopore and macropore channels contributes to improving the mass transfer performance of type X molecular sieves. Furthermore, the higher micropore volume ensures the adsorption capacity of type X molecular sieves, thereby improving the separation performance of aromatic hydrocarbon isomers, especially p-xylene. According to the preparation method of the modified X-type molecular sieve of the present invention, by combining the high-temperature steam treatment in step (1) with the modification step of treating with an alkaline aqueous solution containing NaOH, SiO2 and an organic ammonium salt in step (2), a modified X-type molecular sieve with high adsorption capacity and significantly improved mass transfer performance can be obtained.

[0030] As described above, the present invention provides a carbon nanotube having a surface area of ​​9.5 to 19 m2 measured by nitrogen physical adsorption. 2 / g, preferably 10 to 18 m 2 / g, e.g., 11m 2 / g, 12m 2 / g, 13m 2 / g, 14m 2 / g, 15m 2 / g, 16m 2 / g, or 17m 2The present invention provides a modified X-type molecular sieve having a pore size of 1000 nm / g. The sum of the mesopore volume and macropore volume accounts for 6% to 18%, preferably 8% to 15%, and more preferably 10.5% to 15% of the total pore volume. The content of amorphous species is 2 to 12% by mass, preferably 2.5 to 10.0% by mass, more preferably 3.0 to 8.0% by mass, for example, 4.0%, 5%, 6%, or 7% by mass. Here, the mesopores refer to pores with a pore size of 10 nm to 50 nm, and the macropores refer to pores with a pore size of more than 50 nm but less than 80 nm. The modified X-type molecular sieve preferably has a micropore volume of 0.290-0.340 g / ml, preferably 0.300-0.330 g / ml, and a total pore volume of 0.340-0.390 g / ml, preferably 0.350-0.380 g / ml, where the micropores refer to pores with a diameter of less than 2 nm in the X-type molecular sieve.

[0031] According to one preferred embodiment, in the modified X-type molecular sieve, the SiO2 / Al2O3 molar ratio is 2.21-2.55, for example, 2.25, 2.3, 2.4 or 2.5, preferably 2.25-2.4.

[0032] According to one preferred embodiment, the particle size of the modified X-type molecular sieve is 0.6 μm to 2.5 μm, for example, 0.8 μm, 0.9 μm, 1.0 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2.0 μm, 2.2 μm, 2.4 μm or 2.5 μm, preferably 0.8 μm to 1.5 μm.

[0033] According to one preferred embodiment, the cations contained in the modified X-type molecular sieve are Na, or the cations contained in the modified X-type molecular sieve are Na and K.

[0034] The present invention also provides a method for producing a method for manufacturing a semiconductor device, comprising the steps of: (1) placing the X-type molecular sieve in a water vapor atmosphere and treating it at a temperature of 250-550°C for at least 0.5 hours, and then washing and drying it to obtain a first product; (2) placing the first product obtained in step (1) in an aqueous solution containing NaOH, SiO2 and an organic ammonium salt, treating at a temperature of 60-120°C for at least 0.5 hours, and then washing, drying and calcining the resulting modified X-type molecular sieve; The present invention provides a method for preparing a modified X-type molecular sieve, comprising:

[0035] According to a preferred embodiment, in step (1) of the preparation method of the modified X-type molecular sieve, the SiO2 / Al2O3 molar ratio of the X-type molecular sieve used is 2.0-2.5, e.g., 2.2, 2.3, or 2.4, and its particle size is 0.6-2.5 μm, e.g., 0.8 μm, 0.9 μm, 1.0 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2.0 μm, 2.2 μm, 2.4 μm, or 2.5 μm. More preferably, the SiO2 / Al2O3 molar ratio of the X-type molecular sieve used is 2.25-2.40, and its particle size is 0.8-1.5 μm.

[0036] According to one preferred embodiment, the water vapor atmosphere used in step (1) of the preparation method comprises water vapor and an inert gas, or water vapor and air, and the inert gas is preferably nitrogen, carbon dioxide, argon, or the like. The temperature of the water vapor atmosphere is preferably 300 to 500°C. The water vapor partial pressure in the water vapor atmosphere is preferably 0.6 to 1.0 bar, for example, 0.7 bar, 0.8 bar, and 0.9 bar. The treatment time is preferably at least 1 hour, preferably at least 2 hours, at least 3 hours, for example, 4 hours, 5 hours, or 6 hours, or up to 50 hours, up to 40 hours, or up to 30 hours, preferably up to 20 hours, and preferably up to 10 hours.

[0037] According to a preferred embodiment, in step (1) of the preparation method of the modified X-type molecular sieve, the X-type molecular sieve is washed with deionized water. Preferably, the ratio of the volume of deionized water to the volume of the X-type molecular sieve used is at least 3:1, preferably 20:1 to 5:1. The X-type molecular sieve is then dried at a temperature of 60 to 130°C for 1 to 20 hours, preferably 2 to 15 hours.

[0038] According to a preferred embodiment, in the aqueous solution containing NaOH, SiO2 and an organic ammonium salt used in step (2) of the preparation method for the modified X-type molecular sieve, the concentration of NaOH is 1.0-2.0 mol / L, preferably 1.2-1.8 mol / L, more preferably 1.4-1.6 mol / L. The concentration of SiO2 is 5.0 to 20.0 g / L, preferably 6.0 to 18.0 g / L, and more preferably 8.0 to 16.0 g / L, and the concentration of the organic ammonium salt is 0.0005 to 0.05 mol / L, for example, 0.003 mol / L, 0.005 mol / L, 0.01 mol / L, 0.013 mol / L, 0.018 mol / L, 0.023 mol / L, 0.028 mol / L, 0.033 mol / L, 0.038 mol / L, 0.043 mol / L, or 0.048 mol / L, preferably 0.001 to 0.04 mol / L, and more preferably 0.008 to 0.03 mol / L. The ratio of the aqueous solution containing NaOH, SiO, and an organic ammonium salt to the first product is 2-5:1, preferably 3-4:1, with the aqueous solution containing NaOH, SiO, and an organic ammonium salt measured in milliliters and the first product measured in grams. Preferably, the time for treating the first product in the aqueous solution containing NaOH, SiO, and an organic ammonium salt is at least 1 hour, preferably at least 1.5 hours, preferably at least 3 hours, and up to 50 hours, preferably up to 40 hours, 30 hours, 20 hours, or 15 hours, and the treatment temperature is 60-120°C, preferably 70-100°C, more preferably 80-90°C.

[0039] According to a preferred embodiment, in step (2) of the preparation method of the modified X-type molecular sieve, the product treated with the aqueous solution is washed with deionized water until the pH value of the deionized water is less than 10, and then dried at a temperature of 60-130°C, preferably 70-120°C, for 1-20 hours, preferably 2-15 hours.

[0040] According to a preferred embodiment, the organic ammonium salt used in step (2) of the preparation method of the modified X-type molecular sieve has a total carbon number of 9 to 25, preferably 11 to 20, and preferably has one or more C3 to C20 alkyl groups. Examples include dodecyltrimethylammonium chloride, tetradecyltrimethylammonium chloride, hexadecyltrimethylammonium chloride, octadecyltrimethylammonium chloride, etc.

[0041] According to a preferred embodiment, the calcination carried out in step (2) of the preparation method of the modified X-type molecular sieve is a multi-stage (n-stage) calcination, where n is 4 or more, e.g., 5, 6, 7, etc., in which the constant temperature time of each stage is 1.0 hour or more, e.g., 1.5 hours, 2 hours, 3 hours, 4 hours, etc., and the maximum temperature of each stage does not exceed 550°C, e.g., 530°C, 500°C, 450°C.

[0042] The steam treatment in step (1) of the preparation method for modified X-type molecular sieves generates amorphous species. When treated with an aqueous solution containing NaOH, SiO2, and an organic ammonium salt in step (2), the amorphous species do not completely crystallize into X-type molecular sieves, and a small amount of amorphous species remains. During the calcination process in step (2), the organic amine burns and the resulting localized high temperature partially destroys the molecular sieve structure, causing the amorphous species to reform.

[0043] Measurement method of amorphous content: The pore volumes of the X-type molecular sieve and the modified X-type molecular sieve measured by nitrogen physical adsorption method are V1 and V2, respectively, and the amorphous content is 100% ~ V2 / V1.

[0044] The present invention also provides an adsorbent for aromatic hydrocarbon isomers, particularly an adsorbent for C8 aromatic hydrocarbons, preferably an adsorbent for p-xylene, comprising a modified X-type molecular sieve, more preferably comprising 88-95 wt. % of the modified X-type molecular sieve, 4-11 wt. % of the converted crystalline X-type molecular sieve, and 1-3 wt. % of a matrix, wherein the surface area of ​​the modified X-type molecular sieve is 9.5-19 m as measured by nitrogen physical adsorption. 2 / g, and the sum of the mesopore volume and macropore volume accounts for 6% to 18% of the total pore volume, where mesopores are pores with a pore diameter of 10 nm to 50 nm, and macropores are pores with a pore diameter of more than 50 nm and less than 80 nm. The adsorption capacity of the adsorbent for aromatic hydrocarbon isomers is 175 to 186 mg / g, preferably 177 to 184 mg / g, as measured by a toluene dynamic adsorption method.

[0045] The converted crystalline X-type molecular sieve refers to a crystallized molecular sieve portion obtained by in situ crystallizing a sintered molded body containing a binder and a modified molecular sieve using an alkaline solution such as a mixed solution of sodium hydroxide and potassium hydroxide in the production of an adsorbent.

[0046] In the present application, the matrix is ​​a binder, which may be selected from, for example, kaolin, dickite, perlite, firestone, halloysite, hydromica, montmorillonite, or a combination thereof.

[0047] As a second object of the present invention, the present invention provides a method for preparing the above-mentioned adsorbent for aromatic hydrocarbon isomers, the method comprising the following steps: (1) placing the X-type molecular sieve in a water vapor atmosphere to perform hydrothermal treatment, and then washing and drying to obtain a first product; (2) treating the first product obtained in step (1) in an aqueous solution containing NaOH, SiO2 and an organic ammonium salt, followed by washing, drying and calcining to obtain a modified X-type molecular sieve; (3) mixing the modified X-type molecular sieve obtained in step (2) with a binder, molding the mixture, and calcining the mixture to obtain a molded body; (4) treating the molded body obtained in step (3) with an alkaline solution to in-situ crystallize the binder therein, and drying; (5) barium ion-exchanging the product obtained in step (4), optionally potassium ion-exchanging it, and then drying it to obtain an adsorbent for aromatic isomers; Includes.

[0048] In step (3) of the method for preparing the adsorbent, the shaping can be achieved by various shaping methods commonly used in the art, and the present application does not impose any strict limitations thereon.

[0049] In particular, the present invention relates to a method for preparing an adsorbent for aromatic hydrocarbon isomers, in particular an adsorbent for C8 aromatic hydrocarbons, preferably an adsorbent for p-xylene, comprising the following steps: (1) placing the X-type molecular sieve in a water vapor atmosphere to perform hydrothermal treatment at a temperature of 250-550°C for at least 0.5 hours, and then washing and drying to obtain a first product; (2) placing the first product obtained in step (1) in an aqueous solution containing NaOH, SiO2 and an organic ammonium salt, treating at a temperature of 60-120°C for at least 0.5 hours, and then washing, drying and calcining to obtain a modified X-type molecular sieve; (3) uniformly mixing the modified X-type molecular sieve obtained in step (2) with a binder, molding the mixture, and then drying and calcining the mixture to obtain a molded body, the shape of which is preferably small spheres; (4) treating the molded body obtained at the end of step (3) with a mixed solution of sodium hydroxide and potassium hydroxide to in-situ crystallize the binder therein, and then drying; (5) subjecting the dried compact obtained in step (4) to cation exchange with a soluble barium salt solution or a solution of a soluble barium salt and a soluble potassium salt, followed by drying and activation; The present invention provides a method comprising:

[0050] According to a preferred embodiment, the SiO2 / Al2O3 molar ratio of the X-type molecular sieve used in step (1) of the adsorbent preparation method is 2.0-2.5, e.g., 2.2, 2.3, or 2.4, and the particle size of the X-type molecular sieve is 0.6-2.5 μm, e.g., 0.8 μm, 0.9 μm, 1.0 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2.0 μm, 2.2 μm, 2.4 μm, or 2.5 μm. More preferably, the SiO2 / Al2O3 molar ratio of the X-type molecular sieve used is 2.25-2.40, and the particle size of the X-type molecular sieve is 0.8-1.5 μm.

[0051] According to one preferred embodiment, the water vapor atmosphere used in step (1) of the method for preparing the adsorbent contains water vapor and an inert gas or air. The inert gas is preferably nitrogen, carbon dioxide, argon, or the like. The water vapor partial pressure in the water vapor atmosphere is preferably 0.6 to 1.0 bar, for example, 0.7 bar, 0.8 bar, and 0.9 bar. Preferably, the treatment time is at least 1 hour, at least 2 hours, for example, 4 hours, 5 hours, or 6 hours, and is at most 50 hours, at most 40 hours, or at most 30 hours, preferably at most 20 hours, and preferably at most 10 hours.

[0052] According to one preferred embodiment, in step (1) of the method for preparing the adsorbent, the X-type molecular sieve is washed with deionized water, preferably in a ratio of the volume of deionized water to the volume of the X-type molecular sieve of at least 3:1, preferably 20:1 to 5:1, and then dried at a temperature of 60 to 130°C for 1 to 20 hours, preferably 2 to 15 hours.

[0053] According to one preferred embodiment, in the aqueous solution containing NaOH, SiO2, and an organic ammonium salt used in step (2) of the adsorbent preparation method, the concentration of NaOH is 1.0 to 2.0 mol / L, preferably 1.2 to 1.8 mol / L, more preferably 1.4 to 1.6 mol / L, and the concentration of SiO2 is 5.0 to 20.0 g / L, preferably 6 to 18 g / L, more preferably 8 to 16 g / L. The concentration of the organic ammonium salt is 0.0005 to 0.05 mol / L, for example, 0.001 mol / L, 0.003 mol / L, 0.005 mol / L, 0.01 mol / L, 0.013 mol / L, 0.018 mol / L, 0.023 mol / L, 0.028 mol / L, 0.033 mol / L, 0.038 mol / L, 0.043 mol / L, or 0.048 mol / L, preferably 0.001 to 0.04 mol / L, more preferably 0.01 to 0.03 mol / L. The ratio of the aqueous solution containing NaOH, SiO, and organic ammonium salt to the first product is 2 to 5:1, for example, 3:1 or 4:1, where the aqueous solution containing NaOH, SiO, and organic ammonium salt is measured in milliliters and the first product is measured in grams. Preferably, the treatment time of the first product in the aqueous solution comprising NaOH, SiO2 and an organic ammonium salt is at least 1 hour, preferably at least 1.5 hours, preferably at least 3 hours, and up to 50 hours, preferably up to 40 hours, 30 hours, 20 hours, or 15 hours.

[0054] According to one preferred embodiment, in step (2) of the method for preparing the adsorbent, the treated product is washed with deionized water until the pH value of the deionized water is less than 10, and then dried at a temperature of 60 to 130°C for 1 to 20 hours, preferably 2 to 15 hours.

[0055] According to one preferred embodiment, the organic ammonium salt used in step (2) of the method for preparing the adsorbent has a total carbon number of 9 to 25, preferably 11 to 20, and preferably has one or more C3 to C20 alkyl groups. Examples include dodecyltrimethylammonium chloride, tetradecyltrimethylammonium chloride, hexadecyltrimethylammonium chloride, and octadecyltrimethylammonium chloride.

[0056] According to one preferred embodiment, the calcination carried out in step (2) of the method for preparing the adsorbent is a multi-stage calcination, and preferably, the number of calcination stages n is 4 or more, for example, n=5, 6, 7, etc. In the multi-stage calcination, the constant temperature time of each stage is 1.0 hour or more, for example, 1.5 hours, 2 hours, 3 hours, or 4 hours, etc., and the maximum temperature of each stage does not exceed 550°C, for example, 530°C, 500°C, or 400°C.

[0057] According to a preferred embodiment, in step (3) of the method for preparing the adsorbent, the mass ratio of the modified X-type molecular sieve to the binder is 88-95:5-12, for example, 89:11, 90:10, 91:9, 92:8, 93:7 or 94:6.

[0058] According to one preferred embodiment, in step (3) of the method for preparing the adsorbent, the shaping is carried out by ball rolling, which involves gradually agglomerating and growing the shaping powder obtained by mixing the X-type molecular sieve with a binder in a rotating disk, and continuously spraying water during the ball rolling to wet the surface of the small globules and allow the powder to adhere.

[0059] According to one preferred embodiment, in step (3) of the method for preparing the adsorbent, the shaping is performed by ball rolling, and the amount of water added during ball rolling is 6 to 22% by mass of the total amount of solid powder, for example, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 16%, 17%, 18%, 19%, and 20% by mass.

[0060] According to one preferred embodiment, the binder used in step (3) of the adsorbent preparation method is selected from kaolin, dickite, perlite, firestone, halloysite, hydromica, montmorillonite, or a combination thereof. More preferably, the binder used contains 75 to 95% by mass of kaolin and 5 to 15% by mass of halloysite. A binder with this composition can be more easily converted into X-type molecular sieves during in situ crystallization in step (4), thereby improving the adsorption capacity and separation performance of the adsorbent.

[0061] According to one preferred embodiment, in step (3) of the method for preparing the adsorbent, the drying temperature is 80 to 150°C, for example, 90°C, 100°C, 110°C, 120°C, 130°C, or 140°C, and the drying time is 0.5 to 20.0 hours, for example, 1.0 hour, 2.0 hours, 3.0 hours, 4.0 hours, 5.0 hours, 6.0 hours, 9.0 hours, or 12.0 hours.

[0062] According to one preferred embodiment, in step (3) of the method for preparing the adsorbent, the calcination temperature is 500 to 700°C, for example, 500°C, 520°C, 540°C, 560°C, 580°C, 600°C, 620°C, 640°C, 660°C, 680°C, or 700°C, and the calcination time is 0.5 to 6.0 hours, for example, 0.5 hours, 1.0 hours, 1.5 hours, 2.0 hours, 2.5 hours, 3.0 hours, 3.5 hours, 4.0 hours, 4.5 hours, 5.0 hours, 5.5 hours, or 6.0 hours.

[0063] According to one preferred embodiment, in step (4) of the method for preparing the adsorbent, the in situ crystallization temperature is 80 to 100°C, for example, 85°C, 90°C, or 95°C, and the in situ crystallization time is 1.5 to 6.0 hours, for example, 1.5 hours, 2.0 hours, 2.5 hours, 3.0 hours, 3.5 hours, 4.0 hours, 4.5 hours, 5.0 hours, 5.5 hours, or 6.0 hours.

[0064] According to a preferred embodiment, in the alkaline solution treatment in step (4) of the method for preparing the adsorbent, the liquid-solid volume ratio of the alkaline solution to the spheres is 1.2 to 4.0:1, for example, 1.2:1, 1.4:1, 1.6:1, 1.8:1, 2.0:1, 2.2:1, 2.4:1, 2.6:1, 2.8:1 or 3.0:1, preferably 2.0 to 3.0:1.

[0065] According to one preferred embodiment, in step (4) of the method for preparing the adsorbent, the hydroxide ion concentration in the mixed solution is 0.1 to 2.0 mol / L, preferably 0.3 to 1.8 mol / L, more preferably 0.5 to 1.5 mol / L, and the K / (Na+K) molar ratio is 0.1 to 0.6, for example, 0.2, 0.3, 0.4, or 0.5.

[0066] In step (5) of the method for preparing the p-xylene adsorbent, the spheres obtained in step (4) are subjected to cation exchange with a mixed solution of a soluble barium salt and a soluble potassium salt. Alternatively, the spheres obtained in step (4) are subjected to cation exchange with a solution of a soluble barium salt or a soluble potassium salt, thereby converting at least a part of the cation sites of the X-type molecular sieve contained therein to Ba. 2+ and / or K + Preferably, the cations in the exchange solution used are 2+ and / or K + ) and the total moles of Na in the molecular sieve + The ratio of the number of moles of 1 to 3.0, ie, the exchange ratio, is 1.5 to 3.0:1.

[0067] Without being limited to a particular theory, the applicant believes that the cation exchange treatment in step (5) allows barium ions, or barium ions and potassium ions, to coordinate with oxygen ions in the framework of the modified X-type molecular sieve, thereby generating a highly PX selective adsorption force field with D2 group symmetry within the modified X-type molecular sieve supercage, and the resulting adsorbent has higher separation performance.

[0068] According to one preferred embodiment, only barium ion exchange is performed in step (5), said barium ion exchange being performed with a solution of a soluble barium salt, said soluble barium salt preferably being selected from barium chloride, barium nitrate, or a combination thereof.

[0069] According to one preferred embodiment, in step (5), barium ion exchange is carried out first, followed by potassium ion exchange, or potassium ion exchange is carried out first, followed by barium ion exchange. The barium ion exchange is carried out using a solution of a soluble barium salt, preferably selected from barium chloride, barium nitrate, or a combination thereof. The potassium ion exchange is carried out using a solution of a soluble potassium salt, preferably selected from potassium chloride, potassium nitrate, or a combination thereof.

[0070] According to one preferred embodiment, in step (5), the barium ion exchange and the potassium ion exchange are simultaneously carried out using a mixed solution containing a soluble barium salt and a soluble potassium salt, and the soluble barium salt and the soluble potassium salt are selected as described above.

[0071] According to one preferred embodiment, the conditions for the barium ion exchange and optional potassium ion exchange in step (5) include a temperature of 60 to 97°C, for example, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, or 95°C, preferably 80 to 95°C, and a time of 2.0 to 48.0 hours, for example, 2.0 hours, 6.0 hours, 10.0 hours, 14.0 hours, 18.0 hours, 22.0 hours, 26.0 hours, 30.0 hours, 34.0 hours, 38.0 hours, 42.0 hours, 46.0 hours, or 48.0 hours, preferably 12.0 to 36.0 hours.

[0072] According to one preferred embodiment, the volumetric space velocities of the barium salt solution, the potassium salt solution, and the mixed solution of barium salt and potassium salt in the ion exchange in step (5) are each independently 1.0 to 20.0 h -1 For example, 1.0h -1 , 2.0h -1 , 3.0h -1 , 4.0h -1 , 5.0h -1 , 6.0h -1 , 7.0h -1 , 8.0h -1 , 9.0h -1 , 10.0h -1 , 12.0h -1 , 14.0h -1 , 16.0h -1 , 18.0h -1 or 20.0h -1 and preferably 1.0 to 10.0 h -1 is.

[0073] According to a preferred embodiment, the product obtained after ion exchange in step (5) is dried to obtain the modified X-type molecular sieve-based adsorbent. The drying temperature is preferably 60-130°C, preferably 70-120°C, and the drying time is 1.0-24.0 hours, preferably 3-15 hours.

[0074] According to one preferred embodiment, the cation-exchanged spheres in step (5) are washed with deionized water, wherein the ratio of the volume of deionized water to the volume of molecular sieve is 3-20, preferably 5-15, more preferably 6-12.

[0075] According to one preferred embodiment, the activation in step (5) is carried out under a nitrogen atmosphere at 50 to 120° C., preferably 60 to 100° C., for 5 to 30 hours, preferably 10 to 24 hours.

[0076] The present invention will be further explained below with reference to examples, but the present invention is not limited to these examples.

[0077] The surface area and pore volume of the X-type molecular sieve samples were measured using an ASAP 2020 physical adsorption apparatus manufactured by Micromeritics, USA. Before the measurement, the X-type molecular sieve samples were heated at 300-450°C and vacuum (10 -2 The X-type molecular sieve samples were degassed at a pressure of less than 1000 Pa for 6 to 16 hours, preferably at 300°C for 10 hours, and then subjected to nitrogen physical adsorption at 77 K. The micropore volume V1 of the X-type molecular sieve samples was measured using the t-plot method. The sum of the mesopore and macropore volumes was calculated by subtracting the micropore volume V1 from the total pore volume V at P / P0 = 0.99, where P is the pressure at the time of measurement and P0 is 0.1 MPa.

[0078] The elemental chemical composition of the molecular sieves was characterized by X-ray fluorescence spectroscopy (XRF), using a Shimadzu XRF-1800 X-ray fluorescence analyzer. Qualitative analysis of BaO, K2O, Na2O, Al2O3, and SiO2 was performed based on the correspondence between the wavelength of their characteristic X-ray fluorescence and their atomic numbers. Quantitative analysis of BaO, K2O, Na2O, Al2O3, and SiO2 was performed based on a comparison of their peak intensities at the X-ray fluorescence wavelengths with those of standard samples. The SiO2 / Al2O3 molar ratio of the molecular sieves was calculated based on the relative masses of SiO2 and Al2O3.

[0079] The crystal size information of the molecular sieve is characterized by FE-SEM photographs. The equipment used is a Hitachi S-4800 scanning electron microscope (Japan). The crystal size within the range of 10.0 μm × 10.0 μm is selected for measurement and calculation. The measured crystal size is the average value of all crystal sizes.

[0080] A dynamic pulse test apparatus is used to measure the separation performance of the X-type molecular sieve and the separation performance of the adsorbent containing the X-type molecular sieve.

[0081] The adsorption capacity of an adsorbent is determined by contacting a fixed mass of nitrogen gas loaded with toluene (toluene partial pressure 0.05 MPa) with the adsorbent at 35°C until the toluene reaches adsorption equilibrium. The adsorption capacity of the tested adsorbent material is calculated based on the mass difference between the adsorbent before and after toluene adsorption. Because toluene and p-xylene have similar kinetic diameters and can both be adsorbed in the micropore channels of X-type molecular sieves, the adsorption capacity of p-xylene on X-type molecular sieves is positively correlated with the adsorption capacity measured for toluene.

[0082] The dynamic pulse test equipment consists of a feed system, an adsorption column, a heating furnace, and a pressure control valve. The adsorption column is a Φ6 × 1800 mm stainless steel tube with a 50 ml adsorbent filling capacity. The lower inlet of the adsorption column is connected to the feed system and nitrogen system, and the upper outlet is connected to a pressure control valve and then to a discharge collector. The desorbent used in the experiment was 30 vol% p-diethylbenzene (PDEB) and 70 vol% n-heptane. The pulse feed liquid consisted of 5 vol% ethylbenzene (EB), p-xylene (PX), m-xylene (MX), o-xylene (OX), and n-nonane (NC9), and 75 vol% desorbent.

[0083] Before the dynamic pulse test evaluation, the X-type molecular sieve samples were subjected to ion exchange. The specific procedure was as follows: the powdered molecular sieve was formed into tablets at a pressure of 25 MPa, crushed, and sieved to obtain particles of 300-850 μm. The ion exchange was carried out using a mixed solution of 0.18 mol / L barium chloride and 0.07 mol / L potassium chloride. The ion exchange was carried out in a column vessel at an exchange temperature of 90°C for 8 hours. The liquid volumetric space velocity of the ion exchange was 6 h. -1 is.

[0084] The adsorption selectivity was measured as follows: the adsorbent to be measured, with a particle size of 300 to 850 μm, was weighed, packed into an adsorption column, and shaken. After dehydration and activation at 160 to 190 °C under a nitrogen atmosphere, a desorbent was introduced to remove the gas from the system. The system pressure was increased to 0.8 MPa, the temperature was raised to 177 °C, the supply of the desorbent was stopped, and the volumetric space velocity was increased to 1.0 h -1 8 ml of pulsed feed solution was supplied at a volumetric space velocity of 1.5 h -1 The desorbent is supplied at 1000 kJ / min, and three drops of the desorbent sample are taken every two minutes and analyzed by gas chromatography. The desorption curves for the components NC9, EB, PX, MX, and OX are plotted with the desorbent volume on the horizontal axis and the concentration of each component (NC9, EB, PX, MX, and OX) on the vertical axis. NC9 is not adsorbed and can be used as a tracer to obtain the dead volume of the adsorption system. The midpoint of the tracer's half-width is set as zero, and the net retention volume R of each component (EB, PX, MX, and OX) is measured from the midpoint of the half-width to zero. The net retention volume of each component is proportional to the distribution coefficient at the adsorption equilibrium and reflects the interaction between each component and the adsorbent. The ratio of the net retention volumes of two components is the selectivity β. For example, the ratio of the net retention volume of PX to the net retention volume of EB is the ratio of the adsorption capacity of the adsorbent for PX to that of the adsorbent for EB, and is expressed as the adsorption selectivity of PX over EB, i.e., βP / E. The half-width W of PX is 1 / 2 indicates mass transfer performance, and W 1 / 2 The smaller the value, the better the mass transfer performance.

[0085] The adsorbent prepared by this invention is suitable for the liquid-phase adsorption separation of aromatic hydrocarbon isomers, particularly for the adsorption separation of p-xylene from a mixture of o-xylene, m-xylene, p-xylene, and ethylbenzene. Liquid-phase adsorption separation can be carried out using a multi-column series system or a simulated moving bed system using rotary valves or solenoid valves. The operating pressure for adsorption separation is 0.3 to 1.5 MPa, and the operating temperature is 120 to 180°C.

[0086] The present invention will be further described below with reference to examples, but the present invention is not limited to these. In the following examples and comparative examples, all reagents and raw materials used are commercially available products unless otherwise specified. [Example]

[0087] Example 1 Preparation of modified X-type molecular sieve: (1) X-type molecular sieve (SiO / AlO molar ratio 2.43, particle size 1.0 μm, micropore volume 0.335 g / mL, total pore volume 0.351 g / mL, surface area 5.5 m) 2 100 g of the sintered silica (100 g / g, the sum of the mesopore volume and macropore volume accounts for 4.6% of the total pore volume, and the pore size distribution is shown in Figure (1)) was placed in a steam atmosphere of a mixture of steam and air with a steam partial pressure of 0.7 bar and treated at 300 °C for 5 hours. It was then washed with deionized water and dried at 110 °C for 5 hours to obtain the first product. (2) 60 g of the first product obtained in step (1) was added to 200 ml of an alkaline solution containing 1.2 mol / L NaOH, 8.0 g / L SiO, and 0.003 mol / L hexadecyltrimethylammonium chloride, and treated at 95°C for 3.0 hours. The resulting solution was washed with deionized water until the pH was less than 10, dried at 100°C for 5 hours, and then calcined at constant temperatures of 200°C for 1.5 hours, 300°C for 1.5 hours, 400°C for 1.5 hours, and 550°C for 3.0 hours to obtain modified X-type molecular sieve sample A.

[0088] The surface area of ​​modified X-type molecular sieve sample A measured by nitrogen physical adsorption was 10.3 m 2 The total pore volume was 0.355 g / mL, the micropore volume was 0.324 g / mL, and the total pore volume was 0.355 g / mL. The sum of the mesopore volume and macropore volume accounted for 8.7% of the total pore volume, and the amorphous species content was 3.3% by mass. The pore size distribution is shown in Figure 2.

[0089] Modified X-type molecular sieve A was tableted under a pressure of 25 MPa, crushed, and sieved to obtain particles of 300 to 850 μm. Ion exchange was carried out in a column using a mixed solution of 0.18 mol / L barium chloride and 0.07 mol / L potassium chloride. The exchange temperature was 90°C, and the ion exchange was carried out in the column for 8 hours. The liquid volumetric space velocity of the ion exchange was 6 h -1 The mixture was then filtered under reduced pressure, and the resulting product was washed with 2000 mL of deionized water and dried at 90 °C for 12.0 hours. The adsorption selectivity and PX half-width of the modified X-type molecular sieve sample A were evaluated using a pulse test. The results are shown in Table 1.

[0090] Example 2 The preparation and evaluation were carried out according to the method of Example 1, except that in step (1), the X-type molecular sieve was placed in a water vapor atmosphere of a mixture of water vapor and nitrogen at a water vapor partial pressure of 0.9 bar and treated at 500°C for 2 hours to obtain modified X-type molecular sieve sample B.

[0091] The surface area of ​​modified X-type molecular sieve sample B measured by nitrogen physical adsorption was 10.4 m 2 / g, the micropore volume was 0.307 g / mL, the total pore volume was 0.343 g / mL, the sum of the mesopore volume and macropore volume accounted for 10.5% of the total pore volume, and the amorphous species content was 8.4 mass%.

[0092] The adsorption selectivity and PX half-width are shown in Table 1.

[0093] Example 3-1 The preparation and evaluation were carried out according to the method of Example 1, except that in step (2), the first product obtained in step (1) was treated with an alkaline solution containing 1.6 mol / L of NaOH, 12.0 g / L of SiO2, and 0.01 mol / L of dodecyltrimethylammonium chloride to obtain modified X-type molecular sieve sample C-1.

[0094] The surface area of ​​the modified X-type molecular sieve sample C-1 measured by nitrogen physical adsorption method was 12.6 m 2 / g, the micropore volume was 0.327 g / mL, the total pore volume was 0.365 g / mL, the sum of the mesopore volume and macropore volume accounted for 10.4% of the total pore volume, and the amorphous species content was 2.4 mass%.

[0095] The adsorption selectivity and PX half-width are shown in Table 1.

[0096] Example 3-2 The preparation and evaluation were carried out according to the method of Example 1, except that in step (2), the first product obtained in step (1) was treated with an alkaline solution containing 1.6 mol / L of NaOH, 12.0 g / L of SiO2, and 0.03 mol / L of dodecyltrimethylammonium chloride to obtain modified X-type molecular sieve sample C-2.

[0097] The surface area of ​​the modified X-type molecular sieve sample C-2 measured by nitrogen physical adsorption method was 13.2 m 2 / g, the micropore volume was 0.322 g / mL, the total pore volume was 0.375 g / mL, the sum of the mesopore volume and macropore volume accounted for 14.1% of the total pore volume, and the amorphous species content was 2.6 mass%.

[0098] The adsorption selectivity and PX half-width are shown in Table 1.

[0099] Comparative Example 3-3 The preparation and evaluation were carried out according to the method of Example 1, except that in step (2), the first product obtained in step (1) was treated with an alkaline solution containing 1.6 mol / L of NaOH, 12.0 g / L of SiO2, and 0 mol / L of dodecyltrimethylammonium chloride to obtain modified X-type molecular sieve sample C-3.

[0100] The surface area of ​​the modified X-type molecular sieve sample C-3 measured by nitrogen physical adsorption method was 5.8 m 2 / g, the micropore volume was 0.325 g / mL, the total pore volume was 0.344 g / mL, the sum of the mesopore volume and macropore volume accounted for 5.5% of the total pore volume, and the amorphous species content was 3.0 mass%.

[0101] The adsorption selectivity and PX half-width are shown in Table 1.

[0102] Example 4 The preparation and evaluation were carried out according to the method of Example 1, except that in step (2), the sample was dried at 100°C for 5 hours, and then calcined at constant temperatures of 150°C for 1.0 hour, 260°C for 1.0 hour, 380°C for 1.0 hour, 450°C for 1.0 hour, and 550°C for 4.0 hours to obtain modified X-type molecular sieve sample D.

[0103] The surface area of ​​modified X-type molecular sieve sample D measured by nitrogen physical adsorption was 16.8 m 2 / g, the micropore volume was 0.325 g / mL, the total pore volume was 0.377 g / mL, the sum of the mesopore volume and macropore volume accounted for 13.9% of the total pore volume, and the amorphous species content was 3.0 mass%.

[0104] The adsorption selectivity and PX half-width are shown in Table 1.

[0105] Example 5 Modified X-type molecular sieve sample E was prepared and evaluated according to the method of Example 1, except that in step (2), the first product obtained in step (1) was treated with 400 mL of an alkaline solution containing 1.2 mol / L NaOH, 8.0 g / L SiO2, and 0.003 mol / L hexadecyltrimethylammonium chloride.

[0106] The surface area of ​​the modified X-type molecular sieve sample E measured by nitrogen physical adsorption was 11.2 m 2 / g, the micropore volume was 0.320 g / mL, the total pore volume was 0.354 g / mL, the sum of the mesopore volume and macropore volume accounted for 9.6% of the total pore volume, and the amorphous species content was 4.5 mass%.

[0107] The adsorption selectivity and PX half-width are shown in Table 1.

[0108] Example 6 The preparation and evaluation were carried out according to the method of Example 1, except that in step (2), the sample was calcined at constant temperatures of 200°C for 1.5 hours, 300°C for 1.5 hours, and 550°C for 3.0 hours to obtain modified X-type molecular sieve sample F.

[0109] The surface area of ​​the modified X-type molecular sieve sample F measured by nitrogen physical adsorption was 15.6 m 2 / g, the micropore volume was 0.307 g / mL, the total pore volume was 0.360 g / mL, the sum of the mesopore volume and macropore volume accounted for 14.7% of the total pore volume, and the amorphous species content was 8.3 mass%.

[0110] The adsorption selectivity and PX half-width are shown in Table 1.

[0111] Comparative Example 1 100 g of X-type molecular sieve (SiO2 / Al2O3 molar ratio 2.43, particle size 1.0 μm, micropore volume 0.335 g / mL, total pore volume 0.351 g / mL, surface area 5.5 m) 2 / g, the sum of the mesopore volume and macropore volume accounts for 4.6% of the total pore volume) was placed in a steam atmosphere of a mixture of steam and air at a steam partial pressure of 0.7 bar and treated at 300°C for 5 hours, then washed with deionized water and dried at 110°C for 5 hours to obtain modified X-type molecular sieve comparison sample DB1.

[0112] The surface area of ​​the modified X-type molecular sieve comparison sample DB1 measured by nitrogen physical adsorption was 25.4 m 2 / g, the micropore volume was 0.256 g / mL, the total pore volume was 0.306 g / mL, the sum of the mesopore volume and macropore volume accounted for 16.3% of the total pore volume, and the amorphous species content was 23.5 mass%.

[0113] The adsorption selectivity and PX half-width are shown in Table 1.

[0114] Comparative Example 2 100 g of X-type molecular sieve (SiO2 / Al2O3 molar ratio 2.43, particle size 1.0 μm, micropore volume 0.335 g / mL, total pore volume 0.351 g / mL, surface area 5.5 m) 2The modified X-type molecular sieve (DB2) was placed in 200 mL of an alkaline solution containing 1.2 mol / L NaOH, 8.0 g / L SiO2, and 0.003 mol / L hexadecyltrimethylammonium chloride and treated at 95°C for 3.0 hours. The resulting solution was washed with deionized water until the pH reached less than 10, dried at 100°C for 5 hours, and calcined at constant temperatures of 200°C for 1.5 hours, 300°C for 1.5 hours, 400°C for 1.5 hours, and 550°C for 3.0 hours to obtain a comparative modified X-type molecular sieve (DB2).

[0115] The surface area of ​​the modified X-type molecular sieve comparison sample DB2 measured by nitrogen physical adsorption was 8.6 m 2 / g, the micropore volume was 0.328 g / mL, the total pore volume was 0.347 g / mL, the sum of the mesopore volume and macropore volume accounted for 5.5% of the total pore volume, and the amorphous species content was 2.1 mass%.

[0116] The adsorption selectivity and PX half-width are shown in Table 1.

[0117] Comparative Example 3 X-type molecular sieve (SiO2 / Al2O3 molar ratio 2.43, particle size 1.0 μm, micropore volume 0.335 g / mL, total pore volume 0.351 g / mL, surface area 5.5 m 2 / g, the sum of the mesopore volume and macropore volume accounts for 4.6% of the total pore volume) and the adsorption selectivity and PX half-width are shown in Table 1.

[0118] [Table 1]

[0119] In Table 1, W 1 / 2 is a value that directly reflects mass transfer performance. 1 / 2The smaller the value, the better the mass transfer performance. Therefore, the mass transfer performance of Examples 1 to 6 is significantly superior to that of Comparative Examples 1 to 4. Example 6 employs a three-stage calcination process, which results in a faster temperature rise rate than the four-stage or five-stage calcinations of Examples 1 to 5. Therefore, when localized high temperatures are generated by the combustion of the organic amine produced by the organic ammonium salt, the X-type molecular sieve is destroyed, resulting in a decrease in adsorption capacity and mass transfer performance, and a corresponding decrease in adsorption selectivity. The adsorption capacity is related to the crystallinity of the X-type molecular sieve.

[0120] In Table 1, the adsorption selectivity is influenced by both mass transfer performance and adsorption capacity. In Comparative Example 1, the use of only steam damages the X-type molecular sieve, reducing its crystallinity and producing a large amount of amorphous species. These amorphous species not only clog the mesopores but also significantly reduce the adsorption capacity. Therefore, the adsorption selectivity is the lowest. In Comparative Example 2, the X-type molecular sieve is treated with only an alkaline solution without steam treatment. Although the percentage increase in the sum of the mesopore volume and macropore volume to the total pore volume is smaller than that of the unmodified X-type molecular sieve, the calcination process slightly damages the X-type molecular sieve, reducing its adsorption capacity and mass transfer performance, and correspondingly reducing its adsorption selectivity. In Comparative Example 3, the unmodified X-type molecular sieve has fewer mesopores and macropores, resulting in poor mass transfer performance and poor adsorption selectivity for the prepared adsorbent. Comparing Examples 1, 3-1, and 3-2 with Comparative Example 3-3, it is clear that the presence of a relatively low content of organic ammonium salt in the alkaline solution is necessary and important when treating the X-type molecular sieve with an alkaline solution. The organic ammonium salt increases the proportion of mesopores and macropores, thereby significantly improving the mass transfer performance of the modified X-type molecular sieve. However, if the content of organic ammonium salt in the alkaline solution is too high, the mass transfer performance and adsorption capacity of the modified X-type molecular sieve will be adversely affected.

[0121] Example 7 Preparation of adsorbent containing modified X-type molecular sieve: (1) 100 kg of X-type molecular sieve (SiO / AlO molar ratio 2.43, particle size 1.0 μm, micropore volume 0.335 g / mL, total pore volume 0.351 g / mL, surface area 5.5 m) 2 / g, the sum of mesopore and macropore volumes accounts for 4.6% of the total pore volume) was placed in a steam atmosphere of a mixture of steam and air with a steam partial pressure of 0.7 bar and treated at 300°C for 5 hours to obtain the first product; (2) 98 kg of the first product obtained in step (1) was added to 300 L of an alkaline solution containing 1.2 mol / L NaOH, 8.0 g / L SiO2, and 0.003 mol / L hexadecyltrimethylammonium chloride, and treated at 95°C for 3.0 hours. The solution was washed with deionized water until the pH value was less than 10, dried at 100°C for 5 hours, and then calcined at constant temperatures of 200°C for 1.5 hours, 300°C for 1.5 hours, 400°C for 1.5 hours, and 550°C for 3.0 hours to obtain a modified X-type molecular sieve sample (g); (3) 92 kg of modified X-type molecular sieve and 8 kg of kaolin were mixed uniformly, placed on a rotating disk, and rolled while simultaneously spraying water to agglomerate the solid into small spheres. Small spheres with a particle size of 300 to 850 μm were collected, dried at 80°C for 10 hours, and then calcined at 540°C for 4 hours to obtain adsorbent matrix spheres. (4) The spheres obtained in step (3) were subjected to in situ crystallization using a mixed solution of sodium hydroxide and potassium hydroxide. The hydroxide ion concentration in the mixed solution was 1.0 mol / L, the K / (Na+K) molar ratio was 0.2, and the liquid / solid ratio was 3.0 L / kg. After treatment at 95°C for 4 hours, the spheres were washed with deionized water until the pH value was less than 10, and then dried at 100°C for 8 hours. (5) 130 mL of the spheres obtained in step (4) was packed into an ion exchange column, and cation exchange was performed using a mixed solution of 0.18 mol / L barium nitrate and 0.07 mol / L potassium nitrate at 0.1 MPa, 94 °C, and a volumetric space velocity of 8.0 h -1 The ion exchange was continued for 6 hours at 70°C. The total volume of the mixed solution was 5000 mL. After the ion exchange was completed, the solid was washed with 700 mL of deionized water at 70°C and activated for 24 hours at 70°C under a nitrogen atmosphere to obtain Adsorbent G.

[0122] The surface area of ​​the modified X-type molecular sieve sample g measured by nitrogen physical adsorption method was 10.3 m 2 / g, the micropore volume was 0.324 g / mL, the total pore volume was 0.355 g / mL, and the sum of the mesopore volume and macropore volume accounted for 8.7% of the total pore volume.

[0123] The adsorption selectivity, PX half-width, and toluene adsorption capacity of adsorbent G were evaluated by pulse tests. The results are shown in Table 2.

[0124] Example 8 The preparation and evaluation were carried out in the same manner as in Example 7, except that in step (1), the X-type molecular sieve was placed in a mixed atmosphere of water vapor and nitrogen with a water vapor partial pressure of 0.9 bar and treated at 500 °C for 2 hours to obtain a modified X-type molecular sieve sample h, from which adsorbent H was prepared.

[0125] The surface area of ​​the modified X-type molecular sieve sample H measured by nitrogen physical adsorption was 10.4 m 2 / g, the micropore volume was 0.307 g / mL, the total pore volume was 0.343 g / mL, and the sum of the mesopore volume and macropore volume accounted for 10.5% of the total pore volume.

[0126] The adsorption selectivity, PX half-width, and toluene adsorption capacity of adsorbent H are shown in Table 2.

[0127] Example 9-1 The preparation and evaluation were carried out according to the method of Example 7, except that in step (2), the first product obtained in step (1) was treated with an alkaline solution containing 1.6 mol / L of NaOH, 12.0 g / L of SiO2, and 0.01 mol / L of dodecyltrimethylammonium chloride. Modified X-type molecular sieve sample i-1 was obtained, and adsorbent I-1 was prepared from it.

[0128] The surface area of ​​the modified X-type molecular sieve sample i-1 measured by nitrogen physical adsorption method was 12.6 m 2 / g, the micropore volume was 0.327 g / mL, the total pore volume was 0.365 g / mL, and the sum of the mesopore volume and macropore volume accounted for 10.4% of the total pore volume.

[0129] The adsorption selectivity, PX half-width, and toluene adsorption capacity of adsorbent I-1 are shown in Table 2.

[0130] Example 9-2 The preparation and evaluation were carried out according to the method of Example 7, except that in step (2), the first product obtained in step (1) was treated with an alkaline solution containing 1.6 mol / L of NaOH, 12.0 g / L of SiO2, and 0.03 mol / L of dodecyltrimethylammonium chloride. Modified X-type molecular sieve sample i-2 was obtained, and adsorbent I-2 was obtained from it.

[0131] The surface area of ​​the modified X-type molecular sieve sample i-2 measured by nitrogen physical adsorption method was 13.2 m 2 / g, the micropore volume was 0.322 g / mL, the total pore volume was 0.375 g / mL, and the sum of the mesopore volume and macropore volume accounted for 14.1% of the total pore volume.

[0132] The adsorption selectivity, PX half-width, and toluene adsorption capacity of adsorbent I-2 are shown in Table 2.

[0133] Comparative Example 9-3 The preparation and evaluation were carried out in accordance with the method of Example 7. However, in step (2), an alkaline solution containing 1.6 mol / L of NaOH, 12.0 g / L of SiO2, and 0 mol / L of dodecyltrimethylammonium chloride was used to treat the first product obtained in step (1). Modified X-type molecular sieve sample db3 was obtained, and adsorbent DB3 was obtained from this.

[0134] The surface area of ​​the modified X-type molecular sieve sample db3 measured by nitrogen physical adsorption was 5.8 m 2 / g, the micropore volume was 0.325 g / mL, the total pore volume was 0.344 g / mL, and the sum of the mesopore volume and macropore volume accounted for 5.5% of the total pore volume.

[0135] The adsorption selectivity, PX half-width, and toluene adsorption capacity of adsorbent DB3 are shown in Table 2.

[0136] Example 10 The preparation and evaluation were carried out according to the method of Example 7, except that in step (2), the sample was dried at 100°C for 5 hours, and then calcined at 150°C for 1.0 hour, 260°C for 1.0 hour, 380°C for 1.0 hour, 450°C for 1.0 hour, and 550°C for 4.0 hours to obtain modified X-type molecular sieve sample j. This gave adsorbent J.

[0137] The surface area of ​​the modified X-type molecular sieve sample j measured by nitrogen physical adsorption was 16.8 m 2 / g, the micropore volume was 0.325 g / mL, the total pore volume was 0.377 g / mL, and the sum of the mesopore volume and macropore volume accounted for 13.9% of the total pore volume.

[0138] The adsorption selectivity, PX half-width, and toluene adsorption capacity of adsorbent J are shown in Table 2.

[0139] Example 11 The preparation and evaluation were carried out according to the method of Example 7, except that in step (2), 390 L of an alkaline solution containing 1.2 mol / L NaOH, 8.0 g / L SiO2, and 0.003 mol / L hexadecyltrimethylammonium chloride was used to treat the first product obtained in step (1). Modified X-type molecular sieve sample k was obtained, and adsorbent K was obtained from this.

[0140] The surface area of ​​the modified X-type molecular sieve sample k measured by nitrogen physical adsorption was 11.2 m 2 / g, the micropore volume was 0.320 g / mL, the total pore volume was 0.354 g / mL, and the sum of the mesopore volume and macropore volume accounted for 9.6% of the total pore volume.

[0141] The adsorption selectivity, PX half-width, and toluene adsorption capacity of adsorbent K are shown in Table 2.

[0142] Example 12 The preparation and evaluation were carried out according to the method of Example 7, except that in step (2), the modified X-type molecular sieve sample l was obtained by constant temperature calcination at 200°C for 1.5 hours, at 300°C for 1.5 hours, and at 550°C for 3.0 hours, and the adsorbent L was obtained.

[0143] The surface area of ​​the modified X-type molecular sieve sample l measured by nitrogen physical adsorption method was 15.6 m 2 / g, the micropore volume was 0.307 g / mL, the total pore volume was 0.360 g / mL, and the sum of the mesopore volume and macropore volume accounted for 14.7% of the total pore volume.

[0144] The adsorption selectivity, PX half-width, and toluene adsorption capacity of adsorbent L are shown in Table 2.

[0145] Comparative Example 4 The preparation and evaluation were carried out in accordance with the method of Example 7, except that the first product obtained in step (1) was not subjected to the treatment in step (2), thereby obtaining a modified X-type molecular sieve comparison sample db4. Thus, adsorbent DB4 was obtained.

[0146] The surface area of ​​the modified X-type molecular sieve comparison sample db4 measured by nitrogen physical adsorption was 25.4 m 2 / g, the micropore volume was 0.256 g / mL, the total pore volume was 0.306 g / mL, and the sum of the mesopore volume and macropore volume accounted for 16.3% of the total pore volume.

[0147] The adsorption selectivity, PX half-width, and toluene adsorption capacity of adsorbent DB4 are shown in Table 2.

[0148] Comparative Example 5 The preparation and evaluation were carried out according to the method of Example 7. The X-type molecular sieve (SiO / AlO molar ratio 2.43, particle size 1.0 μm, micropore volume 0.335 g / mL, total pore volume 0.351 g / mL, surface area 5.5 m) was used. 2 / g, the sum of the mesopore volume and macropore volume (4.3%) of the total pore volume was not subjected to the treatment in step (1) but was directly carried to step (2) to obtain the modified X-type molecular sieve comparison sample db5, thereby preparing the adsorbent DB5.

[0149] The surface area of ​​the modified X-type molecular sieve comparison sample db5 measured by nitrogen physical adsorption was 8.6 m 2 / g, the micropore volume was 0.328 g / mL, the total pore volume was 0.347 g / mL, and the sum of the mesopore volume and macropore volume accounted for 5.5% of the total pore volume.

[0150] The adsorption selectivity, PX half-width, and toluene adsorption capacity of adsorbent DB5 are shown in Table 2.

[0151] Comparative Example 6 The preparation and evaluation were carried out according to the method of Example 7. The X-type molecular sieve (SiO / AlO molar ratio 2.43, particle size 1.0 μm, micropore volume 0.335 g / mL, total pore volume 0.351 g / mL, surface area 5.5 m) was used. 2 / g, and the sum of the mesopore volume and macropore volume was 4.6% of the total pore volume, which was not subjected to the treatments in steps (1) and (2). The adsorption selectivity, PX half-width, and toluene adsorption capacity of the obtained adsorbent DB6 are shown in Table 2.

[0152] [Table 2]

[0153] In Table 2, W 1 / 2 is a direct reflection of mass transfer performance, and W 1 / 2 The smaller the value, the better the mass transfer performance. Therefore, the mass transfer performance of Examples 7 to 12 is significantly better than that of Comparative Examples 4 to 6. Example 12 employs a three-stage calcination process, which results in a faster temperature rise rate than the four-stage or five-stage calcinations of Examples 7 to 11. Therefore, when localized high temperatures are generated by the combustion of the organic amine produced by the organic ammonium salt, the X-type molecular sieve is destroyed, resulting in a decrease in mass transfer performance and adsorption selectivity.

[0154] In Table 2, the adsorption selectivity is influenced by both mass transfer performance and micropore adsorption capacity. In Comparative Example 4, steam treatment alone damaged the X-type molecular sieve, reducing its crystallinity and producing a large amount of amorphous species. These amorphous species not only blocked the mesopores but also significantly reduced the micropore adsorption capacity. Therefore, the prepared adsorbent had the lowest adsorption selectivity. In Comparative Example 5, the X-type molecular sieve was treated with only an alkaline solution without steam treatment. Although the percentage increase in the sum of the mesopore volume and macropore volume to the total pore volume was small compared to the unmodified X-type molecular sieve, the X-type molecular sieve was slightly damaged by the calcination process. As a result, the adsorption capacity and mass transfer performance of the prepared adsorbent were reduced, as was the adsorption selectivity. In Comparative Example 6, the unmodified X-type molecular sieve had a small mesopore and macropore structure, resulting in low mass transfer performance and low adsorption selectivity. Comparing Examples 7, 9-1, and 9-2 with Comparative Example 9-3, it is clear that the presence of a relatively low content of organic ammonium salt in the alkaline solution is necessary and important when treating the X-type molecular sieve with an alkaline solution. The organic ammonium salt increases the proportion of mesopore volume and macropore volume, resulting in a significant improvement in the mass transfer performance of the modified X-type molecular sieve. However, if the content of organic ammonium salt in the alkaline solution is too high, it will have a detrimental effect on the mass transfer performance and adsorption capacity of the modified X-type molecular sieve.

[0155] Example 13 Continuous countercurrent separation of p-xylene was carried out using adsorbent G in a small simulated moving bed.

[0156] The small-scale simulated moving-bed system contained 24 serially connected adsorption columns, each 195 mm long and 30 mm inner diameter, with a total adsorbent loading of 3300 mL. As shown in Figure 3, the two ends of the 24 serially connected adsorption columns were connected by a circulation pump to form a closed loop. The 24 adsorption columns were divided into four sections by four flow paths: the adsorption feed, desorbent, extract, and raffinate. The seven adsorption columns between the adsorption feed (column 15) and the raffinate (column 21) constituted the adsorption section; the nine adsorption columns between the extract (column 6) and the adsorption feed (column 14) constituted the purification section; the five adsorption columns between the desorbent (column 1) and the extract (column 5) constituted the desorption section; and the three adsorption columns between the raffinate (column 22) and the desorbent (column 24) constituted the buffer section. The temperature and pressure of the entire adsorption system were controlled at 177 °C and 0.8 MPa, respectively.

[0157] During operation, the desorbent p-diethylbenzene and the feed were continuously injected into the simulated moving bed at flow rates of 1420 mL / h and 2010 mL / h, respectively, and the extract and raffinate were removed from the unit at flow rates of 895 mL / h and 2535 mL / h, respectively. The feed composition was 9.3 mass% ethylbenzene, 18.5 mass% p-xylene, 45.5 mass% m-xylene, 17.4 mass% o-xylene, and 9.4 mass% non-aromatic components.

[0158] The flow rate of the circulation pump was set to 3720 mL / h, and the four material streams were simultaneously moved in the same direction as the liquid flow, one absorption column length, every 50 seconds (e.g., from the solid line to the dotted line in Figure 3). Under stable operating conditions, the purity of p-xylene obtained with adsorbent G was 99.83 mass%, and the yield was 98.33 mass%.

[0159] Example 14 Adsorbent H was packed into a small simulated moving bed apparatus, and an adsorption and separation experiment of p-xylene was carried out in accordance with the method of Example 13. The purity of p-xylene obtained under stable operating conditions was 99.82% by mass, and the yield was 98.15% by mass.

[0160] Comparative Example 7 The adsorbent DB4 was packed into a small simulated moving bed apparatus, and an adsorption and separation experiment of p-xylene was carried out in accordance with the method of Example 13. The purity of p-xylene obtained under stable operating conditions was 82.26% by mass, and the yield was 80.65% by mass.

[0161] Comparative Example 8 The adsorbent DB5 was packed into a small simulated moving bed apparatus, and an adsorption and separation experiment of p-xylene was carried out in accordance with the method of Example 13. The purity of p-xylene obtained under stable operating conditions was 99.50% by mass, and the yield was 90.33% by mass.

[0162] Comparative Example 9 The adsorbent DB6 was packed into a small simulated moving bed apparatus, and an adsorption and separation experiment of p-xylene was carried out in accordance with the method of Example 13. The purity of p-xylene obtained under stable operating conditions was 99.56% by mass, and the yield was 93.62% by mass.

[0163] As is clear from the above Example 14 and Comparative Examples 7, 8, and 9, the use of the adsorbent according to the present invention in a small simulated moving bed apparatus significantly increases the purity and yield of p-xylene compared to the use of the comparative adsorbent.

Claims

1. A modified X-type molecular sieve, The surface area of ​​the modified X-type molecular sieve is measured by nitrogen physical adsorption method to be 9.5 to 19 m ２ / g, preferably 10 to 18 m ２ / g, and the sum of the mesopore volume and macropore volume accounts for 6 to 18%, preferably 8 to 15%, of the total pore volume, wherein the mesopores are pores having a pore diameter of 10 nm to 50 nm, and the macropores are pores having a pore diameter of more than 50 nm and less than 80 nm. A modified X-type molecular sieve, characterized in that:

2. In the modified X-type molecular sieve, SiO ２ / Al ２ O ３ The modified X-type molecular sieve according to claim 1, characterized in that the molar ratio of is 2.21-2.55, preferably 2.25-2.

4.

3. 3. The modified X-type molecular sieve according to claim 1 or 2, characterized in that the micropore volume of the modified X-type molecular sieve is 0.290-0.340 g / ml, preferably 0.300-0.330 g / ml, the total pore volume is 0.340-0.390 g / ml, preferably 0.350-0.380 g / ml, and preferably the amorphous species content in the modified X-type molecular sieve is 2-12 wt%, more preferably 3.0-8.0 wt%.

4. A process for preparing a modified X-type molecular sieve, in particular a modified X-type molecular sieve according to any one of claims 1 to 3, comprising the following steps: (1) placing the X-type molecular sieve under a water vapor atmosphere to carry out a hydrothermal treatment at a temperature of preferably 250-550°C for at least 0.5 hours, and then washing and drying to obtain a first product; (2) The first product obtained in step (1) is treated with NaOH, SiO ２ and an organic ammonium salt at a temperature of preferably 60-120°C for at least 0.5 hours, followed by washing, drying and calcination to obtain the modified X-type molecular sieve; A preparation method comprising:

5. 5. The preparation method according to claim 4, characterized in that the water vapor atmosphere in step (1) comprises water vapor and an inert gas or air, preferably the inert gas is selected from nitrogen, carbon dioxide and argon, preferably the water vapor partial pressure in the water vapor atmosphere is 0.6-1.0 bar, preferably the treatment time in the water vapor atmosphere is at least 1 hour, more preferably at least 2 hours.

6. The NaOH, SiO ２ and an aqueous solution containing an organic ammonium salt, the NaOH concentration is 1.0 to 2.0 mol / L, preferably 1.2 to 1.8 mol / L, and SiO ２ The preparation method according to claim 4 or 5, characterized in that the concentration is 5.0 to 20.0 g / L, preferably 6.0 to 18.0 g / L, and the concentration of the organic ammonium salt is 0.0005 to 0.05 mol / L, preferably 0.001 to 0.04 mol / L.

7. In step (2), the NaOH, SiO ２ and the ratio of the aqueous solution containing the organic ammonium salt to the first product is 2 to 5:1, preferably 3 to 4:1, wherein the ratio of the aqueous solution containing the NaOH, SiO ２ and the aqueous solution comprising the organic ammonium salt is measured in milliliters, and the first product is measured in grams.

8. The preparation method according to any one of claims 4 to 7, characterized in that the organic ammonium salt has a total carbon number of 9 to 25, preferably 11 to 20, and is preferably selected from one or more of dodecyltrimethylammonium chloride, tetradecyltrimethylammonium chloride, hexadecyltrimethylammonium chloride, and octadecyltrimethylammonium chloride.

9. The preparation method according to any one of claims 4 to 8, characterized in that in step (2), the calcination is an n-stage calcination, where n is 4 or more, preferably the constant temperature time of each stage is 1.0 hour or more, and preferably the maximum temperature of each stage does not exceed 550°C.

10. The X-type molecular sieve used in step (1) is SiO ２ / Al ２ O ３ The molar ratio is 2.0-2.5, and the particle size is 0.6-2.5 μm. Preferably, the X-type molecular sieve used is SiO ２ / Al ２ O ３ A preparation method according to any one of claims 4 to 9, characterized in that the molar ratio is between 2.25 and 2.40 and the particle size is between 0.8 and 1.5 μm.

11. In step (2), the first product is ２ and an organic ammonium salt for at least 1 hour, preferably at least 1.5 hours, and the treatment temperature is 60 to 120°C, preferably 70 to 100°C.

12. A method for adsorption separation of aromatic hydrocarbon isomers, comprising the steps of: The method, characterized in that the modified X-type molecular sieve according to any one of claims 1 to 3 is used as an adsorbent, and preferably, the aromatic hydrocarbon isomers are selected from ethylbenzene, p-xylene, o-xylene and m-xylene.

13. 1. An adsorbent for aromatic hydrocarbon isomers, in particular for p-xylene, comprising: The adsorbent contains the modified X-type molecular sieve according to any one of claims 1 to 3 or the modified X-type molecular sieve prepared by the method according to any one of claims 4 to 9, preferably the adsorbent contains the modified X-type molecular sieve in an amount of 88 to 95% by mass.

14. The adsorbent for aromatic hydrocarbon isomers according to claim 13, further comprising 4 to 11% by weight of a transformed crystalline X-type molecular sieve and 1 to 3% by weight of a matrix.

15. The adsorbent for aromatic hydrocarbon isomers according to claim 13 or 14, characterized in that the adsorption capacity measured by toluene dynamic adsorption method is 175 to 186 mg / g, preferably 177 to 184 mg / g.

16. 15. A method for preparing an adsorbent for aromatic hydrocarbon isomers according to claim 13 or 14, the method comprising the following steps: (1) placing the X-type molecular sieve under a water vapor atmosphere to perform hydrothermal treatment, and then washing and drying to obtain a first product; (2) The first product obtained in step (1) is treated with NaOH, SiO ２ and treating the resulting mixture in an aqueous solution containing an organic ammonium salt, followed by washing, drying and calcining to obtain the modified X-type molecular sieve; (3) mixing the modified X-type molecular sieve obtained in step (2) with a binder to form a molded body, and then calcining the molded body; (4) treating the molded body obtained in step (3) with an alkaline solution to in-situ crystallize the binder therein, and drying; (5) barium ion-exchanging the product obtained in step (4), optionally potassium ion-exchanging it, followed by drying and activation to obtain an adsorbent for aromatic isomers; A method comprising:

17. Steps below: (1) subjecting the X-type molecular sieve to hydrothermal treatment in a water vapor atmosphere at a temperature of 250-550°C for at least 0.5 hours, followed by washing and drying to obtain a first product; (2) The first product obtained in step (1) is treated with NaOH, SiO ２ and placing in an aqueous solution containing an organic ammonium salt, treating at a temperature of 60-120°C for at least 0.5 hours, and then washing, drying and calcining to obtain a modified X-type molecular sieve; (3) molding the modified X-type molecular sieve obtained in step (2) with a binder, drying, and calcining to obtain a molded body, wherein the shape of the molded body is preferably small spheres; (4) treating the molded body obtained in step (3) with a mixed solution of sodium hydroxide and potassium hydroxide to in-situ crystallize the binder therein, and then drying; (5) subjecting the dried shaped body obtained in step (4) to cation exchange with a solution of a soluble barium salt or a solution of a soluble barium salt and a soluble potassium salt, followed by drying and activation; 17. The method of claim 16, comprising:

18. 18. The method according to claim 16 or 17, characterized in that in step (3), the mass ratio of the modified X-type molecular sieve to the binder is 88-95:5-12; preferably, the amount of water added is 6-22% by mass based on the total amount of solid powder; the drying temperature is 80-150°C, preferably, the drying time is 0.5-20 hours; and preferably, the calcination temperature is 500-700°C, preferably, the calcination time is 0.5-6.0 hours.

19. The preparation method according to any one of claims 16 to 18, characterized in that in step (4), the hydroxide ion concentration in the mixed solution is 0.1-2.0 mol / L, the K / (Na+K) molar ratio is 0.1-0.6, the temperature of in-situ crystallization is preferably 80-100°C, and the time of in-situ crystallization is preferably 1.5-6.0 hours.

20. 19. The preparation method according to any one of claims 16 to 18, characterized in that in step (5), the soluble barium salt is selected from barium nitrate and barium chloride, and the soluble potassium salt is selected from potassium nitrate and potassium chloride, preferably the drying temperature is 60-130°C, preferably 70-120°C, and the drying time is 1.0-24.0 hours, preferably 3-15 hours, and preferably the activation is carried out under nitrogen atmosphere at 50-120°C, preferably 60-100°C, for 5-30 hours.

21. A method for adsorption separation of aromatic hydrocarbon isomers, comprising the steps of: The method uses the adsorbent according to any one of claims 13 to 15, and preferably the aromatic hydrocarbon isomers are selected from ethylbenzene, p-xylene, o-xylene and m-xylene.

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