EMT / FAU composite molecular sieve, preparation method therefor and use thereof

Abstract

This invention relates to the field of molecular sieve adsorbent technology, and particularly to an EMT / FAU composite molecular sieve, its preparation method, and its application. The EMT / FAU composite molecular sieve has a multi-level pore structure of micropores, mesopores, and macropores; and the EMT / FAU composite molecular sieve includes an EMT topological molecular sieve and a FAU topological molecular sieve; the FAU topological molecular sieve is formed by in-situ crystallization of a binder and chemically bonded to the EMT topological molecular sieve. The advantages of this invention are: shortening the intracrystalline diffusion path through small-grained EMT; constructing a multi-level pore network and enhancing compressive strength through in-situ crystallization; and precisely controlling the pore size and adsorption sites through stepwise ion exchange, achieving a high degree of matching with the toluene process using light desorbents; the resulting Sr / Ba-EMT / FAU composite molecular sieve, when used in the separation of p-xylene using light desorbents, exhibits advantages such as fast mass transfer, high selectivity, and good compressive strength.

Description

Technical Field

[0001] This invention relates to the field of molecular sieve adsorbent technology, and in particular to an EMT / FAU composite molecular sieve, its preparation method, and its application. Background Technology

[0002] Polyester (PET), ubiquitous in daily life, relies heavily on purified terephthalic acid (PTA) for its production. PTA production begins with a highly dependent and currently irreplaceable process: the synthesis of high-purity para-xylene (PX). During the selective toluene disproportionation process (MSTDP) for PX synthesis, byproducts such as o-xylene (OX), m-xylene (MX), and ethylbenzene (EB) are inevitably generated. Because these four C8 aromatic isomers have very similar boiling points, especially para-xylene and m-xylene, whose boiling points differ by only 0.7°C, traditional distillation methods struggle to efficiently obtain high-purity PX. Therefore, industrially, a continuous separation process using simulated moving bed adsorption (SMB) is widely employed. This process simulates the countercurrent flow of a solid adsorbent and liquid feedstock by periodically switching valves, achieving precise and efficient separation of PX. High-performance adsorbents are the core of this technology, but the requirements for the supporting processes (including process flow, process parameters, etc.) and adsorbent vary depending on the desorbent composition.

[0003] Traditional processes often use heavy desorbents such as p-diethylbenzene (PDEB), with the accompanying adsorbent typically being an X-type molecular sieve modified with cations to achieve separation and performance enhancement of xylene. Patent CN120532446A reports a modification of the X-type molecular sieve to create mesoporous and macroporous channels while maintaining a high microporous structure, thus improving mass transfer performance while maintaining a high adsorption capacity. Patent CN116408044B reports a composite adsorbent of attapulgite and NaX molecular sieve modified with potassium and barium, which improves both the adsorbent's compressive strength and its xylene adsorption capacity. Patent CN115990454B reports an ammonium salt-modified X-type zeolite that possesses both microporous and mesoporous channels, exhibiting good xylene separation performance. Patent CN121715148A discloses a modification method based on X-type molecular sieve through barium ion-ammonium salt-barium, potassium ion exchange, which demonstrates good adsorption selectivity and mass transfer performance in xylene separation.

[0004] The LD-Parex™ process, first proposed by UOP (Universal Plastics Group) for separating para-xylene using the light desorbent toluene, has lower requirements for raw materials and effectively reduces energy consumption compared to the heavy desorbent Parex™ process, making it the mainstream technology for para-xylene separation. However, because the toluene molecule is smaller than para-xylene, the mass transfer rate is faster, placing higher demands on the adsorbent. Patent CN118558292A reports that by adjusting the content of active metals in Na-X zeolite, namely 20-28% barium oxide, 2-5% potassium oxide, and 1-2% fluoride ions, the separation of para-xylene using a light desorbent at a lower adsorption temperature was achieved.

[0005] Patent CN118204052A describes the direct synthesis of FAU / EMT symbiotic molecular sieves, followed by ion exchange and the addition of a binder to form the final product, which can be used for multi-component liquid-phase separation in simulated moving beds. However, the coexistence of the two phases in the symbiotic molecular sieve exhibits randomness, easily forming disordered phase boundaries. Because it is difficult to precisely control the changes in the pathways at these boundaries, it cannot be accurately used for PX adsorption and separation in light desorbent processes. Furthermore, the directly synthesized symbiotic molecular sieve requires the addition of a binder after synthesis to meet the needs of practical applications. Therefore, the binder dilutes the effectively adsorbed components in the molecular sieve, resulting in a loss of its effective adsorption capacity. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide an EMT / FAU composite molecular sieve, its preparation method and application. By shortening the intracrystalline diffusion path through small-crystal EMT, constructing a multi-level pore network and enhancing compressive strength through in-situ crystallization, and precisely controlling the pore size and adsorption sites through stepwise ion exchange, a high degree of matching with the process of light desorbent toluene is achieved.

[0007] The present invention is achieved through the following technical solution: providing an EMT / FAU composite molecular sieve, wherein the EMT / FAU composite molecular sieve has a multi-level pore structure of micropore-mesopore-macropore; and the EMT / FAU composite molecular sieve includes an EMT topological molecular sieve and a FAU topological molecular sieve; The FAU topological molecular sieve is formed by in-situ crystallization of a binder and chemically bonded to the EMT topological molecular sieve.

[0008] Furthermore, the EMT topology molecular sieve is a small-grained EMT molecular sieve with a grain size of 1.0 to 1.3 μm.

[0009] Furthermore, the binder is halloysite with a nanotubular hollow structure.

[0010] A Ba-EMT / FAU composite molecular sieve is also provided, wherein the Ba-EMT / FAU composite molecular sieve is obtained by the above-mentioned EMT / FAU composite molecular sieve through a barium ion exchange reaction, and the Ba-EMT / FAU composite molecular sieve contains barium ions; And / or, the number of barium ion exchanges is 10 to 30.

[0011] Furthermore, a Sr / Ba-EMT / FAU composite molecular sieve is provided, wherein the Sr / Ba-EMT / FAU composite molecular sieve is obtained by the above-mentioned Ba-EMT / FAU composite molecular sieve through a strontium ion exchange reaction, and the Sr / Ba-EMT / FAU composite molecular sieve contains barium ions and strontium ions. And / or, the strontium ions are exchanged 5 to 15 times.

[0012] Furthermore, a method for preparing Sr / Ba-EMT / FAU composite molecular sieves is provided, comprising the following steps: (1) Sodium source, aluminum source, silicon source, 18-crown ether-6 and deionized water were mixed to obtain a gel state, which was then crystallized, washed, dried and calcined to obtain small-crystal EMT molecular sieve raw powder; (2) The EMT molecular sieve raw powder, binder and pore-forming agent are mixed, and then molded, dried and calcined to obtain the EMT molecular sieve molded body; (3) The EMT molecular sieve molded body is pre-absorbed with water, then mixed with alkaline reagent and deionized water, and in-situ crystallization is carried out. After washing and drying, EMT / FAU composite molecular sieve is obtained. (4) The EMT / FAU composite molecular sieve is mixed with an aqueous solution containing barium ions to carry out a barium ion exchange reaction to obtain Ba-EMT / FAU composite molecular sieve; (5) The Ba-EMT / FAU composite molecular sieve is mixed with an aqueous solution containing strontium ions to carry out a strontium ion exchange reaction, and then dried to obtain Sr / Ba-EMT / FAU composite molecular sieve.

[0013] Further, the molar ratio of the gel state in step (1) is SiO2:Al2O3:Na2O:C 12 H 24 O6:H2O = 9~12:1:2.5~3.0:0.05~1:130~170; crystallization temperature is 90~110℃, crystallization time is 12~18 days, and crystallization method is dynamic crystallization; the drying temperature is 70~90℃, and the drying time is 2~4 hours; the calcination temperature is 350~550℃, and the calcination time is 4~7 hours.

[0014] Further, in step (2), the mass ratio of EMT molecular sieve raw powder, binder and pore-forming agent is 87-93:6-14:0.2-2.8; the particle size of the molded body is 0.4-0.8 mm; the drying temperature is 60-90℃, the drying time is 3-5 hours; the calcination temperature is 350-450℃, the heating rate is 4-10℃ / min, the calcination time is 3-5 hours, and the calcination atmosphere is air.

[0015] Further, in step (3), the alkaline reagent includes sodium hydroxide or a sodium hydroxide-silicon source mixture, wherein the concentration of sodium hydroxide, calculated as Na2O, is 60~100g / L, and the concentration of the silicon source, calculated as SiO2, is 5~20g / L; the solid-liquid ratio of the EMT molecular sieve molded body to the alkaline reagent aqueous solution is 100g:200~500mL; the in-situ crystallization temperature is 60~100℃, and the time is 8~15 hours; And / or, in step (4), the concentration of the barium ion-containing aqueous solution is 0.3 to 0.9 mol / L; the solid-liquid ratio of the EMT / FAU composite molecular sieve to the barium ion-containing aqueous solution is 100g:200 to 400mL, the barium ion exchange temperature is 50 to 100℃, the single exchange time is 0.2 to 2 hours, and the number of exchanges is 15 to 25. And / or, in step (5), the concentration of the strontium-containing aqueous solution is 0.2-0.5 mol / L; the solid-liquid ratio of the Ba-EMT / FAU composite molecular sieve to the strontium-containing aqueous solution is 100g:200-400mL, the strontium ion exchange temperature is 60-100℃, the single exchange time is 0.2-2 hours, and the number of exchanges is 8-12; the drying temperature is 280-320℃, the heating rate is 2-8℃ / min, the drying time is 3-5 hours, and the drying atmosphere is air.

[0016] Finally, the application of the aforementioned EMT / FAU composite molecular sieve in the separation of p-xylene in a light desorbent process is presented.

[0017] Beneficial effects This invention utilizes synthesized small-crystal EMT molecular sieves with a three-dimensional pore structure. The small crystal size of the EMT crystals effectively shortens the intracrystalline diffusion path. This characteristic matches the high mass transfer rate of the light desorbent toluene, significantly improving the mass transfer rate during adsorption and ensuring efficient separation even at lower adsorption temperatures.

[0018] After adding a binder and molding, the binder is transformed into a FAU topological molecular sieve through in-situ transcrystalline conversion, forming an EMT / FAU composite molecular sieve. This material constructs a multi-level pore network with synergistic micropore-mesopore-macropore interaction. This unique structure greatly shortens the diffusion path, which is well matched with the high mass transfer rate of toluene, effectively avoiding tailing phenomenon and improving compressive strength, thereby obtaining a product with higher purity and greater durability.

[0019] The EMT / FAU composite molecular sieve platform provides more accessible sites for subsequent metal cation exchange, enabling more thorough and efficient ion exchange. The introduction of Ba / Sr ions can precisely control pore size and adsorption capacity, enhancing the selective adsorption of PX by the adsorbent while suppressing the non-specific adsorption of toluene within the pores, thereby achieving higher adsorption capacity and separation selectivity in a light desorbent system.

[0020] The Sr / Ba-EMT / FAU composite molecular sieve adsorbent provided by this invention is specifically designed in reverse to address the characteristics of the light desorbent toluene. It is systematically optimized from three levels: pore structure, diffusion path, and active sites, enabling efficient matching with the LD-Parex™ process. This provides a superior adsorption material solution for low-energy, high-purity para-xylene separation. Furthermore, the resulting Sr / Ba-EMT / FAU composite molecular sieve, when used in the separation of para-xylene in light desorbent processes, exhibits advantages such as rapid mass transfer, high selectivity, and good compressive strength. The PX purity can reach over 99.86%, and the yield can reach over 98.64%. Attached Figure Description

[0021] Figure 1 A schematic diagram of the preparation process of Sr / Ba-EMT / FAU composite molecular sieve; Figure 2 The image shows a scanning electron microscope (SEM) image of a small-crystal EMT molecular sieve. Figure 3 This is a scanning electron microscope (SEM) image of the EMT / FAU composite molecular sieve. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0023] An EMT / FAU composite molecular sieve includes an EMT topological molecular sieve and a FAU topological molecular sieve; the FAU topological molecular sieve is formed by in-situ crystallization of a binder and chemically bonded to the EMT topological molecular sieve; the EMT / FAU composite molecular sieve has a multi-level pore structure of micropores-mesopores-macropores.

[0024] EMT topology molecular sieves are small-crystal EMT molecular sieves with a grain size of 1.0 to 1.3 μm.

[0025] The binder is halloysite with a nanotube hollow structure.

[0026] A Ba-EMT / FAU composite molecular sieve is obtained by barium ion exchange reaction of the above-mentioned EMT / FAU composite molecular sieve, and the Ba-EMT / FAU composite molecular sieve contains barium ions; the number of barium ion exchange reactions is 10 to 30.

[0027] Another Sr / Ba-EMT / FAU composite molecular sieve is provided, which is obtained by the above-mentioned Ba-EMT / FAU composite molecular sieve through a strontium ion exchange reaction, and the Sr / Ba-EMT / FAU composite molecular sieve contains barium ions and strontium ions; the number of strontium ion exchange times is 5 to 15 times.

[0028] Furthermore, a method for preparing Sr / Ba-EMT / FAU composite molecular sieves is provided, comprising the following steps: (1) Sodium source, aluminum source, silicon source, 18-crown ether-6 and deionized water were mixed to obtain a gel state, which was then crystallized, washed, dried and calcined to obtain small-crystal EMT molecular sieve raw powder; (2) The EMT molecular sieve raw powder, binder and pore-forming agent are mixed, and then molded, dried and calcined to obtain the EMT molecular sieve molded body; (3) The EMT molecular sieve molded body is pre-absorbed with water, then mixed with alkaline reagent and deionized water, and in-situ crystallization is carried out. After washing and drying, EMT / FAU composite molecular sieve is obtained. (4) The EMT / FAU composite molecular sieve is mixed with an aqueous solution containing barium ions to carry out a barium ion exchange reaction to obtain Ba-EMT / FAU composite molecular sieve; (5) The Ba-EMT / FAU composite molecular sieve is mixed with an aqueous solution containing strontium ions to carry out a strontium ion exchange reaction, and then dried to obtain Sr / Ba-EMT / FAU composite molecular sieve.

[0029] In this invention, unless otherwise specified, all raw material components are commercially available products well known to those skilled in the art.

[0030] This invention obtains a gel state by mixing sodium source, aluminum source, silicon source, 18-crown ether-6 and deionized water, followed by crystallization, washing, drying and calcination to obtain small-crystal EMT molecular sieve raw powder.

[0031] In this invention, the sodium source is preferably sodium hydroxide; the aluminum source is preferably one or more of sodium aluminate, boehmite, and aluminum isopropoxide; and the silicon source is preferably one or more of sodium silicate, silica sol, and silica.

[0032] In this invention, the molar ratio of each component in the gel state is SiO2:Al2O3:Na2O:C 12 H 24 O6:H2O = 9~12:1:2.5~3.0:0.05~1:130~170, preferably SiO2:Al2O3:Na2O:C 12 H 24 O6: H2O=9.5~11.5: 1: 2.6~2.9: 0.1~0.8: 140~160.

[0033] In this invention, the crystallization temperature is preferably 90~110℃; the crystallization time is preferably 12~18 days; the crystallization state is preferably dynamic crystallization; the drying temperature is preferably 70~90℃; the drying time is preferably 2~4 hours; the calcination temperature is 350~550℃; and the calcination time is 4~7 hours. In this invention, the specific surface area of ​​the EMT molecular sieve powder is preferably 550~650 m². 2 / g; the crystal size of the small-crystal EMT molecular sieve raw powder is preferably 1.0~1.3 μm.

[0034] After obtaining the EMT molecular sieve raw powder, the present invention mixes the EMT molecular sieve raw powder with a binder and a pore-forming agent, and then performs molding, drying and calcination to obtain an EMT molecular sieve molded body.

[0035] In this invention, the binder is preferably halloysite, which preferably has a nanotube hollow structure; the pore-forming agent is preferably one or more of starch, guar gum powder and sodium cellulose.

[0036] In this invention, the preferred mass ratio of the EMT molecular sieve raw powder, binder and pore-forming agent is 87~93:6~14:0.2~2.8.

[0037] In this invention, the EMT molecular sieve raw powder is mixed with a binder and a pore-forming agent, and then molded. This invention does not have a particular limitation on the mixing method, as long as the raw materials are mixed evenly. The molding method is preferably spheroidization, including shaping the spheroidized particles. This invention does not have a particular limitation on the shaping method, as long as a smooth, rounded EMT molecular sieve molded body is obtained. In this invention, the particle size of the EMT molecular sieve molded body is preferably 0.4~0.8 mm.

[0038] In this invention, the drying temperature is preferably 60~90℃; the drying time is preferably 3~5 hours; the calcination temperature is preferably 350~450℃; the heating rate from room temperature to the calcination temperature is preferably 4~10℃ / min; the calcination time is preferably 3~5 hours; the calcination atmosphere is preferably air; the calcination process can remove ineffective components from the EMT molecular sieve molded body, thereby introducing a partial pore structure, and at the same time activating the binder components therein, which is beneficial to the subsequent in-situ crystallization.

[0039] After obtaining the EMT molecular sieve molded body, it is pre-absorbed with water, mixed with alkaline reagent and water, and then subjected to in-situ crystallization to obtain EMT / FAU composite molecular sieve.

[0040] In this invention, the pre-absorption method is preferably to pre-absorb water by spraying water after the water has been naturally absorbed in the air.

[0041] In this invention, the alkaline reagent is preferably sodium hydroxide or a sodium hydroxide-silicon source mixture; the silicon source is preferably one or more of silicon dioxide, silica sol, sodium silicate, and fumed silica; the sodium hydroxide in the alkaline reagent is calculated as Na2O, and the silicon source is calculated as SiO2; the alkaline reagent is calculated based on the amount of Na2O or the total amount of Na2O and SiO2; the concentration of sodium hydroxide in the alkaline reagent is preferably 60~100 g / L, and the concentration of silicon source in the alkaline reagent is preferably 5~20 g / L; the solid-liquid ratio of the EMT molecular sieve molded body to the alkaline reagent aqueous solution is preferably 100 g: 200~500 mL.

[0042] In this invention, the in-situ crystallization temperature is preferably 60~100℃; the crystallization time is preferably 8~15 hours; during the in-situ crystallization process of the EMT molecular sieve molding body under alkaline conditions, the nucleation and growth of clay results in a more easily obtainable FAU topological structure molecular sieve, and the effective control of the silicon source makes the binder become an X-type molecular sieve. Unlike directly synthesized EMT / FAU symbiotic molecular sieves, the EMT / FAU composite molecular sieve in this invention does not rely on the symbiotic phase boundary to generate defect pores. Instead, it precisely controls the generation of FAU through subsequent crystal transformation, forming a more ordered hierarchical porous structure. In addition, EMT / FAU symbiotic molecular sieves require the addition of an external binder after synthesis, which dilutes the effective adsorption components. However, the EMT / FAU composite molecular sieve in this invention transforms the binder itself into a highly efficient FAU component. Furthermore, the binder is chemically bonded to the EMT molecular sieve after crystal transformation, resulting in higher compressive strength. It also provides more accessible sites for subsequent ion exchange. The hierarchical pore network allows cations to enter the crystal interior, resulting in more thorough and efficient exchange, which is difficult to achieve with directly synthesized symbiotic molecular sieves.

[0043] In this invention, the washing process preferably involves washing the product after solid-liquid separation with water to obtain the EMT / FAU composite molecular sieve. This invention does not specify a particular washing method; washing until the pH of the washing solution is less than 11 is sufficient.

[0044] After obtaining the EMT / FAU composite molecular sieve, the present invention mixes the EMT / FAU composite molecular sieve with an aqueous solution containing barium ions to carry out a barium ion exchange reaction to obtain a Ba-EMT / FAU composite molecular sieve.

[0045] In this invention, the concentration of the barium ion-containing aqueous solution is preferably 0.3~0.9 mol / L, more preferably 0.4~0.8 mol / L; the barium ions preferably originate from water-soluble barium salts, which preferably include barium nitrate and / or barium chloride. In this invention, the solid-liquid ratio of the EMT / FAU composite molecular sieve to the barium ion-containing aqueous solution is preferably 100 g: 200~400 mL.

[0046] In this invention, the preferred barium ion exchange temperature is 50~100℃; the preferred single ion exchange time is 0.2~2 hours, more preferably 0.5~1.5 hours; and the preferred number of exchanges is 15~25 times.

[0047] In this invention, the washing process preferably involves first separating the solid and liquid phases, followed by water washing of the product to obtain the Ba-EMT / FAU composite molecular sieve. This invention does not specify a particular washing method; washing is sufficient until the washing solution is free of barium ions.

[0048] After obtaining the Ba-EMT / FAU composite molecular sieve, the present invention mixes the Ba-EMT / FAU composite molecular sieve with an aqueous solution containing strontium ions, performs a strontium ion exchange reaction, and then dries it to obtain the Sr / Ba-EMT / FAU composite molecular sieve.

[0049] In this invention, the concentration of the strontium-containing aqueous solution is preferably 0.2~0.5 mol / L; the strontium ions preferably originate from water-soluble strontium salts, which preferably include strontium nitrate and / or strontium chloride. In this invention, the solid-liquid ratio of the Ba-EMT / FAU composite molecular sieve to the strontium-containing aqueous solution is preferably 100 g: 200~400 mL.

[0050] In this invention, the strontium ion exchange temperature is preferably 40~100℃; the single ion exchange time is preferably 0.2~2 hours, more preferably 0.5~1.5 hours; and the number of exchanges is preferably 8~12 times.

[0051] In this invention, the washing process preferably involves first separating the solid and liquid phases, followed by water washing of the product to obtain the Sr / Ba-EMT / FAU composite molecular sieve. This invention does not specify a particular washing method; washing is sufficient until the washing solution is free of barium and strontium ions.

[0052] In this invention, the drying temperature is preferably 280~320℃; the heating rate from room temperature to the drying temperature is preferably 2~8℃ / min; the drying time is preferably 3~5 hours; the drying atmosphere is preferably air; and the drying process can remove ineffective moisture while retaining effective moisture.

[0053] This invention provides the application of the EMT / FAU composite molecular sieve described in the above technical solution or the Sr / Ba-EMT / FAU composite molecular sieve prepared in the above technical solution for the separation of p-xylene in a light desorbent process.

[0054] Example 1 A method for preparing a Sr / Ba-EMT / FAU composite molecular sieve includes the following steps: (1) Synthesis of small-crystal EMT molecular sieve raw powder Sodium hydroxide is calculated as Na2O, sodium aluminate as Al2O3, silica sol as SiO2, and 18-crown ether-6 as C. 12 H 24 Based on O6, its molar ratio with deionized water is SiO2:Al2O3:Na2O:C 12 H 24 O6:H2O was mixed in a ratio of 11:1:2.7:0.2:150 and stirred for 2 hours to obtain a uniform gel. The gel was transferred to a stainless steel crystallization vessel and dynamically rotated at 100°C for 60 rpm for 15 days. After cooling, the gel was filtered, washed with deionized water until neutral, dried at 80°C for 3 hours, and then calcined in a muffle furnace at a heating rate of 5°C / min to 450°C for 5 hours in air to obtain small-crystal EMT molecular sieve powder. Figure 2 As shown, the SEM (scanning electron microscope) reveals a hexagonal plate morphology, meaning it is composed of hexagonal crystal particles with complete morphology. The grain size distribution is relatively uniform, the grain edges are clear, and the grain size is mainly concentrated in the range of 1.0~1.3 μm.

[0055] (2) Preparation of the molded body EMT molecular sieve powder, halloysite, and guar gum powder were mixed at a mass ratio of 90:9:1. Halloysite has a nanotubular hollow structure and a specific surface area of ​​65 m². 2 / g. Add an appropriate amount of deionized water, prepare spherical particles using a pelletizing machine, and sieve to obtain 0.4~0.8 mm spheres after shaping. Dry at 80℃ for 4 hours, then heat to 400℃ at 6℃ / min and calcine in air atmosphere for 5 hours to obtain EMT molecular sieve molded body.

[0056] (3) In-situ crystallization preparation of EMT / FAU composite molecular sieves The EMT molecular sieve preform was allowed to absorb water naturally in air for 24 hours, then sprayed with water to achieve a uniform water content of approximately 25 wt%. A sodium hydroxide-sodium silicate mixed aqueous solution was prepared, with a Na₂O concentration of 80 g / L and a SiO₂ concentration of 10 g / L. The pre-absorbed preform was added to the above solution at a solid-liquid ratio of 100 g:300 mL, and in-situ crystallization was carried out at 90°C with stirring for 11 hours. The mixture was filtered, washed with deionized water until the washing solution pH < 10, and dried at 80°C for 4 hours to obtain the EMT / FAU composite molecular sieve. Figure 3 As shown, SEM scanning electron microscopy revealed the formation of fine FAU grains on a substrate that retains the basic hexagonal lamellar structure, indicating the presence of bridging growth of FAU grains without obvious phase boundaries.

[0057] (4) Barium ion exchange The above composite molecular sieve was placed in an aqueous barium chloride solution, Ba 2+ The concentration was 0.7 mol / L, and the solid-liquid ratio was 100 g:300 mL. The mixture was stirred and exchanged at 80 °C for 1 hour, then filtered. The exchange process was repeated 20 times in total. After the final exchange, the mixture was filtered and washed with deionized water until no Ba was found in the washings. 2+ The detection method was that no white precipitate formed upon addition of dilute sulfuric acid. After drying at 80℃ for 4 h, the Ba-EMT / FAU composite molecular sieve was obtained.

[0058] (5) Strontium ion exchange and drying Ba-EMT / FAU composite molecular sieves were placed in an aqueous solution of strontium chloride, and Sr... 2+ Concentration 0.3 mol / L, solid-liquid ratio 100 g: 300 mL. Stir and exchange at 80℃ for 1 hour, then filter. Repeat the exchange 10 times. Wash until no Sr is found in the washings. 2+ and Ba 2+ The temperature was increased to 300℃ at 6℃ / min, and dried in air for 4 hours to obtain the final product, Sr / Ba-EMT / FAU composite molecular sieve.

[0059] Example 2 Prepared according to the method of Example 1, the only difference being that in step (2), the mass ratio of EMT molecular sieve powder, halloysite, and guar gum powder was adjusted to 93:6:1. The remaining steps are the same.

[0060] Example 3 Prepared according to the method of Example 1, the difference from Example 1 is that in step (3), the concentration of Na2O in the sodium hydroxide-sodium silicate aqueous solution is 60 g / L and the concentration of SiO2 is 5 g / L.

[0061] Example 4 Prepared according to the method of Example 1, the difference from Example 1 is that in steps (4) and (5), the ion exchange temperature is 90°C.

[0062] Comparative Example 1 Prepared according to the method of Example 1, the difference from Example 1 is that in step (2), EMT molecular sieve raw powder, halloysite and guar powder are mixed in a mass ratio of 80:19:1.

[0063] Comparative Example 2 Prepared according to the method of Example 1, the difference from Example 1 is that in step (3), the sodium hydroxide-sodium silicate aqueous solution is replaced with a sodium hydroxide solution with a Na2O concentration of 80 g / L.

[0064] Comparative Example 3 Prepared according to the method of Example 1, the difference from Example 1 is that in steps (4) and (5), the ion exchange temperature is 40°C.

[0065] Comparative Example 4 Prepared according to the method of Example 1, the difference from Example 1 is that step (5) is omitted, that is, strontium ion exchange is not performed, and the Ba-EMT / FAU composite molecular sieve is directly dried after obtaining it.

[0066] Effect Example The performance of the adsorbents prepared in Examples 1-4 and Comparative Examples 1-4 was evaluated using a simulated moving bed. The specific test items are as follows: 1. Compressive strength test Using an intelligent particle strength tester, 20 spherical particles with a diameter of 0.4~0.8 mm were randomly selected, and their crushing strength (unit: Newton / particle) was measured. The average value and standard deviation were then recorded.

[0067] 2. Static adsorption test The static adsorption method was used. 0.5 g of the activated adsorbent was placed in an isooctane solution containing 5% toluene and adsorbed at room temperature for 4 hours. The amount of toluene adsorbed was determined by gas chromatography using an FID detector, and the unit was g / g.

[0068] 3. Evaluation of SMB separation performance in simulated moving bed A pilot-scale SMB unit was used, operating at a temperature of 135–140 °C and a pressure of 0.8–1.0 MPa. The composition of the mixed xylene feedstock is shown in Table 1 below. The feed flow rate, desorbent flow rate, and circulation flow rate were optimized based on adsorption equilibrium data. The extract and residue were collected, and their composition was analyzed by gas chromatography to calculate the PX purity and yield.

[0069] Table 1 Properties of Mixed Xylene Feedstock

[0070] The performance test results of the adsorbents prepared in Examples 1-4 and Comparative Examples 1-4 are shown in Table 2 below: Table 2. Adsorption performance of xylene by the adsorbents prepared in Examples 1-4 and Comparative Examples 1-4

[0071] As shown in Table 2 above, the modified EMT / FAU composite molecular sieves prepared in Examples 1-4 all exhibited high PX adsorption performance, possessing both high PX purity and yield. Among them, the Sr / Ba-EMT / FAU composite molecular sieve prepared in Example 1 achieved a PX purity of 99.86% and a PX yield of 98.90%. When the crystallization is incomplete or the FAU topology cannot be fully completed, or when cation exchange is incomplete or strontium ion exchange is omitted, the performance of the modified EMT / FAU composite molecular sieve will be impaired, thus affecting PX purity and yield. Example 1 of this invention avoids the above problems; even at a relatively low adsorption temperature of 135-140°C, the PX yield of Example 1 is still as high as 98.90%.

[0072] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An EMT / FAU composite molecular sieve, characterized in that, The EMT / FAU composite molecular sieve has a multi-level pore structure of micropore-mesopore-macropore; and the EMT / FAU composite molecular sieve includes EMT topological molecular sieve and FAU topological molecular sieve. The FAU topological molecular sieve is formed by in-situ crystallization of a binder and chemically bonded to the EMT topological molecular sieve.

2. The EMT / FAU composite molecular sieve according to claim 1, characterized in that, The EMT topology molecular sieve is a small-grained EMT molecular sieve with a grain size of 1.0 to 1.3 μm.

3. The EMT / FAU composite molecular sieve according to claim 1, characterized in that, The binder is halloysite with a nanotube hollow structure.

4. The EMT / FAU composite molecular sieve according to any one of claims 1-3, characterized in that, Ba-EMT / FAU composite molecular sieve was obtained by barium ion exchange reaction of EMT / FAU composite molecular sieve. And / or, the number of barium ion exchanges is 10 to 30.

5. The EMT / FAU composite molecular sieve according to claim 4, characterized in that, Sr / Ba-EMT / FAU composite molecular sieve was obtained by strontium ion exchange reaction of Ba-EMT / FAU composite molecular sieve; And / or, the strontium ions are exchanged 5 to 15 times.

6. A method for preparing the EMT / FAU composite molecular sieve according to claim 5, characterized in that, Includes the following steps: (1) Sodium source, aluminum source, silicon source, 18-crown ether-6 and deionized water were mixed to obtain a gel state, which was then crystallized, washed, dried and calcined to obtain small-crystal EMT molecular sieve raw powder; (2) The EMT molecular sieve raw powder, binder and pore-forming agent are mixed, and then molded, dried and calcined to obtain the EMT molecular sieve molded body; (3) The EMT molecular sieve molded body is pre-absorbed with water, then mixed with alkaline reagent and deionized water, and in-situ crystallization is carried out. After washing and drying, EMT / FAU composite molecular sieve is obtained. (4) The EMT / FAU composite molecular sieve is mixed with an aqueous solution containing barium ions to carry out a barium ion exchange reaction to obtain Ba-EMT / FAU composite molecular sieve; (5) The Ba-EMT / FAU composite molecular sieve is mixed with an aqueous solution containing strontium ions to carry out a strontium ion exchange reaction, and then dried to obtain Sr / Ba-EMT / FAU composite molecular sieve.

7. The method according to claim 6, characterized in that, The molar ratio of the components in the gel in step (1) is SiO2:Al2O3:Na2O:C 12 H 24 O6:H2O=9~12:1:2.5~3.0:0.05~1:130~170; the crystallization temperature is 90~110℃, the crystallization time is 12~18 days, the crystallization mode is dynamic crystallization; the drying temperature is 70~90℃, the drying time is 2~4 hours; the calcination temperature is 350~550℃, and the calcination time is 4~7 hours.

8. The method according to claim 6, characterized in that, In step (2), the mass ratio of EMT molecular sieve raw powder, binder and pore-forming agent is 87-93:6-14:0.2-2.8; the particle size of the molded body is 0.4-0.8 mm; the drying temperature is 60-90℃ and the drying time is 3-5 hours; the calcination temperature is 350-450℃, the heating rate is 4-10℃ / min, the calcination time is 3-5 hours, and the calcination atmosphere is air.

9. The method according to claim 6, characterized in that, In step (3), the alkaline reagent includes a sodium hydroxide-silicon source mixture, wherein the concentration of sodium hydroxide (Na2O) is 60-100 g / L and the concentration of silicon source (SiO2) is 5-20 g / L; the solid-liquid ratio of the EMT molecular sieve molded body to the alkaline reagent aqueous solution is 100 g: 200-500 mL; the in-situ crystallization temperature is 60-100 °C and the time is 8-15 hours. And / or, in step (4), the concentration of the barium ion-containing aqueous solution is 0.3 to 0.9 mol / L; the solid-liquid ratio of the EMT / FAU composite molecular sieve to the barium ion-containing aqueous solution is 100g:200 to 400mL, the barium ion exchange temperature is 50 to 100℃, the single exchange time is 0.2 to 2 hours, and the number of exchanges is 15 to 25. And / or, in step (5), the concentration of the strontium-containing aqueous solution is 0.2-0.5 mol / L; the solid-liquid ratio of the Ba-EMT / FAU composite molecular sieve to the strontium-containing aqueous solution is 100g:200-400mL, the strontium ion exchange temperature is 60-100℃, the single exchange time is 0.2-2 hours, and the number of exchanges is 8-12; the drying temperature is 280-320℃, the heating rate is 2-8℃ / min, the drying time is 3-5 hours, and the drying atmosphere is air.

10. The application of the EMT / FAU composite molecular sieve according to claim 5 in the separation of p-xylene in a light desorbent process.

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