A twin zsm-5 molecular sieve and a preparation method thereof

Abstract

The application discloses a kind of twin ZSM-5 molecular sieve and synthesis method thereof, belong to inorganic chemistry technical field.The twin ZSM-5 molecular sieve is covered by the (010) crystal surface of one coffin-shaped ZSM-5 to the (100) crystal surface of another coffin-shaped ZSM-5, so that the molecular sieve surface has higher straight channel exposure ratio.Preparation process includes: (i) water, sodium hydroxide, aluminum source, template agent, silicon source are mixed and stirred to obtain synthesis gel A;(ii) three kinds of molecular sieves MCM-35, MOR, MCM-22 are added to alkaline environment according to the ratio of 1:2:4, and alkaline heat treatment is carried out to obtain mixture B containing "mfi, mor, mel" three kinds of structural units;(iii) A, B are mixed according to the water content of 1:1, and ZSM-5 molecular sieve product is obtained by hydrothermal crystallization.For the "primary aromatic hydrocarbon mixture" obtained after benzene, toluene, p-xylene are separated from the aromatic hydrocarbon mixture obtained by petroleum and non-petroleum route, twin ZSM-5 molecular sieve shows enhanced selectivity to o-xylene and m-xylene due to higher "straight channel exposure ratio" on the surface.

Description

Technical Field

[0001] This patent relates to a twinned ZSM-5 molecular sieve formed by two coffin-shaped ZSM-5 molecular sieves intersecting along the c-axis (100) direction and its preparation method, belonging to the field of inorganic chemical synthesis technology. Technical Background

[0002] As a chemical raw material, the demand for aromatics is increasing daily with the rapid development of my country's economy. In terms of applications, p-xylene is mainly used to manufacture terephthalic acid and its condensation to form ethylene terephthalate, which is further used in the production of plastics, beverage and food packaging. m-xylene not only produces isophthalic acid through oxidation to produce unsaturated polyester resins, but can also be further converted into sulfonated isophthalate esters for manufacturing polyester fibers, and can also be ammonitrile produced by ammonia oxidation for the production of epoxy resin curing agents. o-xylene, due to its good solvent properties, is widely used in the manufacture of adhesives, lubricants, and resins. Currently, my country mainly produces aromatics via two routes: petroleum and non-petroleum. The petroleum route mainly includes aromatics produced by petroleum catalytic reforming and aromatics as a byproduct of hydrocarbon steam cracking. The other is a non-petroleum route using coal as a raw material to obtain aromatics, commonly known as the "Fischer-Tropsch route or methanol route," which starts from coal-to-syngas or coal-to-methanol and produces a mixture of hydrocarbons, mainly aromatics, under the action of a catalyst.

[0003] Regardless of whether the route is petroleum-based or non-petroleum-based, the separation of aromatic hydrocarbon mixtures is an unavoidable process. Xylene isomers have similar structures and boiling points, and traditional separation methods include precision distillation, atmospheric pressure low-temperature crystallization, cryogenic crystallization, and pressure crystallization. With further research, traditional techniques are gradually being replaced by novel separation technologies such as gas chromatography, supercritical fluid extraction, and adsorption separation. Among these, adsorption separation has shown great promise in separating para-xylene because its symmetrical structure results in a smaller molecular diameter compared to other isomers, allowing for selective adsorption by adsorbents. However, the primary aromatic hydrocarbon mixture (m-xylene, o-xylene, polyalkylbenzenes, and heavy aromatics) remaining after para-xylene separation still contains significant amounts of o- and m-xylenes that require further separation. Therefore, there is an urgent need to develop highly selective adsorption separation materials for o- and m-xylenes.

[0004] ZSM-5 molecular sieve consists of straight channels parallel to the b-axis. sinusoidal channel parallel to plane ac Composition. Studies have found that when xylene isomers diffuse through straight channels and sinusoidal channels respectively, the narrower sinusoidal channels increase diffusion resistance, widening the diffusion rate difference between xylene isomers. Increasing the "sinusoidal channel exposure ratio" on the ZSM-5 molecular sieve surface can effectively improve its shape selectivity for xylene (Nat. Commun., 2019, 10, 4348). The inventors have conducted extensive research aimed at improving the "sinusoidal channel exposure ratio" on the ZSM-5 molecular sieve surface, such as... Figure 1 As shown in b, a twinned ZSM-5 molecular sieve formed by the intersection of coffin-shaped ZSM-5 molecular sieves along the c-axis (010) direction was synthesized, which significantly increased the number of sinusoidal channels on the surface of the molecular sieve crystal (ZL 2022 1 0796950.4); subsequently, a ZSM-5 molecular sieve with a surface sinusoidal channel exposure ratio of up to 95% was further prepared, which significantly enhanced the selectivity of p-xylene (ZL 2022 10747667.2).

[0005] To address the challenge of separating o-xylene and m-xylene from the "primary aromatic mixture (m-xylene, o-xylene, polyalkylbenzenes, and heavy aromatics)" obtained from petroleum and non-petroleum routes after separating toluene, toluene, and p-xylene, this patent reverse-engineers the sinusoidal pores on the surface of ZSM-5 molecular sieves, increasing the "straight pore exposure ratio" to develop a highly selective adsorption and separation material for o-xylene and m-xylene. Figure 1 As shown in c, this patent discloses a twinned ZSM-5 molecular sieve formed by two coffin-shaped ZSM-5 molecular sieves intersecting along the c-axis (010). By covering the (100) crystal plane with the (010) crystal plane, the sinusoidal channels are suppressed while the number of exposed straight channels is increased, thereby exhibiting significantly enhanced shape selectivity for o-xylene and m-xylene, achieving effective separation of o-xylene and m-xylene in a "primary aromatic hydrocarbon mixture (m-xylene, o-xylene, polyalkylbenzenes, heavy aromatics)". Therefore, the "high straight channel exposure ratio" twinned ZSM-5 molecular sieve reported in this patent is original and has very good commercial application prospects, facilitating industrial promotion. Summary of the Invention

[0006] The first objective of this invention is to provide a twinned ZSM-5 molecular sieve catalyst formed by two coffin-shaped ZSM-5 molecular sieves intersecting along the c-axis (100) direction.

[0007] Furthermore, the aforementioned twinned ZSM-5 molecular sieve, by having the (010) crystal facet of one coffin-shaped ZSM-5 cover the (100) crystal facet of another coffin-shaped ZSM-5, thereby significantly increasing the exposure ratio of straight channels on the surface of the twinned ZSM-5 molecular sieve.

[0008] A second objective of this invention is to provide a method for preparing twinned ZSM-5 molecular sieve catalysts, comprising the following steps:

[0009] Step 1: Mixing of reaction raw materials and preparation of synthetic gel;

[0010] Sodium hydroxide, aluminum source, and template agent were added sequentially to deionized water, and then silicon source was gradually added under stirring. The mixture was stirred at room temperature for 0.5 to 3 hours to obtain synthetic gel A.

[0011] Step 2: Fabrication of "mfi, mor, mel" structural units;

[0012] MCM-35 molecular sieve, MOR molecular sieve, and MCM-22 molecular sieve were added sequentially to C(OH)₂. - The solution was heated at a concentration of 0.1-0.5 mol / L (wt% = 1-10) under the following conditions: 60-120℃ for 8-12 hours; then cooled to obtain mixture B.

[0013] Step 3: Hydrothermal crystallization and product collection;

[0014] The mixture B obtained in step (2) is added to the gel A synthesized in step (1), and the ratio of A to B is 1:1 according to the water content. After stirring at room temperature for 0.5 to 3 hours, the mixture of A and B is packaged in a stainless steel high-pressure reactor and further loaded into a homogeneous reactor for hydrothermal crystallization. The crystallization conditions are: temperature 150 to 200℃, rotation speed 5 to 25 r / min, and time 24 to 48 hours. After crystallization, the product is obtained by filtration, washing, drying and calcination to obtain ZSM-5 molecular sieve product.

[0015] Furthermore, in the above-mentioned "mixing of reaction raw materials and preparation of synthetic gel" scheme, the composition of synthetic gel A is as follows: Si / Al = 0~∞, template agent / Si = 0.05~0.5, H2O / Si = 10~50, NaOH / Si = 0.10~0.50.

[0016] Furthermore, in the above-mentioned "mixing of reaction raw materials and preparation of synthetic gel" scheme, the silicon source used to prepare synthetic gel A can be any one of silica sol, sodium silicate, or silica, but is not limited to this.

[0017] Furthermore, in the above-mentioned "mixing of reaction raw materials and preparation of synthetic gel" scheme, the aluminum source used to prepare synthetic gel A is any one of boehmite, sodium aluminate, aluminum powder or aluminum isopropoxide, but is not limited to this.

[0018] Furthermore, in the above-mentioned "mixing of reaction raw materials and preparation of synthetic gel" scheme, the template agent used to prepare synthetic gel A is any one of ethylenediamine, triethylamine, isopropylamine, tetrapropylammonium hydroxide, propylammonium hydrobromide, n-butylamine, 1,6-hexanediamine, etc., but is not limited to this;

[0019] Furthermore, in the above-mentioned "preparation of MFI, MR, and MILE structural units", MCM-35 molecular sieve is composed of MFI structural units, therefore, MFI structural units can be obtained by alkaline heat treatment of MCM-35 molecular sieve.

[0020] Furthermore, in the above-mentioned "preparation of MFI, MORI, and MILE structural units", MOR molecular sieves are composed of MORI structural units, therefore, MORI structural units can be obtained by alkaline heat treatment of MOR molecular sieves.

[0021] Furthermore, in the above-mentioned "preparation of mfi, mor, mel structural units" scheme, the MCM-22 molecular sieve is composed of mel and D6R structural units, wherein D6R is destroyed in an alkaline heat environment. Therefore, the mel structural unit can be obtained by alkaline heat treatment of MCM-22 molecular sieve.

[0022] Furthermore, in the above-mentioned "preparation of mfi, mor, mel structural units" scheme, the molar ratio of MCM-35 molecular sieve, MOR molecular sieve, and MCM-22 molecular sieve is 1:2:4, or the ratio of mfi:mor:mel structural units obtained by alkaline heat treatment is 1:2:4.

[0023] A third objective of this invention is to provide the formation mechanism of twinned ZSM-5 molecular sieve catalysts, characterized by: Figure 3 As shown, ZSM-5 molecular sieve is assembled from four structural units: "mel, mor, mfi, and cas". A schematic diagram of the ZSM-5 molecular sieve structure was obtained from the Database of Zeolite Structures, and the units of the four structural units were confirmed and identified. Figure 4 ).like Figure 5 As shown, ZSM-5 molecular sieve requires four structural units—mel, mor, mfi, and cas—to grow along either the (010) direction or the b-axis. Figure 6 As shown, the growth of ZSM-5 molecular sieve along the c-axis requires both "mfi" and "cas" structural units; for example... Figure 7 As shown, ZSM-5 molecular sieve requires three structural units, "mfi, mor, and mel", to grow along the (100) direction or the a-axis direction, and the ratio of the number of the three structural units "mfi, mor, and mel" is 1:2:4.

[0024] Furthermore, in the synthetic gel A system, four structural units, "mel, mor, mfi, and cas," are contained. To alter the crystal growth direction and make it grow intersectingly along the (100) direction or the a-axis direction, three existing structural units, "mfi, mor, and mel," are added to the synthetic system, while maintaining a ratio of 1:2:4. Figure 3 As shown, MCM-35 molecular sieve is assembled from "mfi" structural units, MOR molecular sieve is assembled from "mor" structural units, and MCM-22 molecular sieve is assembled from "mel and D6R" structural units (D6R is destroyed in an alkaline heat environment). Therefore, by performing step (2) of the preparation procedure in claim 1, a mixture of MCM-35, MOR, and MCM-22 molecular sieves in the required proportions is subjected to alkaline heat treatment to obtain a mixture B containing the three structural units "mfi, mor, and mel".

[0025] Another aspect of this invention provides the adsorption application of twinned ZSM-5 molecular sieve catalysts in p-xylene, m-xylene, o-xylene, mesitylene, 1,2,4,5-tetramethylbenzene, and naphthalene. For mixed aromatic products obtained from petroleum or non-petroleum routes, after the initial separation of benzene, toluene, and p-xylene, a "primary aromatic mixture" composed of m-xylene, o-xylene, polyalkylbenzenes, and heavy aromatics is obtained; in the subsequent separation of m-xylene and o-xylene, the twinned ZSM-5 molecular sieve reported in this patent exhibits enhanced selectivity for o-xylene and m-xylene in the "primary aromatic mixture" due to its high straight pore exposure ratio.

[0026] The above embodiments describe the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the present invention. Various changes and modifications can be made to the present invention without departing from its principles, and all such changes and modifications fall within the scope of protection of the present invention. Attached Figure Description

[0027] Figure 1 Schematic diagram of coffin-shaped ZSM-5 and its cross-linked twinned ZSM-5 molecular sieves;

[0028] Figure 2 The structural units are composed of four types of molecular sieves: ZSM-5, MCM-22, MOR, and MCM-35.

[0029] Figure 3 Identification of the four structural units of ZSM-5 molecular sieve;

[0030] Figure 4The structural units required for the cross growth of ZSM-5 molecular sieve along the (010) direction or the b-axis direction;

[0031] Figure 5 The ZSM-5 molecular sieve grows the required structural units along the c-axis direction;

[0032] Figure 6 The structural units required for the growth of ZSM-5 molecular sieve along the (100) direction or the a-axis direction;

[0033] Figure 7 SEM image of ZSM-5 molecular sieve prepared in Example 1;

[0034] Figure 8 SEM image of ZSM-5 molecular sieve prepared in Example 2;

[0035] Figure 9 SEM image of ZSM-5 molecular sieve prepared in Example 3;

[0036] Figure 10 SEM image of ZSM-5 molecular sieve prepared in Example 4;

[0037] Figure 11 The adsorption performance of the sample in Example 1 on p-xylene, m-xylene, o-xylene, mesitylene, 1,2,4,5-tetramethylbenzene, and naphthalene is shown. Detailed Implementation

[0038] The present invention will be further described in detail below through examples, but these examples are not intended to limit the scope of the invention.

[0039] Example 1:

[0040] Sodium hydroxide, aluminum source (sodium aluminate), and template agent (n-butylamine) were added sequentially to deionized water. Then, a silicon source (silica sol JN-40) was gradually added while stirring, and the mixture was stirred at room temperature for 0.5 hours to obtain synthetic gel A, with the following composition: [SiO2] / [Al2O3] = 160, [n-butylamine] / [SiO2] = 0.15, [H2O] / [SiO2] = 20, and [Na2O] / [SiO2] = 0.10. MCM-35, MOR, and MCM-22 were mixed in a 1:2:4 ratio and added to C(OH)2. -The solution was heated to 0.15 mol / L (wt% = 5) under the following conditions: 80℃ for 10 hours; then cooled to obtain mixture B. The synthesized gel A in step (1) and the mixture B obtained in step (2) were mixed in a 1:1 ratio according to their water content, stirred at room temperature for 1.5 hours, and then sealed in a stainless steel high-pressure reactor and further loaded into a homogeneous reactor for hydrothermal crystallization. The crystallization conditions were: temperature 180℃, rotation speed 15 r / min, and time 48 hours. After crystallization, the product was obtained by filtration, washing, drying, and calcination to obtain ZSM-5 molecular sieve product.

[0041] Example 2:

[0042] Sodium hydroxide, aluminum source (aluminum isopropoxide), and template agent (1,6-hexanediamine) were added sequentially to deionized water. Then, a silicon source (fumed silica) was gradually added while stirring, and the mixture was stirred at room temperature for 3.0 hours to obtain synthetic gel A, with the following composition: [SiO2] / [Al2O3] = 200, [1,6-hexanediamine] / [SiO2] = 0.10, [H2O] / [SiO2] = 50, and [Na2O] / [SiO2] = 0.20. MCM-35, MOR, and MCM-22 were mixed in a 1:2:4 ratio and added to C(OH)2. - The solution was heated to 0.10 mol / L (wt% = 3) at 100℃ for 12 hours. After cooling, mixture B was obtained. The synthesized gel A in step (1) and mixture B obtained in step (2) were mixed at a 1:1 ratio according to their water content. After stirring at room temperature for 3.0 hours, the mixture was sealed in a stainless steel high-pressure reactor and further loaded into a homogeneous reactor for hydrothermal crystallization. The crystallization conditions were 200℃, 15 r / min, and 36 hours. After crystallization, the product was obtained by filtration, washing, drying, and calcination.

[0043] Example 3:

[0044] Sodium hydroxide, aluminum source (sodium aluminate), and template agent (triethylamine) were added sequentially to deionized water. Then, a silicon source (sodium silicate) was gradually added while stirring, and the mixture was stirred at room temperature for 1.0 hour to obtain synthetic gel A, with the following composition: [SiO2] / [Al2O3] = 100, [triethylamine] / [SiO2] = 0.20, [H2O] / [SiO2] = 15, and [Na2O] / [SiO2] = 0.25. MCM-35, MOR, and MCM-22 were mixed in a 1:2:4 ratio and added to C(OH)2. -The solution was heated to 0.20 mol / L (wt% = 10) at 120℃ for 6 hours. After cooling, mixture B was obtained. The synthesized gel A in step (1) and mixture B obtained in step (2) were mixed in a 1:1 ratio according to their water content. After stirring at room temperature for 1.5 hours, the mixture was sealed in a stainless steel high-pressure reactor and further loaded into a homogeneous reactor for hydrothermal crystallization. The crystallization conditions were: temperature 170℃, rotation speed 10 r / min, and time 48 hours. After crystallization, the product was obtained by filtration, washing, drying, and calcination.

[0045] Example 4:

[0046] Sodium hydroxide, aluminum source (aluminum powder), and template agent (tetrapropylammonium bromide, TPABr) were added sequentially to deionized water. Then, a silicon source (silica sol JN-30) was gradually added while stirring, and the mixture was stirred at room temperature for 2.0 hours to obtain synthetic gel A, with the following composition: [SiO2] / [Al2O3] = 60, [TPABr] / [SiO2] = 0.15, [H2O] / [SiO2] = 15, and [Na2O] / [SiO2] = 0.12. MCM-35, MOR, and MCM-22 were mixed in a 1:2:4 ratio and added to C(OH)2. - The solution was heated to 0.35 mol / L (wt% = 7) under the following conditions: 70℃ for 12 hours; then cooled to obtain mixture B. The synthesized gel A in step (1) and the mixture B obtained in step (2) were mixed in a 1:1 ratio according to their water content, stirred at room temperature for 1.5 hours, and then sealed in a stainless steel high-pressure reactor and further loaded into a homogeneous reactor for hydrothermal crystallization. The crystallization conditions were: temperature 160℃, rotation speed 20 r / min, and time 48 hours. After crystallization, the product was obtained by filtration, washing, drying, and calcination to obtain ZSM-5 molecular sieve product.

[0047] Example 5:

[0048] The adsorption of p-xylene, m-xylene, o-xylene, mesitylene, 1,2,4,5-tetramethylbenzene, and naphthalene by twinned ZSM-5 molecular sieves formed by the intersection of two coffin-shaped ZSM-5 molecular sieves along the c-axis (100) direction was performed on a BELSORP-MAX adsorption instrument in Japan. 0.15 g of the twinned ZSM-5 molecular sieve sample was weighed beforehand and kept under vacuum at 300°C for 12 hours to remove water and impurities from the molecular sieve. Subsequently, p-xylene, m-xylene, o-xylene, mesitylene, 1,2,4,5-tetramethylbenzene, and naphthalene vapors were passed through at -196°C, and adsorption data for p-xylene, m-xylene, o-xylene, mesitylene, 1,2,4,5-tetramethylbenzene, and naphthalene were collected.

[0049] from Figure 11 It can be seen that the three isomers of p-xylene, m-xylene, and o-xylene have very similar adsorption curves on the sample of Example 1. That is, when P / P0 increases from 0 to 0.1, the adsorption capacity of all three isomers increases rapidly; further increasing P / P0 to 1.0, the adsorption capacity of the three isomers increases slowly to the maximum point. Specifically, the adsorption capacity changes are as follows: p-xylene (0→12.41→22.05cm) 3 / g), m-xylene (0→12.37→22.53cm) 3 / g), o-xylene (0→12.75→23.09cm) 3 / g). The three very similar adsorption curves above indicate that, due to its twinned ZSM-5 molecular sieve structure and high "straight pore exposure ratio," the three xylene isomer molecules in the Example 1 sample can diffuse into / out of the molecular sieve along the straight pore direction (Nature Communications, 2021, 12, 3725). Meanwhile, when mesitylene, 1,2,4,5-tetramethylbenzene, and naphthalene were adsorbed on the Example 1 sample, the adsorption capacity of the three molecules gradually increased to a maximum point as P / P0 increased from 0 to 0.35, and then remained stable with increasing pressure. It is noteworthy that the saturated adsorption capacities of mesitylene, 1,2,4,5-tetramethylbenzene, and naphthalene were 0.66 cm⁻¹, respectively. 3 / g, 0.68cm 3 / g, 0.60cm 3 The adsorption capacity is significantly lower than that of xylene molecules ( / g). This is because mesitylene, 1,2,4,5-tetramethylbenzene, and naphthalene have large kinetic molecular diameters and cannot enter the exposed straight channels of the twinned ZSM-5 molecular sieve in Example 1. They can only be adsorbed on the surface of the molecular sieve, and the adsorption capacity no longer increases with increasing pressure after the surface adsorption is saturated. The above adsorption test shows that the twinned ZSM-5 molecular sieve reported in this patent has no selectivity for the three xylene isomers. However, for the "primary aromatic mixture" composed of m-xylene, o-xylene, polyalkylbenzenes, and heavy aromatics obtained from the initial separation of benzene, toluene, and p-xylene from mixed aromatic products obtained from petroleum or non-petroleum routes, the twinned ZSM-5 molecular sieve reported in this patent exhibits enhanced selectivity for o-xylene and m-xylene, and can be used for the separation of o-xylene and m-xylene in the "primary aromatic mixture".

[0050] The above description of the embodiments is intended to enable those skilled in the art to understand and apply this application. This application is not limited to the embodiments described herein. Any improvements and modifications made by those skilled in the art based on the disclosure of this application without departing from the scope and spirit of this application are within the scope of this application.

Claims

1. A method for preparing twinned ZSM-5 molecular sieve catalysts, characterized in that, The specific steps include the following: Step 1: Mixing of reaction raw materials and preparation of synthetic gel; Sodium hydroxide, aluminum source, and template agent were added sequentially to deionized water. Then, silicon source was gradually added while stirring, and the mixture was stirred at room temperature for 0.5 to 3 hours to obtain synthetic gel A. Among them, Si / Al = 0 ~ ∞, template agent / Si = 0.05 ~ 0.5, H2O / Si = 10 ~ 50, and NaOH / Si = 0.10 ~ 0.

50. Step 2: Fabrication of "mfi, mor, mel" structural units; MCM-35 molecular sieve, MOR molecular sieve, and MCM-22 molecular sieve were sequentially added to 0.1-0.5 mol / L solutions. C(OH - ) Alkali heat treatment is performed under the following conditions: 60-120℃ for 8-12 hours; then cooled to obtain mixture B; wherein the molar ratio of MCM-35 molecular sieve, MOR molecular sieve and MCM-22 molecular sieve is 1:2:4, or the ratio of the number of mfi:mor:mel structural units obtained by alkali heat treatment is 1:2:

4. Step 3: Hydrothermal crystallization and product collection; The mixture B obtained in step (2) is added to the gel A synthesized in step (1). The ratio of A to B is 1:1 according to the water content. After stirring at room temperature for 0.5 to 3 hours, the mixture of A and B is packaged in a stainless steel high-pressure reactor and further loaded into a homogeneous reactor for hydrothermal crystallization. The crystallization conditions are: temperature 150 to 200℃, rotation speed 5 to 25 r / min, and time 24 to 48 hours. After crystallization, the product is obtained by filtration, washing, drying and calcination. The molecular sieve catalyst is formed by two coffin-shaped ZSM-5 molecular sieves intersecting along the c-axis (100) direction. The (010) crystal face of one coffin-shaped ZSM-5 covers the (100) crystal face of the other coffin-shaped ZSM-5, thereby greatly increasing the exposure ratio of the straight channels on the surface of the twinned ZSM-5 molecular sieve.

2. The method for preparing the twinned ZSM-5 molecular sieve catalyst according to claim 1, characterized in that: In the first step, the silicon source is selected from water glass, silica sol, sodium silicate, or silica fume.

3. The method for preparing the twinned ZSM-5 molecular sieve catalyst according to claim 1, characterized in that: In the first step, the aluminum source is selected from boehmite, sodium aluminate, aluminum powder, or aluminum isopropoxide.

4. The method for preparing the twinned ZSM-5 molecular sieve catalyst according to claim 1, characterized in that: In the first step, the template agent is selected from ethylenediamine, triethylamine, isopropylamine, tetrapropylammonium hydroxide, propylammonium hydrobromide, n-butylamine, or 1,6-hexanediamine.

5. The method for preparing the twinned ZSM-5 molecular sieve catalyst according to claim 1, characterized in that: In the second step, MCM-35 molecular sieve is composed of mfi structural units, and the mfi structural units are obtained by alkaline heat treatment of MCM-35 molecular sieve; MOR molecular sieve is composed of mor structural units, and the mor structural units are obtained by alkaline heat treatment of MOR molecular sieve; MCM-22 molecular sieve is composed of mel and D6R structural units, wherein D6R is destroyed in an alkaline heat environment, and the mel structural units are obtained by alkaline heat treatment of MCM-22 molecular sieve.

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