Method for synthesizing hierarchical pore molecular sieve

Abstract

The invention relates to a method for synthesizing a hierarchical pore molecular sieve, which comprises the following steps: (1) mixing and uniformly stirring a conventional organic template agent and an organic ammonium salt with an asymmetric structure to obtain an organic mixed solution; (2) adding a silicon source, an aluminum source and water into the organic mixed solution obtained in the step (1), and uniformly stirring to obtain synthetic gel; and (3) transferring the synthesized gel obtained in the step (2) into a self-pressure-generating crystallization kettle, sealing, carrying out high-temperature crystallization, and filtering and washing the crystallized molecular sieve to obtain the hierarchical pore molecular sieve product. The organic ammonium salt with the asymmetric structure is an ammonium group-containing organic compound with 2-8 alkyl substituent groups, and the alkyl substituent groups are not completely the same. The conventional organic template agent is one of organic compounds or polyamines with 2-8 alkyl substituent groups, and the alkyl substituent groups are safe and the same. The method is simple in implementation process, existing equipment does not need to be transformed, and the method has wide industrial application prospects.

Description

Technical Field

[0001] The invention relates to the field of molecular sieve synthesis, and in particular to a method for synthesizing multi-level pore molecular sieves by utilizing asymmetric organic molecules and a product thereof. Background Art

[0002] Molecular sieves have unique pores and acid properties, so they are widely used in the fields of adsorption, separation and catalysis. The molecular sieve framework can be regarded as composed of finite or infinite component units, where the finite component units mainly refer to polycyclic rings (i.e. secondary structural units) composed of TO4=(Si, Al, P, etc.) through shared oxygen atoms, while the infinite component units refer to chains or layers composed of secondary structural units through edge sharing.

[0003] Multi-level pore molecular sieve refers to a pore structure with two or more different pore sizes and distributed step by step in the same molecular sieve. It has the advantages of pore structures at different levels, and at the same time has the advantages of classification that a single pore structure does not have. According to the provisions of the International Union of Pure and Applied Chemistry, pores can be divided into micropores (<2nm), mesopores (2-50nm) and macropores (>50nm) according to the pore size. Correspondingly, multi-level pore molecular sieves can be divided into microporous-mesoporous molecular sieves, mesoporous-macroporous molecular sieves or microporous-mesoporous-macroporous molecular sieves, etc.

[0004] In recent years, multi-level pore molecular sieves have been widely used in industrial catalysis, adsorption separation, nanoscience, life sciences, energy and other fields. On the basis of maintaining the catalytic activity and stability of traditional molecular sieves, multi-level pore molecular sieves introduce mesoporous / macroporous structures throughout the entire molecular sieve framework through different synthetic strategies, which greatly improves the diffusion and mass transfer problems caused by a single microporous structure. During the catalytic reaction, the reactants enter the internal active sites of the molecular sieve through the pores to undergo catalytic reactions, and the resulting products are then transported out through the pores. Therefore, the introduction of a multi-level pore structure is conducive to the combination of reactants with the internal active sites of the molecular sieve, thereby effectively improving the catalytic performance of the molecular sieve, and can also significantly improve the diffusion efficiency of reactants and products, thereby effectively inhibiting carbon deposition and slowing down the deactivation of the catalyst. The emergence of multi-level pore molecular sieve catalysts has significantly improved the utilization rate of the catalyst particles in the catalytic reaction, greatly improving the efficiency of the catalytic reaction.

[0005] There are two main methods for synthesizing hierarchical molecular sieves: post-treatment method (top-down) and direct synthesis method (bottom-up). The post-treatment method is to remove part of the silicon and aluminum on the molecular sieve by adding acid and alkali and hydrothermal treatment, so that the original molecular sieve has certain structural defects and produces mesopores. The post-treatment method can be divided into dealumination method, desiliconization method and dealumination and desiliconization combined method. For example: Jong used USY molecular sieve as raw material and desiliconized it with NaOH solution to obtain a hierarchical USY molecular sieve with a mesopore size of 3 to 30 nm. A large number of through holes were observed under transmission electron microscopy and were interconnected. This sample was used as a catalyst in the evaluation of the hydrocracking reaction of vacuum wax oil and showed excellent catalytic performance; An Liangcheng studied the effect of ZSM-5 molecular sieve on MTP reaction before and after steam treatment. The results showed that steam treatment weakened the acid strength of the molecular sieve and reduced the amount of acid, but increased the pore volume and pore size, thereby improving the stability of the catalyst and propylene selectivity. The post-treatment method has the advantages of simple synthesis, economy, and environmental protection, but requires fine optimization of synthesis conditions and has poor repeatability. CN103964458A treats the raw material Beta zeolite with acid twice and calcines it twice to obtain Beta zeolite with high silicon-aluminum ratio and multi-level pores.

[0006] The direct synthesis method includes hard template method, soft template method and template-free self-assembly method. Hard templates usually use carbon materials such as carbon black, carbon nanotubes, and mesoporous carbon as mesoporous templates. The carbon materials used as hard templates can be removed by calcination. For example, Jacobsen added carbon spheres with a size of 12nm as hard templates in a hydrothermal system, and the molecular sieve crystals grew on the outer surface of the carbon spheres to successfully synthesize multi-level pore ZSM-5 molecular sieves. Unlike the hard template method, the soft template method uses the interaction between soft template molecules and silicon-based species during the crystallization process to self-assemble and synthesize multi-level pore molecular sieves. It has the advantages of simple operation and adjustable mesopore diameter. Traditional soft templates include organosilanes, surfactants, and water-soluble cationic polymers. For example: Xiao used polydiallyldimethylammonium chloride as a surfactant to successfully synthesize multi-level pore Beta molecular sieves and multi-level pore ZSM-5 molecular sieves; Zhao used commercial ZSM-5 molecular sieves as raw materials and added CTAB as a soft template to successfully synthesize multi-level pore ZSM-5 molecular sieves. CN101538049 discloses a method for preparing a multi-level pore Beta molecular sieve, which belongs to the field of preparation and application technology of molecular sieves. It is characterized in that the carbon particles generated under the constraint of ordered mesoporous channels are used as hard templates, and then small molecule organic ammonium soft templates are added to convert the mesoporous silicon aluminum wrapped in the carbon particles into microporous Beta molecular sieves in situ, and the Beta molecular sieve containing multi-level channels can be obtained after roasting to remove the soft and hard templates. CN108069437A discloses a method for synthesizing a multi-level pore Beta molecular sieve using enzymatic lignin (EHL) as a surfactant. The mesopore volume of the Beta molecular sieve accounts for 40-60% of the total pore volume, 2-6nm mesopores account for 20-75% of the total mesopore volume, and 15-20nm mesopores account for 10-60% of the total mesopore volume. The Beta molecular sieve is hydrothermally treated at 700℃ for 4h, and the relative crystallinity retention rate is 85-97%.

[0007] A large number of studies have found that soft templates may play two roles in the crystal growth process: on the one hand, soft template molecules will be arranged into ordered micelles in the precursor solution. The micelles are dispersed in the precursor solution to complete the growth of the crystals together, and after calcination, abundant intercrystalline mesopores are formed (drilling effect); on the other hand, soft template cations can be enriched on the surface of negatively charged microcrystals, forming a hydrophobic layer around the microcrystals, cutting off the supply of aluminosilicates in the solution that promote crystal growth, limiting further growth of the crystals and ultimately forming smaller initial nanocrystals (protective effect).

[0008] Although the soft template method is simple to synthesize, the synthesis cost of templates such as organosilane and diquaternary ammonium salt surfactants is high, which is not conducive to industrial application.

[0009] In summary, the formation of dispersed micelles or limiting the continuous growth of crystals is the key to the successful synthesis of hierarchical pore molecular sieves using soft templates. Therefore, if new template molecules with similar effects to soft templates can be discovered, it will provide new ideas for the direct synthesis of hierarchical pore molecular sieves and may significantly reduce the synthesis cost of hierarchical pore molecular sieves. Summary of the invention

[0010] In view of the current status of research on multi-level pore molecular sieves, the present invention proposes a method for synthesizing multi-level pore molecular sieves using an asymmetric organic template. The method is to mix two organic molecules (conventional organic template and asymmetric organic molecule) and add them to a synthetic gel, so as to exert the template effect of the organic template molecule and the effect of the asymmetric organic molecule on inhibiting the continuous growth of crystals, thereby causing a large number of nano-molecular sieve crystals to aggregate with each other during the crystallization process, and obtaining a multi-level pore molecular sieve with a large number of intercrystalline mesopores.

[0011] The inventors have found that the key to obtaining a multi-level pore molecular sieve is to mix conventional template molecules with organic ammonium salt molecules with asymmetric structures and introduce them into the synthetic gel. The organic template has the following three main functions in the crystallization process of the molecular sieve: (1) as a space filler in the process of forming the inorganic skeleton, that is, supporting and stabilizing the skeleton; (2) satisfying the charge matching between the inorganic skeleton and the organic template, that is, the charge matching principle; (3) having the ability of self-assembly, that is, the structure-directed principle.

[0012] When an organic ammonium salt molecule with an asymmetric structure similar to that of a conventional organic template molecule and having a similar size is introduced, the organic ammonium salt with an asymmetric structure often has a size and structure that is relatively compatible with the target molecular sieve pores, and can smoothly enter the molecular sieve pores during the crystallization process to play its space filling and charge matching role, which ensures the smooth crystallization of the molecular sieve. At the same time, the structural guidance effect of the organic ammonium salt with an asymmetric structure is significantly weaker than that of the conventional template molecule. Therefore, the addition of the organic ammonium salt with an asymmetric structure will weaken the structural guidance effect of the template in the synthetic gel, reduce the crystallization rate of the molecular sieve crystals, and form a large number of nano-sized molecular sieve grains.

[0013] By adjusting the addition ratio of organic ammonium salts with asymmetric structures, the number, morphology and size of nano-molecular sieve grains can be significantly changed, thereby regulating the morphology and number of intercrystalline mesopores of the multi-level pore molecular sieve. When the proportion of organic ammonium salts with asymmetric structures is too large, the structural guidance effect of the template in the synthetic gel is too weak, and the pure phase molecular sieve corresponding to the conventional template cannot be obtained at this time, and a multi-level pore composite molecular sieve may be obtained.

[0014] In order to achieve the above-mentioned invention object, the present invention discloses the following technical solutions:

[0015] A method for synthesizing a multi-level pore molecular sieve comprises the following steps:

[0016] (1) mixing a conventional organic template and an organic ammonium salt having an asymmetric structure and stirring them uniformly to obtain an organic mixed solution;

[0017] (2) adding a silicon source, an aluminum source, and water to the organic mixed solution obtained in step (1), and stirring the mixture to obtain a synthetic gel;

[0018] (3) The synthetic gel obtained in step (2) is transferred into a crystallization kettle and sealed for high-temperature crystallization, and the crystallized molecular sieve is filtered and washed to obtain a multi-level pore molecular sieve product.

[0019] The organic ammonium salt with an asymmetric structure is an organic compound having 2-8 alkyl substituents and containing an ammonium group, and the alkyl substituents are not completely the same; the alkyl substituent is a C1-C24 straight chain or straight chain alkyl substituent, more preferably a C1-C18 alkyl substituent, most preferably, the alkyl substituent is one or more of methyl, ethyl, propyl, butyl, benzyl, hexadecyl, and octadecyl; more preferably, the organic ammonium salt with an asymmetric structure is an ammonium halide or ammonium hydroxide having 2-8 alkyl substituents, and further, the organic ammonium salt with an asymmetric structure is an ammonium halide or ammonium hydroxide having 4 alkyl substituents.

[0020] The conventional organic template is an organic compound having 2 to 8 alkyl substituents, and the alkyl substituents are safe and identical, or one of the polyamines.

[0021] In step (1), the molar ratio of the conventional organic template to the organic ammonium salt having an asymmetric structure is 0.1-10:0.1-10; preferably 2-5:2-5.

[0022] The composition of the synthetic gel in step (2) is: conventional organic template: organic ammonium salt with asymmetric structure: inorganic base: aluminum source: silicon source: water = 0.1-10: 0.1-10: 0-20: 0-1: 1-1000: 1-500; preferably 2-5: 2-5: 0-10: 0-1: 20 to 70: 10-100.

[0023] Preferably, the conventional organic template is one or more of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, choline hydroxide, tetrabutylammonium bromide, tetrabutylammonium chloride, tetrapropylammonium bromide, tetrapropylammonium chloride, tetraethylammonium bromide, tetraethylammonium chloride, tetramethylammonium bromide, tetramethylammonium chloride, triethylamine, and ethylenediamine.

[0024] Preferably, the organic molecule having an asymmetric structure is methyltriethylammonium hydroxide, methyltriethylammonium bromide, methyltriethylammonium chloride, methyltripropylammonium hydroxide, methyltripropylammonium bromide, methyltripropylammonium chloride, methyltributylammonium hydroxide, methyltributylammonium bromide, methyltributylammonium chloride, trimethylethylammonium hydroxide, trimethylethylammonium bromide, trimethylethylammonium chloride, trimethylpropylammonium hydroxide, trimethylpropylammonium bromide, trimethylpropylammonium chloride, trimethylbutylammonium hydroxide, trimethylbutylammonium bromide, trimethylbutyl chloride. The organic template structure of the present invention is preferably selected from the group consisting of triethyl propyl ammonium hydroxide, triethyl propyl ammonium bromide, triethyl propyl ammonium chloride, triethyl butyl ammonium hydroxide, triethyl butyl ammonium bromide, triethyl butyl ammonium chloride, tripropyl butyl ammonium hydroxide, tripropyl butyl ammonium bromide, tripropyl butyl ammonium chloride, benzyl trimethyl ammonium hydroxide, benzyl triethyl ammonium hydroxide, benzyl tripropyl ammonium hydroxide, benzyl tributyl ammonium hydroxide, diethyl dimethyl ammonium hydroxide (non-centrosymmetric), hexadecyl trimethyl ammonium hydroxide, hexadecyl trimethyl ammonium bromide, and hexadecyl trimethyl ammonium chloride. Preferably, the conventional organic template structure has a relatively close molecular weight to the organic molecule with an asymmetric structure, and the difference in molecular weight is not more than 100, and more preferably not more than 50.

[0025] The silicon source is one or more of tetraethyl orthosilicate, fumed silica, water glass, silica sol, and macroporous silica gel.

[0026] The aluminum source is one or more of aluminum sulfate, aluminum nitrate, aluminum powder, sodium aluminate, aluminum hydroxide powder, pseudo-boehmite, and aluminum isopropoxide.

[0027] The inorganic base added to the synthetic gel is one or more of LiOH, NaOH and KOH.

[0028] The mixing and stirring time of the organic mixed solution in step (1) is 0.1-24 hours, and the temperature during the mixing and stirring process is between -10 and 80° C. More preferably, the mixing and stirring time is 0.1-2 hours, and the temperature during the mixing and stirring process is between 10 and 40° C.

[0029] The mixing and stirring time of the synthetic gel in step (2) is 0.1-48 hours, and the temperature during the mixing and stirring process is between -10 and 80° C. More preferably, the mixing and stirring time is 12-36 hours, and the temperature during the mixing and stirring process is between 10 and 40° C.

[0030] The crystallization method in step (3) is one of hydrothermal crystallization and steam-assisted crystallization. The crystallization temperature after entering the kettle is 80-250°C, the crystallization time is 0.1-120h, and the pressure is 0.1-10MPa.

[0031] Another aspect of the present invention discloses a multi-level pore molecular sieve prepared by the method.

[0032] The molecular sieve is a pure phase molecular sieve or a composite molecular sieve; the pure phase molecular sieve is one of ZSM-5 molecular sieve, ZSM-11 molecular sieve, ZSM-12 molecular sieve, Beta molecular sieve, and MOR molecular sieve; the composite molecular sieve is one of ZSM-5 / ZSM-11 composite molecular sieve, ZSM-5 / Beta composite molecular sieve, ZSM-5 / MOR composite molecular sieve, ZSM-5 / ZSM-12 composite molecular sieve, Beta / MOR composite molecular sieve, ZSM-11 / / Beta composite molecular sieve, and ZSM-11 / 12 composite molecular sieve.

[0033] Preferably, the mesopore volume of the multi-level pore molecular sieve is increased by 20%-500%, more preferably by 80%-500%, and further preferably by 200%-500%.

[0034] Beneficial technical effects of the present invention: The present invention successfully synthesizes a multi-level pore molecular sieve by simply adding an organic ammonium salt with an asymmetric structure, and realizes the regulation of the morphology, mesopore volume and type (pure phase molecular sieve converted into a composite molecular sieve) of the multi-level pore molecular sieve, which provides a new method and new ideas for the synthesis of multi-level pore molecular sieves. In addition, the method of the present invention is simple to implement, low in consumption, does not require any modification of existing equipment, and compared with traditional soft templates, small molecule asymmetric organic molecules often have lower synthesis costs. In addition, the molecular sieve preparation method is applicable to the synthesis of any type of pure phase molecular sieve and composite molecular sieve, including ZSM-5 molecular sieve, Beta molecular sieve and ZSM-5 / ZSM-12 composite molecular sieve, etc. Therefore, the molecular sieve preparation method of the present invention has broad and good industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 X-ray diffraction spectra of control sample B-0 and target samples B-20, B-40, and B-50;

[0036] Figure 2 X-ray diffraction refinement spectrum of target sample B-50;

[0037] Figure 3 Transmission electron microscope photo of target sample B-20;

[0038] Figure 4 Transmission electron microscope photo of target sample B-40;

[0039] Figure 5 Transmission electron microscope photo of target sample B-50;

[0040] Figure 6 TEM photo of control sample B-0; DETAILED DESCRIPTION

[0041] The following examples are used to further illustrate the present invention, but are not intended to limit the present invention.

[0042] Example 1

[0043] First, weigh 51.85 grams of 25wt% tetraethylammonium hydroxide aqueous solution, 11.72 grams of 25wt% methyltriethylammonium hydroxide aqueous solution and 10.96 grams of water, mix and stir for 5 minutes, then add 0.281 grams of aluminum powder, stir for 24 hours, and finally slowly add 50 grams of 30wt% silica sol, stir for 6 hours, put it into the crystallization kettle, and place it in a 160℃ oven for crystallization for 240 hours. After cooling, the mixed solution in the kettle is centrifuged and dried to obtain the target Beta molecular sieve sample (sample name B-20). Among them, the X-ray diffraction spectrum of the sample is as follows Figure 1 shown.

[0044] Example 2

[0045] First, weigh 38.88 grams of 25wt% tetraethylammonium hydroxide aqueous solution, 23.44 grams of 25wt% methyltriethylammonium hydroxide aqueous solution and 11.84 grams of water, mix and stir for 5 minutes, then add 0.281 grams of aluminum powder, stir for 24 hours, and finally slowly add 50 grams of 30wt% silica sol, stir for 6 hours, put it into the crystallization kettle, and place it in a 160℃ oven for crystallization for 240 hours. After cooling, the mixed solution in the kettle is centrifuged and dried to obtain the target Beta molecular sieve sample (sample name B-40). Among them, the X-ray diffraction spectrum of the sample is as follows Figure 1 shown.

[0046] Example 3

[0047] First, weigh 32.4 grams of 25wt% tetraethylammonium hydroxide aqueous solution, 29.3 grams of 25wt% methyltriethylammonium hydroxide aqueous solution and 12.3 grams of water, mix and stir for 5 minutes, then add 0.28 grams of aluminum powder, stir for 24 hours, and finally slowly add 50 grams of 30wt% silica sol, stir for 6 hours, put it into the crystallization kettle, and place it in a 160℃ oven for crystallization for 240 hours. After cooling, the mixed solution in the kettle was centrifuged and dried to obtain the target ZSM-5 / ZSM-12 composite molecular sieve sample (sample name B-50). Among them, the X-ray diffraction spectrum of the sample is as follows Figure 1 shown.

[0048] Comparative Example 1

[0049] First, weigh 64.35 grams of 25wt% tetraethylammonium hydroxide aqueous solution and 10.4 grams of water, mix and stir for 5 minutes, then add 0.281 grams of aluminum powder, stir for 24 hours, and finally slowly add 50 grams of 30wt% silica sol, stir for 6 hours, put it into a crystallization kettle, and place it in a 160℃ oven for crystallization for 240 hours. After cooling, the mixed solution in the kettle was centrifuged and dried to obtain a control sample Beta molecular sieve sample (sample name B-0). Among them, the X-ray diffraction spectrum of the sample is as follows Figure 1 shown.

[0050] Depend on Figure 1 It can be found that the XRD spectra of Examples 1, 2 and Comparative Example 1 all have obvious BEA structural characteristic diffraction peaks, indicating that they are all well-crystallized Beta molecular sieves, while the XRD refined spectrum of Example 3 also has obvious MFI structural characteristic diffraction peaks and MTW diffraction peaks ( Figure 2 ), indicating that it is a ZSM-5 / ZSM-12 composite molecular sieve. It can be seen that when the proportion of symmetrical molecules is too high, the structure-directing effect of the mixed template agent undergoes a significant change and cannot successfully guide the formation of the BEA structure.

[0051] The pore structures of the obtained embodiments and comparative examples were measured according to the national standard, and the pore structure properties of the molecular sieves were characterized. The instruments used were Quadrasorb evoTM and Autosorb-iQ3 fully automatic specific surface area and porosity analyzers produced by Anton Paar-Quantachrome of Austria. The pore structure data of the molecular sieves were obtained by static low-temperature adsorption capacity method.

[0052] The obtained molecular sieve was placed in a sample tube before testing and pre-treated with vacuum degassing (drying and impurity removal) at 300°C. Subsequently, high-purity nitrogen was used as the adsorbent. At 77K, the surface adsorption of the sample molecular sieve was measured with pressure, and the N2 adsorption-desorption isotherm of the obtained molecular sieve was finally obtained. The specific surface area of ​​the molecular sieve was calculated using the BET (Brunauer-Emmett-Teller) method, the micropore volume and mesopore specific surface area were calculated using the t-plot method, and the pore size distribution was calculated using the (BJH Barret-Joyner-Halenda) method. The results are shown in Table 1.

[0053] Determination of the reaction activity of the catalyst: The catalyst obtained in Example 2 and Comparative Example 1 was evaluated for catalytic cracking reaction performance, and the reaction raw material was vacuum wax oil. Before the reaction, 1 gram of catalyst (20-40 mesh) was mixed with 4 grams of quartz sand (20-40 mesh) and loaded into the reactor. The catalyst was activated for 30 minutes at a nitrogen flow of 40 mL / min and a reaction temperature of 773K. After activation, the feed was injected into the catalyst bed at a constant rate of 1.68 g of vacuum wax oil at a flow rate of 10 mL / min through an injection pump, and nitrogen was used as an inert carrier gas. After completing the catalytic cracking performance test of the catalyst, the spent catalyst was regenerated in flowing air at 923K using an online carbon dioxide analyzer to calculate the amount of coke. The reaction product was subjected to offline chromatographic analysis of its product composition, and the evaluation results are shown in Table 2. It can be found that compared with Comparative Example 1, Example 2 has significant advantages in conversion rate, gasoline yield and liquefied gas yield. This is attributed to the improved diffusion performance brought about by the increase in mesopore content.

[0054] Table 1

[0055]

[0056] Table 2

[0057]

[0058] Note: Reaction raw material: vacuum wax oil; reaction temperature: 500°C; agent-oil ratio: 0.6; conversion rate (%) = (raw material mass - heavy oil mass in product) / raw material mass × 100%.

[0059] Compared with the control sample B-0, the comparative sample B-40 has significant advantages in conversion rate, gasoline yield and liquefied gas yield.

[0060] Those skilled in the art should understand that the above embodiments are only used to illustrate the technical solutions of the present invention and are not used to limit the protection scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

Claims

1. A method for synthesizing a multi-level pore molecular sieve, comprising the following steps: (1) mixing a conventional organic template and an organic ammonium salt having an asymmetric structure and stirring them uniformly to obtain an organic mixed solution; (2) adding an inorganic base, a silicon source, an aluminum source, and water to the organic mixed solution obtained in step (1), and stirring the mixture to obtain a synthetic gel; (3) transferring the synthetic gel obtained in step (2) into a crystallization kettle and sealing it for high-temperature crystallization, filtering and washing the crystallized molecular sieve to obtain a multi-level pore molecular sieve product; The organic ammonium salt having an asymmetric structure is an organic compound having 2 to 8 alkyl substituents and containing an ammonium group, and the alkyl substituents are not completely the same; The conventional organic template is an organic compound having 2 to 8 alkyl substituents, and the alkyl substituents are safe and identical, or one of the polyamines.

2. The method according to claim 1, characterized in that The alkyl substituent is a C1-C24 straight or branched chain alkyl substituent, more preferably a C1-C18 alkyl substituent.

3. The method according to claim 1, characterized in that Most preferably, the alkyl substituent is one or more of methyl, ethyl, propyl, butyl, benzyl, hexadecyl, octadecyl.

4. The method according to claim 1, characterized in that In step (1), the molar ratio of the conventional organic template to the organic ammonium salt having an asymmetric structure is 0.1-10:0.1-10; preferably 2-5:2-5.

5. The method according to claim 1, characterized in that The composition of the synthetic gel in step (2) is: conventional organic template: organic ammonium salt with asymmetric structure: inorganic base: aluminum source: silicon source: water = 0.1-10: 0.1-10: 0-20: 0-1: 1-1000: 1-500; preferably 2-5: 2-5: 0-10: 0-1: 20 to 70: 10-100.

6. The method according to claim 1, characterized in that Preferably, the conventional organic template is one or more of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, choline hydroxide, tetrabutylammonium bromide, tetrabutylammonium chloride, tetrapropylammonium bromide, tetrapropylammonium chloride, tetraethylammonium bromide, tetraethylammonium chloride, tetramethylammonium bromide, tetramethylammonium chloride, triethylamine, and ethylenediamine.

7. The method according to claim 1, characterized in that The organic ammonium salt with an asymmetric structure is methyltriethylammonium hydroxide, methyltriethylammonium bromide, methyltriethylammonium chloride, methyltripropylammonium hydroxide, methyltripropylammonium bromide, methyltripropylammonium chloride, methyltributylammonium hydroxide, methyltributylammonium bromide, methyltributylammonium chloride, trimethylethylammonium hydroxide, trimethylethylammonium bromide, trimethylethylammonium chloride, trimethylpropylammonium hydroxide, trimethylpropylammonium bromide, trimethylpropylammonium chloride, trimethylbutylammonium hydroxide, trimethylbutylammonium bromide, trimethylbutylammonium chloride, triethylpropylammonium hydroxide, triethylpropylammonium bromide, trimethylpropylammonium chloride, trimethylbutylammonium hydroxide, trimethylbutylammonium bromide, trimethylbutylammonium chloride, triethylpropylammonium hydroxide, triethylpropylammonium bromide, trimethylethylammonium hydroxide, trimethylethylammonium bromide, trimethylethylammonium chloride, trimethylpropylammonium hydroxide, trimethylpropylammonium bromide, trimethylpropylammonium chloride, trimethylbutylammonium hydroxide, trimethylbutylammonium bromide, trimethylbutylammonium chloride, triethylpropylammonium hydroxide, triethylpropylammonium bromide, trimethylethylammonium bromide, trimethylethylammonium chloride, trimethylpropylammonium hydroxide, trimethylpropylammonium bromide ... One or more of ethylpropylammonium chloride, triethylbutylammonium hydroxide, triethylbutylammonium bromide, triethylbutylammonium chloride, tripropylbutylammonium hydroxide, tripropylbutylammonium bromide, tripropylbutylammonium chloride, benzyltrimethylammonium hydroxide, benzyltriethylammonium hydroxide, benzyltripropylammonium hydroxide, benzyltributylammonium hydroxide, diethyldimethylammonium hydroxide, hexadecyltrimethylammonium hydroxide, hexadecyltrimethylammonium bromide, and hexadecyltrimethylammonium chloride; preferably, the difference in molecular weight between the conventional organic template structure and the organic ammonium salt having an asymmetric structure is not greater than 100, more preferably not greater than 50.

8. The method according to claim 1, characterized in that The silicon source is one or more of tetraethyl orthosilicate, fumed silica, water glass, silica sol, and macroporous silica gel; The aluminum source is one or more of aluminum sulfate, aluminum nitrate, aluminum powder, sodium aluminate, aluminum hydroxide powder, pseudo-boehmite, and aluminum isopropoxide; The inorganic base added to the synthetic gel is one or more of LiOH, NaOH and KOH.

9. The method according to claim 1, characterized in that The mixing and stirring time of the organic mixed solution in step (1) is 0.1-24 hours, and the temperature during the mixing and stirring process is between -10 and 80°C; more preferably, the mixing and stirring time is 0.1-2 hours, and the temperature during the mixing and stirring process is between 10 and 40°C; The mixing and stirring time of the synthetic gel in step (2) is 0.1-48 hours, and the temperature during the mixing and stirring process is between -10 and 80° C.; more preferably, the mixing and stirring time is 12-36 hours, and the temperature during the mixing and stirring process is between 10 and 40° C.; The crystallization method in step (3) is one of hydrothermal crystallization and steam-assisted crystallization; the crystallization temperature after entering the kettle is 80-250°C, the crystallization time is 0.1-120h, and the pressure is 0.1-10MPa.

10. A multi-level pore molecular sieve prepared according to the method according to any one of claims 1 to 9, characterized in that The molecular sieve is a pure phase molecular sieve or a composite molecular sieve; the pure phase molecular sieve is one of ZSM-5 molecular sieve, ZSM-11 molecular sieve, ZSM-12 molecular sieve, Beta molecular sieve, and MOR molecular sieve; the composite molecular sieve is one of ZSM-5 / ZSM-11 composite molecular sieve, ZSM-5 / Beta composite molecular sieve, ZSM-5 / MOR composite molecular sieve, ZSM-5 / ZSM-12 composite molecular sieve, Beta / MOR composite molecular sieve, ZSM-11 / / Beta composite molecular sieve, and ZSM-11 / 12 composite molecular sieve; The mesopore volume of the multi-level pore molecular sieve is increased by 20%-500%, more preferably 80%-500%, and further preferably 200%-500%.

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