A ZSM-5 molecular sieve with stepped pores and preparation method thereof

Abstract

The present invention discloses a ZSM-5 molecular sieve with stepped pores and a preparation method thereof, comprising the following steps: step 1, mixing an aluminum source precursor, a template agent and a chelating dispersant to obtain an aluminum source precursor solution; step 2, mixing an aluminum source precursor solution with a silicon source precursor solution to obtain a molecular sieve crystallization mother solution; step 3, adding a seed to the molecular sieve crystallization mother solution, aging, crystallization, and obtaining a ZSM-5 molecular sieve with stepped pores; wherein the chelating dispersant is at least one of sodium ethylenediaminetetramethylenephosphonate, hydroxyethylidene diphosphonic acid, and sodium polymethacrylate. The present invention achieves the purpose of adjusting the micropores and mesopore size and ratio of the ZSM-5 molecular sieve by adding a chelating dispersant during the preparation of the ZSM-5 molecular sieve, and controlling the type and dosage of the chelating dispersant, so that the resulting ZSM-5 molecular sieve pore size distribution can meet the requirements of different raw materials, and finally achieves directional matching.

Description

Technical Field

[0001] The invention relates to a ZSM-5 molecular sieve and a preparation method thereof, and in particular to a ZSM-5 molecular sieve with stepped pores and a preparation method thereof. Background Art

[0002] Since its first synthesis in 1972, ZSM-5 molecular sieve has been widely used in many fields such as petrochemical industry, fine chemical industry and environmental protection due to its unique three-dimensional pore structure, shape-selective catalytic performance and hydrothermal stability.

[0003] Conventional ZSM-5 molecular sieves have microporous pores and large crystals. The diffusion distance of raw materials and reaction products in the inner pores is proportional to the internal diffusion resistance. For example, after the target product olefin is generated in the cage of the molecular sieve, the olefin will further undergo hydrogen transfer reaction at the acidic site in the molecular sieve to generate by-product alkane or undergo polymerization reaction to form coke during the outward diffusion process, which reduces the selectivity of the target product and causes the molecular sieve catalyst to coke and deactivate. It is precisely because the microporous channels of the ZSM-5 molecular sieve hinder larger molecules from entering the channels for adsorption, reaction or desorption, limiting the diffusion of larger molecules, making it unable to meet the demand for catalysts for efficient conversion of heavy petroleum resources. Therefore, it is urgent to develop molecular sieve catalytic materials with stepped channels.

[0004] The preparation of molecular sieves with stepped pores is currently a hot topic in the field of their synthesis. The template method and post-treatment method are generally used. The template method is to introduce a macromolecular template into the crystallization mother liquor during the synthesis process to occupy a spatial position. After the hydrothermal crystallization is completed, it is generally removed by roasting to obtain a molecular sieve with a stepped pore structure. The post-treatment method is to first synthesize a microporous molecular sieve, and then remove the species in the molecular sieve framework through acid, alkali or hydrothermal treatment to obtain a molecular sieve with a mesoporous structure.

[0005] CN107128947A discloses a stepped pore ZSM-5 zeolite and a preparation method thereof. The preparation method comprises: (1) uniformly mixing a single-head quaternary ammonium salt surfactant and water to obtain liquid A; uniformly mixing sodium aluminate, sodium hydroxide and water to obtain liquid B; uniformly mixing tetrapropylammonium hydroxide and tetraethyl orthosilicate to obtain liquid C; (2) adding liquid A to liquid B under uniform stirring to obtain liquid D, and continuously stirring; (3) continuously adding liquid C to liquid D under uniform stirring to obtain a gel, and continuously stirring; (4) placing the product obtained in step (3) in a high-pressure reactor for hydrothermal crystallization reaction, washing and filtering with water after crystallization, and then vacuum drying; (5) placing the dried product in step (4) in a muffle furnace for roasting to obtain a medium-micro dual-pore ZSM-5 zeolite molecular sieve. The molar ratio of the above sodium hydroxide, tetraethyl orthosilicate, sodium aluminate, single-head quaternary ammonium salt surfactant and tetrapropylammonium hydroxide is (24-28): (50-300): (1-5): 5: 2. Although the ZSM-5 molecular sieve synthesized in the patent application contains a mesoporous structure, it does not involve how to regulate the size of the mesopores and micropores, and how to regulate the ratio of the mesopores and micropores. Therefore, those skilled in the art still need to further study the synthesis of the ZSM-5 molecular sieve to make it meet the catalytic needs of different raw materials. Summary of the invention

[0006] The main purpose of the present invention is to provide a ZSM-5 molecular sieve with stepped pores and a preparation method thereof. The pore structure of the ZSM-5 molecular sieve obtained by the method of the present invention can be adjusted according to needs to meet the needs of raw materials of different sizes for mesopores and micropores, thereby solving the problem of directional matching of molecular catalytic reactions and transfers in the prior art.

[0007] In order to achieve the above object, the present invention provides a method for preparing a ZSM-5 molecular sieve having stepped pores, comprising the following steps:

[0008] Step 1, mixing an aluminum source precursor, a template agent and a chelating dispersant to obtain an aluminum source precursor solution;

[0009] Step 2, mixing the aluminum source precursor solution and the silicon source precursor solution to obtain a molecular sieve crystallization mother solution;

[0010] Step 3, adding seed crystals to the molecular sieve crystallization mother liquor, aging and crystallizing, to obtain a ZSM-5 molecular sieve with stepped pores;

[0011] Wherein, the chelating dispersant is at least one of sodium ethylenediaminetetramethylenephosphonate, hydroxyethylidene diphosphonic acid, and sodium polymethacrylate.

[0012] The preparation method of the ZSM-5 molecular sieve with stepped pores described in the present invention, wherein the template agent is a macromolecular template agent, and the macromolecular template agent is at least one of poly(ethylene glycol), polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer, and hexadecyltrimethylammonium bromide.

[0013] The method for preparing the ZSM-5 molecular sieve with stepped pores described in the present invention comprises a silicon source precursor solution and an alkaline substance, the silicon source precursor is tetraethyl orthosilicate, and the alkaline substance is at least one of n-butylamine, n-propylamine, and sodium hydroxide; the molar ratio of the silicon source precursor to the alkaline substance is 15-30:2-10.

[0014] The method for preparing the ZSM-5 molecular sieve with stepped pores of the present invention comprises the following steps: the aluminum source precursor is at least one of aluminum sulfate and aluminum nitrate, and the molar ratio of the aluminum source precursor, the template and the chelating dispersant is 100-500:20-100:1-20.

[0015] The method for preparing the ZSM-5 molecular sieve with stepped pores of the present invention comprises the following steps: the molar ratio of the aluminum source precursor to the silicon source precursor is 10-300.

[0016] The method for preparing the ZSM-5 molecular sieve with stepped pores of the present invention comprises the following steps: the seed crystal is a ZSM-5 molecular sieve, the aging temperature is room temperature, and the aging time is 6-24 hours.

[0017] The method for preparing the ZSM-5 molecular sieve with stepped pores of the present invention comprises the following steps: the crystallization temperature is 120-180° C., and the crystallization time is 1-7 days.

[0018] The preparation method of the ZSM-5 molecular sieve with stepped pores described in the present invention, wherein the aluminum source precursor solution and the silicon source precursor solution are mixed by: dripping the aluminum source precursor solution into the silicon source precursor solution; and the crystallization is autogenous hydrothermal crystallization.

[0019] In order to achieve the above object, the present invention also provides a ZSM-5 molecular sieve with stepped pores obtained by the above preparation method, wherein the ZSM-5 molecular sieve with stepped pores includes a micropore diameter and a mesopore diameter, and the mesopore diameter is 2-50 nm.

[0020] The ZSM-5 molecular sieve with stepped pores of the present invention has a specific surface area of ​​100 m 2 / g-350m 2 / g.

[0021] Beneficial effects of the present invention:

[0022] The present invention achieves the purpose of adjusting the size and ratio of micropores and mesopores of ZSM-5 molecular sieve by controlling the type and amount of chelating dispersant. Increasing the amount of chelating dispersant can shift the maximum mesopore size distribution of ZSM-5 molecular sieve toward small pores, and generate mesopore size distribution in a directional manner, thereby achieving the purpose of controllable preparation. The present invention produces a micro-mesoporous composite stepped pore structure with a specific surface area ranging from 100m 2 / g-410m 2 / g, in addition to the micropores of 0.55nm, it also contains mesopores with a diameter of 2-50nm.

[0023] The controllable preparation of ZSM-5 molecular sieves in the present invention can solve the directional generation of the stepped pore ZSM-5 molecular sieve pore structure, couple the existing stepped pore ZSM-5 molecular sieve reaction with transfer, and solve the directional matching problem of existing molecular catalytic reaction and transfer. DETAILED DESCRIPTION

[0024] The following is a detailed description of the embodiments of the present invention. The embodiments are implemented based on the technical solution of the present invention, and detailed implementation methods and processes are given. However, the protection scope of the present invention is not limited to the following embodiments. The experimental methods in the following embodiments where specific conditions are not specified are usually based on conventional conditions.

[0025] The present invention discloses a method for preparing a ZSM-5 molecular sieve with stepped pores, comprising the following steps:

[0026] Step 1, mixing an aluminum source precursor, a template agent and a chelating dispersant to obtain an aluminum source precursor solution;

[0027] Step 2, mixing the aluminum source precursor solution and the silicon source precursor solution to obtain a molecular sieve crystallization mother solution;

[0028] Step 3, adding seed crystals to the molecular sieve crystallization mother liquor, aging and crystallizing, to obtain a ZSM-5 molecular sieve with stepped pores;

[0029] Wherein, the chelating dispersant is at least one of sodium ethylenediaminetetramethylenephosphonate, hydroxyethylidene diphosphonic acid, and sodium polymethacrylate (which may be commercially available products).

[0030] The invention achieves the purpose of adjusting the size and ratio of micropores and mesopores of ZSM-5 molecular sieve by adding a chelating dispersant during the preparation process of ZSM-5 molecular sieve and controlling the type and amount of the chelating dispersant, so that the pore size distribution of the obtained ZSM-5 molecular sieve can meet the requirements of different raw materials and finally achieve directional matching.

[0031] In one embodiment, the aluminum source precursor is at least one of aluminum sulfate and aluminum nitrate; the template agent is a macromolecular template agent, such as one or more of PEG-1000 (poly (ethylene glycol)), P123 (polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer), CTAB (hexadecyl trimethyl ammonium bromide), etc. In another embodiment, the aluminum source precursor: template agent: chelating dispersant = 100-500: 20-100: 1-20 (molar ratio).

[0032] In one embodiment, the silicon source precursor solution of the present invention includes a silicon source precursor and an alkaline substance (silicon source precursor: alkaline substance = 15-30: 2-10 (molar ratio)), the silicon source precursor is, for example, tetraethyl orthosilicate, and the alkaline substance is, for example, at least one of n-butylamine, n-propylamine, and sodium hydroxide.

[0033] In one embodiment, the aluminum source precursor solution and the silicon source precursor solution are mixed by dropping the aluminum source precursor solution into the silicon source precursor solution.

[0034] In one embodiment, the seed is a ZSM-5 molecular sieve, and the ZSM-5 molecular sieve seed can be commercially purchased or self-synthesized, and the present invention is not particularly limited thereto. The mass ratio of the amount of ZSM-5 molecular sieve seed added to the sum of the mass of the chelating dispersant is: ZSM-5 molecular sieve seed: (chelating dispersant) = (1-15): 1.

[0035] In one embodiment, step 3 is: adding an appropriate amount of seed crystals to the crystallization mother solution, aging at room temperature for a period of time, and then hydrothermally crystallizing at 120°C-180°C for a certain period of time, and then rapidly cooling, filtering, and roasting to obtain a step-pore ZSM-5 molecular sieve. In another embodiment, the aging time at room temperature is 6-24 hours, and the hydrothermal crystallization time is 1-7 days.

[0036] In summary, in one embodiment, the preparation method of the ZSM-5 molecular sieve with stepped pores of the present invention is to synthesize a microporous molecular sieve using alkaline silica sol, aluminum sulfate, and n-butylamine as raw materials, introduce one or more of macromolecular template agents such as PEG-1000, P123, and CTAB and mesoporous template stabilizing chelating dispersants such as sodium ethylenediaminetetramethylenephosphonate, hydroxyethylidene diphosphonic acid, and sodium polymethacrylate into the crystallization mother liquor, adopt certain hydrothermal crystallization, filter, dry, and calcine at high temperature to obtain a micro-mesoporous composite stepped pore structure with a specific surface area ranging from 100m 2 / g-410m 2 / g, in addition to the micropores of 0.55nm, it also contains mesopores of 2-50nm. The maximum mesopore size distribution can be regulated by the type and dosage of the stable chelating dispersant. Increasing the dosage of the chelating dispersant can shift the maximum mesopore size distribution toward the small pores, and directionally generate the mesopore size distribution, thus achieving the purpose of controllable preparation.

[0037] The technical solution of the present invention will be further described in detail below through specific embodiments.

[0038] The raw materials in each embodiment are all commercially available products, the mass content of SiO2 in the alkaline silica sol is 30%, the seed crystals used in Example 1 are ZSM-5 molecular sieve products produced by the Catalyst Plant of Nankai University (the molar ratio of SiO2 to Al2O3 is 40), and the seed crystals used in the remaining embodiments are all the molecular sieves prepared in Example 1.

[0039] Example 1

[0040] This embodiment provides a step-pore ZSM-5 molecular sieve, which is prepared by the following steps:

[0041] (1) At room temperature, add 90 ml of deionized water and 20 ml of n-butylamine to 50 g of alkaline silica sol and stir continuously for 1 hour to prepare solution A. Dissolve 0.7 g of aluminum sulfate in 50 ml of deionized water, add 2 g of sodium hydroxide, and stir evenly to prepare solution B.

[0042] (2) Add 0.02 g of a mixture of a macromolecular template and a chelating dispersant (CTAB and sodium polymethacrylate in a mass ratio of 20:1) to solution B, continue stirring evenly, and transfer it completely to a constant pressure dropping funnel, slowly and constantly add it to the continuously stirred solution A to obtain colloid C. Add about 0.1 g of molecular sieve as a seed crystal to colloid C, continue stirring at room temperature until it is evenly mixed, and then transfer it to a crystallization kettle and age it at room temperature for 24 hours.

[0043] (3) The aged crystallization kettle was placed in an oven with a preset temperature of 160° C., and autoclaved for 68 hours. After being taken out, it was quickly cooled to room temperature, the material was filtered and separated, and washed with deionized water until neutral. After drying, it was calcined in a muffle furnace at 550° C. for 6 hours to obtain a ZSM-5 molecular sieve with stepped pores.

[0044] Example 2

[0045] (1) At room temperature, add 90 ml of deionized water and 20 ml of n-butylamine to 50 g of alkaline silica sol and stir continuously for 1 hour to prepare solution A. Dissolve 0.7 g of aluminum sulfate in 50 ml of deionized water, add 2 g of sodium hydroxide, and stir evenly to prepare solution B.

[0046] (2) Add 0.05 g of a mixture of a macromolecular template and a chelating dispersant (CTAB and sodium polymethacrylate in a mass ratio of 100:1) to solution B, continue stirring evenly, and transfer it completely to a constant pressure dropping funnel, slowly and constantly add it to the continuously stirred solution A to obtain colloid C. Add about 0.05 g of molecular sieve as a seed crystal to colloid C, continue stirring at room temperature until it is evenly mixed, and then transfer it to a crystallization kettle and age it at room temperature for 12 hours.

[0047] (3) The aged crystallization kettle was placed in an oven with a preset temperature of 150° C., and autoclaved for 72 hours. After being taken out, it was quickly cooled to room temperature, the material was filtered and separated, and washed with deionized water until neutral. After drying, it was calcined in a muffle furnace at 550° C. for 6 hours to obtain a ZSM-5 molecular sieve with stepped pores.

[0048] Example 3

[0049] (1) At room temperature, add 90 ml of deionized water and 20 ml of n-butylamine to 50 g of alkaline silica sol and stir continuously for 1 hour to prepare solution A. Dissolve 0.7 g of aluminum sulfate in 50 ml of deionized water, add 2 g of sodium hydroxide, and stir evenly to prepare solution B.

[0050] (2) Add 0.03 g of a mixture of a macromolecular template and a chelating dispersant (PEG-1000 and sodium ethylenediaminetetramethylenephosphonate in a mass ratio of 100:1) to solution B, continue stirring evenly, and transfer it completely to a constant pressure dropping funnel, slowly and constantly add it to the continuously stirred solution A to obtain colloid C, add about 0.03 g of molecular sieve as a seed crystal to colloid C, continue stirring at room temperature until it is evenly mixed, and then transfer it to a crystallization kettle and age it at room temperature for 24 hours.

[0051] (3) The aged crystallization kettle was placed in an oven with a preset temperature of 140° C., and autoclaved for 96 hours. After being taken out, it was quickly cooled to room temperature, the material was filtered and separated, and washed with deionized water until neutral. After drying, it was calcined in a muffle furnace at 550° C. for 6 hours to obtain a ZSM-5 molecular sieve with stepped pores.

[0052] Example 4

[0053] (1) At room temperature, add 90 ml of deionized water and 20 ml of n-butylamine to 50 g of alkaline silica sol and stir continuously for 1 hour to prepare solution A. Dissolve 0.7 g of aluminum sulfate in 50 ml of deionized water, add 2 g of sodium hydroxide, and stir evenly to prepare solution B.

[0054] (2) Add 0.04 g of a mixture of a macromolecular template and a chelating dispersant (P123 and sodium ethylenediaminetetramethylenephosphonate in a mass ratio of 100:1) to solution B, continue stirring evenly, and transfer it completely to a constant pressure dropping funnel, slowly and constantly add it to the continuously stirred solution A to obtain colloid C. Add about 0.10 g of molecular sieve as a seed crystal to colloid C, continue stirring at room temperature until it is evenly mixed, and then transfer it to a crystallization kettle and age it at room temperature for 6 hours.

[0055] (3) The aged crystallization kettle was placed in an oven with a preset temperature of 170° C., and autoclaved for 48 hours. After being taken out, it was quickly cooled to room temperature, the material was filtered and separated, and washed with deionized water until neutral. After drying, it was calcined in a muffle furnace at 550° C. for 6 hours to obtain a ZSM-5 molecular sieve with stepped pores.

[0056] Example 5

[0057] (1) At room temperature, add 90 ml of deionized water and 20 ml of n-butylamine to 50 g of alkaline silica sol and stir continuously for 1 hour to prepare solution A. Dissolve 0.7 g of aluminum sulfate in 50 ml of deionized water, add 2 g of sodium hydroxide, and stir evenly to prepare solution B.

[0058] (2) Add 0.10 g of a mixture of a macromolecular template and a chelating dispersant (CTAB and sodium polymethacrylate in a mass ratio of 100:1) to solution B, continue stirring evenly, and transfer it completely to a constant pressure dropping funnel, slowly and constantly add it to the continuously stirred solution A to obtain colloid C. Add about 0.50 g of molecular sieve as a seed crystal to colloid C, continue stirring at room temperature until it is evenly mixed, and then transfer it to a crystallization kettle and age it at room temperature for 12 hours.

[0059] (3) The aged crystallization kettle was placed in an oven with a preset temperature of 180° C., and autoclaved for 24 hours. After being taken out, it was quickly cooled to room temperature, the material was filtered and separated, and washed with deionized water until neutral. After drying, it was calcined in a muffle furnace at 550° C. for 6 hours to obtain a ZSM-5 molecular sieve with stepped pores.

[0060] Example 6

[0061] (1) At room temperature, add 90 ml of deionized water and 20 ml of n-butylamine to 50 g of alkaline silica sol and stir continuously for 1 hour to prepare solution A. Dissolve 0.7 g of aluminum sulfate in 50 ml of deionized water, add 2 g of sodium hydroxide, and stir evenly to prepare solution B.

[0062] (2) Add 0.15 g of a mixture of a macromolecular template and a chelating dispersant (CTAB and sodium polymethacrylate in a mass ratio of 100:1) to solution B, continue stirring evenly, and transfer it completely to a constant pressure dropping funnel, slowly and constantly add it to the continuously stirred solution A to obtain colloid C. Add about 1.5 g of molecular sieve as a seed crystal to colloid C, continue stirring at room temperature until it is evenly mixed, and then transfer it to a crystallization kettle and age it at room temperature for 24 hours.

[0063] (3) The aged crystallization kettle was placed in an oven with a preset temperature of 140° C., and autoclaved for 168 hours. After being taken out, it was quickly cooled to room temperature, the material was filtered and separated, and washed with deionized water until neutral. After drying, it was calcined in a muffle furnace at 550° C. for 6 hours to obtain a ZSM-5 molecular sieve with stepped pores.

[0064] Example 7

[0065] (1) At room temperature, add 90 ml of deionized water and 20 ml of n-butylamine to 50 g of alkaline silica sol and stir continuously for 1 hour to prepare solution A. Dissolve 0.7 g of aluminum sulfate in 50 ml of deionized water, add 2 g of sodium hydroxide, and stir evenly to prepare solution B.

[0066] (2) Add 0.05 g of a mixture of a macromolecular template and a chelating dispersant (PEG-1000 and sodium ethylenediaminetetramethylenephosphonate in a mass ratio of 100:1) to solution B, continue stirring evenly, and transfer it completely to a constant pressure dropping funnel, slowly and constantly add it to the continuously stirred solution A to obtain colloid C, add about 0.75 g of molecular sieve as a seed crystal to colloid C, continue stirring at room temperature until it is evenly mixed, and then transfer it to a crystallization kettle and age it at room temperature for 6 hours.

[0067] (3) The aged crystallization kettle was placed in an oven with a preset temperature of 150° C., and autoclaved for 144 hours. After being taken out, it was quickly cooled to room temperature, the material was filtered and separated, and washed with deionized water until neutral. After drying, it was calcined in a muffle furnace at 550° C. for 6 hours to obtain a ZSM-5 molecular sieve with stepped pores.

[0068] Example 8

[0069] (1) At room temperature, add 90 ml of deionized water and 20 ml of n-butylamine to 50 g of alkaline silica sol and stir continuously for 1 hour to prepare solution A. Dissolve 0.7 g of aluminum sulfate in 50 ml of deionized water, add 2 g of sodium hydroxide, and stir evenly to prepare solution B.

[0070] (2) Add 0.07 g of a mixture of a macromolecular template and a chelating dispersant (PEG-1000 and sodium ethylenediaminetetramethylenephosphonate in a mass ratio of 100:1) to solution B, continue stirring evenly, and transfer it completely to a constant pressure dropping funnel, slowly and constantly add it to the continuously stirred solution A to obtain colloid C, add about 0.56 g of molecular sieve as a seed crystal to colloid C, continue stirring at room temperature until it is evenly mixed, and then transfer it to a crystallization kettle and age it at room temperature for 12 hours.

[0071] (3) The aged crystallization kettle was placed in an oven with a preset temperature of 150° C., and autoclaved for 120 hours. After being taken out, it was quickly cooled to room temperature, the material was filtered and separated, and washed with deionized water until neutral. After drying, it was calcined in a muffle furnace at 550° C. for 6 hours to obtain a ZSM-5 molecular sieve with stepped pores.

[0072] Example 9

[0073] (1) At room temperature, add 90 ml of deionized water and 20 ml of n-butylamine to 50 g of alkaline silica sol and stir continuously for 1 hour to prepare solution A. Dissolve 0.7 g of aluminum sulfate in 50 ml of deionized water, add 2 g of sodium hydroxide, and stir evenly to prepare solution B.

[0074] (2) Add 0.06 g of a mixture of a macromolecular template and a chelating dispersant (P123 and sodium ethylenediaminetetramethylenephosphonate in a mass ratio of 100:1) to solution B, continue stirring evenly, and transfer it completely to a constant pressure dropping funnel, slowly and constantly add it to the continuously stirred solution A to obtain colloid C, add about 0.6 g of molecular sieve as a seed crystal to colloid C, continue stirring at room temperature until it is evenly mixed, and then transfer it to a crystallization kettle and age it at room temperature for 18 hours.

[0075] (3) The aged crystallization kettle was placed in an oven with a preset temperature of 160° C., and autoclaved for 96 hours. After being taken out, it was quickly cooled to room temperature, the material was filtered and separated, and washed with deionized water until neutral. After drying, it was calcined in a muffle furnace at 550° C. for 6 hours to obtain a ZSM-5 molecular sieve with stepped pores.

[0076] Example 10

[0077] (1) At room temperature, add 90 ml of deionized water and 20 ml of n-butylamine to 50 g of alkaline silica sol and stir continuously for 1 hour to prepare solution A. Dissolve 0.7 g of aluminum sulfate in 50 ml of deionized water, add 2 g of sodium hydroxide, and stir evenly to prepare solution B.

[0078] (2) Add 0.12 g of a mixture of a macromolecular template and a chelating dispersant (P123 and sodium ethylenediaminetetramethylenephosphonate in a mass ratio of 100:1) to solution B, continue stirring evenly, and transfer it completely to a constant pressure dropping funnel, slowly and constantly add it to the continuously stirred solution A to obtain colloid C. Add about 0.6 g of molecular sieve as a seed crystal to colloid C, continue stirring at room temperature until it is evenly mixed, and then transfer it to a crystallization kettle and age it at room temperature for 6 hours.

[0079] (3) The aged crystallization kettle was placed in an oven with a preset temperature of 180° C., and autoclaved for 72 hours. After being taken out, it was quickly cooled to room temperature, the material was filtered and separated, and washed with deionized water until neutral. After drying, it was calcined in a muffle furnace at 550° C. for 6 hours to obtain a ZSM-5 molecular sieve with stepped pores.

[0080] Table 1. Specific surface area, pore volume and pore size analysis of molecular sieves in the examples

[0081] <![CDATA[Specific surface area (m 2 / g)]]> <![CDATA[Pore volume (cm 3 / g)]]> Pore ​​size (nm) Example 1 100 0.18 3.53 Example 2 348 0.26 21.75 Example 3 150 0.21 3.46 Example 4 198 0.22 38.23 Example 5 345 0.32 19.89 Example 6 410 0.39 30.39 Example 7 255 0.29 40.84 Example 8 306 0.24 11.58 Example 9 287 0.35 15.67 Example 10 398 0.37 25.13

[0082] As shown in Table 1, the specific surface area, pore volume and pore size of the molecular sieves in the embodiment are quite different, which is mainly caused by the different types and amounts of the macromolecular templates and chelating dispersants used in the preparation of the molecular sieves. In other words, the gradient classification of the obtained molecular sieves can be adjusted by adjusting the types and amounts of the macromolecular templates and chelating dispersants prepared by the molecular sieves, and it is found that CTAB and sodium polymethacrylate have the best adjustment effect, and the molecular sieve has the largest pore size and pore volume, but PEG-1000 and sodium ethylenediaminetetramethylenephosphonate, P123 and sodium ethylenediaminetetramethylenephosphonate also have a good adjustment effect within a certain ratio range. Therefore, the macromolecular templates and chelating dispersants used in the embodiment have the effect of adjusting the gradient of the molecular sieves, and the key is to control the ratio of the templates and dispersants used to the raw materials for preparation.

[0083] Of course, the present invention may have many other embodiments. Without departing from the spirit and essence of the present invention, technicians familiar with the field may make various corresponding changes and deformations based on the present invention, but these corresponding changes and deformations should all fall within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a ZSM-5 molecular sieve having stepped pores, characterized in that: The steps include: Step 1, mixing an aluminum source precursor, a template and a chelating dispersant to obtain an aluminum source precursor solution; Step 2, mixing the aluminum source precursor solution and the silicon source precursor solution to obtain a molecular sieve crystallization mother solution; Step 3, adding seed crystals to the molecular sieve crystallization mother liquor, aging and crystallizing, to obtain a ZSM-5 molecular sieve with stepped pores; Among them, the chelating dispersant is at least one of sodium ethylenediaminetetramethylenephosphonate, hydroxyethylidene diphosphonic acid, and sodium polymethacrylate; the template agent is at least one of poly(ethylene glycol), polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer, and hexadecyltrimethylammonium bromide.

2. The method for preparing a ZSM-5 molecular sieve having stepped pores according to claim 1, characterized in that: The silicon source precursor solution comprises a silicon source precursor and an alkaline substance, wherein the silicon source precursor is tetraethyl orthosilicate, and the alkaline substance is at least one of n-butylamine, n-propylamine and sodium hydroxide; the molar ratio of the silicon source precursor to the alkaline substance is 15-30:2-10.

3. The method for preparing a ZSM-5 molecular sieve having stepped pores according to claim 1, characterized in that: The aluminum source precursor is at least one of aluminum sulfate and aluminum nitrate; the molar ratio of the aluminum source precursor, the template and the chelating dispersant is 100-500:20-100:1-20.

4. The method for preparing a ZSM-5 molecular sieve having stepped pores according to claim 1, characterized in that: The molar ratio of the aluminum source precursor to the silicon source precursor is 10-300.

5. The method for preparing a ZSM-5 molecular sieve having stepped pores according to claim 1, characterized in that: The seed crystal is ZSM-5 molecular sieve, the aging temperature is room temperature, and the aging time is 6-24 hours.

6. The method for preparing a ZSM-5 molecular sieve having stepped pores according to claim 1, characterized in that: The crystallization temperature is 120-180° C., and the crystallization time is 1-7 days.

7. The method for preparing a ZSM-5 molecular sieve having stepped pores according to claim 1, characterized in that: The aluminum source precursor solution and the silicon source precursor solution are mixed by: dropping the aluminum source precursor solution into the silicon source precursor solution; The crystallization is autogenous hydrothermal crystallization.

8. The ZSM-5 molecular sieve with stepped pores obtained by the preparation method according to any one of claims 1 to 7, characterized in that: The ZSM-5 molecular sieve with stepped pores includes a micropore diameter and a mesopore diameter, and the mesopore diameter is 2-50 nm.

9. The ZSM-5 molecular sieve with stepped pores according to claim 8, characterized in that: The specific surface area of ​​the ZSM-5 molecular sieve with stepped pores is 100 m 2 / g-350m 2 / g.