A preparation method of multi-level pore HZSM-5 molecular sieve

Abstract

The present invention relates to a preparation method of a multi-level pore HZSM-5 molecular sieve, which is characterized by comprising the following steps: (1) mixing a boron source, a silicon source, an aluminum source and a template to obtain a uniform gel, and pouring the gel into an open polytetrafluoroethylene liner, wherein the molar ratio of the gel is: B2O3:Al2O3:SiO2:template=0.5-10:1:20-150:1-8; (2) vertically placing the open polytetrafluoroethylene liner containing the gel in step (1) into a polytetrafluoroethylene liner containing an amine solution, wherein the height of the liner containing the gel is lower than the height of the amine solution, and the mass ratio of the liquid to the gel is amine solution:gel=0-2:1, and the liner is placed in a reactor for static crystallization, washing, and drying; and (3) placing the sample obtained in step (2) into a hydrothermal steam device for high-temperature treatment, wherein the condition is 100% water vapor at 600-800°C for 1-6h to obtain the multi-level pore HZSM-5 molecular sieve.

Description

Technical Field

[0001] The invention belongs to the technical field of molecular sieve preparation, and particularly relates to a method for preparing a multi-level pore HZSM-5 molecular sieve. Background Art

[0002] ZSM-5 zeolite, a type of silicate molecular sieve with an MFI pore structure, has been widely used in various fields, including petrochemicals, coal chemical industry, and fine chemicals. In particular, its unique pore structure enables it to selectively catalyze the alkylation, isomerization, and aromatization reactions of gasoline components, thereby reducing the olefin content of gasoline components while increasing the gasoline octane number and improving gasoline quality. However, the small size of the ten-membered ring pores in ZSM-5 zeolite restricts the diffusion and mass transfer of large oil and gas molecules within the pores, hindering their reactions and thus significantly limiting its application. Therefore, the preparation of HZSM-5 zeolites with a meso-micro hierarchical pore structure and a larger pore structure has become a current research hotspot.

[0003] CN111689505A discloses a method for preparing a meso-micro multi-level pore structure ZSM-5 molecular sieve. The method comprises modifying the ZSM-5 molecular sieve with a boron compound, ion-exchanging it, and then subjecting it to steam heat treatment to obtain a multi-level pore ZSM-5 molecular sieve. The synthesized molecular sieve has a high crystallinity and mesoporous specific surface area, providing a new synthesis strategy for the synthesis of multi-level pore ZSM-5 molecular sieves. The disadvantages of this technology or the shortcomings of the present invention are that the molecular sieves in this method require separate synthesis, ion exchange, and steam treatment, resulting in a relatively complex synthesis process.

[0004] Shen et al. (Journal of Catalysis. 2017, 347, 116–126) reported a method for synthesizing a hierarchical Y-type zeolite. Sodium metaborate was added to the NaY synthesis system, followed by ion exchange and steam treatment to produce the hierarchical Y-type zeolite. In heavy oil catalytic cracking tests, the synthesized BY-type zeolite increased gasoline yield by 2.1% compared to USY zeolite.

[0005] Xiao et al. (Science. 2021, 372, 76–80) reported a solvent-free method for synthesizing B-MFI molecular sieves. The B-MFI molecular sieve catalyst was obtained by solvent-free crystallization and calcination. This method significantly reduced the amount of water required for the catalyst and the synthesis cost, shortened the crystallization time, and the synthesized catalyst exhibited high selectivity in the oxidative dehydrogenation of shale gas propane.

[0006] In summary, while some progress has been made in the preparation of meso-micro hierarchical ZSM-5 zeolite molecular sieves, several technical limitations remain. These typically require ion exchange and steam treatment, resulting in complex synthesis steps. Therefore, developing a simple, low-cost, and environmentally friendly process for preparing meso-micro hierarchical ZSM-5 zeolite molecular sieves has become a highly challenging research endeavor. Summary of the Invention

[0007] In view of the defects of the above-mentioned technologies, the purpose of the present invention is to propose a method for preparing multi-level pore HZSM-5 molecular sieve, which can efficiently synthesize multi-level pore HZSM-5 molecular sieve in the absence of solvent and ion exchange, shortens the synthesis time, reduces the synthesis cost of multi-level pore HZSM-5 molecular sieve and is environmentally friendly.

[0008] The method for preparing a multi-level pore HZSM-5 molecular sieve adopted in the present invention comprises the following steps:

[0009] (1) mixing and grinding a boron source, a silicon source, an aluminum source, and a template to obtain a uniform gel, and pouring the gel into an open polytetrafluoroethylene liner, wherein the molar ratio of the gel is: B2O3:Al2O3:SiO2:template = 0.5-10:1:20-150:1-8;

[0010] (2) vertically placing the open polytetrafluoroethylene liner containing the gel in step (1) into the polytetrafluoroethylene liner containing the amine solution, wherein the height of the liner containing the gel is lower than the height of the amine solution, and the mass ratio of the liquid to the gel is amine solution: gel = 0-2:1, and the liner is placed in a reactor for static crystallization, washing, and drying;

[0011] (3) The sample obtained in step (2) is placed in a hydrothermal steam device for high-temperature treatment, with the condition being 100% water vapor at 600-800° C. for 1-6 hours to obtain a multi-level pore HZSM-5 molecular sieve.

[0012] The present invention provides a new synthesis method of multi-level pore HZSM-5 molecular sieve, realizes the synthesis method of anhydrous solvent in an ammonia solution atmosphere, greatly shortens the crystallization time, and reduces the synthesis cost of the molecular sieve.

[0013] In the preparation method of the present invention, in step (1), seed crystals are further added, and the amount of the seed crystals added is 0%-10% of the mass of SiO2 in the gel.

[0014] The addition of an appropriate amount of seed crystals can accelerate and promote the growth of crystals and shorten the synthesis time.

[0015] In the preparation method of the present invention, in step (1), the grinding time is 2-8 hours.

[0016] Appropriate grinding time can make the raw materials mixed more evenly, and the minimum time to ensure sufficient mixing of the raw materials is 2 hours.

[0017] In the preparation method of the present invention, in step (1), the aluminum source is selected from at least one of aluminum sulfate, aluminum chloride, aluminum nitrate and aluminum isopropoxide, the silicon source is selected from at least one of tetraethyl orthosilicate, white carbon black and silica sol, and the boron source is at least one of boric acid, boron trichloride and ammonium pentaborate.

[0018] In the preparation method of the present invention, in step (2), the amine solution is selected from at least one of an aqueous ammonia solution, an ethylenediamine solution, and an n-butylamine solution.

[0019] The use of the above solution can provide an ammonia atmosphere for the formation of molecular sieves during the crystallization process.

[0020] In the preparation method of the present invention, in step (2), the crystallization temperature is 150-250° C., and the crystallization time is 0.5-5 h.

[0021] In the preparation method of the present invention, in step (3), the water vapor high-temperature treatment condition is a temperature of 650-800° C. and a time of 1-2.5 hours.

[0022] After a high-temperature hydrothermal treatment process, the aluminum of the ZSM-5 zeolite molecular sieve framework is released, thereby retaining a high crystallinity of the ZSM-5 molecular sieve while also generating a secondary mesoporous structure, thereby increasing the specific surface area and pore volume of the ZSM-5 molecular sieve.

[0023] The preparation method of the present invention, the seed crystal in step (1) is a mesoporous ZSM-5 molecular sieve, the main body of which is a ZSM-5 type molecular sieve, and has mesopores, and its total specific surface area is 280m 2 / g-450m 2 / g, of which the specific surface area of ​​the mesopores is 40-120m 2 / g, and the crystallinity is greater than 80%.

[0024] During the synthesis process, the addition of seed crystals increases the number of molecular sieve growth points, improves the relative concentration of the system, and accelerates the heat transfer rate, thereby improving the synthesis efficiency.

[0025] Beneficial effects of the present invention:

[0026] Compared with the existing technology, the technology provided by the present invention has the following advantages: (1) Boron element is used for modification, and there is no acid or alkali extraction process in the process, which not only reduces the damage to the molecular sieve structure, but also does not produce acid or alkali waste liquid, reducing damage to the environment; (2) A synthesis method of anhydrous solvent in an ammonia solution atmosphere is realized, which greatly shortens the crystallization time and reduces the synthesis cost of the molecular sieve. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is the X-ray diffraction spectrum of the hierarchical pore HZSM-5 molecular sieve obtained in Example 1 of the present invention.

[0028] Figure 2 This is a graph showing the N2 adsorption and desorption curves of the hierarchical pore HZSM-5 molecular sieve obtained in Example 1 of the present invention. DETAILED DESCRIPTION

[0029] The following is a detailed description of the embodiments of the present invention: This embodiment is implemented based on the technical solution of the present invention, and provides detailed implementation methods and processes. 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 generally based on conventional conditions.

[0030] The test methods described in the following examples, unless otherwise specified, are conventional methods; the reagents and compounds described, unless otherwise specified, can be obtained from commercial sources.

[0031] Source of raw materials: Aluminum sulfate and other raw materials are from China Petroleum Lanzhou Petrochemical Company, all of which are industrial products; the template agent is purchased from Anhui Jinao Chemical Co., Ltd., an industrial product; ethyl orthosilicate, white carbon black, and amine solutions are all commercially available reagents, industrial grade.

[0032] Analytical methods:

[0033] A Shimadzu XRD-7000 X-ray crystal powder diffractometer was used with the following instrument parameters: Cu-Ka ray, wavelength of 0.1543 nm, tube voltage of 40 kV, tube current of 30 mA; and sample test conditions: scanning angle of 5°-40°, scanning speed of 6° / min.

[0034] The adsorption-desorption isotherms of the samples were measured at liquid nitrogen temperature using an ASAP2020M fully automatic adsorption instrument produced by Micromeritics, USA. Nitrogen was used as the adsorbate, and the Brunauer-Emmett-Teller (BET) equation was used to calculate the specific surface area of ​​the samples based on the adsorption equilibrium isotherm between relative pressures of 0.05 and 0.25. The t-plot model was used to distinguish the internal and external surface areas of the samples, and the static capacity method was used to determine the pore volume and pore size distribution, thereby calculating the pore structure parameters.

[0035] Comparative Example 1:

[0036] The difference from Example 1 is that, in Comparative Example 1, deionized water is used as the solvent and ion exchange is performed.

[0037] 5.2g of tetraethyl orthosilicate, 0.17g of aluminum sulfate, 0.04g of boric acid, 0.2g of sodium hydroxide, and 0.2g of tetrapropylammonium hydroxide were placed in 22.5mL of deionized water, and 0.15g of ZSM-5 seed crystals were added. The mixture was stirred for 4 hours, and the resulting gel was placed in a crystallization kettle and hydrothermally crystallized at 170°C for 24 hours. The crystallized product was washed until neutral, dried at 100°C for 10-12 hours, and calcined at 550°C for 6 hours. The resulting product was ion-exchanged with ammonium chloride solution at pH 3-4, washed, dried, and calcined. The resulting product was placed in a hydrothermal steam apparatus and treated with 100% steam at 650°C for 2 hours. Finally, it was dried to obtain the hierarchical HZSM-5 molecular sieve CHZ-1.

[0038] Comparative Example 2

[0039] The difference from Example 2 is that, in Comparative Example 2, deionized water is used as the solvent and ion exchange is performed.

[0040] 9g of silica, 2.13g of aluminum nitrate, 0.89g of boron trichloride, 0.9g of sodium hydroxide, and 2g of tetrapropylammonium bromide were placed in 54mL of deionized water, 0.2g of ZSM-5 seed crystals were added, and the mixture was stirred for 6 hours. The resulting gel was placed in a crystallization kettle and hydrothermally crystallized at 190°C for 24 hours. The crystallized product was washed until neutral, dried at 100°C for 10-12 hours, and calcined at 550°C for 6 hours. The resulting product was ion-exchanged with ammonium chloride solution at a pH of 3-4, washed, dried, and calcined. The resulting product was placed in a hydrothermal steam apparatus and treated with 100% steam at 750°C for 0.5 hours. Finally, it was dried to obtain the hierarchical HZSM-5 molecular sieve CHZ-2.

[0041] Comparative Example 3

[0042] The difference from Example 3 is that, in Comparative Example 3, deionized water is used as the solvent and ion exchange is performed.

[0043] 15.6g of tetraethyl orthosilicate, 0.2g of aluminum isopropoxide, 1.5g of ammonium pentaborate, 0.48g of sodium hydroxide, and 1g of tetrapropylammonium bromide were placed in 22.5mL of deionized water, and 0.05g of ZSM-5 seed crystals were added. The mixture was stirred for 8 hours, and the resulting gel was hydrothermally crystallized at 160°C in a crystallization kettle for 48 hours. The crystallized product was washed until neutral, dried at 100°C for 10-12 hours, and calcined at 550°C for 6 hours. The resulting product was ion-exchanged with ammonium chloride solution at a pH of 3-4, washed, dried, and calcined. The resulting product was then placed in a hydrothermal steam apparatus and treated with 100% water vapor at 650°C for 3 hours. Finally, it was dried to obtain the hierarchical HZSM-5 molecular sieve CHZ-3.

[0044] Example 1

[0045] (1) Place 5.2 g of tetraethyl orthosilicate, 0.17 g of aluminum sulfate, 0.04 g of boric acid, and 0.2 g of tetrapropylammonium hydroxide in a mortar, add 0.15 g of ZSM-5 seed crystals, and grind for 8 h. Place the ground boron-modified silica-alumina gel in a 25 mL open polytetrafluoroethylene liner;

[0046] (2) Place the open liner into a 100 mL polytetrafluoroethylene liner containing 10 mL ammonia solution, transfer it to a reactor, and statically crystallize it at 250°C for 0.5 h. The crystallized product is washed to neutrality and dried at 100°C for 10-12 h.

[0047] (3) The sample obtained in step (2) was placed in a hydrothermal steam device and treated with 100% steam at 650° C. for 2 h, and finally dried to obtain a multi-level pore HZSM-5 molecular sieve BHZ-1.

[0048] Example 2

[0049] (1) 7.5 g of silica, 11.3 g of aluminum nitrate, 0.39 g of boric acid, and 1.04 g of tetrapropylammonium hydroxide were placed in a mortar and ground for 2 h. The ground boron-modified silica-alumina gel was placed in a 25 mL open polytetrafluoroethylene liner.

[0050] (2) Place the open liner into a 100 mL polytetrafluoroethylene liner containing 10 mL ethylenediamine solution, transfer to a reactor, and statically crystallize at 150°C for 5 h. The crystallized product is washed to neutrality and dried at 100°C for 10-12 h.

[0051] (3) The sample obtained in step (2) was placed in a hydrothermal steam device and treated with 100% steam at 800° C. for 1 h, and finally dried to obtain a multi-level pore HZSM-5 molecular sieve BHZ-2.

[0052] Example 3

[0053] (1) 8.8 g of tetraethyl orthosilicate, 0.36 g of aluminum isopropoxide, 0.22 g of ammonium pentaborate, and 0.34 g of tetrapropylammonium hydroxide were placed in a mortar and ground for 4 h. The ground boron-modified silica-alumina gel was placed in a 25 mL open polytetrafluoroethylene liner.

[0054] (2) Place the open liner into a 100 mL polytetrafluoroethylene liner containing 10 mL ammonia solution, transfer it to a reactor, and statically crystallize it at 250°C for 0.5 h. The crystallized product is washed to neutrality and dried at 100°C for 10-12 h.

[0055] (3) The sample obtained in step (2) was placed in a hydrothermal steam device and treated with 100% steam at 700° C. for 2 h, and finally dried to obtain a multi-level pore HZSM-5 molecular sieve BHZ-3.

[0056] Example 4

[0057] (1) Place 10.4 g of tetraethyl orthosilicate, 0.26 g of aluminum chloride, 0.6 g of boron trichloride, and 0.4 g of tetrapropylammonium hydroxide in a mortar and grind for 4 h. Place the ground boron-modified silica-alumina gel in a 25 mL open polytetrafluoroethylene liner.

[0058] (2) Place the open liner into a 100 mL polytetrafluoroethylene liner containing 10 mL ammonia solution, transfer it to a reactor, and statically crystallize it at 200°C for 2 h. The crystallized product is washed to neutrality and dried at 100°C for 10-12 h.

[0059] (3) The sample obtained in step (2) was placed in a hydrothermal steam device, treated with 100% steam at 800° C. for 1 h, and finally dried to obtain a multi-level pore HZSM-5 molecular sieve BHZ-4.

[0060] Example 5

[0061] (1) Place 6.76 g of tetraethyl orthosilicate, 0.13 g of aluminum isopropoxide, 0.06 g of boric acid, and 0.2 g of tetrapropylammonium hydroxide in a ball mill, add 0.2 g of ZSM-5 seed crystals, and grind for 2 h. Place the ground boron-modified silica-alumina gel in a 25 mL open polytetrafluoroethylene liner;

[0062] (2) Place the open liner into a 100 mL polytetrafluoroethylene liner containing 15 mL ammonia solution, transfer it to a reactor, and statically crystallize it at 190°C for 3 h. The crystallized product is washed to neutrality and dried at 100°C for 10-12 h.

[0063] (3) The sample obtained in step (2) was placed in a hydrothermal steam device and treated with 100% steam at 650° C. for 2 h, and finally dried to obtain a multi-level pore HZSM-5 molecular sieve BHZ-5.

[0064] Example 6

[0065] (1) 8 g of white carbon black, 1.23 g of aluminum nitrate, 0.46 g of boric acid, and 0.96 g of tetrapropylammonium hydroxide were placed in a mortar and ground for 2 h. The ground boron-modified silica-alumina gel was placed in a 25 mL open polytetrafluoroethylene liner.

[0066] (2) Place the open liner into a 100 mL polytetrafluoroethylene liner containing 10 mL ethylenediamine solution, transfer to a reactor, and statically crystallize at 200°C for 2 h. The crystallized product is washed to neutrality and dried at 100°C for 10-12 h.

[0067] (3) The sample obtained in step (2) was placed in a hydrothermal steam device and treated with 100% steam at 700° C. for 1 h, and finally dried to obtain a multi-level pore HZSM-5 molecular sieve BHZ-6.

[0068] Example 7

[0069] (1) Place 11 g of tetraethyl orthosilicate, 0.10 g of aluminum chloride, 0.35 g of boric acid, and 0.6 g of tetrapropylammonium hydroxide in a mortar and grind for 4 h. Add 0.2 g of ZSM-5 seed crystals. Place the ground boron-modified silica-alumina gel in a 25 mL open polytetrafluoroethylene liner.

[0070] (2) Place the open liner into a 100 mL polytetrafluoroethylene liner containing 10 mL ammonia solution, transfer it to a reactor, and statically crystallize it at 200°C for 3 h. The crystallized product is washed to neutrality and dried at 100°C for 10-12 h;

[0071] (3) The sample obtained in step (2) was placed in a hydrothermal steam device and treated with 100% steam at 700° C. for 2.5 h, and finally dried to obtain a multi-level pore HZSM-5 molecular sieve BHZ-7.

[0072] Example 8

[0073] (1) Place 10.4 g of tetraethyl orthosilicate, 0.26 g of aluminum chloride, 0.6 g of boron trichloride, and 0.4 g of tetrapropylammonium hydroxide in a mortar and grind for 4 h. Place the ground boron-modified silica-alumina gel in a 25 mL open polytetrafluoroethylene liner.

[0074] (2) Place the open liner into a 100 mL polytetrafluoroethylene liner containing 10 mL ammonia solution, transfer it to a reactor, and statically crystallize it at 200°C for 2 h. The crystallized product is washed to neutrality and dried at 100°C for 10-12 h.

[0075] (3) The sample obtained in step (2) was placed in a hydrothermal steam device and treated with 100% steam at 600° C. for 6 h, and finally dried to obtain a multi-level pore HZSM-5 molecular sieve BHZ-8.

[0076] Table 1 lists the structures and physicochemical parameters of the molecular sieves synthesized in Examples 1-7 and Comparative Examples 1-3.

[0077] Table 1

[0078] sample <![CDATA[S total / m 2 ·g -1 ]]> <![CDATA[S mic / m 2 ·g -1 ]]> <![CDATA[S mes / m 2 ·g -1 ]]> <![CDATA[V mes / cm 3 ·g -1 ]]> Relative crystallinity Comparative Example 1 328.4 211.7 116.7 0.10 84.2％ Comparative Example 2 303.7 210.1 93.6 0.09 78.7％ Comparative Example 3 335.4 208.7 126.7 0.11 87.6％ Example 1 363.1 233.8 129.3 0.11 94.6％ Example 2 320.2 226.0 94.2 0.08 83.5％ Example 3 383.5 245.2 138.3 0.13 98.6％ Example 4 320.4 217.2 103.2 0.10 84.6％ Example 5 376.9 240.6 136.3 0.13 95.1％ Example 6 305.4 206.9 98.5 0.09 78.2％ Example 7 355.6 218.7 136.9 0.12 91.9％ Example 8 330.5 216.7 113.8 0.13 84.1％

[0079] Table 1 lists the physical parameters of the molecular sieves synthesized in Examples 1-8 and Comparative Examples 1-3, which are: total pore area S total , micropore area S mic , mesopore specific surface area S mes 、Mesopore volume V mes By comparing the physical parameters of Examples 1-3 and Comparative Examples 1-3, it can be seen that the pore area S of Comparative Examples 1-3 is less than 100 nm without the use of an anhydrous system and an amine solution atmosphere. total , micropore area S mic , mesopore specific surface area S mes The crystallinity is obviously lower. Taking Comparative Example 1 and Example 1 as examples, the above parameters of Comparative Example 1 are 328.4 (m 2 / g)、211.7(m 2 / g)、116.7(m 2 / g), 84%, the pore area S of Example 1 total , micropore area S mic , mesopore specific surface area S mes and crystallinity were improved, which were 363.1(m 2 / g)、233.8(m 2 / g)、129.3(m 2 / g), 94.6%, from Figure 1 It can be seen from the XRD pattern that there are sharp diffraction peaks. These characteristic diffraction peaks indicate that the crystals obtained by the determination can achieve the growth of molecular sieves under the guidance of organic templates to obtain ordered mesoporous and Figure 2 The results of N2 adsorption and desorption curves of multi-level pore HZS M-5 molecular sieve are consistent with those of

[0080] In summary, the present invention provides a method for synthesizing a hierarchically porous HZSM-5 molecular sieve. This method involves crystallizing a boron-doped silica-alumina gel in an amine solution vapor and then treating it with high-temperature steam to obtain the resulting product. This method significantly shortens the crystallization time and eliminates the need for the addition of solvents such as water and mesoporous templates. The resulting HZSM-5 molecular sieve exhibits a large mesoporous specific surface area, is simple to synthesize, requires a short crystallization time, and is environmentally friendly.

[0081] Of course, the present invention may have many other embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art may make various corresponding changes and modifications based on the present invention, but these corresponding changes and modifications should all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a multi-level pore HZSM-5 molecular sieve, characterized in that: The following steps are involved: (1) Mix and grind the boron source, silicon source, aluminum source and template to obtain a uniform gel, and pour the gel into an open polytetrafluoroethylene liner. The molar ratio of the gel is: B2O3:Al2O3:SiO2:template = 0.5-10:1:20-150:1-8; (2) vertically placing the open polytetrafluoroethylene liner containing the gel in step (1) into the polytetrafluoroethylene liner containing the amine solution, with the height of the liner containing the gel being lower than the height of the amine solution, and the mass ratio of the liquid to the gel being amine solution: gel = 0-2:1, and placing the liner into a reactor for static crystallization, washing, and drying; (3) The sample obtained in step (2) is placed in a hydrothermal steam device for high-temperature treatment under the condition of 100% steam at 600-800°C for 1-6 h to obtain a multi-level pore HZSM-5 molecular sieve.

2. The method for preparing a multi-level pore HZSM-5 molecular sieve according to claim 1, characterized in that: In step (1), seed crystals are also added, and the amount of the seed crystals added is 0%-10% of the mass of SiO2 in the gel.

3. The method for preparing the multi-level pore HZSM-5 molecular sieve according to claim 1, characterized in that: In step (1), the grinding time is 2-8 hours.

4. The method for preparing a multi-level pore HZSM-5 molecular sieve according to claim 1, characterized in that: In step (1), the aluminum source is selected from at least one of aluminum sulfate, aluminum chloride, aluminum nitrate and aluminum isopropoxide.

5. The method for preparing the multi-level pore HZSM-5 molecular sieve according to claim 1, characterized in that: In step (1), the silicon source is selected from at least one of ethyl orthosilicate, white carbon black, and silica sol, and the boron source is at least one of boric acid, boron trichloride, and ammonium pentaborate.

6. The method for preparing the multi-level pore HZSM-5 molecular sieve according to claim 1, characterized in that: In step (2), the amine solution is selected from at least one of an aqueous ammonia solution, an ethylenediamine solution, and an n-butylamine solution.

7. The method for preparing a multi-level pore HZSM-5 molecular sieve according to claim 1, characterized in that: In step (2), the crystallization temperature is 150-250° C., and the crystallization time is 0.5-5 h.

8. The method for preparing a multi-level pore HZSM-5 molecular sieve according to claim 1, characterized in that: In step (3), the high temperature treatment temperature is 650-800°C and the time is 1-2.5h.

9. The method for preparing a multi-level pore HZSM-5 molecular sieve according to claim 2, characterized in that: In step (1), the seed crystal is a mesoporous ZSM-5 molecular sieve, the main body of which is a ZSM-5 type molecular sieve and has mesopores, and the total specific surface area is 280 m 2 / g -450 m 2 / g, of which the specific surface area of ​​mesopores is 40-120 m 2 / g, crystallinity greater than 80%.

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