High-crystallinity hierarchical pore zsm-5 molecular sieve and preparation method thereof

Abstract

This invention discloses a highly crystalline hierarchical porous ZSM-5 molecular sieve and its preparation method. The method mainly utilizes the capillary effect of the microporous molecular sieve, uniformly dispersing a passivating agent within the sieve channels. Under rapid drying conditions, the molecular sieve framework is passivated, followed by alkali and acid treatment, and finally calcination to obtain the target product of this invention. This invention offers high product yield, and the prepared ZSM-5 molecular sieve product exhibits high crystallinity, large total specific surface area, regular mesoporous channels, and a rich mesoporous system. Compared with direct alkali and acid treatment methods, this invention's preparation method can significantly maintain the original molecular sieve's crystallinity and retain its microporous system, which is beneficial for applications in catalysis, adsorption, and other fields. This invention's method is easy to industrialize and is environmentally friendly.

Description

Technical Field

[0001] This invention belongs to the field of hierarchical porous catalytic / adsorption materials and their preparation technology, and mainly provides a highly crystalline hierarchical porous ZSM-5 molecular sieve and its preparation method. This molecular sieve possesses both mesoporous and microporous structures, and the product exhibits high crystallinity, large total specific surface area, regular mesoporous channels, and a rich mesoporous system. Background Technology

[0002] ZSM-5 molecular sieves are widely used in chemical industries such as catalytic cracking, catalytic pyrolysis, isomerization, aromatization, and alkylation due to their suitable pore structure, moderate acidity, and excellent hydrothermal stability. Simultaneously, ZSM-5 molecular sieves are also excellent adsorbents used in VOCs treatment. Especially in the adsorption treatment of benzene and xylene series compounds, the hierarchical porous structure of ZSM-5 molecular sieves exhibits extremely high adsorption capacity and excellent economic benefits. In macromolecular catalytic cracking and pyrolysis reactions, the hierarchical porous structure of ZSM-5 molecular sieves demonstrates excellent diffusion properties and low hydrogen transfer activity, allowing for the production of more low-carbon olefins and promoting the oil-to-olefins conversion process.

[0003] ZSM-5 molecular sieves with hierarchical porous structures combine the characteristics of micropores and mesopores, and are generally synthesized through two methods: direct synthesis and post-processing. The direct synthesis method mainly uses organic templates (soft and hard templates) to crystallize with silicon and aluminum sources, followed by calcination to remove the organic templates and produce a mesoporous-microporous structure. Other methods use polyether polyols and fluorides, or add appropriate amounts of macroporous resins as porogens to the gel of the synthesis system to obtain hierarchical porous ZSM-5 molecular sieves. However, these templates are extremely expensive, and the calcination decomposition products often produce highly toxic gases, and the resulting wastewater severely restricts their industrialization. Furthermore, these methods have strict requirements on the silicon-to-aluminum ratio of the product, making them unsuitable for widespread application.

[0004] Most post-processing methods for preparing hierarchical porous ZSM-5 molecular sieves involve etching the molecular sieve framework with alkaline substances to remove part of the silicon-aluminum structure, thereby generating new mesopores. While both organic and inorganic alkaline substances are relatively inexpensive, they severely damage the molecular sieve framework, ultimately leading to low product yield, low crystallinity, and poor hydrothermal performance. Therefore, developing a method for preparing hierarchical porous ZSM-5 molecular sieves that offers excellent crystallinity and other physical properties, is easily industrialized, and is environmentally friendly is of great significance. Summary of the Invention

[0005] The purpose of this invention is to provide a highly crystalline hierarchical porous ZSM-5 molecular sieve and its preparation method. This method is relatively environmentally friendly, can maximize the preservation of molecular sieve crystallinity, and improve product yield.

[0006] This invention provides a method for preparing highly crystalline hierarchical porous ZSM-5 molecular sieve, comprising the following steps:

[0007] S1. Microporous ZSM-5 molecular sieve and passivating agent are mixed and reacted in water to obtain a mixture; the passivating agent is C1-6 short-chain organic aluminum alkoxide; in the composition of the mixture, the molar ratio of SiO2, Al2O3, alcohol and water is 1:0.001~0.1:0.001~0.1:0.1~10;

[0008] S2. The mixture obtained in step S1 is rapidly dried and calcined to obtain a passivated molecular sieve.

[0009] S3. Disperse the passivated molecular sieve obtained in step S2 in water, and perform alkali washing, acid washing, and water washing in sequence, and then dry to obtain a highly crystalline hierarchical porous ZSM-5 molecular sieve.

[0010] Preferably, in step S1, the molar ratio of silicon to aluminum oxide in the microporous ZSM-5 molecular sieve is 10 to 2000; the C1-6 short-chain organic aluminum alcohol is one or more of aluminum isopropoxide, aluminum tert-butoxide, and aluminum isobutoxide.

[0011] Preferably, in step S1, the temperature of the mixing reaction is 5 to 50°C, and the time is 0.5 to 8 hours.

[0012] Preferably, in step S2, the rapid drying rate is not less than 3 kg. 水 ·h -1 ·kg -1 产物 The rapid drying temperature shall not exceed 200°C.

[0013] Preferably, in step S2, the calcination conditions are calcination at 550–750°C for 0.5–4 hours.

[0014] Preferably, in step S3, the alkali source used for alkaline washing is sodium hydroxide, and the slurry composition of the alkaline washing contains SiO2 and OH... - The molar ratio of water to alkali is 1:0.1 to 10:5 to 50; the preferred temperature for alkaline washing is 25 to 100°C.

[0015] Preferably, in step S3, the acid source used for pickling is one or more of hydrochloric acid, sulfuric acid, nitric acid, oxalic acid, citric acid, and acetic acid; the pickling temperature is preferably 25-100°C, and the pickling time is 0.5-10h.

[0016] The present invention provides a highly crystalline hierarchical porous ZSM-5 molecular sieve obtained by the preparation method described above. The highly crystalline hierarchical porous ZSM-5 molecular sieve has both mesoporous and microporous structures and a crystallinity higher than 85%.

[0017] Preferably, the mesopores of the highly crystalline hierarchical ZSM-5 molecular sieve are regular, and the micropore specific surface area is greater than 280 m². 2 / g.

[0018] Preferably, the total specific surface area of ​​the highly crystalline hierarchical porous ZSM-5 molecular sieve is greater than 550 m². 2 / g.

[0019] Compared with existing technologies, the method of this invention involves mixing and reacting a microporous ZSM-5 molecular sieve with a passivating agent in water to obtain a mixture; the passivating agent is C1-6 short-chain organic aluminum alcohol; then it is rapidly dried and calcined, followed by alkali washing, acid washing, and water washing, and then dried and calcined again to obtain the highly crystalline hierarchical porous ZSM-5 molecular sieve. This invention uses short-chain organic aluminum alcohol as the passivating agent and utilizes the capillary effect of the microporous molecular sieve to siphon the passivating agent solution into the pores of the molecular sieve, achieving high dispersion and precise positioning of aluminum ions. Simultaneously, this invention utilizes the aluminum ions generated by the hydrolysis of the passivating agent to passivate the conventional ZSM-5 molecular sieve framework, which can reduce the deep structural damage caused by alkali treatment, maximize the preservation of the crystallinity of the molecular sieve, improve product yield, and broaden the applicable silicon-to-aluminum ratio range for alkali and acid treatment of ZSM-5 molecular sieves. Furthermore, the present invention concludes with an acid treatment process, which effectively removes amorphous silicon and aluminum from the molecular sieve channels and aluminum ion passivators from the framework, fully exposing the molecular sieve channels and increasing the specific surface area. The method for preparing the multi-level porous ZSM-5 molecular sieve provided by this invention is green and environmentally friendly, has low cost, and is easy to industrialize. According to the preferred embodiment, the ZSM-5 molecular sieve product prepared by the embodiments of this invention possesses both mesoporous and microporous structures, exhibiting high crystallinity, large total specific surface area, regular mesoporous channels, and a rich mesoporous system. Attached Figure Description

[0020] Figure 1 The image shown is a scanning electron microscope (SEM) image of the sample (S-1) prepared in Example 1. The sample retains the initial crystal form of ZSM-5 molecular sieve, and has uniformly distributed "pores" on the crystal surface with an opening diameter of about 30 nm. Detailed Implementation

[0021] The technical solutions in the embodiments of this application are described clearly and completely below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0022] This invention discloses a method for preparing highly crystalline hierarchical porous ZSM-5 molecular sieve, comprising the following steps:

[0023] S1. Microporous ZSM-5 molecular sieve and passivating agent are mixed and reacted in water to obtain a mixture; the passivating agent is C1-6 short-chain organic aluminum alkoxide; in the composition of the mixture, the molar ratio of SiO2, Al2O3, alcohol and water is 1:0.001~0.1:0.001~0.1:0.1~10;

[0024] S2. The mixture obtained in step S1 is rapidly dried and calcined to obtain a passivated molecular sieve.

[0025] S3. Disperse the passivated molecular sieve obtained in step S2 in water, and perform alkali washing, acid washing, and water washing in sequence, and then dry to obtain a highly crystalline hierarchical porous ZSM-5 molecular sieve.

[0026] The method for preparing hierarchical porous ZSM-5 molecular sieves in this invention mainly relies on passivating the molecular sieve framework with a passivating agent. This avoids etching of the framework during alkali and acid post-treatment, maximizing the preservation of molecular sieve crystallinity and improving product yield. Furthermore, this method can broaden the applicable silica-alumina ratio range for alkali and acid treatment of ZSM-5 molecular sieves (existing alkali treatment methods are only effective for ZSM-5 molecular sieves with lower silica-alumina ratios, and are not applicable to molecular sieves with higher silica-alumina ratios).

[0027] First, in this embodiment of the invention, the passivating agent (C1-6 short-chain organic aluminum alkoxide, Al(R-OH)3) is dispersed in water (generally deionized water) in a certain proportion, and then added to a microporous ZSM-5 molecular sieve. The mixture is stirred thoroughly to ensure uniform mixing, and reacted under certain conditions to obtain a mixture with the following composition (molar ratio): SiO2:Al2O3:R-OH:H2O = 1:0.001~0.1:0.001~0.1:0.1~10.

[0028] This invention uses conventional microporous ZSM-5 molecular sieve as raw material, wherein the molar ratio of silicon to aluminum oxide (the molar ratio of silicon oxide to aluminum oxide) can be 10–2000, preferably 20–500. For example, the molar ratio of silicon oxide to aluminum oxide in the ZSM-5 molecular sieve is selected from 26.3 and 411.5, respectively; their total specific surface areas are 367.5 and 389.6 m², respectively. 2 / g, with microporous specific surface areas of 355.1 and 375.4 m², respectively. 2 / g, with pore volumes of 0.25 and 0.27 ml / g, and mesopore volumes of 0 ml / g. The passivating agent described in this invention is a short-chain organic aluminum alkoxide with the chemical formula Al(R-OH)3, including but not limited to aluminum isopropoxide, aluminum tert-butoxide, and aluminum isobutoxide, or a mixture thereof, preferably aluminum isopropoxide or aluminum isobutoxide, or a mixture thereof.

[0029] Preferably, the mixture described in the above embodiments is obtained by reacting at 5–50°C for 0.5–8 hours, and its composition (molar ratio) is: SiO2:Al2O3:R-OH:H2O = 1:0.001–0.1:0.001–0.1:0.1–10. In a further preferred embodiment, the reaction conditions for preparing the mixture are: standing at 10–40°C for 1–6 hours. The preferred composition (molar ratio) is: SiO2:Al2O3:R-OH:H2O = 1:0.01–0.2:0.03–0.6:0.1–5. In the embodiments of the present invention, the passivating agent, organic aluminum alkoxide, is adsorbed into the pores of the molecular sieve under the "capillary" adsorption effect, and then hydrolyzed inside the pores. The released aluminum ions can uniformly cover the inside of the pores, forming a non-skeleton aluminum layer, which facilitates subsequent processing.

[0030] In this embodiment of the invention, the prepared mixture is transferred to a drying device for rapid drying. After drying, the material is calcined to obtain a passivated molecular sieve. By rapidly drying the obtained mixture, this invention ensures that the formed alumina interlayer does not migrate or agglomerate with the evaporation of water vapor, thus preventing pore blockage. The main function of the calcination is to form a dense alumina layer (more resistant to alkali corrosion) of aluminum ions, protecting the molecular sieve framework.

[0031] The rapid drying method can be either atmospheric pressure drying or vacuum drying, with vacuum drying being preferred. The rapid drying temperature should not exceed 200℃, preferably not exceeding 150℃, and can be between 120℃ and 140℃; the drying rate should not be less than 3 kg / kg. 水 ·h -1 ·kg -1 产物 Preferably not less than 5kg 水 ·h -1 ·kg -1 产物 Furthermore, the preferred calcination conditions are calcination at 550–750°C for 0.5–4 hours, and more preferably calcination at 550–700°C for 1–2 hours.

[0032] After obtaining the passivated molecular sieve, the present invention provides an alkaline washing slurry prepared in a certain proportion. The passivated molecular sieve can be dispersed in deionized water for alkaline washing. The alkaline substances in the slurry etch the molecular sieve framework to a certain extent, removing part of the silicon-aluminum structure and generating new mesopores. Then, the molecular sieve product of the present invention is obtained by sequentially washing with water, acid washing, and water washing, followed by drying and calcination.

[0033] In an embodiment of the present invention, the alkaline washing process conditions include: 1) slurry composition (molar ratio): SiO2: OH -1) H2O = 1:0.1~10:5~50; 2) Alkali washing temperature: 25~100℃; 3) Alkali washing time: 0.5~10h; The alkali source used is sodium hydroxide. Preferred alkali washing conditions are: 1) Slurry composition: SiO2:OH - :H2O=1:0.1~5:20~40; 2) Alkali washing temperature: 50~80℃; 3) Alkali washing time: 1~5h.

[0034] Furthermore, the pickling conditions described in the embodiments of the present invention include: 1) Slurry composition: SiO2:H - 1) H2O = 1:0.1~1:5~50; 2) Pickling temperature: 25~100℃; 3) Pickling time: 0.5~10h. Preferred pickling conditions are: 1) Slurry composition: SiO2:H2O = 1:0.1~1:5~50; 2) Pickling temperature: 25~100℃; 3) Pickling time: 0.5~10h. - 1) H2O = 1:0.1~1:30~50; 2) Pickling temperature: 50~80℃; 3) Pickling time: 1~5h. The acid source used can be one or a mixture of hydrochloric acid, sulfuric acid, nitric acid, oxalic acid, citric acid, and acetic acid, preferably one or a mixture of hydrochloric acid, sulfuric acid, and nitric acid, and more preferably sulfuric acid.

[0035] In the preferred embodiments and examples, the washing process involves washing until the washing solution is neutral; for example, after alkaline washing, the solution is washed until neutral, and then acid washing is performed. This invention ends with an acid treatment process, which can remove the amorphous silicon and aluminum in the molecular sieve channels and the aluminum ion passivating agent on the framework, fully exposing the molecular sieve channels and increasing the specific surface area.

[0036] After acid washing, the present invention embodiment filters and washes with water until the filtrate is neutral; finally, the water-neutral molecular sieve can be dried and calcined at 500-600℃ for 1-2 hours to dehydrate and stabilize the molecular sieve structure, thereby obtaining a multi-level porous ZSM-5 molecular sieve product with high crystallinity.

[0037] This invention provides a highly crystalline hierarchical porous ZSM-5 molecular sieve prepared by the method described above. The highly crystalline hierarchical porous ZSM-5 molecular sieve possesses both mesoporous and microporous structures, with a crystallinity exceeding 85%. Furthermore, the mesoporous channels of the highly crystalline hierarchical porous ZSM-5 molecular sieve are regular, and the micropore specific surface area is greater than 280 m². 2 / g; Total specific surface area greater than 550m² 2 / g.

[0038] The ZSM-5 molecular sieve product prepared in this embodiment of the invention possesses both mesoporous and microporous structures. The product exhibits high crystallinity, a large total specific surface area, regular mesoporous channels, and a rich mesoporous system, which is beneficial for applications. Through optimized embodiments, the obtained hierarchical porous ZSM-5 molecular sieve can achieve a crystallinity of 91.3% and a total specific surface area of ​​611.3 m². 2 / g, microporous specific surface area 321.6m²2 / g, pore volume 0.58ml / g, mesopore volume 0.37ml / g, product yield 79.1%. The product prepared by the multi-level porous ZSM-5 molecular sieve preparation method described in this embodiment of the invention has excellent physical properties, a wide applicable range of silicon-aluminum ratio, is easy to industrialize, and is environmentally friendly.

[0039] The following examples further illustrate the embodiments of the present invention, but the present invention is not limited to these examples. In the embodiments of the present invention, the molar ratio of silica to alumina in the ZSM-5 molecular sieve raw material (conventional microporous ZSM-5 molecular sieve) is selected from 26.3 and 411.5, respectively; their total specific surface areas are 367.5 and 389.6 m², respectively. 2 / g, with microporous specific surface areas of 355.1 and 375.4 m², respectively. 2 / g, with pore volumes of 0.25 and 0.27 ml / g, and mesoporous pore volumes of 0 ml / g.

[0040] Examples 1-4:

[0041] Passivated molecular sieves, denoted as D-1 to D-6, were prepared according to the raw materials and proportions given in Table 1. The passivating agent was dispersed in deionized water and added to the microporous ZSM-5 molecular sieve. The mixture was stirred until homogeneous and reacted at 30°C for 4 hours. The resulting mixture was then transferred to a vacuum drying oven for rapid drying at a controlled temperature of 120–140°C, following the drying rate given in Table 1. After drying, the material was calcined at 600°C for 2 hours to obtain the passivated molecular sieve.

[0042] Then, the passivated molecular sieve, sodium hydroxide, and water are mixed in a molar ratio of SiO2:OH. - A slurry was prepared by mixing SiO2 with H2O at a ratio of 1:0.75:30 and treating it at 60°C for 4 hours. After alkali treatment (alkali washing), the solution was filtered and washed with water until the filtrate was neutral. Then, the alkali-treated molecular sieve, sulfuric acid, and water were mixed according to a molar ratio of SiO2:H2O. - A slurry for acid washing was prepared by mixing H₂O at a ratio of 1:0.25:40 and treating it at 70°C for 2 hours. After acid washing, the slurry was filtered and washed with water until the filtrate was neutral. Finally, the washed molecular sieve was calcined at 600°C for 2 hours to obtain molecular sieve product samples for the examples and comparative examples, denoted as S-1~4 (corresponding to Examples 1~4), DB-1, and DB-2, respectively.

[0043] Comparative Examples 1-2:

[0044] The DB-1 and DB-2 samples were passivated with a passivating agent to passivate the molecular sieve framework, but were not dried rapidly (the drying rate was low, corresponding to D-5 and D-6). After conventional drying and calcination, they underwent the same washing treatment as in the example.

[0045] Comparative Examples 3-4

[0046] Microporous ZSM-5 molecular sieves with a silicon-to-aluminum ratio of 26.3 to 411.5, sodium hydroxide, and water were mixed in a molar ratio of SiO2:OH-:H2O = 1:0.75:30 to prepare a slurry, which was then treated at 60°C for 4 hours. After alkali treatment, the mixture was filtered and washed with water until the filtrate was neutral. The alkali-treated molecular sieves, sulfuric acid, and water were then mixed in a molar ratio of SiO2:H-:H2O = 1:0.25:40 to prepare a slurry, which was then treated at 70°C for 2 hours. After acid washing, the mixture was filtered and washed with water until the filtrate was neutral. Finally, the water-washed molecular sieves were calcined at 600°C for 2 hours to obtain the products of Comparative Examples 3 and 4, respectively designated as DB-3 and DB-4.

[0047] Table 1. Raw materials, proportions, and drying parameters for passivated molecular sieves

[0048]

[0049] Figure 1 Here is a scanning electron microscope image of sample (S-1) from Example 1. Figure 1 It can be seen that the sample retains the initial crystal form of ZSM-5 molecular sieve, and there are uniform "pores" distributed on the crystal surface with a pore diameter of about 30 nm.

[0050] Furthermore, the physical properties of the product samples from the embodiments and comparative examples of the present invention were tested, and the results are as follows:

[0051] Table 2 Physical property parameters of examples and comparative examples

[0052]

[0053] Note: The relative crystallinity is based on untreated molecular sieves, i.e., the relative crystallinity is 100%.

[0054] As shown in Table 2, the examples and comparative examples all used hierarchical porous ZSM-5 molecular sieves. However, the samples from examples (S-1 to S-4) exhibited high crystallinity (minimum 89.2%), high yield (minimum 76.5%), and a lower total specific surface area (minimum 596.4 m²). 2 The S-2 and S-4 samples also showed relatively high total pore volume (minimum 0.56 ml / g), especially the micropore specific surface area (which directly reflects the integrity of the molecular sieve crystal form or framework). Compared to the DB-4 sample, the S-2, S-4, and DB-2 samples all produced additional mesopore specific surface area, indicating that the "passivation" step is beneficial for broadening the silica-alumina ratio range of the ZSM-5 molecular sieve treated with alkali and acid.

[0055] Samples DB-1 and DB-2 used a passivating agent to passivate the molecular sieve framework, but the drying process was not rapid (low drying rate), resulting in uneven dispersion of the passivating agent and failing to achieve the desired "passivation of the framework" effect. Consequently, after subsequent alkali and acid treatments, the crystallinity, yield, and micropore specific surface area of ​​the products all decreased significantly.

[0056] Samples DB-3 and DB-4 did not employ the passivation method of this invention for the molecular sieve. After subsequent alkali and acid treatments, the product yield (51.8%, 55.4%) and crystallinity (57.8%, 61.5%) decreased significantly. Simultaneously, the micropore specific surface area (207.4 m²) also decreased. 2 / g、212.8m 2 The percentage of molecular sieves (g) also decreased significantly, indicating that the molecular sieve framework was severely damaged.

[0057] As can be seen from the above embodiments, the specific steps of the embodiments of the present invention are as follows: a) Disperse the passivating agent in deionized water in a certain proportion, then add it to the microporous ZSM-5 molecular sieve, stir and mix thoroughly until uniform, and obtain a mixture under certain conditions. The composition (molar ratio) is: SiO2:Al2O3:R-OH:H2O=1:0.001~0.1:0.001~0.1:0.1~10; b) Quickly dry and calcine the mixture obtained in step a) to obtain the passivated molecular sieve; c) Disperse the passivated molecular sieve in step b) in deionized water, and perform alkali washing-water washing-acid washing-water washing in sequence, and then dry and calcine to obtain the product of the present invention. The product of the present invention has a high yield, and the prepared ZSM-5 molecular sieve product has high crystallinity, large total specific surface area, regular mesoporous channels, and rich mesoporous system, which is beneficial for applications in catalysis, adsorption, etc. The method of the present invention is easy to industrialize and is green and environmentally friendly. Compared with direct alkali and acid treatment methods, the preparation method of this invention can significantly maintain the crystallinity of the original molecular sieve and preserve its microporous system. Through optimized embodiments, the prepared hierarchical porous ZSM-5 molecular sieve achieved a crystallinity of 91.3% and a total specific surface area of ​​611.3 m². 2 / g, microporous specific surface area 321.6m² 2 / g, pore volume 0.58ml / g, mesopore volume 0.37ml / g, product yield 79.1%.

[0058] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing a highly crystalline hierarchical porous ZSM-5 molecular sieve, characterized in that, Includes the following steps: S1. Microporous ZSM-5 molecular sieve and a passivating agent are mixed and reacted in water to obtain a mixture; the passivating agent is C1-6 short-chain organic aluminum alkoxide; the C1-6 short-chain organic aluminum alkoxide is Al(R-OH)3, which is one or both of aluminum isopropoxide and aluminum isobutoxide; the mixing reaction temperature is 5~50℃, and the time is 0.5~8 hours; in the composition of the mixture, the molar ratio of SiO2, Al2O3, R-OH and water is 1:0.001~0.1:0.001~0.1:0.1~10; S2. The mixture obtained in step S1 is rapidly dried and calcined at 550-750°C for 0.5-4 hours to obtain passivated molecular sieves; the rapid drying rate is not less than 3 kg / min. 水 ·h -1 ·kg -1 产物 The rapid drying temperature shall not exceed 200℃. S3. Disperse the passivated molecular sieve obtained in step S2 in water, and perform alkali washing, acid washing, and water washing in sequence, and then dry to obtain a highly crystalline hierarchical porous ZSM-5 molecular sieve.

2. The preparation method according to claim 1, characterized in that, In step S1, the molar ratio of silicon to aluminum oxide in the microporous ZSM-5 molecular sieve is 10 to 2000.

3. The preparation method according to any one of claims 1-2, characterized in that, In step S3, the alkali source used for alkaline washing is sodium hydroxide, and the slurry composition of the alkaline washing contains SiO2 and OH... - The molar ratio of water to water is 1:0.1~10:5~50.

4. The preparation method according to claim 3, characterized in that, In step S3, the temperature of the alkaline washing is 25~100℃.

5. The preparation method according to claim 3, characterized in that, In step S3, the acid source used for pickling is one or more of hydrochloric acid, sulfuric acid, nitric acid, oxalic acid, citric acid, and acetic acid.

6. The preparation method according to claim 5, characterized in that, In step S3, the pickling temperature is 25~100℃ and the time is 0.5~10h.

7. The highly crystalline hierarchical porous ZSM-5 molecular sieve obtained by the preparation method according to any one of claims 1-6, characterized in that, The highly crystalline hierarchical porous ZSM-5 molecular sieve has both mesoporous and microporous structures, with a crystallinity higher than 85%.

8. The highly crystallinity hierarchical porous ZSM-5 molecular sieve according to claim 7, characterized in that, The highly crystalline hierarchical porous ZSM-5 molecular sieve has regular mesopore channels and a micropore specific surface area greater than 280 m². 2 / g.

9. The highly crystallinity hierarchical porous ZSM-5 molecular sieve according to claim 8, characterized in that, The total specific surface area of ​​the highly crystalline hierarchical porous ZSM-5 molecular sieve is greater than 550 m². 2 / g.

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