A method for synthesizing a hierarchical pore zsm-5 molecular sieve

Abstract

The application relates to a method for synthesizing a multi-level hole ZSM-5 molecular sieve, which directly obtains the multi-level hole ZSM-5 molecular sieve through hydrothermal crystallization of amorphous high-silicon mineral soil raw materials and activated low-silicon mineral soil raw materials and seed crystals activated by hot alkali. In the method, the silicate and aluminate in the mineral provide all the silicon source and aluminum source for synthesis, without adding external silicon source or aluminum source, and without adding expensive organic amine template agents, so that the method belongs to an environment-friendly low-cost molecular sieve green synthesis method, and the prepared multi-level hole ZSM-5 has high crystallinity and rich mesoporous structures and can be applied to petroleum chemical catalysts.

Description

Technical Field

[0001] This invention belongs to the field of molecular sieve synthesis technology, and relates to a hierarchical porous ZSM-5 molecular sieve and its synthesis method. Background Technology

[0002] In the late 1960s, Mobil Corporation in the United States successfully developed ZSM-5 molecular sieve (USP 3702886), which features a unique Zigzag-type three-dimensional channel structure. It is characterized by a high silicon-to-aluminum ratio, high thermal stability, and high catalytic activity, and is widely used in petroleum refining, fine chemicals, and coal chemicals, making it one of the most important molecular sieve materials for industrial catalysis. ZSM-5 molecular sieves possess both cylindrical (0.54nm × 0.56nm) and Zigzag-type (0.52nm × 0.58nm) channels, exhibiting a two-dimensional ten-membered ring channel structure. In practical applications, some macromolecular raw materials struggle to enter these two types of microporous channels to react. Developing a hierarchical porous ZSM-5 molecular sieve with both microporous and mesoporous systems can effectively alleviate the diffusion problem of macromolecules in catalytic materials, further improving catalyst performance.

[0003] Crystallization using natural mineral clay is a crucial method for modern industrial molecular sieve preparation. Natural mineral clay, primarily composed of silicon and aluminum oxides, can provide some or all of the silicon and aluminum sources required for molecular sieve synthesis after activation. This significantly reduces production costs, improves the atom economy of the synthesis process, and aligns with green production principles. Furthermore, during hydrothermal synthesis, the voids formed during mineral clay crystallization introduce unique mesoporous structures into the product molecular sieve, resulting in hierarchical porous molecular sieves and enhancing the reaction efficiency of large molecules such as heavy oil feedstocks.

[0004] ZSM-5 molecular sieves are characterized by a high silica-to-alumina ratio. Therefore, controlling the feed of the synthesis system based on the silica-to-alumina content characteristics of natural mineral clays and the silica-to-alumina ratio of the target molecular sieve is a key factor for successful crystallization. Furthermore, most natural mineral clays have a layered crystal structure. To fully utilize the silica and alumina sources within them, methods such as heat treatment are used to break down the alumina octahedral and silica tetrahedral structures of the layered crystals, thus activating the mineral clay. This is another key factor for successful crystallization. Currently, there are reports on the preparation of ZSM-5 molecular sieves from natural mineral clay raw materials. For example, USP4091007, CN101332995A, and CN101462740A prepared ZSM-5 molecular sieves with high zeolite content and abundant mesopores using kaolin-based raw materials, which can be used in catalysts in the petrochemical field. However, the above reports only partially utilize the silica and alumina elements in the minerals and still rely on external chemical silica sources (such as water glass, silica sol, and sodium silicate) to adjust the silica-to-alumina ratio. CN103848439A reported a method for preparing ZSM-5 molecular sieves entirely from natural minerals without the addition of external chemical silicon or aluminum sources. However, this method requires high-temperature or molten salt activation of all the minerals involved, resulting in high energy consumption. Furthermore, the molten salt method consumes a large amount of alkali, and subsequent acid neutralization is required to neutralize the excess alkali in the crystallization system, generating a significant amount of waste liquid.

[0005] Natural mineral soil crystallization methods mostly rely on template agents to induce the formation of primary crystal nuclei in ZSM-5 molecular sieves. Subsequently, the crystal nuclei undergo slow growth followed by rapid growth to achieve full crystallization. Conventional template agents, such as tetrapropylammonium hydroxide, tetrapropylammonium bromide, and tetraethylammonium bromide, are organic amines that are expensive and environmentally unfriendly. Furthermore, they usually require high-temperature calcination of the crystallized product to remove residual template agents within the crystals. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide an environmentally friendly green synthesis method for molecular sieves, which directly utilizes amorphous high-silica mineral soil raw materials and thermally activated low-silica mineral soil raw materials to synthesize ZSM-5 molecular sieves.

[0007] This invention provides a method for preparing hierarchical porous ZSM-5 molecular sieves from natural mineral soil, comprising the following steps:

[0008] (S1) Obtain high-silica mineral soil fine powder; the average particle size of the high-silica mineral soil fine powder is preferably not more than 10 micrometers;

[0009] (S2) Obtain activated low-silica mineral soil fine powder, wherein the average particle size of the activated low-silica mineral soil fine powder is preferably not more than 10 micrometers;

[0010] (S3) Obtaining seed activation solution: The sodium-type ZSM-5 molecular sieve is ground into fine seed powder, wherein the average particle size of the fine seed powder is preferably not more than 5 micrometers; the fine seed powder is treated with hot alkaline solution to obtain seed activation solution;

[0011] (S4) Synthesis of multi-level porous molecular sieve crystallization: The high-silica mineral clay fine powder described in step (S1), the activated low-silica mineral clay fine powder described in step (S2), and the seed activation liquid described in step (S3) are mixed to obtain a crystallization precursor liquid, and then crystallized.

[0012] (S5) Recover ZSM-5 molecular sieve.

[0013] Furthermore, the present invention provides a hierarchical ZSM-5 molecular sieve, wherein a large number of ZSM-5 nanoribs are exposed on the surface of the ZSM-5 molecular sieve particles, exhibiting intercrystalline mesopores, and the volume of mesopores accounts for 40-50% of the total volume of micropores and mesopores.

[0014] The present invention provides a method for preparing ZSM-5 molecular sieves from natural mineral clay. Sodium-type ZSM-5 molecular sieve is used as a primary seed crystal, activated with hot alkali solution, and then directly mixed with mineral clay raw materials. The mixture is then crystallized via a hydrothermal method to directly obtain hierarchical porous ZSM-5 molecular sieves. This method allows for the direct preparation of hierarchical porous ZSM-5 molecular sieves from natural mineral clay. The present invention has at least one of the following beneficial effects, and preferably has several or all of them:

[0015] (1) The synthesis of ZSM-5 molecular sieve in this invention is based on natural mineral soil providing all the silicon and aluminum sources. No other small molecule silicon-aluminum compounds need to be introduced into the crystallization process system. No expensive organic amine template agent is used, which reduces the production cost. The high-silicon mineral soil does not need to be activated, which reduces the energy consumption required for mineral soil activation. The silicon-aluminum ratio of the product can be flexibly controlled by adjusting the composition of the crystallization raw material mineral soil. It belongs to the environmentally friendly green synthesis route of molecular sieve.

[0016] (2) The ZSM-5 molecular sieve of the present invention is synthesized from natural mineral soil as raw material. By controlling the naturally derived accumulation pores and fissure pores during the crystallization process of natural mineral soil, a multi-level pore structure is formed in the crystallization product. No external mesoporous template agent is required, which is economical and efficient.

[0017] (3) In the process of synthesizing ZSM-5 molecular sieve in this invention, it is not necessary to acid treat the crystallized raw material mineral soil to adjust the silicon-aluminum ratio of the raw material. Therefore, no additional waste acid liquid is generated, the process flow is shortened, and the production can achieve green environmental protection, energy saving and consumption reduction.

[0018] (4) The multi-level porous ZSM-5 molecular sieve obtained by the present invention has the advantages of high crystallinity, high silicon-aluminum ratio of product skeleton and rich mesoporous structure, which can improve the reaction efficiency of macromolecular raw materials.

[0019] (5) The natural mineral soil raw materials used in this invention are inexpensive and readily available, and the synthesis method is simple, making it suitable for industrial production and enabling the low-cost preparation of multi-level porous ZSM-5 molecular sieves.

[0020] (6) The ZSM-5 molecular sieve provided by the present invention, after being exchanged to become a hydrogen-type molecular sieve, is used for catalytic cracking of naphtha, resulting in a higher propylene yield. For example, when industrial naphtha is used to react at a reaction temperature of 675°C, a catalyst-to-oil ratio (by weight) of 0.6, and an oil inlet time of 70 seconds, the propylene yield can reach 12-16% by weight. In contrast, the ZSM-5 molecular sieve prepared by the prior art, under the same conditions, has a propylene yield of 7-10% by weight. Attached Figure Description

[0021] Figure 1 To obtain a scanning electron microscope (SEM) image of the product magnified 40,000 times for Example 1.

[0022] Figure 2 The high-resolution transmission electron microscope (HRTEM) image of the product obtained in Example 1 is shown.

[0023] Figure 3 The X-ray diffraction (XRD) pattern of the product was obtained for Example 1.

[0024] Figure 4 The image shows the BET adsorption-desorption curves of the product obtained in Example 1.

[0025] Figure 5 The diagram shows the pore distribution curve of the product BJH obtained in Example 1.

[0026] Figure 6 The product obtained in Example 1 29 Si nuclear magnetic resonance (NMR) spectrum peak fitting diagram. In the figure, 1 to 4 are the results obtained by peak fitting of the experimental results. The peak positions of 1, 2, 3 and 4 are -102ppm, -106ppm, -112ppm and -116ppm, respectively. 5 is the experimental result (solid line) and 6 is the fitting result (dashed line). Detailed Implementation

[0027] The method for preparing ZSM-5 molecular sieve provided by the present invention comprises a high-silica mineral clay or high-silica clay containing 85-100% by weight, for example 85-99% by weight, and an alumina content of 0-15% by weight, for example 1-15% by weight; preferably, the high-silica mineral clay is diatomaceous earth with a SiO2 content higher than 90% by weight.

[0028] The average particle size of the high-silica mineral clay powder is preferably less than 10 μm, for example 0.5-10 micrometers, preferably 0.5-5 micrometers or 0.5-8 micrometers, for example 1-7 micrometers or 1-3 micrometers.

[0029] The high-silica mineral soil powder can be obtained by grinding the high-silica mineral soil raw material to obtain high-silica mineral soil powder with an average particle size of less than 10 μm. The grinding can be completed using a ball mill. In one embodiment, a planetary ball mill can be used for ball milling, with a milling time of 1–5 hours and a rotation speed of 100–500 rpm.

[0030] The ball mill described in this invention can be an existing ball mill, such as the JC-QM series vertical planetary ball mill from Juchuang Environmental Protection.

[0031] The method for preparing ZSM-5 molecular sieve provided by this invention uses a low-silica mineral clay with a silica content of 40-75% by weight and an alumina content of 25-60% by weight. In a further embodiment of this invention, the low-silica mineral clay is one or more of rettoiter, kaolin, bentonite, and montmorillonite.

[0032] The method for preparing ZSM-5 molecular sieve provided by this invention, wherein the activated low-silica mineral clay powder can be obtained by the following method:

[0033] (1) Grind the low-silica mineral soil raw material to obtain low-silica mineral soil fine powder with an average particle size of less than 10 micrometers, for example 0.5-10 micrometers, preferably 0.5-5 micrometers, for example 1-4 micrometers or 2-4 micrometers;

[0034] The grinding can be accomplished using a ball mill. In one embodiment, a planetary ball mill is used for ball milling, with a milling time of 1–5 hours and a rotation speed of 100–400 rpm.

[0035] (2) The low-silica mineral soil powder is calcined at 600-950℃ for a preferred time of 2-5 hours to obtain activated low-silica mineral soil powder.

[0036] The present invention provides a method for preparing ZSM-5 molecular sieves, which involves activating sodium-type ZSM-5 molecular sieves to obtain a seed activation solution, which serves as the seed crystal for crystallization. The seed activation solution is obtained by grinding sodium-type ZSM-5 molecular sieves into fine seed powder, wherein the average particle size of the fine seed powder does not exceed 5 micrometers, for example, 0.5–5 micrometers or 1–3 micrometers. The fine seed powder is then treated with a hot alkaline solution to obtain the seed activation solution. By activating the sodium-type ZSM-5 molecular sieve with hot alkaline solution, partial depolymerization occurs, resulting in smaller structural units that serve as seed crystals. This facilitates interaction with the mineral raw materials during hydrothermal synthesis, promoting crystal growth.

[0037] In one embodiment, the hot alkaline solution treatment involves heating and stirring the seed powder in a sodium hydroxide solution for 1 to 3 hours.

[0038] The preferred temperature for the hot alkaline solution treatment is 70–90°C.

[0039] According to one embodiment of the method for preparing ZSM-5 molecular sieve provided by the present invention, in the treatment with hot alkaline solution, the ratio of NaOH to water in the mixture of seed powder and sodium hydroxide solution is 1:15-30 (mass ratio) and the ratio of NaOH to seed powder is 1:0.8-2.5 (mass ratio).

[0040] The method for preparing ZSM-5 molecular sieve provided by this invention involves grinding the sodium-type ZSM-5 molecular sieve using a ball mill. In one embodiment, a planetary ball mill is used, with a milling time of 1–5 hours and a rotation speed of 100–400 rpm.

[0041] In the method for preparing ZSM-5 molecular sieve provided by the present invention, preferably, the sodium-type ZSM-5 molecular sieve has a relative crystallinity of 85-100%, a silicon-to-aluminum ratio (the molar ratio of bulk SiO2 / Al2O3) of 20-200, and an average particle size of the sodium-type ZSM-5 molecular sieve not exceeding 5 micrometers, for example 0.5-5 micrometers, preferably 1-3 micrometers.

[0042] The method for preparing ZSM-5 molecular sieve according to the present invention involves mixing high-silica mineral clay powder, activated low-silica mineral clay powder, and a seed crystal activation solution to form a crystallization precursor solution, followed by crystallization. Alternatively, the high-silica mineral clay powder and activated low-silica mineral clay powder can be added to the seed crystal activation solution, the crystallization precursor solution can be loaded into a crystallization reactor, and then crystallization can be carried out.

[0043] According to the method for preparing ZSM-5 molecular sieve provided by the present invention, the ratio of high-silica mineral clay powder: activated low-silica mineral clay powder: seed crystal in the crystallization precursor solution is (5-10):1:(1.2-3.5) (mass ratio).

[0044] According to the method for preparing ZSM-5 molecular sieve provided by the present invention, the pH value of the crystallization precursor solution is 10-13, preferably 11-13.

[0045] The crystallization can be carried out at 150–190°C for 12–60 hours. Preferably, a dynamic crystallization method is used, such as crystallization under stirring.

[0046] According to the method for preparing ZSM-5 molecular sieve provided by the present invention, after crystallization, the prepared ZSM-5 molecular sieve product is recovered. The recovery of the ZSM-5 molecular sieve may, for example, involve solid-liquid separation of the crystallized mixture, such as filtration, washing, and drying, to obtain a hierarchical porous ZSM-5 molecular sieve product.

[0047] According to the invention, the ZSM-5 molecular sieve with multi-level pores has a large number of ZSM-5 nanoribs exposed on the particle surface, exhibiting intercrystalline mesopores, and the volume of mesopores accounts for 40-50% of the total volume of micropores and mesopores.

[0048] The multi-level porous ZSM-5 molecular sieve provided by the invention has an average particle size of 2 to 5 μm.

[0049] The relative crystallinity of the multi-level porous ZSM-5 molecular sieve provided by the invention can exceed 90%.

[0050] According to the invention, the multi-level porous ZSM-5 molecular sieve has a framework silicon-to-aluminum ratio of 30 to 130 in terms of Si / Al atomic molar ratio.

[0051] According to the multi-level porous ZSM-5 molecular sieve provided by the invention, its N2 adsorption and desorption curves show a significant hysteresis loop.

[0052] The following embodiments will further illustrate the present invention, but are not intended to limit the invention.

[0053] The average particle size of the ZSM-5 seed powder and mineral soil powder was the equivalent volume diameter obtained by laser particle size distribution method. Experimental instrument: Malvern Mastersizer 3000.

[0054] The relative crystallinity was determined according to ASTM D3906-03 standard, using commercial ZSM-5 molecular sieve (Tianjin Nanhua Catalyst Co., Ltd., Na-type ZSM-5 molecular sieve, Si / A ratio 38) as the standard, and the crystallinity of commercial ZSM-5 was defined as 100%. The relative crystallinity was defined as the ratio of the area of ​​the characteristic peak at 2θ angles between 22.5-25.0° in the XRD pattern of the crystallized product to the area of ​​the characteristic peak of the standard molecular sieve. Experimental instrument: Siemens D5005 X-ray diffractometer. Experimental conditions: Cu target, Kα radiation, solid-state detector, tube voltage 40kV, tube current 40mA, step scan, step size 0.02°, pre-set time 2s, scan range 5°~70°.

[0055] The mesoporous surface area, specific surface area, pore volume (total pore volume), and pore size distribution were measured using the low-temperature nitrogen adsorption capacity method. Experimental instrument: Micromeritics ASAP2400 static nitrogen adsorption instrument. Experimental conditions: The sample was degassed under vacuum at 1.33 Pa and 300 °C for 4 h, then contacted with liquid nitrogen at 77 K for isothermal adsorption and desorption. Adsorption and desorption isotherms were measured, and the specific surface area and pore volume were calculated using the BET formula. The average pore size was calculated using the BJH formula.

[0056] The bulk SiO2 / Al2O3 molecular molar ratio was quantitatively characterized by X-ray fluorescence. Experimental instrument: Rigaku Electric Industries, Ltd., Japan, X-ray fluorescence spectrometer 3271E. Experimental conditions: powder samples were pressed into tablets, rhodium target was used, excitation voltage was 50 kV, excitation current was 50 mA, and the intensity of each element's spectral line was detected using a scintillation counter and a proportional counter. Quantitative and semi-quantitative analysis of elemental content was performed using the external standard method.

[0057] The atomic molar ratio of Si / Al in the molecular sieve framework was quantitatively characterized by solid-state nuclear magnetic resonance (NMR). Experimental instrument: Bruker Avance III 500MHz NMR spectrometer. Test conditions: Resonance frequency: 99.36MHz ( 29 Si), spectral width: 200, sampling time: 25.9ms, delay time: 5s, pulse width: 1.5μs, number of samples: 4096, rotation speed: 4000Hz.

[0058] The specific calculation method for the Si / Al molar ratio of the molecular sieve framework is as follows: 29 The chemical shift in the NMR spectrum of Si is sensitive to the chemical environment of silicon atoms. The tetrahedral coordination of SiO4 is represented as Q. n (mAl), where Q represents a silicon-oxygen tetrahedron, n represents the total number of silicon or aluminum atoms connected to the tetrahedron via oxygen bridging bonds (n is an integer between 0 and 4), and m is the number of aluminum atoms connected to the tetrahedron via oxygen bridging bonds (m is an integer between 0 and 4). The product molecular sieve... 29 Peak fitting was performed on the Si MAS NMR spectrum. The peak at a chemical shift of -102 ppm was assigned to Q. 3 Silicon species, representing the presence of silanol groups in the sample, are typically located on the outer surface, the surface of pores within the grain, or at defect sites within the grain; the peak at -106 ppm is attributed to Q. 4 (1A1); The peak at -112 to -118 ppm is attributed to Q. 4 (0A1). Calculate the Si / Al molar ratio of the product molecular sieve framework according to the following formula.

[0059]

[0060] in For Q 4 (mAl) is the integral area of ​​the NMR fitting peak.

[0061] In the following examples and comparative examples, the room temperature was 25°C.

[0062] Example 1

[0063] (1) Preparation of high-silica mineral soil fine powder: Diatomaceous earth (Lingshou County Fengheng Mineral Products Processing Plant, diatomaceous earth powder, chemical composition and silicon-aluminum ratio are shown in Table 1) was fully ball-milled using Juchuang Environmental Protection Vertical Planetary Ball Mill (JC-QM-0.4) (300 rpm, ball milling for 2 hours) to obtain high-silica mineral soil fine powder with an average particle size of 2.8 μm, which was directly used as raw material for subsequent crystallization.

[0064] (2) Preparation of low-silica mineral clay fine powder: Bentonite (Jiushi Mineral Products Processing Plant, Lingshou County, Hebei Province, sodium-based bentonite, chemical composition and silicon-aluminum ratio are shown in Table 1) was fully ball-milled using Juchuang Environmental Protection Vertical Planetary Ball Mill (JC-QM-0.4) (300 rpm, ball milling for 2 hours) to obtain low-silica mineral clay fine powder with an average particle size of 3.9 μm.

[0065] (3) Activation of low-silica mineral soil powder: The low-silica mineral soil powder obtained in step (2) is calcined at 750°C for 3 hours and then cooled to room temperature as raw material for subsequent crystallization.

[0066] (4) Seed activation: Sodium-type ZSM-5 molecular sieve (Nankai Catalyst Plant, Na-type ZSM-5 molecular sieve, chemical composition, silicon-aluminum ratio and relative crystallinity are shown in Table 2) was used as seed crystals. The seed crystals were thoroughly ball-milled using a JC-QM-0.4 vertical planetary ball mill (300 rpm, 2 hours) to obtain fine seed crystal powder with an average particle size of 1.9 μm. 2.00 g of NaOH was weighed and added to 32.00 g of water to obtain an alkaline solution. 1.70 g of fine seed crystal powder was added to the alkaline solution, and the mixture was heated and stirred at 80°C for 2 hours to obtain a seed activation solution. In this embodiment, NaOH:water = 1:16 (mass ratio); NaOH:seed crystal = 1:0.85 (mass ratio).

[0067] (5) Synthesis of multi-level porous molecular sieve crystallization: Weigh 6.07g of the high-silica mineral clay powder obtained in step 1 and 1.21g of the activated low-silica mineral clay powder obtained in step (3) and add them to the seed activation solution in step (4) to obtain the crystallization precursor solution. The crystallization precursor solution is loaded into a crystallization kettle and crystallized at 170℃ for 40h using the dynamic crystallization method. In this embodiment, the ratio of high-silica mineral clay powder: activated low-silica mineral clay powder: seed crystal in the crystallization precursor solution is 5:1:1.4 (mass ratio); the pH of the crystallization precursor solution is 12.

[0068] (6) Post-processing: After crystallization, the crystallized mixture is subjected to solid-liquid separation, followed by filtration, washing, and drying to obtain the multi-level porous ZSM-5 product. The relative crystallinity and pore size distribution of the crystallized product are shown in Table 3.

[0069] Example 2

[0070] (1) Preparation of high-silica mineral soil fine powder: Diatomaceous earth (Lingshou County Fengheng Mineral Products Processing Plant, diatomaceous earth powder, chemical composition and silicon-aluminum ratio are shown in Table 1) was fully ball-milled using Juchuang Environmental Protection Vertical Planetary Ball Mill (JC-QM-0.4) (350 rpm, ball milling for 2 hours) to obtain high-silica mineral soil fine powder with an average particle size of 4.2 μm, which was directly used as raw material for subsequent crystallization.

[0071] (2) Preparation of low-silica mineral clay fine powder: Bentonite (Jiushi Mineral Products Processing Plant, Lingshou County, Hebei Province, sodium-based bentonite, chemical composition and silicon-aluminum ratio are shown in Table 1) was fully ball-milled using Juchuang Environmental Protection Vertical Planetary Ball Mill (JC-QM-0.4) (350 rpm, ball milling for 2 hours) to obtain low-silica mineral clay fine powder with an average particle size of 3.4 μm.

[0072] (3) Activation of low-silica mineral soil powder: The low-silica mineral soil powder obtained in step (2) is calcined at 850°C for 4 hours and then cooled to room temperature as a raw material for subsequent crystallization.

[0073] (4) Seed activation: Sodium-type ZSM-5 molecular sieve was used as seed crystal (Nankai Catalyst Factory, Na-type ZSM-5 molecular sieve, chemical composition, silicon-aluminum ratio and relative crystallinity are shown in Table 2). It was fully ball-milled using a Juchuang Environmental Protection vertical planetary ball mill (JC-QM-0.4) (350 rpm, ball milling for 2 hours) to obtain fine seed crystal powder with an average particle size of 1.6 μm. 2.00 g of NaOH was weighed and added to 40.00 g of water to obtain an alkaline solution; 3.00 g of fine seed crystal powder was added to the alkaline solution, and the mixture was heated and stirred at 80 °C for 2 hours to obtain a seed activation solution; in this example, NaOH:water = 1:20 (mass ratio); NaOH:seed crystal = 1:1.5 (mass ratio).

[0074] (5) Multi-level porous molecular sieve crystallization synthesis: Weigh 10.50g of the high-silica mineral clay powder obtained in step 1 and 1.50g of the activated low-silica mineral clay powder obtained in step 3, and add them to the seed activation solution in step (4) to obtain the crystallization precursor solution. The crystallization precursor solution is placed in a crystallization kettle and crystallized at 160℃ for 55h using a dynamic crystallization method. In this embodiment, the ratio of high-silica mineral clay powder: activated low-silica mineral clay powder: seed crystal in the crystallization precursor solution is 7:1:2 (mass ratio); the pH of the crystallization precursor solution is 12.

[0075] (6) Post-processing: After crystallization, the crystallized mixture is subjected to solid-liquid separation, followed by filtration, washing, and drying to obtain a multi-level porous ZSM-5 product. The relative crystallinity and pore distribution of the crystallized product are shown in Table 3.

[0076] Example 3

[0077] (1) Preparation of high-silica mineral soil fine powder: Diatomite (Lingshou County Fengheng Mineral Products Processing Plant, diatomite powder, chemical composition and silicon-aluminum ratio are shown in Table 1) was fully ball-milled using Juchuang Environmental Protection Vertical Planetary Ball Mill (JC-QM-0.4) (250 rpm, ball milling for 4 hours) to obtain high-silica mineral soil fine powder with an average particle size of 6.1 μm, which was directly used as raw material for subsequent crystallization.

[0078] (2) Preparation of low-silica mineral clay fine powder: Montmorillonite (Jushi Mineral Products Processing Plant, Lingshou County, Hebei Province, white montmorillonite, chemical composition and silicon-aluminum ratio are shown in Table 1) was fully ball-milled using Juchuang Environmental Protection Vertical Planetary Ball Mill (JC-QM-0.4) (250 rpm, ball milling for 2 hours) to obtain low-silica mineral clay fine powder with an average particle size of 2.4 μm.

[0079] (3) Activation of low-silica mineral soil powder: The low-silica mineral soil powder obtained in step (2) is calcined at 680°C for 4 hours and then cooled to room temperature as raw material for subsequent crystallization.

[0080] (4) Seed activation: Sodium-type ZSM-5 molecular sieve was used as seed crystal (Nankai Catalyst Factory, Na-type ZSM-5 molecular sieve, chemical composition, silicon-aluminum ratio and relative crystallinity are shown in Table 2). It was fully ball-milled using a Juchuang Environmental Protection vertical planetary ball mill (JC-QM-0.4) (250 rpm, 2 hours) to obtain fine seed crystal powder with an average particle size of 2.8 μm. 2.00 g of NaOH was weighed and added to 50.00 g of water to obtain an alkaline solution; 4.00 g of fine seed crystal powder was added to the alkaline solution and heated and stirred at 75 °C for 2 hours to obtain a seed activation solution; in this example, NaOH:water = 1:25 (mass ratio); NaOH:seed crystal = 1:2 (mass ratio).

[0081] (5) Synthesis of multi-level porous molecular sieve crystallization: Weigh 14.40g of the high-silica mineral clay powder obtained in step 1 and 1.60g of the activated low-silica mineral clay powder obtained in step 3, and add them to the seed activation solution in step (4) to obtain the crystallization precursor solution. The crystallization precursor solution is placed in a crystallization kettle and crystallized at 180℃ for 36h using a dynamic crystallization method. In this embodiment, the ratio of high-silica mineral clay powder: activated low-silica mineral clay powder: seed crystal in the crystallization precursor solution is 9:1:2.5 (mass ratio); the pH of the crystallization precursor solution is 11.

[0082] (6) Post-processing: After crystallization, the crystallized mixture is subjected to solid-liquid separation, followed by filtration, washing, and drying to obtain a multi-level porous ZSM-5 product. The relative crystallinity and pore distribution of the crystallized product are shown in Table 3.

[0083] Example 4

[0084] (1) Preparation of high-silica mineral soil fine powder: Diatomite (Lingshou County Fengheng Mineral Products Processing Plant, diatomite powder, chemical composition and silicon-aluminum ratio are shown in Table 1) was fully ball-milled using Juchuang Environmental Protection Vertical Planetary Ball Mill (JC-QM-0.4) (300 rpm, ball milling for 2 hours) to obtain high-silica mineral soil fine powder with an average particle size of 3.8 μm, which was directly used as raw material for subsequent crystallization.

[0085] (2) Preparation of low-silicon mineral clay fine powder: Kaolin (Lingshou County Anda Mineral Powder Factory, chemical composition and silicon-aluminum ratio are shown in Table 1) was fully ball-milled using Juchuang Environmental Protection Vertical Planetary Ball Mill (JC-QM-0.4) (300 rpm, ball milling for 2 hours) to obtain low-silicon mineral clay fine powder with an average particle size of 2.7 μm.

[0086] (3) Activation of low-silica mineral soil powder: The low-silica mineral soil powder obtained in step (2) is calcined at 850°C for 4 hours and then cooled to room temperature as a raw material for subsequent crystallization.

[0087] (4) Seed activation: Sodium-type ZSM-5 molecular sieve was used as seed crystal (Nankai Catalyst Factory, Na-type ZSM-5 molecular sieve, chemical composition, silicon-aluminum ratio and relative crystallinity are shown in Table 2). It was fully ball-milled using a Juchuang Environmental Protection vertical planetary ball mill (JC-QM-0.4) (300 rpm, ball milling for 2 hours) to obtain fine seed crystal powder with an average particle size of 2.2 μm. 2.00 g of NaOH was weighed and added to 58.00 g of water to obtain an alkaline solution; 4.80 g of fine seed crystal powder was added to the alkaline solution, and the mixture was heated and stirred at 85 °C for 2 hours to obtain a seed activation solution; in this example, NaOH:water = 1:29 (mass ratio); NaOH:seed = 1:2.4 (mass ratio).

[0088] (5) Synthesis of multi-level porous molecular sieve crystallization: Weigh 15.00g of the high-silica mineral clay powder obtained in step 1 and 1.50g of the activated low-silica mineral clay powder obtained in step 3, and add them to the seed activation solution in step (4) to obtain the crystallization precursor solution. The crystallization precursor solution is placed in a crystallization kettle and crystallized at 170℃ for 48h using a dynamic crystallization method. In this embodiment, the ratio of high-silica mineral clay powder: activated low-silica mineral clay powder: seed crystal in the crystallization precursor solution is 10:1:3.2 (mass ratio); the pH of the crystallization precursor solution is 11.

[0089] (6) Post-processing: After crystallization, the crystallized mixture is subjected to solid-liquid separation, followed by filtration, washing, and drying to obtain a multi-level porous ZSM-5 product. The relative crystallinity and pore distribution of the crystallized product are shown in Table 3.

[0090] Comparative Example 1

[0091] Following the material ratio in Example 1, 2.00 g of NaOH, 1.70 g of seed powder, 6.07 g of high-silica mineral clay powder, and 1.21 g of activated low-silica mineral clay powder were added to 32.00 g of water and stirred for 1 hour to obtain a crystallization precursor solution. The ratio of NaOH to water was 1:16 (mass ratio), and the ratio of NaOH to seed powder was 1:0.85 (mass ratio). The mass ratio of high-silica mineral clay powder to activated low-silica mineral clay powder to seed powder in the crystallization precursor solution was 5:1:1.4. The pH value of the crystallization precursor solution was 12, and other conditions were the same as in Example 1.

[0092] Comparative Example 2

[0093] The commercially available ZSM-5 molecular sieve (Tianjin Nanhua Catalyst Co., Ltd., H-type ZSM-5 molecular sieve) has a bulk silicon-to-aluminum ratio (SiO2 / Al2O3 molecular molar ratio) of 60 according to XRF testing, and an XRD test result showing that the molecular sieve has a crystallinity of 91.2%.

[0094] Table 1

[0095]

[0096] Note 1: The SiO2 and Al2O3 contents in the table are XRF test results. The silicon-to-aluminum ratio is the molar ratio of bulk SiO2 / Al2O3 molecules, i.e., n(SiO2) / n(Al2O3).

[0097] Table 2

[0098] <![CDATA[SiO2%]]> <![CDATA[Al2O3%]]> <![CDATA[Silica-alumina ratio 2 > Relative crystallinity % Example 1 93.5 6.21 25.6 91.0 Example 2 96.0 3.69 44.1 86.2 Example 3 98.3 1.26 132.4 90.8 Example 4 94.3 0.82 194 85.5

[0099] Note 1: The SiO2 and Al2O3 contents in the table are XRF test results.

[0100] Note 2: The molar ratio of bulk SiO2 to Al2O3 molecules in the silicon-aluminum ratio is n(SiO2) / n(Al2O3).

[0101] Table 3

[0102]

[0103] Note 1: The bulk silicon-aluminum molecular molar ratio in the table is calculated based on XRF results, i.e., n(SiO2) / n(Al2O3).

[0104] Note 2: The proportion of mesopore volume in the table = mesopore volume / (mesopore volume + micropore volume)

[0105] Note 3: The atomic molar ratio of silicon and aluminum in the table is based on... 29 Si / Al atomic molar ratio calculated from Si NMR results

[0106] Note 4: The crystallinity of the comparative example is low, and the error is large when using the Si NMR peak-separation method, making it impossible to accurately calculate its framework silicon-aluminum atomic molar ratio.

[0107] From scanning electron microscope images ( Figure 1 As can be seen, the average particle size of the crystallized product is 2–5 μm, and each grain surface exposes a large number of ZSM-5 nanoribbons. The accumulation of nanoribbons forms intergranular mesopores, which is beneficial to improving the accessibility of the active sites of solid acid. (Transmission electron microscopy image) Figure 2 The transmission profile of the stacked nanoribbons is visible, and the difference in internal contrast indicates the presence of intracrystalline mesopores. As shown in Table 3, compared to the comparative example, the ZSM-5 molecular sieve provided by this invention has a higher crystallinity. The relative crystallinity of the product in Comparative Example 1 is only 28.2%, and the crystalline component in the product almost entirely comes from the added seed crystals; the natural mineral clay raw material undergoes almost no transformation. Figure 4 As can be seen, the N2 adsorption-desorption curve of the molecular sieve provided by this invention exhibits a type IV H2 hysteresis loop, and simultaneously possesses both microporous and mesoporous structures; Figure 5 It can be seen that the mesopores are widely distributed; the mesopore volume ratio is 40-50%, which indicates that it is a hierarchical porous material.

[0108] The ZSM-5 molecular sieves prepared in Examples 1-4 and Comparative Example 1 were subjected to ammonium exchange treatment to reduce the sodium oxide content to below 0.1% by weight, resulting in hydrogen-form molecular sieves. The ammonium exchange conditions were: molecular sieve: ammonium chloride: H₂O = 1:0.5:10, ammonium exchange temperature 80℃, and reaction time 2 h. After ammonium exchange, the samples were filtered, washed, dried, and calcined at 550℃ for 3 h. The hydrogen-form molecular sieve samples obtained above were evaluated on a fixed-bed microreactor (FB) using industrial naphtha as the feedstock. The evaluation conditions were: reaction temperature 675℃, reactant-to-oil ratio (by weight) 0.6, and oil inlet time 70 seconds. The results are listed in Table 4.

[0109] Table 4

[0110] sample Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Reaction temperature / ℃ 675 675 675 675 675 675 Reaction pressure / MPa 0.1 0.1 0.1 0.1 0.1 0.1 Conversion rate / weight% 62.4 59.5 48.8 41.3 10.8 36.6 propylene yield / weight % 13.5 15.2 12.9 13.9 4.5 8.9

[0111] As shown in Table 1, the ZSM-5 molecular sieve provided by this invention has higher conversion activity, higher naphtha catalytic cracking activity, and higher propylene yield.

Claims

1. A method for preparing ZSM-5 molecular sieves from natural mineral clay, comprising the following steps: (S1) Obtain fine powder of high-silica mineral soil; the average particle size of the fine powder of high-silica mineral soil does not exceed 10 micrometers; the silica content in the high-silica mineral soil is 85-100% by weight and the alumina content is 0-15% by weight. (S2) Obtain activated low-silica mineral soil fine powder, wherein the average particle size of the activated low-silica mineral soil fine powder does not exceed 10 micrometers; the silica content of the low-silica mineral soil is 40-75% by weight and the alumina content is 25-60% by weight; the activated low-silica mineral soil fine powder is obtained by the following method: grinding the low-silica mineral soil to obtain low-silica mineral soil fine powder with an average particle size not exceeding 10 micrometers, calcining to obtain activated low-silica mineral soil fine powder; the calcination temperature is 600-950 ℃, and the calcination time is 2-5 h. (S3) Obtaining seed activation solution: The sodium-type ZSM-5 molecular sieve is ground into fine seed powder, the average particle size of which does not exceed 5 micrometers; the seed powder is treated with hot alkaline solution to obtain seed activation solution; The seed powder is treated with a hot alkaline solution, with a water:NaOH mass ratio of 15~30:1 and a seed powder:NaOH mass ratio of 0.8~2.5:

1. The seed powder is heated and stirred in a sodium hydroxide solution for 1~3 hours at a temperature of 70~90°C. o C; (S4) Synthesis of multi-level porous molecular sieve crystallization: The high-silica mineral powder described in step (S1), the activated low-silica mineral powder described in step (S2), and the seed activation solution described in step (S3) are mixed to obtain a crystallization precursor solution, followed by crystallization; wherein, The mass ratio of high-silica mineral soil fine powder to activated low-silica mineral soil fine powder is (5~10):1; Seed crystals: The mass ratio of activated low-silica mineral clay powder to fine powder is 1.2~3.5:1; The pH value of the crystallization precursor solution is 10~13; (S5) Recover ZSM-5 molecular sieve; The ZSM-5 molecular sieve has a mesopore volume accounting for 40-50% of the total volume of micropores and mesopores, and a framework silicon-to-aluminum ratio of 30-130, which is a Si / Al molar ratio.

2. The method according to claim 1, characterized in that, The pH value of the crystallization precursor solution is 11-13.

3. The method according to any one of claims 1 to 2, characterized in that, The high-silica mineral soil contains 85-99% by weight of silicon oxide and 1-15% by weight of aluminum oxide; the low-silica mineral soil is one or more of bentonite, rettoitite, kaolinite, and montmorillonite; the high-silica mineral soil is diatomite.

4. The method according to claim 1, characterized in that, The treatment of the seed crystal powder with hot alkaline solution includes: heating and stirring the seed crystal powder in a sodium hydroxide solution for 2 hours.

5. The method according to claim 1 or 3, characterized in that, The seed powder is treated with a hot alkaline solution: Water:NaOH = 16~29:1 mass ratio; Seed powder: NaOH = 0.85~2.4:1 mass ratio; The processing temperature is 75~85℃. o C.

6. The method according to claim 1, characterized in that, The sodium-type ZSM-5 molecular sieve has a relative crystallinity of 85~100% and a bulk silicon-aluminum ratio of 20~200 (SiO2 / Al2O3 molar ratio).

7. The method according to claim 1 or 6, characterized in that, The average particle size of the sodium-type ZSM-5 molecular sieve is 0.5~5 micrometers.

8. The method according to claim 1, characterized in that, Crystallization temperature is 150~190℃ o C, crystallization time is 12~60h; crystallization is carried out by dynamic crystallization method.

9. The method according to claim 1, characterized in that, The average particle size of the high-silica mineral soil fine powder is 0.5-8 micrometers, the average particle size of the activated low-silica mineral soil fine powder is 0.5-5 micrometers, and the average particle size of the seed crystal fine powder is 1-3 micrometers.

10. A hierarchical porous ZSM-5 molecular sieve, characterized in that, The ZSM-5 molecular sieve particles have ZSM-5 nanoribs exposed on their surface, and the average particle size of the molecular sieve particles is 2~5 μm. They exhibit intercrystalline mesopores, with the mesopore volume accounting for 40~50% of the total volume of micropores and mesopores. The framework silicon-aluminum ratio is 30~130, which is a Si / Al molar ratio. The hierarchical porous ZSM-5 molecular sieve is prepared by the method described in any one of claims 1 to 9.

11. The hierarchical porous ZSM-5 molecular sieve according to claim 10, characterized in that, It has all of the following characteristics: (1) relative crystallinity exceeds 90%; (2) obvious hysteresis loop is shown in the N2 adsorption and desorption curves.

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