A method for preparing a hierarchical porous molecular sieve

Abstract

A method for preparing a hierarchical porous molecular sieve, belonging to the field of molecular sieves, is disclosed. The method involves first preparing a gel and then hydrothermally crystallizing the nano-molecular sieve. At the end of the molecular sieve crystallization, an inorganic alkali solution is pressurized with nitrogen under stirring and injected into a crystallization vessel containing the crystallized material, ensuring sufficient contact and reaction between the inorganic alkali and the molecular sieve. After the reaction between the inorganic alkali and the crystallized material is complete, the product is collected. This invention introduces a fully silica-based precursor molecular sieve as a seed crystal during the molecular sieve crystallization process to guide the crystallization. At the end of crystallization, an inorganic alkali is added to dissolve and remove the fully silica-based seed crystal, resulting in a hierarchical porous nano-molecular sieve with mesoporous structures. The obtained molecular sieve product has a uniform mesopore distribution, a large specific surface area, and is easy to filter.

Description

Technical Field

[0001] This application relates to a method for preparing a multi-level porous molecular sieve, belonging to the technical field of molecular sieve preparation. Background Technology

[0002] Zeolite molecular sieves are among the most important components of inorganic microporous materials. They are crystalline materials capable of sieving substances at the molecular level, with a framework composed of a multidimensional four-dimensional interconnected structure formed by shared vertices between TO4 tetrahedra, where T represents Si, Al, or other heteroatoms. Due to their regular pore structure, unique ion exchange capacity, shape-selective adsorption, easily tunable composition and properties, and high activity and selectivity in numerous small molecule catalytic reactions, zeolite molecular sieves are widely used in many fields, including industrial processes and high-tech materials, particularly in catalysis, adsorption, and ion exchange research in petroleum processing, petrochemicals, fine chemicals, and daily chemical products. Among them, the MFI family of zeolite molecular sieves, represented by ZSM-5 and TS-1, and the BEA family, represented by Beta, have become very important catalytic materials due to their unique pore structure and excellent catalytic performance.

[0003] (1) ZSM-5 zeolite (USP 3702886), invented by Mobil Petroleum Corporation of the United States, has become a very important shape-selective catalytic material due to its unique pore structure and good catalytic performance. Well-known processes developed using ZSM-5 zeolite include: Mobil Middle Distillate Dewaxing (MDDW), Lubricating Oil Dewaxing (MLDW), Catalytic Reforming, Selective Reforming and M-Reformation of Gasoline, Cyclar Process (LPG BTX) for synthesizing aromatics from light hydrocarbons, Mobil-Badger Ethylbenzene Synthesis Process, Toluene Gasification Process (MTDP), Xylene Isomerization Process (MVPI), Methanol to Gasoline Process (MTG), and P-toluene Synthesis Process (PET).

[0004] (2) Titanium silicate molecular sieve TS-1 (GB2071071A, USP4410501) is a novel catalytic material in which Ti atoms replace Al atoms in ZSM-5, thus possessing selective oxidation active centers and the shape-selective catalytic properties of ZSM-5. TS-1 plays an irreplaceable catalytic role in a series of low-temperature selective oxidation reactions involving dilute hydrogen peroxide, such as propylene epoxidation and phenol hydroxylation. It is particularly noteworthy that the application of TS-1 in propylene epoxidation is expected to completely eliminate the polluting production mode of existing processes, and has enormous industrial application potential.

[0005] (3) Beta zeolite (US 3308069) is a high-silica zeolite with a three-dimensional twelve-membered ring cross-channel structure. Due to its unique structure and good thermal and hydrothermal stability, it is used as a catalyst in petroleum refining and petrochemical processes such as hydrocracking, hydroisomerization, dewaxing, aromatic alkylation and olefin hydration. It is an important industrial zeolite molecular sieve.

[0006] These types of zeolite catalytic materials belong to microporous zeolites, with small pore sizes. Large molecules face significant diffusion resistance within the zeolite pores, thus limiting their application in macromolecular catalytic reactions. Currently, there are two main methods to address this issue: one is to introduce mesoporous structures into the zeolite microporous structure or crystallize the pore walls of mesoporous materials into micropores, forming transport channels conducive to the diffusion of macromolecular compounds; the other method is to synthesize ultrafine molecular sieves with nanoscale dimensions. Materials with zeolite-mesoporous-microporous composite structures can improve the diffusion performance of products, compensating for the shortcomings of microporous molecular sieves and providing favorable spatial configurations for macromolecular reactions. However, problems such as weak acidity and relatively low hydrothermal stability persist. Furthermore, reducing the crystal particle size of molecular sieves from the micrometer scale to the nanometer scale alters their mass transfer, adsorption, and catalytic properties. Compared with micron-sized zeolites, nano-zeolites have a larger external surface area and a higher intracrystalline diffusion rate, shorter pores, and a large number of intercrystalline pores. They exhibit superior performance in improving catalyst utilization, enhancing macromolecular conversion ability, reducing deep reaction, and improving selectivity. They also show better activity, selectivity, and strong resistance to coking and deactivation in some hydrocarbon catalytic conversion reactions.

[0007] Chinese Patent Application No. 02155482.X (2002-12-16) discloses a method for rapidly synthesizing strong acid-type ZSM-5 zeolite molecular sieves. Its technical features include: preparing a directing agent by mixing a silicon source with a template agent, an aluminum source, an inorganic acid, and deionized water in a certain proportion; then preparing a crystallization mother liquor by mixing the silicon source with the template agent, aluminum source, inorganic acid, and deionized water in a certain proportion; and adding 5-10% of the directing agent by volume to the mother liquor. The resulting gel is then subjected to hydrothermal crystallization to obtain small-grained ZSM-5 zeolite with crystals of approximately 100 nm. This method also utilizes a directing agent to synthesize small-grained zeolite molecular sieves.

[0008] European Patent EP 19850110256 (August 16, 1985) discloses a method for synthesizing ZSM-5. Its technical feature is that a raw material mixture is pretreated at 80°C for 6 hours, and then the pretreated material is mixed with a freshly prepared raw material mixture at a ratio of 15% and subjected to hydrothermal crystallization at 175°C for 8 hours to obtain ZSM-5 zeolite molecular sieves with a silicon-to-aluminum ratio of 60 and a grain size of approximately 100–300 nm. This method also utilizes a directing agent to synthesize small-grained zeolite molecular sieves.

[0009] Patent CN112875721A discloses a method for rapidly preparing macroscopic mesoporous ZSM-5 molecular sieves. This method involves thoroughly mixing a dilute solution containing ZSM-5 seed crystals with starch or cyclodextrin, an aluminum source, a silicon source, and a template agent to form a slurry. This slurry is then extruded to form sheets or strips. The sheets or strips are placed in a wheel-drawer container and treated under a high-temperature, high-pressure steam atmosphere to convert both the silicon and aluminum sources into ZSM-5 macroscopic particles. Finally, the mixture is calcined under an oxygen-containing gas atmosphere to produce the mesoporous ZSM-5 macroscopic particles.

[0010] Patent CN110028080A discloses a method for rapidly synthesizing highly crystalline mesoporous ZSM-5 molecular sieves via crystallization, including precursor preparation, crystallization, filtration, drying, and calcination. Two crystallization methods are used. Method one involves preparing the precursor using a dry gel conversion method and crystallizing it using the self-generated pressure of ethanol. Method two involves heating the precursor in a sealed container with saturated steam for crystallization. The temperature of the saturated steam for crystallization is 160–180°C, and the crystallization time is 1–6 hours. During the crystallization process, a silicon source and a template agent are added to the precursor at a mass ratio of 1:(0.01–0.5), and the initial mass ratio of the precursor to the silicon source is 2–15%.

[0011] The above preparation method is complex to operate, and the final product quality is not high. Summary of the Invention

[0012] The purpose of this invention is to provide a method for preparing a multi-level porous nano-molecular sieve. By using an all-silica precursor nano-molecular sieve as a seed crystal, the nano-molecular sieve crystals are synthesized during the crystallization process. After crystallization, an inorganic alkaline solution is added to dissolve the precursor crystal seed crystal. The resulting ZSM-5 molecular sieve crystals are small in size and contain a large number of mesoporous structures with uniform mesopores.

[0013] According to one aspect of this application, a method for preparing a nanomolecular sieve with hierarchical pores is provided.

[0014] The technical solution of the present invention is as follows: A method for preparing a multi-level porous nanomolecular sieve, comprising the following steps:

[0015] (1) Prepare a gel according to the MFI family molecular sieve or the BEA family molecular sieve, and add the corresponding crystalline all-silicon molecular sieve as seed crystals to the gel, and perform hydrothermal crystallization of the nano molecular sieve; the total weight of the seed crystals accounts for 4%-6% of the total weight of SiO2 in the gel.

[0016] The all-silica precursor nanocrystalline molecular sieve is synthesized using a system with the same formulation as the target molecular sieve synthesis gel, without introducing an aluminum source. After aging at room temperature to 50°C for a certain period, amorphous primary structural units with strong structure-directing properties are obtained and used for the synthesis of the target molecular sieve.

[0017] (2) After the molecular sieve crystallization is completed, an inorganic alkali solution is added to the crystallization vessel and stirred evenly to allow the inorganic alkali to react fully with the molecular sieve; the molar ratio of the inorganic alkali R to SiO2 is R / SiO2 = 0.01-2, and the reaction time is no more than 48 hours; after the inorganic alkali reacts with the crystals, the product is collected.

[0018] After the molecular sieve crystallization is completed, an inorganic alkali solution is pressurized with nitrogen under stirring and injected into a crystallization vessel containing the crystals. The mixture is stirred evenly to ensure that the inorganic alkali reacts fully with the molecular sieve. The molar ratio of the inorganic alkali R to SiO2 is R / SiO2 = 0.01 to 2, and the reaction time is no more than 48 hours. After the inorganic alkali reacts with the crystals, the product is collected.

[0019] Furthermore, the preparation method of the multi-level porous nanomolecular sieve includes the following steps:

[0020] Step 1: Preparation of synthetic gel

[0021] Engineers skilled in the art can formulate gels for synthesizing small crystallites or nanomolecular sieves using techniques reported in existing literature and patents. The silicon source is selected from at least one of silica sol, tetraethyl orthosilicate, sodium silicate, and silica. The aluminum source is selected from at least one of aluminum isopropoxide, boehmite, sodium aluminate, aluminum nitrate, and aluminum sulfate. The template agent is selected from at least one of tetramethylammonium hydroxide, tetramethylammonium bromide, tetrapropylammonium hydroxide, tetrapropylammonium bromide, tetraethylammonium hydroxide, and tetraethylammonium bromide.

[0022] The required gels can be prepared according to the methods described in the following literature: ZL200510200328.9, ZL01145256.0, ZL00107486.5, ZL200710064979.9, ZL200810204229.1, ZL200510025147.7, Micropor.Mesopor.Mater, 57(2003)83-92, Catalysis today, 158(2010)510-514, Journal of Nankai University (Natural Science Edition), 39(2006)4. As an example, according to Example 1 of patent ZL200510200328.9, small-crystal ZSM-5 was prepared: 8.6 grams of industrial aluminum sulfate were weighed and dissolved in 230 grams of deionized water. Then, 28 grams of sulfuric acid were added to adjust the alkalinity of the solution. 10 grams of sodium chloride were added and stirred continuously until completely dissolved. Then, 1.5 grams of isopropanol were added to form solution A. 517 grams of water glass were diluted with 100 grams of deionized water, and then 2.5 grams of all-silicon spore molecular sieve seed crystals were added. During the addition process, mechanical stirring was continuously carried out. After slowly adding n-butylamine, solution B was formed. Under continuous stirring, solution B was slowly added to solution A, and then emulsified in an emulsifier for 15 minutes. The reaction mixture was then loaded into a reaction vessel and stirred and crystallized at 100°C for 24 hours. Then, the temperature was raised to 170°C and crystallized for another 24 hours.

[0023] Step 2: Add an inorganic alkali solution to the crystallization system when the gel crystallization is complete.

[0024] At the end of molecular sieve crystallization, an inorganic alkali solution is pressurized with nitrogen under stirring and injected into a crystallization vessel containing the crystals, ensuring sufficient contact and reaction between the inorganic alkali and the molecular sieve. The term "end of molecular sieve crystallization" refers to the crystallization completion time determined by examining the molecular sieve's crystallization curve; this operation can be performed by engineers skilled in the art. The selected inorganic alkali can be any one of sodium hydroxide and potassium hydroxide, or any mixture thereof. The amount of inorganic alkali (R) added is R / SiO2 = 0.01–2 (molar ratio). The reaction time is 0–48 h, preferably 2–10 h. The reaction temperature is room temperature to 200 °C, preferably 100–160 °C. Applicable molecular sieves include MFI and Beta molecular sieves.

[0025] Step 3: Collect Products

[0026] After the inorganic alkali reacts with the crystals, the product is collected using conventional methods. For example, solid-liquid separation is performed using plate and frame filtration, the product is washed with deionized water until the pH reaches 8-9, then dried at 110°C for 24 hours, and calcined at 540°C for 6 hours to obtain a multi-level porous nano-zeolite molecular sieve product.

[0027] The beneficial effects of this invention are as follows: Adding a seed crystal of pre-crystallized all-silica molecular sieve during the crystallization process can rapidly guide the formation of the nano-molecular sieve. By adding an inorganic alkali in the later stages of molecular sieve crystallization, the seed crystal of all-silica molecular sieve can be effectively removed, resulting in a hierarchical porous nano-molecular sieve with a mesoporous structure. The resulting molecular sieve product exhibits good dispersibility, a large external specific surface area, and is easy to filter. Furthermore, our research shows that the seed crystal of all-silica molecular sieve possesses a strong structure-directing ability, forming a large number of crystal nuclei while inhibiting crystal transformation in the system. The molecular sieve prepared using this method has a large number of catalytically active centers exposed on its outer surface, which is beneficial for preparing high-performance catalysts. Attached Figure Description

[0028] Figure 1 These are infrared spectra of all-silicon rudimentary crystals aged at different temperatures. Detailed Implementation

[0029] The present invention will be further illustrated by the following embodiments, but the present invention is not limited to these embodiments.

[0030] Comparative Example 1

[0031] The all-silica ZSM-5 molecular sieve seed crystals were prepared using the same system as the ZSM-5 molecular sieve synthesis gel, without introducing an aluminum source. Aging at room temperature -50℃ for 6 hours yielded amorphous primary structural units with strong structure-directing properties. These were then used for the synthesis of the target molecular sieve. The degree of aging was determined using infrared spectroscopy, such as... Figure 1 As shown.

[0032] According to patent ZL200510200328.9, a typical formulation was selected for the synthesis of ZSM-5 molecular sieves. Specifically, water glass (SiO2), water, sulfuric acid, aluminum sulfate (Al2O3), isopropanol (IPA), and n-butylamine (NBA) were mixed in a molar ratio of SiO2 / Al2O3 = 178, OH... - A homogeneous gel was prepared with SiO2 = 0.58, NBA / SiO2 = 0.40, IPA / SiO2 = 0.01, and H2O / SiO2 = 15. Then, 5% of the total weight of the SiO2 in the gel was added to the gel with rudimentary all-silicon ZSM-5 molecular sieve seed crystals (the rudimentary all-silicon ZSM-5 molecular sieve seed crystals were obtained by aging at 50°C for 6 hours).

[0033] The gel was placed in a crystallization vessel and aged at 100℃ for 24 hours with stirring, then the temperature was raised to 170℃ for another 24 hours of crystallization. After crystallization, the pressure reducing valve was opened to allow some of the water, vaporizable isopropanol, and n-butylamine in the crystallization liquid to be recovered by condensation. The recovered liquid could be used for the next synthesis of ZSM-5 molecular sieve. The obtained solid product was washed with deionized water to pH 8-9, dried at 110℃ for 24 hours, and calcined at 540℃ for 6 hours to obtain pure ZSM-5 molecular sieve. The relative crystallinity of the product was 100%. SEM characterization showed that the product was a highly aggregated nano-zeolite. N2 physical adsorption characterization showed that its BET external surface area was 86 m². 2 / g, product filtration is slow.

[0034] Comparative Example 2

[0035] Following the report in Catalysis Today, 158(2010) 510-514, a typical formulation was selected for the synthesis of TS-1 molecular sieves. Specifically, tetrabutyl orthosilicate (TEOS), water, tetrabutyl titanate (TBOT), ethanol (EtOH), isopropanol (IPA), and tetrapropylammonium hydroxide (TPAOH) were mixed in molar ratios of SiO2 / TiO2 = 30.0, H2O / SiO2 = 20.0, and TPA... + A homogeneous gel was prepared using a SiO2 / IPA ratio of 0.20 and a TiO2 / IPA ratio of 1.5. Then, 5% by weight of a precursor all-silica S-1 molecular sieve seed crystal was added to the gel. The precursor all-silica S-1 molecular sieve seed crystal was obtained by using a system with the same formulation as the target molecular sieve synthesis gel, without introducing an aluminum source, and aging at 50°C for 6 hours.

[0036] After removing alcohol from the gel at 70℃ for 4 hours, an equal volume of water was added, and the mixture was stirred for 1 hour. The mixture was then transferred to a crystallization vessel and dynamically crystallized at 165℃ for 30 hours. After crystallization, the pressure reducing valve was opened to allow some of the water, vaporizable ethanol, and isopropanol in the crystallization liquid to be recovered via condensation. The recovered liquid can be used for the next synthesis of TS-1 molecular sieves. The resulting solid product was washed with deionized water to pH 8-9, dried at 110℃ for 24 hours, and calcined at 540℃ for 6 hours to obtain pure TS-1 molecular sieves. The relative crystallinity of the product was 100%. SEM characterization showed that the product morphology consisted of aggregated spheres of approximately 100-200 nm. N2 physical adsorption characterization showed that its BET external surface area was 92 m². 2 / g, the product cannot be filtered and is collected by centrifugation.

[0037] Comparative Example 3

[0038] According to the published patent ZL00107486.5, a typical formulation was selected for the synthesis of Beta molecular sieves. Specifically, coarse-porous silica gel, water, sodium hydroxide, boehmite, vacuum pump oil, and tetraethylammonium hydroxide (TEAOH) were prepared into a homogeneous gel with the following molar ratios: SiO2 / Al2O3 = 30, Na2O / SiO2 = 0.075, TEAOH / SiO2 = 0.09, H2O / SiO2 = 6.5, and vacuum pump oil / SiO2 = 0.5. Then, 5% by weight of nascent all-silica Beta molecular sieve seed crystals were added to the gel. The nascent all-silica Beta molecular sieve seed crystals were obtained using the same formulation as the target molecular sieve synthesis gel, without introducing an aluminum source, and aged at 50°C for 6 hours.

[0039] After mechanically stirring the reaction gel for 1 hour, it was transferred to a crystallization vessel and crystallized at 120℃ for 24 hours, followed by further crystallization at 148℃ for 48 hours. After crystallization, the pressure reducing valve was opened to vaporize some of the water in the crystallization liquid, which was then condensed and discharged. The resulting solid product was washed with deionized water to pH 8–9, dried at 110℃ for 24 hours, and calcined at 540℃ for 6 hours to obtain pure Beta molecular sieve. The relative crystallinity of the product was 100%. SEM characterization showed that the product was a highly aggregated nano-zeolite. N2 physical adsorption characterization showed that its BET external specific surface area was 128 m². 2 / g, product filtration is slow.

[0040] Example 1

[0041] Comparative Example 1 was repeated, with water glass (SiO2), water, sulfuric acid, aluminum sulfate (Al2O3), isopropanol (IPA), and n-butylamine (NBA) mixed in a molar ratio of SiO2 / Al2O3 = 178, OH - A homogeneous gel was prepared with SiO2 = 0.58, NBA / SiO2 = 0.40, IPA / SiO2 = 0.01, and H2O / SiO2 = 15. A seed crystal of pre-crystal all-silica ZSM-5 molecular sieve, accounting for 5% of the total weight of SiO2, was added to the gel. The seed crystal of pre-crystal all-silica ZSM-5 molecular sieve was prepared using the same system as the target molecular sieve synthesis gel, without introducing an aluminum source. The gel was aged at 50°C for 6 hours.

[0042] The gel was placed in a crystallization vessel and aged at 100℃ for 24 hours with stirring, then the temperature was raised to 170℃ for another 24 hours. When the crystallization time of the zeolite molecular sieve reached 24 hours, NaOH solution (based on a molar ratio R / SiO2 = 0.25) was pressurized into the crystallization vessel containing the crystallized material under nitrogen pressure, stirred evenly, and reacted at 170℃ for another 5 hours. The resulting slurry was filtered through a plate and frame filter, washed, dried, and calcined to obtain pure ZSM-5 molecular sieve. The relative crystallinity of the product was 90.0%, and SEM characterization showed that the product was dispersed nano-zeolite. N2 physical adsorption characterization showed that its BET external surface area was 156 m². 2 / g, and the product filtration speed is 20 times that of Comparative Example 1.

[0043] Example 2

[0044] Repeating step 1, but replacing NaOH with the same molar amount of KOH each time, yielded products that, according to X-ray diffraction analysis, were all pure ZSM-5 molecular sieves with a relative crystallinity of 90%. SEM characterization showed the products to be dispersed nano-zeolites. N2 physisorption characterization revealed their BET external surface areas to be 136 m² / s. 2 / g, and the product filtration speed is 20 times that of Comparative Example 1.

[0045] Example 3

[0046] Repeat Example 1. When the crystallization time of the zeolite molecular sieve reached 24 hours, heating was stopped, and circulating water was turned on to cool the reaction material. After the temperature dropped to 50°C, NaOH solution was injected into the reactor containing the crystallized material liquid, stirred evenly, and reacted at 50°C for 6 hours. The resulting solid product was filtered through a plate and frame filter, washed, dried, and calcined to obtain pure ZSM-5 molecular sieve. The relative crystallinity of the product was 95.0%. SEM characterization showed that the product was dispersed nano-zeolite. N2 physical adsorption characterization showed that its BET external surface area was 166 m². 2 / g, and the product filtration speed is 20 times that of Comparative Example 1.

[0047] Example 4

[0048] Comparative Example 2 was repeated, with tetrabutyl orthosilicate (TEOS), water, tetrabutyl titanate (TBOT), ethanol (EtOH), isopropanol (IPA), and tetrapropylammonium hydroxide (TPAOH) mixed in molar ratios of SiO2 / TiO2 = 30.0, H2O / SiO2 = 20.0, and TPA = 10.0. + A homogeneous gel was prepared with SiO2 = 0.20 and IPA / TiO2 = 1.5. Then, 5% by weight of a precursor all-silica S-1 molecular sieve seed crystal was added to the gel. The precursor all-silica S-1 molecular sieve seed crystal was obtained by using the same system as the target molecular sieve synthesis gel, without introducing an aluminum source, and aging at 50°C for 6 hours.

[0049] After removing alcohol from the gel at 70℃ for 4 hours, an equal volume of water was added, and the mixture was stirred for 1 hour. The mixture was then transferred to a crystallization vessel and dynamically crystallized at 165℃ for 30 hours. When the zeolite molecular sieve crystallization time reached 30 hours, NaOH solution (based on a molar R / SiO2 ratio of 0.25) was pressurized into the crystallization vessel containing the crystals under nitrogen pressure. The mixture was stirred thoroughly and reacted at 165℃ for another 5 hours. The resulting slurry was filtered through a plate and frame filter, washed, dried, and calcined to obtain pure TS-1 molecular sieve. The relative crystallinity of the product was 90%. SEM characterization showed that the product morphology consisted of small spheres approximately 100-200 nm in size. N2 physical adsorption characterization showed that its BET external surface area was 185.0 m². 2 / g, and the product can be collected using plate and frame filtration.

[0050] Example 5

[0051] Example 4 was repeated, but with the same molar amount of KOH instead of NaOH. X-ray diffraction analysis confirmed that the resulting products were all pure TS-1 molecular sieves with a relative crystallinity of 90%. SEM characterization showed that the products were small spheres of approximately 100-200 nm in morphology. N2 physisorption characterization showed that their BET external surface area was 167 m² / s. 2 / g, and the product can be collected using plate and frame filtration.

[0052] Example 6

[0053] Comparative Example 3 was repeated, with coarse-pore silica gel, water, sodium hydroxide, pseudoboehmite, vacuum pump oil, and tetraethylammonium hydroxide (TEAOH) in molar ratios of SiO2 / Al2O3 = 30, Na2O / SiO2 = 0.075, TEAOH / SiO2 = 0.09, H2O / SiO2 = 6.5, and vacuum pump oil / SiO2 = 0.5, to prepare a homogeneous gel. Then, 5% by weight of the total SiO2 of the gel was added to the pre-crystal all-silica Beta molecular sieve seed crystals. The pre-crystal all-silica S-1 molecular sieve seed crystals were obtained using the same system as the target molecular sieve synthesis gel, without introducing an aluminum source, and aged at 50°C for 6 hours.

[0054] After mechanically stirring the reaction gel for 1 hour, it was transferred to a crystallization vessel and crystallized at 120℃ for 24 hours, followed by further crystallization at 148℃ for 48 hours. When the crystallization time of the zeolite molecular sieve reached 48 hours, NaOH solution (based on a molar ratio R / SiO2 = 0.25) was pressurized into the crystallization vessel containing the crystallized material under nitrogen pressure, stirred evenly, and reacted again at 148℃ for 5 hours. The resulting slurry was filtered through a plate and frame filter, washed, dried, and calcined to obtain pure Beta molecular sieve. The relative crystallinity of the product was 90%, and SEM characterization showed that the product was dispersed nano-zeolite. N2 physical adsorption characterization showed that its BET external surface area was 182 m².2 / g, and the product filtration speed is 20 times that of Comparative Example 3.

[0055] Example 7

[0056] Example 6 was repeated, but with the same molar amount of KOH instead of NaOH. X-ray diffraction analysis confirmed that the resulting products were all pure Beta molecular sieves with a relative crystallinity of 88%. SEM characterization showed that the products were dispersed nano-zeolites. N2 physisorption characterization revealed that their BET external surface areas were 152 m² / s. 2 / g, and the product filtration speed is 20 times that of Comparative Example 3.

[0057] Example 8

[0058] Example 6 was repeated, but with the NaOH solution having a molar ratio R / SiO2 = 0.5. X-ray diffraction analysis confirmed that the obtained products were all pure Beta molecular sieves with a relative crystallinity of 90%. SEM characterization showed that the products were dispersed nano-zeolites. N2 physisorption characterization showed that their BET external surface areas were 195 m² / s. 2 / g, and the product filtration speed is 20 times that of Comparative Example 3.

[0059] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for preparing a nanomolecular sieve having a plurality of levels of pores, characterized by, Includes the following steps: (1) Prepare a gel according to the MFI family molecular sieve or the BEA family molecular sieve, and add the corresponding crystalline all-silica molecular sieve as seed crystals to the gel, and perform hydrothermal crystallization of the nano molecular sieve; the total weight of the seed crystals accounts for 4%-6% of the total weight of SiO2 in the gel. The nascent all-silica molecular sieve is synthesized using the same system as the target molecular sieve gel with no aluminum source introduced; it is aged at room temperature to 50°C for 4-6 hours to obtain an amorphous primary structural unit with strong structure guiding effect. (2) After the molecular sieve crystallization is completed, the inorganic alkali solution is pressed into the crystallization vessel containing the crystallized material under nitrogen pressure while stirring. The mixture is stirred evenly to allow the inorganic alkali to fully react with the molecular sieve. The molar ratio of the inorganic alkali R to SiO2 is R / SiO2 = 0.01~2, and the reaction time is no more than 48 h. After the inorganic alkali reacts with the crystallized material, the product is collected.

2. The production method according to claim 1, characterized by, The inorganic base is sodium hydroxide and / or potassium hydroxide.

3. The production method according to claim 1, characterized by, The reaction temperature after adding the inorganic base is room temperature to 200℃.

4. The method of claim 1, wherein, The conditions for hydrothermal crystallization are: a temperature of 100~200℃ and a time of 8~96h.

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