A multi-level pore pure silicon molecular sieve, a preparation method thereof and a cyclohexanone oxime catalytic reaction method

Abstract

The present disclosure relates to a kind of multi-level hole pure silicon molecular sieve and its preparation method and cyclohexanone oxime catalytic reaction method.The multi-level hole pure silicon molecular sieve has the following diffusion coefficient characteristics: with cyclohexane as probe molecule, the diffusion coefficient of the probe molecule in the multi-level hole pure silicon molecular sieve is 0.015-0.02 μm 2 / min, measured by zero-length column method.The present disclosure can effectively improve the molecular diffusion performance of molecular sieve, and when the molecular sieve is used for cyclohexanone oxime gas phase Beckmann rearrangement reaction, the selectivity of caprolactam and the service life of catalyst can be effectively improved.

Description

Technical Field

[0001] This disclosure relates to the field of all-silica molecular sieve preparation, specifically to a hierarchical porous pure silica molecular sieve and its preparation method and a cyclohexanone oxime catalytic reaction method. Background Technology

[0002] The caprolactam industry began in the 1940s. By the 1960s, caprolactam production capacity reached 200,000 tons per year. With the expansion of the synthetic fiber market, production capacity rapidly increased to 3 million tons per year by the end of the 1970s. In the 1980s and 1990s, with the rise of the economies of Asia, especially China, India, and South Korea, caprolactam production facilities were introduced, further expanding production capacity. By the beginning of the 21st century, caprolactam production capacity had reached 4.16 million tons per year.

[0003] In recent years, with the further development of the automotive and electronics industries, global caprolactam production capacity has steadily increased. In 2012, global caprolactam production capacity was 4.91 million tons per year; in 2015, it was 6.6 million tons per year; and in 2019, it reached 7.69 million tons per year. This growth was mainly driven by the release of production capacity in China. Currently, over 90% of CPL is prepared using the cyclohexanone oxime (CHO) liquid-phase Beckmann rearrangement reaction, using concentrated sulfuric acid (or fuming sulfuric acid) as both catalyst and solvent. This process presents serious problems such as equipment corrosion and environmental pollution. After the reaction, liquid ammonia is used to neutralize the waste sulfuric acid, generating a large amount of low-value ammonium sulfate byproduct (1.9 tons of ammonium sulfate / ton of CPL), resulting in poor techno-economic performance for this route.

[0004] Therefore, the CHO gas-phase Beckmann rearrangement process based on heterogeneous catalysts has received high attention from academia and industry. Compared with the traditional liquid-phase method, this process avoids the use of ammonia and fuming sulfuric acid at the source, achieving 100% atom utilization and making it an environmentally friendly green production process for CPL. However, the CHO gas-phase Beckmann rearrangement route suffers from two major challenges: poor product CPL selectivity and short catalyst single-pass lifetime. These issues affect the techno-economic efficiency and operational stability, resulting in extremely slow progress in subsequent large-scale industrial scale-up and commercialization. This is because the micropore size of the MFI structure is small, close to the size of reactant and product molecules, leading to slow diffusion of guest molecules within the molecular sieve-confined pores and a significantly prolonged residence time within the crystals. This, in turn, exacerbates the formation of byproducts and the blockage of pores by carbon deposits.

[0005] Therefore, researchers have attempted to improve the diffusion properties of molecular sieves by constructing hierarchical porous structures, thereby enhancing reaction selectivity and lifetime. Ferdi Schüth's group synthesized a hierarchical porous Silicalite-1 molecular sieve by adding a 1,7-dichlorooctamethyltetraoxysilane oxidizing agent during the crystallization process of the molecular sieve to create pores. This molecular sieve maintained a product yield of 1.6 mmol CPL g after 30 h. -1 cat h -1 Chao Ge et al. synthesized a hierarchical porous Silicalite-1 molecular sieve with orthographic stacking of layers by adjusting the alkyl chain length in the bisquaternary ammonium salt template agent. The conversion rate of the molecular sieve remained above 80% and the selectivity remained at around 92.5% after 84 hours of reaction.

[0006] However, when the synthesized hierarchical porous Silicalite-1 molecular sieve was used for the gas-phase Beckmann rearrangement of cyclohexanone oxime, the improvement in diffusion performance, caprolactam selectivity and catalyst lifetime was not ideal. Summary of the Invention

[0007] The purpose of this disclosure is to provide a hierarchical porous pure silica molecular sieve and its preparation method, as well as a cyclohexanone oxime catalytic reaction method, which can effectively improve the molecular diffusion performance of the molecular sieve. When this molecular sieve is used in the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime, it can effectively improve the selectivity of caprolactam and the catalyst lifetime.

[0008] To achieve the above objectives, the first aspect of this disclosure provides a hierarchical porous pure silica molecular sieve, which has the following diffusion coefficient characteristics: using cyclohexane as a probe molecule, the diffusion coefficient of the probe molecule in the hierarchical porous pure silica molecular sieve, measured by the zero-length column method, is 0.015–0.020 μm. 2 Any value between / min.

[0009] Optionally, the hierarchical porous pure silica molecular sieve has the following characteristics: 31 P-TMPO MAS NMR characteristics:

[0010] The peak intensity of the characteristic peak at a chemical shift of 48–50 ppm of the multi-level porous pure silica molecular sieve is denoted as N1, and the peak intensity of the characteristic peak at a chemical shift of 28–32 ppm is denoted as N2. X1 is defined as below 8% as in the following formula (1):

[0011] X1 = N2 / N1 × 100% Equation (1);

[0012] Preferably, X1 is any value between 2% and 8%; more preferably, it is any value between 4% and 6%.

[0013] Optionally, the hierarchical porous pure silica molecular sieve has the following characteristics:29 Si MAS NMR characteristics:

[0014] The peak area of ​​the chemical shift of the hierarchical porous pure silica molecular sieve in the range of -102 to -104 ppm is denoted as Q. 3 The peak area of ​​the spectral peak with a chemical shift in the range of -112 to -114 ppm is denoted as Q. 4 As defined in equation (2), X2 is any value between 5% and 15%.

[0015] X2 = Q 3 / Q 4 ×100% Equation (2);

[0016] Preferably, X2 is any value between 8% and 12%.

[0017] Optionally, the hierarchical porous pure silica molecular sieve has the following FT-IR characteristics:

[0018] The FT-IR spectrum of the microporous pure silica molecular sieve is shown in the range of 3200–3800 cm⁻¹. -1 In the peak fractionation results within the wavenumber range: the wavenumber of the hierarchical porous pure silica molecular sieve is 3730–3750 cm⁻¹. -1 The peak area of ​​the spectral peak within the range is denoted as A1, and the wavenumbers are 3660–3720 cm⁻¹. -1 The peak area of ​​the spectral peak within the range is denoted as A2, and the wavenumbers are 3400–3500 cm⁻¹. -1 The peak area of ​​the spectral peaks within the range is denoted as A3, and the total area of ​​the above three spectral peaks is denoted as A0;

[0019] X is defined by the following equation (3-1) 3-1 Any value between 40% and 50%;

[0020] X 3-1 =A1 / A0×100% Equation (3-1);

[0021] X is defined by the following equation (3-2) 3-2 Any value between 10% and 20%;

[0022] X 3-2 =A2 / A0×100% Equation (3-2);

[0023] X is defined by the following equation (3-3) 3-3 Any value between 35% and 46%;

[0024] X 3-3 =A3 / A0×100% Equation (3-1).

[0025] Optionally, the multi-level porous pure silicon molecular sieve includes molecular sieve particles composed of a single crystal grain, and / or molecular sieve particles composed of multiple crystal grains aggregated together.

[0026] Optionally, the average particle size of the molecular sieve particles is 0.15–0.5 μm, preferably 0.2–0.35 μm; the BET specific surface area is 400–650 m². 2 / g, preferably 450-600m 2 / g; Microporous specific surface area is 300-580m² 2 / g, preferably 350-520 2 / g; total pore volume is 0.2–0.7 cm³. 3 / g, preferably 0.3-0.5cm 3 / g; micropore volume is 0.15–0.4 cm³. 3 / g, preferably 0.18~0.35cm 3 / g; mesopore volume is 0.1~0.5cm³ 3 / g, preferably 0.12~0.4cm 3 / g;

[0027] Preferably, a hysteresis loop exists between the adsorption isotherm and desorption isotherm of the low-temperature nitrogen adsorption of the multi-level porous pure silicon molecular sieve.

[0028] A second aspect of this disclosure provides a method for preparing hierarchical porous pure silica molecular sieves, the method comprising the following steps:

[0029] S1. Mix the silicon source, template agent, water, silanizing agent and structural filler to obtain a reaction mixture, wherein the structural filler is selected from one or more of amphiphilic surfactants and hard template agents;

[0030] S2. The reaction mixture is subjected to hydrothermal crystallization and calcination treatment in sequence.

[0031] Optionally, in step S1, the molar ratio of silicon source: template agent: water: silanizing agent is 1:(0.01~2):(1~50):(0.02~0.2), and the weight ratio of the silicon source to the structural filler in the form of SiO2 is (2~20):1;

[0032] Preferably, in step S1, the molar ratio of silicon source: template agent: water: silanizing agent is 1:(0.02-0.3):(10-30):(0.04-0.15), and the weight ratio of the silicon source to the structural filler in the form of SiO2 is (5-15):1.

[0033] Optionally, in step S1, the silicon source is selected from at least one of silicone grease, solid silica gel, fumed silica, and silica sol; preferably, it is selected from at least one of silicone grease, solid silica gel, and fumed silica.

[0034] A further preferred option is a silicone grease, wherein the silicone grease has the general formula shown in formula (A):

[0035]

[0036] Where R a R b R c R d Each is independently selected from alkyl groups having 1 to 6 carbon atoms, wherein the alkyl group is branched or straight-chain alkyl; preferably, R a R b R c R d Each is independently selected from straight-chain alkyl groups having 1 to 4 carbon atoms or branched alkyl groups having 3 to 4 carbon atoms; more preferably, the R a R b R c R d Each of the following is independently selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, or tert-butyl; more preferably, the silicone grease is selected from one or more of tetramethyl silicate, tetraethyl silicate, tetrabutyl silicate, and dimethyl diethyl silicone grease.

[0037] Optionally, in step S1, the template agent is an organic base; preferably, it is selected from at least one of quaternary ammonium bases, aliphatic amines, and aliphatic alcohol amines.

[0038] More preferably, the template agent is selected from at least one of quaternary ammonium bases having the structure shown in formula (B):

[0039] R1, R2, R3 and R4 are each selected from alkyl groups having 1 to 4 carbon atoms, preferably one or more of straight-chain alkyl groups having 1 to 4 carbon atoms and branched alkyl groups having 3 to 4 carbon atoms, and more preferably, R1, R2, R3 and R4 are each selected from one or more of methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl and tert-butyl.

[0040] More preferably, the template agent is tetrapropylammonium hydroxide or a mixture of tetrapropylammonium hydroxide and one or more selected from tetrapropylammonium chloride and tetrapropylammonium bromide.

[0041] Optionally, in step S1, the silanizing agent has the general formula R5Si(R6)(R7)R8, wherein R5, R6, R7, and R8 are each independently a halogen, alkyl, alkoxy, aromatic, mercapto, or amino group, and at least one of R5, R6, R7, and R8 is an alkyl, alkoxy, aromatic, mercapto, or amino group; the alkyl, alkoxy, mercapto, and amino groups each have an independent number of carbon atoms of C1 to C2. 18 ;

[0042] Preferably, the silanizing agent is selected from one or more of dimethyldichlorosilane, N-phenyl-3-aminopropyltrimethoxysilane, phenyltrimethoxysilane, 1,7-dichlorooctylmethyltetrasiloxane, hexadecyltrimethoxysilane, octyltriethoxysilane, 3-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, and 3-mercaptopropyltrimethoxysilane; more preferably, it is selected from one or more of N-phenyl-3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, and 3-mercaptopropyltrimethoxysilane.

[0043] Optionally, in step S1, the amphiphilic surfactant is selected from one or more of anionic surfactants and cationic surfactants;

[0044] Preferably, the anionic surfactant is selected from one or more of sodium dodecyl sulfate, linear sodium dodecylbenzene sulfonate, branched sodium dodecylbenzene sulfonate, α-olefin sulfonates with 14 to 16 carbon atoms, secondary alkyl sulfonates, and hexadecyl diphenyl ether disulfonate; the cationic surfactant is selected from one or more of hexadecyltrimethylammonium bromide, hexadecyltrimethoxyorganosilicone ammonium chloride, and octadecyltrimethoxyorganosilicone ammonium chloride.

[0045] Preferably, the hard template agent is selected from one or more of PEO-PPO-PEO triblock copolymer, mesoporous carbon, natural cellulose, and carbon nanotubes;

[0046] More preferably, the structural filler is selected from one or more of hexadecyltrimethylammonium bromide, sodium dodecylbenzenesulfonate, PEO-PPO-PEO triblock copolymer, mesoporous carbon, and natural cellulose.

[0047] Optionally, step S1 includes:

[0048] a. Mix the silicon source, template agent, and water to obtain a silicon hydrolysate sol;

[0049] b. Add the silanizing agent and the structural filler to the hydrolyzed sol of the silicon respectively, and mix them to obtain the reaction mixture;

[0050] Optionally, the mixing conditions in step a include stirring at 40–90°C for 6–12 hours;

[0051] Optionally, the mixing conditions in step b include stirring at 20–50°C for 2–4 hours;

[0052] Preferably, the silicon source is an organosilicon grease, and step a further includes a hydrolysis and alcohol removal treatment after mixing the silicon source, template agent and water to obtain the silicon hydrolysate;

[0053] Optionally, the conditions for the hydrolysis and alcohol removal treatment include: stirring and hydrolyzing at 40–90°C for 6–12 hours; preferably, stirring and hydrolyzing at 60–85°C for 8–10 hours.

[0054] Optionally, in step S1, the conditions for the hydrothermal crystallization treatment include: a hydrothermal crystallization temperature of 130–200°C and a hydrothermal crystallization time of 6–168 h; preferably, a hydrothermal crystallization temperature of 150–180°C and a hydrothermal crystallization time of 24–72 h; and the pressure is self-generated pressure.

[0055] The conditions for the roasting treatment include: a roasting temperature of 300–700°C and a roasting time of 1–16 hours; preferably, a roasting temperature of 400–600°C and a roasting time of 2–5 hours.

[0056] The third aspect of this disclosure provides a multi-level porous pure silica molecular sieve prepared according to the method described in the second aspect of this disclosure.

[0057] This fourth aspect of the disclosure provides the application of the hierarchical porous pure silica molecular sieves described in the first and third aspects of the disclosure in the catalytic gas-phase Beckmann rearrangement reaction of cyclohexanone oxime.

[0058] Through the above technical solutions, this disclosure provides a hierarchical porous pure silica molecular sieve, its preparation method, and a cyclohexanone oxime catalytic reaction method. Using cyclohexane as a probe molecule, the diffusion coefficient of the probe molecule in the hierarchical porous pure silica molecular sieve is measured to be 0.015–0.02 μm using the zero-length column method. 2 The multi-level porous pure silica molecular sieve has an open and well-developed multi-level pore structure, which has extremely strong macromolecular diffusion performance, enabling products to diffuse rapidly out of the molecular sieve, thereby improving the product selectivity and catalyst lifetime of the reaction. At the same time, the abundant pore structure provides a large number of silanol active centers. This molecular sieve has high cyclohexanone oxime conversion and caprolactam selectivity, as well as high reaction stability in the gas-phase Beckmann reaction of cyclohexanone oxime.

[0059] Other features and advantages of this disclosure will be described in detail in the following detailed description section. Attached Figure Description

[0060] The accompanying drawings are provided to further illustrate the present disclosure and form part of the specification. They are used together with the following detailed description to explain the present disclosure, but do not constitute a limitation thereof. In the drawings:

[0061] Figure 1 These are zero-length column test images of the molecular sieves prepared in Example 1 and Comparative Example 2 of this disclosure;

[0062] Figure 2 The image shown is a TEM image of the molecular sieve prepared in Example 1 of this disclosure.

[0063] Figure 3 The molecular sieve prepared in Example 1 of this disclosure 31 P-TMPO MAS NMR spectrum;

[0064] Figure 4 The molecular sieve prepared in Example 1 of this disclosure 29 Si-MAS NMR spectrum;

[0065] Figure 5 The FT-IR spectrum of the molecular sieve prepared in Example 1 of this disclosure;

[0066] Figure 6 The XRD pattern of the molecular sieve prepared in Example 1 of this disclosure;

[0067] Figure 7 SEM images of the molecular sieve prepared in Example 1 of this disclosure;

[0068] Figure 8 The BET curve of the molecular sieve prepared in Example 1 of this disclosure;

[0069] Figure 9 The XRD pattern of the molecular sieve prepared in Example 11 of this disclosure;

[0070] Figure 10 The XRD pattern of the molecular sieve prepared in Example 12 of this disclosure is shown. Detailed Implementation

[0071] The following provides a detailed description of specific embodiments of this disclosure. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit this disclosure.

[0072] The first aspect of this disclosure provides a hierarchical porous pure silica molecular sieve, which has the following diffusion coefficient characteristics: using cyclohexane as a probe molecule, the diffusion coefficient of the probe molecule in the hierarchical porous pure silica molecular sieve, measured by the zero-length column method, is 0.015–0.02 μm. 2 Any value between / min.

[0073] This disclosure provides a hierarchical porous pure silica molecular sieve. The hierarchical porous pure silica molecular sieve has an open and well-developed hierarchical pore structure, which has extremely strong macromolecular diffusion properties, enabling products to diffuse rapidly out of the molecular sieve, thereby improving the product selectivity and catalyst lifetime of the reaction. At the same time, the abundant pore structure provides a large number of silanol active centers. This molecular sieve exhibits high cyclohexanone oxime conversion and caprolactam selectivity, as well as high reaction stability in the gas-phase Beckmann reaction of cyclohexanone oxime.

[0074] The instrument and method for determining the diffusion coefficient using the zero-length column method in this disclosure are conventional instruments and methods used in the field, such as those disclosed in the literature (Acta Petrolei Sinica (Petroleum Processing), 2021, 37, 176-180).

[0075] In a preferred embodiment, the diffusion coefficient of the hierarchical porous pure silica molecular sieve is 0.016–0.020 μm. 2 Any value between / min.

[0076] The inventors of this disclosure have discovered that the multi-level porous pure silica molecular sieve has a weak... Acid properties, using trimethylphosphorus oxide as a probe molecule, in this hierarchical porous pure silica molecular sieve 31 In the p-TMPO MAS NMR spectrum, the characteristic peak is represented by a chemical shift of 49 ± 1 ppm. Acid characteristic peaks, with the characteristic peak at a chemical shift of 30±2 ppm representing the physical adsorption characteristic peaks, are present in the hierarchical porous pure silica molecular sieve. The ratio of the acid characteristic intensity to the physical adsorption characteristic peak intensity is within a certain range.

[0077] In a preferred embodiment, the hierarchical porous pure silica molecular sieve has the following characteristics: 31 P-TMPO MAS NMR characteristics:

[0078] The peak intensity of the characteristic peak at a chemical shift of 49±1ppm of the multi-level porous pure silica molecular sieve is denoted as N1, and the peak intensity of the characteristic peak at a chemical shift of 30±2ppm is denoted as N2. X1 is defined as below 8% as in the following formula (1):

[0079] X1 = N2 / N1 × 100% Equation (1);

[0080] Preferably, X1 is any value between 2% and 8%; more preferably, it is any value between 4% and 6%. When the X1 of the hierarchical porous pure silica molecular sieve is within the range of this embodiment, it can have higher catalytic activity and catalytic stability.

[0081] In a preferred embodiment, the hierarchical porous pure silica molecular sieve has the following characteristics: 29Si MAS NMR characteristics:

[0082] The peak area of ​​the chemical shift of the hierarchical porous pure silica molecular sieve in the range of -102 to -104 ppm is denoted as Q. 3 The peak area of ​​the spectral peak with a chemical shift in the range of -112 to -114 ppm is denoted as Q. 4 As defined in equation (2), X2 is any value between 5% and 15%.

[0083] X2 = Q 3 / Q 4 ×100% Equation (2);

[0084] Preferably, X2 is any value between 8% and 12%. A peak with a chemical shift near -103 ppm indicates a tricoordinated silicon group, and a peak with a chemical shift near -113 ppm indicates a tetracoordinated silicon group. The hierarchical porous pure silicon molecular sieve provided in this disclosure has abundant surface silanol groups.

[0085] In a preferred embodiment, the hierarchical porous pure silica molecular sieve has the following FT-IR characteristics: [Further details about the FT-IR spectrum of the hierarchical porous pure silica molecular sieve are needed for accurate translation]. -1 Peak segmentation results for spectral peaks in the wavenumber range:

[0086] The wavenumber of the multi-level porous pure silica molecular sieve is 3730-3750 cm⁻¹. -1 The peak area of ​​the spectral peak within the range is denoted as A1, and the wavenumbers are 3660–3720 cm⁻¹. -1 The peak area of ​​the spectral peak within the range is denoted as A2, and the wavenumbers are 3400–3500 cm⁻¹. -1 The peak area of ​​the spectral peaks within the range is denoted as A3, and the total area of ​​the above three spectral peaks is denoted as A0;

[0087] X is defined by the following equation (3-1) 3-1 Any value between 40% and 50%;

[0088] X 3-1 =A1 / A0×100% Equation (3-1);

[0089] X is defined by the following equation (3-2) 3-2 Any value between 10% and 20%;

[0090] X 3-2 =A2 / A0×100% Equation (3-2);

[0091] X is defined by the following equation (3-3) 3-3 Any value between 35% and 45%;

[0092] X3-3 =A3 / A0×100% Equation (3-1).

[0093] The molecular sieve provided in this disclosure has abundant nested silanol groups and ortho-silanol groups, and a 3740 cm⁻¹ -1 The terminal silanol peak near the wavenumber, 3690 cm⁻¹ -1 The ortho-silanol peak near the wavenumber and the 3500 cm⁻¹ peak -1 The peak areas of the nested silanol peaks near the wavenumber satisfy X 3-1 ~X 3-3 When the above-mentioned range is met, the hierarchical porous pure silica molecular sieve exhibits excellent catalytic activity and catalytic stability.

[0094] In one specific embodiment, the configuration of the multi-level porous pure silica molecular sieve is selected from one or more of the MFI topology, MEL topology, BEA topology and SVR topology; preferably, it is an MFI topology.

[0095] In one embodiment, the multi-level porous pure silicon molecular sieve includes molecular sieve particles composed of a single crystal grain, and / or molecular sieve particles composed of aggregates of multiple crystal grains.

[0096] In a preferred embodiment, the molecular sieve particles have an average particle size of 0.15–0.5 μm, preferably 0.2–0.35 μm; and a BET specific surface area of ​​400–650 m². 2 / g, preferably 450-600m 2 / g; Microporous specific surface area is 300-580m² 2 / g, preferably 350-520 2 / g; total pore volume is 0.2–0.7 cm³. 3 / g, preferably 0.3-0.5cm 3 / g; micropore volume is 0.15–0.4 cm³. 3 / g, preferably 0.18~0.35cm 3 / g; mesopore volume is 0.1~0.5cm³ 3 / g, preferably 0.2~0.4cm 3 / g.

[0097] In a preferred embodiment, a hysteresis loop exists between the adsorption isotherm and desorption isotherm of the low-temperature nitrogen adsorption of the multi-level porous pure silicon molecular sieve.

[0098] In one specific embodiment, the initial relative pressure (P / P0) at which the hysteresis loop appears is 0.2 to 0.7, preferably 0.3 to 0.5.

[0099] A second aspect of this disclosure provides a method for preparing hierarchical porous pure silica molecular sieves, the method comprising the following steps:

[0100] S1. Mix the silicon source, template agent, water, silanizing agent and structural filler to obtain a reaction mixture, wherein the structural filler is selected from one or more of amphiphilic surfactants and hard template agents;

[0101] S2. The reaction mixture is subjected to hydrothermal crystallization and calcination treatment in sequence.

[0102] This disclosure provides a method for preparing hierarchical porous pure silica molecular sieves. By introducing silanizing reagents and macromolecular structural fillers into the molecular sieve synthesis raw materials, a layer-supporting and pore-expanding effect can be achieved during the molecular sieve synthesis process, resulting in hierarchical porous molecular sieves with open channels and excellent macromolecular diffusion properties. The silanizing reagent's silanol groups hydrolyze and condense with the silanol groups of the organosilicon source to form stable Si-O-Si bonds, thus ensuring the layer-supporting and pore-expanding effect. Furthermore, the long carbon chain of the silanizing reagent and the amphiphilic surfactant structural filler can form stable and controllable structural units (the long carbon chain of the silanizing reagent and the hydrophobic group of the surfactant are close to each other and interact by van der Waals forces), thereby finely modulating the layer-supporting and pore-expanding effect; or a size-controllable hard template agent can be used for space filling. This results in a final molecular sieve with an ordered, mesoporous structure with controllable pore size (controlled by the chain length of the alkyl chain of the silanizing reagent).

[0103] In one embodiment, in step S1, the molar ratio of silicon source: template agent: water: silanizing agent is 1:(0.01~2):(1~50):(0.02~0.2), and the weight ratio of the silicon source to the structural filler in the form of SiO2 is (2~20):1.

[0104] In a preferred embodiment, in step S1, the molar ratio of silicon source:templating agent:water:silanizing agent is 1:(0.02-0.3):(10-30):(0.04-0.15), and the weight ratio of the silicon source to the structural filler, in SiO2 form, is (5-15):1. The hierarchical porous pure silicon molecules prepared according to this embodiment can exhibit higher catalytic activity, showing higher cyclohexanone oxime conversion and caprolactam selectivity in the gas-phase Beckmann reaction of cyclohexanone oxime.

[0105] In one embodiment, in step S1, the silicon source is selected from at least one of silicone grease, solid silicone, fumed silica, and silica sol; preferably, it is selected from at least one of silicone grease, solid silicone, and fumed silica.

[0106] A further preferred option is a silicone grease, wherein the silicone grease has the general formula shown in formula (A):

[0107]

[0108] Where R a R b R c R d Each is independently selected from alkyl groups having 1 to 6 carbon atoms, wherein the alkyl group is branched or straight-chain alkyl; preferably, R a R b R c R d Each is independently selected from straight-chain alkyl groups having 1 to 4 carbon atoms or branched alkyl groups having 3 to 4 carbon atoms; more preferably, the R a R b R c R d Each is independently selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, or tert-butyl.

[0109] In a preferred embodiment, the silicone grease is selected from one or more of tetramethyl silicate, tetraethyl silicate, tetrabutyl silicate, and dimethyl diethyl silicone grease.

[0110] In one embodiment, in step S1, the template agent is an organic base; preferably, it is selected from at least one of quaternary ammonium bases, aliphatic amines, and aliphatic alcoholic amines.

[0111] More preferably, the template agent is selected from at least one of quaternary ammonium bases having the structure shown in formula (B):

[0112] R1, R2, R3 and R4 are each selected from alkyl groups having 1 to 4 carbon atoms, preferably one or more of straight-chain alkyl groups having 1 to 4 carbon atoms and branched alkyl groups having 3 to 4 carbon atoms, and more preferably, R1, R2, R3 and R4 are each selected from one or more of methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl and tert-butyl.

[0113] In a preferred embodiment, the template agent is at least one of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide (including various isomers of tetrapropylammonium hydroxide, such as tetra-n-propylammonium hydroxide and tetraisopropylammonium hydroxide), and tetrabutylammonium hydroxide (including various isomers of tetrabutylammonium hydroxide, such as tetra-n-butylammonium hydroxide and tetraisobutylammonium hydroxide).

[0114] In a preferred embodiment, the multi-level porous pure silica molecular sieve is an MFI type molecular sieve, and the template agent is tetrapropylammonium hydroxide or a mixture of tetrapropylammonium hydroxide and one or more selected from tetrapropylammonium chloride and tetrapropylammonium bromide.

[0115] In one embodiment, in step S1, the silanizing agent has the general formula R5Si(R6)(R7)R8, wherein R5, R6, R7, and R8 are each independently a halogen, alkyl, alkoxy, aromatic, mercapto, or amino group, and at least one of R5, R6, R7, and R8 is an alkyl, alkoxy, aromatic, mercapto, or amino group; the alkyl, alkoxy, mercapto, and amino groups each have an independent number of carbon atoms of C1 to C2. 18 .

[0116] In a preferred embodiment, the silanizing agent is selected from one or more of dimethyldichlorosilane, N-phenyl-3-aminopropyltrimethoxysilane, phenyltrimethoxysilane, 1,7-dichlorooctylmethyltetrasiloxane, hexadecyltrimethoxysilane, octyltriethoxysilane, 3-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, and 3-mercaptopropyltrimethoxysilane; more preferably, it is selected from one or more of N-phenyl-3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, and 3-mercaptopropyltrimethoxysilane.

[0117] In one embodiment, in step S1, the amphiphilic surfactant is selected from one or more of anionic surfactants and cationic surfactants;

[0118] Preferably, the anionic surfactant is selected from one or more of sodium dodecyl sulfate, linear sodium dodecylbenzene sulfonate, branched sodium dodecylbenzene sulfonate, α-olefin sulfonates with 14 to 16 carbon atoms, secondary alkyl sulfonates, and hexadecyl diphenyl ether disulfonate; the cationic surfactant is selected from one or more of hexadecyltrimethylammonium bromide, hexadecyltrimethoxyorganosilicone ammonium chloride, and octadecyltrimethoxyorganosilicone ammonium chloride.

[0119] The hard template agent is selected from one or more of PEO-PPO-PEO triblock copolymers, mesoporous carbon, natural cellulose, and carbon nanotubes. The hard template agent used in this disclosure can be of sizes conventionally used in the art. In one specific embodiment, when the hard template agent is in particulate form (e.g., carbon nanoparticles, ordered mesoporous carbon, calcium carbonate, magnesium hydroxide, etc.), the average particle size of the hard template agent can be 1–100 nm; when the hard template agent is carbon nanotubes, the diameter of the hard template agent is 5–50 nm and the length is 2–30 μm; when the hard template agent is carbon nanofibers, the diameter of the hard template agent is 3–80 nm and the length is 1–40 μm.

[0120] In a more preferred embodiment, the structural filler is selected from one or more of hexadecyltrimethylammonium bromide, sodium dodecylbenzenesulfonate, PEO-PPO-PEO block copolymer, mesoporous carbon, and natural cellulose.

[0121] In one specific embodiment, step S1 includes:

[0122] a. Mix the silicon source, template agent, and water to obtain a silicon hydrolysate sol;

[0123] b. Add the silanizing agent and the structural filler to the hydrolyzed sol of the silicon respectively, and mix them to obtain the reaction mixture;

[0124] Optionally, the mixing conditions in step a include stirring at 40–90°C for 6–12 hours;

[0125] Optionally, the mixing conditions in step b include stirring at 20–50°C for 2–4 hours.

[0126] In a preferred embodiment, the silicon source is an organosilicon grease, and step a further includes a hydrolysis and alcohol removal treatment after mixing the silicon source, template agent and water to obtain the silicon hydrolysate;

[0127] Optionally, the conditions for the hydrolysis-induced alcohol removal treatment include: stirring and hydrolyzing at 40–90°C for 6–12 hours; preferably, stirring and hydrolyzing at 60–85°C for 8–10 hours. Preferably, the hydrolysis-induced alcohol removal treatment results in the alcohol content in the silicone hydrolysate of the obtained silicone grease being below 10 ppm by mass.

[0128] In one embodiment, in step S1, the conditions for the hydrothermal crystallization treatment include: a hydrothermal crystallization time of 6–168 h, a hydrothermal crystallization temperature of 130–200 °C, and an autogenous pressure.

[0129] The conditions for the roasting treatment include: a roasting temperature of 300–700°C and a roasting time of 1–16 hours.

[0130] In a preferred embodiment, in step S1, the conditions for the hydrothermal crystallization treatment include: a hydrothermal crystallization time of 24–72 h, a hydrothermal crystallization temperature of 150–180 °C, and an autogenous pressure.

[0131] The calcination conditions include a calcination temperature of 400–600°C and a calcination time of 2–5 hours. The hierarchical porous pure silica molecular sieve prepared according to this embodiment exhibits higher catalytic activity and stability in the catalytic gas-phase Beckmann rearrangement of cyclohexanone oxime.

[0132] The third aspect of this disclosure provides a multi-level porous pure silica molecular sieve prepared according to the method described in the second aspect of this disclosure.

[0133] This fourth aspect of the disclosure provides the application of the hierarchical porous pure silica molecular sieves described in the first and third aspects of the disclosure in the catalytic gas-phase Beckmann rearrangement reaction of cyclohexanone oxime.

[0134] In one specific embodiment, the gas-phase Beckmann rearrangement reaction conditions for cyclohexanone oxime include: a reaction temperature of 350–400 °C, a reaction pressure of 0–0.2 MPa, a nitrogen to cyclohexanone oxime molar ratio of 0.1–30:1, cyclohexanone oxime accounting for 5–50% by weight of the total amount of cyclohexanone oxime and solvent, and a cyclohexanone oxime weight hourly space velocity of 1–10 h⁻¹. -1 .

[0135] The present disclosure will be described in detail below through examples.

[0136] The diffusion coefficient of the sample was determined by using a zero-length column to test the diffusion coefficient of the probe molecule cyclohexane in the molecular sieve. This involved replacing the packed column in the gas chromatograph (Agilent Technologies, 7890B) with a zero-length column filled with the sample to be tested. The temperature was kept constant at 200°C during the experiment. The diffusion curve was measured and recorded, and the diffusion coefficient was calculated based on the slope.

[0137] The transmission electron microscope (TEM) images of the samples were obtained using a Tecnai G2F20S-TWIN transmission electron microscope manufactured by FEI.

[0138] Scanning electron microscopy (SEM) images of the samples were obtained using a Hitachi S4800 high-resolution cold field emission scanning electron microscope. The average particle size of the samples was determined by measuring the SEM images (average value was taken after testing the particle size of 50 molecular sieves).

[0139] The sample 31 P-TMPO MAS NMR characterization was performed on an AVANCEⅢ 600WB nuclear magnetic resonance spectrometer using a 4mm dual resonance probe, a Ф4mm ZrO2 rotor, a resonance frequency of 242.9MHz, a rotor speed of 10kHz, a pulse width of 1.4μs, a cycle delay of 1s, and approximately 6000 scans.

[0140] The sample 29 Si MAS NMR characterization was performed on an AVANCEⅢ500WB nuclear magnetic resonance spectrometer using a 7mm dual resonance probe, a Ф7mm ZrO2 rotor, a resonance frequency of 99.3MHz, a rotation speed of 5kHz, a pulse width of 1.8μs, a cycle delay of 2s, and approximately 3000 scans.

[0141] The Fourier transform infrared (FT-IR) spectra of the samples were measured on a Nicolet 8210 Fourier transform infrared spectrometer, with a measurement range of 400–4000 cm⁻¹.-1 .

[0142] The BET specific surface area and microporous specific surface area of ​​the samples, as well as the total pore volume, micropore volume, and mesopore volume, were determined using a Micromeritics ASAP245 static nitrogen adsorption analyzer according to the ASTM D4222-98 standard method. The adsorption and desorption isotherms of the samples at low temperatures were determined according to the ASTM D4222-98 standard method.

[0143] The reagents used in the following examples and comparative examples were all purchased through conventional channels.

[0144] Example 1

[0145] (1) Add 104g of tetraethyl silicate, 65g of 25% tetrapropylammonium hydroxide (TPAOH) aqueous solution and 140g of water to a 500mL beaker, place it on a magnetic stirrer with heating and stirring functions and mix evenly. Stir at 60℃ for 5 hours, and replenish the evaporated water periodically to obtain a colorless and transparent silica gel solution.

[0146] (2) Add 9g of N-phenyl-3-aminopropyltrimethoxysilane (PHAPTMS, 0.035mol) and 3g of PEO-PPO-PEO triblock copolymer (P123, purchased from Inokai, weight average molecular weight 5800) to the mixture in step (1) and stir for 2 hours.

[0147] (3) The mixture obtained in step (2) is transferred to a stainless steel closed reactor and crystallized at 170°C for 24 hours to obtain a sample. The sample is filtered, washed, dried at 110°C for 3 hours, and then calcined in a muffle furnace at 550°C for 3 hours to obtain molecular sieve product S-1.

[0148] The characterization parameters of S-1, such as BET specific surface area, micropore specific surface area, total pore volume, micropore volume, and mesopore volume, are listed in Table 2.

[0149] The zero-length column test spectra of molecular sieve D-2 prepared by S-1 and Comparative Example 2 (existing technology) are as follows: Figure 1 As shown in the figure, the diffusion coefficient of molecular sieve S-1 prepared by the method provided in this disclosure is 0.018, while the diffusion coefficient of D-2 is 0.001. S-1 is significantly increased compared to D-2, increasing by about 17 times, indicating that the molecular sieve S-1 prepared in this embodiment is more conducive to the diffusion of macromolecules.

[0150] TEM electron microscope images of S-1 are as follows Figure 2 As shown in the figure, the molecular sieve has a well-developed open hierarchical pore structure.

[0151] S-1 31 p-TMPOMASNMR spectrum as shown Figure 3 As shown in the figure, product S-1 has spectral peaks near chemical shifts of 49 ppm and 30 ppm, respectively. The peak intensity N1 of the characteristic peak at chemical shift of 49 ppm is 158226, and the peak intensity N2 of the characteristic peak at chemical shift of 30 ppm is 6867. The values ​​of X1 calculated by equation (1) are listed in Table 3.

[0152] S-1 29 SiMAS NMR spectrum as follows Figure 4 As shown in the figure, product S-1 has peaks at chemical shifts of -103 ppm and -113 ppm, respectively. The peak area Q of the peak at chemical shift -103 ppm is calculated by integration. 3 The peak area Q of the spectrum with a chemical shift of -113 ppm is 158226. 4 The value of X2 calculated by formula (2) is 1387954 and is listed in Table 3;

[0153] The FT-IR spectrum of S-1 and its peak fractionation results are as follows: Figure 5 As shown in the figure, product S-1 at a wavenumber of 3740 cm⁻¹ -1 3690cm -1 And 35000cm -1 The positions have spectral peaks, and the peak areas of the three peaks calculated by integration are: A1 = 31.1, A2 = 11, and A3 = 27.2, with a total area of ​​69.3. X is calculated from equations (3-1) to (3-3). 3-1 ~X 3-3 The values ​​are listed in Table 3;

[0154] The XRD pattern of S-1 is as follows: Figure 6 As shown, the molecular sieve S-1 prepared in this embodiment has an MFI topology.

[0155] SEM images of S-1 are as follows: Figure 7 As shown, the average particle size of the molecular sieve particles was measured to be 0.26 μm.

[0156] The BET curve of S-1 is as follows: Figure 8 As shown in the figure, there is a clear hysteresis loop between the nitrogen adsorption and desorption curves. The initial relative pressure (P / P0) at which this hysteresis loop occurs is 0.44.

[0157] Comparative Example 1

[0158] The method of Example 1 is used, except that no silanizing agent or structural filler is added. The resulting product is denoted as D-1. The preparation conditions are listed in Table 1, and the characterization results of the resulting molecular sieve are listed in Table 2.

[0159] Comparative Example 2

[0160] This comparative example prepared a conventional all-silica Silicalite-1 molecular sieve according to the method disclosed in patent CN1338427A, specifically including the following steps:

[0161] (1) Add 104g of tetraethyl silicate, 90g of 22.5% by weight tetrapropylammonium hydroxide (TPAOH) aqueous solution and 110g of water to a 500mL beaker, place it on a magnetic stirrer with heating and stirring functions and mix evenly. Stir at 75℃ for 5 hours, and replenish the evaporated water periodically to obtain a colorless and transparent silica gel solution.

[0162] (2) The above sol was transferred to a stainless steel sealed reactor and crystallized at 170°C for 2 days. After filtration and washing, it was dried at 120°C for 24 hours and then calcined in a muffle furnace at 550°C for 5 hours.

[0163] (3) Take 15g of the calcined product and mix it with 55g of a 22.5% by weight tetrapropylammonium hydroxide (TPAOH) aqueous solution. Crystallize at 170℃ for 1 day, filter, wash, dry at 110℃ for 12 hours, and then calcine at 550℃ for 4 hours in a muffle furnace. The obtained product is denoted as D-2. The characterization results of the obtained molecular sieve are shown in Table 2.

[0164] Comparative Example 3

[0165] This comparative example prepared conventional all-silica Silicalite-1 molecular sieves according to the method disclosed in patent CN102432032A, specifically including the following steps:

[0166] (1) Place 18.39 g of tetraethyl silicate and 30.65 g of 17.5% by weight tetrapropylammonium hydroxide (TPAOH) aqueous solution in a 200 mL beaker and mix them evenly on a magnetic stirrer with heating and stirring functions to obtain a transparent solution.

[0167] (2) Add 0.06g of lysine to the above transparent solution and stir at 80℃ for 24 hours. Add the evaporated water regularly to obtain a colorless and transparent silica gel solution.

[0168] (3) The above sol was transferred to a stainless steel sealed reactor and crystallized at 170℃ for 3 days. After filtration, washing, and drying, it was calcined in a muffle furnace at 550℃ for 3 hours. The obtained product was designated as D-3. The characterization results of the obtained molecular sieve are shown in Table 2.

[0169] Examples 2-10

[0170] Multi-level porous pure silica molecular sieves were prepared according to the method of Example 1, except that the ratio and synthesis conditions were changed to obtain multi-level porous pure silica molecular sieve samples denoted as S-2 to S-10; the preparation conditions are listed in Table 1, and the characterization results of the obtained molecular sieves are listed in Table 2.

[0171] Example 11

[0172] Hierarchical porous pure silica molecular sieves were prepared according to the method of Example 1, except that the template agent was changed to tetrabutylammonium hydroxide (TBAOH) to prepare the MEL topology, resulting in a hierarchical porous molecular sieve sample denoted as S11. The preparation conditions are listed in Table 1, and the characterization results of the obtained molecular sieve are listed in Table 2. The XRD pattern of S-11 is shown in Table 2. Figure 9 As shown, S-11 is a MEL structure.

[0173] Example 12

[0174] Hierarchical porous pure silica molecular sieves were prepared according to the method of Example 1, except that the proportions and template agent were changed. Tetraethylammonium hydroxide (TEAOH) was used as the template agent to prepare a BEA topology, resulting in a hierarchical porous molecular sieve sample designated S-12. The preparation conditions are listed in Table 1, and the characterization results of the obtained molecular sieve are listed in Table 2. The XRD pattern of S-12 is shown in Table 2. Figure 10 As shown, S-12 is a BEA structure.

[0175] Table 1

[0176]

[0177]

[0178] In Table 1, TPAOH is tetrapropylammonium hydroxide, TBAOH is tetrabutylammonium hydroxide, and TEAOH is tetraethylammonium hydroxide; PHAPTMS is N-phenyl-3-aminopropyltrimethoxysilane, APTMS is 3-aminopropyltriethoxysilane, GCPMS is 3-epoxypropoxypropyl(dimethoxy)methylsilane, and TOMS is methyltrimethoxysilane; P123 is PEO-PPO-PEO block copolymer, and CTAB is hexadecyltrimethylammonium bromide. The reagents used in this disclosure can be obtained through conventional purchasing channels. The water in the "Water / Silicon Source" calculation in Table 1 also includes water from the template agent aqueous solution.

[0179] Table 2

[0180]

[0181] The diffusion coefficients D, X1, X2, and X of the products obtained in the above examples and comparative examples are compared. 3-1 ~X 3-1 The values ​​are listed in Table 3 below.

[0182] Table 3

[0183]

[0184] Test case

[0185] The molecular sieves prepared in the above examples and comparative examples were evaluated. The prepared molecular sieves were compressed into tablets, then crushed. 20-60 mesh particles were used as catalysts for the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime. The catalytic performance of the obtained molecular sieves was evaluated under the following conditions:

[0186] The evaluation apparatus was an atmospheric pressure continuous flow fixed-bed reactor with an inner diameter of 5 mm and a catalyst loading of 2 g. After catalyst loading, the reactor was pretreated for 3 hours at atmospheric pressure and 350 °C under a nitrogen atmosphere. The feedstock cyclohexanone oxime had a concentration of 35% by weight, and methanol was used as the solvent. The reaction conditions included a cyclohexanone oxime weight hourly space velocity (WHSV, cyclohexanone oxime flow rate in feed / catalyst weight in reactor) of 2 h⁻¹. -1 The reaction temperature was 380℃, the nitrogen flow rate was 4 liters / hour, and the reaction time was 24h and 120h, respectively.

[0187] The cooled reaction products were collected, and the concentrations of each substance were quantitatively analyzed by gas chromatography (GC). An Agilent 6890 GC was used, with an HP-5 column. The test conditions included: vaporization chamber temperature 250℃, detection chamber temperature 230℃, and a programmed column temperature ramp: 110℃ for 8 minutes, ramped to 230℃ at a rate of 15℃ / min, and then held for 14 minutes. The results are shown in Table 4 below.

[0188] Wherein, the conversion rate of cyclohexanone oxime (mol%) = (molar content of cyclohexanone oxime in feed - molar content of cyclohexanone oxime in product) / molar content of cyclohexanone oxime in feed × 100%

[0189] Caprolactam selectivity (mol%) = (mol percentage of caprolactam in the product) / (100 - mol percentage of cyclohexanone oxime in the product) × 100%;

[0190] Cyclohexanone oxime conversion reduction rate (%) = (24h cyclohexanone conversion rate - 120h cyclohexanone conversion rate) / 24h cyclohexanone conversion rate × 100%;

[0191] The rate of decrease in caprolactam selectivity = (24h caprolactam selectivity - 120h caprolactam selectivity) / 24h caprolactam selectivity × 100%.

[0192] Table 4

[0193]

[0194]

[0195] As can be seen from the data in the table above, compared with the molecular sieves D-1 to D-3 prepared by comparative examples 1 to 3, the molecular sieves S-1 to S-12 prepared by the method provided in this disclosure have higher cyclohexanone oxime conversion and caprolactam selectivity at 24h and 120h of reaction; and under long-term reaction conditions (120h), the reduction rate of cyclohexanone oxime conversion and caprolactam selectivity of the molecular sieves is lower, indicating higher molecular sieve stability and longer service life.

[0196] Comparing S-9 and S-1, it can be seen that when S-1 is prepared according to the reaction conditions provided in the preferred embodiment of this disclosure, the diffusion coefficient of S-1 is between 0.016 and 0.020 μm. 2 Within the range of / min, S-1 exhibits higher cyclohexanone oxime conversion and caprolactam selectivity in the gas-phase Beckmann rearrangement of cyclohexanone oxime, and also demonstrates higher molecular sieve stability.

[0197] Comparing S-10 and S-1, it can be seen that S-1 was synthesized with the following molar ratios: silicon source: template agent: water: silanizing agent: 1:(0.02~0.3):(10~30):(0.04~0.15), and silicon source: structural filler weight ratio:(5~15):1. The diffusion coefficient of S-1 is 0.016~0.020μm. 2 Within the range of / min, S-1 exhibits higher cyclohexanone oxime conversion and caprolactam selectivity in the gas-phase Beckmann rearrangement of cyclohexanone oxime, and also demonstrates higher molecular sieve stability.

[0198] The preferred embodiments of this disclosure have been described in detail above. However, this disclosure is not limited to the specific details of the above embodiments. Within the scope of the technical concept of this disclosure, various simple modifications can be made to the technical solutions of this disclosure, and these simple modifications all fall within the protection scope of this disclosure.

[0199] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, this disclosure will not describe the various possible combinations separately.

[0200] Furthermore, various different embodiments of this disclosure can be combined in any way, as long as they do not violate the spirit of this disclosure, they should also be regarded as the content disclosed in this disclosure.

Claims

1. A multi-level porous pure silica molecular sieve, characterized in that, This hierarchical porous pure silica molecular sieve exhibits the following diffusion coefficient characteristics: Using cyclohexane as a probe molecule, the diffusion coefficient D of the probe molecule in the hierarchical porous pure silica molecular sieve was measured to be 0.015~0.020 μm using the zero-length column method. 2 Any value between / min; The hierarchical porous pure silica molecular sieve is prepared by a method including the following steps: S1. A silicon source, a template agent, water, a silanizing agent, and a structural filler are mixed to obtain a reaction mixture, wherein the structural filler is selected from one or more of amphiphilic surfactants and hard template agents; the template agent is an organic base; the silanizing agent has the general formula R5Si(R6)(R7)R8, wherein R5, R6, R7, and R8 are each independently a halogen, alkyl, alkoxy, aromatic, mercapto, or amino group, and at least one of R5, R6, R7, and R8 is an alkyl, alkoxy, aromatic, mercapto, or amino group; the alkyl, alkoxy, mercapto, and amino groups each have an independent number of carbon atoms of C1~C6. 18 ; S2. The reaction mixture is subjected to hydrothermal crystallization and calcination treatment in sequence.

2. The multi-level porous pure silica molecular sieve according to claim 1, characterized in that, This hierarchical porous pure silica molecular sieve has the following characteristics: 31 P-TMPO MAS NMR characteristics: The peak intensity of the characteristic peak at a chemical shift of 48-50 ppm of the multi-level porous pure silica molecular sieve is denoted as N1, and the peak intensity of the characteristic peak at a chemical shift of 28-32 ppm is denoted as N2. X1 is defined as below 8% as in the following formula (1): X1 = N2 / N1 × 100% (1) 3. The multi-level porous pure silica molecular sieve according to claim 1, characterized in that, X1 is any value between 2% and 8%.

4. The multi-level porous pure silica molecular sieve according to claim 3, characterized in that, X1 is any value between 4% and 6%.

5. The multi-level porous pure silica molecular sieve according to claim 1, characterized in that, This hierarchical porous pure silica molecular sieve has the following characteristics: 29 Si MAS NMR characteristics: The peak area of ​​the chemical shift of the hierarchical porous pure silica molecular sieve in the range of -102 to -104 ppm is denoted as Q. 3 The peak area of ​​the spectral peak with a chemical shift in the range of -112 to -114 ppm is denoted as Q. 4 As defined in equation (2), X2 is any value between 5% and 15% in the following formula: X2=Q 3 / Q 4 ×100% formula (2).

6. The multi-level porous pure silica molecular sieve according to claim 5, characterized in that, X2 is any value between 8% and 12%.

7. The multi-level porous pure silica molecular sieve according to claim 1, characterized in that, This hierarchical porous pure silica molecular sieve exhibits the following FT-IR characteristics: The FT-IR spectrum of the microporous pure silica molecular sieve is located in the 3200-3800 cm⁻¹ range. -1 In the peak fractionation results within the wavenumber range: the wavenumber of the hierarchical porous pure silica molecular sieve is 3730~3750 cm⁻¹. -1 The peak area of ​​the spectral peak within the range is denoted as A1, and the wavenumbers are 3660~3720 cm⁻¹. -1 The peak area of ​​the spectral peak within the range is denoted as A2, and the wavenumbers are 3400~3500 cm⁻¹. -1 The peak area of ​​the spectral peaks within the range is denoted as A3, and the total area of ​​the above three spectral peaks is denoted as A0; X is defined by the following equation (3-1) 3-1 Any value between 40% and 50%; X 3-1 =A1 / A0×100% (3-1); X is defined by the following equation (3-2) 3-2 Any value between 10% and 20%; X 3-2 =A2 / A0×100% (3-2); X is defined by the following equation (3-3) 3-3 Any value between 35% and 46%; X 3-3 =A3 / A0×100% (3-1).

8. The multi-level porous pure silica molecular sieve according to claim 1, characterized in that, The multi-level porous pure silicon molecular sieve includes molecular sieve particles composed of single crystals, and / or molecular sieve particles composed of aggregates of multiple crystals.

9. The multi-level porous pure silica molecular sieve according to claim 8, characterized in that, The molecular sieve particles have an average particle size of 0.15~0.5μm and a BET specific surface area of ​​400~650m². 2 / g; Microporous specific surface area is 300~580m² 2 / g; total pore volume is 0.2~0.7cm³. 3 / g; micropore volume is 0.15~0.4cm³ 3 / g; mesopore volume is 0.1~0.5cm³ 3 / g.

10. The multi-level porous pure silica molecular sieve according to claim 9, characterized in that, The molecular sieve particles have an average particle size of 0.2~0.35μm and a BET specific surface area of ​​450~600m². 2 / g; Microporous specific surface area is 350~520 2 / g; total pore volume is 0.3~0.5cm³. 3 / g; micropore volume is 0.18~0.35cm³ 3 / g; mesopore volume is 0.12~0.4cm³ 3 / g.

11. The multi-level porous pure silica molecular sieve according to claim 1, characterized in that, There is a hysteresis loop between the adsorption isotherm and desorption isotherm of the low-temperature nitrogen adsorption of the multi-level porous pure silicon molecular sieve.

12. The multi-level porous pure silica molecular sieve according to claim 1, characterized in that, In step S1, the molar ratio of silicon source: template agent: water: silanizing agent is 1:(0.01~2):(1~50):(0.02~0.2), and the weight ratio of the silicon source to the structural filler in the form of SiO2 is (2~20):

1.

13. The multi-level porous pure silica molecular sieve according to claim 12, characterized in that, In step S1, the molar ratio of silicon source: template agent: water: silanizing agent is 1: (0.02~0.3): (10~30): (0.04~0.15), and the weight ratio of the silicon source to the structural filler in the form of SiO2 is (5~15):

1.

14. The multi-level porous pure silica molecular sieve according to claim 1, characterized in that, In step S1, the silicon source is selected from at least one of organosilicon grease, solid silica gel, fumed silica, and silica sol.

15. The multi-level porous pure silica molecular sieve according to claim 14, characterized in that, In step S1, the silicon source is selected from at least one of silicone grease, solid silicone and silica.

16. The multi-level porous pure silica molecular sieve according to claim 15, characterized in that, In step S1, the silicon source is silicone grease, and the general formula of the silicone grease is shown in formula (A): （A）； Where R a R b R c R d Each is independently selected from alkyl groups having 1 to 6 carbon atoms, wherein the alkyl group is a branched or straight-chain alkyl group.

17. The multi-level porous pure silica molecular sieve according to claim 16, characterized in that, In formula (A), R a R b R c R d Each is independently selected from straight-chain alkyl groups having 1 to 4 carbon atoms or branched alkyl groups having 3 to 4 carbon atoms.

18. The multi-level porous pure silica molecular sieve according to claim 17, characterized in that, In formula (A), R a R b R c R d Each is independently selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, or tert-butyl.

19. The multi-level porous pure silica molecular sieve according to claim 18, characterized in that, The silicone grease is selected from one or more of tetramethyl silicate, tetraethyl silicate, tetrabutyl silicate, and dimethyl diethyl silicone grease.

20. The multi-level porous pure silica molecular sieve according to claim 1, characterized in that, In step S1, the template agent is selected from at least one of quaternary ammonium bases, aliphatic amines, and aliphatic alcoholic amines.

21. The multi-level porous pure silica molecular sieve according to claim 20, characterized in that, The template agent is selected from at least one of quaternary ammonium bases having the structure shown in formula (B): (B); R1, R2, R3 and R4 are each selected from alkyl groups having 1 to 4 carbon atoms.

22. The multi-level porous pure silica molecular sieve according to claim 21, characterized in that, In formula (B), R1, R2, R3 and R4 are each selected from one or more straight-chain alkyl groups having 1 to 4 carbon atoms and branched alkyl groups having 3 to 4 carbon atoms.

23. The multi-level porous pure silica molecular sieve according to claim 22, characterized in that, In formula (B), R1, R2, R3 and R4 are each selected from one or more of methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl and tert-butyl.

24. The multi-level porous pure silica molecular sieve according to claim 1, characterized in that, The template agent is tetrapropylammonium hydroxide or a mixture of tetrapropylammonium hydroxide and one or more selected from tetrapropylammonium chloride and tetrapropylammonium bromide.

25. The multi-level porous pure silica molecular sieve according to claim 1, characterized in that, The silanizing agent is selected from one or more of dimethyldichlorosilane, N-phenyl-3-aminopropyltrimethoxysilane, phenyltrimethoxysilane, 1,7-dichlorooctylmethyltetrasiloxane, hexadecyltrimethoxysilane, octyltriethoxysilane, 3-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, and 3-mercaptopropyltrimethoxysilane.

26. The multi-level porous pure silica molecular sieve according to claim 25, characterized in that, The silanizing agent is selected from one or more of N-phenyl-3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, and 3-mercaptopropyltrimethoxysilane.

27. The multi-level porous pure silica molecular sieve according to claim 1, characterized in that, In step S1, the amphiphilic surfactant is selected from one or more of anionic and cationic surfactants.

28. The multi-level porous pure silica molecular sieve according to claim 27, characterized in that, The anionic surfactant is selected from one or more of sodium dodecyl sulfate, linear sodium dodecylbenzene sulfonate, branched sodium dodecylbenzene sulfonate, α-olefin sulfonates with 14 to 16 carbon atoms, secondary alkyl sulfonates, and hexadecyl diphenyl ether disulfonate; the cationic surfactant is selected from one or more of hexadecyltrimethylammonium bromide, hexadecyltrimethoxyorganosilicon ammonium chloride, and octadecyltrimethoxyorganosilicon ammonium chloride.

29. The multi-level porous pure silica molecular sieve according to claim 1, characterized in that, In step S1, the hard template agent is selected from one or more of PEO-PPO-PEO triblock copolymer, mesoporous carbon, natural cellulose, and carbon nanotubes.

30. The multi-level porous pure silica molecular sieve according to claim 1, characterized in that, In step S1, the structural filler is selected from one or more of hexadecyltrimethylammonium bromide, sodium dodecylbenzenesulfonate, PEO-PPO-PEO triblock copolymer, mesoporous carbon, and natural cellulose.

31. The multi-level porous pure silica molecular sieve according to claim 1, characterized in that, Step S1 includes: a. Mix the silicon source, template agent, and water to obtain a silicon hydrolysate sol; b. The silanizing agent and the structural filler are added to the hydrolyzed sol of the silicon, and the mixture is then used to obtain the reaction mixture.

32. The multi-level porous pure silica molecular sieve according to claim 31, characterized in that, The mixing conditions in step a include stirring at 40~90℃ for 6~12 hours; The mixing conditions in step b include stirring at 20~50℃ for 2~4 hours.

33. The multi-level porous pure silica molecular sieve according to claim 31, characterized in that, The silicon source is an organosilicon grease. In step a, after mixing the silicon source, template agent and water, a hydrolysis and alcohol removal treatment is also included to obtain the silicon hydrolysate.

34. The multi-level porous pure silica molecular sieve according to claim 33, characterized in that, The conditions for the hydrolysis and alcohol removal treatment include: hydrolysis with stirring at 40~90 °C for 6~12 h.

35. The multi-level porous pure silica molecular sieve according to claim 34, characterized in that, The conditions for the hydrolysis and alcohol removal treatment include: stirring and hydrolyzing at 60~85℃ for 8~10h.

36. The multi-level porous pure silica molecular sieve according to claim 1, characterized in that, In step S1, the conditions for the hydrothermal crystallization treatment include: a hydrothermal crystallization temperature of 130~200℃ and a hydrothermal crystallization time of 6~168h; The conditions for the roasting treatment include: a roasting temperature of 300~700℃ and a roasting time of 1~16 hours.

37. The multi-level porous pure silica molecular sieve according to claim 36, characterized in that, In step S1, the conditions for the hydrothermal crystallization treatment include: a hydrothermal crystallization temperature of 150~180℃, a hydrothermal crystallization time of 24~72h, and an autogenous pressure. The conditions for the calcination treatment include: a calcination temperature of 400~600℃ and a calcination time of 2~5 hours.

38. The application of the hierarchical porous pure silica molecular sieve according to any one of claims 1 to 37 in the catalytic gas-phase Beckmann rearrangement reaction of cyclohexanone oxime.

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