Hierarchical porous silicalite-1 molecular sieve, preparation method thereof and application thereof in cyclohexanone oxime rearrangement reaction

Abstract

The present disclosure relates to a hierarchical-pore Silicalite-1 molecular sieve, a preparation method thereof and an application thereof in cyclohexanone oxime rearrangement reaction. In the FT-IR spectrum of the hierarchical-pore Silicalite-1 molecular sieve, the peak area of the spectrum peak in the range of 3200-3900 cm ‑1 -1 in the range of 3720-3760 cm ‑1 -1 in the range of 3660-3720 cm ‑1 -1 in the range of 3400-3600 cm ‑1 -1 in the range of 3400-3600 cm, is recorded as Q3; X1 defined by the following formula (1) is any value between 0.6 and 1.6: X1=Q2 / Q1 formula (1); X2 defined by the following formula (2) is any value between 2.5 and 4.5: X2=Q3 / Q1 formula (2). The molecular sieve has abundant nest silicon hydroxyl groups, high catalytic activity and catalytic stability, and can effectively improve the selectivity of caprolactam and the service life of the catalyst.

Description

Technical Field

[0001] This disclosure relates to the field of all-silica molecular sieve preparation, specifically to a hierarchical porous Silicalite-1 molecular sieve, its preparation method, and its application in the cyclohexanone oxime rearrangement reaction. Background Technology

[0002] The discovery of caprolactam (CPL) has a long history, dating back to 1899 when S. Gabriel and TAMaas synthesized it via the cyclization of 6-aminohexanoic acid. Later, O. Wallach prepared caprolactam using the Beckmann rearrangement of cyclohexanone oxime. However, it was P. Schlack who truly gave it commercial value in 1938, obtaining the first spinnable polymer through the polymerization of caprolactam. In 1940, the German company IGFanben industrialized caprolactam, leading to unprecedented development in the industry. Industrial plants sprang up everywhere, and production capacity rapidly increased, reaching 2 million tons worldwide by 1989. With the continuous improvement of people's living standards, global consumption of caprolactam increased from 5.27 million tons in 2015 to 6.4 million tons in 2019, with an average annual growth rate of 4.9%. China is the world's largest consumer of caprolactam, accounting for approximately 52.7% of total consumption.

[0003] Currently, over 90% of CPL (Cyclohexanone oxime) is prepared via the liquid-phase Beckmann rearrangement reaction using cyclohexanone oxime (CHO), employing concentrated sulfuric acid (or fuming sulfuric acid) as both catalyst and solvent. This process suffers from severe equipment corrosion and environmental pollution. Furthermore, the waste sulfuric acid is neutralized with liquid ammonia after the reaction, generating a large amount of low-value ammonium sulfate byproduct (1.9 t ammonium sulfate / t CPL), resulting in poor techno-economic performance for this route. Therefore, the gas-phase Beckmann rearrangement process based on heterogeneous catalysts using CHO has received significant attention from both academia and industry. Compared to the traditional liquid-phase method, this process avoids the use of ammonia and fuming sulfuric acid at the source, achieving 100% atom utilization, making it an environmentally friendly green production process for CPL.

[0004] Currently, various solid catalysts, including molecular sieves, metal oxides, and mesoporous materials, have been applied to the study of the CHO gas-phase Beckmann rearrangement reaction. Among them, the all-silica MFI topological structure Silicalite-1 molecular sieve has demonstrated excellent catalytic performance. Sumitomo Chemical of Japan and Sinopec of China have successively conducted industrial demonstration tests of CHO gas-phase Beckmann rearrangement using Silicalite-1 molecular sieve catalysts. 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 confined pores of the molecular sieve and a significantly prolonged residence time within the crystals. This, in turn, exacerbates the formation of by-products 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. Lei Xu et al. (Catal. Sci. Technol., 2018, 8, 4526-4536) used silicon spheres of different sizes as the silicon source and employed a dissolution-crystallization method, changing the water-to-silicon ratio and the modulus-to-silicon ratio to obtain a hierarchical porous pure silicon molecular sieve with interconnected macropores, mesopores, and micropores. Chengyang Yin et al. (Microporous and Mesoporous Materials, 2020, 307, 110517-110523) introduced carbon dioxide into the molecular sieve synthesis process, utilizing the generated carbonate to accelerate the crystallization process. Simultaneously, the calcination process decomposed the carbonate to generate gas, creating pores, thus synthesizing a hierarchical porous pure silicon molecular sieve with significant voids.

[0006] However, when the hierarchical porous Silicalite-1 molecular sieve synthesized by the above technology is used for the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime, the improvement effect on caprolactam selectivity and catalyst lifetime is not ideal, and it cannot meet the requirements of industrial production. Summary of the Invention

[0007] The purpose of this disclosure is to provide a hierarchical porous Silicalite-1 molecular sieve, its preparation method, and its application in the cyclohexanone oxime rearrangement reaction. This molecular sieve has abundant nested silanol groups, high catalytic activity and catalytic stability, and can effectively improve caprolactam selectivity and catalyst lifetime.

[0008] To achieve the above objectives, the first aspect of this disclosure provides a hierarchical porous Silicalite-1 molecular sieve, which has the following FT-IR characteristics: [Further details about the FT-IR spectra of the hierarchical porous Silicalite-1 molecular sieve are needed for accurate translation]. -1 In the peak fractionation results within the wavenumber range: 3720–3760 cm⁻¹ -1 The peak area of ​​the spectral peak within the wavenumber range is denoted as Q1, and the peak area of ​​the spectral peak in the range of 3660–3720 cm⁻¹ is... -1 The peak area of ​​the spectral peak within the wavenumber range is denoted as Q2, and the peak area of ​​the 3400–3600 cm⁻¹ range is calculated as follows: -1 The peak area of ​​the spectral peak within the wavenumber range is denoted as Q3; X1 is any value between 0.6 and 1.6 as defined by the following formula (1): X1 = Q2 / Q1 (1); X2 is any value between 2.5 and 4.5 as defined by the following formula (2): X2 = Q3 / Q1 (2).

[0009] Optionally, X1 is any value between 0.8 and 1.4; X2 is any value between 2.7 and 4.2.

[0010] Optionally, the hierarchical porous Silicalite-1 molecular sieve has multiple cavity structures within its crystal; wherein the size of a single cavity structure is 10–150 nm, preferably 15–110 nm.

[0011] Preferably, the volume of all the cavity structures accounts for 5-95% of the total volume of the molecular sieve, more preferably 40-90% of the total volume, and even more preferably 70-90% of the total volume.

[0012] Optionally, the shape of the cavity structure is selected from one or more of the following: sphere, cube, ellipsoid, and irregular cube.

[0013] Optionally, the multi-level porous Silicalite-1 molecular sieve includes molecular sieve particles composed of a single crystal, and / or molecular sieve particles composed of aggregates of multiple crystals.

[0014] Optionally, the average particle size of the molecular sieve particles is 0.1–2 μm, preferably 0.18–1.1 μm; the BET specific surface area is 300–570 m². 2 / g, preferably 330-520m 2 / g; microporous specific surface area is 150-500m² 2 / g, preferably 170-480m 2 / g; total pore volume is 0.2–0.7 cm³. 3 / g, preferably 0.3-0.5cm 3 / g; micropore volume is 0.08–0.42 cm³.3 / g, preferably 0.1~0.38cm 3 / g; mesopore volume is 0.1~0.5cm³ 3 / g, preferably 0.15~0.40cm 3 / g;

[0015] Preferably, a hysteresis loop exists between the adsorption isotherm and desorption isotherm of the hierarchical porous Silicalite-1 molecular sieve for low-temperature nitrogen adsorption.

[0016] A second aspect of this disclosure provides a method for preparing hierarchical porous Silicalite-1 molecular sieves, comprising the following steps:

[0017] S1. Mix the silicon source, the first template agent, water and the structural filler to obtain a reaction mixture, wherein the structural filler is selected from one or more of amphiphilic surfactants and / or polymers;

[0018] S2. The reaction mixture is subjected to a first hydrothermal crystallization treatment and a first calcination treatment in sequence to obtain a first intermediate;

[0019] S3. The first intermediate is contacted with an alkaline solution for alkaline treatment to obtain the second intermediate;

[0020] S4. Mix the second intermediate, the second template agent and water, and then perform the second hydrothermal crystallization treatment and the second calcination treatment in sequence.

[0021] Optionally, in step S1, the molar ratio of silicon source: first template agent: water is 1:(0.01~2):(1~50); the weight ratio of silicon source in SiO2 form to structural filler is (2~45):1.

[0022] Preferably, the molar ratio of silicon source: first template agent: water is 1:(0.02~0.3):(5~30); the weight ratio of silicon source in SiO2 form to structural filler is (5~30):1.

[0023] 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.

[0024] A further preferred option is a silicone grease, wherein the silicone grease has the general formula shown in formula (A):

[0025]

[0026] Where R a R b R c R dEach 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.

[0027] Optionally, the first template agent in step S1 and the second template agent in step S4 are organic bases; and each is preferably selected independently from at least one of quaternary ammonium bases, aliphatic amines and aliphatic alcoholic amines;

[0028] More preferably, the first template agent and the second template agent are each independently selected from at least one of quaternary ammonium bases having the structure shown in formula (B):

[0029] 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.

[0030] More preferably, the first template agent and the second template agent are each independently tetrapropylammonium hydroxide or a mixture of tetrapropylammonium hydroxide and one or more selected from tetrapropylammonium chloride and tetrapropylammonium bromide.

[0031] Optionally, in step S1, the amphiphilic surfactant is selected from one or more of anionic surfactants and cationic surfactants;

[0032] 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.

[0033] Preferably, the polymer is selected from one or more of the following: PEO-PPO-PEO block copolymer, polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyvinyl alcohol, polyvinyl acetate, polyacrylonitrile, polymethyl methacrylate, polyvinyl butyral, polyethyleneimine, 4-polyvinylpyridine, and poly(diallyldimethylammonium chloride); optionally, the molecular weight of the polymer is 10,000 to 200,000.

[0034] More preferably, the amphiphilic surfactant is selected from one or more of hexadecyltrimethylammonium bromide, sodium dodecylbenzenesulfonate, PEO-PPO-PEO block copolymer, polyvinyl chloride, polystyrene, polyvinyl alcohol, and polymethyl methacrylate.

[0035] Optionally, step S1 includes:

[0036] a. Mix the silicon source, the first template agent, and water to obtain a silicon hydrolysis sol;

[0037] b. Add the structural filler to the hydrolyzed sol of the silicon, and mix to obtain the reaction mixture;

[0038] Optionally, the mixing conditions in step a include stirring at 40–90°C for 6–12 hours;

[0039] Optionally, the mixing conditions in step b include stirring at 20–50°C for 2–4 hours;

[0040] Preferably, the silicon source is an organosilicon grease, and step a further includes a hydrolysis and alcohol removal treatment after mixing the silicon source, the first template agent and water to obtain the silicon hydrolysate;

[0041] 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.

[0042] Optionally, in step S1, the conditions for the first hydrothermal crystallization treatment include: a hydrothermal crystallization time of 6–168 h and a hydrothermal crystallization temperature of 130–200 °C; preferably, a hydrothermal crystallization time of 24–72 h and a hydrothermal crystallization temperature of 150–180 °C; and the pressure is self-generated pressure.

[0043] The conditions for the first calcination treatment include: a calcination temperature of 300–700°C and a calcination time of 1–16 h; preferably, the calcination temperature is 400–600°C and the calcination time is 2–5 h.

[0044] Optionally, in step S3, the concentration of the alkaline solution is 1-5 mol / L, preferably 2-4 mol / L;

[0045] The weight ratio of the alkaline solution to the first intermediate is (1-15):1, preferably (2-10):1;

[0046] Preferably, the alkaline solution is an aqueous solution of an alkali, wherein the alkali is selected from one or more of sodium hydroxide, potassium hydroxide, and calcium hydroxide;

[0047] Optionally, in step S3, the conditions for alkali treatment include: a treatment temperature of 60–90°C and a treatment time of 4–24 h; preferably, the treatment temperature is 70–80°C and the treatment time is 8–16 h.

[0048] Optionally, in step S4, the weight ratio of the second intermediate, the second template agent, and water is 1:(0.1-5):(1-30); preferably 1:(0.2-2):(3-20).

[0049] Optionally, in step S4, the conditions for the second hydrothermal crystallization treatment include: a hydrothermal crystallization temperature of 90–200°C and a hydrothermal crystallization time of 4–30 hours; preferably, the hydrothermal crystallization temperature is 130–190°C, the hydrothermal crystallization time is 12–24 hours, and the pressure is autogenous pressure.

[0050] The conditions for the second calcination treatment include: a calcination temperature of 300–700°C and a calcination time of 1–8 h; preferably, the calcination temperature is 400–600°C and the calcination time is 2–5 h.

[0051] The third aspect of this disclosure provides a hierarchical porous Silicalite-1 molecular sieve prepared according to the method described in the second aspect of this disclosure.

[0052] This fourth aspect of the disclosure provides the application of the hierarchical porous Silicalite-1 molecular sieve described in the first and third aspects of the disclosure in the catalytic gas-phase Beckmann rearrangement of cyclohexanone oxime.

[0053] Through the above technical solution, this disclosure provides a hierarchical porous Silicalite-1 molecular sieve, its preparation method, and its application in the cyclohexanone oxime rearrangement reaction. This hierarchical porous Silicalite-1 molecular sieve possesses abundant nested silanol groups and ortho-silanol groups, and has a 3740 cm⁻¹ diameter. -1 The terminal silanol peak near wavenumber, the ortho-silanol peak near wavenumber 3690, and the peak at 3500 cm⁻¹ -1When the peak area of ​​the nested silicall peak near the wavenumber satisfies X1 of 0.6–1.6 and X2 of 2.5–4.5, the hierarchical porous Silicalite-1 molecular sieve exhibits excellent catalytic activity and stability. The hierarchical porous structure of the Silicalite-1 molecular sieve, with its interconnected macropores, mesopores, and micropores, enhances the diffusion performance of reactant molecules and possesses a large specific surface area and pore volume. In the gas-phase Beckmann rearrangement of cyclohexanone oxime, the molecular sieve provided in this disclosure significantly improves caprolactam selectivity and extends catalyst lifetime.

[0054] Other features and advantages of this disclosure will be described in detail in the following detailed description section. Attached Figure Description

[0055] 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:

[0056] Figure 1 The FT-IR spectrum and peak fractionation results of the hierarchical porous Silicalite-1 molecular sieve prepared in Example 1 of this disclosure;

[0057] Figure 2 The XRD pattern of the hierarchical porous Silicalite-1 molecular sieve prepared in Example 1 of this disclosure;

[0058] Figure 3 TEM image of the hierarchical porous Silicalite-1 molecular sieve prepared in Example 1 of this disclosure;

[0059] Figure 4 SEM images of the hierarchical porous Silicalite-1 molecular sieve prepared in Example 1 of this disclosure;

[0060] Figure 5 BET curve of the hierarchical porous Silicalite-1 molecular sieve prepared in Example 1 of this disclosure;

[0061] Figure 6 TEM image of the first intermediate prepared in Example 1 of this disclosure;

[0062] Figure 7 TEM image of the second intermediate prepared in Example 1 of this disclosure;

[0063] Figure 8 The XRD pattern of the hierarchical porous Silicalite-1 molecular sieve prepared in Example 9 of this disclosure;

[0064] Figure 9The XRD pattern of the hierarchical porous Silicalite-1 molecular sieve prepared in Example 10 of this disclosure;

[0065] Figure 10 This is a TEM image of the molecular sieve prepared in Comparative Example 2 of this disclosure. Detailed Implementation

[0066] 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.

[0067] The first aspect of this disclosure provides a hierarchical porous Silicalite-1 molecular sieve, which has the following FT-IR characteristics:

[0068] The FT-IR spectra of the hierarchical porous Silicalite-1 molecular sieve at 3200–3900 cm⁻¹ -1 In the peak fractionation results within the wavenumber range: 3720–3760 cm⁻¹ -1 The peak area of ​​the spectral peak within the wavenumber range is denoted as Q1, and the peak area of ​​the spectral peak in the range of 3660–3720 cm⁻¹ is... -1 The peak area of ​​the spectral peak within the wavenumber range is denoted as Q2, and the peak area of ​​the 3400–3600 cm⁻¹ range is calculated as follows: -1 The peak area of ​​the spectral peak within the wavenumber range is denoted as Q3;

[0069] As defined in equation (1), X1 can be any value between 0.6 and 1.6:

[0070] X1 = Q2 / Q1 (Equation (1));

[0071] As defined in equation (2), X2 is any value between 2.5 and 4.5:

[0072] X2 = Q3 / Q1 (Equation 2).

[0073] This disclosure provides a hierarchical porous Silicalite-1 molecular sieve, which has abundant nested silicall groups and ortho-silicall groups, and a 3740 cm⁻¹ diameter. -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 -1When the peak area of ​​the nested silicall peak near the wavenumber satisfies X1 of 0.6–1.6 and X2 of 2.5–4.5, the hierarchical porous Silicalite-1 molecular sieve exhibits excellent catalytic activity and stability. The hierarchical porous structure of the Silicalite-1 molecular sieve, with its interconnected macropores, mesopores, and micropores, enhances the diffusion performance of reactant molecules and possesses a large specific surface area and pore volume. In the gas-phase Beckmann rearrangement of cyclohexanone oxime, the molecular sieve provided in this disclosure significantly improves caprolactam selectivity and extends catalyst lifetime.

[0074] In a preferred embodiment, the X1 of the hierarchical porous Silicalite-1 molecular sieve is any value between 0.8 and 1.4; and the X2 is any value between 2.7 and 4.2. When the X1 and X2 of the hierarchical porous Silicalite-1 molecular sieve meet the requirements of this embodiment, the molecular sieve exhibits higher catalytic activity and catalytic stability in the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime.

[0075] The inventors of this disclosure have discovered that the hierarchical porous Silicalite-1 molecular sieve has a large-sized multi-cavity structure inside, and the cavity structure contains abundant silanol active centers. Its multi-cavity structure provides a large number of independent reaction units. In addition, the large-sized cavity structure meets the requirements of macromolecular reactions, and the reaction products can more easily flow out of the catalyst, avoiding the phenomenon of reduced catalyst activity due to pore blockage.

[0076] In a preferred embodiment, the hierarchical porous Silicalite-1 molecular sieve has multiple cavity structures within its crystal; wherein the size of a single cavity structure is 10–150 nm, preferably 15–110 nm.

[0077] In this disclosure, the cavity structure and its size in the molecular sieve are obtained by transmission electron microscopy (TEM). In this disclosure, the size of the cavity structure refers to the length between two positions on the cavity wall passing through the center of the cavity structure in a TEM image of the molecular sieve; for example, "the size of a single cavity structure is 10–150 nm" means that the length between two positions on the cavity wall passing through the center of any cavity structure in the molecular sieve is within the range of 10–150 nm.

[0078] In a preferred embodiment, the volume of all the cavity structures accounts for 5-95% of the total volume of the molecular sieve, more preferably 40-90%, and even more preferably 70-90% of the total volume. The volume percentage of all the cavity structures in this disclosure is obtained by calculating the cavity volume using transmission electron microscopy.

[0079] In one specific embodiment, the shape of the cavity structure is selected from one or more of the following: sphere, cube, ellipsoid, and irregular cube.

[0080] In one embodiment, the multi-level porous Silicalite-1 molecular sieve includes molecular sieve particles composed of single crystals, and / or molecular sieve particles composed of aggregates of multiple crystals.

[0081] Optionally, the average particle size of the molecular sieve particles is 0.1–2 μm, preferably 0.18–1.1 μm; the BET specific surface area is 300–570 m². 2 / g, preferably 330-520m 2 / g; microporous specific surface area is 150-500m² 2 / g, preferably 170-480m 2 / g; total pore volume is 0.2–0.7 cm³. 3 / g, preferably 0.3-0.5cm 3 / g; micropore volume is 0.08–0.42 cm³. 3 / g, preferably 0.1~0.38cm 3 / g; mesopore volume is 0.1~0.5cm³ 3 / g, preferably 0.15~0.40cm 3 / g.

[0082] In a preferred embodiment, a hysteresis loop exists between the adsorption isotherm and desorption isotherm of the hierarchical porous Silicalite-1 molecular sieve for low-temperature nitrogen adsorption.

[0083] In one specific embodiment, the initial relative pressure (P / P0) at which the hysteresis loop appears is 0.2 to 0.5, preferably 0.25 to 0.45.

[0084] In one specific embodiment, the configuration of the hierarchical porous Silicalite-1 molecular sieve is selected from one or more of the MFI topology, MEL topology, BEA topology and SVR topology.

[0085] A second aspect of this disclosure provides a method for preparing hierarchical porous Silicalite-1 molecular sieves, comprising the following steps:

[0086] S1. Mix the silicon source, the first template agent, water and the structural filler to obtain a reaction mixture, wherein the structural filler is selected from one or more of amphiphilic surfactants and / or polymers;

[0087] S2. The reaction mixture is subjected to a first hydrothermal crystallization treatment and a first calcination treatment in sequence to obtain a first intermediate;

[0088] S3. The first intermediate is contacted with an alkaline solution for alkaline treatment to obtain the second intermediate;

[0089] S4. Mix the second intermediate, the second template agent and water, and then perform the second hydrothermal crystallization treatment and the second calcination treatment in sequence.

[0090] This disclosure provides a method for preparing hierarchical porous Silicalite-1 molecular sieves. A structural filler is introduced into the molecular sieve synthesis raw material. The structural filler and the inorganic molecular sieve framework achieve self-assembly through hydrogen bonding or electrostatic interaction. After a first calcination, the structural filler is removed, forming a molecular sieve material with internal defect sites. Then, further alkaline treatment is used for desilication, expanding the defect sites in the molecular sieve to obtain a hierarchical porous structure with more open channels. Finally, a template agent is added for dissolution-recrystallization, which avoids the reduction in crystallinity and active centers caused by alkaline treatment damaging the molecular sieve framework. This method yields a hierarchical porous Silicalite-1 molecular sieve with a multi-cavity structure.

[0091] In one embodiment, in step S1, the molar ratio of silicon source: first template agent: water is 1:(0.01~2):(1~50); the weight ratio of silicon source in SiO2 form to structural filler is (2~45):1.

[0092] In a preferred embodiment, the molar ratio of silicon source: first template agent: water is 1:(0.02-0.3):(5-30); the weight ratio of silicon source in SiO2 form to structural filler is (5-30):1. The molecular sieve prepared according to this embodiment can further improve the selectivity of caprolactam and the catalyst stability in the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime.

[0093] 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.

[0094] A further preferred option is a silicone grease, wherein the silicone grease has the general formula shown in formula (A):

[0095]

[0096] 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 Rd 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.

[0097] 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.

[0098] In one embodiment, in step S1, the first template agent is an organic base, preferably at least one selected from quaternary ammonium bases, aliphatic amines, and aliphatic alcohol amines.

[0099] In one specific embodiment, the first template agent is selected from at least one of quaternary ammonium bases having the structure shown in formula (B):

[0100] 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.

[0101] In a preferred embodiment, the first template agent is tetrapropylammonium hydroxide or a mixture of tetrapropylammonium hydroxide and one or more selected from tetrapropylammonium chloride and tetrapropylammonium bromide.

[0102] In one embodiment, step S1 includes:

[0103] a. Mix the silicon source, the first template agent, and water to obtain a silicon hydrolysis sol;

[0104] b. Add the structural filler to the hydrolyzed sol of the silicon, and mix to obtain the reaction mixture;

[0105] Optionally, the mixing conditions in step a include stirring at 40–90°C for 6–12 hours;

[0106] Optionally, the mixing conditions in step b include stirring at 20–50°C for 2–4 hours.

[0107] In one specific embodiment, the silicon source is an organosilicon grease, and step a further includes a hydrolysis and alcohol removal treatment after mixing the silicon source, the first template agent and water to obtain the silicon hydrolysate;

[0108] 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.

[0109] In one embodiment, in step S1, the amphiphilic surfactant is selected from one or more of anionic surfactants and cationic surfactants;

[0110] 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, hexadecyltrimethoxyorganosilicon ammonium chloride, and octadecyltrimethoxyorganosilicon ammonium chloride.

[0111] In one embodiment, the polymer in step S1 is one or more selected from PEO-PPO-PEO block copolymer, polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyvinyl alcohol, polyvinyl acetate, polyacrylonitrile, polymethyl methacrylate, polyvinyl butyral, polyethyleneimine, 4-polyvinylpyridine, and poly(diallyldimethylammonium chloride); optionally, the molecular weight of the polymer is 10,000 to 200,000.

[0112] In a preferred embodiment, the amphiphilic surfactant is selected from one or more of hexadecyltrimethylammonium bromide, sodium dodecylbenzenesulfonate, PEO-PPO-PEO block copolymer, polyvinyl chloride, polystyrene, polyvinyl alcohol, and polymethyl methacrylate.

[0113] In one embodiment, in step S1, the conditions for the first hydrothermal crystallization treatment include: hydrothermal crystallization time of 6 to 168 hours, hydrothermal crystallization temperature of 130 to 200°C, and pressure of autogenous pressure; the conditions for the first calcination treatment include: calcination temperature of 300 to 700°C, and calcination time of 1 to 16 hours.

[0114] In a preferred embodiment, in step S1, the conditions for the first hydrothermal crystallization treatment include: a hydrothermal crystallization time of 24–72 h and a hydrothermal crystallization temperature of 150–180 °C; the conditions for the first calcination treatment include: a calcination temperature of 400–600 °C and a calcination time of 2–5 h. The hierarchical porous molecular sieve prepared according to this embodiment has better catalytic activity.

[0115] In one embodiment, in step S3, the concentration of the alkaline solution is 1-5 mol / L, preferably 2-4 mol / L;

[0116] The weight ratio of the alkaline solution to the first intermediate is (1-15):1, preferably (2-10):1;

[0117] Preferably, the alkaline solution is an aqueous solution of an alkali, wherein the alkali is selected from one or more of sodium hydroxide, potassium hydroxide, and calcium hydroxide.

[0118] In one specific embodiment, in step S3, the conditions for alkali treatment include: a treatment temperature of 60–90°C and a treatment time of 4–24 h; preferably, the treatment temperature is 70–80°C and the treatment time is 8–16 h.

[0119] In one embodiment, in step S4, the weight ratio of the second intermediate, the second template agent, and water is 1:(0.1-5):(1-30); preferably 1:(0.2-2):(3-20). Molecular sieve dissolution-recrystallization is performed according to the weight ratio of this embodiment, resulting in a molecular sieve with a superior multi-cavity hierarchical porous structure.

[0120] In one embodiment, the conditions for the second hydrothermal crystallization treatment include: a hydrothermal crystallization temperature of 90–200°C, a hydrothermal crystallization time of 4–30 hours, and an autogenous pressure.

[0121] The conditions for the second calcination treatment include: a calcination temperature of 300–700°C and a calcination time of 1–8 hours.

[0122] In a preferred embodiment, in step S4, the conditions for the second hydrothermal crystallization treatment include: a hydrothermal crystallization temperature of 130–190°C, a hydrothermal crystallization time of 12–24 h, and an autogenous pressure.

[0123] The conditions for the second calcination treatment include: a calcination temperature of 400–600°C and a calcination time of 2–5 hours. The hierarchical porous molecular sieve prepared according to this embodiment exhibits better catalytic activity.

[0124] The third aspect of this disclosure provides a hierarchical porous Silicalite-1 molecular sieve prepared according to the method described in the second aspect of this disclosure.

[0125] This fourth aspect of the disclosure provides the application of the hierarchical porous Silicalite-1 molecular sieve described in the first and third aspects of the disclosure in the catalytic gas-phase Beckmann rearrangement of cyclohexanone oxime.

[0126] 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 .

[0127] The present disclosure will be described in detail below through examples.

[0128] 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 .

[0129] The X-ray diffraction (XRD) phase pattern of the sample was determined on a Siemens D5005 X-ray diffractometer with Kα (Cu) as the X-ray source and the test range 2θ from 0.5° to 70°.

[0130] Transmission electron microscopy (TEM) images of the samples were obtained using a Tecnai G2F20S-TWIN TEM microscope from FEI. The cavity structure and its dimensions were determined based on TEM images: the volume of each cavity in the molecular sieve particle was measured (calculated assuming a spherical shape, using the median of the sum of the maximum and minimum lengths passing through the center of the cavity as the spherical diameter, then calculating the spherical radius, and finally calculating the percentage of the total volume of all cavities to the total volume of the molecular sieve particles; the average value was taken after calculating the cavity volume fraction of 50 molecular sieve particles).

[0131] 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.

[0132] The average particle size of the samples was determined by measuring scanning electron microscopy (SEM) images. The SEM images of the samples were obtained on a Hitachi S4800 high-resolution cold field emission scanning electron microscope (the average value was taken after testing the particle size of 50 molecular sieves).

[0133] The reagents used in the following examples and comparative examples were all purchased through conventional channels.

[0134] Example 1

[0135] (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.

[0136] (2) Add 3g of polystyrene (PS, purchased from Inokai, molecular weight 80000) to the mixture in step (1) and stir at 60°C for 2 hours;

[0137] (3) The mixture obtained in step (2) is transferred to a stainless steel sealed 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 the calcined product S-1-T (first intermediate).

[0138] (4) Transfer the S-1-T obtained in step (3) to a three-necked flask and add a solution of 2.5 mol / L. -1 The NaOH solution and S-1-T were mixed in a weight ratio of 4:1 and refluxed at 75°C for 10 hours. After filtration and washing until neutral, the mixture was dried and calcined to obtain the intermediate product S-1-TN (second intermediate).

[0139] (5) Mix 10g of S-1-TN sample, 20g of 25% by weight tetrapropylammonium hydroxide (TPAOH) aqueous solution and 40g of water evenly (the weight ratio of the second intermediate: the second template agent: water is 1:0.5:5.5), transfer to a stainless steel sealed reactor, and keep at 170℃ for 24h to obtain the sample. Filter and wash the obtained sample, dry it at 110℃ for 3 hours, and then calcine it in a muffle furnace at 550℃ for 3 hours to obtain sample S-1-M.

[0140] The characterization parameters of S-1-M, such as total BET specific surface area, micropore specific surface area, total pore volume, and mesopore volume, are listed in Table 2.

[0141] The FT-IR spectrum of S-1-M and its peak fractionation results are as follows: Figure 1 As shown in the figure, the FT-IR spectrum at 3740 cm⁻¹... -1 3690cm -1 And 3500cm -1 The presence of characteristic peaks at each location indicates that the S-1-M provided in this embodiment has terminal silanol peaks, adjacent silanol peaks, and nested silanol peaks, and the peak areas are calculated to obtain... Figure 1The peak areas of the three spectral peaks mentioned above are: Q1 is 27.9, Q2 is 35.9, and Q3 is 108.8. The values ​​of X1 and X2 obtained by formula (1) to (2) are listed in Table 3.

[0142] The XRD pattern of S-1-M is as follows: Figure 2 As shown, this indicates that S-1-M is an MFI topology;

[0143] TEM electron microscope images of S-1-M as follows Figure 3 As shown, this indicates that S-1-M is a hierarchical porous structure with multiple cavities within the crystal, and the size of a single cavity structure is 20-95 nm.

[0144] SEM images of S-1-M are as follows: Figure 4 As shown, the molecular sieve particles have regular shapes and uniform sizes.

[0145] The S-1-M BET curve is as follows: Figure 5 As shown, there is a clear hysteresis loop between the nitrogen adsorption and desorption curves, and the initial relative pressure (P / P0) at which the hysteresis loop appears is 0.43.

[0146] TEM of the first intermediate of molecular sieve without alkali treatment, such as Figure 6 As shown, the TEM image of the second molecular sieve intermediate after alkali treatment but without dissolution and recrystallization is as follows. Figure 7 As shown, Figure 6 , Figure 7 and Figure 3 A comparison shows that, Figure 3 The molecular sieves prepared using the method provided in this disclosure exhibit a large number of intracrystalline multi-cavity structures.

[0147] Comparative Example 1

[0148] The method of Example 1 is used, but the difference from Example 1 is that no structural filler is added and no alkaline treatment is performed. The resulting product is denoted as D-1. The preparation conditions are listed in Table 1, and the characterization results of the obtained molecular sieve are listed in Table 2.

[0149] Comparative Example 2

[0150] 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:

[0151] (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.

[0152] (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.

[0153] (3) 15g of the calcined product was mixed with 55g of a 22.5% by weight tetrapropylammonium hydroxide (TPAOH) aqueous solution, and crystallized at 170℃ for 1 day. The mixture was then filtered, washed, dried at 110℃ for 12 hours, and finally calcined in a muffle furnace at 550℃ for 4 hours. The resulting product was designated D-2. The characterization results of the obtained molecular sieve are shown in Table 2. The TEM image of D-2 is shown below. Figure 10 As shown in the figure, D-2 molecular sieve does not have an internal cavity structure.

[0154] Examples 2-8

[0155] Multi-level porous Silicalite-1 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 Silicalite-1 molecular sieve samples denoted as S-2-M to S-8-M; the preparation conditions are listed in Table 1, and the characterization results of the obtained molecular sieves are listed in Table 2.

[0156] Example 9

[0157] Hierarchical porous Silialite-2 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 S-9-M. 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-9-M is shown in Table 2. Figure 8 As shown, S-9-M is a MEL structure.

[0158] Example 10

[0159] Hierarchical porous β-zeolite was prepared according to the method of Example 1, except that the ratio and template agent were changed. Tetraethylammonium hydroxide (TEAOH) was used as the template agent to prepare the BEA topology, resulting in a hierarchical porous zeolite sample denoted as S-10-M. The preparation conditions are listed in Table 1, and the characterization results of the obtained zeolite are listed in Table 2. The XRD pattern of S-10-M is shown in Table 2. Figure 9As shown, S-10-M is a BEA structure.

[0160] Example 11

[0161] The hierarchical porous Silicalite-1 molecular sieve was prepared according to the method of Example 1, but the difference from Example 1 is as follows:

[0162] The conditions for the first hydrothermal crystallization treatment are: temperature 130℃, time 4 days; the conditions for the first calcination treatment are: temperature 350℃, time 8 hours.

[0163] The conditions for alkali treatment are: treatment temperature of 60℃, treatment time of 4h, and weight ratio of alkali solution to the first intermediate of 4:1.

[0164] The conditions for the second hydrothermal crystallization treatment are: temperature 130℃, time 4 days; the conditions for the second calcination treatment are: temperature 350℃, time 8 hours.

[0165] The obtained multi-level porous Silicalite-1 molecular sieve sample is designated as S-11-M; the characterization results of the obtained molecular sieve are listed in Table 2.

[0166] Examples 12-13

[0167] Multi-level porous Silicalite-1 molecular sieves were prepared according to the method of Example 1, except that the structural filler or ratio was changed to obtain multi-level porous Silicalite-1 molecular sieve samples denoted as S-12-M to S-13-M; the preparation conditions are listed in Table 1, and the characterization results of the obtained molecular sieves are listed in Table 2.

[0168] Table 1

[0169]

[0170]

[0171] In Table 1, TPAOH is tetrapropylammonium hydroxide, TBAOH is tetrabutylammonium hydroxide, TEAOH is tetraethylammonium hydroxide, PS is polystyrene (molecular weight 80,000), PVC is polyvinyl chloride (molecular weight 60,000), PMMA is polymethyl methacrylate (molecular weight 60,000), and PVB is polyvinyl butyral (molecular weight 50,000). 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 first template agent aqueous solution; the water in the "water / molecular sieve" calculation also includes water from the second template agent aqueous solution.

[0172] Table 2

[0173]

[0174] Test case

[0175] 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:

[0176] 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.

[0177] The reaction products were collected after cooling, 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 3 below.

[0178] 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%;

[0179] Caprolactam selectivity (mol%) = (mol percentage of caprolactam in the product) / (100 - mol percentage of cyclohexanone oxime in the product) × 100%;

[0180] Cyclohexanone oxime conversion reduction rate (%) = (24h cyclohexanone conversion rate - 120h cyclohexanone conversion rate) / 24h cyclohexanone conversion rate × 100%;

[0181] The rate of decrease in caprolactam selectivity = (24h caprolactam selectivity - 120h caprolactam selectivity) / 24h caprolactam selectivity × 100%.

[0182] Table 3

[0183]

[0184]

[0185] As can be seen from the data in the table above, compared with the molecular sieves D-1 to D-2 prepared by Comparative Examples 1 to 2, the molecular sieves S-1-M to S-13-M prepared by the method provided in this disclosure have higher cyclohexanone oxime conversion and caprolactam selectivity at 24h and 120h of reaction; and the molecular sieves have higher stability and longer service life under long-term reaction conditions (120h).

[0186] Comparing S-11-M with S-1-M, it can be seen that S-1-M has a higher cyclohexanone oxime conversion rate and caprolactam selectivity when prepared according to the reaction conditions provided in the preferred embodiments of this disclosure.

[0187] Comparing S-13-M and S-1-M, it can be seen that S-1-M satisfies the following conditions during preparation: the molar ratio of silicon source: first template agent: water is 1:(0.02~0.3):(5~30); the weight ratio of silicon source in SiO2 form to structural filler is (5~30):1; the weight ratio of alkaline solution to first intermediate is (2~10):1; and the weight ratio of second intermediate: second template agent: water is 1:(0.2~2):(3~20). S-1-M has higher cyclohexanone oxime conversion rate and caprolactam selectivity.

[0188] 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.

[0189] 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.

[0190] 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 hierarchical porous Silicalite-1 molecular sieve, characterized in that, The hierarchical porous Silicalite-1 molecular sieve exhibits the following FT-IR characteristics: The FT-IR spectra of the hierarchical porous Silicalite-1 molecular sieve were observed in the 3200–3900 cm⁻¹ range. -1 In the peak fractionation results within the wavenumber range: 3720~3760 cm⁻¹ -1 The peak area of ​​the spectral peak within the wavenumber range is denoted as Q1, and the peak area of ​​the spectral peak in the range of 3660~3720 cm⁻¹ is... -1 The peak area of ​​the spectral peak within the wavenumber range is denoted as Q2, and the peak area of ​​the 3400~3600 cm⁻¹ range is calculated using this value. -1 The peak area of ​​the spectral peak within the wavenumber range is denoted as Q3; As defined in equation (1), X1 can be any value between 0.6 and 1.6: X1 = Q2 / Q1 (1); As defined in equation (2), X2 is any value between 2.5 and 4.5: X2 = Q3 / Q1 (2); The hierarchical porous Silicalite-1 molecular sieve was prepared by a method comprising the following steps: S1. Mix the silicon source, the first template agent, water and the structural filler to obtain a reaction mixture, wherein the structural filler is selected from one or more of amphiphilic surfactants and / or polymers; S2. The reaction mixture is subjected to a first hydrothermal crystallization treatment and a first calcination treatment in sequence to obtain a first intermediate; S3. The first intermediate is contacted with an alkaline solution for alkaline treatment to obtain the second intermediate; S4. Mix the second intermediate, the second template agent and water, and then perform the second hydrothermal crystallization treatment and the second calcination treatment in sequence.

2. The hierarchical porous Silicalite-1 molecular sieve according to claim 1, characterized in that, X1 is any value between 0.8 and 1.4; X2 is any value between 2.7 and 4.

2.

3. The hierarchical porous Silicalite-1 molecular sieve according to claim 1, characterized in that, The hierarchical porous Silicalite-1 molecular sieve has multiple cavity structures within its crystal; the size of a single cavity structure is 10~150 nm.

4. The hierarchical porous Silicalite-1 molecular sieve according to claim 3, characterized in that, The size of a single cavity structure in the hierarchical porous Silicalite-1 molecular sieve is 15~110 nm.

5. The hierarchical porous Silicalite-1 molecular sieve according to claim 3, characterized in that, In the multi-level porous Silicalite-1 molecular sieve, the volume of all the cavity structures accounts for 5 to 95% of the total volume of the molecular sieve.

6. The hierarchical porous Silicalite-1 molecular sieve according to claim 5, characterized in that, In the multi-level porous Silicalite-1 molecular sieve, the volume of all the cavity structures accounts for 40 to 90% of the total volume of the molecular sieve.

7. The hierarchical porous Silicalite-1 molecular sieve according to claim 6, characterized in that, In the multi-level porous Silicalite-1 molecular sieve, the volume of all the cavity structures accounts for 70-90% of the total volume of the molecular sieve.

8. The hierarchical porous Silicalite-1 molecular sieve according to claim 3, characterized in that, The shape of the cavity structure is selected from one or more of the following: sphere, cube, ellipsoid, and irregular cube.

9. The hierarchical porous Silicalite-1 molecular sieve according to claim 1, characterized in that, The multi-level porous Silicalite-1 molecular sieve includes molecular sieve particles composed of single crystals and / or molecular sieve particles composed of aggregates of multiple crystals.

10. The hierarchical porous Silicalite-1 molecular sieve according to claim 9, characterized in that, The molecular sieve particles have an average particle size of 0.1~2μm and a BET specific surface area of ​​300~570m². 2 / g; microporous specific surface area is 150~500m² 2 / g; total pore volume is 0.2~0.7cm³. 3 / g; micropore volume is 0.08~0.42cm³ 3 / g; mesopore volume is 0.1~0.5cm³ 3 / g.

11. The hierarchical porous Silicalite-1 molecular sieve according to claim 10, characterized in that, The molecular sieve particles have an average particle size of 0.18~1.1μm and a BET specific surface area of ​​330~520m². 2 / g; Microporous specific surface area is 170~480m² 2 / g; total pore volume is 0.3~0.5cm³. 3 / g; micropore volume is 0.1~0.38cm³ 3 / g; mesopore volume is 0.15~0.40cm³ 3 / g.

12. The hierarchical porous Silicalite-1 molecular sieve according to claim 1, characterized in that, There is a hysteresis loop between the adsorption isotherm and desorption isotherm of the hierarchical porous Silicalite-1 molecular sieve at low temperature nitrogen adsorption.

13. The hierarchical porous Silicalite-1 molecular sieve according to claim 1, characterized in that, In step S1, the molar ratio of silicon source: first template agent: water is 1:(0.01~2):(1~50); the weight ratio of silicon source in SiO2 form to structural filler is (2~45):

1.

14. The hierarchical porous Silicalite-1 molecular sieve according to claim 13, characterized in that, In step S1, the molar ratio of silicon source: first template agent: water is 1:(0.02~0.3):(5~30); the weight ratio of silicon source in SiO2 form to structural filler is (5~30):

1.

15. The hierarchical porous Silicalite-1 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.

16. The hierarchical porous Silicalite-1 molecular sieve according to claim 15, characterized in that, The silicon source is selected from at least one of organosilicon grease, solid silica gel, and precipitated silica.

17. The hierarchical porous Silicalite-1 molecular sieve according to claim 16, characterized in that, The silicon source is an organosilicone grease, and the organosilicone grease has the general formula 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.

18. The hierarchical porous Silicalite-1 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 straight-chain alkyl groups having 1 to 4 carbon atoms or branched alkyl groups having 3 to 4 carbon atoms.

19. The hierarchical porous Silicalite-1 molecular sieve according to claim 18, 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.

20. The hierarchical porous Silicalite-1 molecular sieve according to claim 19, characterized in that, The silicone grease is selected from one or more of tetramethyl silicate, tetraethyl silicate, tetrabutyl silicate, and dimethyl diethyl silicone grease.

21. The hierarchical porous Silicalite-1 molecular sieve according to claim 1, characterized in that, The first template agent in step S1 and the second template agent in step S4 are organic bases.

22. The hierarchical porous Silicalite-1 molecular sieve according to claim 21, characterized in that, The first template agent and the second template agent are each independently selected from at least one of quaternary ammonium bases, aliphatic amines and aliphatic alcoholic amines.

23. The hierarchical porous Silicalite-1 molecular sieve according to claim 22, characterized in that, The first template agent and the second template agent are each independently 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.

24. The hierarchical porous Silicalite-1 molecular sieve according to claim 23, 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.

25. The hierarchical porous Silicalite-1 molecular sieve according to claim 24, 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.

26. The hierarchical porous Silicalite-1 molecular sieve according to claim 1, characterized in that, The first template agent and the second template agent are each independently tetrapropylammonium hydroxide or a mixture of tetrapropylammonium hydroxide and one or more selected from tetrapropylammonium chloride and tetrapropylammonium bromide.

27. The hierarchical porous Silicalite-1 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 hierarchical porous Silicalite-1 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 hierarchical porous Silicalite-1 molecular sieve according to claim 28, characterized in that, The polymers are PEO-PPO-PEO block copolymers, polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyvinyl alcohol, polyvinyl acetate, polyacrylonitrile, polymethyl methacrylate, polyvinyl butyral, polyethyleneimine, 4-polyvinylpyridine, and poly(diallyldimethylammonium chloride), one or more of these.

30. The hierarchical porous Silicalite-1 molecular sieve according to claim 29, characterized in that, The molecular weight of the polymer is 10,000 to 200,000.

31. The hierarchical porous Silicalite-1 molecular sieve according to claim 1, characterized in that, The amphiphilic surfactant is selected from one or more of hexadecyltrimethylammonium bromide, sodium dodecylbenzenesulfonate, PEO-PPO-PEO block copolymer, polyvinyl chloride, polystyrene, polyvinyl alcohol, and polymethyl methacrylate.

32. The hierarchical porous Silicalite-1 molecular sieve according to claim 1, characterized in that, Step S1 includes: a. Mix the silicon source, the first template agent, and water to obtain a silicon hydrolysis sol; b. Add the structural filler to the hydrolyzed silicon sol, and mix to obtain the reaction mixture.

33. The hierarchical porous Silicalite-1 molecular sieve according to claim 32, characterized in that, The mixing conditions in step a include stirring at 40~90℃ for 6~12h; the mixing conditions in step b include stirring at 20~50℃ for 2~4h.

34. The hierarchical porous Silicalite-1 molecular sieve according to claim 32, characterized in that, The silicon source is an organosilicon grease. In step a, after mixing the silicon source, the first template agent and water, a hydrolysis and alcohol removal treatment is also included to obtain the silicon hydrolysate.

35. The hierarchical porous Silicalite-1 molecular sieve according to claim 34, characterized in that, The conditions for the hydrolysis and alcohol removal treatment include: hydrolysis with stirring at 40~90 °C for 6~12 h.

36. The hierarchical porous Silicalite-1 molecular sieve according to claim 35, characterized in that, The conditions for the hydrolysis and alcohol removal treatment include: stirring and hydrolyzing at 60~85 °C for 8~10 h.

37. The hierarchical porous Silicalite-1 molecular sieve according to claim 1, characterized in that, In step S1, the conditions for the first hydrothermal crystallization treatment include: hydrothermal crystallization time of 6~168h and hydrothermal crystallization temperature of 130~200℃; The conditions for the first calcination treatment include: a calcination temperature of 300~700℃ and a calcination time of 1~16h.

38. The hierarchical porous Silicalite-1 molecular sieve according to claim 37, characterized in that, In step S1, the conditions for the first hydrothermal crystallization treatment include: hydrothermal crystallization time of 24~72h, hydrothermal crystallization temperature of 150~180℃, and pressure of self-generated pressure; The conditions for the first calcination treatment include: a calcination temperature of 400~600℃ and a calcination time of 2~5h.

39. The hierarchical porous Silicalite-1 molecular sieve according to claim 1, characterized in that, In step S3, the concentration of the alkaline solution is 1~5 mol / L; The weight ratio of the alkaline solution to the first intermediate is (1~15):

1.

40. The hierarchical porous Silicalite-1 molecular sieve according to claim 39, characterized in that, In step S3, the concentration of the alkaline solution is 2~4 mol / L; The weight ratio of the alkaline solution to the first intermediate is (2~10):

1.

41. The hierarchical porous Silicalite-1 molecular sieve according to claim 1, characterized in that, The alkaline solution is an aqueous solution of an alkali, and the alkali is selected from one or more of sodium hydroxide, potassium hydroxide, and calcium hydroxide.

42. The hierarchical porous Silicalite-1 molecular sieve according to claim 1, characterized in that, In step S3, the conditions for alkali treatment include: a treatment temperature of 60~90℃ and a treatment time of 4~24h.

43. The hierarchical porous Silicalite-1 molecular sieve according to claim 42, characterized in that, In step S3, the conditions for alkali treatment include: a treatment temperature of 70~80℃ and a treatment time of 8~16.

44. The hierarchical porous Silicalite-1 molecular sieve according to claim 1, characterized in that, In step S4, the weight ratio of the second intermediate, the second template agent, and water is 1:(0.1~5):(1~30).

45. The hierarchical porous Silicalite-1 molecular sieve according to claim 44, characterized in that, In step S4, the weight ratio of the second intermediate, the second template agent, and water is 1:(0.2~2):(3~20).

46. ​​The hierarchical porous Silicalite-1 molecular sieve according to claim 1, characterized in that, In step S4, the conditions for the second hydrothermal crystallization treatment include: a hydrothermal crystallization temperature of 90~200℃ and a hydrothermal crystallization time of 4~30 hours; The conditions for the second calcination treatment include: a calcination temperature of 300~700℃ and a calcination time of 1~8h.

47. The hierarchical porous Silicalite-1 molecular sieve according to claim 46, characterized in that, In step S4, the conditions for the second hydrothermal crystallization treatment include: hydrothermal crystallization temperature of 130~190℃, hydrothermal crystallization time of 12~24h, and pressure of autogenous pressure; The conditions for the second calcination treatment include: a calcination temperature of 400~600℃ and a calcination time of 2~5h.

48. The use of the hierarchical porous Silicalite-1 molecular sieve according to any one of claims 1 to 47 in the catalytic gas-phase Beckmann rearrangement of cyclohexanone oxime.

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