Hierarchical porous titanium silicalite molecular sieve, preparation method thereof and application of hierarchical porous titanium silicalite molecular sieve in preparation of caprolactam

Abstract

The invention relates to a hierarchical porous titanium silicalite molecular sieve, a preparation method thereof and application of the hierarchical porous titanium silicalite molecular sieve in preparation of caprolactam. The titanium silicalite molecular sieve has the following FT-IR characteristics: in peak division results of an FT-IR spectrogram within the wave number range of 3100-3900 cm <-1 > of the titanium silicalite molecular sieve, the peak area of a spectral peak within the wave number range of 3720-3760 cm <-1 > is marked as Q1, the peak area of a spectral peak within the wave number range of 3660-3720 cm <-1 > is marked as Q2, and the peak area of a spectral peak within the wave number range of 3400-3600 cm <-1 > is marked as Q3; x1 defined by the following formula (1) is any numerical value between 0.8 and 2.2: X1 = Q2 / Q1 formula (1); x2 as defined by the following formula (2) is any numerical value between 2.0 and 5.5: X2 = Q3 / Q1 formula (2). The catalytic performance and the inactivation resistance of the molecular sieve in a catalytic reaction are improved, and the cyclohexanone-oxime conversion rate and the caprolactam selectivity in a cyclohexanone-oxime gas-phase Beckmann rearrangement reaction are improved.

Description

[0001] Related applications This application is a divisional application of Chinese patent application No. 202211330134.0, filed on October 27, 2022. Technical Field

[0002] This disclosure relates to the field of titanium-silicon molecular sieve preparation, specifically to a multi-level porous titanium-silicon molecular sieve, its preparation method, and its application in the preparation of caprolactam. Background Technology

[0003] In 2021, the global caprolactam production capacity reached 8.8 million tons, of which China's capacity accounted for more than 60%, reaching 5.03 million tons, a year-on-year increase of 16.2%, with actual output of 3.95 million tons, a year-on-year increase of 11.9%. Its main use is to produce chips (usually called nylon-6 chips) through polymerization, which can be further processed into nylon fibers, engineering plastics, and plastic films.

[0004] Currently, domestic production facilities use fuming sulfuric acid as a catalyst in the process of cyclohexanone oxime rearrangement to produce caprolactam, which inevitably leads to problems such as corrosion and pollution. The most significant issue is that after the reaction, liquid ammonia is needed to neutralize the reaction system, resulting in the generation of a large amount of low-value ammonium sulfate. For every ton of caprolactam, 1.6 tons of ammonium sulfate are produced, severely diminishing the economic viability of the process.

[0005] Therefore, the gas-phase Beckmann rearrangement process for cyclohexanone oxime based on molecular sieve catalysts has received high attention from both 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, making it an environmentally friendly green production process for caprolactam. Pure silica molecular sieves with the MFI topology exhibit excellent catalytic performance. At the beginning of this century, Sumitomo Chemical of Japan and Sinopec of China successively conducted industrial-scale experiments on the gas-phase Beckmann rearrangement of cyclohexanone oxime using pure silica molecular sieves.

[0006] However, the gas-phase Beckmann rearrangement route suffers from two major challenges: poor CPL selectivity for the product and short catalyst single-pass lifetime. These issues affect the techno-economic efficiency and operational stability, resulting in extremely slow progress in 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 exacerbates byproduct formation and pore blockage by carbon deposits. Furthermore, the silanol active centers of pure silicon molecules are unstable and easily deactivated by heat and alkaline byproducts. Therefore, it is necessary to introduce a new active center to enhance the catalyst's resistance to deactivation.

[0007] Baojun Li's research group (RSC Adv., 2013, 3, 20811–20815) synthesized titanium-silicon molecular sieves with different particle sizes by adding S-1 and TS-1 molecular sieves as seed crystals during the molecular sieve crystallization process. These sieves were used for the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime. However, the conversion rate of these molecular sieves decreased to 95% after 6 h, and the selectivity stabilized at 86%, indicating unsatisfactory reaction performance. Ferdi Schüth et al. (Microporous and Mesoporous Materials, 2009, 117, 228–232) added a 1,7-dichlorooctamethyltetraoxysilane alkylating agent to create pores during the synthesis of titanium-silicon molecular sieves, obtaining a titanium-silicon molecular sieve with hierarchical pores. This molecular sieve maintained a caprolactam yield of 1.6 mmol CPL g after 30 h of reaction. -1 cat h -1 Therefore, when titanium-silicon molecular sieves synthesized by existing processes are used in the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime, the improvement in caprolactam selectivity and catalyst lifetime is not ideal, and there is still a certain gap from the requirements of industrial production. Summary of the Invention

[0008] The purpose of this disclosure is to provide a hierarchical porous titanium silicate molecular sieve, its preparation method, and its application in the preparation of caprolactam, so as to improve the catalytic performance and resistance to deactivation of the molecular sieve in catalytic reactions, and to increase the conversion rate of cyclohexanone oxime and the selectivity of caprolactam in the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime.

[0009] To achieve the above objectives, the first aspect of this disclosure provides a hierarchical porous titanium-silicon molecular sieve, which has the following FT-IR characteristics: The 3100~3900 cm⁻¹ of the titanium-silicon molecular sieve -1 In the peak fractionation results of the FT-IR spectrum 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 0.8 and 2.2 as defined by the following formula (1): X1 = Q2 / Q1 (1); X2 is any value between 2.0 and 5.5 as defined by the following formula (2): X2 = Q3 / Q1 (2).

[0010] Optionally, the value of X1 is any value between 1.0 and 2.0; the value of X2 is any value between 2.5 and 5.0.

[0011] Optionally, the molar ratio of silicon atoms to titanium atoms in the titanium-silicon molecular sieve is (6~130):1, preferably (8~95):1; Optionally, the configuration of the titanium-silicon molecular sieve is selected from one or more of the MFI topology, MEL topology, BEA topology and SVR topology; preferably, it is the MFI topology.

[0012] Optionally, the titanium-silicon molecular sieve has multiple cavity structures within its crystal; wherein the size of a single cavity structure is 2~55nm, preferably 3~46nm; Preferably, the volume of all the cavity structures accounts for 5-60% of the total volume of the molecular sieve, more preferably 8-55%; 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 titanium-silicon molecular sieve includes molecular sieve particles composed of a single crystal, and / or molecular sieve particles composed of aggregates of multiple crystals; Optionally, the average particle size of the molecular sieve particles is 0.12~0.68μm, preferably 0.16~0.58μm; the BET specific surface area is 270~660m². 2 / g, preferably 300~630m 2 / g; Microporous specific surface area is 260~550m² 2 / g, preferably 285~525m 2 / g; total pore volume is 0.15~0.65cm³. 3 / g, preferably 0.2~0.55cm 3 / g; mesopore volume is 0.12~0.55cm³ 3 / g, preferably 0.15~0.45cm 3 / g; Optionally, a hysteresis loop exists between the adsorption isotherm and desorption isotherm of the low-temperature nitrogen adsorption of the titanium-silicon molecular sieve; preferably, the initial relative pressure (P / P0) at which the hysteresis loop appears is 0.32~0.55, more preferably 0.36~0.48.

[0014] A second aspect of this disclosure provides a method for preparing a titanium-silicon molecular sieve with a hierarchical porous structure, comprising the following steps: S1. The titanium source, silicon source, first template agent, water and structural filler are mixed to obtain a reaction mixture; wherein the structural filler is selected from one or more of amphiphilic surfactants and polymers. S2. The reaction mixture is subjected to a first hydrothermal crystallization treatment and a first calcination treatment in sequence to obtain a first molecular sieve intermediate; S3. The first molecular sieve intermediate is contacted with an alkaline solution for alkaline treatment to obtain the second molecular sieve intermediate. S4. Mix the second molecular sieve intermediate, the second template agent and water, and then perform the second hydrothermal crystallization treatment and the second calcination treatment in sequence.

[0015] Optionally, in step S1, the molar ratio of titanium source: silicon source: first template agent: water is (0.008~0.55):1:(0.05~5):(1~80); the weight ratio of silicon source in SiO2 form to structural filler is (5~90):1; Preferably, in step S1, the molar ratio of titanium source: silicon source: first template agent: water is (0.01~0.45):1:(0.08~3.5):(5~60); the weight ratio of silicon source in SiO2 form to structural filler is (6~70):1.

[0016] 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. A further preferred option is a silicone grease, wherein the silicone 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 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.

[0017] 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; 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): (B); 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; 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.

[0018] Optionally, in step S1, the titanium source is selected from one or more of organic titanium sources and inorganic titanium sources; The organic titanium source is a titanium-containing organic ester, selected from at least one of the structures represented by the general formula (C): (C); R5, R6, R7, and R8 are each selected from alkyl groups having 1 to 6 carbon atoms, preferably straight-chain alkyl groups having 1 to 4 carbon atoms and branched alkyl groups having 3 to 6 carbon atoms, and more preferably straight-chain alkyl groups having 2 to 4 carbon atoms and branched alkyl groups having 2 to 4 carbon atoms; optionally, R5, R6, R7, and R8 are each selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, isopentyl, hexyl, or isohexyl; preferably, each is independently selected from ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, or tert-butyl. The inorganic titanium source is selected from one or more of titanium chloride, nitrate or sulfate; Preferably, the titanium source is selected from one or more of titanium tetrachloride, titanium sulfate, titanium nitrate, tetraethyl titanate, tetrapropyl titanate, and tetrabutyl titanate.

[0019] Optionally, in step S1, the amphiphilic surfactant is selected from one or more of anionic surfactants and cationic surfactants; 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 14-16 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. Optionally, the polymer is selected from one or more of 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); optionally, the molecular weight of the polymer is 10,000 to 200,000. More preferably, the structural filler is selected from one or more of hexadecyltrimethylammonium bromide, sodium dodecylbenzenesulfonate, PEO-PPO-PEO block copolymer, polyvinyl chloride, polystyrene, polyvinyl alcohol, and polymethyl methacrylate.

[0020] Optionally, step S1 includes: a. Mix titanium source, silicon source, first template agent and water to obtain silicon hydrolysis sol; b. Add the structural filler to the silicon hydrolysate sol, and mix to obtain the reaction mixture; Optionally, the mixing conditions in step a include stirring at 40~90℃ for 6~12 hours; Optionally, the mixing conditions in step b include stirring at 20~50℃ for 2~4 hours; Preferably, the silicon source is an organosilicon grease, and step a further includes a hydrolysis and alcohol removal treatment after mixing the titanium source, silicon source, first template agent and water to obtain the silicon hydrolysate sol; Optionally, the conditions for the hydrolysis and alcohol removal treatment include: stirring and hydrolyzing at 40~90℃ for 6~12h; preferably, stirring and hydrolyzing at 60~85℃ for 8~10h.

[0021] Optionally, the conditions for the first hydrothermal crystallization treatment in step S2 and the second hydrothermal crystallization treatment in step S4 each independently include: a hydrothermal crystallization time of 5~240h and a hydrothermal crystallization temperature of 110~220℃; preferably, a hydrothermal crystallization time of 6~80h and a hydrothermal crystallization temperature of 130~185℃; and the pressure is self-generated pressure. The conditions for the first roasting treatment in step S2 and the second roasting treatment in step S4 each independently include: a roasting temperature of 320~680℃ and a roasting time of 1~16h; preferably, a roasting temperature of 350~600℃ and a roasting time of 2~5h.

[0022] Optionally, in step S3, the concentration of the alkaline solution is 1~5 mol / L, preferably 2~4 mol / L; The weight ratio of the alkaline solution to the first molecular sieve intermediate is (1~15):1, preferably (2~10):1; 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; Optionally, in step S3, the conditions for alkali treatment include: a treatment temperature of 60~90℃ and a treatment time of 4~24h; preferably, the treatment temperature is 70~80℃ and the treatment time is 8~16h.

[0023] Optionally, in step S4, the weight ratio of the second template agent: water: second molecular sieve intermediate is (0.05~8):(1~40):1; preferably (0.1~5):(2~35):1.

[0024] The third aspect of this disclosure provides a hierarchical porous titanium-silicon molecular sieve prepared by the method described in the second aspect of this disclosure.

[0025] The fourth aspect of this disclosure provides a method for preparing caprolactam from cyclohexanone oxime via gas-phase Beckmann rearrangement, comprising: reacting cyclohexanone oxime with a catalyst, wherein the catalyst comprises the hierarchical porous titanium-silicon molecular sieve described in the first and third aspects of this disclosure.

[0026] Through the above technical solution, this disclosure provides a hierarchical porous titanium-silicon molecular sieve, its preparation method, and its application in the preparation of caprolactam. The hierarchical porous structure of the titanium-silicon molecular sieve endows it with advantages such as large specific surface area and pore volume, improving the diffusion performance of the molecular sieve. Furthermore, the framework titanium atoms introduced into the molecular sieve also help to improve the overall anti-deactivation performance of the molecular sieve. This titanium-silicon molecular sieve has abundant nested silanol groups and ortho-silanol 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 3520 cm⁻¹ peak -1 The peak areas of the nested silanol spectrum near the wavenumber satisfy the definitions of X1 (0.8~2.2) and X2 (2.0~5.5) in Equations (1) and (2). This titanium-silicon molecular sieve has excellent catalytic activity and catalytic stability. In the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime, the molecular sieve provided in this disclosure can significantly improve the conversion rate of cyclohexanone oxime and the selectivity of caprolactam, and extend the catalyst lifetime.

[0027] Other features and advantages of this disclosure will be described in detail in the following detailed description section. Attached Figure Description

[0028] 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: Figure 1 The FT-IR spectrum of the molecular sieve obtained in Example 1; Figure 2 Here is a TEM image of the molecular sieve obtained in Example 1; Figure 3 The image shown is a TEM image of the first molecular sieve intermediate obtained in Example 1. Figure 4 The image shown is a TEM image of the second molecular sieve intermediate obtained in Example 1. Figure 5 The image shown is a TEM image of the molecular sieve obtained in Comparative Example 2. Detailed Implementation

[0029] 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.

[0030] The first aspect of this disclosure provides a hierarchical porous titanium-silicon molecular sieve, which has the following FT-IR characteristics: The 3100~3900 cm⁻¹ of the titanium-silicon molecular sieve -1 In the peak fractionation results of the FT-IR spectrum 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; As defined in equation (1), X1 can be any value between 0.8 and 2.2: X1 = Q2 / Q1 (1); As defined in equation (2), X2 is any value between 2.0 and 5.5: X2=Q3 / Q1 (2).

[0031] This disclosure provides a hierarchical porous titanium-silicon molecular sieve. The hierarchical porous structure of the titanium-silicon molecular sieve endows it with advantages such as a large specific surface area and pore volume, improving the diffusion performance of the molecular sieve. Furthermore, the framework titanium atoms introduced into the molecular sieve also help improve the overall resistance to deactivation. This titanium-silicon molecular sieve has abundant nested silanol groups and ortho-silanol 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 3520 cm⁻¹ peak -1The peak areas of the nested silanol spectrum near the wavenumber satisfy the definitions of X1 (0.8~2.2) and X2 (2.0~5.5) in Equations (1) and (2). This titanium-silicon molecular sieve has excellent catalytic activity and catalytic stability. In the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime, the molecular sieve provided in this disclosure can significantly improve the conversion rate of cyclohexanone oxime and the selectivity of caprolactam, and extend the catalyst lifetime.

[0032] In this disclosure, FT-IR testing can be performed using conventional testing instruments and methods in the art, as well as conventional processing software and methods to perform peak separation, integration, and other processing on the spectral peaks.

[0033] In a preferred embodiment, the value of X1 is any value between 1.0 and 2.0; and the value of X2 is any value between 2.5 and 5.0. When the values ​​of X1 and X2 of the titanium-silicon molecular sieve are within the range of this embodiment, the titanium-silicon molecular sieve exhibits higher cyclohexanone oxime conversion and caprolactam selectivity in the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime, and its catalytic stability is better under long-term reaction conditions.

[0034] In one embodiment, the molar ratio of silicon atoms to titanium atoms in the titanium-silicon molecular sieve is (6~130):1, preferably (8~95):1. This disclosure obtains the molar ratio of silicon atoms to titanium atoms in the molecular sieve using X-ray fluorescence spectroscopy.

[0035] In a preferred embodiment, the titanium-silicon molecular sieve has multiple cavity structures within its crystal structure; wherein the size of a single cavity structure is 2~55 nm, preferably 3~46 nm. The titanium-silicon molecular sieve provided in this disclosure has a large-size multi-cavity structure, and the cavity structure contains abundant silanol active centers, providing a large number of independent reaction units; furthermore, the large-size cavity structure meets the requirements of macromolecular reactions, and reaction products can more easily flow out of the catalyst, avoiding pore blockage that leads to a decrease in catalyst catalytic activity.

[0036] 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 2~55 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 2~55 nm.

[0037] In a preferred embodiment, all of the cavity structures account for 5-60% of the total volume of the molecular sieve, more preferably 8-55%; Optionally, the shape of the cavity structure is selected from one or more of the following: sphere, cube, ellipsoid, and irregular cube.

[0038] In one specific embodiment, the titanium-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. Optionally, the average particle size of the molecular sieve particles is 0.12~0.68μm, preferably 0.16~0.58μm; the BET specific surface area is 270~660m². 2 / g, preferably 300~630m 2 / g; Microporous specific surface area is 260~550m² 2 / g, preferably 285~525m 2 / g; total pore volume is 0.15~0.65cm³. 3 / g, preferably 0.2~0.55cm 3 / g; mesopore volume is 0.12~0.55cm³ 3 / g, preferably 0.15~0.45cm 3 / g.

[0039] In a preferred embodiment, a hysteresis loop exists between the adsorption isotherm and desorption isotherm of the low-temperature nitrogen adsorption of the titanium-silicon molecular sieve.

[0040] In one specific embodiment, the initial relative pressure (P / P0) at which the hysteresis loop appears is 0.32~0.55, preferably 0.36~0.48.

[0041] In one specific embodiment, the configuration of the titanium-silicon molecular sieve with a hierarchical pore structure is selected from one or more of the MFI topology, MEL topology, BEA topology and SVR topology; more preferably, it is an MFI topology.

[0042] The second aspect of this disclosure provides a method for preparing hierarchical porous titanium-silicon molecular sieves, comprising the following steps: S1. The titanium source, silicon source, first template agent, water and structural filler are mixed to obtain a reaction mixture; wherein the structural filler is selected from one or more of amphiphilic surfactants and polymers. S2. The reaction mixture is subjected to a first hydrothermal crystallization treatment and a first calcination treatment in sequence to obtain a first molecular sieve intermediate; S3. The first molecular sieve intermediate is contacted with an alkaline solution for alkaline treatment to obtain the second molecular sieve intermediate. S4. Mix the second molecular sieve intermediate, the second template agent and water, and then perform the second hydrothermal crystallization treatment and the second calcination treatment in sequence.

[0043] This disclosure provides a method for preparing hierarchical porous titanium-silicon molecular sieves. A titanium source is introduced into the reaction raw materials, enabling the introduction of titanium atom active centers into the molecular sieve framework during synthesis, thereby improving the molecular sieve performance. This disclosure also introduces a structural filler into the molecular sieve synthesis raw materials, which self-assembles with the inorganic molecular sieve framework through hydrogen bonding or classical interactions. After calcination, the structural filler is removed, forming a molecular sieve material with internal defect sites. Then, alkali treatment (desiliconization) is performed by contacting with an alkaline solution to expand the defect sites, resulting in a hierarchical porous structure with more open channels, forming a hierarchical porous first molecular sieve intermediate. The first molecular sieve intermediate is then further mixed with a second template agent for dissolution-recrystallization to prepare a hierarchical porous titanium-silicon molecular sieve with a multi-cavity structure. This method also reduces the decrease in crystallinity and active centers caused by the damage to the molecular sieve framework during alkali treatment.

[0044] In one embodiment, in step S1, the molar ratio of titanium source: silicon source: first template agent: water is (0.008~0.55):1:(0.05~5):(1~80); the weight ratio of silicon source in SiO2 form to structural filler is (5~90):1.

[0045] In a preferred embodiment, in step S1, the molar ratio of titanium source: silicon source: first template agent: water is (0.01~0.45):1:(0.08~3.5):(5~60); the weight ratio of silicon source in SiO2 form to structural filler is (6~70):1. The titanium-silicon molecular sieve prepared according to this embodiment has higher catalytic activity and catalytic stability.

[0046] 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. A further preferred option is a silicone grease, wherein the silicone 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 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 cR d Each is independently selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, or tert-butyl.

[0047] 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.

[0048] 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.

[0049] 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): (B); 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.

[0050] 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.

[0051] In one embodiment, step S1 includes: a. Mix titanium source, silicon source, first template agent and water to obtain silicon hydrolysis sol; b. Add the structural filler to the hydrolyzed silicon sol, and mix to obtain the reaction mixture; Optionally, the mixing conditions in step a include stirring at 40~90℃ for 6~12 hours; Optionally, the mixing conditions in step b include stirring at 20~50°C for 2~4 hours.

[0052] 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 titanium source, silicon source, first template agent and water to obtain the silicon hydrolysate sol; 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.

[0053] In one embodiment, in step S1, the titanium source is selected from one or more of organic titanium sources and inorganic titanium sources; The organic titanium source is a titanium-containing organic ester, selected from at least one of the structures represented by the general formula (C): (C); R5, R6, R7, and R8 are each selected from alkyl groups having 1 to 6 carbon atoms, preferably straight-chain alkyl groups having 1 to 4 carbon atoms and branched alkyl groups having 3 to 6 carbon atoms, and more preferably straight-chain alkyl groups having 2 to 4 carbon atoms and branched alkyl groups having 2 to 4 carbon atoms; optionally, R5, R6, R7, and R8 are each selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, isopentyl, hexyl, or isohexyl; preferably, each is independently selected from ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, or tert-butyl. The inorganic titanium source is selected from one or more of titanium chloride, nitrate or sulfate.

[0054] In a preferred embodiment, the titanium source is selected from one or more of titanium tetrachloride, titanium sulfate, titanium nitrate, tetraethyl titanate, tetrapropyl titanate, and tetrabutyl titanate.

[0055] In one embodiment, in step S1, the amphiphilic surfactant is selected from one or more of anionic surfactants and cationic surfactants; 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.

[0056] In one embodiment, the polymer in step S1 is selected from one or more of 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.

[0057] In a preferred embodiment, the structural filler is selected from one or more of hexadecyltrimethylammonium bromide, sodium dodecylbenzenesulfonate, PEO-PPO-PEO block copolymer, polyvinyl chloride, polystyrene, polyvinyl alcohol, and polymethyl methacrylate.

[0058] The reagents involved in this disclosure can all be purchased through ordinary channels or prepared by methods known in the art.

[0059] In one embodiment, the conditions for the first hydrothermal crystallization treatment in step S2 include: hydrothermal crystallization time of 5~240h, hydrothermal crystallization temperature of 110~220℃; and pressure of autogenous pressure. The conditions for the first calcination treatment in step S2 include: calcination temperature of 320~680℃ and calcination time of 1~16h.

[0060] In a preferred embodiment, the conditions for the first hydrothermal crystallization treatment in step S2 include: a hydrothermal crystallization time of 6 to 80 hours and a hydrothermal crystallization temperature of 130 to 185°C. The conditions for the first calcination treatment in step S2 include: a calcination temperature of 350~600℃ and a calcination time of 2~5h. The titanium-silicon molecular sieve prepared according to this embodiment has better catalytic activity.

[0061] In one specific embodiment, after the first hydrothermal crystallization treatment, the method further includes the steps of subjecting the product of the first hydrothermal crystallization treatment to a first filtration treatment and a first drying treatment, followed by the first calcination treatment. The temperature of the first drying treatment is 50~120℃, and the time is 1~12 hours.

[0062] In one embodiment, in step S3, the concentration of the alkaline solution is 1~5 mol / L, preferably 2~4 mol / L; The weight ratio of the alkaline solution to the first molecular sieve intermediate is (1~15):1, preferably (2~10):1; 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.

[0063] In one specific embodiment, in step S3, the conditions for alkali treatment include: a treatment temperature of 60~90℃ and a treatment time of 4~24h; preferably, the treatment temperature is 70~80℃ and the treatment time is 8~16h.

[0064] In one embodiment, in step S4, the weight ratio of the second molecular sieve intermediate, the second template agent, and water is (0.05~8):(1~40):1; preferably (0.1~5):(2~35):1. 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.

[0065] In one embodiment, the conditions for the second hydrothermal crystallization treatment in step S4 include: hydrothermal crystallization time of 5~240h, hydrothermal crystallization temperature of 110~220℃; and pressure of autogenous pressure. The conditions for the second calcination treatment in step S4 include: a calcination temperature of 320~680℃ and a calcination time of 1~16h.

[0066] In a preferred embodiment, the conditions for the second hydrothermal crystallization treatment in step S4 include: hydrothermal crystallization time of 6-80 hours, hydrothermal crystallization temperature of 130-185°C, and pressure of autogenous pressure; The conditions for the second calcination treatment in step S4 include: a calcination temperature of 350~600℃ and a calcination time of 2~5h. The titanium-silicon molecular sieve prepared according to this embodiment has better catalytic activity.

[0067] In one specific embodiment, after the second hydrothermal crystallization treatment, the method further includes a second filtration treatment, a second drying treatment, and then a second calcination treatment. The second drying treatment is performed at a temperature of 50-120°C for 1-12 hours.

[0068] The third aspect of this disclosure provides a hierarchical porous titanium-silicon molecular sieve prepared according to the method described in the second aspect of this disclosure.

[0069] The fourth aspect of this disclosure provides a method for preparing caprolactam from cyclohexanone oxime via gas-phase Beckmann rearrangement, comprising: reacting cyclohexanone oxime with a catalyst, wherein the catalyst comprises the hierarchical porous titanium-silicon molecular sieve described in the first and third aspects of this disclosure.

[0070] 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 .

[0071] The present disclosure will be described in detail below through examples.

[0072] The Fourier transform infrared (FT-IR) spectra of the samples were measured on a Nicolet 8210 Fourier transform infrared spectrometer, with a test range of 400–4000 cm⁻¹. -1 .

[0073] 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°.

[0074] 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 measurements. The volume fraction of the cavity structure relative to the total volume of the molecular sieve was obtained by measuring the TEM images: the volume of each cavity in the molecular sieve particles was measured based on the TEM images (calculated spherically, using the median of the sum of the maximum and minimum lengths passing through the center of the cavity structure as the spherical diameter, then obtaining the spherical radius, and finally calculating the percentage of the total volume of all cavities relative to the total volume of the molecular sieve particles; the average value was taken after calculating the cavity structure volume fraction of 50 molecular sieve particles).

[0075] 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 (the average value was taken after testing the particle size of 50 molecular sieves).

[0076] The total specific surface area and total pore volume of the samples 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.

[0077] X-ray fluorescence analysis of the samples (determination of the molar ratio of silicon to titanium in the molecular sieve) was performed using a Rigaku Electric Co., Ltd. 3013 instrument with a tungsten target, an excitation voltage of 40 kV, and an excitation current of 250 mA.

[0078] The reagents used in the following examples and comparative examples were all purchased through conventional channels.

[0079] Example 1 (1) 6g tetrabutyl titanate (0.0176mol), 104g tetraethyl silicate (0.5mol), 65g tetrapropylammonium hydroxide (TPAOH, 0.08mol) aqueous solution with a concentration of 25% by weight and 140g water were added to a 500mL beaker, placed on a magnetic stirrer with heating and stirring functions and mixed evenly. The mixture was stirred at 60℃ for 5 hours, and the evaporated water was replenished periodically to obtain a colorless and transparent titanium silica gel solution. (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; (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 first molecular sieve intermediate M-1. (4) Transfer the prepared first molecular sieve intermediate M-1 to a three-necked flask and add 2.5 mol L of the solution. -1 The NaOH solution and the first molecular sieve intermediate M-1 were refluxed at 75°C for 10 hours in a mass ratio of 4:1. After filtration, washing until neutral, drying and calcining, the second molecular sieve intermediate M-2 was obtained. (5) Mix 10g of the second molecular sieve intermediate M-2, 20g of 25% by weight tetrapropylammonium hydroxide (TPAOH, 5g) aqueous solution and 40g of water evenly (the weight ratio of the second template agent: water: second molecular sieve intermediate is 0.5:5.5:1), transfer to a stainless steel sealed reactor, and crystallize at 170℃ for 24h to obtain a 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 a titanium silicon molecular sieve sample, denoted as C-1.

[0080] The structural parameter characterization results of sample C-1 are listed in Table 2; The FT-IR spectrum of sample C-1 is as follows Figure 1 As shown in the figure, it can be seen that there are obvious terminal hydroxyl groups (3740cm). -1 ), ortho-hydroxyl group (3690cm) -1 ) and nested hydroxyl groups (3520cm) -1 The peak signals of the three characteristic peaks are obtained by calculating the peak area of ​​the spectrum. Figure 1 The peak areas of the three spectral peaks mentioned above are: Q1 = 0.64, Q2 = 0.72, and Q3 = 2.36. The values ​​of X1 and X2 obtained by formula (1) to (2) are listed in Table 3. The XRD pattern of sample C-1 indicates that the titanium silicate molecular sieve sample has an MFI topology. TEM image of sample C-1 as follows Figure 2 As shown in the figure, the molecular sieve has a hierarchical porous structure with multiple cavities within the crystal; and the size of a single cavity structure in the molecular sieve sample is 5~28 nm after measurement and calculation. SEM images of sample C-1 show that the molecular sieve consists of uniform ellipsoidal particles. The BET curve of sample C-1 shows a clear hysteresis loop between the nitrogen adsorption and desorption curves, with the initial relative pressure (P / P0) of the hysteresis loop being 0.45. TEM images of the first molecular sieve intermediate M-1 without dissolution and recrystallization are shown below. Figure 3 As shown, the TEM image of the second molecular sieve intermediate that has undergone alkali treatment but has not been dissolved and recrystallized is as follows. Figure 4 As shown, Figures 3-4 and Figure 2 By comparison, it can be seen that Figure 2 The titanium-silicon molecular sieves prepared using the method provided in this disclosure exhibit a large number of intracrystalline multi-cavity structures.

[0081] Comparative Example 1 This comparative example follows the preparation method of Example 1, but differs from Example 1 in that no structural filler is added and no alkali 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.

[0082] Comparative Example 2 This comparative example prepares titanium-silicon molecular sieves according to the method disclosed in existing technology CN112744836A: (1) Weigh out the raw materials in a 25% by weight aqueous solution of tetrapropylammonium hydroxide (TPAOH), tetraethyl orthosilicate (TEOS), tetrabutyl titanate (TBOT), and deionized water according to the molar ratio of TPAOH:TEOS:TBOT:H2O = 0.2:1:0.015:100, and add them sequentially to a beaker. Place the beaker on a magnetic stirrer equipped with heating and stirring functions and mix evenly. Stir at 80°C for 3 hours to carry out the first hydrolysis, and replenish the evaporated water as needed to obtain a colorless and transparent hydrolysate, i.e., the first hydrolysis mixture.

[0083] (2) During the stirring process, activated carbon is added to the first hydrolysis mixture above, wherein the mass ratio of SiO2 to semi-coke-based activated carbon is 1:0.16. The mixture is transferred to a stainless steel sealed reactor and subjected to a first hydrothermal treatment at 170°C for 24 hours. After filtration and washing, the filter cake is dried at 110°C for 24 hours and then calcined at 550°C for 6 hours to obtain the intermediate titanium-silicon molecular sieve, denoted as HS-1.

[0084] (3) Weigh out 25% by weight of tetrapropylammonium hydroxide (TPAOH) aqueous solution, tetraethyl orthosilicate (TEOS), tetrabutyl titanate (TBOT) and deionized water in a molar ratio of TPAOH:TEOS:TBOT:H2O=2:20:1:550, add them to a beaker in sequence, place it on a magnetic stirrer with heating and stirring functions and mix evenly, stir at 70°C for 10 hours to carry out the second hydrolysis, and replenish the evaporated water as needed to obtain a colorless and transparent hydrolysate, i.e. the second hydrolysis mixture.

[0085] (4) The above intermediate titanium-silicon molecular sieve HS-1, the second hydrolysis mixture and ammonium chloride are mixed to obtain a mixture containing TiO2, SiO2 and NH4. + The molar ratio was 1:35:0.3. The mixture was transferred to a stainless steel reactor and subjected to a second hydrothermal treatment at 170°C for 24 hours. After filtration and washing, it was dried at 120°C for 24 hours and calcined at 550°C for 6 hours to obtain the molecular sieve product, denoted as D-2. Its TEM image is shown below. Figure 5 As shown. Figure 5 and Figure 2 A comparison shows that, Figure 2 The molecular sieve prepared in Example 1 shown has a distinct intracrystalline multi-cavity structure.

[0086] Examples 2-9 Titanium-silicon molecular sieves were prepared according to the method of Example 1, except that the ratio and synthesis conditions were changed to obtain titanium-silicon molecular sieve samples denoted as C-2 to C-9; the preparation conditions are listed in Table 1, and the characterization results of the obtained molecular sieves are listed in Table 2.

[0087] Example 10 MEL-structured titanium-silicon molecular sieves were prepared according to the method of Example 1, except that the template agent was changed to tetrabutylammonium hydroxide (TBAOH), and the resulting titanium-silicon molecular sieve sample was designated C-10. 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 C-10 indicates that C-10 has a MEL structure.

[0088] Example 11 Hierarchical porous β-zeolites were 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 a BEA topology, and the resulting titanium silicate zeolite sample was designated C-11. 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 C-11 shows that C-11 has a BEA structure.

[0089] Example 12 Titanium-silicon molecular sieves were prepared according to the method of Example 1, but the difference from Example 1 is as follows: The temperature of the first hydrothermal crystallization treatment was 110℃ and the time was 96h; the temperature of the first calcination treatment was 320℃ and the time was 8h. The second hydrothermal crystallization treatment was carried out at a temperature of 110℃ for 96 hours; the second calcination treatment was carried out at a temperature of 320℃ for 8 hours. The obtained titanium-silicon molecular sieve sample is designated as C-12; the characterization results of the obtained molecular sieve C-12 are listed in Table 2.

[0090] Table 1

[0091] 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 aqueous solution of the first template agent; the water in the "water / second molecular sieve intermediate" calculation also includes water from the aqueous solution of the second template agent.

[0092] Table 2

[0093] According to the data in Table 2 above, compared with the molecular sieves D-1 to D-2 prepared by Comparative Examples 1 to 2, the molecular sieves C-1 to C-12 prepared by the publicly provided method have larger cavity sizes and a larger percentage of the total volume of the molecular sieve structure.

[0094] Test case 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: 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 200h, respectively.

[0095] 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.

[0096] 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%; Caprolactam selectivity (mol%) = (mol percentage of caprolactam in the product) / (100 - mol percentage of cyclohexanone oxime in the product) × 100%; Cyclohexanone oxime conversion reduction rate (%) = (24h cyclohexanone conversion rate - 200h cyclohexanone conversion rate) / 24h cyclohexanone conversion rate × 100%; The decrease in caprolactam selectivity (%) = (24h caprolactam selectivity - 200h caprolactam selectivity) / 24h caprolactam selectivity × 100%.

[0097] Table 3

[0098] According to the data in Table 3 above: Compared with the molecular sieves D-1 to D-2 prepared by Comparative Examples 1 and 2, the molecular sieves C-1 to C-12 prepared by the publicly provided method have X1 in the range of 0.8 to 2.2 and X2 in the range of 2.0 to 5.5 in the FT-IR spectrum characteristics. Molecular sieves C-1 to C-12 have higher catalytic activity in the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime, higher cyclohexanone oxime conversion and caprolactam selectivity, and lower reduction rate of cyclohexanone oxime conversion and caprolactam selectivity under long-term reaction conditions (200 h), indicating that molecular sieves C-1 to C-12 have higher catalytic stability.

[0099] Furthermore, the X1 of the molecular sieves C-1~C-8 and C-10~C-11 prepared in the examples is in the range of 1.0~2.0, and the X2 is in the range of 2.5~5.0. Compared with molecular sieves C-9 and C-12, the cyclohexanone oxime conversion rate and caprolactam selectivity are higher in the reaction using molecular sieves C-1~C-8 and C-10~C-11, and the catalytic stability is higher under long-term reaction conditions (200h).

[0100] Comparing Example 1 with Example 9, Example 1 prepared molecular sieves according to the raw material addition ratio in the preferred embodiment. The resulting molecular sieve C-1 had higher cyclohexanone oxime conversion and caprolactam selectivity in the catalytic reaction, and higher catalytic stability under long-term reaction conditions (200h).

[0101] Comparing Example 1 with Example 12, the molecular sieve C-1 prepared in Example 1 according to the reaction conditions in the preferred embodiment showed higher cyclohexanone oxime conversion and caprolactam selectivity in the catalytic reaction, and higher catalytic stability under long reaction conditions (200h).

[0102] 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.

[0103] 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.

[0104] 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 titanium-silicon molecular sieve, characterized in that, The titanium-silicon molecular sieve has the following FT-IR characteristics: The 3100~3900 cm⁻¹ of the titanium-silicon molecular sieve -1 In the peak fractionation results of the FT-IR spectrum 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; As defined in equation (1), X1 can be any value between 0.8 and 2.2: X1 = Q2 / Q1 (1); As defined in equation (2), X2 is any value between 2.0 and 5.5: X2=Q3 / Q1 (2).

2. The titanium-silicon molecular sieve according to claim 1, characterized in that, The value of X1 is any value between 1.0 and 2.0; the value of X2 is any value between 2.5 and 5.

0.

3. The titanium-silicon molecular sieve according to claim 1, characterized in that, The molar ratio of silicon atoms to titanium atoms in the titanium-silicon molecular sieve is (6~130):1, preferably (8~95):1; Optionally, the configuration of the titanium-silicon molecular sieve is selected from one or more of the MFI topology, MEL topology, BEA topology and SVR topology; preferably, it is the MFI topology.

4. The titanium-silicon molecular sieve according to claim 1, characterized in that, The titanium-silicon molecular sieve has multiple cavity structures within its crystal; wherein the size of a single cavity structure is 2~55nm, preferably 3~46nm. Preferably, the volume of all the cavity structures accounts for 5-60% of the total volume of the molecular sieve, more preferably 8-55%; Optionally, the shape of the cavity structure is selected from one or more of the following: sphere, cube, ellipsoid, and irregular cube.

5. The titanium-silicon molecular sieve according to claim 1, characterized in that, The titanium-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. Optionally, the average particle size of the molecular sieve particles is 0.12~0.68μm, preferably 0.16~0.58μm; the BET specific surface area is 270~660m². 2 / g, preferably 300~630m 2 / g; Microporous specific surface area is 260~550m² 2 / g, preferably 285~525m 2 / g; total pore volume is 0.15~0.65cm³. 3 / g, preferably 0.2~0.55cm 3 / g; mesopore volume is 0.12~0.55cm³ 3 / g, preferably 0.15~0.45cm 3 / g; Optionally, a hysteresis loop exists between the adsorption isotherm and desorption isotherm of the low-temperature nitrogen adsorption of the titanium-silicon molecular sieve; preferably, the initial relative pressure (P / P0) at which the hysteresis loop appears is 0.32~0.55, more preferably 0.36~0.

48.

6. A method for preparing hierarchical porous titanium-silicon molecular sieves, characterized in that, Includes the following steps: S1. The titanium source, silicon source, first template agent, water and structural filler are mixed to obtain a reaction mixture; wherein the structural filler is selected from one or more of amphiphilic surfactants and polymers. S2. The reaction mixture is subjected to a first hydrothermal crystallization treatment and a first calcination treatment in sequence to obtain a first molecular sieve intermediate; S3. The first molecular sieve intermediate is contacted with an alkaline solution for alkaline treatment to obtain the second molecular sieve intermediate. S4. Mix the second molecular sieve intermediate, the second template agent and water, and then perform the second hydrothermal crystallization treatment and the second calcination treatment in sequence.

7. The method according to claim 6, characterized in that, In step S1, the molar ratio of titanium source: silicon source: first template agent: water is (0.008~0.55):1:(0.05~5):(1~80); the weight ratio of silicon source in SiO2 form to structural filler is (5~90):1; Preferably, in step S1, the molar ratio of titanium source: silicon source: first template agent: water is (0.01~0.45):1:(0.08~3.5):(5~60); the weight ratio of silicon source in SiO2 form to structural filler is (6~70):

1.

8. The method according to claim 6, characterized in that, 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. A further preferred option is a silicone grease, wherein the silicone 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 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.

9. The method according to claim 6, characterized in that, 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 alcohol amines; 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): (B); 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; 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.

10. The method according to claim 6, characterized in that, In step S1, the titanium source is selected from one or more of organic titanium sources and inorganic titanium sources; The organic titanium source is a titanium-containing organic ester, selected from at least one of the structures represented by the general formula (C): （C）； R5, R6, R7, and R8 are each selected from alkyl groups having 1 to 6 carbon atoms, preferably straight-chain alkyl groups having 1 to 4 carbon atoms and branched alkyl groups having 3 to 6 carbon atoms, and more preferably straight-chain alkyl groups having 2 to 4 carbon atoms and branched alkyl groups having 2 to 4 carbon atoms; optionally, R5, R6, R7, and R8 are each selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, isopentyl, hexyl, or isohexyl; preferably, each is independently selected from ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, or tert-butyl. The inorganic titanium source is selected from one or more of titanium chloride, nitrate or sulfate; Preferably, the titanium source is selected from one or more of titanium tetrachloride, titanium sulfate, titanium nitrate, tetraethyl titanate, tetrapropyl titanate, and tetrabutyl titanate.

11. The method according to claim 6, characterized in that, In step S1, the amphiphilic surfactant is selected from one or more of anionic surfactants and cationic surfactants; 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 14-16 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. Optionally, the polymer is selected from one or more of 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); optionally, the molecular weight of the polymer is 10,000 to 200,000. More preferably, the structural filler is selected from one or more of hexadecyltrimethylammonium bromide, sodium dodecylbenzenesulfonate, PEO-PPO-PEO block copolymer, polyvinyl chloride, polystyrene, polyvinyl alcohol, and polymethyl methacrylate.

12. The method according to claim 6, characterized in that, Step S1 includes: a. Mix titanium source, silicon source, first template agent and water to obtain silicon hydrolysis sol; b. Add the structural filler to the silicon hydrolysate sol, and mix to obtain the reaction mixture; Optionally, the mixing conditions in step a include stirring at 40~90℃ for 6~12 hours; Optionally, the mixing conditions in step b include stirring at 20~50℃ for 2~4 hours; Preferably, the silicon source is an organosilicon grease, and step a further includes a hydrolysis and alcohol removal treatment after mixing the titanium source, silicon source, first template agent and water to obtain the silicon hydrolysate sol; Optionally, the conditions for the hydrolysis and alcohol removal treatment include: stirring and hydrolyzing at 40~90℃ for 6~12h; preferably, stirring and hydrolyzing at 60~85℃ for 8~10h.

13. The method according to claim 6, characterized in that, The conditions for the first hydrothermal crystallization treatment in step S2 and the second hydrothermal crystallization treatment in step S4 each independently include: hydrothermal crystallization time of 5~240h, hydrothermal crystallization temperature of 110~220℃; preferably, hydrothermal crystallization time of 6~80h, hydrothermal crystallization temperature of 130~185℃; and pressure of self-generated pressure. The conditions for the first roasting treatment in step S2 and the second roasting treatment in step S4 each independently include: a roasting temperature of 320~680℃ and a roasting time of 1~16h; preferably, a roasting temperature of 350~600℃ and a roasting time of 2~5h.

14. The method according to claim 6, characterized in that, In step S3, the concentration of the alkaline solution is 1~5 mol / L, preferably 2~4 mol / L; The weight ratio of the alkaline solution to the first molecular sieve intermediate is (1~15):1, preferably (2~10):1; 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; Optionally, in step S3, the conditions for alkali treatment include: a treatment temperature of 60~90℃ and a treatment time of 4~24h; preferably, the treatment temperature is 70~80℃ and the treatment time is 8~16h.

15. The method according to claim 6, characterized in that, In step S4, the weight ratio of the second template agent: water: second molecular sieve intermediate is (0.05~8):(1~40):1; preferably (0.1~5):(2~35):

1.

16. The hierarchical porous titanium-silicon molecular sieve prepared by the method according to any one of claims 6 to 15.

17. A method for preparing caprolactam from cyclohexanone oxime via gas-phase Beckmann rearrangement, comprising: The reaction is carried out by contacting cyclohexanone oxime with a catalyst, characterized in that the catalyst comprises the hierarchical porous titanium silicate molecular sieve as described in any one of claims 1 to 5 and 16.

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