Titanium silical molecular sieve with hierarchical pore structure, method for preparing the same and method for preparing caprolactam

Abstract

This disclosure relates to a titanium-silicon molecular sieve with a hierarchical porous structure, a method for preparing the same, and a method for preparing caprolactam. The titanium-silicon molecular sieve has the following characteristics: 1 ¹H MAS NMR characteristics: The peak area at the chemical shift position of 1.8±0.1ppm is denoted as A1, the peak area at the chemical shift position of 2.2ppm±0.1ppm is denoted as A2, the peak area at the chemical shift position of 2.8ppm±0.1ppm is denoted as A3, the peak area at the chemical shift position of 3.8±0.1ppm is denoted as A4, and the peak area at the chemical shift position of 4.6±0.1ppm is denoted as A5; X1 is defined as any value between 0.5 and 2.2 as in Equation (1): X1=(A2+A3) / A1 (Equation (1)); X2 is defined as any value between 0.1 and 1.2 as in Equation (2): X2=A4 / A1 (Equation (2)); X3 is defined as any value between 0.05 and 0.65 as in Equation (3): X3=A5 / A1 (Equation (3)).

Description

Technical Field

[0001] This disclosure relates to the field of titanium-silicon molecular sieve preparation, specifically to a titanium-silicon molecular sieve with a hierarchical porous structure, its preparation method, and a method for preparing caprolactam. Background Technology

[0002] The Beckmann rearrangement is a process that converts ketoxime compounds into amides. Its most important application in chemical production is the production of caprolactam. Caprolactam is an important monomer for the synthesis of nylon-6 and is widely used in the production of engineering plastics, nylon-6 fibers, and industrial tire cord fabrics, among other important downstream products. It can also be used in coatings, pharmaceuticals, and fine chemicals.

[0003] Currently, over 95% of caprolactam production uses the cyclohexanone oxime liquid-phase Beckmann rearrangement process, which uses concentrated sulfuric acid (or fuming sulfuric acid) as a catalyst and solvent. This process suffers from serious equipment corrosion and environmental pollution. After the reaction, liquid ammonia is used to neutralize the waste sulfuric acid, generating a large amount of low-value ammonium sulfate byproducts (1.9 t ammonium sulfate / t caprolactam), resulting in poor techno-economic performance of this route.

[0004] 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, and has an atom utilization rate of nearly 100%, making it an environmentally friendly green production process for caprolactam. Among them, pure silica molecular sieves with the MFI topology have shown 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.

[0005] 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 carbon deposits clogging the pores. Furthermore, the silanol active centers of pure silicon molecules are unstable, and thermal and alkaline byproducts easily deactivate them, necessitating the development of processes to further enhance the catalyst's resistance to deactivation.

[0006] For example, Baojun Li's research group (RSC Adv., 2013, 3, 20811–20815) added S-1 and TS-1 molecular sieves as seed crystals during the molecular sieve crystallization process to synthesize titanium silicate molecular sieves with different particle sizes for the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime. The conversion rate of this molecular sieve 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 silicate molecular sieves, obtaining a titanium silicate molecular sieve with hierarchical pores. The yield of caprolactam remained at 1.6 mmol CPL g after 30 hours of reaction with this molecular sieve. -1 cat h -1 .

[0007] 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 titanium-silicon molecular sieve with a hierarchical porous structure, a method for preparing the same, and a method for preparing caprolactam. This method introduces titanium atomic active centers into the molecular sieve, significantly enhancing the molecular sieve's resistance to deactivation. It also significantly improves 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 titanium-silicon molecular sieve with a hierarchical porous structure, wherein the titanium-silicon molecular sieve has the following characteristics: 1 HMAS NMR characteristics:

[0010] The titanium-silicon molecular sieve 1 In the peak separation results of the 1–6 ppm range of chemical shifts in the 1–6 ppm HMAS NMR spectrum:

[0011] The peak area at the chemical shift position of 1.8±0.1ppm is recorded as A1, the peak area at the chemical shift position of 2.2ppm±0.1ppm is recorded as A2, the peak area at the chemical shift position of 2.8ppm±0.1ppm is recorded as A3, the peak area at the chemical shift position of 3.8±0.1ppm is recorded as A4, and the peak area at the chemical shift position of 4.6±0.1ppm is recorded as A5.

[0012] X1, as defined in equation (1), is any value between 0.5 and 2.2:

[0013] X1 = (A2 + A3) / A1, Equation (1);

[0014] X2, as defined in equation (2), is any value between 0.1 and 1.2:

[0015] X2 = A4 / A1, Equation (2);

[0016] As defined in equation (3), X3 is any value between 0.05 and 0.65:

[0017] X3 = A5 / A1, equation (3).

[0018] Optionally, the value of X1 is any value between 0.6 and 1.8; the value of X2 is any value between 0.15 and 1.10; and the value of X3 is any value between 0.10 and 0.55.

[0019] Optionally, the molar ratio of silicon atoms to titanium atoms in the titanium-silicon molecular sieve is (8-150):1, preferably (15-120):1;

[0020] 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.

[0021] Optionally, the titanium-silicon molecular sieve has multiple cavity structures within its crystal; wherein the size of a single cavity structure is 2–50 nm, preferably 4–45 nm;

[0022] Preferably, the volume of all the cavity structures accounts for 8-55% of the total volume of the molecular sieve, more preferably 12-50%;

[0023] Optionally, the shape of the cavity structure is selected from one or more of the following: sphere, cube, ellipsoid, and irregular cube.

[0024] 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;

[0025] Optionally, the average particle size of the molecular sieve particles is 0.1–0.7 μm, preferably 0.13–0.62 μm; the BET specific surface area is 260–620 m². 2 / g, preferably 280-540m 2 / g; microporous specific surface area is 280-500m² 2 / g, preferably 300-480m 2 / g; total pore volume is 0.16–0.55 cm³. 3 / g, preferably 0.22~0.45cm 3 / g; mesopore volume is 0.09–0.38 cm³ 3 / g, preferably 0.12~0.34cm 3 / g;

[0026] 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 0.35 to 0.55.

[0027] The 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, mixing a titanium source, a silicon source, a first template agent, water, a hard template agent, and a polymer to obtain a reaction mixture; S2, subjecting the reaction mixture to a first hydrothermal crystallization treatment and a first calcination treatment in sequence to obtain a molecular sieve intermediate; S3, mixing the molecular sieve intermediate, a second template agent, and water, and then subjecting the mixture to a second hydrothermal crystallization treatment and a second calcination treatment in sequence.

[0028] Optionally, in step S1, the molar ratio of titanium source: silicon source: first template agent: water is (0.005~0.55):1:(0.02~1.8):(1~50); preferably (0.01~0.42):1:(0.04~1.5):(10~45); the silicon source is in the form of SiO2, and the weight ratio of hard template agent: polymer: silicon source is (0.02~0.75):(0.01~0.55):1, preferably (0.04~0.55):(0.03~0.4):1.

[0029] 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.

[0030] A further preferred option is a silicone grease, wherein the silicone grease has the general formula shown in formula (A):

[0031]

[0032] 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 dEach 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.

[0033] Optionally, the first template agent in step S1 and the second template agent in step S3 are organic bases; and each is preferably selected independently from at least one of quaternary ammonium bases, aliphatic amines and aliphatic alcohol amines;

[0034] 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):

[0035] 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.

[0036] 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.

[0037] Optionally, in step S1, the titanium source is selected from one or more of organic titanium sources and inorganic titanium sources;

[0038] The organic titanium source is a titanium-containing organic ester, selected from at least one of the structures represented by the general formula (C) below:

[0039]

[0040] 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.

[0041] The inorganic titanium source is selected from one or more of titanium chloride, nitrate or sulfate;

[0042] Preferably, the titanium source is selected from one or more of titanium tetrachloride, titanium sulfate, titanium nitrate, tetraethyl titanate, tetrapropyl titanate, and tetrabutyl titanate.

[0043] Optionally, in step S1, the hard template agent is selected from one or more of carbon-based materials, resin-based materials, and inorganic solid compound materials;

[0044] Preferably, the carbon-based material is selected from one or more of carbon nanoparticles, carbon nanotubes, carbon nanofibers, and ordered mesoporous carbon;

[0045] Preferably, the resin material is selected from one or more of phenolic resin, polyester resin and polyamide resin;

[0046] Preferably, the inorganic solid compound material is selected from one or more of calcium carbonate, magnesium hydroxide, and sodium carbonate.

[0047] Optionally, in step S1, the polymer is selected from one or more of polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyvinyl alcohol, polyvinyl acetate, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol butyral, polyethyleneimine, 4-polyvinylpyridine, and poly(diallyldimethylammonium chloride).

[0048] Further preferably, the polymer is selected from one or more of polyethylene, polypropylene, polystyrene, and polyacrylonitrile;

[0049] Optionally, the molecular weight of the polymer is 10,000 to 200,000.

[0050] Optionally, step S1 includes:

[0051] a. Mix titanium source, silicon source, first template agent and water to obtain silicon hydrolysis sol;

[0052] b. Add the hard template agent and the polymer to the hydrolyzed sol of the silicon respectively, and mix them to obtain the reaction mixture;

[0053] Optionally, the mixing conditions in step a include stirring at 40–90°C for 6–12 hours;

[0054] Optionally, the mixing conditions in step b include stirring at 20–50°C for 2–4 hours;

[0055] 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;

[0056] 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.

[0057] Optionally, in step S3, the weight ratio of the second template agent: water: molecular sieve intermediate is (0.08-3.5):(0.5-25):1; preferably (0.12-2.5):(2-18):1.

[0058] Optionally, the conditions for the first hydrothermal crystallization treatment in step S2 and the second hydrothermal crystallization treatment in step S3 each independently include: a hydrothermal crystallization time of 4–180 h and a hydrothermal crystallization temperature of 120–220 °C; preferably, a hydrothermal crystallization time of 6–80 h and a hydrothermal crystallization temperature of 140–185 °C; and the pressure is self-generated pressure.

[0059] The conditions for the first roasting treatment in step S2 and the second roasting treatment in step S3 each independently include: a roasting temperature of 350-750°C and a roasting time of 1-15 h; preferably, a roasting temperature of 380-620°C and a roasting time of 1.5-4.5 h.

[0060] The third aspect of this disclosure provides a titanium-silicon molecular sieve with a hierarchical porous structure prepared according to the method described in the second aspect of this disclosure.

[0061] 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 titanium silicate molecular sieve with a hierarchical porous structure described in the first and third aspects of this disclosure.

[0062] Through the above technical solutions, this disclosure provides a titanium-silicon molecular sieve with a hierarchical porous structure, its preparation method, and a method for preparing caprolactam. This method introduces active titanium atom centers into the molecular sieve framework, effectively improving the molecular sieve's resistance to deactivation and helping to extend its service life under alkaline reaction conditions. The titanium-silicon molecular sieve provided by this disclosure has abundant hydrogen-bonded silanol groups, and the molecular sieve satisfies the values ​​of X1 (0.5–2.2), X2 (0.1–1.2), and X3 (0.05–0.65) as defined in formulas (1) to (3). This titanium-silicon molecular sieve significantly improves the selectivity of caprolactam in the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime. The hierarchical porous structure of the titanium-silicon molecular sieve also endows it with advantages such as a large specific surface area and pore volume, which is beneficial for catalytic reactions.

[0063] Other features and advantages of this disclosure will be described in detail in the following detailed description section. Attached Figure Description

[0064] 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:

[0065] Figure 1 The molecular sieve obtained in Example 1 1 HMAS NMR spectrum;

[0066] Figure 2 The XRD pattern of the molecular sieve obtained in Example 1;

[0067] Figure 3 Here is a TEM image of the molecular sieve obtained in Example 1;

[0068] Figure 4 Here is an SEM image of the molecular sieve obtained in Example 1;

[0069] Figure 5 The BET curve of the molecular sieve obtained in Example 1 is shown below.

[0070] Figure 6 Here is a TEM image of the intermediate product obtained in Example 1;

[0071] Figure 7 Here is a TEM image of the molecular sieve obtained in Comparative Example 2;

[0072] Figure 8 The XRD pattern of the molecular sieve product obtained in Example 10;

[0073] Figure 9 This is the XRD pattern of the molecular sieve product obtained in Example 11. Detailed Implementation

[0074] 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.

[0075] The first aspect of this disclosure provides a titanium-silicon molecular sieve having a hierarchical porous structure, wherein the titanium-silicon molecular sieve has the following characteristics: 1 HMAS NMR characteristics:

[0076] The titanium-silicon molecular sieve 1 In the peak separation results of the 1–6 ppm range of chemical shifts in the 1–6 ppm HMAS NMR spectrum:

[0077] The peak area at the chemical shift position of 1.8±0.1ppm is recorded as A1, the peak area at the chemical shift position of 2.2ppm±0.1ppm is recorded as A2, the peak area at the chemical shift position of 2.8ppm±0.1ppm is recorded as A3, the peak area at the chemical shift position of 3.8±0.1ppm is recorded as A4, and the peak area at the chemical shift position of 4.6±0.1ppm is recorded as A5.

[0078] X1, as defined in equation (1), is any value between 0.5 and 2.2:

[0079] X1 = (A2 + A3) / A1, Equation (1);

[0080] X2, as defined in equation (2), is any value between 0.1 and 1.2:

[0081] X2 = A4 / A1, Equation (2);

[0082] As defined in equation (3), X3 is any value between 0.05 and 0.65:

[0083] X3 = A5 / A1, equation (3).

[0084] This disclosure provides a titanium-silicon molecular sieve with a hierarchical porous structure, which can introduce titanium atom active centers into the molecular sieve framework, effectively improving the molecular sieve's resistance to deactivation and helping to extend the service life of the molecular sieve under alkaline reaction conditions. The titanium-silicon molecular sieve provided by this disclosure has abundant hydrogen-bonded silanol groups, and the molecular sieve satisfies the values ​​of X1 (0.5-2.2), X2 (0.1-1.2), and X3 (0.05-0.65) as defined in formulas (1) to (3). This titanium-silicon molecular sieve significantly improves the selectivity of caprolactam in the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime. The hierarchical porous structure of the titanium-silicon molecular sieve also endows it with advantages such as large specific surface area and pore volume, which are beneficial to the catalytic reaction.

[0085] The inventors of this disclosure have discovered through extensive experimental research that, in titanium-silicon molecular sieves... 1 The ¹H MAS NMR spectrum reveals two types of silanol active centers: independent silanol active centers with a chemical shift of 1.8 ± 0.1 ppm, and hydrogen-bonded silanol active centers with chemical shifts in the range of 2–6 ppm. Peak segmentation results show that the peaks of hydrogen-bonded silanol active centers include 2.2 ± 0.1 ppm, 2.8 ± 0.1 ppm, 3.8 ± 0.1 ppm, and 4.6 ± 0.1 ppm. Furthermore, the ratio of the peak areas of different types of silanol active centers meets the range of X1–X3. This titanium-silicon molecular sieve exhibits good catalytic activity and stability, especially in the gas-phase Beckmann rearrangement of cyclohexanone oxime, where it can effectively improve the conversion rate of cyclohexanone oxime and the selectivity of caprolactam.

[0086] In this disclosure, 1 HMAS NMR testing can be performed using conventional testing instruments and methods in the field, as well as conventional processing software and methods to perform peak separation, integration, and other processing on the spectral peaks.

[0087] In a preferred embodiment, the value of X1 is any value between 0.6 and 1.8; the value of X2 is any value between 0.15 and 1.10; and the value of X3 is any value between 0.10 and 0.55. When the values ​​of X1 to X3 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 the catalytic stability of the molecular sieve is better under long-term reaction conditions.

[0088] In one embodiment, the molar ratio of silicon atoms to titanium atoms in the titanium-silicon molecular sieve is (8-150):1, preferably (15-120):1. This disclosure obtains the molar ratio of silicon atoms to titanium atoms in the molecular sieve using X-ray fluorescence spectroscopy.

[0089] 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 2–50 nm, preferably 4–45 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.

[0090] 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 2–50 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 2–50 nm.

[0091] In a preferred embodiment, all of the cavity structures account for 8-55% of the total volume of the molecular sieve, more preferably 12-50%;

[0092] Optionally, the shape of the cavity structure is selected from one or more of the following: sphere, cube, ellipsoid, and irregular cube.

[0093] 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.

[0094] Optionally, the average particle size of the molecular sieve particles is 0.1–0.7 μm, preferably 0.13–0.62 μm; the BET specific surface area is 260–620 m². 2 / g, preferably 280-540m 2 / g; microporous specific surface area is 280-500m² 2 / g, preferably 300-480m 2 / g; total pore volume is 0.16–0.55 cm³. 3 / g, preferably 0.22~0.45cm 3 / g; mesopore volume is 0.09–0.38 cm³ 3 / g, preferably 0.12~0.34cm 3 / g.

[0095] 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.

[0096] In one specific embodiment, the initial relative pressure (P / P0) at which the hysteresis loop appears is 0.35 to 0.55, preferably 0.38 to 0.48.

[0097] 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.

[0098] 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:

[0099] S1. The titanium source, silicon source, first template agent, water, hard template agent and polymer are mixed to obtain a reaction mixture;

[0100] S2. The reaction mixture is subjected to a first hydrothermal crystallization treatment and a first calcination treatment in sequence to obtain a molecular sieve intermediate;

[0101] S3. Mix the molecular sieve intermediate, the second template agent and water, and then perform a second hydrothermal crystallization treatment and a second calcination treatment in sequence.

[0102] This disclosure provides a method for preparing titanium-silicon molecular sieves with hierarchical porous structures. Introducing a titanium source into the reaction raw materials allows for the introduction of active titanium atom centers into the molecular sieve framework during synthesis, improving molecular sieve performance. Furthermore, this disclosure introduces a hard template agent and a polymer into the molecular sieve synthesis raw materials. The hard template agent and the inorganic molecular sieve framework primarily expand pores through space-filling. The introduction of the polymer also helps address the issue of closed, isolated spaces in the hierarchical porous structure synthesized by the hard template method. The polymer self-assembles with the inorganic aluminosilicate through hydrogen bonding or electrostatic attraction. After calcination, the hard template agent and polymer are removed, forming a molecular sieve material with abundant open channels. Then, a template agent is added for dissolution and recrystallization to prepare a hierarchical porous titanium-silicon molecular sieve with a multi-cavity structure.

[0103] In this disclosure, the space-filling effect of the hard template agent and the hydrogen bonding between the polymer and the silanol groups of the organosilicon source are combined to ensure the realization of a rich open-pore expansion effect. Then, the template agent is introduced into the molecular sieve with open pores, and the dissolution-recrystallization mechanism is used to obtain a multi-level porous titanium-silicon molecular sieve.

[0104] In one embodiment, in step S1, the molar ratio of titanium source: silicon source: first template agent: water is (0.005~0.55):1:(0.02~1.8):(1~50); the silicon source is in the form of SiO2, and the weight ratio of hard template agent: polymer: silicon source is (0.02~0.75):(0.01~0.55):1.

[0105] In a preferred embodiment, in step S1, the molar ratio of titanium source: silicon source: first template agent: water is (0.01–0.42):1:(0.04–1.5):(10–45); the silicon source is in the form of SiO2, and the weight ratio of hard template agent: polymer: silicon source is (0.04–0.55):(0.03–0.4):1. The titanium-silicon molecular sieve prepared according to this embodiment has higher catalytic activity and catalytic stability.

[0106] 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.

[0107] A further preferred option is a silicone grease, wherein the silicone grease has the general formula shown in formula (A):

[0108]

[0109] Where R a R b R c R d Each is independently selected from alkyl groups having 1 to 6 carbon atoms, wherein the alkyl group is branched or straight-chain alkyl; preferably, R a R b R c R d Each is independently selected from straight-chain alkyl groups having 1 to 4 carbon atoms or branched alkyl groups having 3 to 4 carbon atoms; more preferably, the R a R b R c R d Each is independently selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, or tert-butyl.

[0110] 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.

[0111] 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.

[0112] 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):

[0113] 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.

[0114] 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.

[0115] In one embodiment, step S1 includes:

[0116] a. Mix titanium source, silicon source, first template agent and water to obtain silicon hydrolysis sol;

[0117] b. Add the hard template agent and the polymer to the hydrolyzed sol of the silicon respectively, and mix them to obtain the reaction mixture;

[0118] Optionally, the mixing conditions in step a include stirring at 40–90°C for 6–12 hours;

[0119] Optionally, the mixing conditions in step b include stirring at 20–50°C for 2–4 hours.

[0120] 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;

[0121] 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.

[0122] In one embodiment, in step S1, the titanium source is selected from one or more of organic titanium sources and inorganic titanium sources;

[0123] The organic titanium source is a titanium-containing organic ester, selected from at least one of the structures represented by the general formula (C) below:

[0124]

[0125] 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.

[0126] The inorganic titanium source is selected from one or more of titanium chloride, nitrate or sulfate.

[0127] 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.

[0128] In one embodiment, in step S1, the hard template agent is selected from one or more of carbon-based materials, resin-based materials, and inorganic solid compound materials.

[0129] In one specific embodiment, the carbon-based material is selected from one or more of carbon nanoparticles, carbon nanotubes, carbon nanofibers, and ordered mesoporous carbon.

[0130] The resin material is selected from one or more of phenolic resin, polyester resin and polyamide resin;

[0131] The inorganic solid compound material is selected from one or more of calcium carbonate, magnesium hydroxide, and sodium carbonate.

[0132] The hard template agent used in this disclosure can be of the size specifications commonly used in the art. In one specific embodiment, when the hard template agent is in particulate form (e.g., carbon nanoparticles, ordered mesoporous carbon, calcium carbonate, magnesium hydroxide, etc.), the average particle size of the hard template agent can be 1–100 nm; when the hard template agent is carbon nanotubes, the diameter of the hard template agent is 5–50 nm and the length is 2–30 μm; when the hard template agent is carbon nanofibers, the diameter of the hard template agent is 3–80 nm and the length is 1–40 μm.

[0133] In one embodiment, in step S1, the polymer is selected from one or more of polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), polyvinyl alcohol (PVA), polyvinyl acetate (PVAC), polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), polyvinyl butyral (PVB), polyethyleneimine (PEI), 4-polyvinylpyridine, and poly(diallyldimethylammonium chloride);

[0134] More preferably, the polymer is selected from one or more of polyethylene, polypropylene, polystyrene, and polyacrylonitrile.

[0135] In one specific embodiment, the molecular weight of the polymer is 10,000 to 200,000.

[0136] All reagents used in this disclosure can be purchased through conventional channels or prepared using methods known in the art.

[0137] In one embodiment, the conditions for the first hydrothermal crystallization treatment in step S2 include: hydrothermal crystallization time of 4 to 180 hours, hydrothermal crystallization temperature of 120 to 220°C, and pressure of self-generated pressure;

[0138] The conditions for the first calcination treatment in step S2 include: a calcination temperature of 350–750°C and a calcination time of 1–15 h.

[0139] In a preferred embodiment, the conditions for the first hydrothermal crystallization treatment in step S2 include: hydrothermal crystallization time of 6-80 hours, hydrothermal crystallization temperature of 140-185°C, and pressure of autogenous pressure;

[0140] The conditions for the first calcination treatment in step S2 include: a calcination temperature of 380–620°C and a calcination time of 1.5–4.5 h. The titanium-silicon molecular sieve prepared according to this embodiment exhibits better catalytic activity.

[0141] 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°C, and the time is 1–12 hours.

[0142] In one embodiment, in step S3, the selection range of the second template agent is the same as that of the first template agent, which will not be repeated here; the first template agent and the second template agent used in the reaction can be the same or different; preferably, the first template agent and the second template agent are the same template agent.

[0143] In one embodiment, in step S3, the weight ratio of the second template agent: water: molecular sieve intermediate is (0.08–3.5):(0.5–25):1; preferably (0.12–2.5):(2–18):1. By preparing the sieve according to the preferred weight ratio in this embodiment, a molecular sieve with higher catalytic activity can be obtained.

[0144] In one embodiment, the conditions for the second hydrothermal crystallization treatment in step S3 include: a hydrothermal crystallization time of 4–180 h, a hydrothermal crystallization temperature of 120–220 °C, and an autogenous pressure.

[0145] The conditions for the second calcination treatment in step S3 include: a calcination temperature of 350–750°C and a calcination time of 1–15 h.

[0146] In a preferred embodiment, the conditions for the second hydrothermal crystallization treatment in step S3 include: a hydrothermal crystallization time of 6–80 h, a hydrothermal crystallization temperature of 140–185 °C, and an autogenous pressure;

[0147] The conditions for the second calcination treatment in step S3 include a calcination temperature of 380–620°C and a calcination time of 1.5–4.5 h.

[0148] In one specific embodiment, after the second hydrothermal crystallization treatment, the method further includes a second filtration treatment and a second drying treatment of the product from the second hydrothermal crystallization treatment, followed by the second calcination treatment. The temperature of the second drying treatment is 50–120°C, and the time is 1–12 hours.

[0149] The third aspect of this disclosure provides a titanium-silicon molecular sieve with a hierarchical porous structure prepared according to the method described in the second aspect of this disclosure.

[0150] 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 titanium silicate molecular sieve with a hierarchical porous structure described in the first and third aspects of this disclosure.

[0151] 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 .

[0152] The present disclosure will be described in detail below through examples.

[0153] The sample 1 H MAS NMR spectra were obtained on a Varian Infinityplus-400 spectrometer using a 4mm dual resonance probe, a Ф4mm ZrO2 rotor, a resonance frequency of 400.1MHz, a magic angle rotation speed of 10kHz, a pulse width of 3.57μs, a cycle delay of 1s, and approximately 4000 scans.

[0154] 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°.

[0155] 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).

[0156] 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).

[0157] 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.

[0158] 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.

[0159] The reagents used in the following examples and comparative examples were all purchased through conventional channels.

[0160] Example 1

[0161] (1) Add 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 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 at regular intervals to obtain a colorless and transparent titanium silica gel solution.

[0162] (2) Add 9g of carbon nanoparticles (purchased from Bailingwei, with an average particle size of 15nm) and 3g of polystyrene (PS, purchased from Inokai, with a molecular weight of 20000) to the mixture in step (1) (the weight ratio of hard template agent: polymer: silicon source is 0.3:0.1:1), and stir for 2 hours;

[0163] (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 intermediate product M-1.

[0164] (4) Mix 10g of intermediate product M-1 sample, 20g of 25% by weight tetrapropylammonium hydroxide (TPAOH, 5g) aqueous solution and 40g of water evenly (the weight ratio of second template agent: water: molecular sieve intermediate is 0.5:5.5:1), transfer to a stainless steel closed reactor, and crystallize 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 the titanium silicon molecular sieve sample, which is denoted as C-1.

[0165] The structural parameter characterization results of sample C-1 are listed in Table 2;

[0166] Sample C-1 1 HMAS NMR spectrum as follows Figure 1 As shown in the figure, it can be seen that the titanium-silicon molecular sieve sample has an isolated silanol peak at a chemical shift of 1.8 ppm, and silanol peaks with hydrogen bonds between each other (2.2 ppm, 2.8 ppm, 3.8 ppm and 4.6 ppm, respectively) in the range of 2 to 6 ppm, indicating that the titanium-silicon molecular sieve prepared in this embodiment has a rich variety of silanol active species; the peak areas of the above five peaks were calculated by integration and were as follows: A1 is 77559, A2 is 45005, A3 is 39245, A4 is 30954 and A5 is 19694. The values ​​of X1 to X3 calculated by formulas (1) to (3) are listed in Table 3.

[0167] The XRD pattern of sample C-1 is as follows Figure 2 As shown, this indicates that the titanium silicate molecular sieve sample has an MFI topology.

[0168] TEM image of sample C-1 as follows Figure 3 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 is measured and calculated to be 5–38 nm.

[0169] SEM image of sample C-1 as follows Figure 4 As shown in the figure, the molecular sieve consists of uniform ellipsoidal particles.

[0170] The BET curve of sample C-1 is shown below. Figure 5As 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 0.46.

[0171] TEM of intermediate product M-1 without dissolution and recrystallization, as shown in... Figure 6 As shown, Figure 6 and Figure 3 By comparison, it can be seen that Figure 3 The intermediate products, after being dissolved and recrystallized, formed a large number of intracrystalline multi-cavity structures.

[0172] Comparative Example 1

[0173] This comparative example follows the preparation method of Example 1, but differs from Example 1 in that no hard template agent or polymer is added, and 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.

[0174] Comparative Example 2

[0175] This comparative example prepares titanium-silicon molecular sieves according to the method disclosed in existing technology CN112744836A:

[0176] (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, replenishing the evaporated water as needed, to obtain a colorless and transparent hydrolysate, i.e., the first hydrolysis mixture.

[0177] (2) During the stirring process, activated carbon was added to the first hydrolysis mixture, wherein the mass ratio of SiO2 to semi-coke-based activated carbon was 1:0.16. The mixture was 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 was 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.

[0178] (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 the beaker 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.

[0179] (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 7 As shown. Figure 7 and Figure 3 A comparison shows that, Figure 3 The molecular sieve prepared in Example 1 shown has a distinct intracrystalline multi-cavity structure.

[0180] Examples 2-9

[0181] Titanium silicate molecular sieves were prepared according to the method of Example 1, except that the ratio and synthesis conditions were changed to obtain titanium silicate 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.

[0182] Example 10

[0183] 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). 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 is shown in Table 2. Figure 8 As shown, C-10 is a MEL structure.

[0184] Example 11

[0185] 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, resulting in a titanium-silicon zeolite sample 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 is shown in Table 2. Figure 9 As shown, this indicates that C-11 is a BEA structure.

[0186] Example 12

[0187] Titanium-silicon molecular sieves were prepared according to the method of Example 1, but the difference from Example 1 is as follows:

[0188] The temperature of the first hydrothermal crystallization treatment was 120℃ and the time was 96h; the temperature of the first calcination treatment was 350℃ and the time was 8h.

[0189] The second hydrothermal crystallization treatment was carried out at a temperature of 120°C for 96 hours; the second calcination treatment was carried out at a temperature of 350°C for 8 hours.

[0190] 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.

[0191] Table 1

[0192]

[0193]

[0194] In Table 1, TPAOH is tetrapropylammonium hydroxide, TBAOH is tetrabutylammonium hydroxide, TEAOH is tetraethylammonium hydroxide, CTAB is hexadecyltrimethylammonium bromide, SDS is sodium dodecyl sulfate, LAS is linear sodium dodecylbenzenesulfonate, TPHACl is hexadecyltrimethoxysilane ammonium chloride, PVC is polyvinyl chloride (molecular weight 15000), PS is polystyrene (molecular weight 20000), PMMA is polymethyl methacrylate (molecular weight 18000), and PVB is polyvinyl butyral (molecular weight 22000). The average particle size of carbon nanoparticles is 1–100 nm, the diameter of carbon nanotubes is 5–50 nm, and the length is 2–30 μm; the diameter of carbon nanofibers is 3–80 nm, and the length is 1–40 μm; the average particle size of ordered mesoporous carbon is 10–50 nm; the average particle size of phenolic resins is 30 nm; and the average particle size of calcium carbonate is 20 nm. The reagents used in this disclosure can be obtained through conventional purchasing channels.

[0195] In Table 1, the water in the "water / silicon source" calculation in this embodiment of the present disclosure also includes water from the first template agent aqueous solution; the water in the "water / molecular sieve intermediate" calculation also includes water from the second template agent aqueous solution.

[0196] Table 2

[0197]

[0198]

[0199] 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.

[0200] Test case

[0201] 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:

[0202] 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.

[0203] 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.

[0204] 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%;

[0205] Caprolactam selectivity (mol%) = (mol percentage of caprolactam in the product) / (100 - mol percentage of cyclohexanone oxime in the product) × 100%;

[0206] Cyclohexanone oxime conversion reduction rate (%) = (24h cyclohexanone conversion rate - 200h cyclohexanone conversion rate) / 24h cyclohexanone conversion rate × 100%;

[0207] The decrease in caprolactam selectivity (%) = (24h caprolactam selectivity - 200h caprolactam selectivity) / 24h caprolactam selectivity × 100%.

[0208] Table 3

[0209]

[0210] According to the data in Table 3 above:

[0211] 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 disclosed method have... 1In the H2MAS NMR spectra, X1 is in the range of 0.5–2.2, X2 is in the range of 0.1–1.2, and X3 is in the range of 0.05–0.65. Molecular sieves C-1 to C-12 exhibit higher catalytic activity in the gas-phase Beckmann rearrangement of cyclohexanone oxime, with higher cyclohexanone oxime conversion and caprolactam selectivity. Furthermore, under long-term reaction conditions (200 h), the reduction rate of cyclohexanone oxime conversion and the reduction rate of caprolactam selectivity are lower, indicating that the molecular sieves C-1 to C-12 provided in this disclosure have higher catalytic stability.

[0212] Furthermore, the molecular sieves C-1 to C-8 and C-10 to C-11 prepared in the examples have X1 in the range of 0.6 to 1.8, X2 in the range of 0.15 to 1.10, and X3 in the range of 0.10 to 0.55. 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 to C-8 and C-10 to C-11, and the catalytic stability is higher under long-term reaction conditions (200 h).

[0213] 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).

[0214] Comparing Example 1 with Example 12, the molecular sieve C-1 prepared according to the reaction conditions in the preferred embodiment of Example 1 has higher cyclohexanone oxime conversion and caprolactam selectivity in the catalytic reaction, and higher catalytic stability under long reaction conditions (200h).

[0215] 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.

[0216] 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.

[0217] 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 titanium-silicon molecular sieve with a hierarchical porous structure, characterized in that, The titanium-silicon molecular sieve has the following characteristics: 1 H MASNMR characteristics: The titanium-silicon molecular sieve 1 In the peak separation results of the 1-6 ppm range of chemical shifts in the 1-6 ppm HMAS NMR spectrum: The peak area at the chemical shift position of 1.8±0.1ppm is recorded as A1, the peak area at the chemical shift position of 2.2ppm±0.1ppm is recorded as A2, the peak area at the chemical shift position of 2.8ppm±0.1ppm is recorded as A3, the peak area at the chemical shift position of 3.8±0.1ppm is recorded as A4, and the peak area at the chemical shift position of 4.6±0.1ppm is recorded as A5. As defined in equation (1), X1 is any value between 0.5 and 2.2: X1 = (A2 + A3) / A1, Equation (1); As defined in equation (2), X2 is any value between 0.1 and 1.2: X2 = A4 / A1, Equation (2); As defined in equation (3), X3 is any value between 0.05 and 0.65: X3 = A5 / A1, Equation (3); The titanium-silicon molecular sieve with a hierarchical porous structure is prepared by a method comprising the following steps: S1. The titanium source, silicon source, first template agent, water, hard template agent and polymer are mixed to obtain a reaction mixture; S2. The reaction mixture is subjected to a first hydrothermal crystallization treatment and a first calcination treatment in sequence to obtain a molecular sieve intermediate; S3. Mix the molecular sieve intermediate, the second template agent and water, and then perform a second hydrothermal crystallization treatment and a second calcination treatment in sequence.

2. The titanium-silicon molecular sieve according to claim 1, characterized in that, The value of X1 is any value between 0.6 and 1.8; the value of X2 is any value between 0.15 and 1.10; and the value of X3 is any value between 0.10 and 0.

55.

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 (8~150):

1.

4. The titanium-silicon molecular sieve according to claim 3, characterized in that, The molar ratio of silicon atoms to titanium atoms in the titanium-silicon molecular sieve is (15~120):

1.

5. The titanium-silicon molecular sieve according to claim 1, characterized in that, 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.

6. The titanium-silicon molecular sieve according to claim 5, characterized in that, The titanium-silicon molecular sieve has an MFI topology.

7. The titanium-silicon molecular sieve according to claim 1, characterized in that, The titanium-silicon molecular sieve has multiple cavity structures within its crystal; the size of a single cavity structure is 2~50nm.

8. The titanium-silicon molecular sieve according to claim 7, characterized in that, The size of a single cavity structure is 4~45nm.

9. The titanium-silicon molecular sieve according to claim 7, characterized in that, The volume of all the cavity structures described accounts for 8-55% of the total volume of the molecular sieve.

10. The titanium-silicon molecular sieve according to claim 9, characterized in that, The volume of all the cavity structures accounts for 12-50% of the total volume of the molecular sieve.

11. The titanium-silicon molecular sieve according to claim 7, characterized in that, The shape of the cavity structure is selected from one or more of the following: sphere, cube, ellipsoid, and irregular cube.

12. The titanium-silicon molecular sieve according to claim 1, characterized in that, The titanium-silicon molecular sieve includes molecular sieve particles composed of single crystals, and / or molecular sieve particles composed of aggregates of multiple crystals.

13. The titanium-silicon molecular sieve according to claim 12, characterized in that, The molecular sieve particles have an average particle size of 0.1~0.7μm and a BET specific surface area of ​​260~620m². 2 / g; microporous specific surface area is 280~500m² 2 / g; total pore volume is 0.16~0.55cm³. 3 / g; mesopore volume is 0.09~0.38cm³ 3 / g.

14. The titanium-silicon molecular sieve according to claim 13, characterized in that, The molecular sieve particles have an average particle size of 0.13~0.62μm and a BET specific surface area of ​​280~540m². 2 / g; Microporous specific surface area is 300~480m² 2 / g; total pore volume is 0.22~0.45cm³. 3 / g; mesopore volume is 0.12~0.34cm³ 3 / g.

15. The titanium-silicon molecular sieve according to claim 1, characterized in that, There is a hysteresis loop between the adsorption isotherm and desorption isotherm of the low-temperature nitrogen adsorption of the titanium-silicon molecular sieve.

16. The titanium-silicon molecular sieve according to claim 15, characterized in that, The initial relative pressure (P / P0) at which the hysteresis loop appears is 0.35~0.

55.

17. The titanium-silicon molecular sieve according to claim 1, characterized in that, In step S1, the molar ratio of titanium source: silicon source: first template agent: water is (0.005~0.55):1:(0.02~1.8):(1~50); the silicon source is in the form of SiO2, and the weight ratio of hard template agent: polymer: silicon source is (0.02~0.75):(0.01~0.55):

1.

18. The titanium-silicon molecular sieve according to claim 17, characterized in that, In step S1, the molar ratio of titanium source: silicon source: first template agent: water is (0.01~0.42):1:(0.04~1.5):(10~45); the silicon source is in the form of SiO2, and the weight ratio of hard template agent: polymer: silicon source is (0.04~0.55):(0.03~0.4):

1.

19. The titanium-silicon 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.

20. The titanium-silicon molecular sieve according to claim 19, characterized in that, The silicon source is selected from at least one of organosilicon grease, solid silica gel, and precipitated silica.

21. The titanium-silicon molecular sieve according to claim 20, characterized in that, The silicon source is selected from silicone grease, and the general formula of the silicone grease is shown in the following 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.

22. The titanium-silicon molecular sieve according to claim 21, 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.

23. The titanium-silicon molecular sieve according to claim 22, 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.

24. The titanium-silicon molecular sieve according to claim 21, characterized in that, The silicone grease is selected from one or more of tetramethyl silicate, tetraethyl silicate, tetrabutyl silicate, and dimethyl diethyl silicone grease.

25. The titanium-silicon molecular sieve according to claim 1, characterized in that, The first template agent in step S1 and the second template agent in step S3 are organic bases.

26. The titanium-silicon molecular sieve according to claim 25, 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.

27. The titanium-silicon molecular sieve according to claim 26, 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.

28. The titanium-silicon molecular sieve according to claim 27, 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.

29. The titanium-silicon molecular sieve according to claim 28, 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.

30. The titanium-silicon 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.

31. The titanium-silicon molecular sieve according to claim 1, 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 independently selected from alkyl groups having 1 to 6 carbon atoms; The inorganic titanium source is selected from one or more of titanium chloride, nitrate or sulfate.

32. The titanium-silicon molecular sieve according to claim 31, characterized in that, In formula (C), R5, R6, R7 and R8 are each independently selected from straight-chain alkyl groups having 1 to 4 carbon atoms and branched alkyl groups having 3 to 6 carbon atoms.

33. The titanium-silicon molecular sieve according to claim 32, characterized in that, In formula (C), R5, R6, R7 and R8 are each independently selected from straight-chain alkyl groups having 2 to 4 carbon atoms and branched alkyl groups having 2 to 4 carbon atoms.

34. The titanium-silicon molecular sieve according to claim 32, characterized in that, In formula (C), R5, R6, R7 and R8 are each independently selected from one of methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, isopentyl, hexyl or isohexyl.

35. The titanium-silicon molecular sieve according to claim 34, characterized in that, In formula (C), R5, R6, R7 and R8 are each independently selected from one of ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl or tert-butyl.

36. The titanium-silicon molecular sieve according to claim 31, characterized in that, The titanium source is selected from one or more of titanium tetrachloride, titanium sulfate, titanium nitrate, tetraethyl titanate, tetrapropyl titanate, and tetrabutyl titanate.

37. The titanium-silicon molecular sieve according to claim 1, characterized in that, In step S1, the hard template agent is selected from one or more of carbon-based materials, resin-based materials, and inorganic solid compound materials.

38. The titanium-silicon molecular sieve according to claim 37, characterized in that, The carbon-based materials are selected from one or more of carbon nanoparticles, carbon nanotubes, carbon nanofibers, and ordered mesoporous carbon. The resin material is selected from one or more of phenolic resin, polyester resin and polyamide resin; The inorganic solid compound material is selected from one or more of calcium carbonate, magnesium hydroxide, and sodium carbonate.

39. The titanium-silicon molecular sieve according to claim 1, characterized in that, In step S1, the polymer is selected from one or more of polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyvinyl alcohol, polyvinyl acetate, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol butyl ester, polyethyleneimine, 4-polyvinylpyridine, and poly(diallyldimethylammonium chloride).

40. The titanium-silicon molecular sieve according to claim 39, characterized in that, The polymer is selected from one or more of polyethylene, polypropylene, polystyrene, and polyacrylonitrile.

41. The titanium-silicon molecular sieve according to claim 39, characterized in that, The molecular weight of the polymer is 10,000 to 200,000.

42. The titanium-silicon molecular sieve according to claim 1, 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 hard template agent and the polymer to the hydrolyzed sol of the silicon respectively, and mix to obtain the reaction mixture.

43. The titanium-silicon molecular sieve according to claim 42, characterized in that, The mixing conditions in step a include stirring at 40~90℃ for 6~12 hours; The mixing conditions in step b include stirring at 20~50℃ for 2~4 hours.

44. The titanium-silicon molecular sieve according to claim 43, 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.

45. The titanium-silicon molecular sieve according to claim 44, characterized in that, The conditions for the hydrolysis and alcohol removal treatment include: stirring and hydrolyzing at 40~90℃ for 6~12h.

46. ​​The titanium-silicon molecular sieve according to claim 45, characterized in that, The conditions for the hydrolysis and alcohol removal treatment include: stirring and hydrolyzing at 60~85℃ for 8~10h.

47. The titanium-silicon molecular sieve according to claim 1, characterized in that, In step S3, the weight ratio of the second template agent: water: molecular sieve intermediate is (0.08~3.5):(0.5~25):

1.

48. The titanium-silicon molecular sieve according to claim 47, characterized in that, In step S3, the weight ratio of the second template agent: water: molecular sieve intermediate is (0.12~2.5):(2~18):

1.

49. The titanium-silicon molecular sieve according to claim 1, characterized in that, The conditions for the first hydrothermal crystallization treatment in step S2 and the second hydrothermal crystallization treatment in step S3 each independently include: hydrothermal crystallization time of 4~180h, hydrothermal crystallization temperature of 120~220℃; and pressure of autogenous pressure. The conditions for the first roasting treatment in step S2 and the second roasting treatment in step S3 each independently include: a roasting temperature of 350~750℃ and a roasting time of 1~15h.

50. The titanium-silicon molecular sieve according to claim 49, characterized in that, The conditions for the first hydrothermal crystallization treatment in step S2 and the second hydrothermal crystallization treatment in step S3 each independently include: hydrothermal crystallization time of 6~80h and hydrothermal crystallization temperature of 140~185℃; The conditions for the first roasting treatment in step S2 and the second roasting treatment in step S3 each independently include: a roasting temperature of 380~620℃ and a roasting time of 1.5~4.5h.

51. 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 a titanium silicate molecular sieve with a hierarchical porous structure as described in any one of claims 1 to 50.

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