A framework heteroatom titanium-silicon molecular sieve with hierarchical pores, its preparation method and application

Abstract

This disclosure relates to a framework heteroatom titanium-silicon molecular sieve with hierarchical pores, its preparation method, and its application. The framework heteroatoms include titanium. The framework heteroatom titanium-silicon molecular sieve has the following characteristics: 29 Si MAS NMR characteristics: The peak area of ​​the peak at the chemical shift position of the framework heteroatom titanium-silicon molecular sieve at -103±1ppm is denoted as Q3; the peak area of ​​the peak at the chemical shift position of the framework heteroatom titanium-silicon molecular sieve at -113±1ppm is denoted as Q. 4‑1 The peak area of ​​the spectrum at the position with a chemical shift of -116±1ppm for the framework heteroatom titanium-silicon molecular sieve is denoted as Q. 4‑2 As defined in equation (1), X1 is any value between 0.02 and 0.35: X1 = Q3 / Q 4‑1 Equation (1); X2 is defined as any value between 0.10 and 0.60 as in Equation (2): X2 = Q3 / Q 4‑2 Formula (2). This molecular sieve has high catalytic activity and stability, and significantly improves the conversion rate of cyclohexanone oxime and the selectivity of caprolactam.

Description

Technical Field

[0001] This disclosure relates to the field of titanium-silicon molecular sieve preparation, specifically to a framework heteroatom titanium-silicon molecular sieve with hierarchical pores, its preparation method, and its application. Background Technology

[0002] ε-Caprolactam (CPL) 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 also has applications in coatings, pharmaceuticals, and fine chemicals. Global consumption of caprolactam increased from 5.27 million tons in 2015 to 6.4 million tons in 2019, with an average annual growth rate of 4.9%. China is the world's largest consumer of caprolactam, accounting for approximately 52.7% of total consumption.

[0003] The gas-phase Beckmann rearrangement process for cyclohexanone oxime based on molecular sieve catalysts has received significant attention from both academia and industry. Compared to traditional liquid-phase methods, this process avoids the use of ammonia and fuming sulfuric acid at the source, achieving 100% atom utilization and representing an environmentally friendly green production process for caprolactam. Pure silica molecular sieves with an MFI topology have demonstrated excellent catalytic performance. At the beginning of this century, Sumitomo Chemical of Japan and Sinopec of China conducted industrial-scale experiments on the gas-phase Beckmann rearrangement of cyclohexanone oxime using pure silica molecular sieves.

[0004] 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.

[0005] 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 hours, and the selectivity stabilized at 86%, indicating unsatisfactory reaction results. 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 hours of reaction. -1 cat h -1 .

[0006] Therefore, the titanium-silicon molecular sieves synthesized by existing preparation processes do not achieve ideal results in improving caprolactam selectivity and catalyst lifetime when used in the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime, and there is still a certain gap between the requirements of industrial production and the actual results. Summary of the Invention

[0007] The purpose of this disclosure is to provide a hierarchical porous framework heteroatom titanium silicate molecular sieve, its preparation method and application, which has high catalytic activity and stability, and significantly improves the conversion rate of cyclohexanone oxime and the selectivity of caprolactam.

[0008] To achieve the above objectives, the first aspect of this disclosure provides a framework heteroatom titanium-silicon molecular sieve with hierarchical pores; the framework heteroatom titanium-silicon molecular sieve has the following characteristics: 29 Si MAS NMR characteristics: The peak area of ​​the peak at the position with a chemical shift of -103±1ppm for the framework heteroatom titanium-silicon molecular sieve is denoted as Q. 3 The peak area of ​​the spectral peak at the position with a chemical shift of -113±1ppm for the framework heteroatom titanium-silicon molecular sieve is denoted as Q. 4-1 The peak area of ​​the spectral peak at the position with a chemical shift of -116±1ppm for the framework heteroatom titanium-silicon molecular sieve is denoted as Q. 4-2 As defined in equation (1), X1 is any value between 0.02 and 0.35: X1 = Q 3 / Q 4-1 Equation (1); X2 is defined as any value between 0.10 and 0.60 as in Equation (2): X2 = Q 3 / Q 4-2 Equation (2).

[0009] Optionally, the value of X1 is any value between 0.05 and 0.25; the value of X2 is any value between 0.15 and 0.45.

[0010] Optionally, the molar ratio of silicon atoms to titanium atoms in the framework heteroatom titanium silicon molecular sieve is (8-120):1, preferably (10-90):1;

[0011] Optionally, the configuration of the framework heteroatom titanium silicate 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 framework heteroatom titanium silicon molecular sieve has multiple cavity structures within its crystal; wherein the size of a single cavity structure is 3 to 50 nm, preferably 4 to 40 nm;

[0013] Preferably, the volume of all the cavity structures accounts for 8-45% of the total volume of the molecular sieve, more preferably 12-40%;

[0014] Optionally, the shape of the cavity structure is selected from one or more of the following: sphere, cube, ellipsoid, and irregular cube.

[0015] Optionally, the framework heteroatom titanium silicon molecular sieve includes molecular sieve particles composed of a single crystallite, and / or molecular sieve particles composed of aggregates of multiple crystallites.

[0016] Optionally, the average particle size of the molecular sieve particles is 0.12–0.75 μm, preferably 0.15–0.55 μm; the BET specific surface area is 280–670 m². 2 / g, preferably 300-620m 2 / g; microporous specific surface area is 240-520m² 2 / g, preferably 270-440m 2 / g; total pore volume is 0.18–0.67 cm³. 3 / g, preferably 0.22~0.55cm 3 / g; mesopore volume is 0.15~0.48cm³ 3 / g, preferably 0.22~0.39cm 3 / g;

[0017] Optionally, a hysteresis loop exists between the adsorption isotherm and desorption isotherm of the low-temperature nitrogen adsorption of the framework heteroatom titanium silicate molecular sieve; preferably, the initial relative pressure (P / P0) at which the hysteresis loop appears is 0.3 to 0.55.

[0018] The second aspect of this disclosure provides a method for preparing a framework heteroatom titanium-silicon molecular sieve with hierarchical pores, comprising the following steps: S1, mixing a titanium source, a silicon source, a first template agent, water, a surfactant, 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.

[0019] Optionally, in step S1, the molar ratio of titanium source: silicon source: first template agent: water: surfactant is (0.006~0.08):1:(0.01~3):(1~50):(0.05~0.25); preferably (0.01~0.06):1:(0.02~1.8):(10~30):(0.08~0.15); the silicon source is in the form of SiO2, and the weight ratio of SiO2 to polymer is (8~100):1, preferably (10~60):1.

[0020] 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.

[0021] A further preferred option is a silicone grease, wherein the silicone grease has the general formula shown in formula (A):

[0022]

[0023] 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.

[0024] 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;

[0025] 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):

[0026] 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.

[0027] 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.

[0028] Optionally, in step S1, the titanium source is selected from one or more of organic titanium sources and inorganic titanium sources;

[0029] Preferably, the organic titanium source is a titanium-containing organic ester, selected from at least one structure of the following formula (C):

[0030]

[0031] 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.

[0032] Preferably, the inorganic titanium source is selected from one or more of titanium chloride, nitrate or sulfate;

[0033] More preferably, the titanium source is selected from one or more of titanium tetrachloride, titanium sulfate, titanium nitrate, tetraethyl titanate, tetrapropyl titanate, and tetrabutyl titanate.

[0034] Optionally, in step S1, the surfactant is selected from one or more of anionic surfactants and cationic surfactants;

[0035] 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.

[0036] Preferably, the cationic surfactant is selected from one or more of hexadecyltrimethylammonium bromide, hexadecyltrimethoxyorganosilicone ammonium chloride, and octadecyltrimethoxyorganosilicone ammonium chloride;

[0037] More preferably, the surfactant is selected from one or more of sodium dodecyl sulfate, sodium linear dodecylbenzene sulfonate, and hexadecyltrimethylammonium bromide.

[0038] 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).

[0039] Further preferably, the polymer is selected from one or more of polyethylene, polypropylene, polystyrene, and polyacrylonitrile;

[0040] Optionally, the molecular weight of the polymer is 10,000 to 200,000.

[0041] Optionally, step S1 includes:

[0042] a. Mix titanium source, silicon source, first template agent and water to obtain silicon hydrolysis sol;

[0043] b. The surfactant and the polymer are added to the hydrolyzed sol of the silicon, and the mixture is then used to obtain the reaction mixture.

[0044] Optionally, the mixing conditions in step a include stirring at 40–90°C for 6–12 hours;

[0045] Optionally, the mixing conditions in step b include stirring at 20–50°C for 2–4 hours;

[0046] 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;

[0047] 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.

[0048] Optionally, in step S3, the weight ratio of the second template agent: water: molecular sieve intermediate is (0.1-3):(1-20):1; preferably (0.15-2):(2-18):1.

[0049] 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 6–168 h and a hydrothermal crystallization temperature of 130–200 °C; preferably, a hydrothermal crystallization time of 24–72 h and a hydrothermal crystallization temperature of 150–180 °C; and the pressure is self-generated pressure.

[0050] 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 300-700℃ and a roasting time of 1-16h; preferably, a roasting temperature of 400-600℃ and a roasting time of 2-5h.

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

[0052] 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 a hierarchical porous framework heteroatom titanium silicate molecular sieve as described in the first and third aspects of this disclosure.

[0053] Through the above technical solution, this disclosure provides a framework heteroatom titanium-silicon molecular sieve with hierarchical pores, its preparation method, and its application. Introducing new heteroatom active centers, such as titanium atoms, into the molecular sieve during synthesis can improve its resistance to deactivation in the reaction system. Furthermore, the hierarchical porous structure of this framework heteroatom titanium-silicon molecular sieve endows it with advantages such as large specific surface area and pore volume. The molecular sieve also possesses abundant silanol active centers, exhibiting high catalytic activity. In the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime, it significantly improves caprolactam selectivity and ensures that the conversion rate of cyclohexanone oxime and the selectivity of caprolactam remain low even under long-term reaction conditions, thus extending the catalyst's lifespan.

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

[0055] The accompanying drawings are provided to further illustrate the present disclosure and form part of the specification. They are used together with the following detailed description to explain the present disclosure, but do not constitute a limitation thereof. In the drawings:

[0056] Figure 1 The molecular sieve obtained in Example 1 29 Si MAS NMR spectrum;

[0057] Figure 2 The XRD pattern of the molecular sieve obtained in Example 1;

[0058] Figure 3 Here is a TEM image of the molecular sieve obtained in Example 1;

[0059] Figure 4 Here is an SEM image of the molecular sieve obtained in Example 1;

[0060] Figure 5 The BET curve of the molecular sieve obtained in Example 1 is shown below.

[0061] Figure 6 Here is a TEM image of the intermediate product obtained in Example 1;

[0062] Figure 7 Here is a TEM image of the molecular sieve obtained in Comparative Example 2;

[0063] Figure 8 The XRD pattern of the molecular sieve obtained in Example 10;

[0064] Figure 9 The image shows the XRD pattern of the molecular sieve obtained in Example 11. Detailed Implementation

[0065] 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.

[0066] Through extensive experimental research, the inventors of this disclosure have discovered that framework heteroatom titanium-silicon molecular sieves (such as titanium-silicon molecular sieves) 29 In the Si MAS NMR spectrum, the peak area (Q) of the peak at the position with a chemical shift of -103 ± 1 ppm is... 3 The peak area (Q) of the spectral peak at a chemical shift of -113±1ppm. 4-1 The peak area (Q) of the spectral peak at a chemical shift of -116±1ppm. 4-2The ratio of the above three spectral peaks is related to the catalytic activity of the framework heteroatom titanium silicate molecular sieve. When the ratio of the above three spectral peaks is within a certain range, the framework heteroatom titanium silicate molecular sieve has suitable characteristics for catalyzing the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime.

[0067] The first aspect of this disclosure provides a framework heteroatom titanium-silicon molecular sieve with hierarchical pores, wherein the framework heteroatom titanium-silicon molecular sieve has the following characteristics: 29 Si MAS NMR characteristics:

[0068] The peak area of ​​the spectral peak at the position with a chemical shift of -103±1ppm for the framework heteroatom titanium-silicon molecular sieve is denoted as Q. 3 ;

[0069] The peak area of ​​the spectral peak at the position with a chemical shift of -113±1ppm for the framework heteroatom titanium-silicon molecular sieve is denoted as Q. 4-1 ;

[0070] The peak area of ​​the spectral peak at the position with a chemical shift of -116±1ppm for the framework heteroatom titanium-silicon molecular sieve is denoted as Q. 4-2 ;

[0071] As defined in equation (1), X1 can be any value between 0.02 and 0.35:

[0072] X1 = Q 3 / Q 4-1 Equation (1);

[0073] As defined in equation (2), X2 is any value between 0.10 and 0.60:

[0074] X2 = Q 3 / Q 4-2 Equation (2).

[0075] This disclosure provides a framework heteroatom titanium-silicon molecular sieve with hierarchical pores. Introducing new heteroatom active centers, such as titanium atoms, into the molecular sieve during synthesis enhances its resistance to deactivation in the reaction system. Furthermore, the hierarchical porous structure of this framework heteroatom titanium-silicon molecular sieve provides advantages such as a large specific surface area and pore volume. The molecular sieve also possesses abundant silanol active centers, exhibiting high catalytic activity. In the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime, it significantly improves caprolactam selectivity and ensures that the conversion rate of cyclohexanone oxime and the selectivity of caprolactam remain low even under long-term reaction conditions, thus extending the catalyst's lifespan.

[0076] In this disclosure, 29 Si MAS NMR testing employs conventional testing instruments and methods in this field.

[0077] In a preferred embodiment, the value of X1 is any value between 0.05 and 0.25; and the value of X2 is any value between 0.15 and 0.45. When the X1 and X2 of the framework heteroatom titanium silicate molecular sieve meet the range of this embodiment, the framework heteroatom titanium silicate molecular sieve can obtain higher caprolactam selectivity and better catalyst reaction stability.

[0078] In one embodiment, the molar ratio of silicon atoms to titanium atoms in the framework heteroatom titanium-silicon molecular sieve is (8-120):1, preferably (10-90):1. This disclosure obtains the molar ratio of silicon atoms to titanium atoms in the molecular sieve using X-ray fluorescence spectroscopy.

[0079] In a preferred embodiment, the framework heteroatom titanium silicon molecular sieve has multiple cavity structures within its crystal; wherein the size of a single cavity structure is 3 to 50 nm, preferably 4 to 40 nm.

[0080] The framework heteroatom titanium-silicon molecular sieve disclosed herein has a large-size multi-cavity structure with abundant silanol active centers. Its multi-cavity structure provides a large number of independent reaction units. In addition, the large-size cavity structure meets the requirements of macromolecular reactions, and the reaction products can more easily flow out of the catalyst, avoiding the phenomenon of reduced catalyst activity due to pore blockage.

[0081] 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 3–50 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 3–50 nm.

[0082] In a preferred embodiment, all of the cavity structures account for 8-45% of the total volume of the molecular sieve, more preferably 12-40%;

[0083] Optionally, the shape of the cavity structure is selected from one or more of the following: sphere, cube, ellipsoid, and irregular cube.

[0084] In one specific embodiment, the framework heteroatom 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.

[0085] Optionally, the average particle size of the molecular sieve particles is 0.12–0.75 μm, preferably 0.15–0.55 μm; the BET specific surface area is 280–670 m². 2 / g, preferably 300-620m 2 / g; microporous specific surface area is 240-520m² 2 / g, preferably 270-440m 2 / g; total pore volume is 0.18–0.67 cm³. 3 / g, preferably 0.22~0.55cm 3 / g; mesopore volume is 0.15~0.48cm³ 3 / g, preferably 0.22~0.39cm 3 / g.

[0086] In a preferred embodiment, a hysteresis loop exists between the adsorption isotherm and desorption isotherm of the low-temperature nitrogen adsorption of the framework heteroatom titanium-silicon molecular sieve.

[0087] In one specific embodiment, the initial relative pressure (P / P0) at which the hysteresis loop appears is 0.3 to 0.55, preferably 0.35 to 0.48.

[0088] In one specific embodiment, the configuration of the framework heteroatom titanium silicate molecular sieve is selected from one or more of the MFI topology, MEL topology, BEA topology and SVR topology; more preferably, the MFI topology is selected.

[0089] A second aspect of this disclosure provides a method for preparing a framework heteroatom titanium-silicon molecular sieve with hierarchical pores, comprising the following steps:

[0090] S1. Mix the titanium source, silicon source, first template agent, water, surfactant and polymer to obtain a reaction mixture;

[0091] 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;

[0092] 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.

[0093] This disclosure provides a method for preparing a hierarchical porous framework of heteroatom-based titanium-silicon molecular sieves. Introducing a titanium source into the reaction raw materials introduces active titanium atom centers into the molecular sieve framework during synthesis, improving the molecular sieve performance. By introducing surfactants and polymers into the molecular sieve synthesis raw materials, these materials self-assemble with inorganic aluminosilicates through hydrogen bonding or electrostatic attraction, occupying space within the molecular sieve crystals after crystallization. After calcination, the surfactants and polymers are removed, forming a molecular sieve material with abundant open channels. Then, a template agent is added for dissolution-recrystallization to prepare a hierarchical porous molecular sieve with a multi-cavity structure. The surfactants and polymers form hydrogen bonds with the silanol groups of the organosilicon source, ensuring the achievement of the pore-expanding effect. Furthermore, adjusting the carbon chain of the surfactant can finely modulate the pore-expanding effect, resulting in an ordered, mesoporous structure with controllable pore size (controlled by the chain length of the surfactant alkyl chain).

[0094] In one embodiment, in step S1, the molar ratio of titanium source: silicon source: first template agent: water: surfactant is (0.006~0.08):1:(0.01~3):(1~50):(0.05~0.25); the silicon source is in the form of SiO2, and the weight ratio of SiO2 to polymer is (8~100):1.

[0095] In a preferred embodiment, in step S1, the molar ratio of titanium source: silicon source: first template agent: water: surfactant is (0.01~0.06):1:(0.02~1.8):(10~30):(0.08~0.15); the silicon source is in the form of SiO2, and the weight ratio of SiO2 to the polymer is (10~60):1. This embodiment has a more optimized raw material addition ratio, and the prepared framework heteroatom titanium-silicon molecular sieve has better catalytic activity and resistance to deactivation.

[0096] 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.

[0097] A further preferred option is a silicone grease, wherein the silicone grease has the general formula shown in formula (A):

[0098]

[0099] 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 aR 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.

[0100] 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.

[0101] 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.

[0102] 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):

[0103] 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.

[0104] 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.

[0105] In one embodiment, step S1 includes:

[0106] a. Mix titanium source, silicon source, first template agent and water to obtain silicon hydrolysis sol;

[0107] b. The surfactant and the polymer are added to the hydrolyzed sol of the silicon, and the mixture is then used to obtain the reaction mixture.

[0108] Optionally, the mixing conditions in step a include stirring at 40–90°C for 6–12 hours;

[0109] Optionally, the mixing conditions in step b include stirring at 20–50°C for 2–4 hours.

[0110] 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;

[0111] 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.

[0112] In one embodiment, in step S1, the titanium source is selected from one or more of organic titanium sources and inorganic titanium sources;

[0113] 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:

[0114]

[0115] 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.

[0116] The inorganic titanium source is selected from one or more of titanium chloride, nitrate or sulfate.

[0117] 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.

[0118] In one embodiment, in step S1, the surfactant is selected from one or more of anionic surfactants and cationic surfactants;

[0119] 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.

[0120] Preferably, the cationic surfactant is selected from one or more of hexadecyltrimethylammonium bromide, hexadecyltrimethoxyorganosilicon ammonium chloride, and octadecyltrimethoxyorganosilicon ammonium chloride.

[0121] In one specific embodiment, the surfactant is selected from one or more of sodium dodecyl sulfate, sodium linear dodecylbenzene sulfonate, and hexadecyltrimethylammonium bromide.

[0122] In one embodiment, 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).

[0123] In one specific embodiment, the polymer is selected from one or more of polyethylene, polypropylene, polystyrene, and polyacrylonitrile.

[0124] In one specific embodiment, the molecular weight of the polymer is 10,000 to 200,000.

[0125] All reagents used in this disclosure can be purchased through conventional channels or prepared using methods known in the art.

[0126] In one embodiment, the conditions for the first hydrothermal crystallization treatment in step S2 include: hydrothermal crystallization time of 6 to 168 hours, hydrothermal crystallization temperature of 130 to 200°C, and pressure of autogenous pressure;

[0127] The conditions for the first calcination treatment in step S2 include: a calcination temperature of 300–700°C and a calcination time of 1–16 h.

[0128] In a preferred embodiment, the conditions for the first hydrothermal crystallization treatment in step S2 include: a hydrothermal crystallization time of 24–72 h, a hydrothermal crystallization temperature of 150–180 °C, and an autogenous pressure.

[0129] The conditions for the first calcination treatment in step S2 include: a calcination temperature of 400–600°C and a calcination time of 2–5 h. The framework heteroatom titanium-silicon molecular sieve prepared according to the reaction conditions of this embodiment has better catalytic activity.

[0130] 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.

[0131] 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; preferably, the first template agent and the second template agent are the same template agent.

[0132] In one embodiment, in step S3, the weight ratio of the second template agent: water: molecular sieve intermediate is (0.1-3):(1-20):1; preferably (0.15-2):(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.

[0133] In one embodiment, the conditions for the second hydrothermal crystallization treatment in step S3 include: a hydrothermal crystallization time of 6–168 h, a hydrothermal crystallization temperature of 130–200 °C, and an autogenous pressure;

[0134] The conditions for the second calcination treatment in step S3 include: a calcination temperature of 300–700°C and a calcination time of 1–16 h.

[0135] In a preferred embodiment, the conditions for the second hydrothermal crystallization treatment in step S3 include: a hydrothermal crystallization time of 24–72 h, a hydrothermal crystallization temperature of 150–180 °C, and an autogenous pressure.

[0136] The conditions for the second calcination treatment in step S3 include: a calcination temperature of 400–600°C and a calcination time of 2–5 hours.

[0137] 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.

[0138] The third aspect of this disclosure provides a hierarchical porous framework heteroatom titanium-silicon molecular sieve prepared according to the method described in the second aspect of this disclosure.

[0139] 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 a hierarchical porous framework heteroatom titanium silicate molecular sieve as described in the first and third aspects of this disclosure.

[0140] 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 .

[0141] The present disclosure will be described in detail below through examples.

[0142] Q of the sample 3 / Q 4 Measurement method adopted 29 The Si MAS NMR method was used on an AVANCEⅢ500WB nuclear magnetic resonance spectrometer with a 7mm dual resonance probe, a Ф7mm ZrO2 rotor, a resonance frequency of 99.3MHz, a magic angle rotation speed of 5kHz, a pulse width of 1.8μs, a cycle delay time of 2s, and approximately 3000 scans.

[0143] 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°.

[0144] 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).

[0145] 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).

[0146] 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.

[0147] 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.

[0148] The reagents used in the following examples and comparative examples were all purchased through conventional channels.

[0149] Example 1

[0150] (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.

[0151] (2) Add 9g of cetyltrimethylammonium bromide (CTAB, 0.0247mol) and 3g of polystyrene (PS, molecular weight 20000) to the mixture in step (1) and stir for 2 hours;

[0152] (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.

[0153] (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, crystallize at 170℃ for 24h to obtain the sample, filter and wash the obtained sample, dry at 110℃ for 3h, and then calcine at 550℃ for 3h in a muffle furnace to obtain titanium silicon molecular sieve sample A1.

[0154] The structural parameter characterization results of sample A1 are listed in Table 2;

[0155] Sample A1 29 Si MAS NMR spectrum as shown Figure 1 As shown, by Figure 1 Characteristic peaks appear at chemical shifts of -103 ppm, -113 ppm, and -116 ppm, indicating that sample S-1 molecular sieve contains silicon without hydroxyl groups, which have both silanol active centers and two coordination environments. The peak areas are denoted as Q. 3 Q 4-1 and Q 4-2 Q is obtained through integration. 3 The value is 315505, Q 4-1 The value is 4491045, Q. 4-2 The values ​​of X1 and X2 obtained by formulas (1) to (2) are listed in Table 3, with a value of 1987713.

[0156] The XRD pattern of sample A1 is as follows Figure 2 As shown, this indicates that the titanium silicate molecular sieve sample has an MFI topology.

[0157] TEM image of sample A1 as follows Figure 3 As shown in the figure, the molecular sieve has a hierarchical porous structure with multiple cavities within the crystal; the size of a single cavity structure in sample A1 was measured and calculated to be 6–34 nm.

[0158] SEM image of sample A1 as follows Figure 4 As shown in the figure, the molecular sieve consists of uniform ellipsoidal particles.

[0159] The BET curve of sample A1 is shown below. Figure 5 As shown, there is a clear hysteresis loop between the nitrogen adsorption and desorption curves, and the initial relative pressure (P / P0) at which the hysteresis loop appears is 0.41.

[0160] TEM of intermediate product M-1 without dissolution and recrystallization, as shown in the figure. 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.

[0161] Comparative Example 1

[0162] This comparative example follows the method of Example 1, but differs from Example 1 in that no surfactant (hexadecyltrimethylammonium bromide) and polymer (polystyrene) are added. The resulting molecular sieve product is denoted as D-1. Its preparation conditions are listed in Table 1, and the characterization results of the obtained molecular sieve are listed in Table 2.

[0163] Comparative Example 2

[0164] This comparative example prepares titanium-silicon molecular sieves according to the method disclosed in existing technology CN112744836A:

[0165] (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.

[0166] (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.

[0167] (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.

[0168] (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.

[0169] Examples 2-9

[0170] Framework heteroatom titanium-silicon molecular sieves were prepared according to the method of Example 1, except that the ratio and synthesis conditions were changed to obtain framework heteroatom titanium-silicon molecular sieve samples, denoted as A2 to A9; the preparation conditions are listed in Table 1, and the characterization results of the obtained molecular sieves are listed in Table 2.

[0171] Example 10

[0172] MEL-structured framework heteroatom 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 framework heteroatom titanium-silicon molecular sieve sample was designated A10. 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 A10 is shown in Table 2. Figure 8 As shown, A10 is a MEL structure.

[0173] Example 11

[0174] 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 framework heteroatom titanium silicate zeolite sample denoted as A11. 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 A11 is shown in Table 2. Figure 9 As shown, A11 is a BEA structure.

[0175] Example 12

[0176] The framework heteroatom titanium-silicon molecular sieve was prepared according to the method of Example 1, but the difference from Example 1 is as follows:

[0177] The temperature of the first hydrothermal crystallization treatment was 130℃ and the time was 96h; the temperature of the first calcination treatment was 350℃ and the time was 8h.

[0178] The second hydrothermal crystallization treatment was carried out at a temperature of 130℃ for 96 hours; the second calcination treatment was carried out at a temperature of 350℃ for 8 hours.

[0179] The obtained framework heteroatom titanium silicate molecular sieve sample is designated as A12; the characterization results of the obtained molecular sieve are listed in Table 2.

[0180] Table 1

[0181]

[0182]

[0183] 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 alcohol butyl ester (molecular weight 22000). The reagents used in this disclosure can be obtained through conventional purchasing channels.

[0184] 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.

[0185] Table 2

[0186]

[0187]

[0188] 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 A1 to A12 prepared by the publicly provided method have larger cavity sizes and a larger percentage of the total volume of the molecular sieve structure.

[0189] Test case

[0190] 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:

[0191] 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.

[0192] 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.

[0193] 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%;

[0194] Caprolactam selectivity (mol%) = (mol percentage of caprolactam in the product) / (100 - mol percentage of cyclohexanone oxime in the product) × 100%;

[0195] Cyclohexanone oxime conversion reduction rate (%) = (24h cyclohexanone conversion rate - 200h cyclohexanone conversion rate) / 24h cyclohexanone conversion rate × 100%;

[0196] The decrease in caprolactam selectivity (%) = (24h caprolactam selectivity - 200h caprolactam selectivity) / 24h caprolactam selectivity × 100%.

[0197] Table 3

[0198]

[0199] According to the data in Table 3 above:

[0200] Compared with the molecular sieves D-1 to D-2 prepared by Comparative Examples 1 and 2, the molecular sieves A1 to A12 prepared by the publicly disclosed method have... 29 In the Si MAS NMR spectrum, X1 is in the range of 0.02–0.35 and X2 is in the range of 0.10–0.60. Molecular sieves A1–A12 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 decrease rate of cyclohexanone oxime conversion and the decrease rate of caprolactam selectivity are lower, indicating that molecular sieves A1–A12 have higher catalytic stability.

[0201] Furthermore, the X1 of the molecular sieves A1-A8 and A10-A11 prepared in the examples is in the range of 0.05-0.27, and the X2 is in the range of 0.15-0.45. Compared with molecular sieves A9 and A12, molecular sieves A1-A8 and A10-A11 have higher cyclohexanone oxime conversion and caprolactam selectivity in the reaction, and higher catalytic stability under long-term reaction conditions (200h).

[0202] 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 A1 had higher cyclohexanone oxime conversion and caprolactam selectivity in the catalytic reaction, and higher catalytic stability under long-term reaction conditions (200h).

[0203] Comparing Example 1 with Example 12, the molecular sieve prepared in Example 1 was prepared according to the reaction conditions in the preferred embodiment. The obtained molecular sieve A1 had higher cyclohexanone oxime conversion and caprolactam selectivity in the catalytic reaction, and higher catalytic stability under long reaction conditions (200h).

[0204] 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.

[0205] 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.

[0206] 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 framework heteroatom titanium-silicon molecular sieve with hierarchical pores, characterized in that, The framework heteroatom titanium-silicon molecular sieve has the following characteristics: 29 Si MAS NMR characteristics: The peak area of ​​the spectral peak at the position with a chemical shift of -103±1ppm for the framework heteroatom titanium-silicon molecular sieve is denoted as Q. 3 ; The peak area of ​​the spectral peak at the position with a chemical shift of -113±1ppm for the framework heteroatom titanium-silicon molecular sieve is denoted as Q. 4-1 ; The peak area of ​​the spectral peak at the position with a chemical shift of -116±1ppm for the framework heteroatom titanium-silicon molecular sieve is denoted as Q. 4-2 ; As defined in equation (1), X1 can be any value between 0.02 and 0.35: X1=Q 3 / Q 4-1 Equation (1); As defined in equation (2), X2 can be any value between 0.10 and 0.60: X2=Q 3 / Q 4-2 Equation (2); The framework heteroatom titanium-silicon molecular sieve with hierarchical pores is prepared by a method including the following steps: S1. Mix the titanium source, silicon source, first template agent, water, surfactant and polymer 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 framework heteroatom titanium-silicon molecular sieve according to claim 1, characterized in that, The value of X1 is any value between 0.05 and 0.27; the value of X2 is any value between 0.15 and 0.

45.

3. The framework heteroatom titanium-silicon molecular sieve according to claim 1, characterized in that, The molar ratio of silicon atoms to titanium atoms in this heteroatom titanium-silicon molecular sieve is (8~120):

1.

4. The framework heteroatom titanium-silicon molecular sieve according to claim 3, characterized in that, The molar ratio of silicon atoms to titanium atoms in this heteroatom titanium-silicon molecular sieve is (10~90):

1.

5. The framework heteroatom titanium-silicon molecular sieve according to claim 1, characterized in that, The configuration of the framework heteroatom titanium silicate molecular sieve is selected from one or more of the MFI topology, MEL topology, BEA topology and SVR topology.

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

7. The framework heteroatom titanium-silicon molecular sieve according to claim 1, characterized in that, The framework heteroatom titanium silicon molecular sieve has multiple cavity structures within its crystal; the size of a single cavity structure is 3~50nm.

8. The framework heteroatom titanium-silicon molecular sieve according to claim 7, characterized in that, The size of a single cavity structure is 4~40nm.

9. The framework heteroatom titanium-silicon molecular sieve according to claim 7, characterized in that, The volume of all the cavity structures described accounts for 8-45% of the total volume of the molecular sieve.

10. The framework heteroatom titanium-silicon molecular sieve according to claim 9, characterized in that, The volume of all the cavity structures accounts for 12-40% of the total volume of the molecular sieve.

11. The framework heteroatom 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 framework heteroatom titanium-silicon molecular sieve according to claim 1, characterized in that, The framework heteroatom 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 framework heteroatom titanium-silicon molecular sieve according to claim 12, characterized in that, The molecular sieve particles have an average particle size of 0.12~0.75μm and a BET specific surface area of ​​280~670m². 2 / g; Microporous specific surface area is 240~520m² 2 / g; total pore volume is 0.18~0.67cm³. 3 / g; mesopore volume is 0.15~0.48cm³ 3 / g.

14. The framework heteroatom titanium-silicon molecular sieve according to claim 13, characterized in that, The molecular sieve particles have an average particle size of 0.15~0.55μm and a BET specific surface area of ​​300~620m². 2 / g; Microporous specific surface area is 270~440m² 2 / g; total pore volume is 0.22~0.55cm³. 3 / g; mesopore volume is 0.22~0.39cm³ 3 / g.

15. The framework heteroatom 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 framework heteroatom titanium-silicon molecular sieve.

16. The framework heteroatom titanium-silicon molecular sieve according to claim 15, characterized in that, The initial relative pressure (P / P0) at which the hysteresis loop appears is 0.3~0.

55.

17. The framework heteroatom 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: surfactant is (0.006~0.08):1:(0.01~3):(1~50):(0.05~0.25); the silicon source is in the form of SiO2, and the weight ratio of SiO2 to polymer is (8~100):

1.

18. The framework heteroatom 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: surfactant is (0.01~0.06):1:(0.02~1.8):(10~30):(0.08~0.15); the silicon source is in the form of SiO2, and the weight ratio of SiO2 to polymer is (10~60):

1.

19. The framework heteroatom 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 framework heteroatom 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 framework heteroatom 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 framework heteroatom 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 framework heteroatom 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 framework heteroatom 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 framework heteroatom 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 framework heteroatom 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 framework heteroatom 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 framework heteroatom 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 framework heteroatom 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 framework heteroatom 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 framework heteroatom 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.

32. The framework heteroatom titanium-silicon molecular sieve according to claim 31, characterized in that, 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.

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

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

35. The framework heteroatom titanium-silicon molecular sieve according to claim 33, characterized in that, In formula (C), R5, R6, R7 and R8 are each selected from one of methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, isopentyl, hexyl or isohexyl.

36. The framework heteroatom titanium-silicon molecular sieve according to claim 35, 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.

37. The framework heteroatom titanium-silicon molecular sieve according to claim 31, characterized in that, The inorganic titanium source is selected from one or more of titanium chloride, nitrate or sulfate.

38. The framework heteroatom 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.

39. The framework heteroatom titanium-silicon molecular sieve according to claim 1, characterized in that, In step S1, the surfactant is selected from one or more of anionic surfactants and cationic surfactants.

40. The framework heteroatom titanium-silicon molecular sieve according to claim 39, characterized in that, The anionic surfactant is selected from one or more of sodium dodecyl sulfate, linear sodium dodecylbenzene sulfonate, branched sodium dodecylbenzene sulfonate, α-olefin sulfonates with 14 to 16 carbon atoms, secondary alkyl sulfonates, and hexadecyl diphenyl ether disulfonate. The cationic surfactant is selected from one or more of hexadecyltrimethylammonium bromide, hexadecyltrimethoxyorganosilicon ammonium chloride, and octadecyltrimethoxyorganosilicon ammonium chloride.

41. The framework heteroatom titanium-silicon molecular sieve according to claim 40, characterized in that, The surfactant is selected from one or more of sodium dodecyl sulfate, sodium linear dodecylbenzene sulfonate, and hexadecyltrimethylammonium bromide.

42. The framework heteroatom 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).

43. The framework heteroatom titanium-silicon molecular sieve according to claim 42, characterized in that, The polymer is selected from one or more of polyethylene, polypropylene, polystyrene, and polyacrylonitrile.

44. The framework heteroatom titanium-silicon molecular sieve according to claim 42, wherein the molecular weight of the polymer is 10,000 to 200,000.

45. The framework heteroatom 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. The surfactant and the polymer are added to the hydrolyzed sol of the silicon, and the mixture is then used to obtain the reaction mixture.

46. ​​The framework heteroatom titanium-silicon molecular sieve according to claim 45, 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.

47. The framework heteroatom titanium-silicon molecular sieve according to claim 45, 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.

48. The framework heteroatom titanium-silicon molecular sieve according to claim 47, characterized in that, The conditions for the hydrolysis and alcohol removal treatment include: stirring and hydrolyzing at 40~90℃ for 6~12h.

49. The framework heteroatom titanium-silicon molecular sieve according to claim 48, characterized in that, The conditions for the hydrolysis and alcohol removal treatment include: stirring and hydrolyzing at 60~85℃ for 8~10h.

50. The framework heteroatom 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 (0.1~3):(1~20):

1.

51. The framework heteroatom titanium-silicon molecular sieve according to claim 50, characterized in that, The weight ratio of the second template agent, water, and molecular sieve intermediate is (0.15~2):(2~18):

1.

52. The framework heteroatom 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 6~168h, hydrothermal crystallization temperature of 130~200℃; 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 300~700℃ and a roasting time of 1~16h.

53. The framework heteroatom titanium-silicon molecular sieve according to claim 52, 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 24~72h and hydrothermal crystallization temperature of 150~180℃; 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 400~600℃ and a roasting time of 2~5h.

54. 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 hierarchical porous framework heteroatom titanium silicate molecular sieve as described in any one of claims 1 to 53.

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