A multi-level pore titanosilicate molecular sieve, a preparation method thereof and a method for preparing caprolactam from cyclohexanone oxime

Abstract

This disclosure relates to a hierarchical porous titanium-silicon molecular sieve and its preparation method, as well as a method for preparing caprolactam from cyclohexanone oxime. The titanium-silicon molecular sieve has the following ultraviolet-visible absorption spectral characteristics: In the peak division results of the ultraviolet-visible absorption spectrum of the titanium-silicon molecular sieve in the wavelength range of 200-450 nm: the peak area of ​​the peak at the wavelength position of 210±2 nm is recorded as A1, the peak area of ​​the peak at the wavelength position of 270±5 nm is recorded as A2, and the peak area of ​​the peak at the wavelength position of 320±5 nm is recorded as A3; X1 is any value between 1.5 and 5.1 as defined by the following formula (1): X1=A1 / A2 (1); X2 is any value between 0.5 and 4.5 as defined by the following formula (2): X2=A1 / A3 (2). This titanium-silicon molecular sieve can effectively improve the conversion rate of cyclohexanone oxime and the selectivity of caprolactam in the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime, and maintain good catalytic performance under long-term reaction, avoiding catalyst deactivation.

Description

Technical Field

[0001] This disclosure relates to the field of titanium-silicon molecular sieve preparation, specifically to a multi-level porous titanium-silicon molecular sieve and its preparation method, and a method for preparing caprolactam from cyclohexanone oxime. Background Technology

[0002] Zeolite molecular sieves are a class of solid acid catalysts with regular microporous structures. Currently, as many as 248 crystal structures have been reported, among which the microporous fission sieve (MFI) topology has important applications in petrochemical production and has attracted widespread attention. The MFI topology is a three-dimensional framework structure formed by the intersection of cylindrical and Z-shaped ten-membered ring channels. Titanium silicate molecular sieves, specifically TS-1 molecular sieves, are a typical example of the MFI topology. Heteroatom titanium doping into the MFI topological framework forms unique framework-coordinated titanium active centers, exhibiting important catalytic performance for liquid-phase selective oxidation reactions such as ammoniation, hydroxylation, and epoxidation.

[0003] 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. The cyclohexanone oxime gas-phase Beckmann rearrangement process based on molecular sieve catalysts avoids the use of ammonia and fuming sulfuric acid at the source compared to the traditional liquid-phase method. It has an atom utilization rate of 100% and is an environmentally friendly green production process for caprolactam.

[0004] 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 performance. Ferdi Schüth et al. (Microporous and Mesoporous Materials, 2009, 117, 228–232) added a 1,7-dichlorooctamethyltetraoxysilane alkylating agent to create pores during the synthesis of titanium-silicon molecular sieves, obtaining a titanium-silicon molecular sieve with hierarchical pores. This molecular sieve maintained a caprolactam yield of 1.6 mmol CPL g after 30 hours of reaction. -1 cat h -1 .

[0005] 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

[0006] The purpose of this disclosure is to provide a hierarchical porous titanium-silicon molecular sieve and its preparation method, as well as a method for preparing caprolactam from cyclohexanone oxime. The titanium-silicon molecular sieve can effectively improve the conversion rate of cyclohexanone oxime and the selectivity of caprolactam in the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime, and maintain good catalytic performance under long-term reaction, avoiding catalyst deactivation.

[0007] To achieve the above objectives, the first aspect of this disclosure provides a hierarchical porous titanium-silicon molecular sieve, which has the following ultraviolet-visible absorption spectral characteristics:

[0008] In the peak division results of the ultraviolet-visible absorption spectrum of the titanium-silicon molecular sieve in the wavelength range of 200-450nm: the peak area of ​​the peak at the wavelength position of 210±2nm is recorded as A1, the peak area of ​​the peak at the wavelength position of 270±5nm is recorded as A2, and the peak area of ​​the peak at the wavelength position of 320±5nm is recorded as A3.

[0009] As defined in equation (1), X1 can be any value between 1.5 and 5.1:

[0010] X1 = A1 / A2 (Equation 1);

[0011] As defined in equation (2), X2 is any value between 0.5 and 4.5:

[0012] X2 = A1 / A3 (Equation 2).

[0013] Optionally, the value of X1 is any value between 1.8 and 4.8; the value of X2 is any value between 0.8 and 3.6.

[0014] Optionally, the molar ratio of silicon atoms to titanium atoms in the titanium-silicon molecular sieve is (5-170):1, preferably (12-102):1;

[0015] 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.

[0016] Optionally, the titanium-silicon molecular sieve has multiple cavity structures within its crystal; wherein the size of a single cavity structure is 12–180 nm, preferably 15–150 nm;

[0017] Preferably, the volume of all the cavity structures accounts for 20-90% of the total volume of the molecular sieve, more preferably 30-85%;

[0018] Optionally, the shape of the cavity structure is selected from one or more of the following: sphere, cube, ellipsoid, and irregular cube.

[0019] 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;

[0020] Optionally, the average particle size of the molecular sieve particles is 0.15–0.68 μm, preferably 0.18–0.60 μm; and the BET specific surface area is 265–585 m². 2 / g, preferably 280-560m 2 / g; microporous specific surface area is 255-535m² 2 / g, preferably 265-520m 2 / g; total pore volume is 0.22–0.56 cm³. 3 / g, preferably 0.28~0.48cm 3 / g; mesopore volume is 0.12–0.46 cm³. 3 / g, preferably 0.15~0.38cm 3 / g;

[0021] 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 0.30 to 0.52, more preferably 0.32 to 0.48.

[0022] The second aspect of this disclosure provides a method for preparing hierarchical porous titanium-silicon molecular sieves, comprising the following steps:

[0023] S1. The silicon source, the first template agent, water, the silanizing agent and the structural filler are mixed to obtain a reaction mixture;

[0024] S2. The reaction mixture is subjected to a first hydrothermal crystallization treatment and a first calcination treatment in sequence to obtain a first molecular sieve intermediate;

[0025] S3. Mix the first molecular sieve intermediate, the second template agent and water, and then perform the second hydrothermal crystallization treatment and the second calcination treatment in sequence to obtain the second molecular sieve intermediate.

[0026] S4. The second molecular sieve intermediate is mixed with the titanium source and then subjected to a third calcination process.

[0027] Optionally, in step S1, the molar ratio of silicon source: first template agent: water: silanizing agent is 1:(0.01-5):(1-50):(0.005-3); preferably 1:(0.02-3):(10-30):(0.01-2.5); the silicon source is SiO2, and the weight ratio of SiO2 to structural filler is (5-45):1, preferably (8-40):1.

[0028] 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.

[0029] A further preferred option is a silicone grease, wherein the silicone grease has the general formula shown in formula (A):

[0030]

[0031] 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.

[0032] 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;

[0033] 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):

[0034] 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.

[0035] 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;

[0036] Optionally, the first template agent and the second template agent may be the same or different; preferably they are the same.

[0037] Optionally, in step S1, the silanizing agent is selected from those with the general formula R. e Si(R f (R) g )R h , where R e R f R g R h Each group can be independently halogenated, alkyl, alkoxy, aromatic, mercapto, or amino, and R e R f R g R h At least one of them is an alkyl, alkoxy, aromatic, mercapto, or amino group; the alkyl, alkoxy, mercapto, and amino groups each have an independent number of carbon atoms of C1 to C2. 18 ;

[0038] Preferably, the silanizing agent is selected from one or more of dimethyldichlorosilane, N-phenyl-3-aminopropyltrimethoxysilane, phenyltrimethoxysilane, 1,7-dichlorooctylmethyltetrasiloxane, hexadecyltrimethoxysilane, octyltriethoxysilane, 3-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, and 3-mercaptopropyltrimethoxysilane; more preferably, it is selected from one or more of N-phenyl-3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, and 3-mercaptopropyltrimethoxysilane.

[0039] Optionally, in step S1, the structural filler is an amphiphilic surfactant and / or a hard template agent;

[0040] Preferably, the amphiphilic surfactant is selected from one or more of hexadecyltrimethylammonium bromide, sodium dodecylbenzene sulfonate, branched sodium dodecylbenzene sulfonate, α-olefin sulfonates with 14 to 16 carbon atoms, and secondary alkyl sulfonates.

[0041] Preferably, the hard template agent is selected from one or more of PEO-PPO-PEO block copolymers, mesoporous carbon, natural fibers, polyethylene, polypropylene, polyvinyl chloride, polystyrene, and polyvinyl alcohol;

[0042] More preferably, the structural filler is selected from one or more of hexadecyltrimethylammonium bromide, sodium dodecylbenzenesulfonate, PEO-PPO-PEO block copolymer, mesoporous carbon, and natural cellulose.

[0043] Optionally, step S1 includes:

[0044] a. Mix the silicon source, the first template agent, and water to obtain a silicon hydrolysis sol;

[0045] b. Add the silanizing agent and the structural filler to the hydrolyzed sol of the silicon, and mix to obtain the reaction mixture;

[0046] Optionally, the mixing conditions in step a include stirring at 40–90°C for 6–12 hours;

[0047] Optionally, the mixing conditions in step b include stirring at 20–50°C for 2–4 hours;

[0048] 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;

[0049] 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.

[0050] 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 8–220 h and a hydrothermal crystallization temperature of 125–210 °C; preferably, a hydrothermal crystallization time of 10–80 h and a hydrothermal crystallization temperature of 140–185 °C; and the pressure is self-generated pressure.

[0051] 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.

[0052] Optionally, in step S3, the weight ratio of the second template agent: water: first molecular sieve intermediate is (0.08-5):(1-30):1; preferably (0.1-3.5):(2-20):1.

[0053] Optionally, in step S4, the titanium source is selected from one or more of organic titanium sources and inorganic titanium sources;

[0054] 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:

[0055]

[0056] 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.

[0057] The inorganic titanium source is selected from one or more of anatase, rutile, brookite, titanium chloride, titanium nitrate, and titanium sulfate.

[0058] Preferably, the titanium source is selected from one or more of anatase, rutile, brookite, titanium tetrachloride, titanium sulfate, titanium nitrate, tetraethyl titanate, tetrapropyl titanate, and tetrabutyl titanate.

[0059] More preferably, the molar ratio of the titanium source to the silicon source is (0.002-3):1, more preferably (0.01-2.2):1.

[0060] Optionally, in step S4, the conditions for the third calcination treatment include: a calcination temperature of 200–600°C, preferably 250–580°C; and a calcination time of 0.5–6 h, preferably 1–3.5 h.

[0061] The third aspect of this disclosure provides a hierarchical porous titanium-silicon molecular sieve prepared according to the method described in the second aspect of this disclosure.

[0062] The fourth aspect of this disclosure provides a method for preparing caprolactam from cyclohexanone oxime, comprising: contacting cyclohexanone oxime with a catalyst to carry out a gas-phase Beckmann rearrangement reaction, wherein the catalyst comprises the hierarchical porous titanium silicate molecular sieve described in the first and third aspects of this disclosure.

[0063] Through the above technical solutions, this disclosure provides a hierarchical porous titanium-silicon molecular sieve and its preparation method, as well as a method for preparing caprolactam from cyclohexanone oxime. The ultraviolet-visible absorption spectrum of the titanium-silicon molecular sieve has a framework titanium absorption peak, a six-coordinate titanium species absorption peak, and anatase absorption peak. The peak areas of the three species are in the range of X1 being 1.5 to 5.1 and X2 being 0.5 to 4.5. The titanium-silicon molecular sieve has abundant framework titanium centers, as well as abundant silanol active centers and a large specific surface area and pore volume. The hierarchical porous titanium-silicon molecular sieve exhibits high caprolactam selectivity and a long reaction lifetime in the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime.

[0064] Other features and advantages of this disclosure will be described in detail in the following detailed description section. Attached Figure Description

[0065] 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:

[0066] Figure 1 The image shows the UV-Vis absorption spectrum of the molecular sieve obtained in Example 1.

[0067] Figure 2 The XRD pattern of the molecular sieve obtained in Example 1;

[0068] Figure 3 Here is a TEM image of the molecular sieve obtained in Example 1;

[0069] Figure 4 Here is an SEM image of the molecular sieve obtained in Example 1;

[0070] Figure 5 The nitrogen adsorption-desorption curve of the molecular sieve obtained in Example 1 is shown below.

[0071] Figure 6 The XRD pattern of the molecular sieve obtained in Example 10;

[0072] Figure 7 The image shows the XRD pattern of the molecular sieve obtained in Example 11. Detailed Implementation

[0073] 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.

[0074] The first aspect of this disclosure provides a hierarchical porous titanium-silicon molecular sieve, which has the following ultraviolet-visible absorption spectrum characteristics:

[0075] In the peak division results of the ultraviolet-visible absorption spectrum of the titanium-silicon molecular sieve in the wavelength range of 200-450nm: the peak area of ​​the peak at the wavelength position of 210±2nm is recorded as A1, the peak area of ​​the peak at the wavelength position of 270±5nm is recorded as A2, and the peak area of ​​the peak at the wavelength position of 320±5nm is recorded as A3.

[0076] As defined in equation (1), X1 can be any value between 1.5 and 5.1:

[0077] X1 = A1 / A2 (Equation 1);

[0078] As defined in equation (2), X2 is any value between 0.5 and 4.5:

[0079] X2 = A1 / A3 (Equation 2).

[0080] This disclosure provides a hierarchical porous titanium-silicon molecular sieve. The ultraviolet-visible absorption spectrum of the titanium-silicon molecular sieve has a framework titanium absorption peak, a six-coordinate titanium species absorption peak, and anatase absorption peak. The peak areas of the three species are in the range of X1 being 1.5 to 5.1 and X2 being 0.5 to 4.5. The titanium-silicon molecular sieve has abundant framework titanium centers, as well as abundant silanol active centers and a large specific surface area and pore volume. The hierarchical porous titanium-silicon molecular sieve exhibits high caprolactam selectivity and a long reaction lifetime in the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime.

[0081] In this disclosure, ultraviolet-vis absorption spectroscopy (UV-vis) testing can be performed using conventional testing instruments and methods in the art, as well as conventional processing software and methods to perform peak separation, integration, and other processing on the spectral peaks.

[0082] In this disclosure, the UV-Vis absorption spectrum of the hierarchical porous titanium-silicon molecular sieve contains three titanium species, including: a framework titanium absorption peak at 210±2 nm, a six-coordinate titanium species absorption peak at 270±5 nm, and an anatase absorption peak at 320±5 nm. Through experimental research, the inventors of this disclosure surprisingly discovered that the ratio of the peak areas A1 to A3 of the above three absorption peaks in the titanium-silicon molecular sieve satisfies the range of X1 to X2, and the titanium-silicon molecular sieve has excellent molecular sieve catalytic performance.

[0083] In a preferred embodiment, the value of X1 is any value between 1.8 and 4.8; and the value of X2 is any value between 0.8 and 3.6. When the values ​​of X1 and X2 of the titanium-silicon molecular sieve are within the range of this embodiment, the titanium-silicon molecular sieve exhibits higher cyclohexanone oxime conversion and caprolactam selectivity in the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime, and its catalytic stability is better under long-term reaction conditions.

[0084] In one embodiment, the molar ratio of silicon atoms to titanium atoms in the titanium-silicon molecular sieve is (5-170):1, preferably (12-102):1. This disclosure obtains the molar ratio of titanium atoms to silicon atoms in the molecular sieve using X-ray fluorescence spectroscopy.

[0085] 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 12–180 nm, preferably 15–150 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 activity.

[0086] 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 12–180 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 12–180 nm.

[0087] In a preferred embodiment, all of the cavity structures account for 20-90% of the total volume of the molecular sieve, more preferably 30-85%;

[0088] Optionally, the shape of the cavity structure is selected from one or more of the following: sphere, cube, ellipsoid, and irregular cube.

[0089] 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.

[0090] Optionally, the average particle size of the molecular sieve particles is 0.15–0.68 μm, preferably 0.18–0.60 μm; and the BET specific surface area is 265–585 m². 2 / g, preferably 280-560m 2 / g; microporous specific surface area is 255-535m² 2 / g, preferably 265-520m 2 / g; total pore volume is 0.22–0.56 cm³. 3 / g, preferably 0.28~0.48cm 3 / g; mesopore volume is 0.12–0.46 cm³. 3 / g, preferably 0.15~0.38cm 3 / g.

[0091] 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.

[0092] In one specific embodiment, the initial relative pressure (P / P0) at which the hysteresis loop appears is 0.30 to 0.52, preferably 0.32 to 0.48.

[0093] 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.

[0094] The second aspect of this disclosure provides a method for preparing hierarchical porous titanium-silicon molecular sieves, comprising the following steps:

[0095] S1. The silicon source, the first template agent, water, the silanizing agent and the structural filler are mixed to obtain a reaction mixture;

[0096] S2. The reaction mixture is subjected to a first hydrothermal crystallization treatment and a first calcination treatment in sequence to obtain a first molecular sieve intermediate;

[0097] S3. Mix the first molecular sieve intermediate, the second template agent and water, and then perform the second hydrothermal crystallization treatment and the second calcination treatment in sequence to obtain the second molecular sieve intermediate.

[0098] S4. The second molecular sieve intermediate is mixed with the titanium source and then subjected to a third calcination process.

[0099] This disclosure provides a method for preparing hierarchical porous titanium-silicon molecular sieves. First, silanizing agents and macromolecular structure fillers are introduced into the molecular sieve synthesis raw materials to produce the effect of molecular sieve layer expansion and pore expansion, thus preparing molecular sieve materials with open channels. Then, a template agent is added for dissolution and recrystallization to prepare hierarchical porous pure silicon molecular sieves. Finally, a titanium source is introduced to obtain hierarchical porous titanium-silicon molecular sieves with intracrystalline multi-cavity structures.

[0100] In this disclosure, the silanol groups of the silanizing agent and the silanol groups of the organosilicon source undergo hydrolytic condensation to generate stable Si-O-Si bonds, thereby ensuring the achievement of the sieve expansion effect. Furthermore, the long carbon chain of the silanizing agent and the structural filler of the amphiphilic surfactant can form stable and controllable structural units (the long carbon chain of the silanizing agent and the hydrophobic group of the surfactant are close to each other and interact by van der Waals forces), thus playing a fine-tuning role in the sieve expansion; or a hard template agent with controllable size can be used to fill space. This results in an ordered, mesoporous structure with controllable pore size (controlled by the chain length of the alkyl chain of the silanizing agent). Then, a template agent is introduced into the molecular sieve with open pores, and its dissolution-recrystallization mechanism is used to obtain a pure silicon molecular sieve with a hierarchical porous structure. Finally, a titanium source is introduced, and the advantages of hierarchical pores are utilized to effectively disperse titanium species (a titanium source is loaded onto a hierarchical porous pure silicon molecular sieve with multiple cavities within the crystal), ultimately obtaining a titanium-silicon molecular sieve with a multiple cavity structure within the crystal.

[0101] In one embodiment, in step S1, the molar ratio of silicon source: first template agent: water: silanizing agent is 1:(0.01~5):(1~50):(0.005~3); the silicon source is SiO2, and the weight ratio of SiO2 to structural filler is (5~45):1.

[0102] In a preferred embodiment, in step S1, the molar ratio of silicon source: first template agent: water: silanizing agent is 1:(0.02-3):(10-30):(0.01-2.5); the silicon source is SiO2, and the weight ratio of SiO2 to structural filler is (8-40):1. The titanium-silicon molecular sieve prepared according to this embodiment has higher catalytic activity and catalytic stability.

[0103] 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.

[0104] A further preferred option is a silicone grease, wherein the silicone grease has the general formula shown in formula (A):

[0105]

[0106] 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 is independently selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, or tert-butyl.

[0107] 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.

[0108] 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.

[0109] 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):

[0110] 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.

[0111] 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.

[0112] In one embodiment, step S1 includes:

[0113] a. Mix the silicon source, the first template agent, and water to obtain a silicon hydrolysis sol;

[0114] b. Add the silanizing agent and the structural filler to the hydrolyzed sol of the silicon respectively, and mix them to obtain the reaction mixture;

[0115] Optionally, the mixing conditions in step a include stirring at 40–90°C for 6–12 hours;

[0116] Optionally, the mixing conditions in step b include stirring at 20–50°C for 2–4 hours.

[0117] 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;

[0118] 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 less than 10 ppm by mass.

[0119] In one embodiment, in step S1, the silanizing agent is selected from those with the general formula R. e Si(R f (R) g )R h , where R e R f R g R h Each group can be independently halogenated, alkyl, alkoxy, aromatic, mercapto, or amino, and R e R f R g R h At least one of them is an alkyl, alkoxy, aromatic, mercapto, or amino group; the alkyl, alkoxy, mercapto, and amino groups each have an independent number of carbon atoms of C1 to C2. 18 .

[0120] In a preferred embodiment, the silanizing agent is selected from one or more of dimethyldichlorosilane, N-phenyl-3-aminopropyltrimethoxysilane, phenyltrimethoxysilane, 1,7-dichlorooctylmethyltetrasiloxane, hexadecyltrimethoxysilane, octyltriethoxysilane, 3-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, and 3-mercaptopropyltrimethoxysilane; more preferably, it is selected from one or more of N-phenyl-3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, and 3-mercaptopropyltrimethoxysilane.

[0121] In one embodiment, in step S1, the structural filler is selected from one or more of amphiphilic surfactants and / or hard template agents.

[0122] In one specific embodiment, the amphiphilic surfactant is selected from one or more of hexadecyltrimethylammonium bromide, sodium dodecylbenzene sulfonate, branched sodium dodecylbenzene sulfonate, α-olefin sulfonates with 14 to 16 carbon atoms, and secondary alkyl sulfonates.

[0123] The hard template agent is selected from one or more of PEO-PPO-PEO block copolymers, mesoporous carbon, natural fibers, polyethylene, polypropylene, polyvinyl chloride, polystyrene, and polyvinyl alcohol.

[0124] In a preferred embodiment, the structural filler is selected from one or more of hexadecyltrimethylammonium bromide, sodium dodecylbenzenesulfonate, PEO-PPO-PEO block copolymer, mesoporous carbon, and natural cellulose.

[0125] The reagents involved in this disclosure can all be purchased through ordinary channels or prepared by 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 8 to 220 hours, hydrothermal crystallization temperature of 125 to 210°C, and pressure of autogenous pressure; the conditions for the first calcination treatment in step S2 include: calcination temperature of 300 to 700°C, and calcination time of 1 to 16 hours.

[0127] In a preferred embodiment, the conditions for the first hydrothermal crystallization treatment in step S2 include: a hydrothermal crystallization time of 10–80 h and a hydrothermal crystallization temperature of 140–185 °C; and an autogenous pressure. 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 titanium-silicon molecular sieve prepared according to this embodiment exhibits better catalytic activity.

[0128] 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.

[0129] In one embodiment, in step S3, the weight ratio of the second template agent: water: first molecular sieve intermediate is (0.08-5):(1-30):1; preferably (0.1-3.5):(2-20):1.

[0130] In this disclosure, the selection range of the second template agent is the same as that of the first template agent, and therefore will not be repeated here. Furthermore, the first and second template agents can be the same or different; preferably, they are template agents of the same type.

[0131] In one embodiment, the conditions for the second hydrothermal crystallization treatment in step S3 include: hydrothermal crystallization time of 8 to 220 hours, hydrothermal crystallization temperature of 125 to 210°C, and pressure of self-generated pressure; the conditions for the second calcination treatment in step S3 include: calcination temperature of 300 to 700°C, and calcination time of 1 to 16 hours.

[0132] In a preferred embodiment, the conditions for the second hydrothermal crystallization treatment in step S3 include: a hydrothermal crystallization time of 10–80 h and a hydrothermal crystallization temperature of 140–185 °C; and an autogenous pressure. 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 h. The titanium-silicon molecular sieve prepared according to this embodiment exhibits better catalytic activity.

[0133] 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.

[0134] In one embodiment, in step S4, the titanium source is selected from one or more of organic titanium sources and inorganic titanium sources.

[0135] The organotitanium source is an organic ester containing titanium atoms, selected from at least one of the structures shown in formula (C) below:

[0136]

[0137] 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.

[0138] The inorganic titanium source is selected from one or more of anatase, rutile, brookite, titanium chloride, titanium nitrate, and titanium sulfate.

[0139] In a preferred embodiment, the titanium source is selected from one or more of anatase, rutile, brookite, titanium tetrachloride, titanium sulfate, titanium nitrate, tetraethyl titanate, tetrapropyl titanate, and tetrabutyl titanate.

[0140] In a more preferred embodiment, the molar ratio of titanium source to silicon source is (0.002–3):1, preferably (0.01–2.2):1. Introducing a titanium source according to this embodiment yields a molecular sieve with superior performance. In this disclosure, the molar number of silicon sources in the "molar ratio of titanium source to silicon source" is calculated based on the molecular weight of pure silicon (SiO2) of 60, by dividing the mass of the second molecular sieve intermediate added by 60.

[0141] In one specific embodiment, in step S4, the conditions for the third calcination treatment include: a calcination temperature of 200–600°C, preferably 250–580°C; and a calcination time of 0.5–6 h, preferably 1–3.5 h.

[0142] The third aspect of this disclosure provides a hierarchical porous titanium-silicon molecular sieve prepared according to the method described in the second aspect of this disclosure.

[0143] The fourth aspect of this disclosure provides a method for preparing caprolactam from cyclohexanone oxime, comprising: contacting cyclohexanone oxime with a catalyst to carry out a gas-phase Beckmann rearrangement reaction, wherein the catalyst comprises the hierarchical porous titanium-silicon molecular sieve described in the first and third aspects of this disclosure.

[0144] 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 .

[0145] The present disclosure will be described in detail below through examples.

[0146] The UV-Vis spectra of the samples were measured on an Agilent CARY300 UV spectrophotometer with a scanning range of 190-800 nm, a step size of 1 nm, and a scanning rate of 600 nm / min.

[0147] 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°.

[0148] 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).

[0149] 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).

[0150] 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.

[0151] 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.

[0152] The reagents used in the following examples and comparative examples were all purchased through conventional channels.

[0153] Example 1

[0154] (1) 104g tetraethyl silicate (0.5mol), 65g tetrapropylammonium hydroxide (TPAOH, 0.08mol) aqueous solution with a concentration of 25% by weight and 140g water were added to a 500mL beaker, placed on a magnetic stirrer with heating and stirring functions and mixed evenly. The mixture was stirred at 60℃ for 5 hours, and the evaporated water was replenished periodically to obtain a colorless and transparent silica gel solution.

[0155] (2) Add 9g of N-phenyl-3-aminopropyltrimethoxysilane (PHAPTMS, 0.035mol) and 3g of PEO-PPO-PEO triblock copolymer (P123, purchased from Inokai, weight average molecular weight 5800) to the mixture in step (1) and stir for 2 hours.

[0156] (3) The mixture obtained in step (2) is transferred to a stainless steel sealed reactor and crystallized at 170°C for 24 hours to obtain a sample. The sample is filtered, washed, dried at 110°C for 3 hours, and then calcined in a muffle furnace at 550°C for 3 hours to obtain the intermediate product S-1-T (first molecular sieve intermediate).

[0157] (4) Mix 10g of S-1-T 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: first 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 sample S-1-M (second molecular sieve intermediate).

[0158] (5) Dissolve 0.3g titanium tetrachloride (0.00158mol) in 3g anhydrous ethanol and gradually add it dropwise to 3.16g S-1-M molecular sieve (the molar number of S-1-M molecular sieve is calculated based on pure silicon dioxide, and the mass of S-1-M molecular sieve added / 60 = 0.0527mol; then the molar ratio of titanium source to silicon source is 0.03). After grinding evenly, calcine it in a muffle furnace at 550℃ for 3 hours to obtain sample STS-1.

[0159] The structural parameter characterization results of sample STS-1 are listed in Table 2;

[0160] The UV-Vis spectrum of sample STS-1 is as follows Figure 1 As shown in the figure, sample STS-1 has three obvious peak signals: skeletal titanium (210ppm), hexacoordinate titanium (270ppm), and anatase (320ppm). After calculating the peak area, the peak areas of the above three peaks are: A1 is 51.9, A2 is 17.5, and A3 is 24.2. The values ​​of X1 and X2 obtained by formula (1) to (2) are listed in Table 3.

[0161] The XRD pattern of sample STS-1 is as follows Figure 2 As shown, this indicates that the titanium silicate molecular sieve sample has an MFI topology.

[0162] TEM electron microscope image of sample STS-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 of the molecular sieve is measured and calculated to be 18-130 nm.

[0163] SEM images of sample STS-1 are shown below. Figure 4As shown in the figure, the molecular sieve consists of uniform ellipsoidal particles.

[0164] The BET curve of sample STS-1 is shown below. Figure 5 As shown in the figure, there is a clear hysteresis loop between the nitrogen adsorption and desorption curves. The initial relative pressure (P / P0) at which the hysteresis loop appears is 0.47.

[0165] Comparative Example 1

[0166] This comparative example follows the preparation method of Example 1, but differs from Example 1 in that no silanizing agent or structural filler is added, and the resulting 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.

[0167] Comparative Example 2

[0168] This comparative example shows the preparation of conventional titanium-silicon molecular sieves according to existing methods (Zeolites, 1992, Vol. 12, pp. 943-950).

[0169] 22.5 g of tetraethyl silicate and 7.0 g of tetrapropylammonium hydroxide were mixed, and then 59.8 g of deionized water was added and mixed thoroughly. The mixture was then hydrolyzed at 60 °C for 1.0 h to obtain a hydrolyzed solution of tetraethyl silicate. A solution consisting of 1.1 g of tetrabutyl titanate and 5.0 g of isopropanol was then slowly added dropwise to the above solution under vigorous stirring. The mixture was stirred at 75 °C for 3 h to obtain a clear and transparent colloid. This colloid was then transferred to a sealed stainless steel reactor and crystallized at 170 °C for 3 days to obtain conventional TS-1 molecular sieve, denoted as D-2.

[0170] Comparative Example 3

[0171] This comparative example was prepared according to the method of Comparative Example 2, except that a silanizing agent and a structural filler were added. The specific steps included are as follows:

[0172] (1) Mix 22.5g of tetraethyl silicate with 7.0g of tetrapropylammonium hydroxide, add 59.8g of deionized water and mix evenly; then hydrolyze at 60℃ for 1.0h to obtain a hydrolyzed solution of tetraethyl silicate. Then, under vigorous stirring, slowly add a solution composed of 1.1g of tetrabutyl titanate and 5.0g of isopropanol to the above solution, and stir the mixture at 75℃ for 3h to obtain a clear and transparent colloid.

[0173] (2) Add 1.9g of N-phenyl-3-aminopropyltrimethoxysilane (PHAPTMS) and 0.65g of PEO-PPO-PEO triblock copolymer (P123, purchased from Inokai, weight average molecular weight 5800) to the mixture in step (1) and stir for 2 hours.

[0174] (3) The colloid is then transferred to a stainless steel sealed reactor and crystallized at 170°C for 3 days to obtain the expanded-pore TS-1 molecular sieve, denoted as D-3. The preparation conditions are shown in Table 1, and the characterization results of the obtained molecular sieve are shown in Table 2.

[0175] Examples 2-9

[0176] 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 STS-2 to STS-9; the preparation conditions are listed in Table 1, and the characterization results of the obtained molecular sieves are listed in Table 2.

[0177] Example 10

[0178] 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 STS-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 STS-10 is shown in Table 2. Figure 6 As shown, this indicates that STS-10 is a MEL structure.

[0179] Example 11

[0180] 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 STS-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 STS-11 is shown in Table 2. Figure 7 As shown, this indicates that STS-11 is a BEA structure.

[0181] Example 12

[0182] Titanium-silicon molecular sieves were prepared according to the method of Example 1, but the difference from Example 1 is as follows:

[0183] 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.

[0184] 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.

[0185] The third roasting treatment was carried out at a temperature of 200℃ for 0.5 hours.

[0186] The obtained titanium-silicon molecular sieve sample is designated as STS-12; the characterization results of the obtained molecular sieve STS-12 are listed in Table 2.

[0187] Table 1

[0188]

[0189]

[0190] In Table 1, TPAOH is tetrapropylammonium hydroxide, TBAOH is tetrabutylammonium hydroxide, TEAOH is tetraethylammonium hydroxide, PHAPTMS is N-phenyl-3-aminopropyltrimethoxysilane, APTMS is 3-aminopropyltriethoxysilane, GCPMS is 3-epoxypropoxypropyl(dimethoxy)methylsilane, TOMS is methyltrimethoxysilane; P123 is PEO-PPO-PEO triblock copolymer, and CTAB is hexadecyltrimethylammonium bromide. The reagents used in this disclosure can be obtained through conventional purchasing channels. The water in the "Water / Silicon Source" calculation in Table 1 also includes water from the aqueous solution of the first template agent; the water in the "Water: First Molecular Sieve Intermediate" calculation also includes water from the aqueous solution of the second template agent.

[0191] Table 2

[0192]

[0193] According to the data in Table 2 above, compared with the molecular sieves D-1 to D-3 prepared by Comparative Examples 1 to 3, the molecular sieves STS-1 to STS-12 prepared by the publicly provided method have larger cavity sizes and a larger percentage of the total volume of the molecular sieve structure.

[0194] Test case

[0195] 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:

[0196] 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.

[0197] The reaction products were collected after cooling, and the concentrations of each substance were quantitatively analyzed by gas chromatography. An Agilent 6890 gas chromatograph 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.

[0198] 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%;

[0199] Caprolactam selectivity (mol%) = (mol percentage of caprolactam in the product) / (100 - mol percentage of cyclohexanone oxime in the product) × 100%;

[0200] Cyclohexanone oxime conversion reduction rate (%) = (24h cyclohexanone conversion rate - 200h cyclohexanone conversion rate) / 24h cyclohexanone conversion rate × 100%;

[0201] The decrease in caprolactam selectivity (%) = (24h caprolactam selectivity - 200h caprolactam selectivity) / 24h caprolactam selectivity × 100%.

[0202] Table 3

[0203]

[0204] According to the data in Table 3 above:

[0205] Compared with the molecular sieves D-1 to D-3 prepared by Comparative Examples 1 to 3, the molecular sieves STS-1 to STS-12 prepared by the publicly provided method have X1 in the range of 1.5 to 5.1 and X2 in the range of 0.5 to 4.5 in the UV-Vis absorption spectrum characteristics. Molecular sieves STS-1 to STS-12 have higher catalytic activity in the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime, higher cyclohexanone oxime conversion and caprolactam selectivity, and higher catalytic stability under long-term reaction conditions (200 h).

[0206] Furthermore, the X1 of the molecular sieves STS-1 to STS-8 and STS-10 to STS-11 prepared in the examples is in the range of 1.8 to 4.8, and the X2 is in the range of 0.8 to 3.6. Compared with molecular sieves STS-9 and STS-12, the cyclohexanone oxime conversion rate and caprolactam selectivity are higher in the reaction using molecular sieves STS-1 to STS-8 and STS-10 to STS-11, and the catalytic stability is higher under long-term reaction conditions (200 h).

[0207] Comparing Example 1 with Example 9, Example 1 prepared molecular sieves according to the raw material addition ratio in the preferred embodiment. The obtained molecular sieve STS-1 had higher cyclohexanone oxime conversion and caprolactam selectivity in the catalytic reaction, and higher catalytic stability under long reaction conditions (200h).

[0208] Comparing Example 1 with Example 12, Example 1 prepared a molecular sieve according to the reaction conditions in the preferred embodiment. The obtained molecular sieve STS-1 had higher cyclohexanone oxime conversion and caprolactam selectivity in the catalytic reaction, and higher catalytic stability under long-term reaction conditions (200h).

[0209] 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.

[0210] 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.

[0211] Furthermore, various different embodiments of this disclosure can be combined in any way, as long as they do not violate the spirit of this disclosure, they should also be regarded as the content disclosed in this disclosure.

Claims

1. A multi-level porous titanium-silicon molecular sieve, characterized in that, The titanium-silicon molecular sieve has the following ultraviolet-visible absorption spectrum characteristics: In the peak division results of the ultraviolet-visible absorption spectrum of the titanium-silicon molecular sieve in the wavelength range of 200~450nm: the peak area of ​​the peak at the wavelength position of 210±2nm is recorded as A1, the peak area of ​​the peak at the wavelength position of 270±5nm is recorded as A2, and the peak area of ​​the peak at the wavelength position of 320±5nm is recorded as A3. As defined in equation (1), X1 can be any value between 1.5 and 5.1: X1 = A1 / A2 (1); As defined in equation (2), X2 is any value between 0.5 and 4.5: X2 = A1 / A3 (2); The hierarchical porous titanium-silicon molecular sieve is prepared by a method including the following steps: S1. The silicon source, the first template agent, water, the silanizing agent and the structural filler 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 first molecular sieve intermediate; S3. Mix the first molecular sieve intermediate, the second template agent and water, and then perform the second hydrothermal crystallization treatment and the second calcination treatment in sequence to obtain the second molecular sieve intermediate. S4. The second molecular sieve intermediate is mixed with the titanium source and then subjected to a third calcination process.

2. The titanium-silicon molecular sieve according to claim 1, characterized in that, The value of X1 is any value between 1.8 and 4.8; the value of X2 is any value between 0.8 and 3.

6.

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 (5~170):

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 (12~102):

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 12~180nm.

8. The titanium-silicon molecular sieve according to claim 7, characterized in that, The size of a single cavity structure is 15~150nm.

9. The titanium-silicon molecular sieve according to claim 7, characterized in that, The volume of all the cavity structures accounts for 20-90% 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 30-85% 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 0.15~0.68μm and a BET specific surface area of ​​265~585m². 2 / g; Microporous specific surface area is 255~535m² 2 / g; total pore volume is 0.22~0.56cm³. 3 / g; mesopore volume is 0.12~0.46cm³ 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 0.18~0.60 μm and a BET specific surface area of ​​280~560 m². 2 / g; Microporous specific surface area is 265~520m² 2 / g; total pore volume is 0.28~0.48cm³. 3 / g; mesopore volume is 0.12~0.46cm³ 3 / g 0.15~0.38cm 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 0.30~0.

52.

17. The titanium-silicon molecular sieve according to claim 16, characterized in that, The initial relative pressure (P / P0) at which the hysteresis loop appears is 0.32~0.

48.

18. The titanium-silicon molecular sieve according to claim 1, characterized in that, In step S1, the molar ratio of silicon source: first template agent: water: silanizing agent is 1: (0.01~5): (1~50): (0.005~3); the silicon source is SiO2, and the weight ratio of SiO2 to structural filler is (5~45):

1.

19. The titanium-silicon molecular sieve according to claim 18, characterized in that, In step S1, the molar ratio of silicon source: first template agent: water: silanizing agent is 1: (0.02~3): (10~30): (0.01~2.5); the silicon source is SiO2, and the weight ratio of SiO2 to structural filler is (8~40):

1.

20. 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.

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

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

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 straight-chain alkyl groups having 1 to 4 carbon atoms or branched alkyl groups having 3 to 4 carbon atoms.

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

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

26. 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.

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, aliphatic amines and aliphatic alcoholic amines.

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

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 straight-chain alkyl groups having 1 to 4 carbon atoms and branched alkyl groups having 3 to 4 carbon atoms.

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

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

32. The titanium-silicon molecular sieve according to claim 26, characterized in that, The first template agent and the second template agent may be the same or different.

33. The titanium-silicon molecular sieve according to claim 32, characterized in that, The first template agent and the second template agent are the same.

34. The titanium-silicon molecular sieve according to claim 1, characterized in that, In step S1, the general formula of the silanizing agent is R. e Si(R) f (R) g R h , where R e R f R g R h Each group can be independently halogenated, alkyl, alkoxy, aromatic, mercapto, or amino, and R e R f R g R h At least one of them is an alkyl, alkoxy, aromatic, mercapto, or amino group; the alkyl, alkoxy, mercapto, and amino groups each have an independent number of carbon atoms of C1 to C2. 18 .

35. The titanium-silicon molecular sieve according to claim 34, characterized in that, The silanizing agent is selected from one or more of dimethyldichlorosilane, N-phenyl-3-aminopropyltrimethoxysilane, phenyltrimethoxysilane, 1,7-dichlorooctylmethyltetrasiloxane, hexadecyltrimethoxysilane, octyltriethoxysilane, 3-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, and 3-mercaptopropyltrimethoxysilane.

36. The titanium-silicon molecular sieve according to claim 35, characterized in that, The silanizing agent is selected from one or more of N-phenyl-3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, and 3-mercaptopropyltrimethoxysilane.

37. The titanium-silicon molecular sieve according to claim 1, characterized in that, In step S1, the structural filler is selected from one or more of amphiphilic surfactants and / or hard template agents.

38. The titanium-silicon molecular sieve according to claim 37, characterized in that, The amphiphilic surfactant is selected from one or more of hexadecyltrimethylammonium bromide, sodium dodecylbenzene sulfonate, branched sodium dodecylbenzene sulfonate, α-olefin sulfonates with 14 to 16 carbon atoms, and secondary alkyl sulfonates.

39. The titanium-silicon molecular sieve according to claim 37, characterized in that, The hard template agent is selected from one or more of PEO-PPO-PEO block copolymers, mesoporous carbon, natural fibers, polyethylene, polypropylene, polyvinyl chloride, polystyrene, and polyvinyl alcohol.

40. The titanium-silicon molecular sieve according to claim 37, characterized in that, The structural filler is selected from one or more of hexadecyltrimethylammonium bromide, sodium dodecylbenzenesulfonate, PEO-PPO-PEO block copolymer, mesoporous carbon, and natural cellulose.

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

42. The titanium-silicon molecular sieve according to claim 41, 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.

43. The titanium-silicon molecular sieve according to claim 41, 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.

44. The titanium-silicon molecular sieve according to claim 43, characterized in that, The conditions for the hydrolysis and alcohol removal treatment include: stirring and hydrolyzing at 40~90℃ for 6~12h.

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 60~85℃ for 8~10h.

46. ​​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 8~220h, hydrothermal crystallization temperature of 125~210℃; 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.

47. The titanium-silicon molecular sieve according to claim 46, 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 10~80h 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 400~600℃ and a roasting time of 2~5h.

48. The titanium-silicon molecular sieve according to claim 1, characterized in that, In step S3, the weight ratio of the second template agent: water: first molecular sieve intermediate is (0.08~5):(1~30):

1.

49. The titanium-silicon molecular sieve according to claim 48, characterized in that, In step S3, the weight ratio of the second template agent: water: first molecular sieve intermediate is (0.1~3.5):(2~20):

1.

50. The titanium-silicon molecular sieve according to claim 1, characterized in that, In step S4, the titanium source is selected from one or more of organic titanium sources and inorganic titanium sources; The organic titanium source is a titanium-containing organic ester, selected from at least one of the structures represented by the general formula (C): （C）； R5, R6, R7 and R8 are each selected from alkyl groups having 1 to 6 carbon atoms; The inorganic titanium source is selected from one or more of anatase, rutile, brookite, titanium chloride, titanium nitrate, and titanium sulfate.

51. The titanium-silicon molecular sieve according to claim 50, 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.

52. The titanium-silicon molecular sieve according to claim 51, 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.

53. The titanium-silicon molecular sieve according to claim 51, 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.

54. The titanium-silicon molecular sieve according to claim 52, 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.

55. The titanium-silicon molecular sieve according to claim 50, characterized in that, The titanium source is selected from one or more of anatase, rutile, brookite, titanium tetrachloride, titanium sulfate, titanium nitrate, tetraethyl titanate, tetrapropyl titanate, and tetrabutyl titanate.

56. The titanium-silicon molecular sieve according to claim 1, characterized in that, The molar ratio of the titanium source to the silicon source is (0.002~3):

1.

57. The titanium-silicon molecular sieve according to claim 56, characterized in that, The molar ratio of the titanium source to the silicon source is (0.01~2.2):

1.

58. The titanium-silicon molecular sieve according to claim 1, characterized in that, In step S4, the conditions for the third calcination treatment include: calcination temperature of 200~600℃; and calcination time of 0.5~6h.

59. The titanium-silicon molecular sieve according to claim 58, characterized in that, In step S4, the conditions for the third calcination treatment include: calcination temperature of 250~580℃; and calcination time of 1~3.5h.

60. A method for preparing caprolactam from cyclohexanone oxime, comprising: The reaction of cyclohexanone oxime with a catalyst to carry out a gas-phase Beckmann rearrangement is characterized in that the catalyst comprises the hierarchical porous titanium-silicon molecular sieve as described in any one of claims 1 to 59.

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