Titanium silicalite molecular sieves with hierarchical porous structure and their preparation and application

Abstract

Titanium silicalite molecular sieve with hierarchical porous structure. Titanium silicalite molecular sieve, 1 Peak fitting of the peaks in the 1-6 ppm range in the H MAS NMR spectrum yielded five peaks with chemical shifts of 1.8±0.1 ppm, 2.2±0.1 ppm, 2.8±0.1 ppm, 3.8±0.1 ppm, and 4.6±0.1 ppm, respectively, with the peak areas satisfying a specific proportional relationship. Molecular sieves have significantly improved deactivation resistance, and when used in the vapor-phase Beckmann rearrangement of cyclohexanone oxime, they can significantly improve the conversion of cyclohexanone oxime and the selectivity for caprolactam.

Description

Detailed Description of the Invention

[0001] [Technical Field] The present application relates to the technical field of titanium silicalite molecular sieves, and in particular to titanium silicalite molecular sieves with hierarchical porous structure and their preparation and application.

[0002] [Background technology] The Beckmann rearrangement is a process that converts ketoximes to amides. Its most important application in the chemical industry is the production of caprolactam, a key monomer in the synthesis of nylon 6. Caprolactam is widely used in the production of important downstream products such as engineering plastics, nylon 6 fiber, and industrial cord textiles. Caprolactam can also be used in coatings, pharmaceuticals, and fine chemicals.

[0003] Currently, over 95% of caprolactam production is carried out using the cyclohexanone oxime liquid-phase Beckmann rearrangement reaction process, which uses concentrated sulfuric acid (or fuming sulfuric acid) as both the catalyst and solvent, resulting in serious problems such as equipment corrosion and environmental pollution. Liquid ammonia is used to neutralize the waste sulfuric acid after the reaction, resulting in the generation of large amounts of low-value ammonium sulfate as a by-product (1.9 tonnes of ammonium sulfate per tonne of caprolactam), resulting in poor technical and economic performance for this route.

[0004] Therefore, the vapor-phase Beckmann rearrangement process for cyclohexanone oxime based on molecular sieve catalysts has attracted considerable attention from both academia and industry. Compared to conventional liquid-phase processes, this process eliminates the need for ammonia and oleum as raw materials, achieves near-100% atomic utilization, and is an environmentally friendly, green caprolactam production process. Previous research has shown that all-silica molecular sieves with MFI topology exhibit excellent catalytic performance in the vapor-phase Beckmann rearrangement of cyclohexanone oxime. Therefore, at the beginning of this century, Sumitomo and Sinopec in Japan conducted industrial experiments on the vapor-phase Beckmann rearrangement of cyclohexanone oxime using continuous all-silica molecular sieves.

[0005] However, the vapor-phase Beckmann rearrangement route suffers from two problems: low CPL selectivity and short catalyst single-pass life. These problems affect the economics of the technology, as well as the sustainability and stability of the business, significantly slowing subsequent large-scale industrial deployment and commercial adoption. This is due to the small micropore size of the MFI structure, which is close to the molecular size of the reactants and products. This slows the diffusion of guest molecules within the confined pores of the molecular sieve, significantly increasing their residence time within the crystal, exacerbating the generation of by-products and pore clogging by carbon deposits. Furthermore, the silanol group active centers of all-silica molecular sieves are unstable and easily deactivated by heat and alkaline by-products. Process development is needed to further improve catalyst resistance to deactivation.

[0006] To this end, Baojun Li's research group (RSC Adv., 2013, 3, 20811-20815) synthesized titanium silicalite molecular sieves with different particle sizes for the vapor-phase Beckmann rearrangement of cyclohexanone oxime by adding S-1 and TS-1 molecular sieves as seeds during crystallization. Ferdi Schuth et al. (Microporous and Mesoporous Materials, 2009, 117, 228-232) added 1,7-dichlorooctamethyltetraoxysilane during the synthesis of titanium silicalite molecular sieves to form pores, resulting in hierarchically porous titanium silicalite molecular sieves, which were then used in the vapor-phase Beckmann rearrangement of cyclohexanone oxime.

[0007] However, when titanium silicalite molecular sieves synthesized by existing processes are used in the vapor-phase Beckmann rearrangement of cyclohexanone oxime, the improvement effects on caprolactam selectivity and catalyst life are not ideal, and there is still a certain gap between them and the requirements for industrial production.

[0008] Summary of the Invention The purpose of this application is to provide a hierarchically porous molecular sieve, as well as its preparation and application, which has significantly improved anti-deactivation performance and can significantly improve the cyclohexanone oxime conversion and caprolactam selectivity when used in the vapor-phase Beckmann rearrangement reaction of cyclohexanone oxime.

[0009] In order to achieve the above object, in one aspect, the present application provides a titanium silicalite molecular sieve having a hierarchical porous structure, and the titanium silicalite molecular sieve 1The spectral peaks in the chemical shift range of 1 ppm to 6 ppm in the H MAS NMR spectrum were separated to obtain five spectral peaks with chemical shifts corresponding to the peak positions of 1.8 ± 0.1 ppm, 2.2 ppm ± 0.1 ppm, 2.8 ppm ± 0.1 ppm, 3.8 ± 0.1 ppm, and 4.6 ± 0.1 ppm, respectively, where: The peak area of ​​the spectral peak whose peak is at 1.8 ± 0.1 ppm is recorded as A1, the peak area of ​​the spectral peak whose peak is at 2.2 ppm ± 0.1 ppm is recorded as A2, the peak area of ​​the spectral peak whose peak is at 2.8 ppm ± 0.1 ppm is recorded as A3, the peak area of ​​the spectral peak whose peak is at 3.8 ± 0.1 ppm is recorded as A4, and the peak area of ​​the spectral peak whose peak is at 4.6 ± 0.1 ppm is recorded as A5, where: X1 defined by the following formula (1) is in the range of 0.5 to 2.2: X1=(A2+A3) / A1(1); X2 defined by the following formula (2) is in the range of 0.1 to 1.2: X2=A4 / A1(2); X3 defined by the following formula (3) is in the range of 0.05 to 0.65: X3=A5 / A1(3).

[0010] In another aspect, the present application provides a method for preparing the present titanium silicalite molecular sieve having a hierarchical porous structure, the method comprising the steps of: 1) mixing a titanium source, a silicon source, a first templating agent, water, a hard templating agent, and a high molecular weight polymer to obtain a reaction mixture, wherein the hard templating agent is selected from one or more of a carbon material, a resin material, and a solid inorganic compound; 2) sequentially subjecting the reaction mixture to a first hydrothermal crystallization treatment and a first calcination treatment to obtain a molecular sieve intermediate; 3) mixing the molecular sieve intermediate, a second template agent and water, and then sequentially carrying out a second hydrothermal crystallization treatment and a second calcination treatment;

[0011] Preferably, the first template agent and the second template agent are organic bases, independently selected from a quaternary ammonium base, an aliphatic amine, an aliphatic alcohol amine, or a combination thereof.

[0012] In another aspect, the present application provides a method for preparing caprolactam from cyclohexanone oxime, comprising subjecting cyclohexanone oxime to a vapor-phase Beckmann rearrangement reaction in the presence of the present titanium silicalite molecular sieve having a hierarchical porous structure.

[0013] The titanium silicalite molecular sieve of the present invention introduces a novel titanium atom active center into the molecular sieve framework, which effectively improves the molecular sieve's anti-deactivation ability and helps to extend the molecular sieve's service life under alkaline reaction conditions. At the same time, its hierarchical porous structure provides the molecular sieve with abundant silanol groups with hydrogen bonding interactions, and X1, X2, and X3 defined in formulas (1) to (3) are within a specific numerical range, so that when the titanium silicalite molecular sieve is used in the vapor-phase Beckmann rearrangement reaction of cyclohexanone oxime, it can significantly improve the cyclohexanone oxime conversion and caprolactam selectivity. Furthermore, the hierarchical porous structure of the titanium silicalite molecular sieve also provides the titanium silicalite molecular sieve with advantages such as a large specific surface area and pore volume, which promote the catalytic reaction.

[0014] Other features and advantages of the present application are detailed in the Detailed Description section that follows.

[0015] DESCRIPTION OF THE DRAWINGS The drawings are used to provide a further understanding of the present application and constitute a part of this specification. The drawings, together with the following specific embodiments, are used to explain, but not to limit, the present application. In the drawings: FIG. 1 shows the molecular sieve obtained in Example 1. 1 1 H MAS NMR spectrum. FIG. 2 shows the molecular sieve obtained in Example 1. 31 P MAS NMR spectrum. FIG. 3 is an XRD spectrum of the molecular sieve obtained in Example 1. FIG. 4 is a TEM electron microscope image of the molecular sieve obtained in Example 1. FIG. 5 is an SEM electron microscope image of the molecular sieve obtained in Example 1. FIG. 6 is a BET curve diagram of the molecular sieve obtained in Example 1. FIG. 7 is a TEM electron microscope image of the intermediate product obtained in Example 1. FIG. 8 shows the structure of the intermediate product obtained in Example 1. 1 1 H MAS NMR spectrum. FIG. 9 shows the intermediate product obtained in Example 1. 31 P MAS NMR spectrum. FIG. 10 is a TEM electron microscope image of the molecular sieve obtained in Comparative Example 2. FIG. 11 shows the molecular sieve obtained in Comparative Example 2. 1 1 H MAS NMR spectrum. FIG. 12 shows the molecular sieve obtained in Comparative Example 2. 31 P MAS NMR spectrum. FIG. 13 is an XRD spectrum of the molecular sieve product obtained in Example 10. FIG. 14 is an XRD spectrum of the molecular sieve product obtained in Example 11.

[0016] [Specific Mode for Carrying Out the Invention] Specific embodiments of the present application are described in detail below. It should be understood that the specific embodiments described herein are used only to illustrate and explain the present application, and are not intended to limit the present application.

[0017] Any specific numerical value disclosed herein (including the endpoints of a numerical range) is not limited to the exact value of the numerical value, but should be understood to cover values ​​close to the exact value, such as all possible values ​​within a range of ±5% of the exact value. Furthermore, for the disclosed numerical ranges, the endpoints of the ranges, and the endpoints and specific values ​​within the ranges, and the specific values, can be combined in any way to create one or more new numerical ranges, and these new numerical ranges should also be considered to be specifically disclosed herein.

[0018] Unless otherwise specified, terms used herein have the same meaning as commonly understood by those skilled in the art. If a term is defined herein and that definition differs from the meaning commonly understood by those skilled in the art, the definition herein shall prevail.

[0019] In this application, the term "hierarchical porous structure" has the meaning commonly understood in the art, and specifically refers to a molecular sieve having multiple levels of pore size, for example, a molecular sieve having two levels of pore size, i.e., micropores (pore size < 2 nm) and mesopores (pore size 2 nm to 50 nm), micropores and macropores (pore size > 50 nm), or mesopores and macropores, or a molecular sieve having three levels of pore size, i.e., micropores, mesopores, and macropores (pore size > 50 nm).

[0020] In this application, the cavity structure in a molecular sieve crystal grain, as well as its size and volume, are measured by a transmission electron microscope (TEM) test. The size of a single cavity refers to the maximum length of a line between two positions on the cavity wall of the cavity structure in a transmission electron microscope image of the molecular sieve, and the average value of the sizes of all the cavity structures in the crystal grain is calculated as the size of the cavity structure of the crystal grain. The average value of the sizes of the cavity structures of 50 molecular sieve crystal grains is taken as the size of the cavity structure of the molecular sieve. For example, "the size of the cavity structure is within the range of 5 nm to 50 nm" means that the size of the cavity structure of the molecular sieve expressed by the average value is within the range of 5 nm to 50 nm; preferably, the length of a line connecting any two positions on the cavity wall of any cavity structure in each molecular sieve crystal grain, passing through the center of the cavity structure, is within the range of 5 nm to 50 nm. The volume of the cavity structure is estimated according to a sphere, where the arithmetic mean of the sum of the longest and shortest lines between two positions on the cavity wall passing through the center of the cavity structure is regarded as the diameter of the sphere, the radius of the sphere is then determined, and the volume of the corresponding cavity structure is calculated according to the sphere volume formula. The percentage of the sum of the volumes of all the cavity structures in the molecular sieve crystal grain to the volume of the corresponding molecular sieve crystal grain is calculated, and the average volume fraction of the cavity structures of 50 molecular sieve crystal grains is regarded as the percentage of the volume of the cavity structures of the molecular sieve to the volume of the molecular sieve.

[0021] In this application, the molecular sieve 31 The peak intensity of each characteristic peak in a P MAS NMR spectrum is expressed as the integrated area of ​​the corresponding characteristic peak.

[0022] In this application, except for the contents explicitly described, any unmentioned matters or items can be directly applied to those known in the art without any changes. Furthermore, any embodiment described in this specification can be freely combined with one or more other embodiments described in this specification, and the technical solutions or technical ideas formed thereby shall be considered to be part of the original disclosure or original record of this specification, and shall not be considered to be new contents not disclosed or anticipated in this specification, unless a person skilled in the art considers the combination to be obviously unreasonable.

[0023] All patent and non-patent literature referred to herein, including but not limited to textbooks and journal articles, is hereby incorporated by reference in its entirety.

[0024] The inventors of the present application have conducted many experimental studies to determine the effectiveness of titanium silicalite molecular sieves. 1 The H MAS NMR spectrum revealed the presence of two silanol group active centers: an independent silanol group active center with a chemical shift at 1.8±0.1 ppm, and a silanol group active center with hydrogen-bonding interactions with a chemical shift in the range of 2 ppm to 6 ppm. Peak separation revealed that the peak of the silanol group active center with hydrogen-bonding interactions contained four peaks with chemical shifts at 2.2±0.1 ppm, 2.8±0.1 ppm, 3.8±0.1 ppm, and 4.6±0.1 ppm, respectively. When the peak area ratios X1 to X3 of the peaks of the different types of silanol group active centers were within a specific range, the resulting titanium silicalite molecular sieve exhibited good catalytic activity and stability. In particular, when used in the vapor-phase Beckmann rearrangement of cyclohexanone oxime, it effectively improved the cyclohexanone oxime conversion and caprolactam selectivity, thereby achieving the present invention.

[0025] As described above, in a first aspect, the present application provides a titanium silicalite molecular sieve having a hierarchical porous structure, wherein the titanium silicalite molecular sieve 1 The spectral peaks in the chemical shift range of 1 ppm to 6 ppm of the H MAS NMR spectrum are separated to obtain five spectral peaks whose chemical shifts corresponding to the peak positions are 1.8 ± 0.1 ppm, 2.2 ppm ± 0.1 ppm, 2.8 ppm ± 0.1 ppm, 3.8 ± 0.1 ppm, and 4.6 ± 0.1 ppm, respectively. Here, the peak area of ​​the spectral peak whose peak is at 1.8 ± 0.1 ppm is recorded as A1, the peak area of ​​the spectral peak whose peak is at 2.2 ppm ± 0.1 ppm is recorded as A2, the peak area of ​​the spectral peak whose peak is at 2.8 ppm ± 0.1 ppm is recorded as A3, the peak area of ​​the spectral peak whose peak is at 3.8 ± 0.1 ppm is recorded as A4, and the peak area of ​​the spectral peak whose peak is at 4.6 ± 0.1 ppm is recorded as A5, where: X1 defined by the following formula (1) is in the range of 0.5 to 2.2: X1=(A2+A3) / A1(1); X2 defined by the following formula (2) is in the range of 0.1 to 1.2: X2=A4 / A1(2); X3 defined by the following formula (3) is in the range of 0.05 to 0.65: X3=A5 / A1(3).

[0026] Without being limited to any particular theory, the titanium silicalite molecular sieve of the present application introduces a novel hexacoordinated titanium atom active center into the molecular sieve framework, which effectively improves the molecular sieve's anti-deactivation ability and helps to extend the molecular sieve's service life under alkaline reaction conditions; at the same time, its hierarchical porous structure provides the molecular sieve with abundant silanol groups with hydrogen bonding interactions, and X1, X2, and X3 defined in formulas (1) to (3) are within a specific numerical range, so that when the titanium silicalite molecular sieve is used in the vapor-phase Beckmann rearrangement reaction of cyclohexanone oxime, it can significantly improve the cyclohexanone oxime conversion and caprolactam selectivity; furthermore, the hierarchical porous structure of the titanium silicalite molecular sieve also provides the titanium silicalite molecular sieve with advantages such as a large specific surface area and pore volume, which are believed to be beneficial for the catalytic reaction.

[0027] In this application, 1 H MAS NMR testing can be performed using conventional testing equipment and methods in the art, and conventional processing software and methods can be used to perform peak separation, integration, and other processing on the spectral peaks.

[0028] In a preferred embodiment, the value of X1 is in the range of 0.6 to 1.8, the value of X2 is in the range of 0.15 to 1.10, and the value of X3 is in the range of 0.10 to 0.55. When the values ​​of X1 to X3 of the titanium silicalite molecular sieve are in the above preferred ranges, the titanium silicalite molecular sieve exhibits higher cyclohexanone oxime conversion and caprolactam selectivity in the vapor-phase Beckmann rearrangement reaction of cyclohexanone oxime, and the catalytic stability of the molecular sieve is better under long-term reaction conditions.

[0029] In a preferred embodiment, solid-state nuclear magnetic resonance characterization is performed using trimethylphosphine (TMP) as a probe molecule to characterize the molecular sieves.31 The P MAS NMR spectrum shows three characteristic peaks at chemical shifts of -5±1 ppm, -34±1 ppm, and -61±1 ppm, respectively, where the peak intensity of the characteristic peak at chemical shift -5±1 ppm is recorded as N1, the peak intensity of the characteristic peak at chemical shift -34±1 ppm is recorded as N2, and the peak intensity of the characteristic peak at chemical shift -61±1 ppm is recorded as N3, where: Y1 defined by the following formula (4) is in the range of 0.005 to 0.15, preferably in the range of 0.02 to 0.12: Y1=N1 / N3(4); and Y2 defined by the following formula (5) is in the range of 0.10 to 0.30, preferably in the range of 0.12 to 0.26: Y2 = N2 / N3(5).

[0030] After extensive research, the present inventors have also found that when trimethylphosphine (TMP) is used as a probe molecule for characterizing titanium silicalite molecular sieves by solid-state nuclear magnetic resonance techniques, 31 In the P MAS NMR spectrum, a characteristic peak characterizing Bronsted acidity appears at a chemical shift of -5±1 ppm, a characteristic peak characterizing Lewis acidity appears at a chemical shift of -34±1 ppm, and a characteristic peak characterizing TMP physical adsorption appears at a chemical shift of -61±1 ppm. Using the characteristic peak of TMP physical adsorption as a reference, the peak intensities of the characteristic peaks of Bronsted acidity and Lewis acidity are compared with the characteristic peak of TMP physical adsorption. The ratio of the peak intensities of the characteristic peaks characterizing the two acidic properties of the titanium silicalite molecular sieve to the peak intensity of the characteristic peak of TMP physical adsorption falls within a specific range, which allows the molecular sieve to have suitable acidity and exert a synergistic catalytic effect on the vapor-phase Beckmann rearrangement of cyclohexanone oxime, thereby further improving caprolactam selectivity and extending catalyst life.

[0031] In this application, titanium silicalite molecular sieve 31 Trimethylphosphine (TMP) was used as the probe molecule in the P MAS NMR spectroscopy study, and the test method is conventional in the art.

[0032] In a preferred embodiment, the molar ratio of silicon atoms to titanium atoms in the titanium silicalite molecular sieve of the present invention is (8 to 150): 1, preferably (15 to 120): 1. In the present invention, the molar ratio of silicon atoms to titanium atoms in the molecular sieve can be obtained by X-ray fluorescence spectroscopy.

[0033] In a preferred embodiment, the titanium silicalite molecular sieve of the present invention has a plurality of void structures in the crystal grains, the size of the void structures being in the range of 5 nm to 50 nm, preferably in the range of 7 nm to 45 nm, and in such a preferred embodiment, the void structures are in communication with the outside through micropores, and the void structures and the micropores communicating therewith form a hierarchical porous structure.

[0034] In such a preferred embodiment, the titanium silicalite molecular sieve of the present invention has a plurality of relatively large cavity structures inside, thereby having a large specific surface area and pore volume. At the same time, the cavity structures have abundant silanol group active centers, thereby providing a large number of independent reaction units, and the plurality of cavity structures form more defect sites, thereby generating more silanol groups, resulting in stronger hydrogen bond interactions between them; Furthermore, the relatively large cavity structures meet the needs of polymer reactions, making it easier for reaction products to flow out of the catalyst, and avoiding the phenomenon of reduced catalytic activity of the catalyst due to pore blockage.

[0035] In a more preferred embodiment, the volume of the cavity structure of the molecular sieve occupies 8% to 55%, more preferably 12% to 50%, and even more preferably 20% to 50% of the volume of the molecular sieve. The shape of the cavity structure is not strictly limited and may be, for example, one or more of a sphere, an ellipsoid, a cylinder, a polyhedron (such as a cube and an irregular cube), and an irregular shape, and usually may be an irregular shape.

[0036] In some specific embodiments, the titanium silicalite molecular sieve comprises molecular sieve particles composed of single crystal grains and / or molecular sieve particles composed of agglomerates of multiple crystal grains. Optionally, the molecular sieve particles have an average particle size of 0.1 μm to 0.7 μm, preferably 0.13 μm to 0.62 μm; a BET specific surface area of ​​260 m 2 / g~620m 2 / g, preferably 280m 2 / g~540m 2 / g; micropore specific surface area is 280m 2 / g~500m 2 / g, preferably 300m 2 / g~480m 2 / g; total pore volume is 0.16 cm 3 / g~0.55cm 3 / g, preferably 0.22 cm 3 / g~0.45cm 3 / g; mesopore volume is 0.09 cm 3 / g~0.38cm 3 / g, preferably 0.12 cm 3 / g~0.34cm 3 / g.

[0037] In a preferred embodiment, a hysteresis loop exists between the adsorption isotherm and the desorption isotherm in the low-temperature nitrogen adsorption of the titanium silicalite molecular sieve. More preferably, the initial relative pressure (P / P0) at which the hysteresis loop appears is in the range of 0.35 to 0.55, and more preferably in the range of 0.38 to 0.48.

[0038] In preferred embodiments, the titanium silicalite molecular sieve configuration is selected from the group consisting of an MFI topological structure, an MEL topological structure, a BEA topological structure, and an SVR topological structure; the MFI topological structure is more preferred.

[0039] In a second aspect, the present application provides a method for preparing a titanium silicalite molecular sieve having a hierarchical porous structure, particularly the present titanium silicalite molecular sieve, comprising the steps of: 1) mixing a titanium source, a silicon source, a first template agent, water, a hard template agent, and a high molecular weight polymer to obtain a reaction mixture, wherein the hard template agent is selected from one or more of a carbon material, a resin material, and a solid inorganic compound; 2) sequentially subjecting the reaction mixture to a first hydrothermal crystallization treatment and a first calcination treatment to obtain a molecular sieve intermediate; 3) mixing the molecular sieve intermediate, a second template agent, and water, and then sequentially performing a second hydrothermal crystallization treatment and a second calcination treatment.

[0040] In the present method, the space-filling effect of the hard template and the hydrogen bonding effect between the high molecular weight polymer and the silanol group of the organosilicon source are combined to ensure the realization of abundant open pore channels and pore enlargement effects. At this time, the template is introduced into the molecular sieve with open pore channels, and the titanium silicalite molecular sieve with a hierarchical porous structure is obtained through the mechanism of dissolution and recrystallization of the template.

[0041] Specifically, in the present method, a titanium source is introduced into the molecular sieve synthesis raw material, and titanium atomic active centers are introduced into the molecular sieve framework during molecular sieve synthesis to improve molecular sieve performance; simultaneously, a hard template and a high-molecular-weight polymer are further introduced into the molecular sieve synthesis raw material, which enlarges the pores between the hard template and the inorganic molecular sieve framework mainly by space-filling. The high-molecular-weight polymer also helps to alleviate the problem of the hierarchical porous structure synthesized by the hard template method being an isolated, unconnected space. The high-molecular-weight polymer can self-assemble with the inorganic aluminosilicate through hydrogen bonding or electrostatic attraction, and after the hard template and high-molecular-weight polymer are removed by a first calcination treatment, a molecular sieve intermediate with abundant open channels is formed. Next, in step 3), a second template agent is introduced into the molecular sieve intermediate with open channels, and the dissolution and recrystallization mechanism is utilized to obtain the titanium silicalite molecular sieve of the present invention, which has a specific distribution of silanol group active centers and a hierarchical porous structure. Specifically, in step 3), the interior of the crystal grains of the molecular sieve intermediate obtained in step 2) is dissolved in a hydrothermal environment in the presence of the second template agent, generating void structures with sizes ranging from 5 nm to 50 nm, which then recrystallizes on the surface of the crystal grains, changing the morphology of the crystal grains. At the same time, the formation of this multi-void structure increases the curvature of the silanol group distribution, causing changes in the density and orientation of the silanol groups, increasing the hydrogen bonding effect, enhancing the hydrogen bonding effect, and increasing the adsorption force to reactant molecules, thereby further improving the reaction performance.

[0042] In a preferred embodiment, in step 1), the molar ratio of the titanium source:silicon source:first template agent:water is (0.005-0.55):1:(0.02-1.8):(1-50); the silicon source is calculated in the form of SiO, and the weight ratio of the hard template agent:high molecular weight polymer:silicon source is (0.02-0.75):(0.01-0.55):1.

[0043] In a more preferred embodiment, in step 1), the molar ratio of titanium source: silicon source: first template agent: water is (0.01-0.42):1:(0.04-1.5):(10-45); the silicon source is calculated in the form of SiO, and the weight ratio of hard template agent: high molecular weight polymer: silicon source is (0.04-0.55):(0.03-0.4):1. The titanium silicalite molecular sieve prepared in this preferred embodiment has higher catalytic activity and catalytic stability.

[0044] According to the present application, the silicon source described in step 1) is not strictly limited and can be various silicon sources suitable for preparing titanium silicalite molecular sieve.In a preferred embodiment, in step 1), the silicon source is selected from organic silicate, solid silica gel, white carbon black and silica sol, or a combination thereof;preferably, selected from organic silicate, solid silica gel and white carbon black, or a combination thereof.

[0045] In a further preferred embodiment, the silicon source is selected from at least one organosilicate having a structure represented by formula (A): [ka] In the formula, R a , R b , R c and R d are each independently selected from linear or branched alkyl groups having 1 to 6 carbon atoms, preferably R a , R b , R c and R d are each independently selected from a linear alkyl group having 1 to 4 carbon atoms or a branched alkyl group having 3 to 4 carbon atoms, and more preferably, R a , R b , R c and R dare each independently selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, or tert-butyl.

[0046] In particularly preferred embodiments, the organosilicate is selected from tetramethyl silicate, tetraethyl silicate, tetrabutyl silicate, dimethyldiethyl silicate, or combinations thereof.

[0047] According to the present application, the first template agent in step 1) and the second template agent in step 3) can be independently selected from various template agents suitable for preparing titanium silicalite molecular sieves, and the present application does not have any strict limitations. In a preferred embodiment, the first template agent and the second template agent are both organic bases, preferably independently selected from quaternary ammonium bases, aliphatic amines, aliphatic alcohol amines, or combinations thereof.

[0048] In a further preferred embodiment, the first template agent and the second template agent are each independently selected from at least one quaternary ammonium base having a structure represented by formula (B): [ka] In the formula, R1, R2, R3 and R4 are each independently selected from alkyl groups having 1 to 4 carbon atoms, preferably selected from linear alkyl groups having 1 to 4 carbon atoms and branched alkyl groups having 3 to 4 carbon atoms, and more preferably selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl and tert-butyl.

[0049] In particularly preferred embodiments, the first template agent and the second template agent are each independently selected from tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, tetrapropylammonium chloride, tetrapropylammonium bromide, or combinations thereof.

[0050] In a preferred embodiment, step 1) further comprises: a) mixing a titanium source, a silicon source, a first template agent and water to obtain a hydrolyzed sol containing titanium and silicon; b) adding a hard template agent and a high molecular weight polymer to the hydrolyzed sol containing titanium and silicon, respectively, and mixing them to obtain a reaction mixture; Optionally, the mixing conditions in step a) include stirring at 40°C to 90°C for 6 hours to 12 hours; and Optionally, the mixing conditions in step b) include stirring at 20°C to 50°C for 2 hours to 4 hours.

[0051] In a more preferred embodiment, the silicon source in step a) is an organic silicate, and step a) further comprises mixing a titanium source, a silicon source, a first templating agent, and water to obtain a hydrolyzed sol containing titanium and silicon, followed by hydrolysis and alcohol removal treatment; optionally, the hydrolysis and alcohol removal treatment conditions include stirring and hydrolysis at 40°C to 90°C for 6 to 12 hours; or preferably stirring and hydrolysis at 60°C to 85°C for 8 to 10 hours. Preferably, the hydrolysis and alcohol removal treatment is performed so that the mass content of alcohol generated by hydrolysis of the organic silicate in the hydrolyzed sol containing titanium and silicon is 10 ppm or less.

[0052] According to the present application, the titanium source in step 1) is not strictly limited and can be any titanium source suitable for preparing titanium silicalite molecular sieve. In a preferred embodiment, in step 1), the titanium source is selected from one or more of an organic titanium source and an inorganic titanium source.

[0053] In a further preferred embodiment, the organotitanium source is selected from at least one titanium-containing organic acid ester having the structure shown in formula (C): [ka] In the formula, R5, R6, R7 and R8 are each independently selected from alkyl groups having 1 to 6 carbon atoms, preferably selected from linear alkyl groups having 1 to 4 carbon atoms or branched alkyl groups having 3 to 6 carbon atoms, more preferably selected from linear alkyl groups having 2 to 4 carbon atoms or branched alkyl groups having 3 to 4 carbon atoms; optionally, R5, R6, R7 and R8 are each independently selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, isopentyl, hexyl or isohexyl; preferably, each independently selected from ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl or tert-butyl.

[0054] In some further preferred embodiments, the inorganic titanium source is selected from one or more of titanium chlorides, nitrates, and sulfates.

[0055] In particularly preferred embodiments, the titanium source is selected from titanium tetrachloride, titanium sulfate, titanium nitrate, tetraethyl titanate, tetrapropyl titanate, and tetrabutyl titanate, or combinations thereof.

[0056] In a preferred embodiment, in step 1): The carbon material used as the hard template agent is selected from carbon nanoparticles, carbon nanotubes, carbon nanofibers, and ordered mesoporous carbon, or a combination thereof; The resin material used as the hard template agent is selected from phenolic resins, polyester resins, and polyamide resins, or combinations thereof; The solid inorganic compound used as the hard template agent is selected from calcium carbonate, magnesium hydroxide and sodium carbonate, or a combination thereof.

[0057] The hard template used herein may have a size specification commonly used in the art. In a specific embodiment, when the hard template is in the form of particles (such as carbon nanoparticles, regular mesoporous carbon, calcium carbonate, or magnesium hydroxide), the average particle size of the hard template may be 1 nm to 100 nm; when the hard template is a carbon nanotube, the diameter of the hard template may be 5 nm to 50 nm and the length of the hard template may be 2 μm to 30 μm; when the hard template is a carbon nanofiber, the diameter of the hard template may be 3 nm to 80 nm and the length of the hard template may be 1 μm to 40 μm.

[0058] In a preferred embodiment, in step 1), the high molecular weight polymer is selected from polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), polyvinyl alcohol (PVA), polyvinyl acetate (PVAC), polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), polyvinyl butyral (PVB), polyethyleneimine (PEI), 4-polyvinylpyridine and poly(diallyldimethylammonium chloride), or a combination thereof.

[0059] In particularly preferred embodiments, the high molecular weight polymer is selected from polyethylene, polypropylene, polystyrene, polyvinyl chloride, polymethyl methacrylate, polyvinyl butyral, and polyacrylonitrile, or combinations thereof.

[0060] In a preferred embodiment, the high molecular weight polymer has a weight average molecular weight of 10,000 to 200,000.

[0061] In a preferred embodiment, the conditions for the first hydrothermal crystallization treatment in step 2) include: a hydrothermal crystallization temperature of 120°C to 220°C, a hydrothermal crystallization time of 4 hours to 180 hours, and an autogenous pressure; and the conditions for the first calcination treatment in step 2) include: a calcination temperature of 350°C to 750°C, and a calcination time of 1 hour to 15 hours.

[0062] In another preferred embodiment, the conditions for the first hydrothermal crystallization in step 2) include: a hydrothermal crystallization temperature of 140°C to 185°C, a hydrothermal crystallization time of 6 hours to 80 hours, and an autogenous pressure; and the conditions for the first calcination in step 2) include: a calcination temperature of 380°C to 620°C, and a calcination time of 1.5 hours to 4.5 hours. The titanium silicalite molecular sieve prepared by such a preferred embodiment has better catalytic activity.

[0063] In a specific embodiment, in step 2), after the first hydrothermal crystallization treatment, the product of the first hydrothermal crystallization treatment is further subjected to a first filtration treatment, a first drying treatment, and then a first calcination treatment. Preferably, the temperature of the first drying treatment is 50°C to 120°C, and the time is 1 hour to 12 hours.

[0064] In a preferred embodiment, in step 3), the weight ratio of the second template agent:water:molecular sieve intermediate is (0.08-3.5):(0.5-25):1, preferably (0.12-2.5):(2-18):1. The titanium silicalite molecular sieve prepared by such a preferred embodiment has higher catalytic activity.

[0065] In a preferred embodiment, in step 3), the conditions for the second hydrothermal crystallization treatment include: a hydrothermal crystallization temperature of 120°C to 220°C, a hydrothermal crystallization time of 4 hours to 180 hours, and an autogenous pressure; and the conditions for the second calcination treatment in step 3) include: a calcination temperature of 350°C to 750°C, and a calcination time of 1 hour to 15 hours.

[0066] In a more preferred embodiment, in step 3), the conditions for the second hydrothermal crystallization treatment include: a hydrothermal crystallization temperature of 140°C to 185°C, a hydrothermal crystallization time of 6 hours to 80 hours, and an autogenous pressure; and the conditions for the second calcination treatment in step 3) include: a calcination temperature of 380°C to 620°C, and a calcination time of 1.5 hours to 4.5 hours.

[0067] In a specific embodiment, after the second hydrothermal crystallization treatment, the product of the second hydrothermal crystallization treatment is further subjected to a second filtration treatment, a second drying treatment, and then a second calcination treatment. Preferably, the temperature of the second drying treatment is 50°C to 120°C, and the time is 1 hour to 12 hours.

[0068] In a third aspect, there is provided a titanium silicalite molecular sieve having a hierarchical porous structure prepared according to the method of the second aspect of the present application.

[0069] In a fourth aspect, there is provided the use of a titanium silicalite molecular sieve having a hierarchical porous structure as described in the first and third aspects of the present application in catalyzing the vapor phase Beckmann rearrangement reaction of cyclohexanone oxime.

[0070] In a fifth aspect, there is provided a method for preparing caprolactam from cyclohexanone oxime, comprising subjecting cyclohexanone oxime to a vapor-phase Beckmann rearrangement reaction in the presence of a titanium silicalite molecular sieve having a hierarchical porous structure as described in the first or third aspect of the present application.

[0071] In a preferred embodiment, the method comprises contacting a feed containing cyclohexanone oxime with a titanium silicalite molecular sieve under a nitrogen atmosphere to react the feed. Preferably, the feed contains cyclohexanone oxime and a solvent, and the solvent is an alcohol, such as methanol, ethanol, butanol, or cyclohexanol.

[0072] In a more preferred embodiment, the conditions for the vapor-phase Beckmann rearrangement reaction include a reaction temperature of 350°C to 400°C, a reaction pressure of 0 MPa to 0.2 MPa, a molar ratio of nitrogen to cyclohexanone oxime of 0.1 to 30:1, cyclohexanone oxime accounting for 5 wt% to 50 wt% of the total amount of cyclohexanone oxime and the solvent, and a weight hourly space velocity of cyclohexanone oxime of 1 h -1 ~10h -1 is.

[0073] In certain embodiments, the present application provides the following technical solutions: In one embodiment, the present application provides a titanium silicalite molecular sieve having a hierarchical porous structure, wherein the titanium silicalite molecular sieve has the following: 1 Characterized by the H MAS NMR characteristics: Titanium silicalite molecular sieve 1 The peak separation results for spectral peaks with chemical shifts in the range of 1 ppm to 6 ppm in H MAS NMR spectra are as follows: The peak area of ​​the peak at chemical shift 1.8 ± 0.1 ppm was recorded as A1, the peak area of ​​the peak at chemical shift 2.2 ppm ± 0.1 ppm was recorded as A2, the peak area of ​​the peak at chemical shift 2.8 ppm ± 0.1 ppm was recorded as A3, the peak area of ​​the peak at chemical shift 3.8 ± 0.1 ppm was recorded as A4, and the peak area of ​​the peak at chemical shift 4.6 ± 0.1 ppm was recorded as A5; X1 defined in the following formula (1) is an arbitrary value from 0.5 to 2.2: X1=(A2+A3) / A1, formula (1); X2 defined in the following formula (2) is an arbitrary value between 0.1 and 1.2: X2=A4 / A1, formula (2); X3 defined in the following formula (3) is an arbitrary value between 0.05 and 0.65: X3=A5 / A1, equation (3).

[0074] Preferably, the titanium silicalite molecular sieve is characterized in that X1 has a value of any value from 0.6 to 1.8; X2 has a value of any value from 0.15 to 1.10; and X3 has a value of any value from 0.10 to 0.55.

[0075] Preferably, the titanium silicalite molecular sieve is characterized in that the molar ratio of silicon atoms to titanium atoms in the titanium silicalite molecular sieve is (8-150):1, preferably (15-120):1; Optionally, the configuration of the titanium silicalite molecular sieve is selected from one or more of an MFI topological structure, an MEL topological structure, a BEA topological structure, and an SVR topological structure; preferably an MFI topological structure.

[0076] Preferably, the titanium silicalite molecular sieve has a plurality of cavity structures present in the titanium silicalite molecular sieve crystal; wherein the size of a single cavity structure is 5 nm to 50 nm, preferably 7 nm to 45 nm; more preferably, the volume of all the cavity structures occupies 8% to 55%, more preferably 12% to 50% of the total volume of the molecular sieve; and optionally, the shape of the cavity structures is selected from one or more of a sphere, a cube, an ellipsoid, and an irregular cube.

[0077] Preferably, the titanium silicalite molecular sieve comprises a molecular sieve particle composed of a single crystal grain and / or a molecular sieve particle composed of an aggregate of multiple crystal grains; optionally, the molecular sieve particle has an average particle size of 0.1 μm to 0.7 μm, preferably 0.13 μm to 0.62 μm;2 / g~620m 2 / g, preferably 280m 2 / g~540m 2 BET specific surface area: 280 m 2 / g~500m 2 / g, preferably 300m 2 / g~480m 2 Micropore specific surface area: 0.16cm / g 3 / g~0.55cm 3 / g, preferably 0.22 cm 3 / g~0.45cm 3 / g total pore volume: 0.09 cm 3 / g~0.38cm 3 / g, preferably 0.12 cm 3 / g~0.34cm 3 / g mesopore volume; optionally, a hysteresis loop exists between the adsorption isotherm and desorption isotherm of low-temperature nitrogen adsorption of the titanium silicalite molecular sieve, and preferably, the initial relative pressure (P / P0) at which the hysteresis loop appears is 0.35 to 0.55.

[0078] In another embodiment, the present application provides a method for preparing a titanium silicalite molecular sieve having a hierarchical porous structure, comprising the steps of: S1) mixing a titanium source, a silicon source, a first template agent, water, a hard template agent, and a high molecular weight polymer to obtain a reaction mixture; S2) sequentially subjecting the reaction mixture to a first hydrothermal crystallization treatment and a first calcination treatment to obtain a molecular sieve intermediate; S3) Mixing the molecular sieve intermediate, a second template agent and water, and then sequentially carrying out a second hydrothermal crystallization treatment and a second calcination treatment.

[0079] Preferably, in step S1), the molar ratio of the titanium source:silicon source:first template agent:water is (0.005-0.55):1:(0.02-1.8):(1-50), preferably (0.01-0.42):1:(0.04-1.5):(10-45); the silicon source is calculated in the form of SiO, and the weight ratio of the hard template agent:high molecular weight polymer:silicon source is (0.02-0.75):(0.01-0.55):1, preferably (0.04-0.55):(0.03-0.4):1.

[0080] Preferably, in step S1), the method comprises the step of: the silicon source is selected from at least one of organic silicates, solid silica gel, white carbon black, and silica sol; preferably, the silicon source is selected from at least one of organic silicates, solid silica gel, and white carbon black; More preferably, the silicon source is an organic silicate, and the general formula of the organic silicate is a structure represented by the following formula (A): [ka] In the formula, R a , R b , R c and R d are each independently selected from linear or branched alkyl groups having 1 to 6 carbon atoms, preferably R a , R b , R c and R d are each independently selected from a linear alkyl group having 1 to 4 carbon atoms or a branched alkyl group having 3 to 4 carbon atoms, and more preferably, R a , R b , R c and R dare each independently selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, or tert-butyl; and more preferably, the organosilicate is selected from one or more of tetramethyl silicate, tetraethyl silicate, tetrabutyl silicate, and dimethyldiethyl silicate.

[0081] Preferably, the method comprises the steps of: the first template agent in step S1) and the second template agent in step S3) are organic bases; each independently, preferably, at least one selected from a quaternary ammonium base, an aliphatic amine, and an aliphatic alcohol amine; More preferably, the first template agent and the second template agent are each independently selected from at least one quaternary ammonium base having a structure represented by formula (B): [ka] wherein R1, R2, R3 and R4 are each selected from alkyl groups having 1 to 4 carbon atoms, preferably one or more of linear alkyl groups having 1 to 4 carbon atoms and branched alkyl groups having 3 to 4 carbon atoms, 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; Even 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.

[0082] Preferably, the method comprises the steps of: in step S1), the titanium source is selected from one or more of an organic titanium source and an inorganic titanium source; The organotitanium source is a titanium-containing organic acid ester selected from at least one structure represented by formula (C): [ka] wherein R5, R6, R7 and R8 are each selected from an alkyl group having 1 to 6 carbon atoms, preferably a linear alkyl group having 1 to 4 carbon atoms and a branched alkyl group having 3 to 6 carbon atoms, more preferably R5, R6, R7 and R8 are each selected from a linear alkyl group having 2 to 4 carbon atoms and a branched alkyl group having 2 to 4 carbon atoms; optionally, 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; preferably, each independently selected from one of ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl or tert-butyl; The inorganic titanium source is selected from one or more of titanium chloride, nitrate, and sulfate; Preferably, the titanium source is selected from one or more of titanium tetrachloride, titanium sulfate, titanium nitrate, tetraethyl titanate, tetrapropyl titanate and tetrabutyl titanate.

[0083] Preferably, the method is characterized in that in step S1), the hard template agent is selected from one or more of a carbon material, a resin material, and an inorganic solid compound material; preferably, the carbon material is selected from one or more of a carbon nanoparticle, a carbon nanotube, a carbon nanofiber, and an ordered mesoporous carbon; preferably, the resin material is selected from one or more of a phenolic resin, a polyester resin, and a polyamide resin; preferably, the inorganic solid compound material is selected from one or more of a calcium carbonate, a magnesium hydroxide, and a sodium carbonate.

[0084] Preferably, the method is characterized in that in step S1), the high molecular weight polymer is selected from one or more of polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyvinyl alcohol, polyvinyl acetate, polyacrylonitrile, polymethyl methacrylate, polyvinyl butyral, polyethyleneimine, 4-polyvinylpyridine, and poly(diallyldimethylammonium chloride); more preferably, the high molecular weight polymer is selected from one or more of polyethylene, polypropylene, polystyrene, and polyacrylonitrile; and optionally, the high molecular weight polymer has a weight average molecular weight of 10,000 to 200,000.

[0085] Preferably, the method is characterized in that step S1) comprises: a. mixing a titanium source, a silicon source, a first template agent and water to obtain a silicon hydrolysis sol; b. adding a hard template agent and a high molecular weight polymer to the silicon hydrolyzed sol and mixing them to obtain a reaction mixture; Optionally, the mixing conditions in step a include stirring at 40°C to 90°C for 6 hours to 12 hours; Optionally, the mixing conditions in step b include stirring at 20°C to 50°C for 2 hours to 4 hours; Preferably, the silicon source is an organic silicate, and step a further comprises hydrolysis and alcohol removal treatment after mixing the silicon source, the first template agent and water to obtain the silicon hydrolysis sol; Optionally, the conditions for the hydrolysis and alcohol removal treatment include stirring and hydrolyzing at 40°C to 90°C for 6 to 12 hours; preferably stirring and hydrolyzing at 60°C to 85°C for 8 to 10 hours.

[0086] Preferably, the method is characterized in that in step S3), the weight ratio of the second template agent:water:molecular sieve intermediate is (0.08-3.5):(0.5-25):1; preferably, (0.12-2.5):(2-18):1.

[0087] Preferably, the method includes the following conditions independently for the first hydrothermal crystallization treatment in step S2) and the second hydrothermal crystallization treatment in step S3): the hydrothermal crystallization time is 4 hours to 180 hours, and the hydrothermal crystallization temperature is 120°C to 220°C; preferably, the hydrothermal crystallization time is 6 hours to 80 hours, and the hydrothermal crystallization temperature is 140°C to 185°C; and the pressure is autogenous pressure; The conditions for the first firing treatment in step S2) and the second firing treatment in step S3) independently include: a firing temperature of 350°C to 750°C and a firing time of 1 hour to 15 hours; preferably, a firing temperature of 380°C to 620°C and a firing time of 1.5 hours to 4.5 hours.

[0088] In another embodiment, there is provided a titanium silicalite molecular sieve having a hierarchical porous structure prepared according to the method of the above embodiment.

[0089] In another embodiment, there is provided a method for preparing caprolactam by vapor phase Beckmann rearrangement of cyclohexanone oxime, the method comprising: contacting cyclohexanone oxime with a reaction catalyst, the catalyst comprising a titanium silicalite molecular sieve having a hierarchical porous structure according to the above embodiment.

[0090] [Example] The present invention will be described in detail below through examples, but the present invention is not limited to these examples.

[0091] In the following examples and comparative examples: of the sample 1H MAS NMR spectra were acquired on a Varian Infinityplus-400 spectrometer using a 4 mm double resonance probe, a Φ4 mm ZrO2 rotor, a resonance frequency of 400.1 MHz, a magic angle speed of 10 kHz, a pulse width of 3.57 μs, a cycle delay time of 1 s, and approximately 4000 scans. Peak separation software, Origin 8.0, was used for calculations, using multi-peak fitting and peak areas and intensities.

[0092] of the sample 31 P MAS NMR spectra were acquired using trimethylphosphine (TMP) as the probe molecule on an AVANCE III 600WB NMR spectrometer with a 4 mm double resonance probe, a Φ4 mm ZrO2 rotor, a resonance frequency of 242.9 MHz, a magic angular velocity of 10 kHz, a pulse width of 1.4 μs, a cycle delay time of 1 s, and approximately 6000 scans.

[0093] The X-ray diffraction (XRD) crystalline phase diagram of the sample was measured by a Siemens X-ray diffractometer D5005, the radiation source was Kα(Cu), and the test range 2θ was 0.5° to 70°.

[0094] Transmission electron microscope (TEM) images of the samples were obtained using a Tecnai G2F20S-TWIN transmission electron microscope manufactured by FEI Co., Ltd. The TEM electron microscope examination determined the void structure and size of the samples, and the volume fraction of the void structure volume relative to the molecular sieve volume was determined by measuring the TEM images. The specific method is as follows: the volume of each cavity structure in the molecular sieve crystal grain is measured by TEM imaging (the volume of the cavity structure is estimated according to its sphere, and the arithmetic mean of the sum of the lengths of the longest and shortest lines among all lines connecting two positions on the cavity wall passing through the center of the cavity structure is taken as the sphere diameter, and then the sphere radius is determined, and the volume of the corresponding cavity structure is calculated according to the sphere volume formula), the percentage of the sum of the volumes of all cavity structures in the molecular sieve crystal grain to the volume of the corresponding molecular sieve crystal grain is calculated, and the average value of the volume fraction of the cavity structures of 50 molecular sieve crystal grains is considered to be the percentage of the volume of the cavity structures of the molecular sieve to the volume of the molecular sieve.

[0095] Scanning electron microscope (SEM) images of the samples were obtained by a Hitachi S4800 high-resolution cold cathode field emission scanning electron microscope. The average particle size of the samples was obtained by measuring the SEM images, measuring the particle sizes of 50 molecular sieve particles, and the arithmetic mean was considered as the average particle size of the molecular sieve.

[0096] The total specific surface area and total pore volume of the samples were measured using a Micromeritics ASAP245 static nitrogen adsorption apparatus according to the ASTM D4222-98 standard method.

[0097] The BET specific surface area, micropore specific surface area and mesopore volume of the samples were determined by low-temperature nitrogen adsorption-desorption method according to GB / T 19587-2004 standard and calculated using the BET equation.

[0098] The low temperature nitrogen adsorption and desorption isotherms of the samples were measured according to the ASTM D4222-98 standard method.

[0099] X-ray fluorescence analysis of the samples (determination of the molar ratio of silicon to titanium in the molecular sieve) was carried out using a 3013 instrument from Rigaku Corporation, Japan, with a tungsten target, an excitation voltage of 40 kV, and an excitation current of 250 mA.

[0100] In the following examples and comparative examples, all reagents and raw materials used are commercially available products unless otherwise specified.

[0101] Example 1 1a) 6 g (0.0176 mol) of tetrabutyl titanate, 104 g (0.5 mol) of tetraethyl silicate, 65 g of 25 wt% aqueous tetrapropylammonium hydroxide (TPAOH, 0.08 mol), and 140 g of water were added sequentially to a 500 mL beaker, and the mixture was mixed uniformly on a magnetic stirrer equipped with a heating and stirring function. The mixture was stirred at 60°C for 5 hours, and evaporated water was periodically replenished to obtain a colorless and transparent titanium silica gel solution; 1b) 9 g of carbon nanoparticles (purchased from J&K Chemicals, average particle size 15 nm) and 3 g of polystyrene (PS, purchased from Inotech, molecular weight 20,000) were added to the mixture of step 1a) to give a weight ratio of carbon nanoparticles:polystyrene:tetraethylsilicate (calculated as SiO2) of 0.3:0.1:1, and the mixture was stirred for 2 hours; 2) The mixture obtained in step 1b) was transferred to a stainless steel sealed reactor and isothermally crystallized at 170°C for 24 hours. The resulting product was washed, dried at 110°C for 3 hours, and then calcined in a muffle furnace at 550°C for 3 hours to obtain molecular sieve intermediate M-1. The characterization results of its structural parameters are shown in Table 2. The values ​​of X1 to X3 calculated by equations (1) to (3) are shown in Table 3; 3) 10 g of molecular sieve intermediate M-1, 20 g of 25 wt% tetrapropylammonium hydroxide (TPAOH, 5 g) aqueous solution, and 40 g of water were homogeneously mixed (the weight ratio of the second template agent (i.e., tetrapropylammonium hydroxide):water:molecular sieve intermediate was 0.5:5.5:1), transferred to a stainless steel sealed reactor, and isothermally crystallized at 170 °C for 24 hours. The resulting product was washed, dried at 110 °C for 3 hours, and then calcined in a muffle furnace at 550 °C for 3 hours to obtain a titanium silicalite molecular sieve sample designated C-1. The structural parameters and characterization results are shown in Table 2.

[0102] Molecular sieve C-1 1 The H MAS NMR spectrum is shown in Figure 1. After peak separation, the titanium silicalite molecular sieve exhibited a peak for an isolated silanol group at a chemical shift of 1.8 ppm, and peaks for silanol groups with hydrogen bond interactions at 2.2 ppm, 2.8 ppm, 3.8 ppm, and 4.6 ppm, respectively, in the chemical shift range of 2 ppm to 6 ppm. This indicates that the titanium silicalite molecular sieve possesses abundant silanol group active species. The peak areas of the above five peaks obtained by integral calculation were: A1 77559, A2 45005, A3 39245, A4 30954, and A5 19694. The values ​​of X1 to X3 calculated by Equations (1) to (3) are shown in Table 3.

[0103] Molecular sieve C-1 31 The MAS NMR spectrum of p-TMP is shown in Figure 2. Figure 2 shows a spectral peak corresponding to a Brønsted acid at a chemical shift of -5 ± 1 ppm, and a spectral peak corresponding to a Lewis acid at a chemical shift of -34 ± 1 ppm, indicating that the molecular sieve possesses the properties of both a Brønsted acid and a Lewis acid. The peak intensities N1, N2, and N3 are 23597, 54809, and 326304, respectively. The values ​​of Y1 and Y2 calculated using Equations (4) and (5) are shown in Table 3.

[0104] The XRD spectrum of molecular sieve C-1 is shown in Figure 3, which indicates that the titanium silicalite molecular sieve has an MFI topological structure.

[0105] A TEM electron microscope image of molecular sieve C-1 is shown in Figure 4. The molecular sieve grains have a hierarchical porous structure with multiple cavity structures inside. After measurement and calculation, it can be seen that the size of each cavity structure is in the range of 5 nm to 41 nm.

[0106] An SEM image of molecular sieve C-1 is shown in Figure 5. It can be seen from Figure 5 that the molecular sieve is a uniform ellipsoidal particle.

[0107] The results of the low-temperature nitrogen adsorption test of molecular sieve C-1 are shown in Figure 6. It can be seen that there is a clear hysteresis loop between the nitrogen adsorption isotherm and the desorption isotherm. The initial relative pressure (P / P0) at which the hysteresis loop appears is 0.46.

[0108] A TEM image of the molecular sieve intermediate M-1 that has not undergone the dissolution-recrystallization process (i.e., the second hydrothermal crystallization treatment) of step 3) is shown in Figure 7. Comparing Figure 7 with Figure 4, it can be seen that the molecular sieve intermediate M-1 has formed numerous cavity structures within the particles after the second hydrothermal crystallization treatment of step 3).

[0109] Molecular sieve intermediate M-1 1 The H MAS NMR spectrum is shown in Figure 8. After peak separation, it can be seen from Figure 8 that the titanium silicalite molecular sieve exhibits a peak for an isolated silanol group at a chemical shift of 1.8 ppm, as well as peaks for silanol groups with hydrogen bond interactions at 2.2 ppm, 2.8 ppm, 3.8 ppm, and 4.6 ppm, respectively, in the chemical shift range of 2 ppm to 6 ppm. The peak areas of the above five peaks obtained by integration calculation are: A1 31578, A2 0, A3 61089, A4 142592, and A5 61428. The calculated values ​​of X1 to X3 are shown in Table 3.

[0110] Molecular sieve intermediate M-1 31 The MAS NMR spectrum of p-TMP is shown in Figure 9. In Figure 9, there is a spectral peak corresponding to a Brønsted acid at a chemical shift of -5 ± 1 ppm, and a spectral peak corresponding to a Lewis acid at a chemical shift of -34 ± 1 ppm. The peak intensities N1, N2, and N3 are 163607, 24923, and 367232, respectively. The calculated values ​​of Y1 and Y2 are shown in Table 3.

[0111] Comparative Example 1 Titanium silicalite molecular sieves were prepared according to the method of Example 1, except that the hard template carbon nanoparticles and the high-molecular-weight polymer polystyrene were not added. The specific preparation conditions are shown in Table 1. The resulting molecular sieve was designated D-1. The characterization results of the structural parameters of D-1 are shown in Table 2, and the calculated values ​​of X1-X3 and Y1-Y2 are shown in Table 3.

[0112] Comparative Example 2 In this comparative example, titanium silicalite molecular sieve was prepared according to the method disclosed in the prior art CN112744836A, and the specific steps are as follows: 1) A 25 wt % aqueous solution of tetrapropylammonium hydroxide (TPAOH), tetraethyl orthosilicate (TEOS), tetrabutyl titanate (TBOT), and deionized water was weighed out in a molar ratio of TPAOH:TEOS:TBOT:HO of 0.2:1:0.015:100, added sequentially to a beaker, mixed uniformly on a magnetic stirrer equipped with a heating and stirring function, and stirred at 80°C for 3 hours to perform the first hydrolysis. Evaporated water was periodically replenished to obtain a colorless and transparent hydrolyzate, i.e., the first hydrolysis mixture.

[0113] 2) Activated carbon was added to the first hydrolysis mixture while stirring. The mass ratio of SiO2 to semi-coke 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 filtering and washing the product, the filter cake was dried at 110°C for 24 hours and then calcined at 550°C for 6 hours to obtain an intermediate titanium silicalite molecular sieve designated as HS-1.

[0114] 3) A 25 wt% aqueous solution of tetrapropylammonium hydroxide (TPAOH), tetraethyl orthosilicate (TEOS), tetrabutyl titanate (TBOT), and deionized water was weighed out in a molar ratio of TPAOH:TEOS:TBOT:HO of 2:20:1:55, added sequentially to a beaker, mixed uniformly on a magnetic stirrer equipped with a heating and stirring function, and stirred at 70°C for 10 hours to perform the second hydrolysis. Evaporated water was periodically replenished to obtain a colorless and transparent hydrolyzate, i.e., the second hydrolysis mixture.

[0115] (4) The intermediate titanium silicalite molecular sieve HS-1, the second hydrolysis mixture, and ammonium chloride are mixed to obtain TiO2, SiO2, and NH4 + A mixed material having a molar ratio of 1:35:0.3 was obtained, which was transferred to a stainless steel reactor and subjected to a second hydrothermal treatment at 170°C for 24 hours, filtered, washed, dried at 120°C for 24 hours, and calcined at 550°C for 6 hours to obtain a molecular sieve product designated as D-2.

[0116] The TEM image of molecular sieve D-2 is shown in Figure 10. Comparing Figure 10 with Figure 4, it can be seen that molecular sieve C-1 prepared in Example 1 has a clear multi-cavity structure within the crystal grains compared to molecular sieve D-2.

[0117] Molecular sieve D-2 1The H MAS NMR spectrum is shown in Figure 11. It can be seen from Figure 11 that A1 is 123510, A2 is 60045, A3 is 0, A4 is 71389, and A5 is 40722. The calculated values ​​of X1 to X3 are shown in Table 3.

[0118] Molecular sieve D-2 31 The P-TMP MAS NMR spectrum is shown in Figure 12, where the peak intensities N1 are 4387, N2 are 15086, and N3 are 1710413. The calculated values ​​of Y1 and Y2 are shown in Table 3.

[0119] Comparative Example 3 Titanium silicalite molecular sieves were prepared according to the method of Example 1, except that carbon nanoparticles, a hard template agent, were not added. Specific preparation conditions are shown in Table 1. The resulting molecular sieve was designated D-3. The characterization results of the structural parameters of D-3 are shown in Table 2, and the calculated values ​​of X1 to X3 and Y1 to Y2 are shown in Table 3.

[0120] Examples 2 to 9 Titanium silicalite molecular sieves were prepared according to the method of Example 1, except that the ratios and synthesis conditions were changed as shown in Table 1. The obtained titanium silicalite molecular sieves were designated C-2 to C-9, respectively. The characterization results of the structural parameters of C-2 to C-9 are shown in Table 2, and the calculated values ​​of X1 to X3 and Y1 to Y2 are shown in Table 3.

[0121] Example 10 Titanium silicalite molecular sieve was prepared according to the method of Example 1, except that the template agent was changed as shown in Table 1, where tetrapropylammonium hydroxide, the template agent used in step 1a) and step 3), was replaced with tetrabutylammonium hydroxide (TBAOH). Specific preparation conditions are shown in Table 1. The obtained titanium silicalite molecular sieve was designated C-10. The characterization results of the structural parameters of C-10 are shown in Table 2, and the calculated values ​​of X1-X3 and Y1-Y2 are shown in Table 3.

[0122] The XRD spectrum of molecular sieve C-10 is shown in Figure 13. Figure 13 shows that the molecular sieve has a MEL topological structure.

[0123] Example 11 Titanium silicalite molecular sieves were prepared according to the method of Example 1, except that the ratio and template agent were changed as shown in Table 1, where the template agent tetrapropylammonium hydroxide used in steps 1a) and 3) was replaced with tetrabutylammonium hydroxide (TBAOH). The specific preparation conditions are shown in Table 1. The obtained titanium silicalite molecular sieve was designated C-11. The characterization results of the structural parameters of C-11 are shown in Table 2, and the calculated values ​​of X1-X3 and Y1-Y2 are shown in Table 3.

[0124] FIG. 14 shows the XRD spectrum of molecular sieve C-11, which indicates that the molecular sieve has a BEA topological structure.

[0125] Example 12 Titanium silicalite molecular sieve was prepared according to the method of Example 1 with the following exceptions: The temperature of the first hydrothermal crystallization treatment was 120°C, and the time was 96 hours; the temperature of the first calcination treatment was 350°C, and the time was 8 hours; The temperature of the second hydrothermal crystallization treatment was 120°C, and the time was 96 hours; the temperature of the second calcination treatment was 350°C, and the time was 8 hours; The resulting titanium silicalite molecular sieve sample was designated C-12. The properties of the resulting molecular sieve C-12 are shown in Table 2.

[0126] Examples 13 to 15 Titanium silicalite molecular sieves were prepared according to the method of Example 1, except that the ratio, silicon source, and template agent were changed as shown in Table 1. The resulting titanium silicalite molecular sieves were designated C-13 to C-15, respectively. The characterization results of the structural parameters of C-13 to C-15 are shown in Table 2, and the calculated values ​​of X1 to X3 and Y1 to Y2 are shown in Table 3.

[0127] [Table 1] JPEG2025535950000009.jpg172169

[0128] In Table 1, TPAOH is tetrapropylammonium hydroxide, TBAOH is tetrabutylammonium hydroxide, and TEAOH is tetraethylammonium hydroxide; PVC is polyvinyl chloride (weight average molecular weight 15,000), PS is polystyrene (weight average molecular weight 20,000), PMMA is polymethyl methacrylate (weight average molecular weight 18,000), and PVB is polyvinyl butyral (weight average molecular weight 22,000); the average particle size of carbon nanoparticles is 50 nm, the diameter of carbon nanotubes is 20 nm, and the length is 15 μm; the diameter of carbon nanofibers is 60 nm, and the length is 30 μm. The average particle size of ordered mesoporous carbon is 10 nm, the average particle size of phenolic resin is 30 nm, and the average particle size of calcium carbonate is 20 nm.

[0129] In Table 1, the water in the calculation of "water / silicon source" in the examples of the present application includes water from the first aqueous template solution; the water in the calculation of "water / molecular sieve intermediate" includes water from the second aqueous template solution.

[0130] [Table 2]

[0131] According to the data in Table 2 above, it can be seen that compared with the molecular sieves D-1 to D-3 prepared in Comparative Examples 1 to 3, the molecular sieves C-1 to C-15 prepared by the method of the present application have larger cavity sizes and a larger percentage of the total volume of the cavity structure to the total volume of the molecular sieve.

[0132] Test Example The molecular sieves prepared in the above Examples and Comparative Examples were evaluated. The prepared molecular sieves were tableted and then pulverized. Particles with sizes of 20 mesh to 60 mesh were used as catalysts for the vapor-phase Beckmann rearrangement reaction of cyclohexanone oxime. The catalytic performance of the obtained molecular sieves was evaluated. The evaluation conditions were as follows: The evaluation equipment was a continuous-flow fixed-bed reactor at atmospheric pressure with an inner diameter of 5 mm and a catalyst loading of 2 g. After the catalyst loading, pretreatment was carried out in a nitrogen atmosphere at atmospheric pressure and 350°C for 3 hours. The concentration of the raw material cyclohexanone oxime was 35 wt%, and the solvent was methanol. The reaction conditions were a cyclohexanone oxime weight hourly space velocity (WHSV, flow rate of cyclohexanone oxime in the raw material / weight of catalyst in the reactor) of 2 h. -1 The reaction temperature was 380°C, the nitrogen flow rate was 4 L / h, and the reaction time was 24 h and 200 h, respectively.

[0133] The reaction products were cooled and collected, and the concentrations of various substances were quantitatively analyzed by gas chromatography using an Agilent 6890 gas chromatograph and an HP-5 column for analytical chromatography. The test conditions included: vaporizer temperature 250°C, detector temperature 230°C, programmable column temperature, constant temperature 110°C for 8 minutes, temperature increase to 230°C at 15°C / min, and constant temperature for 14 minutes. The results are shown in Table 3 below.

[0134] In Table 3: Cyclohexanone oxime conversion (mol%) = (molar content of cyclohexanone oxime in the feed - molar content of cyclohexanone oxime in the product) / molar content of cyclohexanone oxime in the feed × 100%; Caprolactam selectivity (mol%) = mole percentage of caprolactam in the product / (100 - mole percentage of cyclohexanone oxime in the product) × 100%; Cyclohexanone oxime conversion decrease rate (%) = (cyclohexanone conversion rate in 24 hours - cyclohexanone conversion rate in 200 hours) / cyclohexanone conversion rate in 24 hours × 100%; Caprolactam selectivity decrease rate (%)=(24-hour caprolactam selectivity−200-hour caprolactam selectivity) / 24-hour caprolactam selectivity×100%.

[0135] [Table 3]

[0136] According to the data in Table 3 above, compared with the molecular sieves D-1 to D-3 prepared in Comparative Examples 1 to 3, the molecular sieves C-1 to C-15 prepared by the method of the present application have X1 in the range of 0.5 to 2.2, X2 in the range of 0.1 to 1.2, and X3 in the range of 0.05 to 0.65. 1 The molecular sieves C-1 to C-15 have H MAS NMR spectra. In the vapor-phase Beckmann rearrangement reaction of cyclohexanone oxime, the molecular sieves C-1 to C-15 have higher catalytic activity, higher cyclohexanone oxime conversion and caprolactam selectivity, and show lower declines in cyclohexanone oxime conversion and caprolactam selectivity under long-term reaction conditions (200 hours). This indicates that the molecular sieves C-1 to C-15 provided herein have higher catalytic stability.

[0137] Furthermore, the molecular sieves C-1 to C-8, C-10 to C-11, and C-13 to C-15 prepared in the examples have X1 in the range of 0.6 to 1.8, X2 in the range of 0.15 to 1.10, and X3 in the range of 0.10 to 0.55. Compared with the molecular sieves C-9 and C-12, the molecular sieves C-1 to C-8, C-10 to C-11, and C-13 to C-15 have higher cyclohexanone oxime conversion and caprolactam selectivity, and have higher catalyst stability under long-term reaction conditions (200 hours).

[0138] Comparing Example 1 with Example 9, Example 1 prepared a molecular sieve according to the raw material addition ratio in the preferred embodiment, and the resulting molecular sieve C-1 had high cyclohexanone oxime conversion and caprolactam selectivity in the catalytic reaction, and high catalytic stability under long-term reaction conditions (200 hours).

[0139] Comparing Example 1 with Example 12, Example 1 prepared a molecular sieve according to the reaction conditions of the preferred embodiment, and the resulting molecular sieve C-1 had high cyclohexanone oxime conversion and caprolactam selectivity in the catalytic reaction, and high catalytic stability under long-term reaction conditions (200 hours).

[0140] Although the preferred embodiments of the present application have been described in detail above, the present application is not limited to the specific contents of the above embodiments. Within the scope of the technical concept of the present application, various simple modifications can be made to the technical solutions of the present application, and all of these simple modifications fall within the protection scope of the present application.

[0141] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction, and in order to avoid unnecessary repetition, the present application will not further describe the various possible combinations.

[0142] It should be noted that the embodiments of the present application can be combined in any manner, and as long as they do not contradict the concept of the present application, they should also be considered as the contents disclosed in the present application. [Brief explanation of the drawings]

[0143] [Figure 1] FIG. 1 is a 1H MAS NMR spectrum of the molecular sieve obtained in Example 1. [Figure 2] FIG. 2 is the 31P MAS NMR spectrum of the molecular sieve obtained in Example 1. [Figure 3] FIG. 3 is an XRD spectrum of the molecular sieve obtained in Example 1. [Figure 4] FIG. 4 is a TEM electron microscope image of the molecular sieve obtained in Example 1. [Figure 5] FIG. 5 is an SEM electron microscope image of the molecular sieve obtained in Example 1. [Figure 6] FIG. 6 is a BET curve diagram of the molecular sieve obtained in Example 1. [Figure 7] FIG. 7 is a TEM electron microscope image of the intermediate product obtained in Example 1. [Figure 8] FIG. 8 is a 1H MAS NMR spectrum of the intermediate product obtained in Example 1. [Figure 9] FIG. 9 is a 31P MAS NMR spectrum of the intermediate product obtained in Example 1. [Figure 10] FIG. 10 is a TEM electron microscope image of the molecular sieve obtained in Comparative Example 2. [Figure 11] FIG. 11 is a 1H MAS NMR spectrum of the molecular sieve obtained in Comparative Example 2. [Figure 12] FIG. 12 is a 31P MAS NMR spectrum of the molecular sieve obtained in Comparative Example 2. [Figure 13]FIG. 13 is an XRD spectrum of the molecular sieve product obtained in Example 10. [Figure 14] FIG. 14 is an XRD spectrum of the molecular sieve product obtained in Example 11.

Claims

1. A titanium silicalite molecular sieve having a hierarchical porous structure, comprising: １ The spectral peaks in the chemical shift range of 1 ppm to 6 ppm in the H MAS NMR spectrum were resolved to obtain five spectral peaks with chemical shifts corresponding to the peak positions of 1.8±0.1 ppm, 2.2 ppm±0.1 ppm, 2.8 ppm±0.1 ppm, 3.8±0.1 ppm, and 4.6±0.1 ppm, respectively, where: The peak area of ​​the spectrum peak at 1.8±0.1 ppm is A １ The peak area of ​​the spectral peak at 2.2 ppm ± 0.1 ppm is recorded as A ２ The peak area of ​​the spectral peak at 2.8 ppm ± 0.1 ppm is recorded as A ３ The peak area of ​​the spectrum peak at 3.8±0.1 ppm is recorded as A ４ and the peak area of ​​the spectral peak at 4.6±0.1 ppm is recorded as A ５ This is recorded as: X defined by the following formula (1) １ is in the range of 0.5 to 2.2, preferably in the range of 0.6 to 1.8: X １ =(A ２ +A ３ ) / A １ (1); X defined by the following formula (2) ２ is in the range of 0.1 to 1.2, preferably in the range of 0.15 to 1.10: X ２ =A ４ / A １ (2); X defined by the following formula (3) ３ is in the range of 0.05 to 0.65, preferably in the range of 0.10 to 0.55: X ３ =A ５ / A １ (3) , titanium silicalite molecular sieve.

2. The molecular sieves were characterized by solid-state nuclear magnetic resonance using trimethylphosphine (TMP) as a probe molecule. ３１ The P MAS NMR spectrum shows three characteristic peaks at chemical shifts of −5±1 ppm, −34±1 ppm, and −61±1 ppm, respectively, and the peak intensity of the characteristic peak at chemical shift of −5±1 ppm is N １ The peak intensity of the characteristic peak at chemical shift −34±1 ppm is recorded as N ２ and the peak intensity of the characteristic peak at chemical shift −61±1 ppm is recorded as N ３ This is recorded as: Y defined by the following formula (4) １ is in the range of 0.005 to 0.15, preferably in the range of 0.02 to 0.12: Y １ = N １ / N ３ (4); and Y defined by the following formula (5) ２ is in the range of 0.10 to 0.30, preferably in the range of 0.1 to 0.26: Y ２ =N ２ / N ３ (5) 2. The titanium silicalite molecular sieve of claim 1.

3. The molar ratio of silicon atoms to titanium atoms in the titanium silicalite molecular sieve is (8 to 150):1, preferably (15 to 120):1; Optionally, the titanium silicalite molecular sieve has a structure selected from the group consisting of an MFI topological structure, an MEL topological structure, a BEA topological structure and an SVR topological structure, and is preferably an MFI topological structure.

4. The titanium silicalite molecular sieve has a plurality of cavity structures in its crystal grains; the size of the cavity structures is in the range of 5 nm to 50 nm, preferably in the range of 7 nm to 45 nm; Preferably, the volume of the void structure of the molecular sieve occupies 8% to 55%, more preferably 12% to 50% of the volume of the molecular sieve; 4. The titanium silicalite molecular sieve of claim 1, wherein the shape of the cavity structures is selected from the group consisting of spheres, ellipsoids, cylinders, polyhedrons, and irregular shapes, or combinations thereof.

5. The titanium silicalite molecular sieve comprises molecular sieve particles composed of single crystal grains and / or molecular sieve particles composed of agglomerates of multiple crystal grains; Optionally, the molecular sieve particles have an average particle size of 0.1 μm to 0.7 μm, preferably 0.13 μm to 0.62 μm; and a BET specific surface area of ​​260 m ２ / g~620m ２ / g, preferably 280m ２ / g~540m ２ / g; the micropore specific surface area is 280 m ２ / g to 500m ２ / g, preferably 300m ２ / g~480m ２ / g; total pore volume is 0.16 cm ３ / g ~ 0.55 cm ３ / g, preferably 0.22 cm ３ / g ~ 0.45 cm ３ / g; mesopore volume is 0.09 cm ３ / g ~ 0.38 cm ３ / g, preferably 0.12 cm ３ / g ~ 0.34 cm ３ / g, 5. The titanium silicalite molecular sieve according to claim 1.

6. a hysteresis loop exists between the adsorption isotherm and desorption isotherm of the low-temperature nitrogen adsorption of the titanium silicalite molecular sieve; Preferably, the initial relative pressure (P / P ０ ) is in the range of 0.35 to 0.55, preferably in the range of 0.38 to 0.48; 6. The titanium silicalite molecular sieve according to claim 1.

7. A method for preparing the titanium silicalite molecular sieve having a hierarchical porous structure according to any one of claims 1 to 6, comprising the steps of: 1) mixing a titanium source, a silicon source, a first template agent, water, a hard template agent, and a high molecular weight polymer to obtain a reaction mixture, wherein the hard template agent is selected from one or more of a carbon material, a resin material, and a solid inorganic compound; 2) sequentially subjecting the reaction mixture to a first hydrothermal crystallization treatment and a first calcination treatment to obtain a molecular sieve intermediate; 3) mixing the molecular sieve intermediate, a second template agent, and water, followed by a second hydrothermal crystallization treatment and a second calcination treatment; Preferably, the first template agent and the second template agent are organic bases, independently selected from a quaternary ammonium base, an aliphatic amine, an aliphatic alcohol amine, or a combination thereof.

8. In step 1), the molar ratio of the titanium source: the silicon source: the first template agent: water is (0.005-0.55):1:(0.02-1.8):(1-50), preferably (0.01-0.42):1:(0.04-1.5):(10-45); and the ratio of the hard template agent: the high-molecular-weight polymer: the silicon source (SiO ２ 8. The method of claim 7, wherein the weight ratio of (calculated as) is (0.02-0.75):(0.01-0.55):1, preferably (0.04-0.55):(0.03-0.4):

1.

9. In step 1), the silicon source is selected from organic silicates, solid silica gel, white carbon black, and silica sol, or a combination thereof; preferably, selected from organic silicates, solid silica gel, and white carbon black, or a combination thereof; More preferably, the silicate is selected from at least one organic silicate having a structure represented by the following formula (A): 【Chemistry 1】 In the formula, R ａ , R ｂ , R ｃ and R ｄ are each independently selected from straight chain or branched alkyl groups having 1 to 6 carbon atoms, preferably R ａ , R ｂ , R ｃ and R ｄ are each independently selected from a linear alkyl group having 1 to 4 carbon atoms or a branched alkyl group having 3 to 4 carbon atoms, and more preferably, R ａ , R ｂ , R ｃ and R ｄ are each independently selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, or tert-butyl; 9. The method according to claim 7 or 8, wherein the organosilicate is selected from tetramethyl silicate, tetraethyl silicate, tetrabutyl silicate, dimethyldiethyl silicate, or a combination thereof.

10. The first template agent and the second template agent are each independently selected from at least one quaternary ammonium base having a structure represented by formula (B): 【Chemistry 2】 In the formula, R １ , R ２ , R ３ and R ４ are each independently selected from alkyl groups having 1 to 4 carbon atoms, preferably selected from linear alkyl groups having 1 to 4 carbon atoms or branched alkyl groups having 3 to 4 carbon atoms, and more preferably selected from R １ , R ２ , R ３ and R ４ are each independently selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, and tert-butyl; or 10. The method of claim 7, wherein the first template agent and the second template agent are each independently selected from tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, tetrapropylammonium chloride, tetrapropylammonium bromide, or a combination thereof.

11. In step 1), the titanium source is selected from one or more of an organic titanium source and an inorganic titanium source; The organotitanium source is selected from at least one titanium-containing organic acid ester having a structure represented by formula (C): 【Transformation 3】 In the formula, R ５ , R ６ , R ７ and R ８ are each independently selected from alkyl groups having 1 to 6 carbon atoms, preferably selected from straight chain alkyl groups having 1 to 4 carbon atoms or branched alkyl groups having 3 to 6 carbon atoms, and more preferably selected from R ５ , R ６ , R ７ and R ８ are each independently selected from a linear alkyl group having 2 to 4 carbon atoms or a branched alkyl group having 3 to 4 carbon atoms; optionally, R ５ , R ６ , R ７ and R ８ are each independently selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, isopentyl, hexyl or isohexyl; preferably are each independently selected from ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl or tert-butyl; The inorganic titanium source is selected from one or more of titanium chloride, nitrate, and sulfate; 11. The method of any one of claims 7 to 10, wherein the titanium source is selected from titanium tetrachloride, titanium sulfate, titanium nitrate, tetraethyl titanate, tetrapropyl titanate and tetrabutyl titanate, or a combination thereof.

12. In step 1), the carbon material used as the hard template is selected from carbon nanoparticles, carbon nanotubes, carbon nanofibers, and ordered mesoporous carbon, or a combination thereof; The resin material used as the hard template agent is selected from a phenolic resin, a polyester resin, and a polyamide resin, or a combination thereof; 12. The method according to any one of claims 7 to 11, wherein the solid inorganic compound used as the hard template agent is selected from calcium carbonate, magnesium hydroxide and sodium carbonate, or a combination thereof.

13. In step 1), the high molecular weight polymer is selected from polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyvinyl alcohol, polyvinyl acetate, polyacrylonitrile, polymethyl methacrylate, polyvinyl butyral, polyethyleneimine, 4-polyvinylpyridine, and poly(diallyldimethylammonium chloride), or a combination thereof; Preferably, the high molecular weight polymer is selected from polyethylene, polypropylene, polystyrene, and polyacrylonitrile, or a combination thereof; Optionally, the high molecular weight polymer has a weight average molecular weight of 10,000 to 200,000.

14. 14. The method of any one of claims 7 to 13, wherein step 1) comprises the following steps: a) mixing the titanium source, the silicon source, the first template agent, and water to obtain a hydrolyzed sol containing titanium and silicon; b) adding the hard template agent and the high molecular weight polymer to the hydrolyzed sol containing titanium and silicon, respectively, and mixing to obtain a reaction mixture; Optionally, the mixing conditions in step a) include stirring at 40°C to 90°C for 6 hours to 12 hours; Optionally, the mixing conditions in step b) include stirring at 20°C to 50°C for 2 hours to 4 hours; Preferably, the silicon source is an organic silicate, and step a) further comprises mixing the titanium source, the silicon source, the first template agent and water, followed by hydrolysis and alcohol removal treatment to obtain the hydrolyzed sol containing titanium and silicon: Optionally, the conditions for the hydrolysis and alcohol removal treatment include stirring and hydrolyzing at 40°C to 90°C for 6 to 12 hours; preferably stirring and hydrolyzing at 60°C to 85°C for 8 to 10 hours.

15. the conditions of the first hydrothermal crystallization treatment in step 2) and the second hydrothermal crystallization treatment in step 3) independently comprise: a hydrothermal crystallization temperature of 120°C to 220°C, preferably 140°C to 185°C; a hydrothermal crystallization time of 4 hours to 180 hours, preferably 6 hours to 80 hours; and an autogenous pressure; and / or 15. The method of any one of claims 7 to 14, wherein conditions of the first calcination treatment in step 2) and the second calcination treatment in step 3) independently comprise: a calcination temperature of 350°C to 750°C, preferably 380°C to 620°C; and a calcination time of 1 hour to 15 hours, preferably 1.5 hours to 4.5 hours.

16. 16. The method according to any one of claims 7 to 15, wherein in step 3), the weight ratio of the second template agent:water:molecular sieve intermediate is (0.08-3.5):(0.5-25):1; preferably (0.12-2.5):(2-18):

1.

17. 7. A method for preparing caprolactam from cyclohexanone oxime, comprising subjecting cyclohexanone oxime to a vapor-phase Beckmann rearrangement reaction in the presence of the titanium silicalite molecular sieve having a hierarchical porous structure according to any one of claims 1 to 6.

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