Hierarchically porous all-silica molecular sieves, their preparation method and applications

Abstract

We disclose hierarchically porous all-silica molecular sieves characterized by solid-state nuclear magnetic resonance techniques 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. The peak intensity of the characteristic peak at -5 ± 1 ppm is recorded as N1; the peak intensity of the characteristic peak at -34 ± 1 ppm is recorded as N2; and the peak intensity of the characteristic peak at -61 ± 1 ppm is recorded as N3. Consequently, X1, defined in equation (1), is in the range of 0.10 to 0.30; X1 = N1 / N3(1); and X2, defined in equation (2), is in the range of 0.15 to 0.45; X2 = N2 / N3(2). The use of molecular sieves in the vapor-phase Beckmann rearrangement of cyclohexanone oxime can improve caprolactam product selectivity and extend catalyst life.

Description

[Technical Field]

[0001] The present application relates to the technical field of all-silica molecular sieves, and in particular to hierarchically porous all-silica molecular sieves, and their preparation methods and applications. [Background technology]

[0002] ε-Caprolactam (ε-CPL) is a key monomer for the synthesis of nylon-6. ε-CPL is widely used in the production of important downstream products, such as engineering plastics, nylon-6 fiber, and industrial twisted textiles. It can also be used in coatings, pharmaceuticals, and fine chemicals. Currently, over 90% of CPL is prepared by the liquid-phase Beckmann rearrangement reaction using cyclohexanone oxime (CHO), using concentrated sulfuric acid (or fuming sulfuric acid) as the catalyst and solvent. This process poses serious problems, such as equipment corrosion and environmental pollution. After the reaction, liquid ammonia is used to neutralize the waste sulfuric acid, resulting in the generation of a large amount of low-value ammonium sulfate by-product (1.9 t ammonium sulfate / t CPL). As a result, the technical and economic performance of this route is poor.

[0003] Therefore, the heterogeneous catalyst-based gas-phase Beckmann rearrangement process for CHO 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 100% atom utilization, and is an environmentally friendly, green CPL production process. Currently, various solid catalysts, including molecular sieves, metal oxides, and porous materials, have been applied in research on the gas-phase Beckmann rearrangement of CHO. Among these, silicalite-1 molecular sieves with an MFI topology have demonstrated excellent catalytic performance. Sumitomo and SINOPEC of Japan are conducting industrial demonstration tests of the gas-phase Beckmann rearrangement of CHO using a silicalite-1 molecular sieve catalyst in a continuous manner.

[0004] However, the CHO vapor-phase Beckmann rearrangement route suffers from two problems: low selectivity to the product CPL and short catalyst single-pass lifetime. These problems affect the technical economics and the continuity and stability of operation, 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.

[0005] Ferdi Schuth's research group synthesized hierarchically structured porous silicalite-1 all-silica molecular sieves by adding 1,7-dichlorooctamethyltetrasilylating agent to form pores during the crystallization process of the molecular sieve (Li WC, Lu AH, Palkovits R, et al. Hierarchically structured monolithic silicalite-1 consisting of crystallized nanoparticles and its performance in the Beckmann rearrangement of cyclohexanone oxime[J]. Journal of the American Chemical Society, 2005, 127(36): 12595-12600). Chao Ge and colleagues synthesized hierarchically porous silicalite-1 all-silica molecular sieves with orthogonal stacking of layers by adjusting the alkyl chain length of the diquaternary ammonium salt templating agent (Ge, C.; Sun, XJ; Lian, DD; Li, ZK; Wu, JB. Controllable synthesis and structure-performance relationship of silicalite-1 nanosheets in vapor phase Beckmann rearrangement of cyclohexanone oxime. Catal. Lett. 2020, 151, 1488-1498).

[0006] However, when the hierarchical porous all-silica molecular sieve synthesized by the above technique was used in the vapor-phase Beckmann rearrangement of cyclohexanone oxime, the improvement in caprolactam selectivity and catalyst life were not ideal, and still fall short of the requirements for industrial production. Summary of the Invention

[0007] The purpose of this application is to provide a hierarchically porous all-silica molecular sieve, its preparation method, and application. When this molecular sieve is used in the vapor-phase Beckmann rearrangement of cyclohexanone oxime, it improves caprolactam selectivity and extends catalyst life.

[0008] To achieve the above object, in one aspect, the present application provides a hierarchically porous all-silica molecular sieve characterized by a solid-state nuclear magnetic resonance technique using trimethylphosphine (TMP) as a probe molecule, 31 P MAS NMR spectrum ( 31 The P-TMP MAS NMR spectrum (also referred to as the P-TMP MAS NMR spectrum) shows three characteristic peaks at chemical shifts of -5±1 ppm, -34±1 ppm, and -61±1 ppm, the peak intensity of the characteristic peak at the chemical shift of -5±1 ppm is recorded as N1, the peak intensity of the characteristic peak at the chemical shift of -34±1 ppm is recorded as N2, and the peak intensity of the characteristic peak at the chemical shift of -61±1 ppm is recorded as N3: X1 defined in the following formula (1) is in the range of 0.10 to 0.30, preferably in the range of 0.15 to 0.25: X1=N1 / N3(1); and X2 defined in the following formula (2) is in the range of 0.15 to 0.45, preferably in the range of 0.2 to 0.35: X2=N2 / N3(2).

[0009] In another embodiment, there is provided a method for preparing the hierarchically porous all-silica molecular sieve of the present application, comprising the steps of: 1) mixing a silicon source, a first templating agent, water, a silanizing agent, and a structural filler to obtain a reaction mixture, wherein the structural filler is selected from an amphiphilic surfactant, a hard templating agent, or a combination thereof, and the hard templating agent is selected from a natural polymer material or a synthetic polymer material; 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 sequentially carrying out a second hydrothermal crystallization treatment and a second calcination treatment.

[0010] 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.

[0011] In another aspect, there is provided a method for preparing caprolactam from cyclohexanone oxime, the method comprising subjecting cyclohexanone oxime to a vapor-phase Beckmann rearrangement reaction in the presence of the hierarchical porous all-silica molecular sieve of the present application.

[0012] The present hierarchical porous all-silica molecular sieve has abundant silanol group active centers and possesses both Bronsted and Lewis acid properties. The X1 value is in the range of 0.10-0.30, and the X2 value is in the range of 0.15-0.45. Therefore, the molecular sieve has appropriate acidity and exerts a synergistic catalytic effect on the vapor-phase Beckmann rearrangement of cyclohexanone oxime, thereby significantly improving caprolactam selectivity and extending the catalyst life.

[0013] Other features and advantages of the present application are detailed in the Detailed Description section that follows. [Brief explanation of the drawings]

[0014] 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: [Figure 1] 31P-TMP MAS NMR spectra of the molecular sieve product obtained in Example 1 and the molecular sieve product obtained in Comparative Example 2; [Figure 2] 1 is an XRD spectrum of the molecular sieve product obtained in Example 1; [Figure 3] 1 is a TEM electron microscope image of the molecular sieve product obtained in Example 1; [Figure 4] 1 is a SEM electron microscope image of the molecular sieve product obtained in Example 1; [Figure 5] 1 is a BET curve of the molecular sieve product obtained in Example 1; [Figure 6] 1 is an infrared hydroxyl spectrum of the molecular sieve product obtained in Example 1; [Figure 7] 1 is a TEM electron microscope image of the intermediate obtained in Example 1; [Figure 8] 1 is an XRD spectrum of the molecular sieve product obtained in Example 9; [Figure 9] 1 is an XRD spectrum of the molecular sieve product obtained in Example 10; [Figure 10] 1 is a TEM electron microscope image of the molecular sieve product obtained in Comparative Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0015] Specific embodiments of the present application will be described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present application, and are not used to limit the present application.

[0016] 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 ​​near the exact value, such as all possible values ​​within a range of ±5% of the exact value. Furthermore, for any disclosed numerical range, the range endpoints, range endpoints and specific point values, and specific point 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.

[0017] 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.

[0018] In the present application, the term "hierarchically porous" has the meaning generally understood in the art, and specifically refers to a molecular sieve having multiple pore sizes, for example, a molecular sieve having two pore sizes of 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 pore sizes of micropores, mesopores, and macropores (pore size > 50 nm).

[0019] As used herein, the term "all-silica molecular sieve," also known as a pure silica molecular sieve or an all-silica zeolite, has its usual meaning in the art. Specifically, the framework of such a molecular sieve contains only the elements Si and O, but does not contain other elements such as aluminum.

[0020] In this application, the cavity structure in the molecular sieve crystal grain, as well as its size and volume, are measured by transmission electron microscope (TEM) examination. The size of a single cavity structure refers to the maximum length of the line between two positions on the cavity wall of the cavity structure in the 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 150 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 150 nm; preferably, the length of the line connecting any two positions on the cavity wall of any cavity structure of each molecular sieve crystal grain, passing through the center of the cavity structure, is within the range of 5 nm to 150 nm. The volume of the cavity structure is estimated according to a sphere, and 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 taken as the sphere diameter, to determine the sphere radius, and the volume of the corresponding cavity structure is calculated according to the sphere volume formula. The ratio 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 volume fraction of the cavity structures of 50 molecular sieve crystal grains is taken as the ratio 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, the matters or items not mentioned shall 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, including but not limited to textbooks and journal articles, referred to herein is hereby incorporated by reference in its entirety.

[0024] After extensive research, the inventors have found that when hierarchically porous all-silica molecular sieves have both Bronsted acid and Lewis acid properties, the molecular sieves can be characterized by solid-state nuclear magnetic resonance techniques using trimethylphosphine (TMP) as a probe molecule. 31 In the P MAS NMR spectrum, a characteristic peak characterizing Bronsted acidity was found at a chemical shift of -5±1 ppm, a characteristic peak characterizing Lewis acidity was found at a chemical shift of -34±1 ppm, and a characteristic peak characterizing TMP physical adsorption was found at a chemical shift of -61±1 ppm. The peak intensities of the characteristic peaks characterizing Bronsted acidity and Lewis acidity were compared with the peak intensity characteristic of TMP physical adsorption. When the ratio of the peak intensities of the characteristic peaks characterizing the two acids to the peak intensity characteristic of TMP physical adsorption was within a certain range, the hierarchical porous all-silica molecular sieve exhibited high cyclohexanone oxime conversion and caprolactam selectivity, as well as a long reaction lifetime in the vapor-phase Beckmann reaction of cyclohexanone oxime, thereby achieving the present invention.

[0025] As described above, in a first aspect, the present application provides a hierarchically porous all-silica molecular sieve characterized by a solid-state nuclear magnetic resonance technique using trimethylphosphine (TMP) as a probe molecule, and the hierarchically porous all-silica molecular sieve 31The P MAS NMR spectrum showed three characteristic peaks at chemical shifts of -5±1 ppm, -34±1 ppm and -61±1 ppm, the peak intensity of the characteristic peak at the chemical shift of -5±1 ppm was recorded as N1, the peak intensity of the characteristic peak at the chemical shift of -34±1 ppm was recorded as N2, and the peak intensity of the characteristic peak at the chemical shift of -61±1 ppm was recorded as N3: X1 defined by the following formula (1) is in the range of 0.10 to 0.30: X1=N1 / N3 (1); and X2 defined by the following formula (2) is in the range of 0.15 to 0.45: X2=N2 / N3 formula (2).

[0026] The present hierarchical porous all-silica molecular sieve has abundant silanol group active centers and possesses both Bronsted and Lewis acid properties. The X1 value is in the range of 0.10-0.30, and the X2 value is in the range of 0.15-0.45. Therefore, the molecular sieve has appropriate acidity and exerts a synergistic catalytic effect on the vapor-phase Beckmann rearrangement of cyclohexanone oxime, thereby significantly improving caprolactam selectivity and extending the catalyst life.

[0027] In this application, the hierarchical porous all-silica 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.

[0028] In a preferred embodiment, X1 is in the range of 0.15 to 0.25, and X2 is in the range of 0.2 to 0.35. When X1 and X2 of the hierarchical porous all-silica molecular sieve are in the above preferred ranges, the hierarchical porous all-silica molecular sieve can achieve higher caprolactam selectivity and longer catalyst life.

[0029] In a preferred embodiment, the molecular sieve crystal has a plurality of cavity structures, each of which has a size of 5 nm to 150 nm, preferably 10 nm to 100 nm, and which communicate with the outside through micropores, and the cavity structures and the micropores communicating with the cavity structures form a hierarchical porous structure.

[0030] In this preferred embodiment, the hierarchical porous all-silica molecular sieve of the present invention has multiple relatively large cavity structures inside, thereby providing 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. Due to the concentrated distribution of nested silanol groups (i.e., multiple silanol groups that are close to each other and interact with each other), the molecular sieve has both Bronsted acid and Lewis acid properties. In addition, the relatively large cavity structures meet the needs of polymer reactions, allowing reaction products to easily flow out of the catalyst, thereby avoiding the phenomenon of reduced catalytic activity due to pore blockage.

[0031] In a more preferred embodiment, the entire cavity structure occupies 10% to 95%, more preferably 15% to 90% of the total 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 is usually an irregular shape.

[0032] In a specific embodiment, the molecular sieve comprises molecular sieve particles consisting of a single crystal grain and / or molecular sieve particles consisting of an aggregate of multiple crystal grains. Optionally, the molecular sieve particles have an average particle size of 0.1 μm to 2 μm, preferably 0.2 μm to 1.2 μm; a BET specific surface area of ​​300 m 2 / g~650m 2 / g, preferably 350m 2 / g~550m 2 / g; the micropore specific surface area is 200m 2 / g~550m 2 / g, preferably 250m 2 / g~450m 2 / g; total pore volume is 0.2 cm 3 / g~0.7cm 3 / g, preferably 0.3 cm 3 / g~0.5cm 3 / g; mesopore volume is 0.1 cm 3 / g~0.5cm 3 / g, preferably 0.2 cm 3 / g~0.4cm 3 / g.

[0033] In a preferred embodiment, a hysteresis loop exists between the adsorption isotherm and the desorption isotherm in the low-temperature nitrogen adsorption of the molecular sieve. More preferably, the initial relative pressure (P / P0) at which the hysteresis loop appears is within a range of 0.2 to 0.99, preferably within a range of 0.4 to 0.99, and more preferably within a range of 0.4 to 0.6.

[0034] In preferred embodiments, the molecular sieve configuration is selected from an MFI topological structure (where the molecular sieve is a silicalite-1 molecular sieve), an MEL topological structure (where the molecular sieve is a silicalite-2 molecular sieve), a BEA topological structure, an SVR topological structure, or a combination thereof.

[0035] In a second aspect, the present application provides a method for preparing a hierarchically porous all-silica molecular sieve, particularly the present molecular sieve, comprising the steps of: 1) mixing a silicon source, a first templating agent, water, a silanizing agent, and a structural filler to obtain a reaction mixture, wherein the structural filler is selected from an amphiphilic surfactant, a hard templating agent, or a combination thereof; 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.

[0036] In the present method for preparing a hierarchically porous all-silica molecular sieve, a silanizing agent and a polymeric structural filler are introduced into the molecular sieve synthesis raw material to produce a molecular sieve layer-stretching and pore-enlarging effect, thereby preparing a molecular sieve material with open pores. A second template agent is then added to the molecular sieve for dissolution-recrystallization (i.e., second hydrothermal crystallization), thereby preparing a hierarchically porous all-silica molecular sieve with special acid properties and an internal multi-cavity structure.

[0037] Specifically, in the method of the present application, in steps 1) and 2), the silanol groups of the silanol group of the silanol group of the organosilicon source undergo hydrolysis and condensation to form stable Si-O-Si bonds, thereby ensuring the layer extension and pore enlargement effects.Furthermore, the long carbon chain of the silanol group of the silanol group and the structural filler of the amphiphilic surfactant can form stable and controllable structural units (the long carbon chain of the silanol group and the hydrophobic group of the surfactant are close to each other and interact through van der Waals forces), thereby playing a role in fine-tuning the layer extension and pore enlargement; Alternatively, a size-controllable hard template agent is used to play a space-filling role, thereby forming an ordered, pore-controllable porous structure of the molecular sieve (controlled by the alkyl chain length of the silanol group); then, in step 3), a second template agent is introduced into the molecular sieve intermediate with open pores, and its dissolution and recrystallization mechanism is used to obtain the all-silica molecular sieve with the specific acidic properties and hierarchical porous structure of the present application. Specifically, in step 3), the interior of the crystal grains of the molecular sieve intermediate obtained in step 2) is dissolved in the presence of a second template agent under a hydrothermal environment, generating smaller cavity structures, which then cause recrystallization on the surface of the crystal grains and change the morphology of the crystal grains; at the same time, the generation of these small cavity structures increases the curvature of the hydroxyl group distribution, changes the density and orientation of the hydroxyl groups, and enhances the hydrogen bonding effect, leading to the generation of pseudo-B acid and pseudo-L acid.

[0038] In a preferred embodiment, in step 1), the molar ratio of silicon source:first template agent:water:silanizing agent is 1:(0.01-2):(1-50):(0.02-0.2); the weight ratio of silicon (SiO2 equivalent) to structural filler in the reaction mixture is (5-40):1.

[0039] In a more preferred embodiment, in step 1), the molar ratio of silicon source:first template agent:water:silanizing agent is 1:(0.02-0.3):(5-30):(0.04-0.15), and the weight ratio of silicon (SiO2 equivalent) to structural filler in the reaction mixture is (5-30):1. According to this preferred embodiment, the obtained molecular sieve can further improve caprolactam selectivity and catalyst life in the vapor-phase Beckmann rearrangement reaction of cyclohexanone oxime.

[0040] 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 all-silica molecular sieves, preferably selected from organic silicates, solid silica gel, white carbon black, silica sol, or a combination thereof; more preferably selected from organic silicates, solid silica gel, white carbon black, or a combination thereof.

[0041] In a further preferred embodiment, the silicon source is selected from organosilicates having a structure represented by the following formula (A), or a combination thereof: [ka] In the formula, R a , R b , R c and R dare each independently selected from linear or branched alkyl groups having 1 to 6 carbon atoms, preferably from linear alkyl groups having 1 to 4 carbon atoms or branched alkyl groups having 3 to 4 carbon atoms, and more preferably from methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, or tert-butyl.

[0042] In particularly preferred embodiments, the silicon source is selected from tetramethyl silicate, tetraethyl silicate, tetrabutyl silicate, dimethyldiethyl silicate, or combinations thereof.

[0043] 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 all-silica 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 (such as trimethylamine, triethylamine, and tripropylamine), aliphatic alcohol amines (such as ethanolamine), or combinations thereof.

[0044] In certain further preferred embodiments, the first template agent and the second template agent are each independently selected from a quaternary ammonium base having a structure represented by formula (B): [ka] R1, R2, R3, and R4 are each independently selected from alkyl groups having 1 to 4 carbon atoms, preferably from linear alkyl groups having 1 to 4 carbon atoms and branched alkyl groups having 3 to 4 carbon atoms, and more preferably from methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, and tert-butyl.

[0045] In a particularly preferred embodiment, the first template agent and the second template agent are each independently tetrapropylammonium hydroxide or a mixture of tetrapropylammonium hydroxide with one or both of tetrapropylammonium chloride and tetrapropylammonium bromide.

[0046] According to the present application, the silanizing agent used in step 1) is not strictly limited, and silanizing agents having various elemental compositions and functional groups commonly used in the art can be used. In a preferred embodiment, the silanizing agent is selected from compounds having the general formula R5Si(R6)(R7)R8, or combinations thereof, where R5, R6, R7, and R8 are each independently halogen, alkyl, alkoxy, aryl, mercapto, or amino, at least one of which is alkyl, alkoxy, aryl, mercapto, or amino; and the alkyl, alkoxy, mercapto, and amino each independently have 1 to 18 carbon atoms.

[0047] In a further preferred embodiment, the silane treating agent is selected from dimethyldichlorosilane, N-phenyl-3-aminopropyltrimethoxysilane, phenyltrimethoxysilane, 1,7-dichlorooctylmethyltetrasiloxane, hexadecyltrimethoxysilane, octyltriethoxysilane, 3-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, or a combination thereof; and even more preferably, selected from N-phenyl-3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, or a combination thereof.

[0048] In certain preferred embodiments, the amphiphilic surfactant used in step 1) is a nonionic or cationic surfactant, such as a natural polysaccharide, hexadecyltrimethylammonium bromide, or sodium dodecylbenzenesulfonate.

[0049] According to the present application, the hard template agent used in step 1) can be selected from a variety of natural or synthetic polymeric substances, such as cellulose, polysaccharides, starch, polyethers, water-soluble polyamides, etc.

[0050] In a particularly preferred embodiment, the structural filler used in step 1) is selected from hexadecyltrimethylammonium bromide, sodium dodecylbenzenesulfonate, PEO-PPO-PEO block copolymer, porous carbon, natural cellulose, or a combination thereof.

[0051] In certain preferred embodiments, step 1) comprises: a) mixing a silicon source, a first template agent and water to obtain a silicon hydrolysis sol; b) adding a silane treatment agent and a structural filler to the silicon hydrolysis sol and mixing them to obtain a reaction mixture.

[0052] In a more preferred embodiment, the mixing conditions in step a) include: stirring at 40°C to 90°C for 6 to 12 hours; and the mixing conditions in step b) include: stirring at 20°C to 50°C for 2 to 4 hours.

[0053] In a more preferred embodiment, the silicon source in step a) is an organic silicate, and step a) further comprises the steps of mixing the silicon source, the first template agent, and water, followed by hydrolysis and alcohol removal to obtain a silicon hydrolyzed sol; more preferably, the hydrolysis and alcohol removal conditions include stirring and hydrolyzing at 40°C to 90°C for 6 to 12 hours, or stirring and hydrolyzing at 60°C to 85°C for 8 to 10 hours. More preferably, the hydrolysis and alcohol removal conditions are such that the mass content of alcohol generated by hydrolysis of the organic silicate in the silicon hydrolyzed sol is 10 ppm or less.

[0054] In a preferred embodiment, the conditions for the first hydrothermal crystallization treatment in step 2) include: a hydrothermal crystallization time of 0.25 days to 7 days, a hydrothermal crystallization temperature of 130°C to 200°C, and an autogenous pressure; and the conditions for the first calcination treatment in step 2) include: a calcination temperature of 300°C to 700°C, and a calcination time of 1 hour to 16 hours.

[0055] In a preferred embodiment, the conditions for the first hydrothermal crystallization treatment in step 2) include: a hydrothermal crystallization time of 1 to 3 days, a hydrothermal crystallization temperature of 150 to 180°C, and an autogenous pressure; and the conditions for the first calcination treatment in step 2) include: a calcination temperature of 400 to 600°C, and a calcination time of 2 to 5 hours. The hierarchically porous all-silica molecular sieve prepared according to this embodiment has better catalytic activity.

[0056] 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, wherein the temperature of the first drying treatment is 50°C to 120°C, and the time is 1 hour to 12 hours.

[0057] In a preferred embodiment, in step 3), the weight ratio of the molecular sieve intermediate, the second template agent, and water is 1:(0.01-1.5):(1-15), preferably 1:(0.1-1):(2-10). By adopting such a preferred embodiment, a molecular sieve with higher catalytic activity can be obtained.

[0058] In a preferred embodiment, the conditions for the second hydrothermal crystallization treatment in step 3) include: a hydrothermal crystallization time of 0.25 days to 7 days, a hydrothermal crystallization temperature of 130°C to 200°C, and an autogenous pressure; and the conditions for the second calcination treatment in step 3) include: a calcination temperature of 300°C to 700°C, and a calcination time of 1 hour to 16 hours.

[0059] In a more preferred embodiment, the conditions for the second hydrothermal crystallization treatment in step 3) include: a hydrothermal crystallization time of 1 to 3 days, a hydrothermal crystallization temperature of 150°C to 180°C; and an autogenous pressure; and the conditions for the second calcination treatment in step 3) include: a calcination temperature of 400°C to 600°C, and a calcination time of 2 to 5 hours.

[0060] In a specific embodiment, in step 3), after the second hydrothermal crystallization, the product of the second hydrothermal crystallization is further subjected to a second filtration treatment, a second drying treatment, and then a second calcination treatment, in which the temperature of the second drying treatment is 50°C to 120°C and the time is 1 hour to 12 hours.

[0061] In a third aspect, there is provided a hierarchically porous all-silica molecular sieve prepared according to the method of the second aspect of the present application.

[0062] In a fourth aspect, there is provided the use of the hierarchical porous all-silica molecular sieve described in the first and third aspects of the present application in catalyzing the vapor phase Beckmann rearrangement reaction of cyclohexanone oxime.

[0063] 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 the hierarchical porous all-silica molecular sieve described in the first and third aspects of the present application.

[0064] In a preferred embodiment, the method includes contacting a raw material containing cyclohexanone oxime with a hierarchical porous all-silica molecular sieve under a nitrogen atmosphere to react with the raw material. Preferably, the raw material contains cyclohexanone oxime and a solvent, and the solvent is an alcohol (e.g., methanol, ethanol, butanol, cyclohexanol, etc.).

[0065] In a more preferred embodiment, the conditions for the vapor phase Beckmann rearrangement of cyclohexanone oxime are: 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, including.

[0066] In certain specific embodiments, the present application provides the following technical solutions: 1. Hierarchical porous silicalite-1 all-silica molecular sieve, comprising: 31 P MAS NMR properties: Record the peak intensity of the characteristic peak of the molecular sieve at the chemical shift of −5±1 ppm as N1, record the peak intensity of the characteristic peak of the molecular sieve at the chemical shift of −34±1 ppm as N2, and record the peak intensity of the characteristic peak of the molecular sieve at the chemical shift of −61±1 ppm as N3; X1 defined in the following formula (1) is an arbitrary value between 0.10 and 0.30; X1=N1 / N3 (1); and X2 defined in the following formula (2) is an arbitrary value between 0.15 and 0.45; Hierarchical porous silicalite-1 all-silica molecular sieve, having X2=N2 / N3 formula (2).

[0067] 2. The hierarchical porous silicalite-1 all-silica molecular sieve according to item 1, wherein X1 is any value between 0.15 and 0.25; and X2 is any value between 0.2 and 0.35.

[0068] 3. The molecular sieve crystal has a plurality of cavity structures; the size of a single cavity structure is 5 nm to 150 nm, preferably 10 nm to 100 nm; Preferably, the volume of all the hollow structures occupies 10% to 95%, more preferably 15% to 90%, of the total volume of the molecular sieve; Optionally, the shape of the cavity structures is selected from one or more of a sphere, a cube, an ellipsoid, and an irregular cube.

[0069] 4. The molecular sieve comprises molecular sieve particles consisting of a single crystal grain and / or molecular sieve particles consisting of an agglomeration of a plurality of crystal grains; Optionally, the molecular sieve particles have an average particle size of 0.1 μm to 2 μm, preferably 0.2 μm to 1.2 μm; 2 / g~650m 2 / g, preferably 350m 2 / g~550m 2 BET specific surface area / g: 200m 2 / g~550m 2 / g, preferably 250m 2 / g~450m 2 Micropore specific surface area: 0.2cm / g 3 / g~0.7cm 3 / g, preferably 0.3 cm 3 / g~0.5cm 3 Total pore volume / g: 0.1 cm 3 / g~0.5cm 3 / g, preferably 0.2 cm 3 / g~0.4cm 3 / g mesopore volume; Optionally, the hierarchical porous silicalite-1 all-silica molecular sieve according to item 1, wherein there is a hysteresis loop between the adsorption isotherm and the desorption isotherm of low temperature nitrogen adsorption of the molecular sieve.

[0070] 5. A method for preparing a hierarchical porous silicalite-1 all-silica molecular sieve, comprising the steps of: 1) mixing a silicon source, a first templating agent, water, a silanizing agent, and a structural filler to obtain a reaction mixture, wherein the structural filler is selected from an amphiphilic surfactant, a hard templating agent, or a combination thereof; 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.

[0071] 6. The method according to Item 5, wherein in step 1), the molar ratio of the silicon source:the first template agent:water:the silanization agent is 1:(0.01-2):(1-50):(0.02-0.2), preferably 1:(0.02-0.3):(5-30):(0.04-0.15); and the weight ratio of SiO to the structural filler in the reaction mixture is (5-40):1, preferably (5-30):1.

[0072] 7. In step 1), the silicon source is selected from organic silicates, solid silica gel, white carbon black, silica sol, or a combination thereof; preferably, selected from organic silicates, solid silica gel, white carbon black, or a combination thereof; More preferably, the organosilicate has 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 d are each independently selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl or tert-butyl; particularly preferably, the organosilicate is selected from tetramethyl silicate, tetraethyl silicate, tetrabutyl silicate, dimethyldiethyl silicate, or a combination thereof.

[0073] 8. The first template agent in step 1) and the second template agent in step 3) are organic bases; and each is 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 a quaternary ammonium base having a structure represented by the following formula (B), or a combination thereof: [ka] R1, R2, R3 and R4 are each independently selected from alkyl groups having 1 to 4 carbon atoms, preferably from linear alkyl groups having 1 to 4 carbon atoms and branched alkyl groups having 3 to 4 carbon atoms, more preferably from methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl and tert-butyl; More preferably, the first template agent and the second template agent are each independently tetrapropylammonium hydroxide or a mixture of tetrapropylammonium hydroxide with one or both of tetrapropylammonium chloride and tetrapropylammonium bromide.

[0074] 9. In step 1), the silanizing agent is selected from compounds having the general formula R5Si(R6)(R7)R8, where R5, R6, R7 and R8 are each independently halogen, alkyl, alkoxy, aryl, mercapto or amino, and at least one of R5, R6, R7 and R8 is alkyl, alkoxy, aryl, mercapto or amino; and the alkyl, alkoxy, mercapto and amino each independently have 1 to 18 carbon atoms; Item 6. The method according to item 5, wherein the silane treating agent is selected from dimethyldichlorosilane, N-phenyl-3-aminopropyltrimethoxysilane, phenyltrimethoxysilane, 1,7-dichlorooctylmethyltetrasiloxane, hexadecyltrimethoxysilane, octyltriethoxysilane, 3-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, or a combination thereof; more preferably, selected from N-phenyl-3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, or a combination thereof.

[0075] 10. The method according to item 5, wherein in step 1), the structural filler is selected from hexadecyltrimethylammonium bromide, sodium dodecylbenzenesulfonate, PEO-PPO-PEO block copolymer, porous carbon, natural cellulose, or a combination thereof.

[0076] 11. Step 1) is the following step: a) mixing the silicon source, the first template agent and water to obtain a silicon hydrolysis sol; b) adding the silanizing agent and the structural filler to the silicon hydrolysis sol and mixing them to obtain the 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, after mixing the silicon source, the first template agent and water, hydrolysis and alcohol removal treatment to obtain the silicon hydrolyzed sol; Optionally, the conditions of the hydrolysis and alcohol removal treatment include: stirring and hydrolysis at 40°C to 90°C for 6 hours to 12 hours; preferably, stirring and hydrolysis at 60°C to 85°C for 8 hours to 10 hours.

[0077] 12. The method according to Item 5, wherein in step 3), the weight ratio of the molecular sieve intermediate: the second template agent: water is 1:(0.01-1.5):(1-15), preferably 1:(0.1-1):(2-10).

[0078] 13. The conditions for the first hydrothermal crystallization treatment in step 2) and the second hydrothermal crystallization treatment in step 3) independently include: a hydrothermal crystallization time of 0.25 days to 7 days, and a hydrothermal crystallization temperature of 130°C to 200°C; preferably, a hydrothermal crystallization time of 1 day to 3 days, and a hydrothermal crystallization temperature of 150°C to 180°C; and an autogenous pressure; The conditions for the first firing treatment in step 2) and the second firing treatment in step 3) each independently include: a firing temperature of 300°C to 700°C and a firing time of 1 hour to 16 hours; preferably, a firing temperature of 400°C to 600°C and a firing time of 2 hours to 5 hours.

[0079] 14. A hierarchically porous silicalite-1 all-silica molecular sieve prepared according to the method of any one of items 5 to 13.

[0080] 15. Use of the hierarchical porous silicalite-1 all-silica molecular sieve according to any one of items 1 to 4 and 14 in catalysis of the vapor-phase Beckmann rearrangement reaction of cyclohexanone oxime. [Example]

[0081] The present invention will be described in detail below through examples, but the present invention is not limited to these examples.

[0082] In the following examples and comparative examples: 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.

[0083] The X-ray diffraction (XRD) spectra of the samples were measured on a Siemens X-ray diffractometer D5005, with the radiation source being Kα(Cu) and the test range 2θ being 0.5° to 70°.

[0084] Transmission electron microscope (TEM) images of the samples were obtained using a FEI Tecnai G2F20S-TWIN transmission electron microscope. The TEM microscopy examination determined the cavity structure and size of the samples, and the volume fraction of the cavity volume relative to the molecular sieve volume was calculated by measuring the TEM images. The specific method was as follows: The volume of each cavity within a molecular sieve grain was measured using TEM images (the volume of the cavity was estimated according to its sphere. The arithmetic mean of the sum of the lengths of the longest and shortest lines connecting two positions on the cavity wall that pass through the center of the cavity was taken as the sphere diameter. The sphere radius was then calculated, and the volume of the corresponding cavity was calculated according to the sphere volume formula). The percentage of the sum of the volumes of all the cavity structures within the corresponding molecular sieve grain was calculated, and the average volume fraction of the cavity structures of 50 molecular sieve grains was used as the percentage of the volume of the cavity structures relative to the molecular sieve volume.

[0085] Scanning electron microscope (SEM) images of the samples were obtained using 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 size of 50 molecular sieve particles, and taking the arithmetic mean as the average particle size of the molecular sieve.

[0086] 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.

[0087] 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.

[0088] The low temperature nitrogen adsorption and desorption isotherms of the samples were measured according to the ASTM D4222-98 standard method.

[0089] Infrared hydroxyl group spectra of the samples were obtained using a Nicolet 8210 Fourier transform infrared spectrometer at 400 cm-1 ~4000cm -1 The measurements were carried out in the range of .

[0090] In the following examples and comparative examples, all reagents and raw materials used are commercially available products unless otherwise specified.

[0091] Example 1 1a) 104 g (0.5 mol) of tetraethyl silicate, 65 g of 25 wt% aqueous tetrapropylammonium hydroxide (TPAOH, 0.08 mol), and 140 g (7.8 mol) of water were sequentially added 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 silica gel solution; 1b) 9 g of N-phenyl-3-aminopropyltrimethoxysilane (PHAPTMS, 0.035 mol) and 3 g of PEO-PPO-PEO triblock copolymer (P123, purchased from InnoChem, weight average molecular weight 5800) were added to the mixture of step 1a) and 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 filtered, 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 S-1-T. The characterization results of its structural parameters are shown in Table 2. The values ​​of X1 and X2 calculated by equations (1) and (2) are shown in Table 3; 3) 10 g of molecular sieve intermediate S-1-T, 20 g of 25 wt% tetrapropylammonium hydroxide (TPAOH, 5 g) aqueous solution, and 40 g of water were homogeneously mixed (the weight ratio of molecular sieve intermediate: second template agent (i.e., tetrapropylammonium hydroxide): water was 1:0.5:5.5), transferred to a stainless steel sealed reactor, and isothermally crystallized at 170 °C for 24 hours. The resulting product was filtered, washed, dried at 110 °C for 3 hours, and then calcined in a muffle furnace at 550 °C for 3 hours to obtain all-silica molecular sieve S-1-M. The structural parameters and characterization results are shown in Table 2.

[0092] Molecular sieve S-1-M31 The MAS NMR spectrum of p-TMP is shown in Figure 1. Figure 1 shows a spectral peak corresponding to a Bronsted 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 Bronsted acid and a Lewis acid; the peak intensities N1, N2, and N3 are 114,450, 158,051, and 545,002, respectively. The calculated values ​​of X1 and X2 are shown in Table 3.

[0093] The XRD spectrum of the molecular sieve S-1-M is shown in Figure 2, which indicates that the molecular sieve has an MFI topological structure and is a silicalite-1 molecular sieve.

[0094] A TEM image of molecular sieve S-1-M is shown in Figure 3. It can be seen that the crystal grains of the molecular sieve have a hierarchical porous structure with multiple cavities inside, and the size of each cavity ranges from 10 nm to 90 nm.

[0095] The SEM image of molecular sieve S-1-M is shown in Figure 4. It can be seen that the particles of the molecular sieve have regular shapes and uniform sizes.

[0096] The low-temperature nitrogen adsorption test results for molecular sieve S-1-M are shown in Figure 5. It can be seen that there is a clear hysteresis loop between the nitrogen adsorption and desorption isotherms. The initial relative pressure (P / P) at which the hysteresis loop appears is 0.45.

[0097] The infrared hydroxyl group spectrum of molecular sieve S-1-M is shown in Figure 6. There are obvious silanol group active centers, among which the 3740 cm -1 The peak at 3690 cm is a terminal hydroxyl group that functions as a side reaction center; -1 The peak at 3500 cm is the orthohydroxyl group; -1 It can be seen that the peak at is a nested silanol group that functions as the main reaction center.

[0098] A TEM image of the molecular sieve intermediate S-1-T, which has not been subjected to the dissolution-recrystallization process of step 3) (i.e., the second hydrothermal crystallization treatment), is shown in Figure 7. Comparing Figure 7 with Figure 3, it can be seen that the molecular sieve intermediate S-1-T has formed numerous multi-cavity structures within its particles after the second hydrothermal crystallization treatment of step 3).

[0099] Comparative Example 1 A molecular sieve was prepared according to the method of Example 1, except that the silanizing agent and structural filler were not added. The specific preparation conditions are shown in Table 1. The resulting molecular sieve was recorded as D-1. The characterization results of the structural parameters of D-1 are shown in Table 2, and the calculated values ​​of X1 and X2 are shown in Table 3.

[0100] Comparative Example 2 Silicalite-1 all-silica molecular sieve was prepared according to the method disclosed in patent application CN1338427A, the specific steps are as follows: 1) 104 g of tetraethyl silicate, 90 g of 22.5 wt% aqueous tetrapropylammonium hydroxide (TPAOH) solution, and 110 g of water were sequentially added 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 75°C for 5 hours, and evaporated water was periodically replenished to obtain a colorless and transparent silica gel solution; 2) The above sol was transferred into a stainless steel sealed reactor, isothermally crystallized at 170°C for 2 days, filtered, washed, dried at 120°C for 24 hours, and then calcined in a muffle furnace at 550°C for 5 hours; 3) 15 g of the calcined product and 55 g of 22.5 wt % tetrapropylammonium hydroxide (TPAOH) aqueous solution were mixed, isothermally crystallized at 170°C for 1 day, filtered, washed, dried at 110°C for 12 hours, and then calcined in a muffle furnace at 550°C for 4 hours. The resulting molecular sieve was recorded as D-2. The characterization results of the structural parameters of D-2 are shown in Table 2, and the calculated values ​​of X1 and X2 are shown in Table 3.

[0101] Molecular sieve D-2 31The P-TMP MAS NMR spectrum is shown in Figure 1. It can be seen that molecular sieve D-2 does not have any obvious peaks corresponding to Bronsted or Lewis acids.

[0102] The TEM image of molecular sieve D-2 is shown in FIG. 10, and it can be seen that there is no cavity structure in the crystal grains of molecular sieve D-2.

[0103] Comparative Example 3 A molecular sieve was prepared according to the method of Example 1, except that N-phenyl-3-aminopropyltrimethoxysilane was not used in step 1b). 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 and X2 are shown in Table 3.

[0104] Comparative Example 4 A molecular sieve was prepared according to the method of Example 1, except that the PEO-PPO-PEO triblock copolymer was not used in step 1b). The resulting molecular sieve was designated D-4. The characterization results of the structural parameters of D-4 are shown in Table 2, and the calculated values ​​of X1 and X2 are shown in Table 3.

[0105] Examples 2 to 8 Molecular sieves were prepared according to the method of Example 1, except that the raw material ratios and synthesis conditions were changed as shown in Table 1. The resulting molecular sieves were recorded as S-2-M to S-8-M, respectively. The characterization results of the structural parameters of S-2-M to S-8-M are shown in Table 2, and the calculated values ​​of X1 and X2 are shown in Table 3.

[0106] Example 9 The molecular sieve was prepared according to the method of Example 1, except that 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 resulting molecular sieve was recorded as S-9-M. The characterization results of the structural parameters of S-9-M are shown in Table 2, and the calculated values ​​of X1 and X2 are shown in Table 3.

[0107] The XRD spectrum of the molecular sieve S-9-M is shown in Figure 8, which indicates that the molecular sieve has a MEL topological structure and is a silialite-2 molecular sieve.

[0108] Example 10 A molecular sieve was prepared according to the method of Example 1, except that the raw material ratio and template agent were changed as shown in Table 1, and the template agent tetrapropylammonium hydroxide used in steps 1a) and 3) was replaced with tetraethylammonium hydroxide (TEAOH). The resulting molecular sieve was recorded as S-10-M. The characterization results of its structural parameters are shown in Table 2, and the calculated values ​​of X1 and X2 are shown in Table 3.

[0109] The XRD spectrum of the molecular sieve S-10-M is shown in FIG. 9, which indicates that the molecular sieve has a BEA topological structure.

[0110] Example 11 The molecular sieves were prepared according to the method of Example 1, with the following exceptions: The temperature of the first hydrothermal crystallization treatment in step 2) is 130°C, and the time is 4 days; the temperature of the first calcination treatment is 350°C, and the time is 8 hours; and The temperature of the second hydrothermal crystallization treatment in step 3) is 130°C, and the time is 4 days; the temperature of the second calcination treatment is 350°C, and the time is 8 hours.

[0111] The resulting molecular sieve was recorded as S-11-M. The characterization results of the structural parameters of S-11-M are shown in Table 2, and the calculated values ​​of X1 and X2 are shown in Table 3.

[0112] Example 12 A molecular sieve was prepared according to the method of Example 1, except that the raw material ratio was changed as shown in Table 1. The resulting molecular sieve was recorded as S-12-M, and the characterization results of the structural parameters of S-12-M are shown in Table 2, and the calculated values ​​of X1 and X2 are shown in Table 3.

[0113] [Table 1]

[0114] In Table 1, TPAOH is tetrapropylammonium hydroxide, TBAOH is tetrabutylammonium hydroxide, TEAOH is tetraethylammonium hydroxide; PHAPTMS is N-phenyl-3-aminopropyltrimethoxysilane, APTMS is 3-aminopropyltriethoxysilane, GCPMS is 3-glycidoxypropyl(dimethoxy)methylsilane, TOMS is methyltrimethoxysilane; P123 is PEO-PPO-PEO triblock copolymer, and CTAB is hexadecyltrimethylammonium bromide.

[0115] In Table 1, the water in the "water / silicon source" calculation includes the water from the first aqueous template solution; the water in the "water / molecular sieve" calculation includes the water from the second aqueous template solution.

[0116] [Table 2]

[0117] 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 times were 24 h and 120 h, respectively.

[0118] 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, and a programmed column temperature, with a constant temperature of 110°C for 8 minutes, a 15°C / min increase to 230°C, and a constant temperature for 14 minutes. The results are shown in Table 3 below.

[0119] In Table 3: Cyclohexanone oxime conversion rate (mol%) = (molar content of cyclohexanone oxime in the raw material - molar content of cyclohexanone oxime in the product) / molar content of cyclohexanone oxime in the raw material × 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 120 hours) / cyclohexanone conversion rate in 24 hours × 100%; Caprolactam selectivity decrease rate (%)=(24-hour caprolactam selectivity−120-hour caprolactam selectivity) / 24-hour caprolactam selectivity×100%.

[0120] [Table 3]

[0121] According to the data in Table 3, compared with the molecular sieve intermediate S-1-T and the molecular sieves obtained in Comparative Examples 1 to 4, the hierarchical porous all-silica molecular sieves S-1-M to S-12-M prepared in the examples of this application have X1 in the range of 0.1 to 0.3 and X2 in the range of 0.15 to 0.45. They have higher catalytic activity in the vapor-phase Beckmann rearrangement reaction of cyclohexanone oxime, higher cyclohexanone oxime conversion and caprolactam selectivity, and higher catalytic stability under long-term reaction conditions (120 hours).

[0122] By comparing S-1-M to S-9-M with S-10-M to S-12-M, it can be seen that S-1-M to S-9-M have higher cyclohexanone oxime conversion and caprolactam selectivity, and are endowed with higher catalyst stability under long-term reaction conditions (120 hours), since X1 of S-1-M to S-9-M is in the range of 0.15 to 0.25 and X2 is in the range of 0.2 to 0.35.

[0123] By comparing S-1-M with S-11-M in Example 1, which corresponds to a preferred embodiment of the present application, it can be seen that the obtained molecular sieve S-1-M has higher cyclohexanone oxime conversion and caprolactam selectivity, and has higher catalytic stability under long-term reaction conditions (120 h).

[0124] Comparing S-1-M with S-12-M, it can be seen that the molecular sieve was synthesized in Example 1 according to the following scheme: the molar ratio of silicon source: first template agent: water: silanizing agent was 1: (0.02-0.3): (5-30): (0.04-0.15), and the weight ratio of molecular sieve intermediate: second template agent: water was 1: (0.1-1): (2-10). The resulting molecular sieve S-1-M had higher cyclohexanone oxime conversion and caprolactam selectivity, and exhibited high catalytic stability under long-term reaction conditions (120 hours).

[0125] 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.

[0126] 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.

[0127] 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.

Claims

1. A hierarchically porous all-silica molecular sieve characterized by solid-state nuclear magnetic resonance techniques using trimethylphosphine (TMP) as a probe molecule, wherein the molecular sieve ３１ The P MAS NMR spectrum showed three characteristic peaks at chemical shifts of −5±1 ppm, −34±1 ppm, and −61±1 ppm, and the peak intensity of the characteristic peak at the chemical shift of −5±1 ppm was determined as N １ and the peak intensity of the characteristic peak at the chemical shift of −34±1 ppm was recorded as N ２ and the peak intensity of the characteristic peak at the chemical shift of −61±1 ppm was recorded as N ３ When recorded as: X defined by the following formula (1) １ is in the range of 0.10 to 0.30, preferably in the range of 0.15 to 0.25: X １ =N １ / N ３ (1); X defined by the following formula (2) ２ is in the range of 0.15 to 0.45, preferably in the range of 0.2 to 0.35: X ２ =N ２ / N ３ (2) Molecular sieve.

2. The molecular sieve has a plurality of cavity structures in its crystal grains, and the size of the cavity structures is in the range of 5 nm to 150 nm, preferably in the range of 10 nm to 100 nm; Preferably, the volume of the cavity structure of the molecular sieve occupies 10% to 95%, more preferably 15% to 90% of the volume of the molecular sieve; 2. The molecular sieve of claim 1, wherein optionally, the shape of the cavity structures is selected from one or more of spheres, ellipsoids, cylinders, polyhedra, and irregular shapes.

3. The molecular sieve contains molecular sieve particles consisting of a single crystal grain and / or molecular sieve particles consisting of an agglomeration of a plurality of crystal grains; Optionally, the molecular sieve particles have an average particle size of 0.1 μm to 2 μm, preferably 0.2 μm to 1.2 μm; ２ / g~650m ２ / g, preferably 350m ２ / g~550m ２ BET specific surface area of ​​200 m ２ / g~550m ２ / g, preferably 250m ２ / g~450m ２ / g micropore specific surface area: 0.2 cm ３ / g to 0.7 cm ３ / g, preferably 0.3 cm ３ / g to 0.5 cm ３ / g total pore volume; and 0.1 cm ３ / g to 0.5 cm ３ / g, preferably 0.2 cm ３ / g to 0.4 cm ３ The molecular sieve according to any one of claims 1 to 2, having a mesopore volume of 1 / g.

4. a hysteresis loop exists between the adsorption isotherm and the desorption isotherm in a low-temperature nitrogen adsorption test of the molecular sieve; Preferably, the initial relative pressure (P / P ０ 4. The molecular sieve according to claim 1, wherein the σ is in the range of 0.2 to 0.99, more preferably in the range of 0.4 to 0.99, and even more preferably in the range of 0.4 to 0.

6.

5. A method for preparing the hierarchical porous all-silica molecular sieve of any one of claims 1 to 4, comprising the following steps: 1) mixing a silicon source, a first templating agent, water, a silanizing agent, and a structural filler to obtain a reaction mixture, wherein the structural filler is selected from an amphiphilic surfactant, a hard templating agent, or a combination thereof, and the hard templating agent is selected from a natural polymeric material or a synthetic polymeric material; 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; 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.

6. In step 1): the molar ratio of the silicon source: the first template agent: water: the silanizing agent is 1: (0.01-2): (1-50): (0.02-0.2); preferably 1: (0.02-0.3): (5-30): (0.04-0.15); and The silicon (SiO ２ 6. The method according to claim 5, wherein the weight ratio of the hydroxybenzoate (as converted) to the structural filler is (5-40):1, preferably (5-30):

1.

7. In step 1), the silicon source is selected from organic silicates, solid silica gel, white carbon black, silica sol, or a combination thereof, preferably selected from organic silicates, solid silica gel, white carbon black, or a combination thereof; More preferably, the silicon source is an organic silicate having a structure represented by the following formula (A): 【Chemical 1】 In the formula, R ａ , R ｂ , R ｃ and R ｄ are each independently selected from a linear or branched alkyl group having 1 to 6 carbon atoms, preferably 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, more preferably each independently selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl or tert-butyl; Particularly preferably, the silicon source is selected from tetramethyl silicate, tetraethyl silicate, tetrabutyl silicate, dimethyldiethyl silicate, or a combination thereof.

8. The first template agent and the second template agent are each independently selected from a quaternary ammonium base having a structure represented by the following formula (B), or a combination thereof: 【Chemistry 2】 R １ , R ２ , R ３ and R ４ are each independently selected from alkyl groups having 1 to 4 carbon atoms, preferably each independently selected from straight chain alkyl groups having 1 to 4 carbon atoms and branched alkyl groups having 3 to 4 carbon atoms, more preferably each independently selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl and tert-butyl; More preferably, the first template agent and the second template agent are each independently tetrapropylammonium hydroxide or a mixture of tetrapropylammonium hydroxide with one or both of tetrapropylammonium chloride and tetrapropylammonium bromide.

9. In step 1), the silane treating agent is a compound represented by the general formula R ５ Si(R ６ ) (R ７ ) R ８ or a combination thereof, wherein R ５ , R ６ , R ７ and R ８ are each independently halogen, alkyl, alkoxy, aryl, mercapto, or amino; R ５ , R ６ , R ７ and R ８ at least one of is alkyl, alkoxy, aryl, mercapto, or amino; and said alkyl, alkoxy, mercapto, and amino each independently have 1 to 18 carbon atoms; 9. The method of any one of claims 5 to 8, wherein the silane treating agent is preferably selected from dimethyldichlorosilane, N-phenyl-3-aminopropyltrimethoxysilane, phenyltrimethoxysilane, 1,7-dichlorooctylmethyltetrasiloxane, hexadecyltrimethoxysilane, octyltriethoxysilane, 3-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, or a combination thereof; more preferably selected from N-phenyl-3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, or a combination thereof.

10. 10. The method according to claim 5, wherein in step 1), the structural filler is selected from hexadecyltrimethylammonium bromide, sodium dodecylbenzenesulfonate, PEO-PPO-PEO block copolymer, porous carbon, natural cellulose, or a combination thereof.

11. Step 1) comprises the following steps: a) mixing the silicon source, the first template agent, and water to obtain a silicon hydrolysis sol; and b) adding the silane treating agent and the structural filler to the silicon hydrolysis sol and mixing them to obtain a reaction mixture; Optionally, the mixing conditions of step a) include: stirring at 40°C to 90°C for 6 hours to 12 hours; Optionally, the mixing conditions of 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, after mixing the silicon source, the first template agent and water, hydrolysis and alcohol removal treatment to obtain the silicon hydrolyzed sol; 11. The method of any one of claims 5 to 10, wherein optionally, the conditions of the hydrolysis and alcohol removal treatment include: stirring and hydrolyzing at a temperature of 40°C to 90°C for 6 hours to 12 hours; preferably stirring and hydrolyzing at a temperature of 60°C to 85°C for 8 hours to 10 hours.

12. 12. The method according to claim 5, wherein in step 3), the weight ratio of the molecular sieve intermediate: the second template agent: water is 1:(0.01-1.5):(1-15); preferably 1:(0.1-1):(2-10).

13. The conditions of the first hydrothermal crystallization treatment in step 2) and the second hydrothermal crystallization treatment in step 3) each independently include: a hydrothermal crystallization time of 0.25 days to 7 days, a hydrothermal crystallization temperature of 130°C to 200°C; preferably, a hydrothermal crystallization time of 1 day to 3 days, a hydrothermal crystallization temperature of 150°C to 180°C; and an autogenous pressure; and 13. The method of any one of claims 5 to 12, wherein conditions for the first firing treatment in step 2) and the second firing treatment in step 3) each independently comprise: a firing temperature of 300°C to 700°C and a firing time of 1 hour to 16 hours; preferably a firing temperature of 400°C to 600°C and a firing time of 2 hours to 5 hours.

14. A method for preparing caprolactam from cyclohexanone oxime, comprising the step of subjecting cyclohexanone oxime to a vapor-phase Beckmann rearrangement reaction in the presence of the hierarchical porous all-silica molecular sieve according to any one of claims 1 to 4.

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