Multistage-pore heteroatomic molecular sieve, preparation method thereof and application thereof in gas-phase beckmann rearrangement reaction of cyclohexanone oxime

Abstract

The present disclosure relates to a multi-level pore heteroatomic molecular sieve, a preparation method thereof and application thereof in a gas-phase Beckmann rearrangement reaction of cyclohexanone oxime. The multi-level pore heteroatomic molecular sieve has the following FT-IR characteristics: the peak area of a spectrum peak at a wave number of 3740±5 cm ‑1 in a FT-IR spectrum of the multi-level pore heteroatomic molecular sieve is recorded as A1; the peak area of a spectrum peak at a wave number of 3690±5 cm ‑1 in the FT-IR spectrum of the multi-level pore heteroatomic molecular sieve is recorded as A2; the peak area of a spectrum peak at a wave number of 3520±10 cm ‑1 in the FT-IR spectrum of the multi-level pore heteroatomic molecular sieve is recorded as A3; X1 defined by the following formula (1) is any value between 0.6 and 1.6: X1=A2 / A1 formula (1); X2 defined by the following formula (2) is any value between 2.0 and 5.5: X2=A3 / A1 formula (2). The multi-level pore structure and the heteroatomic active center are introduced into the molecular sieve, the diffusion capacity and the anti-coking deactivation capacity of the molecular sieve are improved, and thus excellent gas-phase rearrangement reaction performance is obtained.

Description

Technical Field

[0001] This disclosure relates to the field of titanium-silicon molecular sieve preparation, specifically to a hierarchical porous heteroatom molecular sieve, its preparation method, and its application in the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime. Background Technology

[0002] Molecular sieve crystals have a uniform pore structure, a huge specific surface area, and can allow catalytically active metals to be exchanged into the framework. At the same time, the molecular sieve framework structure has high stability. These outstanding properties make molecular sieves not only excellent adsorbents, but also effective catalysts and catalyst supports.

[0003] MFI molecular sieves are the most common type of molecular sieve in industry. They possess three-dimensional ten-membered ring channels with pore sizes of approximately 0.51 × 0.55 nm. They exhibit high thermal stability and catalytic activity. Due to their unique channel structure and surface acidity / alkalinity, they are widely used in the petrochemical industry. MEL molecular sieves have three-dimensional ten-membered ring through-hole channels with pore sizes of approximately 0.53 × 0.54 nm, SVR molecular sieves have three-dimensional ten-membered ring channels with pore sizes of approximately 0.55 × 0.57 nm, and BEA molecular sieves have three-dimensional twelve-membered ring channels with pore sizes of approximately 0.66 × 0.77 nm. This demonstrates that molecular sieves with different topologies possess unique advantages in pore size, allowing molecules of different sizes to pass through, thus achieving shape selection and sieving functions.

[0004] The cyclohexanone oxime gas-phase Beckmann rearrangement process is a green production process for caprolactam. Compared with the traditional liquid-phase method, this process avoids the use of liquid ammonia and fuming sulfuric acid at the source, achieving 100% atom utilization and making it an environmentally friendly green production process for caprolactam. Pure silica molecular sieves with the MFI topology exhibit excellent catalytic performance. At the beginning of this century, Sumitomo Chemical of Japan and Sinopec of China conducted industrial-scale experiments on the cyclohexanone oxime gas-phase Beckmann rearrangement using pure silica molecular sieves. However, due to the small micropore size of the MFI structure, which is close to the size of reactant and product molecules, the diffusion of guest molecules within the confined pores of the molecular sieve is slow, and their residence time within the crystal is significantly prolonged. This exacerbates the formation of by-products and the blockage of pores by carbon deposits, leading to rapid catalyst deactivation. Therefore, a molecular sieve more suitable for this reaction needs to be found.

[0005] Yaquan Wang's research group (Microporous and Mesoporous Materials, 2008, 107, 247–251) expanded the specific surface area and enriched the hydroxyl active centers of hydrothermally synthesized BEA molecular sieves by ammonia hydrothermal treatment. The conversion rate of this molecular sieve stabilized at 96% and the selectivity at 95% after 8 hours, showing a significant improvement in reaction efficiency. L. Forni et al. (Journal of Molecular Catalysis A: Chemical, 2004, 221, 97–103) synthesized MCM-41 molecular sieves with different Si / Al ratios using hexadecyltrimethylammonium hydroxide as a template agent. The selectivity of this molecular sieve for caprolactam remained stable at 70% after 40 hours of reaction.

[0006] However, when the molecular sieves containing heteroatoms synthesized by the above technology are used in the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime, the effect of improving caprolactam selectivity and catalyst lifetime is not ideal, and there is still a certain gap from the requirements of industrial production. Summary of the Invention

[0007] The purpose of this disclosure is to provide a hierarchical porous heteroatom molecular sieve, its preparation method, and its application in the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime. By introducing a hierarchical porous structure and heteroatom active centers into the molecular sieve, the diffusion ability and resistance to carbon deposition and deactivation of the molecular sieve are improved, thereby obtaining excellent gas-phase rearrangement reaction performance.

[0008] To achieve the above objectives, the first aspect of this disclosure provides a hierarchical porous heteroatom molecular sieve, which has the following FT-IR characteristics:

[0009] The wavenumber of the FT-IR spectrum of the hierarchical porous heteroatom molecular sieve was 3740±5 cm⁻¹. -1 The peak area at the specified location is denoted as A1; the wavenumber in the FT-IR spectrum of the hierarchical porous heteroatom molecular sieve is 3690±5 cm⁻¹. -1 The peak area at the specified location is denoted as A2; the wavenumber in the FT-IR spectrum of the hierarchical porous heteroatom molecular sieve is 3520±10 cm⁻¹. -1 The peak area at the specified location is denoted as A3;

[0010] As defined in equation (1), X1 is any value between 0.6 and 1.6:

[0011] X1 = A2 / A1 (Equation (1));

[0012] As defined in equation (2), X2 is any value between 2.0 and 5.5:

[0013] X2 = A3 / A1 (Equation 2).

[0014] Optionally, X1 is any value between 0.8 and 1.5; X2 is any value between 2.5 and 4.0.

[0015] Optionally, the molar ratio of silicon atoms to heteroatoms in the hierarchical porous heteroatom molecular sieve is (6-260):1, preferably (8-170):1;

[0016] Optionally, the heteroatom is selected from one or more elements of Group IVB, Group IIIA, and Group IVA; preferably, it is selected from one or more elements of Ti, B, Zr, and Sn.

[0017] Optionally, the configuration of the hierarchical porous heteroatom molecular sieve is selected from one or more of the MFI topology, MEL topology, BEA topology and SVR topology; preferably, it is an MFI topology.

[0018] Optionally, the hierarchical porous heteroatom molecular sieve has multiple cavity structures within its crystal; wherein the size of a single cavity structure is 2–42 nm, preferably 3–37 nm;

[0019] Preferably, the volume of all the cavity structures accounts for 5-65% of the total volume of the molecular sieve, more preferably 15-60%;

[0020] Optionally, the shape of the cavity structure is selected from one or more of the following: sphere, cube, ellipsoid, and irregular cube.

[0021] Optionally, the hierarchical porous heteroatom molecular sieve includes molecular sieve particles composed of a single crystal, and / or molecular sieve particles composed of aggregates of multiple crystals.

[0022] Optionally, the average particle size of the molecular sieve particles is 0.2–1.0 μm, preferably 0.28–0.85 μm; the BET specific surface area is 300–650 m². 2 / g, preferably 320-560m 2 / g; Microporous specific surface area is 260-520m² 2 / g, preferably 280-490m 2 / g; total pore volume is 0.18–0.55 cm³. 3 / g, preferably 0.22~0.48cm 3 / g; mesopore volume is 0.13~0.54cm³ 3 / g, preferably 0.15~0.38cm 3 / g;

[0023] Optionally, a hysteresis loop exists between the adsorption isotherm and desorption isotherm of the low-temperature nitrogen adsorption of the hierarchical porous heteroatom molecular sieve; preferably, the initial relative pressure (P / P0) at which the hysteresis loop appears is 0.30 to 0.50, more preferably 0.36 to 0.47.

[0024] The second aspect of this disclosure provides a method for preparing hierarchical porous heteroatom molecular sieves, comprising the following steps:

[0025] S1. Mix the first heteroatom source, silicon source, first template agent, water, silanizing agent and structural filler to obtain a reaction mixture;

[0026] S2. The reaction mixture is subjected to a first hydrothermal crystallization treatment and a first calcination treatment in sequence to obtain a molecular sieve intermediate;

[0027] S3. Mix the molecular sieve intermediate, the second template agent, the second heteroatom source and water, and then perform a second hydrothermal crystallization treatment and a second calcination treatment in sequence.

[0028] Optionally, in step S1, the molar ratio of the first heteroatom source: silicon source: first template agent: water: silanizing agent is (0.002~1.5):1:(0.03~4):(1~50):(0.002~3.5); preferably (0.005~0.8):1:(0.06~1.5):(8~30):(0.007~2.5); the silicon source is in the form of SiO2, and the weight ratio of SiO2 to structural filler is (4~50):1, preferably (6~38):1.

[0029] Optionally, in step S1, the silicon source is selected from at least one of silicone grease, solid silica gel, fumed silica, and silica sol; preferably, it is selected from at least one of silicone grease, solid silica gel, and fumed silica.

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

[0031]

[0032] Where R a R b R c R d Each is independently selected from alkyl groups having 1 to 6 carbon atoms, wherein the alkyl group is branched or straight-chain alkyl; preferably, R a R b R c R d Each is independently selected from straight-chain alkyl groups having 1 to 4 carbon atoms or branched alkyl groups having 3 to 4 carbon atoms; more preferably, the R a Rb R c R d Each of the following is independently selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, or tert-butyl; more preferably, the silicone grease is selected from one or more of tetramethyl silicate, tetraethyl silicate, tetrabutyl silicate, and dimethyl diethyl silicone grease.

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

[0034] More preferably, the first template agent and the second template agent are each independently selected from at least one of quaternary ammonium bases having the structure shown in formula (B):

[0035] R1, R2, R3 and R4 are each selected from alkyl groups having 1 to 4 carbon atoms, preferably one or more of straight-chain alkyl groups having 1 to 4 carbon atoms and branched alkyl groups having 3 to 4 carbon atoms, and more preferably, R1, R2, R3 and R4 are each selected from one or more of methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl and tert-butyl.

[0036] More preferably, the first template agent and the second template agent are each independently tetrapropylammonium hydroxide or a mixture of tetrapropylammonium hydroxide and one or more selected from tetrapropylammonium chloride and tetrapropylammonium bromide;

[0037] Optionally, the first template agent and the second template agent may be the same or different, but preferably the same.

[0038] Optionally, the first heteroatom source in step S1 and the second heteroatom source in step S3 are each independently selected from one or more of the following: titanium source, tin source, boron source and zirconium source.

[0039] Preferably, the titanium source is selected from one or more of titanium tetrachloride, titanium sulfate, titanium nitrate, tetraethyl titanate, tetrapropyl titanate, and tetrabutyl titanate;

[0040] The tin source is selected from one or more of tin chloride, tin chloride pentahydrate, stannous chloride, stannous chloride dihydrate, calcium stannate, potassium stannate, sodium stannate, lithium stannate, stannous sulfate, and stannous pyrophosphate; more preferably, tin chloride pentahydrate;

[0041] The boron source is selected from one or more of boric acid, borates and borates;

[0042] The zirconium source is selected from one or more of zirconium n-propoxide, zirconium isopropoxide, zirconium n-butoxide, zirconium dichlorocerocene, zirconium acetate, zirconium propionate, and tetrabenzyl zirconium;

[0043] Optionally, the first heteroatom source and the second heteroatom source may be the same or different, but preferably the same.

[0044] Optionally, in step S1, the silanizing agent is selected from those with the general formula R. e Si(R f (R) g )R h , where R e R f R g R h Each group can be independently halogenated, alkyl, alkoxy, aromatic, mercapto, or amino, and R e R f R g R h At least one of them is an alkyl, alkoxy, aromatic, mercapto, or amino group; the alkyl, alkoxy, mercapto, and amino groups each have an independent number of carbon atoms of C1 to C2. 18 ;

[0045] Preferably, the silanizing agent is selected from one or more of dimethyldichlorosilane, N-phenyl-3-aminopropyltrimethoxysilane, phenyltrimethoxysilane, 1,7-dichlorooctylmethyltetrasiloxane, hexadecyltrimethoxysilane, octyltriethoxysilane, 3-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, and 3-mercaptopropyltrimethoxysilane; more preferably, it is selected from one or more of N-phenyl-3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, and 3-mercaptopropyltrimethoxysilane.

[0046] Optionally, in step S1, the structural filler is selected from one or more of amphiphilic surfactants and hard template agents;

[0047] Preferably, the amphiphilic surfactant is selected from one or more of hexadecyltrimethylammonium bromide, sodium dodecylbenzene sulfonate, branched sodium dodecylbenzene sulfonate, α-olefin sulfonates with 14 to 16 carbon atoms, and secondary alkyl sulfonates.

[0048] Preferably, the hard template agent is selected from one or more of PEO-PPO-PEO block copolymers, mesoporous carbon, natural fibers, polyethylene, polypropylene, polyvinyl chloride, polystyrene, and polyvinyl alcohol;

[0049] More preferably, the structural filler is selected from one or more of hexadecyltrimethylammonium bromide, sodium dodecylbenzenesulfonate, PEO-PPO-PEO block copolymer, mesoporous carbon, and natural cellulose.

[0050] Optionally, step S1 includes:

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

[0052] b. Add the silanizing agent and the structural filler to the hydrolyzed sol of the silicon respectively, and mix them to obtain the reaction mixture;

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

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

[0055] Preferably, the silicon source is an organosilicon grease, and step a further includes a hydrolysis and alcohol removal treatment after mixing the first heteroatom source, the silicon source, the first template agent and water to obtain the silicon hydrolysate;

[0056] Optionally, the conditions for the hydrolysis and alcohol removal treatment include: stirring and hydrolyzing at 40–90°C for 6–12 hours; preferably, stirring and hydrolyzing at 60–85°C for 8–10 hours.

[0057] Optionally, in step S3, the weight ratio of the second heteroatom source: the second template agent: water: the molecular sieve intermediate is (0.01-3.6):(0.06-3.5):(3-30):1; preferably (0.05-2.7):(0.12-2.8):(4-25):1.

[0058] Optionally, the conditions for the first hydrothermal crystallization treatment in step S2 and the second hydrothermal crystallization treatment in step S3 each independently include: a hydrothermal crystallization time of 6–168 h and a hydrothermal crystallization temperature of 130–200 °C; preferably, a hydrothermal crystallization time of 24–72 h and a hydrothermal crystallization temperature of 150–180 °C; and the pressure is self-generated pressure.

[0059] The conditions for the first roasting treatment in step S2 and the second roasting treatment in step S3 each independently include: a roasting temperature of 300-700℃ and a roasting time of 1-16h; preferably, a roasting temperature of 400-600℃ and a roasting time of 2-5h.

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

[0061] The fourth aspect of this disclosure provides a method for preparing caprolactam from cyclohexanone oxime via gas-phase Beckmann rearrangement, comprising: reacting cyclohexanone oxime with a catalyst, wherein the catalyst comprises the hierarchical porous heteroatom molecular sieve described in the first and third aspects of this disclosure.

[0062] Through the above technical solution, this disclosure provides a hierarchical porous heteroatom molecular sieve, its preparation method, and its application in the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime. This disclosure enables the introduction of heteroatoms into molecular sieves with various topologies. Different pore sizes in different topologies provide different reaction pathways, and the unique hierarchical porous structure provides a large number of reaction units. This hierarchical porous heteroatom molecular sieve has stable reactive centers, abundant silanol active centers, and a large specific surface area and pore volume. The FT-IR spectrum of this hierarchical porous heteroatom molecular sieve shows a peak value of 3740±5 cm⁻¹. -1 3690±5cm -1 and 3520±10cm -1 The three peaks have spectral peaks at their respective positions, and the peak areas of the three peaks satisfy the ranges of X1 and X2. In the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime, this hierarchical porous heteroatom molecular sieve can significantly improve the conversion rate of cyclohexanone oxime and the selectivity of caprolactam. It can also significantly reduce the influence of heating or alkaline byproducts on the active silanol sites of the molecular sieve, ensuring the stability of the catalyst reaction and extending the catalyst life.

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

[0064] The accompanying drawings are provided to further illustrate the present disclosure and form part of the specification. They are used together with the following detailed description to explain the present disclosure, but do not constitute a limitation thereof. In the drawings:

[0065] Figure 1 The FT-IR spectrum of the molecular sieve obtained in Example 1;

[0066] Figure 2 The XRD patterns of the molecular sieves with the topologies of MFI (Example 1), MEL (Example 5), BEA (Example 7), and SVR (Example 9) prepared for the examples are shown below.

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

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

[0069] Figure 5 The nitrogen adsorption-desorption curve of the molecular sieve obtained in Example 1;

[0070] Figure 6 This is a TEM image of the molecular sieve intermediate obtained in Example 1. Detailed Implementation

[0071] The following provides a detailed description of specific embodiments of this disclosure. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit this disclosure.

[0072] The first aspect of this disclosure provides a hierarchical porous heteroatom molecular sieve, which has the following FT-IR characteristics:

[0073] The wavenumber of the FT-IR spectrum of the hierarchical porous heteroatom molecular sieve was 3740±5 cm⁻¹. -1 The peak area at the specified location is denoted as A1; the wavenumber in the FT-IR spectrum of the hierarchical porous heteroatom molecular sieve is 3690±5 cm⁻¹. -1 The peak area at the specified location is denoted as A2; the wavenumber in the FT-IR spectrum of the hierarchical porous heteroatom molecular sieve is 3520±10 cm⁻¹. -1 The peak area at the specified location is denoted as A3;

[0074] As defined in equation (1), X1 is any value between 0.6 and 1.6:

[0075] X1 = A2 / A1 (Equation (1));

[0076] As defined in equation (2), X2 is any value between 2.0 and 5.5:

[0077] X2 = A3 / A1 (Equation 2).

[0078] This disclosure provides a hierarchical porous heteroatom molecular sieve, which can introduce heteroatoms into molecular sieves with various topologies. Different topologies provide different reaction pathways with varying pore sizes, and the unique hierarchical structure provides a large number of reaction units. This hierarchical porous heteroatom molecular sieve has stable reactive centers, abundant silanol active centers, and a large specific surface area and pore volume. The FT-IR spectrum of this hierarchical porous heteroatom molecular sieve shows a peak value of 3740±5 cm⁻¹. -1 3690±5cm -1 and 3520±10cm -1 The three peaks have spectral peaks at their respective positions, and the peak areas of the three peaks satisfy the ranges of X1 and X2. In the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime, this hierarchical porous heteroatom molecular sieve can significantly improve the conversion rate of cyclohexanone oxime and the selectivity of caprolactam. It can also significantly reduce the influence of heating or alkaline byproducts on the active silanol sites of the molecular sieve, ensuring the stability of the catalyst reaction and extending the catalyst life.

[0079] Through extensive experimental research, the inventors of this disclosure have surprisingly discovered that, in the FT-IR spectrum of a framework heteroatom molecular sieve, it is possible to achieve a wavenumber of 3740±5 cm⁻¹. -1 The peak at position A1 represents the isolated terminal hydroxyl group in this heteroatom zeolite (its peak area is denoted as A1), with a value of 3690±5 cm⁻¹. -1 The spectral peak at position A2 represents the ortho-silanol group in this heteroatom molecular sieve (its peak area is denoted as A2), with a value of 3520±10 cm⁻¹. -1 The peak at the position indicates the nested silanol group in the heteroatom molecular sieve (its peak area is denoted as A3), and the peak areas of the above three peaks satisfy the range of X1 defined by formula (1) and X2 defined by formula (2). The heteroatom molecular sieve has suitable characteristics for catalyzing the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime.

[0080] In this disclosure, the FT-IR test uses conventional test instruments and methods in the art.

[0081] In a preferred embodiment, X1 is any value between 0.8 and 1.5; and X2 is any value between 2.5 and 4.0. When X1 and X2 of the hierarchical porous heteroatom molecular sieve meet the range of this embodiment, the hierarchical porous heteroatom molecular sieve can achieve higher caprolactam selectivity and better catalyst reaction stability.

[0082] In one specific embodiment, the heteroatom is selected from one or more elements of Group IVB, Group IIIA, and Group IVA; preferably, it is selected from one or more elements of Ti, B, Zr, and Sn.

[0083] In one embodiment, the molar ratio of silicon atoms to heteroatoms in the hierarchical porous heteroatom molecular sieve is (6-260):1, preferably (8-170):1. This disclosure obtains the molar ratio of heteroatoms to silicon atoms in the molecular sieve using X-ray fluorescence spectroscopy.

[0084] In a preferred embodiment, the hierarchical porous heteroatom molecular sieve has multiple cavity structures within its crystal structure; wherein the size of a single cavity structure is 2–38 nm, preferably 3–34 nm. The hierarchical porous heteroatom molecular sieve provided in this disclosure has a large-size multi-cavity structure, and the cavity structure contains abundant silanol active centers, providing a large number of independent reaction units; furthermore, the large-size cavity structure meets the requirements of macromolecular reactions, and reaction products can more easily flow out of the catalyst, avoiding pore blockage that leads to a decrease in catalyst catalytic activity.

[0085] In this disclosure, the cavity structure and its size in the molecular sieve are obtained by transmission electron microscopy (TEM). In this disclosure, the size of the cavity structure refers to the length between two positions on the cavity wall passing through the center of the cavity structure in a TEM image of the molecular sieve; for example, "the size of a single cavity structure is 2–38 nm" means that the length between two positions on the cavity wall passing through the center of any cavity structure in the molecular sieve is within the range of 2–38 nm.

[0086] In a preferred embodiment, all of the cavity structures account for 15-65% of the total volume of the molecular sieve, more preferably 22-58%;

[0087] Optionally, the shape of the cavity structure is selected from one or more of the following: sphere, cube, ellipsoid, and irregular cube.

[0088] In one specific embodiment, the multi-level porous heteroatom molecular sieve includes molecular sieve particles composed of a single crystal grain, and / or molecular sieve particles composed of aggregates of multiple crystal grains.

[0089] Optionally, the average particle size of the molecular sieve particles is 0.2–1.0 μm, preferably 0.28–0.85 μm; the BET specific surface area is 300–650 m². 2 / g, preferably 320-560m 2 / g; Microporous specific surface area is 260-520m² 2 / g, preferably 280-490m 2 / g; total pore volume is 0.18–0.55 cm³. 3 / g, preferably 0.22~0.48cm 3 / g; mesopore volume is 0.13~0.54cm³ 3 / g, preferably 0.15~0.38cm 3 / g.

[0090] In a preferred embodiment, a hysteresis loop exists between the adsorption isotherm and desorption isotherm of the low-temperature nitrogen adsorption of the hierarchical porous heteroatom molecular sieve.

[0091] In one specific embodiment, the initial relative pressure (P / P0) at which the hysteresis loop appears is 0.30 to 0.50, preferably 0.36 to 0.47.

[0092] In one specific embodiment, the configuration of the hierarchical porous heteroatom molecular sieve is selected from one or more of the MFI topology, MEL topology, BEA topology and SVR topology; more preferably, it is the MFI topology.

[0093] The second aspect of this disclosure provides a method for preparing hierarchical porous heteroatom molecular sieves, comprising the following steps:

[0094] S1. Mix the first heteroatom source, silicon source, first template agent, water, silanizing agent and structural filler to obtain a reaction mixture;

[0095] S2. The reaction mixture is subjected to a first hydrothermal crystallization treatment and a first calcination treatment in sequence to obtain a molecular sieve intermediate;

[0096] S3. Mix the molecular sieve intermediate, the second template agent, the second heteroatom source and water, and then perform a second hydrothermal crystallization treatment and a second calcination treatment in sequence.

[0097] This disclosure provides a method for preparing hierarchical porous heteroatom molecular sieves. Introducing heteroatom sources into the reactants allows for the introduction of heteroatom active centers into the molecular sieve framework during synthesis, improving molecular sieve performance. By introducing silanizing agents and macromolecular fillers into the molecular sieve synthesis materials, a pore-expanding effect is achieved, preparing molecular sieve materials with open channels. A template agent is then added for dissolution-recrystallization, resulting in a hierarchical porous heteroatom molecular sieve with a multi-cavity structure. Furthermore, the additional introduction of heteroatom sources during dissolution-recrystallization allows for greater heteroatom distribution on the outer surface of the molecular sieve, enabling the prepared framework heteroatom molecular sieve to contact the reactants more quickly and promoting transformation.

[0098] Specifically, the silanol groups of the silanizing agent hydrolyze and condense with the silanol groups of the organosilicon source to form stable Si-O-Si bonds, thus ensuring the achievement of the stratigraphic expansion effect. Furthermore, the long carbon chain of the silanizing agent and the structural filler of the amphiphilic surfactant can form stable and controllable structural units (the long carbon chain of the silanizing agent and the hydrophobic group of the surfactant are close to each other and interact by van der Waals forces), thereby finely modulating the stratigraphic expansion effect; or, a hard template agent with controllable dimensions can be used for space filling. This results in an ordered, mesoporous structure with controllable pore size (controlled by the chain length of the alkyl chain of the silanizing agent). Then, a template agent is introduced into the molecular sieve with open pores, and by utilizing its dissolution-recrystallization mechanism, a heteroatom molecular sieve with a hierarchical porous structure is obtained.

[0099] In one embodiment, in step S1, the molar ratio of the first heteroatom source: silicon source: first template agent: water: silanizing agent is (0.002~1.5):1:(0.03~4):(1~50):(0.002~3.5); the silicon source is in the form of SiO2, and the weight ratio of SiO2 to structural filler is (4~50):1.

[0100] In a preferred embodiment, in step S1, the molar ratio of the first heteroatom source: silicon source: first template agent: water: silanizing agent is (0.005–0.8):1:(0.06–1.5):(8–30):(0.007–2.5); the silicon source is in the form of SiO2, and the weight ratio of SiO2 to the structural filler is (6–38):1. According to the more optimized raw material addition ratio in this embodiment, the prepared hierarchical porous heteroatom molecular sieve exhibits superior catalytic activity and resistance to deactivation.

[0101] In one embodiment, in step S1, the silicon source is selected from at least one of silicone grease, solid silicone, fumed silica, and silica sol; preferably, it is selected from at least one of silicone grease, solid silicone, and fumed silica.

[0102] A further preferred option is a silicone grease, wherein the silicone grease has the general formula shown in formula (A):

[0103]

[0104] Where R a R b R c R d Each is independently selected from alkyl groups having 1 to 6 carbon atoms, wherein the alkyl group is branched or straight-chain alkyl; preferably, R a R b R c R d Each is independently selected from straight-chain alkyl groups having 1 to 4 carbon atoms or branched alkyl groups having 3 to 4 carbon atoms; more preferably, the R a R b R c R d Each is independently selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, or tert-butyl.

[0105] In a preferred embodiment, the silicone grease is selected from one or more of tetramethyl silicate, tetraethyl silicate, tetrabutyl silicate, and dimethyl diethyl silicone grease.

[0106] In one embodiment, in step S1, the first template agent is an organic base, preferably at least one selected from quaternary ammonium bases, aliphatic amines, and aliphatic alcohol amines.

[0107] In one specific embodiment, the first template agent is selected from at least one of quaternary ammonium bases having the structure shown in formula (B):

[0108] R1, R2, R3 and R4 are each selected from alkyl groups having 1 to 4 carbon atoms, preferably one or more of straight-chain alkyl groups having 1 to 4 carbon atoms and branched alkyl groups having 3 to 4 carbon atoms, and more preferably, R1, R2, R3 and R4 are each selected from one or more of methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl and tert-butyl.

[0109] In a preferred embodiment, the first template agent is tetrapropylammonium hydroxide or a mixture of tetrapropylammonium hydroxide and one or more selected from tetrapropylammonium chloride and tetrapropylammonium bromide.

[0110] In one embodiment, step S1 includes:

[0111] a. Mix the first heteroatom source, titanium source, silicon source, first template agent and water to obtain a silicon hydrolysis sol;

[0112] b. Add the silanizing agent and the structural filler to the hydrolyzed sol of the silicon respectively, and mix them to obtain the reaction mixture;

[0113] Optionally, the mixing conditions in step a include stirring at 40–90°C for 6–12 hours;

[0114] Optionally, the mixing conditions in step b include stirring at 20–50°C for 2–4 hours.

[0115] In one specific embodiment, the silicon source is an organosilicon grease, and step a further includes a hydrolysis and alcohol removal treatment after mixing the first heteroatom source, the silicon source, the first template agent and water to obtain the silicon hydrolysate;

[0116] Optionally, the conditions for the hydrolysis-induced alcohol removal treatment include: stirring and hydrolyzing at 40–90°C for 6–12 hours; preferably, stirring and hydrolyzing at 60–85°C for 8–10 hours. Preferably, the hydrolysis-induced alcohol removal treatment results in the alcohol content in the silicone hydrolysate of the obtained silicone grease being below 10 ppm by mass.

[0117] In one embodiment, in step S1, the first heteroatom source is selected from one or more of titanium, tin, boron and zirconium sources.

[0118] In a preferred embodiment, the titanium source is selected from one or more of titanium tetrachloride, titanium sulfate, titanium nitrate, tetraethyl titanate, tetrapropyl titanate, and tetrabutyl titanate.

[0119] The tin source is selected from one or more of tin chloride, tin chloride pentahydrate, stannous chloride, stannous chloride dihydrate, calcium stannate, potassium stannate, sodium stannate, lithium stannate, stannous sulfate, and stannous pyrophosphate; more preferably, tin chloride pentahydrate;

[0120] The boron source is selected from one or more of boric acid, borates and borates;

[0121] The zirconium source is selected from one or more of zirconium n-propoxide, zirconium isopropoxide, zirconium n-butoxide, zirconium dichlorodicenocene, zirconium acetate, zirconium propionate, and tetrabenzyl zirconium.

[0122] In one embodiment, in step S1, the silanizing agent is selected from those with the general formula R. e Si(R f (R) g )R h , where R e R f R g R h Each group can be independently halogenated, alkyl, alkoxy, aromatic, mercapto, or amino, and R e R f R g R h At least one of them is an alkyl, alkoxy, aromatic, mercapto, or amino group; the alkyl, alkoxy, mercapto, and amino groups each have an independent number of carbon atoms of C1 to C2. 18 .

[0123] In a preferred embodiment, the silanizing agent is selected from one or more of dimethyldichlorosilane, N-phenyl-3-aminopropyltrimethoxysilane, phenyltrimethoxysilane, 1,7-dichlorooctylmethyltetrasiloxane, hexadecyltrimethoxysilane, octyltriethoxysilane, 3-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, and 3-mercaptopropyltrimethoxysilane; more preferably, it is selected from one or more of N-phenyl-3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, and 3-mercaptopropyltrimethoxysilane.

[0124] In one embodiment, in step S1, the structural filler is selected from one or more of amphiphilic surfactants and hard template agents.

[0125] In one specific embodiment, the amphiphilic surfactant is selected from one or more of hexadecyltrimethylammonium bromide, sodium dodecylbenzene sulfonate, branched sodium dodecylbenzene sulfonate, α-olefin sulfonates with 14 to 16 carbon atoms, and secondary alkyl sulfonates.

[0126] The hard template agent is selected from one or more of PEO-PPO-PEO block copolymers, mesoporous carbon, natural fibers, polyethylene, polypropylene, polyvinyl chloride, polystyrene, and polyvinyl alcohol.

[0127] In a preferred embodiment, the structural filler is selected from one or more of hexadecyltrimethylammonium bromide, sodium dodecylbenzenesulfonate, PEO-PPO-PEO block copolymer, mesoporous carbon, and natural cellulose.

[0128] The reagents involved in this disclosure can all be purchased through ordinary channels or prepared by methods known in the art.

[0129] In one embodiment, the conditions for the first hydrothermal crystallization treatment in step S2 include: hydrothermal crystallization time of 6 to 168 hours, hydrothermal crystallization temperature of 130 to 200°C, and pressure of autogenous pressure;

[0130] The conditions for the first calcination treatment in step S2 include: a calcination temperature of 300–700°C and a calcination time of 1–16 h.

[0131] In a preferred embodiment, the conditions for the first hydrothermal crystallization treatment in step S2 include: a hydrothermal crystallization time of 24–72 h, a hydrothermal crystallization temperature of 150–180 °C, and an autogenous pressure.

[0132] The conditions for the first calcination treatment in step S2 include: a calcination temperature of 400–600°C and a calcination time of 2–5 hours. The hierarchical porous heteroatom molecular sieve prepared according to this embodiment exhibits better catalytic activity.

[0133] In one specific embodiment, after the first hydrothermal crystallization treatment, the method further includes the steps of subjecting the product of the first hydrothermal crystallization treatment to a first filtration treatment and a first drying treatment, followed by the first calcination treatment. The temperature of the first drying treatment is 50–120°C, and the time is 1–12 hours.

[0134] In one embodiment, in step S3, the selection range of the second template agent is the same as that of the first template agent, and will not be repeated here. In this disclosure, the first template agent and the second template agent used can be the same or different; preferably, the first template agent and the second template agent are the same template agent.

[0135] In one embodiment, in step S3, the selection range of the second heteroatom source is the same as that of the first heteroatom source, and will not be repeated here. In this disclosure, the first heteroatom source and the second heteroatom source used can be the same or different; preferably, the first heteroatom source and the second heteroatom source are the same reagent.

[0136] In one embodiment, in step S3, the weight ratio of the second heteroatom source: the second template agent: water: the molecular sieve intermediate is (0.01–3.6):(0.06–3.5):(3–30):1; preferably (0.05–2.7):(0.12–2.8):(4–25):1. By preparing the sieve according to the preferred weight ratio in this embodiment, a molecular sieve with higher catalytic activity can be obtained.

[0137] In one embodiment, the conditions for the second hydrothermal crystallization treatment in step S3 include: a hydrothermal crystallization time of 6–168 h, a hydrothermal crystallization temperature of 130–200 °C, and an autogenous pressure;

[0138] The conditions for the second calcination treatment in step S3 include: a calcination temperature of 300–700°C and a calcination time of 1–16 h.

[0139] In a preferred embodiment, the conditions for the second hydrothermal crystallization treatment in step S3 include: a hydrothermal crystallization time of 24–72 h, a hydrothermal crystallization temperature of 150–180 °C, and an autogenous pressure.

[0140] The conditions for the second calcination treatment in step S3 include: a calcination temperature of 400–600°C and a calcination time of 2–5 hours.

[0141] In one specific embodiment, after the second hydrothermal crystallization treatment, the method further includes a second filtration treatment and a second drying treatment of the product from the second hydrothermal crystallization treatment, followed by the second calcination treatment. The temperature of the second drying treatment is 50–120°C, and the time is 1–12 hours.

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

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

[0144] In one specific embodiment, the gas-phase Beckmann rearrangement reaction conditions for cyclohexanone oxime include: a reaction temperature of 350–400 °C, a reaction pressure of 0–0.2 MPa, a nitrogen to cyclohexanone oxime molar ratio of 0.1–30:1, cyclohexanone oxime accounting for 5–50% by weight of the total amount of cyclohexanone oxime and solvent, and a cyclohexanone oxime weight hourly space velocity of 1–10 h⁻¹. -1 .

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

[0146] The Fourier transform infrared (FT-IR) spectra of the samples were measured on a Nicolet 8210 Fourier transform infrared spectrometer, with a measurement range of 400–4000 cm⁻¹. -1 .

[0147] The X-ray diffraction (XRD) phase pattern of the sample was determined on a Siemens D5005 X-ray diffractometer with Kα (Cu) as the X-ray source and the test range 2θ from 0.5° to 70°.

[0148] Transmission electron microscopy (TEM) images of the samples were obtained using a Tecnai G2F20S-TWIN TEM microscope from FEI. The cavity structure and its dimensions were determined based on TEM measurements. The volume fraction of the cavity structure relative to the total volume of the molecular sieve was obtained by measuring the TEM images: the volume of each cavity in the molecular sieve particles was measured based on the TEM images (calculated spherically, using the median of the sum of the maximum and minimum lengths passing through the center of the cavity structure as the spherical diameter, then obtaining the spherical radius, and finally calculating the percentage of the total volume of all cavities relative to the total volume of the molecular sieve particles; the average value was taken after calculating the cavity structure volume fraction of 50 molecular sieve particles).

[0149] Scanning electron microscopy (SEM) images of the samples were obtained using a Hitachi S4800 high-resolution cold field emission scanning electron microscope. The average particle size of the samples was determined by measuring the SEM images (the average value was taken after testing the particle size of 50 molecular sieves).

[0150] The total specific surface area and total pore volume of the samples were determined using a Micromeritics ASAP245 static nitrogen adsorption analyzer according to the ASTM D4222-98 standard method. The adsorption and desorption isotherms of the samples at low temperatures were determined according to the ASTM D4222-98 standard method.

[0151] X-ray fluorescence analysis of the samples (determination of the molar ratio of silicon to titanium in the molecular sieve) was performed using a Rigaku Electric Co., Ltd. 3013 instrument with a tungsten target, an excitation voltage of 40 kV, and an excitation current of 250 mA.

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

[0153] Example 1

[0154] (1) Add 6g tetrabutyl titanate (0.0176mol), 104g tetraethyl silicate (0.5mol), 65g tetrapropylammonium hydroxide (TPAOH, 0.08mol) aqueous solution with a concentration of 25% by weight and 140g water to a 500mL beaker, place it on a magnetic stirrer with heating and stirring functions and mix evenly. Stir at 60℃ for 5 hours, and replenish the evaporated water at regular intervals to obtain a colorless and transparent titanium silica gel solution.

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

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

[0157] (4) Mix 10g of TS-1-T sample, 0.5g of tetrabutyl titanate, 20g of 25% by weight tetrapropylammonium hydroxide (TPAOH) aqueous solution and 40g of water evenly (the weight ratio of the second heteroatom source: the second template agent: water: molecular sieve intermediate is 0.05:0.5:5.5:1), transfer to a stainless steel sealed reactor, and crystallize at 170℃ for 24h to obtain the sample. Filter and wash the obtained sample, dry it at 110℃ for 3 hours, and then calcine it in a muffle furnace at 550℃ for 3 hours to obtain the heteroatom molecular sieve sample, which is denoted as C-1.

[0158] The structural parameter characterization results of sample C-1 are listed in Table 2;

[0159] The FI-IR spectrum of sample C-1 is as follows Figure 1 As shown in the figure, at a wavenumber of 3740 cm⁻¹ -1 3690cm -1 And 3520cm -1 The presence of spectral peaks at the respective positions indicates that the heteroatom molecular sieve sample has three different types of hydroxyl groups. The peak areas of the three peaks are calculated by integrating the peak areas: A1 is 17.5, A2 is 22.8, and A3 is 59.6. The values ​​of X1 and X2 calculated by formulas (1) and (2) are listed in Table 3.

[0160] The XRD pattern of sample C-1 is as follows Figure 2 As shown, this indicates that the hierarchical porous heteroatom molecular sieve sample has an MFI topology.

[0161] TEM image of sample C-1 as follows Figure 3 As shown in the figure, the molecular sieve has a hierarchical porous structure with multiple cavities within the crystal; and the size of a single cavity structure is measured and calculated to be 6–25 nm.

[0162] SEM image of sample C-1 as follows Figure 4 As shown in the figure, the molecular sieve consists of uniform ellipsoidal particles.

[0163] The BET curve of sample C-1 is shown below. Figure 5 As shown, there is a clear hysteresis loop between the nitrogen adsorption and desorption curves, and the initial relative pressure (P / P0) at which the hysteresis loop appears is 0.44.

[0164] TEM images of the molecular sieve intermediate TS-1-T without dissolution and recrystallization are shown below. Figure 6 As shown, Figure 6 and Figure 3 By comparison, it can be seen that Figure 3 The intermediate products, after being dissolved and recrystallized, formed a large number of intracrystalline multi-cavity structures.

[0165] Comparative Example 1

[0166] The method of Example 1 is used, except that no silanizing agent or structural filler is added. The resulting product is denoted as D-1. The preparation conditions are listed in Table 1, and the characterization results of the resulting molecular sieve are listed in Table 2.

[0167] Comparative Example 2

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

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

[0170] Comparative Example 3

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

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

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

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

[0175] Examples 2-11

[0176] Multi-level porous heteroatom molecular sieves were prepared according to the method of Example 1, except that the ratio and synthesis conditions were changed to obtain multi-level porous heteroatom molecular sieve samples denoted as C-2 to C-11; the preparation conditions are listed in Table 1, and the characterization results of the obtained molecular sieves are listed in Table 2.

[0177] Example 12

[0178] The hierarchical porous heteroatom molecular sieve was prepared according to the method of Example 1, but differed from that in Example 1 in that:

[0179] The temperature of the first hydrothermal crystallization treatment was 130℃ and the time was 96h; the temperature of the first calcination treatment was 350℃ and the time was 8h.

[0180] The second hydrothermal crystallization treatment was carried out at a temperature of 130℃ for 96 hours; the second calcination treatment was carried out at a temperature of 350℃ for 8 hours.

[0181] The obtained hierarchical porous heteroatom molecular sieve sample is designated as C-12; the characterization results of the obtained molecular sieve are listed in Table 2.

[0182] Table 1

[0183]

[0184] In Table 1, TPAOH is tetrapropylammonium hydroxide, TBAOH is tetrabutylammonium hydroxide, TEAOH is tetraethylammonium hydroxide, and MTPOH is 1,6-diN-methylpyrrolidone; PHAPTMS is N-phenyl-3-aminopropyltrimethoxysilane, APTMS is 3-aminopropyltriethoxysilane, GCPMS is 3-epoxypropoxypropyl(dimethoxy)methylsilane, and TOMS is methyltrimethoxysilane; P123 is PEO-PPO-PEO triblock copolymer, and CTAB is hexadecyltrimethylammonium bromide. The reagents used in this disclosure can be obtained through conventional purchasing channels. The water in the "water / silicon source" calculation in Table 1 also includes water from the aqueous solution of the first template agent; the water in the "water / molecular sieve intermediate" calculation also includes water from the aqueous solution of the second template agent.

[0185] Table 2

[0186]

[0187] The XRD patterns of molecular sieves C-5, C-7, and C-9 prepared in Examples 5, 7, and 9 are shown below. Figure 2 As shown, it was demonstrated that the hierarchical porous heteroatom molecular sieve C-5 has the MEL configuration, the hierarchical porous heteroatom molecular sieve C-7 has the BEA configuration, and the hierarchical porous heteroatom molecular sieve C-9 has the SVR configuration.

[0188] Test case

[0189] The molecular sieves prepared in the above examples and comparative examples were evaluated. The prepared molecular sieves were compressed into tablets, then crushed. 20-60 mesh particles were used as catalysts for the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime. The catalytic performance of the obtained molecular sieves was evaluated under the following conditions:

[0190] The evaluation apparatus was an atmospheric pressure continuous flow fixed-bed reactor with an inner diameter of 5 mm and a catalyst loading of 2 g. After catalyst loading, the reactor was pretreated for 3 hours at atmospheric pressure and 350 °C under a nitrogen atmosphere. The feedstock cyclohexanone oxime had a concentration of 35% by weight, and methanol was used as the solvent. The reaction conditions included a cyclohexanone oxime weight hourly space velocity (WHSV, cyclohexanone oxime flow rate in feed / catalyst weight in reactor) of 2 h⁻¹. -1 The reaction temperature was 380℃, the nitrogen flow rate was 4 liters / hour, and the reaction time was 24h and 200h, respectively.

[0191] The reaction products were collected after cooling, and the concentrations of each substance were quantitatively analyzed by gas chromatography (GC). An Agilent 6890 GC was used, with an HP-5 column. The test conditions included: vaporization chamber temperature 250℃, detection chamber temperature 230℃, and a programmed column temperature ramp: 110℃ for 8 minutes, ramped to 230℃ at a rate of 15℃ / min, and then held for 14 minutes. The results are shown in Table 3 below.

[0192] Wherein, the conversion rate of cyclohexanone oxime (mol%) = (molar content of cyclohexanone oxime in feed - molar content of cyclohexanone oxime in product) / molar content of cyclohexanone oxime in feed × 100%;

[0193] Caprolactam selectivity (mol%) = (mol percentage of caprolactam in the product) / (100 - mol percentage of cyclohexanone oxime in the product) × 100%;

[0194] Cyclohexanone oxime conversion reduction rate (%) = (24h cyclohexanone conversion rate - 200h cyclohexanone conversion rate) / 24h cyclohexanone conversion rate × 100%;

[0195] The decrease in caprolactam selectivity (%) = (24h caprolactam selectivity - 200h caprolactam selectivity) / 24h caprolactam selectivity × 100%.

[0196] Table 3

[0197]

[0198]

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

[0200] Compared with the molecular sieves D-1 to D-3 prepared by Comparative Examples 1 to 3, the molecular sieves C-1 to C-12 prepared by the publicly provided method have X1 in the range of 0.6 to 1.6 and X2 in the range of 2.0 to 5.5 in the FT-IR spectrum characteristics. Molecular sieves C-1 to C-12 have higher catalytic activity in the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime, higher cyclohexanone oxime conversion and caprolactam selectivity, and higher catalytic stability under long reaction conditions (200 h).

[0201] Furthermore, the X1 of the molecular sieves C-1 to C-10 prepared in the examples is in the range of 0.8 to 1.5, and the X2 is in the range of 2.5 to 4.0. Compared with molecular sieves C-11 to C-12, the reaction using molecular sieves C-1 to C-10 has a higher conversion rate of cyclohexanone oxime and a higher selectivity of caprolactam, and also has higher catalytic stability under long-term reaction conditions (200 h).

[0202] Comparing Example 1 with Example 11, Example 1 prepared molecular sieves according to the raw material addition ratio in the preferred embodiment. The resulting molecular sieve C-1 had higher cyclohexanone oxime conversion and caprolactam selectivity in the catalytic reaction, and higher catalytic stability under long-term reaction conditions (200h).

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

[0204] The preferred embodiments of this disclosure have been described in detail above. However, this disclosure is not limited to the specific details of the above embodiments. Within the scope of the technical concept of this disclosure, various simple modifications can be made to the technical solutions of this disclosure, and these simple modifications all fall within the protection scope of this disclosure.

[0205] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, this disclosure will not describe the various possible combinations separately.

[0206] Furthermore, various different embodiments of this disclosure can be combined in any way, as long as they do not violate the spirit of this disclosure, they should also be regarded as the content disclosed in this disclosure.

Claims

1. A hierarchical porous heteroatom molecular sieve, characterized in that, The hierarchical porous heteroatom molecular sieve has the following FT-IR characteristics: The wavenumber of the FT-IR spectrum of the hierarchical porous heteroatom molecular sieve was 3740±5 cm⁻¹. -1 The peak area at the specified location is denoted as A1; the wavenumber in the FT-IR spectrum of the hierarchical porous heteroatom molecular sieve is 3690±5 cm⁻¹. -1 The peak area at the specified location is denoted as A2; the wavenumber in the FT-IR spectrum of the hierarchical porous heteroatom molecular sieve is 3520±10 cm⁻¹. -1 The peak area at the specified location is denoted as A3; As defined in equation (1), X1 is any value between 0.6 and 1.6: X1 = A2 / A1 (1); As defined in equation (2), X2 is any value between 2.0 and 5.5: X2 = A3 / A1 (2); The hierarchical porous heteroatom molecular sieve is prepared by a method including the following steps: S1. Mix the first heteroatom source, silicon source, first template agent, water, silanizing agent and structural filler to obtain a reaction mixture; S2. The reaction mixture is subjected to a first hydrothermal crystallization treatment and a first calcination treatment in sequence to obtain a molecular sieve intermediate; S3. Mix the molecular sieve intermediate, the second template agent, the second heteroatom source and water, and then perform a second hydrothermal crystallization treatment and a second calcination treatment in sequence.

2. The hierarchical porous heteroatom molecular sieve according to claim 1, characterized in that, X1 is any value between 0.8 and 1.5; X2 is any value between 2.5 and 4.

0.

3. The hierarchical porous heteroatom molecular sieve according to claim 1, characterized in that, The molar ratio of silicon atoms to heteroatoms in the hierarchical porous heteroatom molecular sieve is (6~260):

1.

4. The hierarchical porous heteroatom molecular sieve according to claim 3, characterized in that, The molar ratio of silicon atoms to heteroatoms in the hierarchical porous heteroatom molecular sieve is (8~170):

1.

5. The hierarchical porous heteroatom molecular sieve according to claim 3, characterized in that, The heteroatoms are selected from one or more elements in Group IVB, Group IIIA, and Group IVA.

6. The hierarchical porous heteroatom molecular sieve according to claim 5, characterized in that, The heteroatoms are selected from one or more of Ti, B, Zr and Sn.

7. The hierarchical porous heteroatom molecular sieve according to claim 1, characterized in that, The configuration of the hierarchical porous heteroatom molecular sieve is selected from one or more of the MFI topology, MEL topology, BEA topology and SVR topology.

8. The hierarchical porous heteroatom molecular sieve according to claim 7, characterized in that, The hierarchical porous heteroatom molecular sieve has an MFI topology.

9. The hierarchical porous heteroatom molecular sieve according to claim 1, characterized in that, The hierarchical porous heteroatom molecular sieve has multiple cavity structures within its crystal; the size of a single cavity structure is 2~42nm.

10. The hierarchical porous heteroatom molecular sieve according to claim 9, characterized in that, The size of the individual cavity structure is 3~37nm.

11. The hierarchical porous heteroatom molecular sieve according to claim 9, characterized in that, The volume of all the cavity structures described accounts for 5-65% of the total volume of the molecular sieve.

12. The hierarchical porous heteroatom molecular sieve according to claim 11, characterized in that, The volume of all the cavity structures accounts for 15-60% of the total volume of the molecular sieve.

13. The hierarchical porous heteroatom molecular sieve according to claim 9, characterized in that, The shape of the cavity structure is selected from one or more of the following: sphere, cube, ellipsoid, and irregular cube.

14. The hierarchical porous heteroatom molecular sieve according to claim 1, characterized in that, The multi-level porous heteroatom molecular sieve includes molecular sieve particles composed of single crystals and / or molecular sieve particles composed of aggregates of multiple crystals.

15. The hierarchical porous heteroatom molecular sieve according to claim 14, characterized in that, The molecular sieve particles have an average particle size of 0.2~1.0 μm and a BET specific surface area of ​​300~650 m². 2 / g; Microporous specific surface area is 260~520m² 2 / g; total pore volume is 0.18~0.55cm³. 3 / g; mesopore volume is 0.13~0.54cm³ 3 / g.

16. The hierarchical porous heteroatom molecular sieve according to claim 15, characterized in that, The molecular sieve particles have an average particle size of 0.28~0.85μm and a BET specific surface area of ​​320~600m². 2 / g; Microporous specific surface area is 280~490m² 2 / g; total pore volume is 0.22~0.48cm³. 3 / g; mesopore volume is 0.15~0.38cm³ 3 / g.

17. The hierarchical porous heteroatom molecular sieve according to claim 1, characterized in that, There is a hysteresis loop between the adsorption isotherm and desorption isotherm of the low-temperature nitrogen adsorption of the multi-level porous heteroatom molecular sieve.

18. The hierarchical porous heteroatom molecular sieve according to claim 17, characterized in that, The initial relative pressure (P / P0) at which the hysteresis loop appears is 0.30~0.

50.

19. The hierarchical porous heteroatom molecular sieve according to claim 18, characterized in that, The initial relative pressure (P / P0) at which the hysteresis loop appears is 0.36~0.

47.

20. The hierarchical porous heteroatom molecular sieve according to claim 1, characterized in that, In step S1, the molar ratio of the first heteroatom source: silicon source: first template agent: water: silanizing agent is (0.002~1.5):1:(0.03~4):(1~50):(0.002~3.5); the silicon source is in the form of SiO2, and the weight ratio of SiO2 to structural filler is (4~50):

1.

21. The hierarchical porous heteroatom molecular sieve according to claim 20, characterized in that, In step S1, the molar ratio of the first heteroatom source: silicon source: first template agent: water: silanizing agent is (0.005~0.8):1:(0.06~1.5):(8~30):(0.007~2.5); the silicon source is in the form of SiO2, and the weight ratio of SiO2 to structural filler is (6~38):

1.

22. The hierarchical porous heteroatom molecular sieve according to claim 1, characterized in that, In step S1, the silicon source is selected from at least one of organosilicon grease, solid silica gel, fumed silica, and silica sol.

23. The hierarchical porous heteroatom molecular sieve according to claim 22, characterized in that, The silicon source is selected from at least one of organosilicon grease, solid silica gel, and precipitated silica.

24. The hierarchical porous heteroatom molecular sieve according to claim 23, characterized in that, The silicon source is selected from silicone grease, and the general formula of the silicone grease is shown in the following formula (A): （A）； Where R a R b R c R d Each is independently selected from alkyl groups having 1 to 6 carbon atoms, wherein the alkyl group is a branched or straight-chain alkyl group.

25. The hierarchical porous heteroatom molecular sieve according to claim 24, characterized in that, In formula (A), R a R b R c R d Each is independently selected from straight-chain alkyl groups having 1 to 4 carbon atoms or branched alkyl groups having 3 to 4 carbon atoms.

26. The hierarchical porous heteroatom molecular sieve according to claim 25, characterized in that, In formula (A), R a R b R c R d Each is independently selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, or tert-butyl.

27. The hierarchical porous heteroatom molecular sieve according to claim 24, characterized in that, The silicone grease is selected from one or more of tetramethyl silicate, tetraethyl silicate, tetrabutyl silicate, and dimethyl diethyl silicone grease.

28. The hierarchical porous heteroatom molecular sieve according to claim 1, characterized in that, The first template agent in step S1 and the second template agent in step S3 are organic bases.

29. The hierarchical porous heteroatom molecular sieve according to claim 28, characterized in that, The first template agent and the second template agent are each independently selected from at least one of quaternary ammonium bases, aliphatic amines and aliphatic alcoholic amines.

30. The hierarchical porous heteroatom molecular sieve according to claim 29, characterized in that, The first template agent and the second template agent are each independently selected from at least one of quaternary ammonium bases having the structure shown in formula (B): (B); R1, R2, R3 and R4 are each selected from alkyl groups having 1 to 4 carbon atoms.

31. The hierarchical porous heteroatom molecular sieve according to claim 30, characterized in that, In formula (B), R1, R2, R3 and R4 are each selected from one or more straight-chain alkyl groups having 1 to 4 carbon atoms and branched alkyl groups having 3 to 4 carbon atoms.

32. The hierarchical porous heteroatom molecular sieve according to claim 31, characterized in that, In formula (B), R1, R2, R3 and R4 are each selected from one or more of methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl and tert-butyl.

33. The hierarchical porous heteroatom molecular sieve according to claim 1, characterized in that, The first template agent and the second template agent are each independently tetrapropylammonium hydroxide or a mixture of tetrapropylammonium hydroxide and one or more selected from tetrapropylammonium chloride and tetrapropylammonium bromide.

34. The hierarchical porous heteroatom molecular sieve according to claim 1, characterized in that, The first template agent and the second template agent may be the same or different.

35. The hierarchical porous heteroatom molecular sieve according to claim 34, characterized in that, The first template agent and the second template agent are the same.

36. The hierarchical porous heteroatom molecular sieve according to claim 1, characterized in that, In step S1, the first heteroatom source and in step S3, the second heteroatom source are each independently selected from one or more of the following: titanium source, tin source, boron source, and zirconium source.

37. The hierarchical porous heteroatom molecular sieve according to claim 36, characterized in that, The titanium source is selected from one or more of titanium tetrachloride, titanium sulfate, titanium nitrate, tetraethyl titanate, tetrapropyl titanate, and tetrabutyl titanate. The tin source is selected from one or more of stannous chloride, stannous chloride pentahydrate, stannous chloride dihydrate, calcium stannate, potassium stannate, sodium stannate, lithium stannate, stannous sulfate, and stannous pyrophosphate. The boron source is selected from one or more of boric acid, borates and borates; The zirconium source is selected from one or more of zirconium n-propoxide, zirconium isopropoxide, zirconium n-butoxide, zirconium dichlorodicenocene, zirconium acetate, zirconium propionate, and tetrabenzyl zirconium.

38. The hierarchical porous heteroatom molecular sieve according to claim 37, characterized in that, The tin source is tin chloride pentahydrate.

39. The hierarchical porous heteroatom molecular sieve according to claim 36, characterized in that, The first heteroatom source and the second heteroatom source may be the same or different.

40. The hierarchical porous heteroatom molecular sieve according to claim 39, characterized in that, The first heteroatom source and the second heteroatom source are the same.

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

42. The hierarchical porous heteroatom molecular sieve according to claim 41, characterized in that, The silanizing agent is selected from one or more of dimethyldichlorosilane, N-phenyl-3-aminopropyltrimethoxysilane, phenyltrimethoxysilane, 1,7-dichlorooctylmethyltetrasiloxane, hexadecyltrimethoxysilane, octyltriethoxysilane, 3-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, and 3-mercaptopropyltrimethoxysilane.

43. The hierarchical porous heteroatom molecular sieve according to claim 42, characterized in that, The silanizing agent is selected from one or more of N-phenyl-3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, and 3-mercaptopropyltrimethoxysilane.

44. The hierarchical porous heteroatom molecular sieve according to claim 1, characterized in that, In step S1, the structural filler is selected from one or more of amphiphilic surfactants and hard template agents.

45. The hierarchical porous heteroatom molecular sieve according to claim 44, characterized in that, The amphiphilic surfactant is selected from one or more of hexadecyltrimethylammonium bromide, sodium dodecylbenzene sulfonate, branched sodium dodecylbenzene sulfonate, α-olefin sulfonates with 14 to 16 carbon atoms, and secondary alkyl sulfonates.

46. ​​The hierarchical porous heteroatom molecular sieve according to claim 44, characterized in that, The hard template agent is selected from one or more of PEO-PPO-PEO block copolymers, mesoporous carbon, natural fibers, polyethylene, polypropylene, polyvinyl chloride, polystyrene, and polyvinyl alcohol.

47. The hierarchical porous heteroatom molecular sieve according to claim 1, characterized in that, The structural filler is selected from one or more of hexadecyltrimethylammonium bromide, sodium dodecylbenzenesulfonate, PEO-PPO-PEO block copolymer, mesoporous carbon, and natural cellulose.

48. The hierarchical porous heteroatom molecular sieve according to claim 1, characterized in that, Step S1 includes: a. Mix the first heteroatom source, silicon source, first template agent and water to obtain a silicon hydrolysis sol; b. The silanizing agent and the structural filler are added to the hydrolyzed sol of the silicon, and the mixture is then used to obtain the reaction mixture.

49. The hierarchical porous heteroatom molecular sieve according to claim 48, characterized in that, The mixing conditions in step a include stirring at 40~90℃ for 6~12 hours; The mixing conditions in step b include stirring at 20~50℃ for 2~4 hours.

50. The hierarchical porous heteroatom molecular sieve according to claim 48, characterized in that, The silicon source is an organosilicon grease. In step a, after mixing the first heteroatom source, the silicon source, the first template agent and water, a hydrolysis and alcohol removal treatment is also included to obtain the silicon hydrolysate.

51. The hierarchical porous heteroatom molecular sieve according to claim 50, characterized in that, The conditions for the hydrolysis and alcohol removal treatment include: stirring and hydrolyzing at 40~90℃ for 6~12h.

52. The hierarchical porous heteroatom molecular sieve according to claim 51, characterized in that, The conditions for the hydrolysis and alcohol removal treatment include: stirring and hydrolyzing at 60~85℃ for 8~10h.

53. The hierarchical porous heteroatom molecular sieve according to claim 1, characterized in that, In step S3, the weight ratio of the second heteroatom source, the second template agent, water, and the molecular sieve intermediate is (0.01~3.6):(0.06~3.5):(3~30):

1.

54. The hierarchical porous heteroatom molecular sieve according to claim 53, characterized in that, In step S3, the weight ratio of the second heteroatom source, the second template agent, water, and the molecular sieve intermediate is (0.05~2.7):(0.12~2.8):(4~25):

1.

55. The hierarchical porous heteroatom molecular sieve according to claim 1, characterized in that, The conditions for the first hydrothermal crystallization treatment in step S2 and the second hydrothermal crystallization treatment in step S3 each independently include: hydrothermal crystallization time of 6~168h, hydrothermal crystallization temperature of 130~200℃; and pressure of autogenous pressure. The conditions for the first roasting treatment in step S2 and the second roasting treatment in step S3 each independently include: a roasting temperature of 300~700℃ and a roasting time of 1~16h.

56. The hierarchical porous heteroatom molecular sieve according to claim 55, characterized in that, The conditions for the first hydrothermal crystallization treatment in step S2 and the second hydrothermal crystallization treatment in step S3 each independently include: hydrothermal crystallization time of 24~72h and hydrothermal crystallization temperature of 150~180℃; The conditions for the first roasting treatment in step S2 and the second roasting treatment in step S3 each independently include: a roasting temperature of 400~600℃ and a roasting time of 2~5h.

57. A method for preparing caprolactam from cyclohexanone oxime via gas-phase Beckmann rearrangement, comprising: The reaction is carried out by contacting cyclohexanone oxime with a catalyst, characterized in that the catalyst comprises a hierarchical porous heteroatom molecular sieve as described in any one of claims 1 to 56.

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