A multi-level pore heteroatom molecular sieve, a preparation method thereof and application thereof in a caprolactam reaction

Abstract

The present disclosure relates to a multi-level pore heteroatomic molecular sieve, a preparation method thereof, and an application thereof in a caprolactam reaction. The multi-level pore heteroatomic molecular sieve has the following Raman spectrum characteristics: the peak intensity of a spectrum peak at a wave number of 1120±5 cm ‑1 in a 325 nm Raman spectrum of the multi-level pore heteroatomic molecular sieve is recorded as N1; the peak intensity of a spectrum peak at a wave number of 960±5 cm ‑1 in the 325 nm Raman spectrum of the multi-level pore heteroatomic molecular sieve is recorded as N2; the peak intensity of a spectrum peak at a wave number of 635±5 cm ‑1 in the 325 nm Raman spectrum of the multi-level pore heteroatomic molecular sieve is recorded as N3; X1 defined by the following formula (1) is any numerical value between 0.2 and 1.2: X1=N1 / N3 formula (1); X2 defined by the following formula (2) is any numerical value between 0.4 and 1.6: X2=N2 / N3 formula (2). The present disclosure can significantly improve the caprolactam selectivity of a cyclohexanone oxime gas phase Beckmann rearrangement reaction and the service life of a catalyst.

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 preparation of caprolactam. Background Technology

[0002] In recent years, heterogeneous catalysts have attracted great attention in industrial production processes due to their advantages such as reusability and easy separation. Molecular sieve crystals have a uniform pore structure, a huge specific surface area, and can allow catalytically active metals to exchange 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 structured molecular sieves possess three-dimensional ten-membered ring channels with a pore size of approximately 0.55 nm. They exhibit high thermal stability and catalytic activity, and their unique channel structure and surface acidity / alkalinity make them widely used in the petrochemical industry. Heteroatom molecular sieves can be produced by partially or completely replacing silicon or aluminum in the molecular sieve framework with heteroatoms other than silicon and aluminum. These heteroatoms have a modulating effect on the acidity, acidity, pore size, and channel structure of the molecular sieve, giving it unique properties.

[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 instability of the silanol active centers in pure silica molecules, they are easily deactivated by heat and alkaline byproducts. Therefore, it is necessary to introduce a new active center to enhance the catalyst's resistance to deactivation.

[0005] Baojun Li's research group (RSC Adv., 2013, 3, 20811–20815) synthesized heteroatom molecular sieves with different particle sizes by adding S-1 and TS-1 molecular sieves as seed crystals during the molecular sieve crystallization process. These sieves were used for the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime. However, the conversion rate of these sieves decreased to 95% after 6 hours, and the selectivity stabilized at 86%, indicating unsatisfactory reaction performance. Ferdi Schüth et al. (Microporous and Mesoporous Materials, 2009, 117, 228–232) added a 1,7-dichlorooctamethyltetraoxysilane oxidizing agent to create pores during the synthesis of heteroatom molecular sieves, obtaining heteroatom molecular sieves with hierarchical pores. These sieves maintained a caprolactam yield of 1.6 mmol CPL g after 30 hours of reaction. -1 cat h -1 .

[0006] Therefore, 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 preparation of caprolactam, which can significantly improve the caprolactam selectivity and catalyst lifetime in the gas-phase Beckmann rearrangement of cyclohexanone oxime.

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

[0009] The wavenumber of the 325 nm Raman spectrum of the hierarchical porous heteroatom molecular sieve was 1120 ± 5 cm⁻¹. -1 The peak intensity at the specified location is denoted as N1;

[0010] The wavenumber of the 325 nm Raman spectrum of the hierarchical porous heteroatom molecular sieve was 960 ± 5 cm⁻¹. -1 The peak intensity at the specified location is denoted as N2;

[0011] The wavenumber of the 325 nm Raman spectrum of the hierarchical porous heteroatom molecular sieve was 635 ± 5 cm⁻¹. -1 The peak intensity at the specified location is denoted as N3;

[0012] As defined in equation (1), X1 is any value between 0.2 and 1.2:

[0013] X1 = N1 / N3 (Equation 1);

[0014] As defined in equation (2), X2 is any value between 0.4 and 1.6:

[0015] X2 = N2 / N3 Equation (2).

[0016] Optionally, X1 is any value between 0.4 and 0.9; X2 is any value between 0.5 and 1.2.

[0017] Optionally, the molar ratio of silicon atoms to heteroatoms in the hierarchical porous heteroatom molecular sieve is (5-450):1, preferably (10-300):1;

[0018] 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.

[0019] 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.

[0020] Optionally, the hierarchical porous heteroatom molecular sieve has multiple cavity structures within its crystal; wherein the size of a single cavity structure is 3–46 nm, preferably 4–35 nm;

[0021] Preferably, the volume of all the cavity structures accounts for 5-45% of the total volume of the molecular sieve, more preferably 8-42%;

[0022] Optionally, the shape of the cavity structure is selected from one or more of the following: sphere, cube, ellipsoid, and irregular cube.

[0023] 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.

[0024] Optionally, the average particle size of the molecular sieve particles is 0.2–1.0 μm, preferably 0.23–0.62 μm; the BET specific surface area is 280–610 m². 2 / g, preferably 310-580m 2 / g; microporous specific surface area is 240-550m² 2 / g, preferably 250-530m 2 / g; total pore volume is 0.22–0.58 cm³. 3 / g, preferably 0.25~0.55cm 3 / g; mesopore volume is 0.15~0.48cm³ 3 / g, preferably 0.18~0.38cm3 / g;

[0025] 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 0.35 to 0.50, more preferably 0.37 to 0.48.

[0026] The second aspect of this disclosure provides a method for preparing hierarchical porous heteroatom molecular sieves, comprising the following steps:

[0027] S1. Mix the heteroatom source, the first silicon source, the first template agent, water, the silanizing agent, and the structural filler to obtain a reaction mixture;

[0028] 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;

[0029] S3. Mix the molecular sieve intermediate, the second silicon source, the second template agent and water, and then perform a second hydrothermal crystallization treatment and a second calcination treatment in sequence.

[0030] Optionally, in step S1, the molar ratio of heteroatom source: first silicon source: first template agent: water: silanizing agent is (0.005~1.5):1:(0.05~10):(1~50):(0.004~4); preferably (0.008~0.8):1:(0.08~6):(8~35):(0.006~2.5); the weight ratio of the first silicon source in the form of SiO2 to the structural filler is (6~70):1, preferably (8~35):1.

[0031] Optionally, the first silicon source in step S1 and the second silicon source in step S3 are each independently selected from at least one of silicone grease, solid silicone, fumed silica and silica sol; preferably, they are selected from at least one of silicone grease, solid silicone and fumed silica.

[0032] A further preferred option is a silicone grease, wherein the silicone grease has the general formula shown in formula (A):

[0033]

[0034] Where R a R b R c R d Each is independently selected from alkyl groups having 1 to 6 carbon atoms, wherein the alkyl group is branched or straight-chain alkyl; preferably, R a R b R c R dEach is independently selected from straight-chain alkyl groups having 1 to 4 carbon atoms or branched alkyl groups having 3 to 4 carbon atoms; more preferably, the R a R b R c R d Each 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;

[0035] Optionally, the first silicon source and the second silicon source may be the same or different; preferably they are the same.

[0036] 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;

[0037] 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):

[0038] 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.

[0039] 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;

[0040] Optionally, the first template agent and the second template agent may be the same or different, but preferably the same.

[0041] Optionally, in step S1, the heteroatom source is selected from one or more of titanium source, tin source, boron source and zirconium source;

[0042] Preferably, the titanium source is selected from one or more of titanium tetrachloride, titanium sulfate, titanium nitrate, tetraethyl titanate, tetrapropyl titanate, and tetrabutyl titanate;

[0043] 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;

[0044] The boron source is selected from one or more of boric acid, borates and borates;

[0045] 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.

[0046] 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 ;

[0047] 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.

[0048] Optionally, in step S1, the structural filler is selected from one or more of amphiphilic surfactants and hard template agents;

[0049] 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.

[0050] 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;

[0051] 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.

[0052] Optionally, step S1 includes:

[0053] a. Mix the heteroatom source, the first silicon source, the first template agent and water to obtain a silicon hydrolysis sol;

[0054] 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;

[0055] Optionally, the mixing conditions in step a include stirring at 40–90°C for 6–12 hours;

[0056] Optionally, the mixing conditions in step b include stirring at 20–50°C for 2–4 hours;

[0057] Preferably, the first silicon source is an organosilicon grease, and step a further includes a hydrolysis and alcohol removal treatment after mixing the first silicon source, the first template agent and water to obtain the silicon hydrolysate;

[0058] 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.

[0059] Optionally, in step S3, the weight ratio of the second template agent: the second silicon source: water: molecular sieve intermediate is (0.05-5):(0.02-1.5):(2-45):1; preferably (0.07-3.6):(0.05-0.6):(4-35):1.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] Through the above technical solution, this disclosure provides a hierarchical porous heteroatom molecular sieve, its preparation method, and its application in the preparation of caprolactam. The hierarchical porous heteroatom molecular sieve contains abundant framework heteroatoms and has a large number of silanol active centers; and in the 325nm Raman spectrum, it has a 1120±5cm² depth. -1 960±5cm -1 and 635±5cm -1 The peak intensity at the wavenumber position satisfies the range of X1 and X2, indicating that this hierarchical porous heteroatom molecular sieve exhibits excellent catalytic activity and resistance to deactivation. Furthermore, the hierarchical porous structure endows it with advantages such as large specific surface area and pore volume. 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, and can significantly reduce the influence of thermal or alkaline byproducts on the active silanol sites of the molecular sieve, ensuring the stability of the catalyst reaction and extending the catalyst life.

[0065] Other features and advantages of this disclosure will be described in detail in the following detailed description section. Attached Figure Description

[0066] 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:

[0067] Figure 1 The 325 nm UV Raman spectrum of the molecular sieve obtained in Example 1;

[0068] Figure 2 The XRD pattern of the molecular sieve obtained in Example 1;

[0069] Figure 3 Here is a TEM image of the molecular sieve obtained in Example 1;

[0070] Figure 4 Here is an SEM image of the molecular sieve obtained in Example 1;

[0071] Figure 5 The nitrogen adsorption-desorption curve of the molecular sieve obtained in Example 1;

[0072] Figure 6 The infrared hydroxyl spectrum of the molecular sieve obtained in Example 1;

[0073] Figure 7TEM electron microscope image of intermediate TS-1-T of Example 1;

[0074] Figure 8 The XRD pattern of the molecular sieve obtained in Example 10;

[0075] Figure 9 The image shows the XRD pattern of the molecular sieve obtained in Example 11. Detailed Implementation

[0076] 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.

[0077] The first aspect of this disclosure provides a hierarchical porous heteroatom molecular sieve, which has the following Raman spectral characteristics:

[0078] The wavenumber of the 325 nm Raman spectrum of the hierarchical porous heteroatom molecular sieve was 1120 ± 5 cm⁻¹. -1 The peak intensity at the specified location is denoted as N1;

[0079] The wavenumber of the 325 nm Raman spectrum of the hierarchical porous heteroatom molecular sieve was 960 ± 5 cm⁻¹. -1 The peak intensity at the specified location is denoted as N2;

[0080] The wavenumber of the 325 nm Raman spectrum of the hierarchical porous heteroatom molecular sieve was 635 ± 5 cm⁻¹. -1 The peak intensity at the specified location is denoted as N3;

[0081] As defined in equation (1), X1 is any value between 0.2 and 1.2:

[0082] X1 = N1 / N3 (Equation 1);

[0083] As defined in equation (2), X2 is any value between 0.4 and 1.6:

[0084] X2 = N2 / N3 Equation (2).

[0085] This disclosure provides a hierarchical porous heteroatom molecular sieve, which contains abundant framework heteroatoms and has a large number of silanol active centers; and in the 325 nm Raman spectrum, the sieve has a density of 1120±5 cm⁻¹. -1 960±5cm -1 and 635±5cm -1The peak intensity at the wavenumber position satisfies the range of X1 and X2, indicating that this hierarchical porous heteroatom molecular sieve exhibits excellent catalytic activity and resistance to deactivation. Furthermore, the hierarchical porous structure endows it with advantages such as large specific surface area and pore volume. 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, and can significantly reduce the influence of thermal or alkaline byproducts on the active silanol sites of the molecular sieve, ensuring the stability of the catalyst reaction and extending the catalyst life.

[0086] Through extensive experimental research, the inventors of this invention have surprisingly discovered that, in the ultraviolet Raman spectrum (325 nm) of the framework heteroatom molecular sieve, at a wavenumber of 1120±5 cm⁻¹... -1 The spectral peak at the specified location represents the symmetric stretching vibration peak of the framework heteroatoms in this heteroatom zeolite (its peak intensity is denoted as N1), with a value of 960±5 cm⁻¹. -1 The spectral peak at the location represents the asymmetric stretching vibration peak of the framework heteroatom in this heteroatom molecular sieve (its peak intensity is denoted as N2), with a value of 635±5 cm⁻¹. -1 The peak at the position represents the stretching vibration peak of the non-framework heteroatom in the heteroatom molecular sieve (its peak intensity is denoted as N3), and the peak intensities of the above three peaks satisfy the range of X1 defined by equation (1) and X2 defined by equation (2). The heteroatom molecular sieve has suitable characteristics for catalyzing the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime.

[0087] In this disclosure, the ultraviolet Raman spectroscopy test uses conventional testing instruments and methods in the art, and the excitation source wavelength is 325 nm.

[0088] In a preferred embodiment, X1 is any value between 0.4 and 0.9; and X2 is any value between 0.5 and 1.2. 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.

[0089] 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.

[0090] In one embodiment, the molar ratio of silicon atoms to heteroatoms in the hierarchical porous heteroatom molecular sieve is (5-450):1, preferably (10-300):1. This disclosure obtains the molar ratio of heteroatoms to silicon atoms in the molecular sieve using X-ray fluorescence spectroscopy.

[0091] 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 3–46 nm, preferably 4–35 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.

[0092] In this disclosure, the cavity structure and its size in the molecular sieve are obtained by transmission electron microscopy (TEM). In this disclosure, the size of the cavity structure refers to the length between two positions on the cavity wall passing through the center of the cavity structure in a TEM image of the molecular sieve; for example, "the size of a single cavity structure is 3–46 nm" means that the length between two positions on the cavity wall passing through the center of any cavity structure in the molecular sieve is within the range of 3–46 nm.

[0093] In a preferred embodiment, all of the cavity structures account for 5-45% of the total volume of the molecular sieve, more preferably 8-42%;

[0094] Optionally, the shape of the cavity structure is selected from one or more of the following: sphere, cube, ellipsoid, and irregular cube.

[0095] 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.

[0096] Optionally, the average particle size of the molecular sieve particles is 0.2–1.0 μm, preferably 0.23–0.62 μm; the BET specific surface area is 280–610 m². 2 / g, preferably 310-580m 2 / g; microporous specific surface area is 240-550m² 2 / g, preferably 250-530m 2 / g; total pore volume is 0.22–0.58 cm³. 3 / g, preferably 0.25~0.55cm 3 / g; mesopore volume is 0.15~0.48cm³ 3 / g, preferably 0.18~0.38cm 3 / g.

[0097] 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.

[0098] In one specific embodiment, the initial relative pressure (P / P0) at which the hysteresis loop appears is 0.35 to 0.50, preferably 0.37 to 0.48.

[0099] 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.

[0100] The second aspect of this disclosure provides a method for preparing hierarchical porous heteroatom molecular sieves, comprising the following steps:

[0101] S1. Mix the heteroatom source, the first silicon source, the first template agent, water, the silanizing agent, and the structural filler to obtain a reaction mixture;

[0102] 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;

[0103] S3. Mix the molecular sieve intermediate, the second silicon source, the second template agent and water, and then perform a second hydrothermal crystallization treatment and a second calcination treatment in sequence.

[0104] This disclosure provides a method for preparing hierarchical porous heteroatom molecular sieves. Introducing heteroatom sources into the reaction raw materials 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 structure fillers into the molecular sieve synthesis raw 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, supplementing with a second silicon source during the dissolution-recrystallization process provides sufficient silicon to form a shell around the original molecular sieve crystals, protecting the internal cavity structure.

[0105] 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.

[0106] In one embodiment, in step S1, the molar ratio of heteroatom source: first silicon source: first template agent: water: silanizing agent is (0.005~1.5):1:(0.05~10):(1~50):(0.004~4); the silicon source is in the form of SiO2, and the weight ratio of SiO2 to structural filler is (6~70):1.

[0107] In a preferred embodiment, in step S1, the molar ratio of heteroatom source: first silicon source: first template agent: water: silanizing agent is (0.008~0.8):1:(0.08~6):(8~35):(0.006~2.5); the silicon source is in the form of SiO2, and the weight ratio of SiO2 to structural filler is (8~35):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.

[0108] In one embodiment, in step S1, the first 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.

[0109] A further preferred option is a silicone grease, wherein the silicone grease has the general formula shown in formula (A):

[0110]

[0111] 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.

[0112] 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.

[0113] 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.

[0114] 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):

[0115] 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.

[0116] 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.

[0117] In one embodiment, step S1 includes:

[0118] a. Mix heteroatom source, titanium source, silicon source, first template agent and water to obtain silicon hydrolysis sol;

[0119] 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;

[0120] Optionally, the mixing conditions in step a include stirring at 40–90°C for 6–12 hours;

[0121] Optionally, the mixing conditions in step b include stirring at 20–50°C for 2–4 hours.

[0122] In one specific embodiment, the silicon source is an organosilicon grease, and step a further includes a hydrolysis and alcohol removal treatment after mixing the silicon source, the first template agent and water to obtain the silicon hydrolysate;

[0123] Optionally, the conditions for the hydrolysis-induced alcohol removal treatment include: stirring and hydrolyzing at 40–90°C for 6–12 hours; preferably, stirring and hydrolyzing at 60–85°C for 8–10 hours. Preferably, the hydrolysis-induced alcohol removal treatment results in the alcohol content in the silicone hydrolysate of the obtained silicone grease being less than 10 ppm by mass.

[0124] In one embodiment, in step S1, the heteroatom source is selected from one or more of titanium, tin, boron and zirconium sources.

[0125] 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.

[0126] 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;

[0127] The boron source is selected from one or more of boric acid, borates and borates;

[0128] 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.

[0129] 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 .

[0130] 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.

[0131] In one embodiment, in step S1, the structural filler is selected from one or more of amphiphilic surfactants and hard template agents.

[0132] 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.

[0133] 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.

[0134] 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.

[0135] The reagents involved in this disclosure can all be purchased through ordinary channels or prepared by methods known in the art.

[0136] 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;

[0137] 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.

[0138] 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.

[0139] 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.

[0140] 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.

[0141] 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.

[0142] In one embodiment, in step S3, the selection range of the second silicon source is the same as that of the first silicon source, and will not be repeated here. In this disclosure, the first silicon source and the second silicon source can be the same or different; preferably, the first silicon source and the second silicon source are the same silicon source reagent.

[0143] In one embodiment, in step S3, the weight ratio of the second template agent: the second silicon source: water: the molecular sieve intermediate is (0.05-5):(0.02-1.5):(2-45):1; preferably (0.07-3.6):(0.05-0.6):(4-35):1. By preparing the sieve according to the preferred weight ratio in this embodiment, a molecular sieve with higher catalytic activity can be obtained.

[0144] 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;

[0145] 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.

[0146] 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.

[0147] 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.

[0148] In one specific embodiment, after the second hydrothermal crystallization treatment, the method further includes a second filtration treatment, a second drying treatment, and then a second calcination treatment. The second drying treatment is performed at a temperature of 50–120°C for 1–12 hours.

[0149] 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.

[0150] 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.

[0151] 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 .

[0152] The present disclosure will be described in detail below through examples.

[0153] The ultraviolet Raman spectra of the samples were measured using a LabRAMR UV-NIR confocal micro Raman spectrometer with an excitation wavelength of 325 nm, at room temperature and ambient pressure. The spectral acquisition range was 170–1200 cm⁻¹. -1 Each sampling session lasts 300 seconds, and a total of two sampling sessions are conducted to eliminate fluorescence interference.

[0154] 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°.

[0155] 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).

[0156] 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).

[0157] 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.

[0158] The infrared hydroxyl spectrum (IR-OH) of the samples was measured on a Nicolet 8210 Fourier transform infrared spectrometer, with a measurement range of 400–4000 cm⁻¹. -1 .

[0159] 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.

[0160] The reagents used in the following examples and comparative examples were all purchased through conventional channels.

[0161] Example 1

[0162] (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.

[0163] (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.

[0164] (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).

[0165] (4) Mix 10g of TS-1-T sample, 3g of tetraethyl silicate, 20g of 25% by weight tetrapropylammonium hydroxide (TPAOH) aqueous solution and 40g of water evenly (the weight ratio of second template agent: second silicon source: water: molecular sieve intermediate is 0.5:0.3:5.5:1), transfer to a stainless steel closed reactor, and crystallize at 170℃ for 24h to obtain the sample. Filter and wash the obtained sample, dry it at 110℃ for 3 hours, and then calcine it in a muffle furnace at 550℃ for 3 hours to obtain sample STS-1.

[0166] The structural parameter characterization results of sample STS-1 are listed in Table 2;

[0167] The UV-Raman spectrum of sample STS-1 is as follows Figure 1 As shown in the figure, it can be seen that the sample operates at a wavenumber of 1120 cm⁻¹. -1 960cm -1 And 635cm -1 The positions have Raman spectral peaks respectively, and the intensity values ​​of each peak are: N1 is 518, N2 is 579, and N3 is 788. The values ​​of X1 and X2 calculated by Equation (1) and Equation (2) are listed in Table 3.

[0168] The XRD pattern of sample STS-1 is as follows Figure 2 As shown, this indicates that the hierarchical porous heteroatom molecular sieve sample has an MFI topology.

[0169] TEM electron microscope image of sample STS-1 as follows Figure 3 As shown in the figure, the molecular sieve has a hierarchical porous structure with multiple cavities within the crystal; and the size of a single cavity structure is measured and calculated to be 6–37 nm.

[0170] SEM images of sample STS-1 are shown below. Figure 4 As shown in the figure, the molecular sieve consists of uniform ellipsoidal particles.

[0171] The BET curve of sample STS-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 0.43.

[0172] The infrared hydroxyl spectrum of sample STS-1 is as follows: Figure 6 As shown, distinct silanol active centers can be observed, with the 3740 cm⁻¹ site being particularly prominent. -1 The spectral peak at position 3690 cm⁻¹ represents a terminal hydroxyl group, indicating a side reaction center. -1 The spectral peak at position 3550 cm⁻¹ is for the ortho-hydroxyl group; -1 The spectral peak at the position is a nested silanol, indicating the main reaction center;

[0173] TEM of the intermediate product TS-1-T that has not undergone dissolution and recrystallization, as shown in... Figure 7 As shown, Figure 7 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.

[0174] Comparative Example 1

[0175] The method of Example 1 is used, but the difference from Example 1 is that no silanizing agent or structural filler is added, nor is a second silicon source added. The resulting product is denoted as D-1. Its preparation conditions are listed in Table 1, and the characterization results of the obtained molecular sieve are listed in Table 2.

[0176] Comparative Example 2

[0177] This comparative example shows the preparation of conventional titanium-silicon molecular sieves according to existing methods (Zeolites, 1992, Vol. 12, pp. 943-950).

[0178] 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.

[0179] Comparative Example 3

[0180] 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:

[0181] (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.

[0182] (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.

[0183] (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.

[0184] Examples 2-9

[0185] Multilevel porous heteroatom molecular sieves were prepared according to the method of Example 1, except that the ratio and synthesis conditions were changed to obtain multilevel porous heteroatom molecular sieve samples denoted as STS-2 to STS-9; the preparation conditions are listed in Table 1, and the characterization results of the obtained molecular sieves are listed in Table 2.

[0186] Example 10

[0187] A hierarchical porous heteroatom molecular sieve with a MEL structure was prepared according to the method of Example 1, except that the template agent was changed to tetrabutylammonium hydroxide (TBAOH). The resulting hierarchical porous heteroatom molecular sieve sample was designated STS-10. The preparation conditions are listed in Table 1, and the characterization results of the obtained molecular sieve are listed in Table 2. The XRD pattern of STS-10 is shown in Table 2. Figure 8 As shown, this indicates that STS-10 is a MEL structure.

[0188] Example 11

[0189] Hierarchical porous β-zeolite was prepared according to the method of Example 1, except that the ratio and template agent were changed. Tetraethylammonium hydroxide (TEAOH) was used as the template agent to prepare a BEA topology, resulting in a hierarchical porous heteroatom zeolite sample designated STS-11. The preparation conditions are listed in Table 1, and the characterization results of the obtained zeolite are listed in Table 2. The XRD pattern of STS-11 is shown in Table 2. Figure 9 As shown, this indicates that STS-11 is a BEA structure.

[0190] Example 12

[0191] The hierarchical porous heteroatom molecular sieve was prepared according to the method of Example 1, but differed from that in Example 1 in that:

[0192] 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.

[0193] 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.

[0194] The obtained hierarchical porous heteroatom molecular sieve sample is designated as STS-12; the characterization results of the obtained molecular sieve are listed in Table 2.

[0195] Table 1

[0196]

[0197]

[0198] In Table 1, TPAOH is tetrapropylammonium hydroxide, TBAOH is tetrabutylammonium hydroxide, and TEAOH is tetraethylammonium hydroxide; 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.

[0199] Table 2

[0200]

[0201] Test case

[0202] 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:

[0203] 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.

[0204] 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.

[0205] 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%;

[0206] Caprolactam selectivity (mol%) = (mol percentage of caprolactam in the product) / (100 - mol percentage of cyclohexanone oxime in the product) × 100%;

[0207] Cyclohexanone oxime conversion reduction rate (%) = (24h cyclohexanone conversion rate - 200h cyclohexanone conversion rate) / 24h cyclohexanone conversion rate × 100%;

[0208] The decrease in caprolactam selectivity (%) = (24h caprolactam selectivity - 200h caprolactam selectivity) / 24h caprolactam selectivity × 100%.

[0209] Table 3

[0210]

[0211] According to the data in Table 3 above:

[0212] Compared with the molecular sieves D-1 to D-3 prepared by Comparative Examples 1 to 3, the molecular sieves STS-1 to STS-12 prepared by the publicly disclosed method have Raman spectra in the range of X1 (0.2 to 1.2) and X2 (0.4 to 1.6). Molecular sieves STS-1 to STS-12 have higher catalytic activity in the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime, higher cyclohexanone oxime conversion and caprolactam selectivity, and higher catalytic stability under long-term reaction conditions (200 h).

[0213] Furthermore, the X1 of the molecular sieves STS-1 to STS-8 and STS-10 to STS-11 prepared in the examples is in the range of 0.4 to 0.9, and the X2 is in the range of 0.5 to 1.2. Compared with molecular sieves STS-9 and STS-12, the cyclohexanone oxime conversion rate and caprolactam selectivity are higher in the reaction using molecular sieves STS-1 to STS-8 and STS-10 to STS-11, and the catalytic stability is higher under long-term reaction conditions (200 h).

[0214] Comparing Example 1 with Example 9, Example 1 prepared molecular sieves according to the raw material addition ratio in the preferred embodiment. The obtained molecular sieve STS-1 had higher cyclohexanone oxime conversion and caprolactam selectivity in the catalytic reaction, and higher catalytic stability under long reaction conditions (200h).

[0215] Comparing Example 1 with Example 12, Example 1 prepared a molecular sieve according to the reaction conditions in the preferred embodiment. The obtained molecular sieve STS-1 had higher cyclohexanone oxime conversion and caprolactam selectivity in the catalytic reaction, and higher catalytic stability under long-term reaction conditions (200h).

[0216] 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.

[0217] 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.

[0218] 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 Raman spectral characteristics: The wavenumber of the 325 nm Raman spectrum of the hierarchical porous heteroatom molecular sieve was 1120 ± 5 cm⁻¹. -1 The peak intensity at the specified location is denoted as N1; The wavenumber of the 325 nm Raman spectrum of the hierarchical porous heteroatom molecular sieve was 960 ± 5 cm⁻¹. -1 The peak intensity at the specified location is denoted as N2; The wavenumber of the 325 nm Raman spectrum of the hierarchical porous heteroatom molecular sieve was 635 ± 5 cm⁻¹. -1 The peak intensity at the specified location is denoted as N3; As defined in equation (1), X1 is any value between 0.2 and 1.2: X1=N1 / N3 (1); As defined in equation (2), X2 is any value between 0.4 and 1.6: X2=N2 / N3 (2); The hierarchical porous heteroatom molecular sieve is prepared by a method including the following steps: S1. Mix the heteroatom source, the first silicon source, the first template agent, water, the silanizing agent, and the 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 silicon source, the second template agent 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 0.4 and 0.9; X2 is any value between 0.5 and 1.

2.

3. The hierarchical porous heteroatom molecular sieve according to claim 1, characterized in that, The molar ratio of silicon atoms to heteroatoms in the multi-level porous heteroatom molecular sieve is (5~450):

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 (10~300):

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 3~46 nm.

10. The hierarchical porous heteroatom molecular sieve according to claim 9, characterized in that, The size of the individual cavity structure is 4~35nm.

11. The hierarchical porous heteroatom molecular sieve according to claim 9, characterized in that, The volume of all the cavity structures described accounts for 5-45% 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 described accounts for 8-42% 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 ​​280~610 m². 2 / g; Microporous specific surface area is 240~550m² 2 / g; total pore volume is 0.22~0.58cm³. 3 / g; mesopore volume is 0.15~0.48cm³ 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 0.23~0.62μm and a BET specific surface area of ​​310~580m². 2 / g; Microporous specific surface area is 250~530m² 2 / g; total pore volume is 0.25~0.55cm³. 3 / g; mesopore volume is 0.18~0.38cm³ 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 0.35~0.

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 0.37~0.

48.

20. The hierarchical porous heteroatom molecular sieve according to claim 1, characterized in that, In step S1, the molar ratio of heteroatom source: first silicon source: first template agent: water: silanizing agent is (0.005~1.5):1:(0.05~10):(1~50):(0.004~4); the first silicon source is in the form of SiO2, and the weight ratio of SiO2 to structural filler is (6~70):

1.

21. The hierarchical porous heteroatom molecular sieve according to claim 20, characterized in that, In step S1, the molar ratio of heteroatom source: first silicon source: first template agent: water: silanizing agent is (0.008~0.8):1:(0.08~6):(8~35):(0.006~2.5); the first silicon source is in the form of SiO2, and the weight ratio of SiO2 to structural filler is (8~35):

1.

22. The hierarchical porous heteroatom molecular sieve according to claim 1, characterized in that, In step S1, the first silicon source and in step S3, the second silicon source are each independently selected from at least one of silicone grease, solid silicone, silica, and silica sol.

23. The hierarchical porous heteroatom molecular sieve according to claim 22, characterized in that, The first silicon source and the second silicon source are each independently selected from at least one of silicone grease, solid silicone and silica.

24. The hierarchical porous heteroatom molecular sieve according to claim 23, characterized in that, The first silicon source and the second silicon source are each independently an organosilicone grease, and the organosilicone grease has the general formula shown in 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 26, 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 22, characterized in that, The first silicon source and the second silicon source may be the same or different.

29. The hierarchical porous heteroatom molecular sieve according to claim 28, characterized in that, The first silicon source and the second silicon source are the same.

30. 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.

31. The hierarchical porous heteroatom molecular sieve according to claim 30, 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.

32. The hierarchical porous heteroatom molecular sieve according to claim 31, 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.

33. The hierarchical porous heteroatom molecular sieve according to claim 32, 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.

34. The hierarchical porous heteroatom molecular sieve according to claim 33, 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.

35. 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.

36. 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.

37. The hierarchical porous heteroatom molecular sieve according to claim 36, characterized in that, The first template agent and the second template agent are the same.

38. The hierarchical porous heteroatom molecular sieve according to claim 1, characterized in that, In step S1, the heteroatom source is selected from one or more of titanium source, tin source, boron source and zirconium source.

39. The hierarchical porous heteroatom molecular sieve according to claim 38, 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.

40. The hierarchical porous heteroatom molecular sieve according to claim 39, characterized in that, The tin source is tin chloride pentahydrate.

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 44, 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 heteroatom source, the first silicon source, the 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 first silicon source is an organosilicon grease. In step a, after mixing the first 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 template agent, the second silicon source, water, and the molecular sieve intermediate is (0.05~5):(0.02~1.5):(2~45):

1.

54. The hierarchical porous heteroatom molecular sieve according to claim 53, characterized in that, In step S3, the weight ratio of the second template agent, the second silicon source, water, and the molecular sieve intermediate is (0.07~3.6):(0.05~0.6):(4~35):

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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