Preparation methods of microspherical all-silica-1 molecular sieve catalysts, and preparation methods of catalysts and caprolactam.

Abstract

This invention relates to the field of catalysts and discloses a method for preparing a microsphere-type all-silica-1 molecular sieve catalyst, a method for preparing the catalyst and caprolactam, comprising: (1) mixing a molecular sieve mother liquor, an organosilicate, an organic template agent, and KOH to obtain a colloidal mixture; (2) subjecting the colloidal mixture to a crystallization reaction; (3) performing solid-liquid separation on the crystallized product obtained in step (2) to obtain a wet molecular sieve material and a crystallization mother liquor; (4) optionally concentrating the crystallization mother liquor and then returning to step (1) to provide the molecular sieve mother liquor; (5) mixing the wet molecular sieve material with a binder and slurrying, then performing spray molding and calcination to obtain a catalyst precursor; (6) contacting the catalyst precursor with an alkaline buffer solution containing ammonium salt, ammonia, magnesium salt, and bromide salt, and then drying. The prepared microsphere-type all-silica-1 molecular sieve catalyst can achieve long-cycle, continuous production of caprolactam in a fluidized bed reaction system, with good economic efficiency.

Description

Technical Field

[0001] This invention relates to the field of catalysts, specifically to a method for preparing a microspherical all-silica-1 molecular sieve catalyst, and a method for preparing the catalyst and caprolactam. Background Technology

[0002] Silicalite-1 molecular sieves (abbreviated as all-silica-1 molecular sieves) were first successfully synthesized in 1978 by EMFlanigen et al. of UCC, and belong to the last member of the "Pentasil" family. All-silica-1 molecular sieves are aluminum-free all-silica-1 molecular sieves with a ZSM-5 structure. They are the simplest molecular sieves in the ZSM-5 molecular sieve family, with a framework containing only silicon and oxygen atoms, and the basic structural unit being the SiO4 tetrahedron. The synthesis of all-silica-1 molecular sieves generally employs the traditional organic raw material hydrothermal method. Silicon sources can include solid silica, silica sol, silica fume, tetraethyl orthosilicate (TEOS), etc. Template agents often include tetrapropylammonium hydroxide (TPAOH), low-carbon hydrocarbon quaternary ammonium salts or mixtures of both, amine compounds, etc., and crystallization is carried out at 170°C for three days. Research groups from Union Carbide Corporation (UCC), Stety of Sweden, and P. Ratnasamy of India have conducted research in this area. They mainly apply the all-silica-1 molecular sieve to the research field of inorganic microporous materials.

[0003] Caprolactam is a major raw material for the production of three major series of products: nylon, industrial tire cord, and nylon engineering plastics, and its demand has remained consistently high. Caprolactam is generally obtained through the Beckmann rearrangement reaction of cyclohexanone oxime. Currently, the industrial process typically employs a liquid-phase rearrangement process using concentrated sulfuric acid or fuming sulfuric acid as a catalyst. This process accounts for approximately 90% of the world's total caprolactam production; however, it consumes large amounts of sulfuric acid and ammonia, typically producing 1.3 to 1.8 tons of ammonium sulfate as a byproduct for every ton of caprolactam produced, resulting in high production costs. Furthermore, the use of sulfuric acid causes equipment corrosion and environmental pollution.

[0004] CN1256967A discloses a method for preparing a molecular sieve catalyst containing an MFI structure for the conversion of cyclohexanone oxime to caprolactam. The basic premise of this method is to use acidic silica gel as a binder. Specifically, the method involves mixing a silica oligomer obtained by acidic hydrolysis of alkoxysilanes with an aqueous or alcohol-water dispersion of submicron particles of an MFI-structured molecular sieve at pH ≤ 5, followed by emulsification, solidification, washing, and calcination to obtain gel microspheres.

[0005] Due to the significant difficulties in extrusion molding, tablet molding, and even roll forming of the all-silica-1 molecular sieve, even after molding, the crushing strength of the catalyst is far from ideal (<60N / cm or <1kg / particle), making industrial application impossible. Summary of the Invention

[0006] The purpose of this invention is to overcome the problems of unsatisfactory catalytic activity and strength and high catalyst preparation cost of existing cyclohexanone oxime gas-phase Beckmann rearrangement catalysts. This invention provides a method for preparing microspherical all-silica-1 molecular sieve catalysts, as well as a method for preparing the catalyst and caprolactam. This preparation method has high raw material utilization and good economy, and the obtained microspherical all-silica-1 molecular sieve catalyst has the characteristics of low wear index and good catalytic activity.

[0007] To achieve the above objectives, the first aspect of the present invention provides a method for preparing a microspherical all-silica-1 molecular sieve catalyst, the method comprising:

[0008] (1) Molecular sieve mother liquor, organosilicate, organic template agent and KOH are mixed to obtain colloidal mixture; wherein, the amount of molecular sieve mother liquor and organosilicate is satisfied, and the mass ratio of SiO2 in molecular sieve mother liquor to organosilicate based on SiO2 is 0.01-0.2:1;

[0009] The composition of the colloidal mixture satisfies that the molar ratio of SiO2, KOH, organic template agent, and water is 1:(0.01-0.1):(0.04-0.15):(15-45);

[0010] (2) The colloidal mixture is subjected to a crystallization reaction;

[0011] (3) The crystallization product obtained in step (2) is subjected to solid-liquid separation to obtain molecular sieve wet material and crystallization mother liquor;

[0012] (4) The crystallization mother liquor is optionally concentrated, and then the process is returned to step (1) to provide the molecular sieve mother liquor;

[0013] (5) The molecular sieve wet material is mixed with a binder and pulped, then spray-molded and calcined to obtain a catalyst precursor;

[0014] (6) The catalyst precursor is contacted with an alkaline buffer solution containing ammonium salt, ammonia water, magnesium salt and bromide salt, and then dried.

[0015] The second aspect of the present invention provides a microspherical all-silica-1 molecular sieve catalyst prepared by the above preparation method.

[0016] The third aspect of the present invention provides a method for preparing caprolactam, the method comprising: reacting cyclohexanone oxime with a catalyst in the presence of a solvent under the conditions of a gas-phase Beckmann rearrangement reaction of cyclohexanone oxime, wherein the catalyst is the microsphere-type all-silica-1 molecular sieve catalyst described in the second aspect.

[0017] Preferably, the contact takes place in a fluidized bed reactor.

[0018] By introducing the mother liquor of molecular sieves into the crystallization synthesis of all-silica-1 molecular sieves through the above technical solutions, the synthesis yield of molecular sieves can be improved, the crystallization time shortened, and the synthesis cost of molecular sieves reduced. Simultaneously, this invention breaks through the technical biases in conventional all-silica-1 molecular sieve synthesis by using KOH as an alkali source in combination with an organic template agent, and by reusing the mother liquor of molecular sieves, the amount of organic template agent used can be further effectively reduced, thus reducing the raw material cost of catalyst synthesis. Then, through spray molding, microsphere-type all-silica-1 molecular sieve catalysts with high strength and wear resistance are obtained. In a fluidized bed reaction system, the microsphere-type all-silica-1 molecular sieve catalyst prepared by this invention is used for the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime to prepare caprolactam, enabling long-cycle, continuous production of caprolactam with good economic efficiency. Attached Figure Description

[0019] Figure 1 This is the X-ray diffraction pattern of the all-silica-1 molecular sieve raw powder prepared in Example 1. Detailed Implementation

[0020] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0021] The first aspect of this invention provides a method for preparing a microspherical all-silica-1 molecular sieve catalyst, the method comprising:

[0022] (1) Molecular sieve mother liquor, organosilicate, organic template agent and KOH are mixed to obtain colloidal mixture; wherein, the amount of molecular sieve mother liquor and organosilicate is satisfied, and the mass ratio of SiO2 in molecular sieve mother liquor to organosilicate based on SiO2 is 0.01-0.2:1;

[0023] The composition of the colloidal mixture satisfies that the molar ratio of SiO2, KOH, organic template agent, and water is 1:(0.01-0.1):(0.04-0.15):(15-45);

[0024] (2) The colloidal mixture is subjected to a crystallization reaction;

[0025] (3) The crystallization product obtained in step (2) is subjected to solid-liquid separation to obtain molecular sieve wet material and crystallization mother liquor;

[0026] (4) The crystallization mother liquor is optionally concentrated, and then the process is returned to step (1) to provide the molecular sieve mother liquor;

[0027] (5) The molecular sieve wet material is mixed with a binder and pulped, then spray-molded and calcined to obtain a catalyst precursor;

[0028] (6) The catalyst precursor is contacted with an alkaline buffer solution containing ammonium salt, ammonia water, magnesium salt and bromide salt, and then dried.

[0029] In this invention, the "molecular sieve mother liquor" mentioned in step (1) can be a liquid mixture obtained by solid-liquid separation after conventional all-silicon molecular sieve crystallization synthesis, or it can be provided by the crystallization mother liquor mentioned in step (4). By controlling the proportion of molecular sieve mother liquor reuse and the composition of the colloidal mixture, it is possible to prepare all-silicon molecular sieves with MFI topology structure with a lower amount of organic template agent. This is beneficial to reducing the consumption of raw materials, especially expensive organic template agents, and can effectively reduce environmental pollution. At the same time, since the presence of molecular sieve microcrystals in the mother liquor can act as seed crystals, it is beneficial to shorten the crystallization time, improve the relative crystallinity and yield of the molecular sieve, and further improve the catalytic activity of the obtained catalyst.

[0030] According to some preferred embodiments of the present invention, the molecular sieve mother liquor includes an organic template agent, silicon species, water, and optionally KOH.

[0031] Preferably, the molecular sieve mother liquor contains 5-20 wt% organic template agent, preferably 6-10 wt%, 1-10 wt% silicon species (calculated as SiO2), preferably 1.5-5 wt%, 60-90 wt% water, preferably 65-85 wt%, and 0.1-1 wt% KOH, preferably 0.2-0.8 wt%. The silicon species in the molecular sieve mother liquor exist in the form of SiO2, silicic acid and its oligomers, and molecular sieve microcrystals. In this invention, the silicon species in the molecular sieve mother liquor refer to the total amount of silicon element (calculated as SiO2) in the molecular sieve mother liquor.

[0032] According to the present invention, the molecular sieve mother liquor may also contain low-carbon alcohols, which may originate from the hydrolysis of organosilicon esters during crystallization or alcohols additionally introduced during conventional all-silica molecular sieve crystallization. The present invention does not impose any particular limitation thereon. Preferably, the alcohol content in the molecular sieve mother liquor is 1-15 wt%.

[0033] According to some preferred embodiments of the present invention, the molar ratio of alcohol to SiO2 in the colloidal mixture is (4-9):1. It is understood that the mixing process in step (1) may or may not involve the addition of additional alcohol, such that the alcohol in the colloidal mixture is entirely supplied by the molecular sieve mother liquor, or by the molecular sieve mother liquor and any additional alcohol, as long as the above molar ratio range is met.

[0034] In a preferred embodiment, no additional alcohol is introduced during the mixing process described in step (1).

[0035] According to some preferred embodiments of the present invention, in the initial synthesis process, a molecular sieve mother liquor is first prepared, and then the process is continuously carried out according to the aforementioned method. Preferably, the method for preparing the molecular sieve mother liquor includes:

[0036] a. Mix organosilicate, organic template agent, KOH and water to obtain a colloidal mixture;

[0037] The composition of the colloidal mixture satisfies that the molar ratio of SiO2, KOH, organic template agent, and water is 1:(0.01-0.1):(0.04-0.15):(15-45);

[0038] b. Perform a crystallization reaction on the colloidal mixture;

[0039] c. Perform solid-liquid separation on the crystallized product obtained in step (2) to obtain crystallization mother liquor;

[0040] d. The crystallization mother liquor is optionally concentrated to obtain molecular sieve mother liquor.

[0041] The selection range of materials and crystallization conditions in the above-mentioned molecular sieve mother liquor preparation process are the same as those in the preparation method of MFI topological structure all-silica molecular sieves, which will be described in detail later.

[0042] According to some preferred embodiments of the present invention, the amounts of the molecular sieve mother liquor and the organosilicate are such that the mass ratio of SiO2 in the molecular sieve mother liquor to the mass ratio of the organosilicate based on SiO2 is 0.02-0.15:1, for example, typical but not limiting mass ratios such as 0.02:1, 0.05:1, 0.1:1, 0.15:1, or a range between the two. In the above preferred embodiments, it is beneficial to further improve the relative crystallinity of the molecular sieve.

[0043] Preferably, the composition of the colloidal mixture satisfies the following molar ratio: SiO2, KOH, organic template agent, and water is 1:(0.02-0.08):(0.08-0.2):(20-40). Adopting the above preferred embodiment helps to reduce the amount of organic template agent used while ensuring the synthesis quality of the molecular sieve. In this invention, the SiO2 in the colloidal mixture refers to the sum of the molar amounts of silicon in the molecular sieve mother liquor (calculated as SiO2) and the molar amounts of silicon in the organosilicate (calculated as SiO2). The water in the colloidal mixture can be entirely derived from the molecular sieve mother liquor and water introduced from other raw materials (e.g., organic template agent), or a small amount of water can be added to adjust the balance of the molecular sieve synthesis molar ratio. Those skilled in the art can adjust this according to actual needs.

[0044] According to the present invention, a higher crystallization temperature and a shorter crystallization time are preferably used for the crystallization in step (2). Preferably, in step (2), the crystallization temperature is 95-150°C, more preferably 100-150°C, and the time is 0.5-5 days, more preferably 1-5 days. By adopting the above-mentioned preferred embodiment, with the introduction of appropriate KOH and molecular sieve mother liquor, combined with high-temperature rapid crystallization, it is beneficial to improve the crystallinity of the molecular sieve, thereby further improving the stability of the catalyst.

[0045] According to the present invention, preferably, the silicon source is methyl orthosilicate and / or ethyl orthosilicate, more preferably ethyl orthosilicate.

[0046] In this invention, the silicon source can be obtained commercially. In commercially available organosilicone esters, in addition to the effective components, impurities such as alcohols may also be present. The inventors of this invention have found in experiments that selecting a silicon source with a purity of not less than 98wt%, a platinum-cobalt color of not more than 20mg / L, and a Cl ion concentration of not more than 50ppm as a raw material is beneficial to improving the selectivity of the catalyst.

[0047] In this invention, the purity of the silicon source refers to the content of the effective component in the silicon source. For example, when the effective component of the silicon source is tetraethyl orthosilicate, its purity refers to the mass fraction of tetraethyl orthosilicate in the silicon source.

[0048] The platinum-cobalt colorimetric method uses the color exhibited in 1 L of water containing 1 mg of Pt(Ⅳ) and 2 mg of cobalt chloride hexahydrate(Ⅱ) as a standard unit of colorimetry, generally referred to as 1 degree. In this invention, following the platinum-cobalt colorimetric method, a set of standard colors of 2, 4, 6, 8, 10, 12, 14, 16, 18, and 20 degrees are prepared, and then compared to determine the colorimetry of the silicon source.

[0049] According to the present invention, the organic template agent can be a conventional choice in the art. Preferably, the organic template agent is a quaternary ammonium base compound, preferably tetrapropylammonium hydroxide and / or tetraethylammonium hydroxide, and more preferably tetrapropylammonium hydroxide.

[0050] As is known to those skilled in the art, commercially available alkyl quaternary ammonium bases typically contain small amounts of sodium ions. In the prior art, when using organic bases as template agents alone to synthesize all-silica-1 molecular sieves, the requirements for sodium ions in the alkyl quaternary ammonium bases are quite strict, typically requiring 5-10 ppm. In this invention, by introducing KOH, the requirements for sodium ion content in the alkyl quaternary ammonium bases can be relaxed, and high-quality all-silica-1 molecular sieves can still be synthesized even when the sodium ion content exceeds 10 ppm.

[0051] According to the present invention, preferably, the bromide ion content in the organic template agent is less than 1.5 wt%, and more preferably 0.5-1.5 wt%. The inventors of the present invention have discovered that using an organic template agent containing a certain amount of bromide ions as a synthetic raw material, such as tetrapropylammonium hydroxide containing a certain amount of tetrapropylammonium bromide, is beneficial to further improve the selectivity of caprolactam. The reason for this may be that the bromide present in the organic amine is conducive to the formation of ethyl-ε-caprolactamimide, which can be further converted into caprolactam through hydrolysis, ultimately resulting in improved catalyst selectivity.

[0052] Preferably, the iron ion content in the organic template agent is not greater than 10 ppm.

[0053] Preferably, the organic template agent contains less than 500 ppm sodium ions, no more than 550 ppm free acid, less than 0.2 wt% carbonate ions, and an APHA color value not exceeding 100. The free acid includes, for example, any one or more of formic acid, acetic acid, and propionic acid.

[0054] According to the present invention, preferably, the mixing in step (1) is carried out under stirring conditions, preferably, the mixing temperature is 10-50°C and the time is 0.5-10h.

[0055] In this invention, to facilitate the adjustment of the molar ratio balance in the colloidal mixture, preferably, in step (4), the crystallization mother liquor is concentrated, and then returned to step (1) to provide the molecular sieve mother liquor. The concentration can be carried out by distillation, with water continuously added during the distillation process. By purifying the active ingredient (silicon source) and unreacted organic template agent in the liquid phase through distillation, the purpose of recycling the molecular sieve mother liquor is achieved, increasing the concentration of organic template agent and silicon oxide, so that the composition of the concentrated crystallization mother liquor meets the above-mentioned definition range of molecular sieve mother liquor.

[0056] Preferably, the concentration conditions in step (4) include a temperature of 50-100°C, preferably 70-90°C.

[0057] According to the present invention, in step (3), the crystallized product obtained in step (2) is subjected to solid-liquid separation, which can be performed using various methods conventionally used in the art. For example, the solid-liquid separation can be performed by membrane filtration, wherein the pore size of the filter membrane used in the membrane filtration is preferably no greater than 200 nm, and more preferably no greater than 100 nm. Preferably, the filter membrane is an inorganic membrane.

[0058] Preferably, the filter membrane is an inorganic membrane.

[0059] According to some preferred embodiments of the present invention, step (5) includes: firstly, optionally washing the wet molecular sieve material to obtain a molecular sieve slurry with a solid content of 20-50% by weight; then mixing the molecular sieve slurry with a binder and stirring to obtain a molecular sieve-binder slurry.

[0060] This invention does not specifically limit the washing process and can employ various washing methods already used in the art. Similarly, this invention does not specifically limit the washing agent used in the washing process; for example, it can be water. The water can be purified water, deionized water, ion-exchanged water, chemically treated water, or any water without anions or cations. In this invention, the washing process can be repeated, and the number of repetitions is not specifically limited; for example, it can be repeated 1-10 times until the pH of the washing water is below 9.4, preferably below 9.2, for example, a pH value of 8.5-9.2. Preferably, the temperature of the washing water is 20-80°C.

[0061] Preferably, the solid content of the molecular sieve slurry is 20-50% by weight, more preferably 25-45% by weight. In this preferred case, it is more beneficial to improve the performance of the obtained catalyst.

[0062] According to the present invention, the solid content of the molecular sieve-binder slurry obtained by mixing and pulping the wet molecular sieve material with the binder is 20-60% by weight, preferably 30-50% by weight. In this preferred case, it is more conducive to spray molding, resulting in a lower catalyst attrition index.

[0063] According to the present invention, preferably, the weight ratio of molecular sieve slurry or wet molecular sieve material to binder on a dry basis is 1:(0.05-1), more preferably 1:(0.1-0.7).

[0064] In this invention, preferably, the binder is a precursor of silicon oxide, which can be selected from any substance that can be converted into silicon oxide through calcination; this invention does not have any particular limitation on this. Preferably, the precursor of silicon oxide is silica sol and / or fumed silica, and more preferably silica sol.

[0065] In this invention, the spray molding can be performed using conventional methods. Preferably, the spray molding conditions result in particles with a diameter of 20-400 μm, more preferably 40-250 μm.

[0066] According to some preferred embodiments of the present invention, the spray molding conditions include: an inlet temperature of 180-240°C, preferably 200-220°C; and an outlet temperature of 80-120°C, preferably 90-105°C. Under these preferred embodiments, the resulting catalyst exhibits better performance, thereby more effectively improving the conversion rate of cyclohexanone oxime and the selectivity of caprolactam.

[0067] According to the present invention, preferably, the calcination conditions include: a temperature of 200-600℃, more preferably 250-550℃, and a time of 1-20h.

[0068] According to the present invention, preferably, the roasting can be carried out in stages. Specifically, for example, the roasting can include stage 1) and stage 2); the conditions of stage 1) include: temperature of 200-400℃ and time of 2-10h; the conditions of stage 2) include: temperature of 400-600℃ and time of 2-15h. More preferably, stage 1) includes stage 1-1) and stage 1-2), the conditions of stage 1-1) include: temperature of 200-300℃ and time of 2-5h, the conditions of stage 1-2) include: temperature of 300-400℃ and time of 2-5h; stage 2) includes stage 2-1) and stage 2-2), the conditions of stage 2-1) include: temperature of 400-500℃ and time of 2-5h, the conditions of stage 2-2) include: temperature of 500-600℃ and time of 8-13h.

[0069] To further improve the performance of the catalyst product, preferably, the spray molding in step (5) can be carried out with the addition of additives. The additives can be added to the molecular sieve-binder mixture slurry and then the spray molding can be carried out.

[0070] According to some preferred embodiments of the present invention, an additive is also introduced in the pulping process of step (3), the additive being selected from at least one of guar gum powder, graphite, activated carbon, paraffin wax, glycerin, citric acid, starch, polyethylene glycol, polyvinyl alcohol, nitric acid, hydrochloric acid, acetic acid, formic acid, ammonia, tetramethylammonium hydroxide, tetraethylammonium hydroxide and tetrapropylammonium hydroxide.

[0071] Preferably, the amount of additive introduced is 1-5 wt%, based on the dry weight of the molecular sieve in the molecular sieve slurry.

[0072] The inventors of this invention discovered in their research that post-treatment of the calcined product with an alkaline buffer solution containing ammonium salt, ammonia water, magnesium salt, and bromide salt can further improve the catalytic performance of the catalyst, resulting in higher total selectivity and total yield of caprolactam.

[0073] According to the present invention, preferably, the pH of the alkaline buffer solution is 8.5-13.5, more preferably 10-12, and even more preferably 11-11.5.

[0074] Preferably, based on the total amount of the alkaline buffer solution, the content of magnesium salts (calculated as Mg) is 1-500 ppm, more preferably 10-300 ppm; and the content of bromide salts (calculated as Br) is 1-500 ppm, more preferably 5-300 ppm. Using the above-mentioned preferred embodiments is beneficial for further improving the catalytic performance of the prepared catalyst, exhibiting higher total selectivity and total yield of caprolactam than existing all-silica-1 molecular sieve catalysts.

[0075] The present invention has a wide range of choices for the ammonium salt, ammonia water, magnesium salt and bromide salt. Conventional soluble salts in the art can be used, as long as they can provide nitrogen, magnesium and bromine elements.

[0076] Preferably, the ammonium salt is selected from ammonium nitrate and / or ammonium acetate.

[0077] Preferably, the magnesium salt is selected from at least one of magnesium nitrate hexahydrate, magnesium acetate, magnesium chloride, magnesium sulfate, and magnesium hydrogen phosphate.

[0078] Preferably, the bromide salt is tetrapropylammonium bromide.

[0079] The present invention has a wide range of solvent options for the alkaline buffer solution, with water being the preferred solvent.

[0080] Preferably, the alkaline buffer solution includes ammonia, an aqueous solution of ammonium salt, magnesium salt, and bromide salt.

[0081] Preferably, the weight ratio of ammonia water to ammonium salt aqueous solution is 1-3:1.

[0082] Preferably, the concentration of the ammonia solution is 5-30 wt%, more preferably 20-30 wt%.

[0083] Preferably, the concentration of the ammonium salt aqueous solution is 0.5-10 wt%.

[0084] According to the present invention, preferably, the amount of alkaline buffer solution is 500-1500 parts by weight, more preferably 700-1200 parts by weight, relative to 100 parts by weight of the catalyst precursor on a dry basis.

[0085] Preferably, the contact conditions include: a temperature of 50-120°C, more preferably 70-100°C; and a pressure of 0.5-10 kg / cm². 2 The preferred value is 1.5-4 kg / cm². 2 The time is 0.1-5 hours, preferably 1-3 hours.

[0086] According to the present invention, the contact process can be repeated. The present invention does not particularly limit the number of repetitions, but can determine them based on the effectiveness of the contact, with the aim of improving the performance of the catalyst; for example, it can be repeated 1-3 times.

[0087] Preferably, step (6) may further include: solid-liquid separation, washing and drying of the contacted product.

[0088] The present invention does not particularly limit the washing agent used in the washing process; for example, it can be water. Specifically, the washing process may include washing until the pH of the filtrate is 9-10.5. The drying method can be carried out according to any existing technology in the art, such as heating drying, forced air drying, or natural drying. The drying temperature can be 100-120°C, and the drying time can be 10-24 hours. The catalyst obtained by washing and drying the contacted material is beneficial for improving the conversion rate of cyclohexanone oxime and the selectivity of caprolactam when used in the preparation of caprolactam from cyclohexanone oxime.

[0089] The second aspect of the present invention provides a microspherical all-silica-1 molecular sieve catalyst prepared by the above preparation method.

[0090] Preferably, based on the dry weight of the catalyst, the content of all-silica-1 molecular sieve on a dry basis is 70-95 wt%, preferably 80-90 wt%, and the content of binder on an oxide basis is 5-30 wt%, preferably 10-20 wt%.

[0091] Preferably, the particle size of the catalyst is 20-400 μm, and more preferably 40-200 μm.

[0092] The particle size of the catalyst was determined using a Malvern 3000 laser particle size analyzer. The test method was a wet test, with water as the medium, a sample mass concentration of 0.5%-2%, and a scanning speed of 2000 times / second.

[0093] Preferably, the BET specific surface area of ​​the all-silica-1 molecular sieve is 400-500 m².2 / g.

[0094] Preferably, the wear index K of the catalyst is less than 5.

[0095] In this invention, the wear index K of the catalyst is determined on a wear index analyzer according to the RIPP29-90 method in "Analytical Methods for Petrochemical Products" (Yang Cuiding et al., Science Press, 1990).

[0096] The third aspect of the present invention provides a method for preparing caprolactam, the method comprising: reacting cyclohexanone oxime with a catalyst in the presence of a solvent under the conditions of a gas-phase Beckmann rearrangement reaction of cyclohexanone oxime, wherein the catalyst is the microsphere-type all-silica-1 molecular sieve catalyst described in the second aspect;

[0097] Preferably, the contact takes place in a fluidized bed reactor.

[0098] Preferably, the solvent is a C1-C6 fatty alcohol, preferably methanol and / or ethanol.

[0099] Preferably, the molar ratio of the solvent to cyclohexanone oxime is (2-10):1.

[0100] According to the present invention, preferably, the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime is carried out under an inert atmosphere. In the present invention, the inert atmosphere is provided by an inert gas, preferably selected from at least one of nitrogen, helium, argon and neon, and more preferably nitrogen.

[0101] According to the present invention, preferably, the molar ratio of the inert gas to cyclohexanone oxime is 0.1-10:1, more preferably 0.5-10:1, and more preferably 0.5-5:1.

[0102] According to some preferred embodiments of the present invention, the gas-phase Beckmann rearrangement reaction conditions for cyclohexanone oxime include: a weight hourly space velocity (WHSV) of cyclohexanone oxime of 0.5-20 h⁻¹. -1 Preferably 1-10h -1 The reaction temperature is 300-500℃, preferably 350-400℃, and the reaction pressure is 0.05-0.8MPa, preferably 0.1-0.5MPa. Unless otherwise specified, all pressures mentioned in this invention are gauge pressures.

[0103] According to the present invention, preferably, the method further includes mixing cyclohexanone oxime with water, and then contacting the catalyst in the presence of the solvent to carry out a gas-phase Beckmann rearrangement reaction. This preferred embodiment is more advantageous in improving the stability of the catalyst. Preferably, the molar ratio of cyclohexanone oxime to water is 1:(0.01-2.5).

[0104] The present invention will be described in detail below through embodiments.

[0105] In the following examples, unless otherwise specified, the tetraethyl orthosilicate used was purchased from Zhejiang Kaihua Synthetic Materials Co., Ltd., with a purity of 99 wt%, an ethanol content of no more than 1 wt%, a platinum-cobalt color of no more than 20 mg Pt-Co / L, and a Cl ion content of no more than 50 ppm. The tetrapropylammonium hydroxide used was purchased from Guangzhou Dayou Fine Chemical Co., Ltd., with a tetrapropylammonium hydroxide content of 22.5 wt%, a sodium ion content of no more than 500 ppm, a bromide ion content of no more than 1.5 wt%, a carbonate ion content of no more than 0.2 wt%, an APHA color of no more than 100, a potassium ion content of no more than 1.5% wt%, an iron ion content of no more than 10 ppm, an acetic acid content of no more than 500 ppm, and formic acid and propionic acid contents of no more than 50 ppm. The potassium hydroxide used was purchased from Sinopharm Group.

[0106] Preparation Example - Synthesis of Molecular Sieve Mother Liquor

[0107] Under stirring conditions, 136 kg of a 22.5 wt% tetrapropylammonium hydroxide aqueous solution, 208 kg of tetraethyl orthosilicate, 2.24 kg of KOH, and 344.6 kg of water were mixed and stirred at room temperature for 4 hours to obtain a colloidal mixture; wherein the molar ratio of tetraethyl orthosilicate:tetrapropylammonium hydroxide:KOH:water, calculated as SiO2, was 1:0.15:0.04:25; the above colloidal mixture was fed into a 1M... 3 In a stainless steel reactor, the hydrothermal system was crystallized at 120°C for 2 days with a stirring rate of 45 rpm to obtain a molecular sieve slurry; then, it was filtered under heat on a 50 nm membrane tube to obtain the crystallization mother liquor, which was collected and reserved for use in the example.

[0108] Example 1

[0109] The crystallization mother liquor obtained in the preparation example was concentrated at 70-90℃, with water added continuously during the process, yielding 210 kg of molecular sieve mother liquor. Analysis and adjustment revealed that the SiO2 content was 2.31%, the TPAOH content was 7.0%, the ethanol content was 3.1%, the water content was 87%, the KOH content was 0.54%, and other impurities were 0.05%.

[0110] Under stirring conditions, the above-mentioned 210 kg molecular sieve mother liquor, tetraethyl orthosilicate (TEOS), tetrapropylammonium hydroxide (TPAOH), ethanol, KOH and water were mixed at room temperature for 4 h to obtain a colloidal mixture. The mass ratio of SiO2 in the molecular sieve mother liquor to the mass of organosilicon esters based on SiO2 was 0.081:1. The molar ratio of SiO2:ethanol:tetrapropylammonium hydroxide:KOH:water in the colloidal mixture was 1:4:0.15:0.04:25.

[0111] The above colloidal mixture was fed into a 1M immersion chamber. 3 In a stainless steel reactor, the alcohol-hydrothermal system was crystallized at 120°C for 2 days with a stirring rate of 45 rpm. The crystallization was then filtered through a 50 nm membrane tube to obtain the crystallization mother liquor, which was bottled and reserved for use in the examples. The filtered wet molecular sieve material was then circulated and washed with water at a temperature of 40-60°C at a volume of 6-8 ml. 3 The washing water was washed until the pH value of the crystallized product reached approximately 9.1-9.3. The slurry was then concentrated to obtain a molecular sieve slurry with a solid content of 26.8% by weight. The yield of the molecular sieve was calculated to be 95%.

[0112] A small amount of the molecular sieve slurry was dried at 120℃ for 24 hours to obtain approximately 70.5 grams of silicon molecular sieve powder; then, it was calcined at 550℃ for 6 hours to obtain molecular sieve S1. The X-ray diffraction (XRD) pattern of molecular sieve S1 is shown below. Figure 1 As shown, the standard XRD pattern of the MFI structure is consistent with that described in the literature (Microporous Materials, Vol 22, p637, 1998), indicating that the molecular sieve has an MFI crystal structure.

[0113] The above molecular sieve slurry was mixed with 86.5 kg of 30% alkaline silica sol (pH 9.5, sodium ion content 324 ppm, SiO2 content 40% by weight). After calcination, the surface area of ​​the resulting SiO2 was 225 m². 2 The molecular sieve dry base and alkaline silica sol (calculated as SiO2) in the molecular sieve slurry were mixed at a weight ratio of 1:0.22. The mixture was stirred evenly and then pulped to obtain a molecular sieve-binder mixed slurry with a solid content of 27.5% by weight. This slurry was then fed into a spray forming device (manufactured by Changzhou Hengmai Drying Equipment Co., Ltd., model LPG-5) for spray forming, with inlet and outlet temperatures of 200℃ and 95℃, respectively. Then it was fed into a 3m... 3 In a heating shuttle furnace (manufactured by Hubei Huanggang Huaxia Electromechanical Thermal Equipment Co., Ltd.), the microspheres were calcined at 280℃, 400℃, and 480℃ for 2 hours each, and finally calcined at 550℃ for 12 hours to obtain 130 kg of microsphere molecular sieves, of which the content of all-silica-1 molecular sieve was 80% by weight and the content of binder was 20% by weight.

[0114] 100 kg of the above-mentioned microsphere molecular sieve and 1000 kg of an alkaline buffer solution containing nitrogen compounds (the alkaline buffer solution containing nitrogen compounds is a mixture of ammonia water and ammonium nitrate aqueous solution, wherein the ammonia water content is 26 wt%, the ammonium nitrate content in the ammonium nitrate aqueous solution is 7.5 wt%, the weight ratio of ammonia water to ammonium nitrate aqueous solution is 3:2, the pH value is 11.35, 160 g of tetrapropylammonium bromide, and 26.6 g of magnesium nitrate hexahydrate) were added to a 2M solution.3 In a stainless steel reactor, at 82℃ and 2.3 kg / cm²... 2 The mixture was stirred under pressure for 1.5 hours, then filtered and washed until the pH of the filtrate was 9. The filtrate was then dried at 120°C for 24 hours to obtain the microsphere molecular sieve catalyst, designated A1.

[0115] The particle size of the microsphere molecular sieve catalyst A1 was found to be concentrated in the range of 70-150 μm, and the wear index K = 2.2.

[0116] Example 2

[0117] The crystallization mother liquor obtained in the preparation example was concentrated at 70-90℃ for several hours, with water added continuously during the process, to obtain 245 kg of molecular sieve mother liquor. After analysis and adjustment, the content of SiO2 was 1.95%, TPAOH was 6.56%, ethanol was 12.42%, water was 78.52%, KOH was 0.50%, and other impurities were 0.05%.

[0118] Under stirring conditions, the above-mentioned 245 kg molecular sieve mother liquor, TEOS, TPAOH, ethanol and water were mixed at room temperature for 4 h to obtain a colloidal mixture. The mass ratio of SiO2 in the molecular sieve mother liquor to the mass ratio of organosilicate based on SiO2 was 0.08:1. The molar ratio of SiO2:tetrapropylammonium hydroxide:KOH:water in the colloidal mixture was 1:0.15:0.04:25.

[0119] The above colloidal mixture was fed into a 1M immersion chamber. 3 In a stainless steel reactor, the alcohol-hydrothermal system was crystallized at 120°C for 2 days with a stirring rate of 45 rpm to obtain a molecular sieve slurry. The slurry was then filtered through a 50 nm membrane tube to obtain a crystallization mother liquor, which was bottled and reserved for use in the example. The molecular sieve slurry was then circulated and washed with 6-8 ml of washing water at a temperature of 40-60°C. 3 The washing water is washed until the pH value of the crystallized product reaches about 9.1-9.3. Then the slurry is concentrated to obtain a molecular sieve slurry with a solid content of 24.4% by weight.

[0120] The above molecular sieve slurry was mixed with 60 kg of 30% alkaline silica sol (pH 9.5, sodium ion content 324 ppm, SiO2 content 40% by weight), and after calcination, the surface area of ​​the resulting SiO2 was 225 m². 2 The molecular sieve dry base and alkaline silica sol (calculated as SiO2) in the molecular sieve slurry were mixed in a weight ratio of 1:0.15. Then, 70 kg of water was added, stirred evenly, and slurry was prepared to obtain a molecular sieve-binder mixed slurry with a solid content of 22% by weight. This slurry was then fed into a spray molding device for spray molding, with inlet and outlet temperatures of 205℃ and 100℃, respectively. Finally, it was fed into a 3m...3 In a heated shuttle furnace, the microspheres were calcined at 280℃, 400℃, and 480℃ for 2 hours each, and finally calcined at 550℃ for 12 hours to obtain 120 kg of microsphere molecular sieves, of which the content of all-silica-1 molecular sieve was 85% by weight and the content of binder silica sol was 15% by weight.

[0121] 95 kg of the above-mentioned microsphere molecular sieve and 950 kg of an alkaline buffer solution containing nitrogen compounds (the alkaline buffer solution containing nitrogen compounds is a mixture of ammonia water and ammonium acetate aqueous solution, wherein the ammonia water content is 26 wt%, the ammonium acetate content in the ammonium acetate aqueous solution is 7.5 wt%, the weight ratio of ammonia water to ammonium acetate aqueous solution is 3:2, the pH value is 11.39, 160 g of tetrapropylammonium bromide, and 53 g of magnesium nitrate hexahydrate) were added to a 2M solution. 3 In a stainless steel reactor, at 85℃ and 2.5 kg / cm²... 2 Stirred under pressure for 1.5 hours, then filtered, washed until the pH of the filtrate was 9, and then dried at 120℃ for 24 hours to obtain the microsphere molecular sieve catalyst, designated A2.

[0122] The particle size of the microsphere molecular sieve catalyst A2 was found to be concentrated in the range of 70-150 μm, and the wear index K = 2.6.

[0123] Example 3

[0124] The method is the same as in Example 1, except that the mass ratio of SiO2 in the molecular sieve mother liquor to the mass ratio of organosilicon esters based on SiO2 is 0.2:1, keeping the composition ratio of the colloidal mixture unchanged.

[0125] The microsphere molecular sieve catalyst was obtained, designated A3.

[0126] Example 4

[0127] Following the method of Example 1, except that the amount of KOH used was adjusted so that the composition of the colloidal mixture satisfied the molar ratio of SiO2:ethanol:tetrapropylammonium hydroxide:KOH:water as 1:4.0:0.15:0.1:25. The resulting microsphere molecular sieve catalyst was designated A4.

[0128] Example 5

[0129] The method was followed in Example 1, except that the tetraethyl orthosilicate was sourced from Jiangxi Chenguang New Materials Co., Ltd., with a purity of 99.4 wt%, an ethanol content of 0.4 wt%, a platinum-cobalt color of 12 mg Pt-Co / L, and a Cl ion content of 65 ppm. The tetrapropylammonium hydroxide used was purchased from Tokyo Chemical Reagents, with a tetrapropylammonium hydroxide content of 25 wt%, a sodium ion content of 28.5 ppm, a bromide ion content of 1.2 wt%, a carbonate ion content of 0.2 wt%, an APHA color of 30, a potassium ion content of 1.1% wt%, an iron ion content of 38 ppm, an acetic acid content of 214 ppm, and formic acid and propionic acid contents of 26 ppm.

[0130] The microsphere molecular sieve catalyst was obtained, designated A5.

[0131] Example 6

[0132] The method was followed in Example 1, except that the crystallization temperature was 80°C and the crystallization time was 3 days. The yield of the molecular sieve was calculated to be 56%. Microsphere molecular sieve catalyst, designated A6, was further obtained.

[0133] Example 7

[0134] The method is the same as in Example 1, except that the alkaline buffer solution containing nitrogen compounds is a mixture of ammonia, ammonium nitrate aqueous solution, 160g tetrapropylammonium bromide, and 2.6g magnesium nitrate hexahydrate, wherein the content of ammonia is 26% by weight, the content of ammonium nitrate in the ammonium nitrate aqueous solution is 7.5% by weight, the weight ratio of ammonia to ammonium nitrate aqueous solution is 3:2, and the pH value is 11.35.

[0135] Microsphere molecular sieve catalyst, designated A7, was obtained. The particle size of microsphere molecular sieve catalyst A7 was measured to be concentrated in the range of 70-150 μm, and the wear index K = 3.0.

[0136] Example 8

[0137] The method is the same as in Example 1, except that the alkaline buffer solution containing nitrogen compounds is a mixture of ammonia, ammonium nitrate aqueous solution, 160g tetrapropylammonium bromide, and 1233g magnesium nitrate hexahydrate, wherein the content of ammonia is 26% by weight, the content of ammonium nitrate in the ammonium nitrate aqueous solution is 7.5% by weight, the weight ratio of ammonia to ammonium nitrate aqueous solution is 3:2, and the pH value is 11.35.

[0138] Microsphere molecular sieve catalyst, designated A8, was obtained. The particle size of microsphere molecular sieve catalyst A5 was measured to be concentrated in the range of 70-150 μm, and the wear index K = 3.3.

[0139] Comparative Example 1

[0140] The method of Example 1 is different except that, under stirring conditions, the molecular sieve mother liquor, TEOS and water are mixed at room temperature for 4 hours to obtain a colloidal mixture, wherein the mass ratio of SiO2 in the molecular sieve mother liquor to the mass ratio of organosilicate based on SiO2 is 0.32:1; and the molar ratio of SiO2:tetrapropylammonium hydroxide:water in the colloidal mixture is 1:0.25:25.

[0141] The microsphere molecular sieve catalyst, designated DA1, was obtained. The particle size of the microsphere molecular sieve catalyst A5 was measured to be concentrated in the range of 50-150 μm, and the wear index K = 3.

[0142] Test Implementation Examples

[0143] The cyclohexanone oxime gas-phase Beckmann rearrangement reaction was carried out using the catalysts prepared in the above examples and comparative examples respectively:

[0144] The gas-phase Beckmann rearrangement reaction of cyclohexanone oxime was carried out in a fixed fluidized bed reactor. The vertical 316L stainless steel fluidized bed reactor had an upper diameter of 20 cm and a lower diameter of 10 cm, with upper and lower section lengths of 60 cm and 80 cm respectively. The microsphere molecular sieve catalyst loading in the fixed fluidized bed reactor was 250 g. The reaction conditions in the fluidized bed reactor included: reaction pressure 0.1 MPa, fluidized bed reaction temperature 385 °C, gas atomization spray feeding, vaporization chamber temperature control 190 °C, minimum vaporizer temperature 160 °C, outlet pipeline insulation 200 °C, and a WHSV of 4.2 h⁻¹. -1 Cyclohexanone oxime accounts for 35% by weight of the total amount of cyclohexanone oxime and ethanol, water accounts for 0.8% by weight of the total amount of water, ethanol and cyclohexanone oxime, and the molar ratio of nitrogen to cyclohexanone oxime is 2.

[0145] After 10 hours of reaction, the conversion rate of cyclohexanone oxime and the selectivity of caprolactam were analyzed. The feed of cyclohexanone oxime, ethanol and water was stopped, and nitrogen was continuously introduced into the fluidized bed reactor at a rate of 450 L / h for 30 minutes. Then, the nitrogen was switched to air at a rate of 180 L / h, and the temperature of the fluidized bed reactor was raised from 385 °C to 450 °C. The catalyst was then regenerated at this temperature for 14 hours.

[0146] The reaction products were quantitatively analyzed using an Agilent 6890 gas chromatograph (flame ionization detector, PEG20M capillary column, 50m column length). The vaporization chamber temperature was 250℃, the detection chamber temperature was 240℃, and the column temperature was programmed: 110℃ for 8 minutes, then increased to 230℃ at a rate of 15℃ / min and held for 14 minutes.

[0147] The contents of the rearranged products of caprolactam and cyclohexenone after the reaction were calculated using the area normalization method, and the solvent was not included in the integration.

[0148] The above analysis yielded the molar percentages of cyclohexanone oxime and caprolactam in the reaction products. The conversion rate of cyclohexanone oxime and the selectivity of caprolactam were then calculated using the following formulas. The results are shown in Table 1.

[0149] Cyclohexanone oxime conversion (mol%) = (100 - cyclohexanone oxime molar percentage in reaction product) / 100 × 100%;

[0150] Total selectivity of caprolactam (mol%) = molar percentage of caprolactam in the reaction product / (100 - molar percentage of cyclohexanone oxime in the reaction product) × 100%;

[0151] In the cyclohexanone oxime gas-phase Beckmann rearrangement reaction, methyl-ε-caprolactam accounts for approximately 40% of all byproducts. This byproduct is generated by the alcoholysis of methanol with the enol tautomer of caprolactam. In the presence of water, methyl-ε-caprolactam undergoes hydrolysis to further generate caprolactam. Therefore, the amount of caprolactam generated from the hydrolysis of methyl-ε-caprolactam is included in the calculation of the overall caprolactam selectivity.

[0152] Table 1

[0153]

[0154]

[0155] The comparison of the above examples and comparative examples shows that the microsphere catalyst prepared in the embodiments of the present invention has a high cyclohexanone oxime conversion rate and caprolactam selectivity in fluidized bed process, requires less organic template agent, and has good economic efficiency in preparation process.

[0156] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing a microspherical all-silica-1 molecular sieve catalyst, characterized in that, The preparation method includes: (1) Molecular sieve mother liquor, organosilicate, organic template agent and KOH are mixed to obtain colloidal mixture; wherein, the amount of molecular sieve mother liquor and organosilicate is satisfied, and the mass ratio of SiO2 in molecular sieve mother liquor to organosilicate based on SiO2 is 0.01-0.2:1; The composition of the colloidal mixture satisfies that the molar ratio of SiO2, KOH, organic template agent, and water is 1:(0.01-0.1):(0.04-0.15):(15-45); (2) The colloidal mixture is subjected to a crystallization reaction; (3) The crystallization product obtained in step (2) is subjected to solid-liquid separation to obtain molecular sieve wet material and crystallization mother liquor; (4) The crystallization mother liquor is optionally concentrated, and then the process is returned to step (1) to provide the molecular sieve mother liquor; (5) The molecular sieve wet material is mixed with a binder and pulped, then spray-molded and calcined to obtain a catalyst precursor; (6) The catalyst precursor is contacted with an alkaline buffer solution containing ammonium salt, ammonia water, magnesium salt and bromide salt, and then dried.

2. The preparation method according to claim 1, characterized in that, The amounts of the molecular sieve mother liquor and the organosilicone ester are such that the mass ratio of SiO2 in the molecular sieve mother liquor to the mass ratio of organosilicone ester (calculated as SiO2) is 0.02-0.15:

1. Preferably, the composition of the colloidal mixture satisfies the following: the molar ratio of SiO2, KOH, organic template agent, and water is 1:(0.02-0.08):(0.08-0.2):(20-40); Preferably, in step (2), the crystallization temperature is 95-150℃, more preferably 100-150℃, and the time is 0.5-5 days, more preferably 1-5 days.

3. The preparation method according to claim 1 or 2, characterized in that, The silicon source is methyl orthosilicate and / or ethyl orthosilicate; Preferably, the Cl ion content in the organosilicon ester is not greater than 50 ppm; Preferably, the platinum-cobalt color of the organosilicon ester is not greater than 20 mg / L; Preferably, the purity of the organosilicon ester is not less than 98 wt%; Preferably, the organic template agent is selected from quaternary ammonium base compounds, more preferably tetrapropylammonium hydroxide and / or tetraethylammonium hydroxide, and more preferably tetrapropylammonium hydroxide; Preferably, the organic template agent contains less than 1.5 wt% bromide ions, and more preferably 0.5-1.5 wt%. Preferably, the iron ion content in the organic template agent is not greater than 10 ppm; Preferably, the organic template agent contains less than 500 ppm sodium ions, not more than 550 ppm free acid, less than 0.2 wt% carbonate ions, and an APHA color of no more than 100.

4. The preparation method according to any one of claims 1-3, characterized in that, The molecular sieve mother liquor includes an organic template agent, silicon species, water, and optionally KOH; Preferably, the molecular sieve mother liquor contains 5-20 wt% organic template agent, 1-10 wt% silicon species (calculated as SiO2), 60-90 wt% water, and 0.1-1 wt% KOH, preferably 0.2-0.8 wt%. Preferably, the concentration conditions in step (4) include a temperature of 50-100°C, preferably 70-90°C.

5. The preparation method according to any one of claims 1-4, characterized in that, In step (3), the solid-liquid separation method is membrane filtration separation; Preferably, the pore size of the filter membrane in the membrane filtration separation is not greater than 200 nm, and more preferably not greater than 100 nm; Preferably, the filter membrane is an inorganic membrane.

6. The preparation method according to any one of claims 1-5, characterized in that, Step (5) includes: first, optionally washing the wet molecular sieve material to obtain a molecular sieve slurry with a solid content of 20-50% by weight; then mixing the molecular sieve slurry with a binder and stirring to obtain a molecular sieve-binder slurry. Preferably, the weight ratio of molecular sieve slurry or wet molecular sieve material to binder on a dry basis is 1:(0.05-1); Preferably, the binder is a precursor of silicon oxide, which is silica sol and / or silica, preferably silica sol.

7. The preparation method according to any one of claims 1-6, characterized in that, The spray molding conditions include: an inlet temperature of 180-240℃, preferably 200-220℃; and an outlet temperature of 80-120℃, preferably 90-105℃. Preferably, the calcination conditions include: a temperature of 200-600℃, more preferably 250-550℃, and a time of 1-20h; Preferably, an additive is introduced during the pulping process in step (5), and the additive is selected from at least one of guar gum powder, graphite, activated carbon, paraffin, glycerin, citric acid, starch, polyethylene glycol, polyvinyl alcohol, nitric acid, hydrochloric acid, acetic acid, formic acid, ammonia, tetramethylammonium hydroxide, tetraethylammonium hydroxide and tetrapropylammonium hydroxide. Preferably, the amount of additive introduced is 1-5 wt%, based on the dry weight of the molecular sieve.

8. The preparation method according to any one of claims 1-7, characterized in that, In step (4), the pH of the alkaline buffer solution is 8.5-13.5; Preferably, based on the total amount of the alkaline buffer solution, the content of magnesium salts (calculated as Mg) is 1-500 ppm, and the content of bromide salts (calculated as Br) is 1-500 ppm. Preferably, the alkaline buffer solution comprises ammonia, an ammonium salt aqueous solution, a magnesium salt, and a bromide salt; Preferably, the weight ratio of ammonia water to ammonium salt aqueous solution is 1-3:1; Preferably, the concentration of the ammonia solution is 5-30 wt%. Preferably, the concentration of the ammonium salt aqueous solution is 0.5-10 wt%. Preferably, the amount of alkaline buffer solution used is 500-1500 parts by weight, more preferably 700-1200 parts by weight, relative to 100 parts by weight of the product obtained by calcination on a dry basis. Preferably, the contact conditions include: a temperature of 50-120°C, more preferably 70-100°C; and a pressure of 0.5-10 kg / cm². 2 The preferred value is 1.5-4 kg / cm². 2 The time is 0.1-5 hours, preferably 1-3 hours.

9. The microspherical all-silica-1 molecular sieve catalyst prepared by the preparation method according to any one of claims 1-8.

10. A method for preparing caprolactam, the method comprising: Under the conditions of the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime, in the presence of a solvent, cyclohexanone oxime is reacted with a catalyst, wherein the catalyst is the microsphere-type all-silica-1 molecular sieve catalyst as described in claim 9. Preferably, the contact takes place in a fluidized bed reactor.

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