Preparation method of all-silicon molecular sieve with MFI topology structure, all-silicon molecular sieve with MFI topology structure and application of all-silicon molecular sieve

Abstract

The invention relates to the field of preparation of molecular sieves, and discloses a preparation method of an all-silicon molecular sieve with an MFI topology structure, the all-silicon molecular sieve with the MFI topology structure and application of the all-silicon molecular sieve with the MFI topology structure, the method comprises the following steps: (1) mixing molecular sieve mother liquor, organic silicate ester, an organic template agent and alcohol to obtain a colloid mixture; the mass ratio of SiO2 in the molecular sieve mother liquor to the organic silicate ester based on SiO2 is (0.01-0.2): 1; the molar ratio of the alcohol to SiO2 in the molecular sieve mother liquor is (10-100): 1; (2) carrying out crystallization reaction on the colloid mixture; (3) carrying out solid-liquid separation on the crystallization product obtained in the step (2) to obtain a molecular sieve wet material and crystallization mother liquor; drying and roasting the molecular sieve wet material; and (4) optionally concentrating the crystallized mother liquor, and then returning to the step (1). The preparation method can effectively utilize the molecular sieve mother liquor, saves the cost, is beneficial to environmental protection, and is easy to operate.

Description

Technical Field

[0001] The invention relates to the field of molecular sieve preparation, and in particular to a preparation method of an all-silicon molecular sieve with an MFI topological structure, an all-silicon molecular sieve with an MFI topological structure and applications thereof. Background Art

[0002] The synthesis yield of molecular sieves synthesized in a hydrothermal system under autogenous pressure is generally 50-80%, and may be lower for the synthesis of some molecular sieves. Therefore, the mother liquor after crystallization of the molecular sieve synthesis will contain a large amount of unreacted raw material components, which can be completely dissolved in the zero-order mother liquor after the molecular sieve is filtered. For synthesis in the laboratory, the mother liquor is often directly poured away, but for industrial production, the discharge of the mother liquor will cause waste of raw materials on the one hand, and cause greater pollution to the environment on the other hand.

[0003] The aluminum-free, neutral, submicron-sized all-silicon-1 molecular sieve with MFI topology is generally synthesized in an alcohol-hydrothermal system, and the template agent is used in large amounts and is expensive, resulting in a relatively high cost for the synthesis of all-silicon-1 molecular sieve. At the same time, a large amount of ethanol is present in the synthesis process, resulting in a high BOD in the wastewater discharge, a large amount of amine (nitrogen) emissions, and serious environmental pollution. Therefore, the recycling of mother liquor in the synthesis of MFI topology all-silicon-1 molecular sieve is of greater significance.

[0004] However, the methods for recycling the mother liquor of molecular sieves in the prior art are all applied to framework structures such as silicon-aluminum molecular sieves or titanium-silicon molecular sieves, and there is still a lack of effective means for recycling the mother liquor in the synthesis of MFI topological structure all-silicon-1 molecular sieves. Summary of the invention

[0005] The purpose of the present invention is to overcome the problems in the prior art that the synthesis of an all-silicon molecular sieve with an MFI topology structure is difficult and the mother liquor is difficult to effectively utilize, and to provide a preparation method of an all-silicon molecular sieve with an MFI topology structure, an all-silicon molecular sieve with an MFI topology structure and an application thereof. The preparation method can effectively utilize the molecular sieve mother liquor, which not only saves costs, but also is beneficial to environmental protection and easy to operate.

[0006] In order to achieve the above object, the first aspect of the present invention provides a method for preparing an all-silicon molecular sieve with an MFI topological structure, comprising the following steps:

[0007] (1) mixing a molecular sieve mother liquid, an organic silicate, an organic template, and an alcohol to obtain a colloidal mixture;

[0008] The amounts of the molecular sieve mother liquid and the organosilicate are such that the mass ratio of SiO2 in the molecular sieve mother liquid to the mass ratio of the organosilicate calculated as SiO2 is 0.01-0.2:1;

[0009] The molar ratio of alcohol to SiO2 in the molecular sieve mother liquor is (10-100): 1;

[0010] (2) subjecting the colloidal mixture to a crystallization reaction;

[0011] (3) subjecting the crystallized product obtained in step (2) to solid-liquid separation to obtain a molecular sieve wet material and a crystallization mother liquor; and drying and calcining the molecular sieve wet material to obtain an all-silicon molecular sieve with an MFI topological structure;

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

[0013] Preferably, the preparation method further comprises: before the mixing in step (1), subjecting the molecular sieve mother liquor to a CO2 removal treatment so that the CO2 content in the molecular sieve mother liquor is not higher than 100 ppm.

[0014] The second aspect of the present invention provides an all-silicon molecular sieve with an MFI topological structure obtained by the above preparation method.

[0015] The third aspect of the present invention provides the use of the above-mentioned all-silicon molecular sieve with MFI topology structure in the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime.

[0016] The synthesis of all-silicon-1 molecular sieve uses quaternary ammonium base compounds such as tetrapropylammonium hydroxide as templates and alkali sources, which are used in large quantities and are expensive, resulting in a relatively high cost for the synthesis of all-silicon-1 molecular sieves. At the same time, there is a large amount of alcohol in the synthesis process, which leads to high BOD in wastewater discharge, large amine (nitrogen) emissions, and serious environmental pollution. If the molecular sieve mother liquor can be reused, it will save costs and be beneficial to environmental protection. However, the synthesis of all-silicon-1 molecular sieves has high requirements for silicon sources, and SiO2 in the mother liquor is difficult to form a skeleton, which is not conducive to the synthesis of molecular sieves.

[0017] The preparation method provided by the present invention can effectively utilize the components that do not participate in the reaction in the synthesis mother liquor of the all-silicon-1 molecular sieve, can improve the synthesis yield of the molecular sieve, shorten the crystallization time, reduce the synthesis cost of the molecular sieve, reduce the amount of waste liquid discharged, and is beneficial to environmental protection. Preferably, after the mother liquor obtained by crystallization is subjected to CO2 removal treatment, the crystal structure, grain size and crystal morphology can be further optimized. The obtained all-silicon molecular sieve with MFI topological structure is applied to the production of caprolactam, which can effectively improve the conversion rate of oxime and the selectivity of lactam. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is the XRD spectrum of the molecular sieve A1 prepared in the reference example;

[0019] Figure 2is the XRD spectrum of the molecular sieve S1 prepared in Example 1;

[0020] Figure 3 is a SEM image of the molecular sieve A1 prepared in the reference example;

[0021] Figure 4 is a SEM image of the molecular sieve S1 prepared in Example 1. DETAILED DESCRIPTION

[0022] The endpoints and any values ​​of the ranges disclosed in this article 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 each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0023] The first aspect of the present invention provides a method for preparing an all-silicon molecular sieve with an MFI topological structure, comprising the following steps:

[0024] (1) mixing a molecular sieve mother liquid, an organic silicate, an organic template, and an alcohol to obtain a colloidal mixture;

[0025] The amounts of the molecular sieve mother liquid and the organosilicate are such that the mass ratio of SiO2 in the molecular sieve mother liquid to the mass ratio of the organosilicate calculated as SiO2 is 0.01-0.2:1;

[0026] The molar ratio of alcohol to SiO2 in the molecular sieve mother liquor is (10-100): 1;

[0027] (2) subjecting the colloidal mixture to a crystallization reaction;

[0028] (3) subjecting the crystallized product obtained in step (2) to solid-liquid separation to obtain a molecular sieve wet material and a crystallization mother liquor; and drying and calcining the molecular sieve wet material to obtain an all-silicon molecular sieve with an MFI topological structure;

[0029] (4) The crystallization mother liquor is optionally concentrated, and then returned to step (1) to provide the molecular sieve mother liquor.

[0030] In the present invention, the "molecular sieve mother liquor" described 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 described in step (4). The silicon source in the molecular sieve mother liquor exists in the form of SiO2, silicic acid and its oligomers, and molecular sieve crystallites. By introducing alcohol, it is beneficial to recover the silicon source in the molecular sieve mother liquor, thereby helping to form the molecular sieve skeleton. By recycling the molecular sieve mother liquor, on the one hand, the consumption of raw materials can be reduced, and on the other hand, environmental pollution can be effectively reduced. At the same time, the presence of molecular sieve crystallites in the mother liquor can play the role of crystal seeds, thereby helping to shorten the crystallization time and improve the relative crystallinity and yield of the molecular sieve.

[0031] According to the present invention, preferably, the molecular sieve mother liquor comprises an organic template, SiO2, water and an optional alcohol. The silicon element in the molecular sieve mother liquor exists in the form of SiO2, silicic acid and its oligomers and molecular sieve microcrystals. In the present invention, the SiO2 in the molecular sieve mother liquor refers to the sum of the silicon element in the molecular sieve mother liquor in terms of SiO2.

[0032] According to the present invention, preferably, in the molecular sieve mother liquor, the content of the organic template is 10-20wt%, preferably 12-18wt%; the content of SiO2 is 2-10wt%, preferably 3-8wt%; the content of water is 60-90wt%, preferably 65-85wt%; the content of alcohol is 1-10wt%, preferably 2-8wt%.

[0033] Among them, silicon in the form of SiO2 is difficult to form a full silicon molecular sieve framework, and therefore difficult to be effectively utilized. The inventors of the present invention have found in their research that by introducing an appropriate amount of alcohol to activate the molecular sieve mother liquor and regulating the ratio of the molecular sieve mother liquor and the organic silicate, the silicon element in the molecular sieve mother liquor can be fully utilized, which is beneficial to improving the relative crystallinity of the molecular sieve.

[0034] According to the present invention, the amounts of the molecular sieve mother solution and the organosilicate are such that the mass ratio of SiO2 in the molecular sieve mother solution to the organosilicate calculated as SiO2 is 0.01-0.2:1, preferably 0.02-0.15:1, for example, it can be a typical but non-limiting mass ratio of 0.02:1, 0.05:1, 0.1:1, 0.15:1, or a range therebetween. In the above preferred case, it is beneficial to further improve the relative crystallinity of the molecular sieve.

[0035] According to the present invention, the molar ratio of alcohol to SiO2 in the molecular sieve mother liquor is (10-100):1, for example, it can be 10:1, 20:1, 25:1, 30:1, 35:1, 40:1, 45:1, 50:1, 55:1, 60:1, 65:1, 70:1, 80:1 and other typical but non-limiting molar ratios or ranges therebetween. Preferably, the molar ratio of alcohol to SiO2 in the molecular sieve mother liquor is 30-70:1. The above preferred embodiment is beneficial to the effective utilization of the silicon source in the molecular sieve mother liquor.

[0036] According to the present invention, preferably, in the colloidal mixture, the molar ratio of SiO2, organic template and water is 1: (0.1-0.5): (10-50), preferably 1: (0.1-0.3): (15-35). The SiO2 in the colloidal mixture refers to the sum of the molar amount of silicon in the molecular sieve mother liquor calculated as SiO2 and the molar amount of silicon in the organic silicate calculated as SiO2; the water in the colloidal mixture comes from the molecular sieve mother liquor, and a small amount of water can also be added to adjust the balance of the molecular sieve synthesis molar ratio.

[0037] According to the present invention, during the initial synthesis process, conventional preparation methods in the art can be used to obtain the original molecular sieve mother solution to provide the molecular sieve mother solution in step (1). For example, the preparation method disclosed in CN1338427A can be used.

[0038] In the present invention, in order to facilitate the adjustment of the balance of the molecular sieve synthesis molar ratio, 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, and water is continuously replenished during the distillation process. On the one hand, the active ingredients (silicon source) and unreacted organic templates in the purified liquid phase are distilled to achieve the purpose of recycling the molecular sieve mother liquor. On the other hand, a part or all of the ethanol is recovered by distillation, the concentration of the organic template and silicon oxide is increased, and the composition of the concentrated crystallization mother liquor meets the definition range of the above-mentioned molecular sieve mother liquor. The recovered ethanol can be reused in the molecular sieve crystallization process to improve the economy of the overall process.

[0039] Preferably, the concentration conditions in step (4) include: a temperature of 50-100°C, preferably 70-90°C.

[0040] In a further preferred embodiment, the preparation method further comprises: before the mixing in step (1), subjecting the molecular sieve mother liquor to a CO2 removal treatment so that the CO2 content in the molecular sieve mother liquor is not higher than 100 ppm. Controlling the CO2 content in the molecular sieve mother liquor within the above preferred range is conducive to the synthesis of the all-silicon molecular sieve and obtaining a good crystal structure, grain size and crystal morphology.

[0041] The CO2 content in the molecular sieve mother liquor is determined by the following method:

[0042] (1) Sampling: Use a rubber tube to siphon the molecular sieve mother liquor (evenly stirred) into a 100 mL stoppered colorimetric tube. The tube should be inserted into the bottom of the colorimetric tube and slowly injected until the molecular sieve mother liquor overflows 100-150 mL. Then remove the tube and use a pipette to quickly suck out the excess molecular sieve mother liquor sample so that the molecular sieve mother liquor sample in the tube is exactly 100 mL.

[0043] (2) Preliminary determination: Add 6 drops of 0.5% phenolphthalein to a colorimetric tube and stir with a glass rod. If the molecular sieve mother liquor sample turns red, it means there is no free CO2 in the molecular sieve mother liquor. If the molecular sieve mother liquor is colorless, it means there is free CO2 in the molecular sieve mother liquor. Immediately titrate with sodium hydroxide standard solution, stirring while titrating (stirring should be gentle to reduce CO2 escape). Until a light red color appears and does not disappear within 2 minutes. Record the number of milliliters of sodium hydroxide consumed (A). This number is only used as a reference during the formal titration.

[0044] (3) Formal determination: According to (1), re-take 100 mL of molecular sieve mother solution, add 6 drops of 0.5% phenolphthalein, quickly add a sodium hydroxide standard solution close to A ml (not more) from the burette at a time, cover the lid, and mix by inverting back and forth (do not shake violently). The solution in the tube is red when it is just mixed, but it should quickly fade to colorless. After the red color fades, continue to titrate with sodium hydroxide, adding half a drop or 1 drop each time, cover the lid and mix by inverting back and forth, until the solution turns light red and does not disappear within 2 minutes. Record the volume V consumed.

[0045] CO2(mg / L)=N×V×44.01×1000 / V 样 ;

[0046] Among them, V 样 is the sampling volume during titration (ml), N is the equivalent concentration of sodium hydroxide standard solution (mol / L), V is the volume consumed during titration (ml), and 44.01 is the molecular weight of CO2.

[0047] The present invention has no particular limitation on the method of removing CO2, as long as the CO2 content in the concentrated crystallization mother liquor is met. In order to avoid affecting the composition of the crystallization mother liquor, preferably, the method of removing CO2 is: using an inert gas or air decarbonated with carbon dioxide to purge the concentrated crystallization mother liquor. Preferably, the inert gas is nitrogen.

[0048] According to some specific embodiments of the present invention, the organic silicate is ethyl orthosilicate and / or methyl orthosilicate, preferably ethyl orthosilicate.

[0049] The organic template can be various organic templates conventionally used in the art for preparing all-silicon-1 molecular sieves. Preferably, the organic template is selected from quaternary ammonium base compounds, and the quaternary ammonium base compounds can be alkyl quaternary ammonium base compounds containing 1-4 carbon atoms, further preferably tetrapropylammonium hydroxide and / or tetraethylammonium hydroxide, and more preferably tetrapropylammonium hydroxide.

[0050] According to the present invention, the alcohol may be at least one of a monohydric alcohol and a dihydric alcohol having 1 to 4 carbon atoms. Preferably, the alcohol is methanol and / or ethanol, preferably ethanol.

[0051] According to a particularly preferred embodiment of the present invention, the organic silicate is ethyl orthosilicate, and the alcohol is ethanol.

[0052] The present invention has no particular limitation on the mixing in step (1), as long as the colloidal mixture can be obtained, and the mixing is preferably carried out under stirring conditions. Preferably, the mixing conditions include: mixing at 10-50° C. for 0.5-10 h under stirring conditions. The present invention has no particular limitation on the stirring rate, and those skilled in the art can select it according to actual conditions.

[0053] According to the present invention, the crystallization reaction in step (2) is an alcohol-hydrothermal system crystallization, and preferably, the crystallization conditions include: crystallization at 80-150° C. for 1-5 days, preferably crystallization at 95-135° C. for 1-3 days. By adopting the above preferred embodiment, the decomposition of the organic template that does not participate in the reaction can be avoided as much as possible, and the organic template can be fully recycled when the molecular sieve mother liquor is reused, thereby reducing the amount of organic template added later and reducing the overall process cost.

[0054] According to the present invention, specifically, the two-stage variable temperature alcohol-hydrothermal system crystallization is carried out in a closed system under autogenous pressure, for example, in a closed reactor.

[0055] According to the present invention, in step (3), the crystallized product obtained in step (2) is subjected to solid-liquid separation, and the solid-liquid separation can be carried out by various methods conventionally used in the art. For example, the solid-liquid separation can be carried out by membrane filtration separation, wherein the pore size of the filter membrane used in the membrane filtration separation is preferably 40-60 nm. Preferably, the filter membrane is an inorganic membrane.

[0056] According to the present invention, preferably, before the drying, step (3) further comprises: washing and concentrating the molecular sieve wet material. The washing and concentrating can be carried out in a conventional manner in the art, and the present invention has no particular limitation on the washing agent used in the washing process, for example, it can be water.

[0057] In order to completely remove the dissolved components other than the molecular sieve crystals remaining in the crystals, the crystals may be properly washed with an organic solvent such as methanol or ethanol or water. According to a specific embodiment of the present invention, the washing comprises: washing the molecular sieve wet material until the pH value of the washing water is 9-9.4.

[0058] The present invention has no particular limitation on the specific operation and conditions of the concentration in step (3), as long as the solid content of the product is 20-40% by weight.

[0059] The present invention has a wide range of selection for the drying in step (3). Preferably, the drying conditions include: a temperature of 100-120° C. and a time of 12-48 h;

[0060] According to the present invention, preferably, the calcination conditions include: a temperature of 400-600° C. and a time of 5-12 h.

[0061] The second aspect of the present invention provides an all-silicon molecular sieve with an MFI topological structure obtained by the above-mentioned preparation method. The preparation method provided by the present invention can effectively recover the organic template and silicon element in the molecular sieve mother liquor, and the obtained all-silicon molecular sieve with an MFI topological structure has high relative crystallinity and good catalytic performance.

[0062] The all-silicon molecular sieve prepared by the preparation method provided by the present invention has a high crystallinity. Preferably, the relative crystallinity of the all-silicon molecular sieve is 90-110%.

[0063] The relative crystallinity test method is as follows: using a standard ZSM-5 molecular sieve (a molar ratio of silicon oxide to aluminum oxide is 30) as a standard sample, using the peak area of ​​the XRD characteristic peak of the standard sample as a benchmark, and taking the percentage of the peak area of ​​the XRD characteristic peak of the sample to be tested to the peak area of ​​the standard sample as the relative crystallinity of the sample to be tested.

[0064] The standard ZSM-5 molecular sieve was synthesized in the laboratory according to the method disclosed by Lechert H, Kleinwort R, [Verified Synthesis of Zeolitic Materials, 2nd Ed H. Robson (Ed). Elsevier (2001) P199], using NaOH, TPAOH (20 wt% aqueous solution), silicic acid (Merck, SiO2·H2O), and sodium aluminate (Al2O3: 1.24Na2O: 0.57H2O) as raw materials. (1) 710.3 g of H2O, 13.8 g of NaOH and 117 g of TPAOH solution were fully dissolved and mixed until uniform; (2) 158.9 g of silicic acid was gradually added to the above solution in batches under stirring, and after being fully shaken at room temperature for 1 hour, it was aged at 100°C for 16 hours. (3) 867.8 g of H2O, 8.8 g of NaOH and 10.3 g of sodium aluminate were fully mixed and dissolved; (4) 113.1 g of silicic acid was gradually added to (3) in batches under full stirring and vigorously shaken at room temperature for 1 hour; (5) 50 g of the colloidal seed prepared in step (2) was added to (4) and shaken for another hour; (6) the material was then placed in a stainless steel reactor lined with PTFE, and after crystallization at 180°C for 40 hours, the crystallized product was taken out and filtered, washed with deionized water, dried at 105°C for 24 hours, and calcined at 550°C for 6 hours to obtain a ZSM-5 sample.

[0065] Preferably, the specific surface area of ​​the all-silicon molecular sieve is 380-480m 2 / g, preferably 400-460m 2 / g.

[0066] Preferably, the micro-specific surface area of ​​the all-silicon molecular sieve is 340-440m 2 / g, preferably 360-420m 2 / g.

[0067] Preferably, the pore volume of the all-silicon molecular sieve is 0.2-0.5 mL / g, preferably 0.25-0.4 mL / g.

[0068] Preferably, the micropore volume of the all-silicon molecular sieve is 0.1-0.3 mL / g, preferably 0.1-0.22 mL / g.

[0069] In the present invention, micro specific surface area refers to the total specific surface area of ​​the three-dimensional pores of the MFI topological structure, and micro pore volume refers to the total pore volume of the three-dimensional pores of the MFI topological structure.

[0070] BET specific surface area and pore distribution were measured on an American Micromeritics ASAP-2400 automatic adsorption instrument. Each sample was evacuated to 10 -5 Pa, N2 was used as adsorbate, adsorption was carried out at liquid nitrogen temperature, and the maximum partial pressure (p / p0) was less than 0.3 during measurement. The specific surface area was calculated using the two-parameter BET equation, the pore distribution was calculated using the BJH method, and the micro-specific surface area and micropore volume were calculated using the t method.

[0071] The third aspect of the present invention provides the use of the above-mentioned all-silicon molecular sieve with MFI topology structure in the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime. The all-silicon molecular sieve provided by the present invention can be directly used as the catalyst, or after being optionally formed, it can be used as a catalyst in the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime, which can improve the conversion rate of cyclohexanone oxime and the selectivity of caprolactam.

[0072] The present invention has no special requirements for the molding method, and the molding can be performed in a conventional manner in the art.

[0073] The application provided by the present invention can be to contact cyclohexanone oxime with a catalyst in the presence of a solvent to carry out a gas-phase Beckmann rearrangement reaction.

[0074] Preferably, the molar ratio of the solvent to cyclohexanone oxime is 2-10:1.

[0075] Preferably, the solvent is selected from C1-C6 fatty alcohols, more preferably at least one of methanol, ethanol and n-propanol.

[0076] Preferably, the gas-phase Beckmann rearrangement reaction is carried out in the presence of nitrogen, and the molar ratio of nitrogen to cyclohexanone oxime is 10-80:1, more preferably 20-40:1.

[0077] Preferably, the conditions for the gas phase Beckmann rearrangement reaction include: the weight space velocity of cyclohexanone oxime is 0.1-20h -1 , preferably 5-20h -1 ; The reaction temperature is 300-500°C, preferably 350-400°C; the reaction pressure is 0.1-0.5MPa in gauge pressure.

[0078] Preferably, before contacting cyclohexanone oxime with the catalyst, the method further comprises: pre-treating the molecular sieve under a nitrogen atmosphere at a temperature of 300-400° C. for a time of 0.5-2 h.

[0079] The present invention will be described in detail below through examples.

[0080] Unless otherwise specified, the percentages in the following examples are all by mass.

[0081] Reference ratio

[0082] Under stirring conditions, 202.5 grams of 25 weight % tetrapropylammonium hydroxide aqueous solution, 208 grams of tetraethyl orthosilicate, 92 grams of ethanol and 300 grams of water are mixed, and stirring is continued for 4 hours at room temperature to obtain a colloidal mixture; wherein the molar ratio of tetraethyl orthosilicate: ethanol: tetrapropylammonium hydroxide: water calculated as SiO2 is 1:6:0.25:25; the above colloidal mixture is sent to a stainless steel reactor, stirred at a rate of 45rpm, and crystallized in an alcohol-hydrothermal system at 100°C for 3 days to obtain a molecular sieve slurry; then warm filtration is carried out on a 50nm membrane tube to obtain a crystallization mother liquor, which is bottled for use in examples.

[0083] The molecular sieve slurry was then circulated and washed, with a circulating water temperature of 40-60°C and a washing water volume of 6-8L, until the pH value of the washing water of the crystallized product reached about 9.1-9.3. The slurry was then concentrated and dried at 120°C for 24 hours to obtain about 65.6 grams of silicon molecular sieve raw powder; it was then calcined at 550°C for 6 hours to obtain molecular sieve A1.

[0084] The X-ray diffraction (XRD) spectrum of molecular sieve A1 is as follows: Figure 1 As shown, it is consistent with the standard XRD spectrum characteristics of the MFI structure recorded in the literature (Microporous Materials, Vol 22, p637, 1998), indicating that the molecular sieve has an MFI crystal structure; the scanning electron microscope photo of the molecular sieve A1 is shown in Figure 3 The specific physical and chemical properties of the molecular sieve are shown in Table 1.

[0085] Example 1

[0086] The crystallization mother liquor obtained in the reference example was concentrated at 70-90°C, and water was continuously added during the process to obtain 110 grams of molecular sieve mother liquor, which was then purged with nitrogen to remove CO2. After analysis, the SiO2 content was 4.42%, the TPAOH content was 15%, the ethanol content was 7.5%, the water content was 73%, other impurities were 0.08%, and the CO2 content was undetectable.

[0087] Under stirring conditions, the above-mentioned 110g molecular sieve mother liquor, tetraethyl orthosilicate (TEOS), tetrapropylammonium hydroxide (TPAOH), ethanol 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 organic silicate calculated as SiO2 is 0.081:1; the molar ratio of the added ethanol to the SiO2 in the molecular sieve mother liquor is 31:1; in the colloidal mixture, the molar ratio of SiO2:tetrapropylammonium hydroxide:water is 1:0.25:25.

[0088] The colloidal mixture was fed into a stainless steel reactor with a stirring rate of 45 rpm and crystallized in an alcohol-hydrothermal system at 100°C for 3 days to obtain a molecular sieve slurry; it was then filtered on a 50 nm membrane tube to obtain a crystallization mother liquor, which was bottled for use in the examples. The molecular sieve slurry was then circulated and washed at a circulating water temperature of 40-60°C and a washing water amount of 6-8 L until the pH value of the washing water of the crystallized product reached about 9.1-9.3. The slurry was then concentrated and dried at 120°C for 24 hours to obtain about 70.5 g of silicon molecular sieve raw powder; it was then calcined at 550°C for 6 hours to obtain molecular sieve S1.

[0089] The X-ray diffraction (XRD) spectrum of molecular sieve S1 is as follows: Figure 2 As shown, it is consistent with the standard XRD spectrum characteristics of the MFI structure recorded in the literature (Microporous Materials, Vol 22, p637, 1998), indicating that the molecular sieve has an MFI crystal structure; the scanning electron microscope photo of the molecular sieve S1 is shown in Figure 4 The specific physical and chemical properties of the molecular sieve are shown in Table 1.

[0090] Example 2

[0091] The crystallization mother liquor obtained in the reference example was concentrated at 70-90°C for several hours, with water added continuously during the process, and then nitrogen was used to purge and remove CO2 to obtain 245 grams of molecular sieve mother liquor. After analysis, the SiO2 content was 1.98%, the TPAOH content was 6.75%, the ethanol content was 13%, the water content was 79.2%, and no CO2 was detected.

[0092] Under stirring conditions, the above-mentioned 245g molecular sieve mother liquor, TEOS, TPAOH, ethanol 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 organic silicate calculated as SiO2 is 0.08:1; the molar ratio of the added ethanol to the SiO2 in the molecular sieve mother liquor is 59:1; and the molar ratio of SiO2:tetrapropylammonium hydroxide:water in the colloidal mixture is 1:0.25:25.

[0093] The colloidal mixture was fed into a stainless steel reactor with a stirring rate of 45 rpm, and crystallized in an alcohol-hydrothermal system at 100°C for 3 days to obtain a molecular sieve slurry; it was then filtered on a 50 nm membrane tube to obtain a crystallization mother liquor, which was bottled and reserved for use in the examples. The molecular sieve slurry was then circulated and washed with a circulating water temperature of 40-60°C and a washing water amount of 6-8 L until the pH value of the washing water of the crystallized product reached about 9.1-9.3. The slurry was then concentrated and dried at 120°C for 24 hours to obtain about 70.5 g of silicon molecular sieve raw powder; it was then calcined at 550°C for 6 hours to obtain molecular sieve S2.

[0094] The X-ray diffraction (XRD) spectrum of molecular sieve S2 is Figure 2 Similar, indicating that the molecular sieve has an MFI crystal structure; the scanning electron microscope photo of molecular sieve S2 is similar to Figure 4 Similar; the specific physical and chemical properties of molecular sieves are listed in Table 1.

[0095] Example 3

[0096] According to the method of Example 1, the difference is that the molecular sieve mother liquor, TEOS, TPAOH, ethanol and water are mixed at room temperature for 4 hours under stirring conditions to obtain a colloidal mixture, wherein the mass ratio of SiO2 in the molecular sieve mother liquor to the mass ratio of organic silicate calculated as SiO2 is 0.081:1; the molar ratio of the added ethanol to SiO2 in the molecular sieve mother liquor is 70:1; and the molar ratio of SiO2:tetrapropylammonium hydroxide:water in the colloidal mixture is 1:0.25:25. Molecular sieve S3 is obtained.

[0097] The X-ray diffraction (XRD) spectrum of molecular sieve S3 is Figure 2 The results are similar, indicating that the molecular sieve has an MFI crystal structure. The specific physicochemical properties of the molecular sieve are listed in Table 1.

[0098] Example 4

[0099] The method of Example 1 was followed, except that no CO2 removal treatment was performed. The CO2 content in the obtained molecular sieve mother liquor was 122 ppm. The mother liquor was recycled in the same manner, and the obtained molecular sieve was recorded as S4.

[0100] The X-ray diffraction (XRD) spectrum of molecular sieve S5 is Figure 2 The results are similar, indicating that the molecular sieve has an MFI crystal structure. The specific physicochemical properties of the molecular sieve are listed in Table 1.

[0101] Comparative Example 1

[0102] According to the method of Example 1, the difference is that the molecular sieve mother liquor, TEOS, ethanol and water are mixed at room temperature for 4 hours under stirring conditions to obtain a colloidal mixture (tetrapropylammonium hydroxide is only provided by the molecular sieve mother liquor), wherein the mass ratio of SiO2 in the molecular sieve mother liquor to the mass ratio of organic silicate calculated as SiO2 is 0.32:1; the molar ratio of the added ethanol to SiO2 in the molecular sieve mother liquor is 23:1; in the colloidal mixture, the molar ratio of SiO2:tetrapropylammonium hydroxide:water is 1:0.25:25. Molecular sieve DS1 is obtained.

[0103] The X-ray diffraction (XRD) spectrum of molecular sieve DS1 is Figure 2The results are similar, indicating that the molecular sieve has an MFI crystal structure. The specific physicochemical properties of the molecular sieve are listed in Table 1.

[0104] Comparative Example 2

[0105] The method of Example 1 is followed, except that no additional alcohol is introduced into the colloidal mixture. In the colloidal mixture, the molar ratio of SiO2: tetrapropylammonium hydroxide: water is 1:0.22:30. The obtained molecular sieve is recorded as DS2.

[0106] The X-ray diffraction (XRD) spectrum of molecular sieve DS2 is Figure 2 Similarly, it is consistent with the standard XRD spectrum characteristics of the MFI structure recorded in the literature (Microporous Materials, Vol 22, p637, 1998), indicating that the molecular sieve has an MFI crystal structure. The specific physical and chemical properties of the molecular sieve are listed in Table 1.

[0107] Table 1

[0108]

[0109]

[0110] Test Case

[0111] This test example is used to illustrate the catalytic reaction results of the all-silicon-1 molecular sieve provided by the present invention in a gas-phase Beckmann rearrangement reaction.

[0112] 100 g of the molecular sieves prepared in the above embodiments and comparative examples and 1000 g of an alkaline buffer solution of a nitrogen-containing compound (the alkaline buffer solution of a nitrogen-containing compound is a mixture of ammonia water and an aqueous solution of ammonium nitrate, with a pH value of 11.35, wherein the content of ammonia water is 26% by weight, the content of ammonium nitrate in the aqueous solution of ammonium nitrate is 7.5% by weight, and the weight ratio of ammonia water to the aqueous solution of ammonium nitrate is 3:2) were added to a 2000 mL stainless steel reactor (KCF-2 magnetic stirring autoclave, Yantai High-tech Zone Keli Automatic Control Equipment Research Institute) and heated at 83 ° C and 2.2 kg / cm 2 The mixture was stirred at a constant temperature for 2 hours under pressure, and then filtered and washed until the pH of the filtered clear liquid was about 9, and then dried at 120° C. for 24 hours to obtain a molecular sieve catalyst, which was then used for a gas-phase Beckmann rearrangement reaction.

[0113] The reaction device is carried out in a homemade atmospheric pressure continuous flow fixed bed, the inner diameter of the reactor is 6 mm, the catalyst loading amount is 0.375 g, and the catalyst particle size is 20-60 mesh.

[0114] After the catalyst was loaded into the reaction tube, it was pretreated in a nitrogen atmosphere at normal pressure and 350° C. for 1 hour.

[0115] The conditions for the gas phase Beckmann rearrangement reaction included: a cyclohexanone oxime concentration of 35%, a weight hourly space velocity (WHSV) of 16 h -1 , the solvent is ethanol, the reaction temperature is 380°C, the nitrogen flow rate is 2.7 L / h, and the reaction time is 6 hours.

[0116] The reaction product was collected after cooling by water circulation. The results were shown in Table 2 by capillary gas chromatography and hydrogen flame detector.

[0117] Table 2

[0118]

[0119]

[0120] It can be seen from the results in Table 1 and Table 2 that by adopting the preparation method provided by the present invention, by introducing an appropriate amount of alcohol and recycling the molecular sieve mother liquor, the components that do not participate in the reaction in the synthesis mother liquor of the all-silicon-1 molecular sieve can be effectively utilized, the synthesis yield of the molecular sieve can be improved, and the prepared all-silicon molecular sieve has a higher crystallinity and is close to the physicochemical properties of the reference sample; it is used in the gas-phase Beckmann rearrangement reaction and has a higher conversion rate and selectivity.

[0121] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for preparing an all-silicon molecular sieve with an MFI topological structure, characterized in that: The following steps are involved: (1) mixing a molecular sieve mother liquid, an organic silicate, an organic template, and an alcohol to obtain a colloidal mixture; The amounts of the molecular sieve mother liquid and the organosilicate are such that the mass ratio of SiO2 in the molecular sieve mother liquid to the mass ratio of the organosilicate calculated as SiO2 is 0.01-0.2:1; The molar ratio of alcohol to SiO2 in the molecular sieve mother liquor is (10-100): 1; (2) subjecting the colloidal mixture to a crystallization reaction; (3) subjecting the crystallized product obtained in step (2) to solid-liquid separation to obtain a molecular sieve wet material and a crystallization mother liquor; Drying and calcining the molecular sieve wet material to obtain an all-silicon molecular sieve with an MFI topological structure; (4) The crystallization mother liquor is optionally concentrated, and then returned to step (1) to provide the molecular sieve mother liquor.

2. The preparation method according to claim 1, wherein The amounts of the molecular sieve mother solution and the organosilicate are such that the mass ratio of SiO2 in the molecular sieve mother solution to the mass ratio of the organosilicate calculated as SiO2 is 0.02-0.15:1; And / or, the molar ratio of alcohol to SiO2 in the molecular sieve mother liquor is (30-70):

1.

3. The preparation method according to claim 1 or 2, wherein The molecular sieve mother solution includes an organic template, SiO2, water and optional alcohol; Preferably, in the molecular sieve mother liquid, the content of the organic template is 10-20wt%, the content of SiO2 is 2-10wt%, the content of water is 60-90wt%, and the content of alcohol is 1-10wt%; Preferably, the concentration conditions in step (4) include: a temperature of 50-100° C., preferably 70-90° C., and water is continuously added during the process; Preferably, the preparation method further comprises: before the mixing in step (1), subjecting the molecular sieve mother liquor to a CO2 removal treatment so that the CO2 content in the molecular sieve mother liquor is not higher than 100 ppm.

4. The preparation method according to any one of claims 1 to 3, wherein: In the colloidal mixture, the molar ratio of SiO2, organic template and water is 1:(0.1-0.5):(10-50); And / or, the crystallization conditions in step (2) include: crystallization at 80-150° C. for 1-5 days.

5. The preparation method according to any one of claims 1 to 4, wherein: The organic silicate is ethyl orthosilicate and / or methyl orthosilicate, preferably ethyl orthosilicate; And / or, the organic template is selected from quaternary ammonium base compounds, further preferably tetrapropylammonium hydroxide and / or tetraethylammonium hydroxide, preferably tetrapropylammonium hydroxide; And / or, the alcohol is methanol and / or ethanol, preferably ethanol.

6. The preparation method according to any one of claims 1 to 5, wherein: 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 40-60 nm; Preferably, the filtration membrane is an inorganic membrane.

7. The preparation method according to any one of claims 1 to 6, wherein: Prior to the drying, step (3) further comprises: washing and concentrating the molecular sieve wet material; Preferably, the washing comprises: washing the molecular sieve wet material until the pH value of the washing water is 9-9.4; Preferably, the solid content of the product obtained by the concentration is 20-40 wt%.

8. The preparation method according to any one of claims 1 to 7, wherein: In step (3), the drying conditions include: temperature of 100-120° C. and time of 12-48 h; And / or, the calcination conditions include: temperature of 400-600° C. and time of 5-12 h.

9. An all-silicon molecular sieve with an MFI topological structure obtained by the preparation method according to any one of claims 1 to 8.

10. Use of the all-silicon molecular sieve with MFI topology structure as claimed in claim 9 in the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime.

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