Process for the preparation of a full-silica molecular sieve of mfi topology, full-silica molecular sieve of mfi topology and use thereof

Abstract

This invention relates to the field of all-silica molecular sieve preparation technology, and discloses a method for preparing an MFI topological structure all-silica molecular sieve, the MFI topological structure all-silica molecular sieve and its application, comprising: (1) mixing molecular sieve mother liquor, organosilicate, 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 crystallization product obtained in step (2) to obtain a wet molecular sieve and a crystallization mother liquor; drying and calcining the wet molecular sieve to obtain an MFI topological structure all-silica molecular sieve; (4) optionally concentrating the crystallization mother liquor, and then returning to step (1) to provide the molecular sieve mother liquor. This method can obtain highly crystallized, fine-particle all-silica-1 molecular sieves, reduce the raw material cost of molecular sieve synthesis, and improve the economics of the new gas-phase rearrangement process technology.

Description

Technical Field

[0001] This invention relates to the field of all-silica molecular sieve preparation technology, specifically to a method for preparing an MFI topological all-silica molecular sieve, the MFI topological all-silica molecular sieve and its applications. Background Technology

[0002] Aluminum-free, neutral, submicron-sized all-silica-1 molecular sieves with ZSM-5 structure are generally synthesized in an alcohol-hydrothermal system. This process requires a large amount of expensive template agent, resulting in high synthesis costs. Furthermore, the synthesis process generates significant amounts of ethanol, leading to high COD levels in wastewater discharge, as well as large emissions of amines (nitrogen) and total nitrogen, causing severe environmental pollution.

[0003] The synthesis of molecular sieves under self-generated pressure hydrothermal system generally has a synthesis yield of 50-80%, and the yield may be even lower for some molecular sieves. Therefore, the mother liquor after molecular sieve synthesis and crystallization will contain a large number of unreacted raw material components. These components can be completely dissolved in the zero-time mother liquor after molecular sieve filtration. For laboratory synthesis, the mother liquor is often directly discarded. However, for industrial production, the discharge of mother liquor not only wastes raw materials, but also causes significant environmental pollution.

[0004] However, existing methods for recycling mother liquor in molecular sieve synthesis are all applied to framework structures such as silica-alumina molecular sieves or titanium-silica molecular sieves. Effective methods for recycling mother liquor in the synthesis of ZSM-5 type all-silica-1 molecular sieves are still lacking. Therefore, the recycling of mother liquor in the synthesis of ZSM-5 type all-silica-1 molecular sieves is of greater significance. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of high preparation cost, difficult synthesis, and ineffective utilization of mother liquor in the existing technology of MFI topological structure all-silica molecular sieves. This invention provides a method for preparing MFI topological structure all-silica molecular sieves, the MFI topological structure all-silica molecular sieves and their applications. This preparation method can achieve the preparation of MFI topological structure all-silica molecular sieves at a lower cost. The molecular sieve has good catalytic activity when applied in the production of caprolactam.

[0006] To achieve the above objectives, the present invention provides a method for preparing an all-silica molecular sieve with an MFI topology, comprising:

[0007] (1) Mix the molecular sieve mother liquor, organosilicate, organic template agent and KOH to obtain a colloidal mixture;

[0008] 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 0.01-0.2:1.

[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; the molecular sieve wet material is dried and calcined to obtain an all-silicon molecular sieve with MFI topology;

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

[0013] A second aspect of the present invention provides an all-silica molecular sieve with an MFI topological structure prepared by the above preparation method.

[0014] The third aspect of this invention provides the application of the above-described MFI topological structure of all-silica molecular sieves in the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime.

[0015] The preparation method provided by this invention can effectively utilize the mother liquor for the synthesis of all-silica molecular sieves, thereby improving the synthesis yield of molecular sieves, shortening the crystallization time, and reducing the synthesis cost of molecular sieves. At the same time, this invention breaks through the technical bias in the conventional synthesis of all-silica-1 molecular sieves by creatively introducing an appropriate amount of KOH during the synthesis process. Combined with the reuse of the molecular sieve mother liquor, it can obtain a near-neutral all-silica-1 molecular sieve with high crystallinity, fine particles, and a ZSM-5 type structure. This can further effectively reduce the amount of organic template agent used, reduce the raw material cost of molecular sieve synthesis, and improve the economics of the new gas-phase rearrangement process technology. Attached Figure Description

[0016] Figure 1 This is the X-ray diffraction (XRD) pattern of molecular sieve S1;

[0017] Figure 2 This is a scanning electron microscope image of molecular sieve S1. Detailed Implementation

[0018] 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.

[0019] The first aspect of this invention provides a method for preparing an all-silica molecular sieve with an MFI topology, comprising:

[0020] (1) Mix the molecular sieve mother liquor, organosilicate, organic template agent and KOH to obtain a colloidal mixture;

[0021] 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 0.01-0.2:1.

[0022] 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);

[0023] (2) The colloidal mixture is subjected to a crystallization reaction;

[0024] (3) The crystallization product obtained in step (2) is subjected to solid-liquid separation to obtain molecular sieve wet material and crystallization mother liquor; the molecular sieve wet material is dried and calcined to obtain an all-silicon molecular sieve with MFI topology;

[0025] (4) The crystallized mother liquor is optionally concentrated, and then the process is returned to step (1) to provide the molecular sieve mother liquor.

[0026] The method for preparing MFI topological structured all-silica molecular sieves provided by this invention uses the molecular sieve mother liquor obtained in the molecular sieve preparation as raw material and introduces KOH at the same time. This can obtain a nearly neutral all-silica-1 molecular sieve with high crystallinity, fine particles, and ZSM-5 structure. It can further effectively reduce the amount of organic template agent used and obtain a nearly neutral all-silica-1 molecular sieve with high crystallinity, fine particles, and ZSM-5 structure.

[0027] 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-silica 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-silica molecular sieves with MFI topological structures with a lower amount of organic template agent. This is beneficial for reducing the consumption of raw materials, especially expensive organic template agents, and can effectively reduce environmental pollution. At the same time, the presence of molecular sieve microcrystals in the mother liquor can act as seed crystals, thereby helping to shorten the crystallization time and improve the relative crystallinity and yield of the molecular sieve.

[0028] 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.

[0029] 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.

[0030] 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%.

[0031] 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.

[0032] In a preferred embodiment, no additional alcohol is introduced during the mixing process described in step (1).

[0033] 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:

[0034] a. Mix organosilicate, organic template agent, KOH and water to obtain a colloidal mixture;

[0035] 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);

[0036] b. Perform a crystallization reaction on the colloidal mixture;

[0037] c. Perform solid-liquid separation on the crystallized product obtained in step (2) to obtain crystallization mother liquor;

[0038] d. The crystallization mother liquor is optionally concentrated to obtain molecular sieve mother liquor.

[0039] 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.

[0040] 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.

[0041] According to the present invention, 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 is beneficial for reducing the amount of organic template agent used while ensuring the synthesis quality of the molecular sieve.

[0042] In this invention, 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 organosilicate (calculated as SiO2); the water in the colloidal mixture can be entirely derived from the molecular sieve mother liquor and water introduced from the raw materials of other components, 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 make adjustments according to actual needs.

[0043] 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.

[0044] According to the present invention, preferably, the silicon source is methyl orthosilicate and / or ethyl orthosilicate, more preferably ethyl orthosilicate.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] Preferably, the iron ion content in the organic template agent is not greater than 10 ppm.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] Preferably, the concentration conditions in step (4) include a temperature of 50-100°C, preferably 70-90°C.

[0056] 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.

[0057] According to the present invention, preferably, prior to the drying process, in order to completely remove the dissolved components other than the molecular sieve crystals remaining in the crystals, a washing treatment may be performed using an organic solvent such as methanol or ethanol, or water. According to a specific embodiment of the present invention, the washing includes: washing the wet molecular sieve material until the pH value of the washing water is 9-9.4.

[0058] The present invention has a wide range of options for the drying process in step (3). Preferably, the drying conditions include: a temperature of 100-120°C and a time of 12-48h.

[0059] According to the present invention, preferably, the calcination conditions include: a temperature of 400-600°C and a time of 5-24 hours.

[0060] A second aspect of the present invention provides an all-silica molecular sieve with an MFI topological structure prepared by the above preparation method.

[0061] In this invention, the molecular sieve configuration of the product can be determined by X-ray diffraction spectroscopy. X-ray diffraction spectral data were obtained using a SIEMENS D5005D diffractometer (Germany), under the following conditions: Cu target Kα radiation, Ni filter, tube voltage 40 kV, and tube current 40 mA. The X-ray diffraction (XRD) pattern is consistent with the standard XRD pattern characteristics of the MFI structure described in Microporous Materials, Vol 22, p637, 1998, indicating that the molecular sieve possesses an MFI crystal structure (i.e., ZSM-5 type).

[0062] The all-silica molecular sieve prepared by the method provided by the present invention has a high degree of crystallinity. Preferably, the relative crystallinity of the all-silica molecular sieve is not less than 90%, and more preferably 90-110%.

[0063] The method for testing relative crystallinity is as follows: using standard ZSM-5 molecular sieve (molar ratio of silicon dioxide to alumina of 30) as a standard sample, and taking the peak area of ​​the XRD characteristic peak of the standard sample as a benchmark, the percentage of the peak area of ​​the XRD characteristic peak of the sample to be tested relative to the peak area of ​​the standard sample is taken 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 (20wt% aqueous solution), silicic acid (Merck, SiO2·H2O), and sodium aluminate (Al2O3: 1.24Na2O: 0.57H2O) as raw materials. (1) 710.3 g H2O, 13.8 g NaOH and 117 g TPAOH solution were fully dissolved and mixed until uniform; (2) 158.9 g silicic acid was gradually added to the above solution in batches under stirring. After shaking fully at room temperature for 1 hour, it was aged at 100℃ for 16 hours. (3) Mix 867.8 g H2O, 8.8 g NaOH and 10.3 g sodium aluminate thoroughly; (4) Add 113.1 g silicic acid gradually in batches to dissolve (3) under thorough stirring, and shake vigorously at room temperature for 1 hour; (5) Add 50 g of the colloidal seed crystals obtained in step (2) to (4) and shake for another 1 hour; (6) Then place the material in a stainless steel reactor lined with PTFE, crystallize at 180°C for 40 hours, remove the crystallized product, filter, wash thoroughly with deionized water, dry at 105°C for 24 hours, and calcine at 550°C for 6 hours to obtain ZSM-5 sample.

[0065] Preferably, the specific surface area of ​​the all-silica molecular sieve is 380-480 m². 2 / g, preferably 400-460m 2 / g.

[0066] Preferably, the micro specific surface area of ​​the all-silica molecular sieve is 340-440 m². 2 / g, preferably 360-420m 2 / g.

[0067] Preferably, the pore volume of the all-silica molecular sieve is 0.2-0.6 mL / g, and more preferably 0.3-0.6 mL / g.

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

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

[0070] The specific surface area and pore distribution of BET samples were determined using a Micromeritics ASAP-2400 automated adsorption analyzer. Each sample was evacuated to 10 °C at a specific temperature. -5 Pa and N2 were used as adsorbates, and liquid nitrogen was used for temperature adsorption. The maximum partial pressure (p / p0) was less than 0.3 during the 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 this invention provides the application of the above-described MFI topological structure of all-silica molecular sieves in the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime.

[0072] The all-silica molecular sieve provided by this invention can be used directly as a catalyst for the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime, or optionally after being shaped, as a catalyst for the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime, which can improve the conversion rate of cyclohexanone oxime and the selectivity of caprolactam.

[0073] The present invention does not particularly limit the mode and conditions of the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime, and can be carried out in accordance with conventional methods in the art.

[0074] Preferably, 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.

[0075] Preferably, the molar ratio of the solvent to cyclohexanone oxime is 2-10:1.

[0076] Preferably, the solvent is selected from C1-C6 fatty alcohols, and more preferably at least one of methanol, ethanol and n-propanol.

[0077] 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 0.1-100:1, more preferably 0.5-50:1.

[0078] Preferably, the conditions for the gas-phase Beckmann rearrangement reaction include a cyclohexanone oxime weight hourly space velocity (WHSV) of 0.1-20 h⁻¹. -1 Preferably 0.5-20h -1 The reaction temperature is 300-500℃, preferably 350-400℃; the reaction pressure is 0.1-0.5MPa using a gauge manometer.

[0079] Preferably, before contacting the cyclohexanone oxime with the catalyst, the process further includes pretreating the catalyst under a nitrogen atmosphere. The pretreatment temperature is 300-400°C, and the time is 0.5-2 hours.

[0080] The present invention will be described in detail below through embodiments.

[0081] 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.

[0082] Preparation Example - Synthesis of Molecular Sieve Mother Liquor

[0083] 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. The molar ratio of tetraethyl orthosilicate:tetrapropylammonium hydroxide:KOH:water, calculated as SiO2, was 1:0.15:0.04:25. The colloidal mixture was then fed into a stainless steel reactor and subjected to hydrothermal crystallization at 120°C for 2 days with a stirring rate of 45 rpm to obtain a molecular sieve slurry. The slurry was then filtered at a temperature on a 50 nm membrane tube to obtain a crystallization mother liquor, which was reserved for use in the examples.

[0084] The following examples illustrate the preparation of the all-silica molecular sieve with MFI topology in this invention.

[0085] Example 1

[0086] 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%.

[0087] 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.

[0088] The above colloidal mixture was fed into a stainless steel reactor and crystallized in an alcohol-hydrothermal system 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 for use in the example. The filtered molecular sieve slurry was then subjected to circulating washing with water at a temperature of 40-60°C and a washing water volume of 6-8 ml. 3 The washing water for the crystallized product was washed until the pH value reached approximately 9.1-9.3. The slurry was then concentrated and dried at 120℃ for 24 hours to obtain silicon molecular sieve powder. This powder was then calcined at 550℃ for 6 hours to obtain molecular sieve S1. The yield of the molecular sieve was calculated to be 95%.

[0089] The X-ray diffraction (XRD) pattern of molecular sieve S1 is shown below. Figure 1 As shown, the XRD pattern is consistent with the standard XRD pattern of the MFI structure described in the literature (Microporous Materials, Vol 22, p637, 1998), indicating that the molecular sieve has an MFI crystal structure; the scanning electron microscope image of molecular sieve S1 is shown below. Figure 2 As shown; the specific physicochemical properties of the molecular sieve are listed in Table 1.

[0090] Example 2

[0091] 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%.

[0092] Under stirring conditions, the above 245 kg molecular sieve mother liquor, TEOS, TPAOH 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.

[0093] The above colloidal mixture was fed into a stainless steel reactor and crystallized in an alcohol-hydrothermal system 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 for use in the example. The filtered molecular sieve slurry was then subjected to circulating washing with water at a temperature of 40-60°C and a washing water volume of 6-8 ml. 3The washing water for the crystallized product is washed until the pH value reaches about 9.1-9.3. Then the slurry is concentrated and dried at 120℃ for 24 hours to obtain silicon molecular sieve raw powder. Then it is calcined at 550℃ for 6 hours to obtain molecular sieve S2.

[0094] X-ray diffraction (XRD) pattern of molecular sieve S2 and Figure 1 Similarly, this indicates that the molecular sieve possesses an MFI crystal structure; the scanning electron microscope image of molecular sieve S2 is similar to... Figure 2 Similarly, the specific physicochemical properties of molecular sieves are listed in Table 1.

[0095] Example 3

[0096] The method of Example 1 is followed, except that the mass ratio of SiO2 to organosilicon ester (calculated as SiO2) in the molecular sieve mother liquor is 0.2:1, keeping the composition ratio of the colloidal mixture unchanged. Molecular sieve S3 is obtained.

[0097] X-ray diffraction (XRD) pattern of molecular sieve S3 and Figure 1 Similarly, this indicates that the molecular sieve has an MFI crystal structure, and 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 the amount of KOH used was adjusted so that the composition of the colloidal mixture satisfied the molar ratio of SiO2:tetrapropylammonium hydroxide:KOH:water as 1:0.15:0.1:25. Molecular sieve S4 was obtained.

[0100] X-ray diffraction (XRD) pattern of molecular sieve S4 and Figure 1 Similarly, this indicates that the molecular sieve has an MFI crystal structure, and the specific physicochemical properties of the molecular sieve are listed in Table 1.

[0101] Example 5

[0102] Following the method of Example 1, except that the tetraethyl orthosilicate was obtained from Jiangxi Chenguang New Material 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. Molecular sieve S5 was obtained.

[0103] Example 6

[0104] The method was followed in Example 1, except that the crystallization temperature was 80°C and the crystallization time was 3 days. Molecular sieve S6 was obtained. The yield of the molecular sieve was calculated to be 56%.

[0105] Comparative Example 1

[0106] 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.

[0107] The X-ray diffraction (XRD) pattern of the prepared molecular sieve DS1 and Figure 1 Similarly, this indicates that the molecular sieve has an MFI crystal structure, and the specific physicochemical properties of the molecular sieve are listed in Table 1.

[0108] Parameter

[0109] Synthesize all-silica-1 molecular sieve according to method two disclosed in CN1338427A:

[0110] 139 g of tetraethyl orthosilicate (TEOS) was poured into a 1000 mL beaker at room temperature and stirred for 30 minutes. 120 g of a 22.5% tetrapropylammonium hydroxide aqueous solution was added to TEOS, and the mixture was stirred and hydrolyzed at room temperature for 5 hours. 147 g of water and 267 g of ethanol were added, and the mixture was stirred until a sol was formed. The chemical composition of the sol was H₂O / SiO₂ = 20, EtOH / SiO₂ = 12.7, and TPAOH / SiO₂ = 0.20. The mixture was crystallized at 100 °C for 3 days, washed, filtered, dried at 120 °C for 24 hours, and calcined at 550 °C for 5 hours to obtain the all-silica-1 molecular sieve product.

[0111] Table 1

[0112]

[0113]

[0114] Test case

[0115] This test example illustrates the catalytic reaction results of the all-silica-1 molecular sieve provided by this invention in a gas-phase Beckmann rearrangement reaction.

[0116] 100g of the molecular sieves prepared in the above examples and comparative examples were added to 1000g of an alkaline buffer solution containing nitrogen compounds (the alkaline buffer solution containing nitrogen compounds was a mixture of ammonia water and ammonium nitrate aqueous solution, with a pH value of 11.35, wherein the content of ammonia water was 26 wt%, the content of ammonium nitrate in the ammonium nitrate aqueous solution was 7.5 wt%, and the weight ratio of ammonia water to ammonium nitrate aqueous solution was 3:2) in a 2000mL stainless steel reactor (KCF-2 type magnetic stirring high-pressure reactor, Yantai High-tech Zone Keli Automation Equipment Research Institute). The reactor was subjected to a reaction at 83℃ and 2.2kg / cm². 2 The mixture was stirred under pressure and kept at a constant temperature for 2 hours, then filtered and washed until the pH of the filtrate was about 9. It was then dried at 120°C for 24 hours to obtain a molecular sieve catalyst, which was then used in the gas-phase Beckmann rearrangement reaction.

[0117] The reaction was carried out in a self-made atmospheric pressure continuous flow fixed bed reactor with an inner diameter of 6 mm, a catalyst loading of 0.375 g, and a catalyst particle size of 20-60 mesh.

[0118] After the catalyst is loaded into the reaction tube, it is pretreated for 1 hour in a nitrogen atmosphere at atmospheric pressure and 350°C.

[0119] The conditions for the gas-phase Beckmann rearrangement reaction included: a cyclohexanone oxime concentration of 35% and a weight hourly space velocity (WHSV) of 16 h⁻¹. -1 The solvent was ethanol, the reaction temperature was 380℃, the nitrogen flow rate was 2.7 L / h, and the reaction time was 6 hours.

[0120] The reaction products were collected after being cooled by water circulation. They were determined by capillary gas chromatography with a flame ionization detector. The results are shown in Table 2.

[0121] Table 2

[0122] serial number Conversion rate % CPL selectivity % AEH selectivity % Example 1 99.52 95.39 2.11 Example 2 99.55 95.51 2.16 Example 3 98.30 95.25 2.00 Example 4 99.24 94.90 1.95 Example 5 99.35 94.67 1.92 Example 6 99.54 95.33 2.06 Comparative Example 1 96.10 95.22 1.90 Reference 99.67 95.54 2.20

[0123] As can be seen from the results in Table 2, the molecular sieves prepared in the embodiments of the present invention have comparable catalytic activity to those prepared in the reference ratio, with higher conversion rates and selectivity. Compared with the conventional preparation method in the reference ratio, the introduction of molecular sieve mother liquor and KOH can significantly reduce the preparation cost of molecular sieves and improve the economy of the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime.

[0124] 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 an all-silica molecular sieve with an MFI topological structure, characterized in that, include: (1) Mix molecular sieve mother liquor, organosilicate, organic template agent and KOH to obtain colloidal mixture; 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 0.01-0.2:

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; the molecular sieve wet material is dried and calcined to obtain an all-silicon molecular sieve with MFI topology; (4) The crystallized mother liquor is optionally concentrated, and then the process is returned to step (1) to provide the molecular sieve mother liquor.

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.

3. The preparation method according to claim 1 or 2, characterized in that, The composition of the colloidal mixture satisfies that 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.

4. The preparation method according to any one of claims 1-3, 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%.

5. The preparation method according to any one of claims 1-4, characterized in that, The organic template agent is selected from quaternary ammonium base compounds, 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.

6. The preparation method according to any one of claims 1-5, 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.

7. The preparation method according to any one of claims 1-6, 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.

8. The preparation method according to any one of claims 1-7, characterized in that, Prior to the drying process, step (3) further includes washing and concentrating the wet molecular sieve material; Preferably, the washing includes: washing the wet molecular sieve material until the pH value of the washing water is 9-9.4; Preferably, the solid content of the product obtained by concentration is 20-40 wt%. Preferably, in step (3), the drying conditions include: a temperature of 100-120°C and a time of 12-48 hours; Preferably, the calcination conditions include: a temperature of 400-600℃ and a time of 5-24h.

9. The all-silica molecular sieve with MFI topology obtained by the preparation method according to any one of claims 1-8.

10. The application of the all-silica molecular sieve with the MFI topology structure according to claim 9 in the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime.

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