Process for the preparation of all-silica-1 molecular sieves from spent catalyst, all-silica-1 molecular sieves and their use

Abstract

This invention relates to the field of all-silica-1 molecular sieve preparation technology, and discloses a method for preparing all-silica-1 molecular sieves from waste catalysts, all-silica-1 molecular sieves and their applications, comprising: (1) carbonizing the waste cyclohexanone oxime gas-phase Beckmann rearrangement catalyst; (2) mixing the product obtained in step (1) with water and slurrying, and grinding until the particle diameter in the slurry is less than 20 μm; (3) mixing the slurry, KOH, organic template agent and alcohol to obtain a colloidal mixture; the composition of the colloidal mixture satisfies the following: the molar ratio of silicon species, KOH, organic template agent, alcohol and water (calculated as SiO2) is 1:(0.01-0.1):(0.04-0.15):(3.5-20):(15-45); (4) crystallizing the colloidal mixture, and then drying and calcining it. This method can eliminate solid waste, save the amount of silicon source and organic template agent used, 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-1 molecular sieve preparation technology, specifically to a method for preparing all-silica-1 molecular sieve from waste catalyst, all-silica-1 molecular sieve and its applications. Background Technology

[0002] MFI-structured all-silica-1 molecular sieve, also known as Silicalite-1 molecular sieve or pure silicon-1 molecular sieve, was first successfully synthesized in 1978 by Flanigen E.M. et al. of Union Carbide Corporation (UCC). It is the last member of the "Pentasil" family. All-silica-1 molecular sieve is an aluminum-free molecular sieve with a ZSM-5 structure. It is the simplest molecular sieve in the ZSM-5 family, with a framework containing only silicon and oxygen atoms, and its basic structural unit is the SiO4 tetrahedron. MFI-structured all-silica-1 molecular sieve possesses abundant microporous structure and regular, uniform three-dimensional channels. It exhibits a defined crystal structure of ZSM-5 molecular sieves, a high microporous specific surface area, good thermal stability, and excellent adsorption and desorption properties, making it a good catalyst material. MFI-structured all-silica-1 molecular sieve can be used as a material for membrane separation and as a catalyst for the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime to produce caprolactam.

[0003] The synthesis of MFI-structured all-silica-1 molecular sieves generally employs the traditional organic raw material hydrothermal method. Silicon sources can include solid silica, silica sol, silica fume, and tetraethyl orthosilicate (TEOS). Template agents typically include tetrapropylammonium hydroxide (TPAOH), low-carbon hydrocarbon quaternary ammonium salts or mixtures thereof, and amine compounds. Crystallization is carried out at temperatures above 150°C for several days. All-silica-1 molecular sieves with a silicon / aluminum ratio exceeding 50,000 usually use tetraethyl orthosilicate as the silicon source and tetrapropylammonium hydroxide as the template agent and alkali source. In current industrial synthesis, synthesizing one ton of molecular sieve generally requires four tons of tetraethyl orthosilicate. The raw material cost of tetraethyl orthosilicate accounts for more than one-third (approximately 40%) of the total raw material cost. Therefore, the synthesis cost of MFI-structured all-silica-1 molecular sieves remains high. Summary of the Invention

[0004] The purpose of this invention is to overcome the problem of high synthesis cost of MFI structure all-silica-1 molecular sieves in the prior art, and to provide a method for preparing all-silica-1 molecular sieves from waste catalysts, all-silica-1 molecular sieves and their applications. This method can prepare all-silica-1 molecular sieves using waste catalysts, and the obtained molecular sieves have high specific surface area and external specific surface area.

[0005] To achieve the above objectives, a first aspect of the present invention provides a method for preparing all-silica-1 molecular sieves from spent catalysts, the method comprising:

[0006] (1) Carbonization treatment of waste cyclohexanone oxime gas-phase Beckmann rearrangement catalyst;

[0007] The waste cyclohexanone oxime gas-phase Beckmann rearrangement catalyst contains all-silica-1 molecular sieve;

[0008] (2) Mix the product obtained in step (1) with water and grind it until the particle diameter in the slurry is less than 20 μm, the particle diameter of 90% of the volume is less than 10 μm, and the particle diameter of 70% of the volume is less than 5 μm.

[0009] (3) The slurry, KOH, organic template agent and alcohol are mixed to obtain a colloidal mixture;

[0010] The composition of the colloidal mixture satisfies the following: the molar ratio of silicon species (calculated as SiO2), KOH, organic template agent, alcohol and water is 1:(0.01-0.1):(0.04-0.15):(3.5-20):(15-45);

[0011] (4) The colloidal mixture is crystallized, then dried and calcined.

[0012] The second aspect of the present invention provides an all-silica-1 molecular sieve obtained by the above-described method for preparing all-silica-1 molecular sieves from waste catalysts.

[0013] The third aspect of this invention provides the application of the all-silica-1 molecular sieve described in the second aspect in the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime.

[0014] Through the above technical solution, the method provided by this invention can utilize industrial waste catalyst from the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime. By burning carbon, pulping, and grinding, a silicon-containing slurry with a suitable particle size is obtained as a silicon source. In the synthesis process, an appropriate amount of KOH is creatively introduced to obtain a near-neutral all-silica-1 molecular sieve with high crystallinity, fine particles, and ZSM-5 type structure. This not only eliminates solid waste and significantly saves silicon source costs, but also effectively reduces the amount of organic template agent used, reduces the raw material cost of molecular sieve synthesis, and improves the economics of the new gas-phase rearrangement process technology. Attached Figure Description

[0015] Figure 1 This is the XRD diffraction pattern of the all-silica-1 molecular sieve prepared in Example 1;

[0016] Figure 2 This is a SEM image of the all-silica-1 molecular sieve prepared in Example 1. Detailed Implementation

[0017] 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.

[0018] The first aspect of this invention provides a method for preparing all-silica-1 molecular sieves from spent catalysts, the method comprising:

[0019] (1) Carbonization treatment of waste cyclohexanone oxime gas-phase Beckmann rearrangement catalyst;

[0020] The waste cyclohexanone oxime gas-phase Beckmann rearrangement catalyst contains all-silica-1 molecular sieve;

[0021] (2) Mix the product obtained in step (1) with water and grind it until the particle diameter in the slurry is less than 20 μm, the particle diameter of 90% of the volume is less than 10 μm, and the particle diameter of 70% of the volume is less than 5 μm.

[0022] (3) The slurry, KOH, organic template agent and alcohol are mixed to obtain a colloidal mixture;

[0023] The composition of the colloidal mixture satisfies the following: the molar ratio of silicon species (calculated as SiO2), KOH, organic template agent, alcohol and water is 1:(0.01-0.1):(0.04-0.15):(3.5-20):(15-45);

[0024] (4) The colloidal mixture is crystallized, then dried and calcined.

[0025] According to this invention, a silicon-containing slurry with suitable particle size is obtained through carbonization, pulping, and grinding, which serves as the silicon source. An appropriate amount of KOH is creatively introduced during the synthesis process, resulting in a near-neutral all-silica-1 molecular sieve with high crystallinity, fine particles, and a ZSM-5 type structure. This eliminates solid waste, significantly reduces silicon source costs, and effectively reduces the amount of organic template agent used, thereby decreasing the raw material costs of molecular sieve synthesis and improving the economics of the new gas-phase rearrangement process. The all-silica-1 molecular sieve prepared using the above method has a high specific surface area and external specific surface area. When applied to the production of caprolactam, it can improve the conversion rate of oximes and the selectivity of caprolactams.

[0026] In this invention, the “waste cyclohexanone oxime gas-phase Beckmann rearrangement catalyst” refers to the deactivated all-silica-1 molecular sieve catalyst (silicon / aluminum ratio exceeding 50,000) discharged from the cyclohexanone oxime gas-phase Beckmann rearrangement reactor, which has lost its regeneration significance, has no economic value, and is prepared for disposal or landfill.

[0027] This invention does not impose any particular limitation on the shape of the spent cyclohexanone oxime gas-phase Beckmann rearrangement catalyst; it can be a strip-shaped catalyst, a spherical catalyst, or a microsphere catalyst. This invention also does not impose any particular limitation on the composition of the spent cyclohexanone oxime gas-phase Beckmann rearrangement catalyst, as long as it contains all-silica-1 molecular sieve. Preferably, the content of all-silica-1 molecular sieve in the spent cyclohexanone oxime gas-phase Beckmann rearrangement catalyst is 50-95 wt%, more preferably 60-90 wt%.

[0028] According to the present invention, the spent cyclohexanone oxime gas-phase Beckmann rearrangement catalyst may also contain a binder. Typically, the binder in existing spent cyclohexanone oxime gas-phase Beckmann rearrangement catalysts is silica. Using the method provided by the present invention, the silicon species in the all-silica-1 molecular sieve and optionally the silica binder in the spent cyclohexanone oxime gas-phase Beckmann rearrangement catalyst can be recovered to provide the silicon source required for the synthesis of the all-silica-1 molecular sieve.

[0029] According to the present invention, the spent cyclohexanone oxime gas-phase Beckmann rearrangement catalyst also contains carbon deposits formed by the reaction, preferably, the amount of carbon deposits in the spent cyclohexanone oxime gas-phase Beckmann rearrangement catalyst is 1-15 wt%.

[0030] In this invention, the carbonization process described in step (1) can be carried out in a manner conventional in the art, with the aim of removing carbon deposits from the surface of the waste cyclohexanone oxime gas-phase Beckmann rearrangement catalyst. The calcination time and temperature can be determined according to the degree of catalyst deactivation. Preferably, strip-shaped or spherical deactivated catalysts discharged from a fixed-bed reactor require higher temperatures and longer calcination times; spherical deactivated catalysts discharged from a moving-bed reactor can have their calcination temperature reduced and their calcination time shortened by several hours; and microsphere deactivated catalysts discharged from a fluidized-bed reactor cyclone separator can have their calcination temperature further reduced and their calcination time shortened by several hours.

[0031] According to some preferred embodiments of the present invention, in step (1), the carbonization process is carried out under a protective atmosphere, the temperature of the carbonization process is 550-650°C, preferably 580-630°C, and the time is 5-48h, preferably 10-48h.

[0032] According to the present invention, preferably, the protective atmosphere is provided by at least one of nitrogen, argon and neon.

[0033] According to some preferred embodiments of the present invention, the method further includes: pulverizing the product from the charcoal treatment and then passing it through a 100-1000 mesh sieve, preferably a 200-1000 mesh sieve. Using the above preferred embodiments facilitates the dissolution of solids during the pulping process in step (2), which is beneficial for subsequent pulping and grinding.

[0034] According to the present invention, by controlling the particle diameter in the slurry to be less than 20 μm, the particle diameter of 90% by volume to be less than 10 μm, and the particle diameter of 70% by volume to be less than 5 μm through the pulping and grinding steps in step (2), it is beneficial to fully utilize the silicon species in the waste cyclohexanone oxime gas-phase Beckmann rearrangement catalyst. Combined with KOH, it is possible to form an all-silica-1 molecular sieve framework with a lower template agent dosage. Preferably, the particle diameter in the slurry is less than 20 μm, more preferably 90% by volume the particle diameter is less than 10 μm, and even more preferably 70% by volume the particle diameter is less than 5 μm. Using the above preferred embodiments is beneficial to further improve the specific surface area and external specific surface area of ​​the obtained all-silica-1 molecular sieve, and further improve the catalytic activity of the all-silica-1 molecular sieve in the gas-phase Beckmann rearrangement reaction.

[0035] This invention does not impose particular limitations on the specific operation method and conditions of the grinding process, as long as the aforementioned particle size distribution can be achieved. Those skilled in the art can select the appropriate method based on actual needs. Preferably, a colloid mill is used for the grinding process.

[0036] In this invention, the particle diameter distribution in the slurry is determined by a laser particle size analyzer.

[0037] According to some preferred embodiments of the present invention, in step (2), the mass ratio of the product obtained in step (1) to water is 1:(0.5-10), preferably 1:(1-3).

[0038] According to the present invention, the composition of the colloidal mixture satisfies the following: the molar ratio of silicon species (calculated as SiO2), KOH, organic template agent, alcohol, and water is 1:(0.01-0.1):(0.04-0.15):(3.5-20):(15-45). It is understood that the silicon species in the colloidal mixture originate from the slurry after grinding of spent catalyst, referring to the total silicon element in the colloidal mixture (calculated as SiO2). Compared with conventional synthesis methods for existing all-silica-1 molecular sieves, the method provided by the present invention uses spent catalyst to provide the silicon source, replacing the originally expensive organosilicon esters, and simultaneously introduces KOH and alcohol. This allows for further reduction of the amount of organic template agent added while ensuring the formation of the all-silica-1 molecular sieve framework, thereby reducing the overall process cost.

[0039] In a further preferred embodiment, in step (3), the composition of the colloidal mixture satisfies the following: the molar ratio of silicon species, KOH, organic template agent, alcohol and water, calculated as SiO2, is 1:(0.01-0.1):(0.05-0.20):(4-15):(15-30).

[0040] According to the present invention, preferably, the mixing in step (3) is carried out under stirring conditions. The present invention does not particularly limit the specific stirring conditions, as long as the components are mixed evenly.

[0041] The water in the colloidal mixture can come entirely from the slurry, or a small amount of water can be added to balance the molecular sieve synthesis molar ratio. Those skilled in the art can adjust this according to actual needs.

[0042] According to some preferred embodiments of the present invention, step (3) includes: mixing the slurry, KOH, organic template agent, alcohol and optional water to obtain a colloidal mixture.

[0043] The present invention does not impose any particular limitation on the mixing order of the components in step (3), as long as the components are mixed evenly. According to some preferred embodiments of the present invention, step (3) includes: first mixing the alcohol, KOH and organic template agent, and then adding the slurry and optionally water. Using the above-mentioned preferred feeding order helps to dissolve and depolymerize the silicon species (SiO2·nH2O) in the slurry.

[0044] According to the present invention, the alcohol may be a conventional low-carbon alcohol in the art, preferably methanol and / or ethanol, and more preferably ethanol.

[0045] According to the present invention, the organic template agent can be any organic template agent in the art that can be used to prepare all-silica-1 molecular sieves. Preferably, the organic template agent is selected from at least one of aliphatic amine compounds, alkanolamine compounds, and quaternary ammonium base compounds. The quaternary ammonium base compound is preferably an alkyl quaternary ammonium base compound containing 1-4 carbon atoms, and more preferably tetraethylammonium hydroxide and / or tetrapropylammonium hydroxide.

[0046] As is known to those skilled in the art, commercially available organic template agents, especially alkyl quaternary ammonium bases, typically contain small amounts of sodium ions. In the prior art, when using organic bases alone as the alkali source and template agent to synthesize all-silica-1 molecular sieves, the requirements for sodium ions in the alkyl quaternary ammonium bases are quite strict, usually 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.

[0047] According to the present invention, preferably, the bromide ion content in the organic base is less than 1.5 wt%, more preferably 0.5-1.5 wt%. The inventors of the present invention discovered in their research that using an organic base 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 the molecular sieve catalyst for 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.

[0048] Preferably, the iron ion content in the organic base is not greater than 10 ppm.

[0049] Preferably, the organic base 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 value not exceeding 100. The free acid includes, for example, any one or more of formic acid, acetic acid, and propionic acid.

[0050] According to some preferred embodiments of the present invention, the crystallization temperature is 100-150°C, and the time is 0.5-5 days. Preferably, the crystallization temperature is 110-140°C, and the time is 1-3 days. (The crystallization temperature can be about 5°C higher than the conventional crystallization temperature, and the crystallization time can be extended by 12 hours to ensure successful crystallization.)

[0051] According to the present invention, preferably, the method further includes: optionally washing and separating the crystallization mother liquor obtained by crystallization. The present invention does not particularly limit the washing and solid-liquid separation method; conventional methods in the art can be used to separate the solid product and the liquid phase. For example, the solid-liquid separation can be performed using membrane filtration, with repeated washing and membrane filtration until pH = 9-9.4.

[0052] According to the present invention, in step (4), the drying temperature is 100-120°C, and the drying time is 20-30 hours. The present invention does not impose any particular limitation on the drying method; those skilled in the art can select the appropriate method according to actual needs, such as microwave drying, vacuum drying, etc.

[0053] According to the present invention, preferably, in step (4), the calcination temperature is 400-600℃ and the calcination time is 1-10h.

[0054] The second aspect of the present invention provides a method for preparing all-silica-1 molecular sieves using the above-mentioned waste catalyst to obtain an all-silica-1 molecular sieve.

[0055] The all-silica-1 molecular sieve prepared by the above method has an MFI crystal structure, and the molecular sieve configuration of the product can be determined by X-ray diffraction spectroscopy. X-ray diffraction 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 this molecular sieve has an MFI crystal structure (i.e., ZSM-5 type).

[0056] According to the present invention, preferably, the specific surface area of ​​the all-silica-1 molecular sieve is not less than 400 m². 2 / g, preferably 400-500m 2 / g.

[0057] Preferably, the external specific surface area of ​​the all-silica-1 molecular sieve is 30-80 m². 2 / g.

[0058] The BET specific surface area and external specific surface area 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, and the specific surface area was calculated using the two-parameter BET equation.

[0059] Preferably, the molar ratio of silicon oxide to aluminum oxide in the all-silica-1 molecular sieve is above 50,000.

[0060] Preferably, the grain size of the all-silica-1 molecular sieve is 0.1-0.3 μm. The grain surface morphology of the sample was determined using a Hitachi S-4800 field emission scanning electron microscope from NEC Corporation.

[0061] The third aspect of this invention provides the application of the above-mentioned all-silica-1 molecular sieve in the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime.

[0062] The all-silica-1 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 shaping, as a catalyst for the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime. It has good catalytic activity, and the conversion rate of cyclohexanone oxime and the selectivity of caprolactam can be comparable to those of all-silica-1 molecular sieves prepared by conventional methods.

[0063] The present invention will be described in detail below through embodiments.

[0064] The physicochemical properties of the waste cyclohexanone oxime gas-phase Beckmann rearrangement catalyst used in the following examples are shown in Table 1.

[0065] Table 1

[0066]

[0067] In the table above, catalyst dimensions refer to the condition of the fresh catalyst corresponding to the spent catalyst.

[0068] In the following examples, unless otherwise specified, the tetrapropylammonium hydroxide solution used was purchased from Guangzhou Dayou Fine Chemical Co., Ltd., with a tetrapropylammonium hydroxide content of 22.5 wt%, sodium ion content not exceeding 500 ppm, bromide ion content not exceeding 1.5 wt%, carbonate ion content not exceeding 0.2 wt%, APHA color not exceeding 100, potassium ion content not exceeding 1.5% wt%, iron ion content not exceeding 10 ppm, acetic acid content not exceeding 500 ppm, and formic acid and propionic acid content not exceeding 50 ppm. The potassium hydroxide used was purchased from Sinopharm Group.

[0069] Example 1

[0070] (1) Take a certain amount of waste catalyst A and roast it in an air atmosphere at 620°C for 20 hours in a rotary roasting furnace to burn off the carbon deposits and coke. The catalyst is white. Then, use a 60-mesh sieve to grind the catalyst in a grinding mill.

[0071] (2) Pulping is carried out according to the mass ratio of powder to water of 1:2. The slurry is then passed through a colloid mill for colloid milling so that 70% of the particles in the final slurry have a diameter of less than 5μm. This slurry is marked A1 for later use.

[0072] (3) At room temperature, 184 kg of ethanol, 135.6 kg of 22.5% tetrapropylammonium hydroxide solution and 1.96 kg of KOH were poured into a stainless steel reactor and stirred evenly. 135 kg of water was added and stirred for 30 minutes. Then 180 kg of viscous slurry A1 was added to the stainless steel reactor and stirred evenly at room temperature to form a sol with molar concentrations of TPAOH / SiO2 = 0.15, EtOH / SiO2 = 4, KOH / SiO2 = 0.035, and H2O / SiO2 = 20.

[0073] (4) The above mixture was crystallized at 120°C for 2 days with a stirring speed of 45 rpm, filtered, washed, dried at 120°C for 24 hours, and calcined at 550°C for 5 hours to obtain the all-silica-1 molecular sieve.

[0074] X-ray diffraction pattern as shown Figure 1As 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 this molecular sieve possesses an MFI crystal structure. Transmission electron microscopy images are shown below. Figure 2 As shown, the particle size is 0.15-0.25 μm.

[0075] Its BET specific surface area is 442m². 2 / g, external specific surface area is 58m 2 / g, the silicon / aluminum ratio reaches over 50,000.

[0076] Example 2

[0077] (1) Take a certain amount of waste catalyst B and roast it in an air atmosphere at 620°C for 20 hours in a drum-type powder roasting furnace to completely burn off the carbon deposits and coke. The catalyst is light gray-white. Then, use an 80-mesh sieve to grind the catalyst in a grinding mill. Repeat once.

[0078] (2) Pulping is carried out according to the mass ratio of powder to water of 1:2. The slurry is then passed through a colloid mill for colloid milling so that 70% of the particles in the final slurry have a diameter of less than 5μm. This slurry is marked A2 for later use.

[0079] (3) At room temperature, 184 kg of ethanol, 135.6 kg of 22.5% tetrapropylammonium hydroxide solution and 2.24 kg of KOH were poured into a stainless steel reactor and stirred evenly. 135 kg of water was added and stirred for 30 minutes. Then 180 kg of viscous slurry A2 was added to the stainless steel reactor and stirred evenly at room temperature to form a sol with molar concentrations of TPAOH / SiO2 = 0.15, EtOH / SiO2 = 4, KOH / SiO2 = 0.04, and H2O / SiO2 = 20.

[0080] (4) The above mixture was crystallized at 125°C for 2 days with a stirring speed of 45 rpm, filtered, washed, dried at 120°C for 24 hours, and calcined at 550°C for 5 hours to obtain the all-silica-1 molecular sieve.

[0081] X-ray diffraction pattern and Figure 1 Similarly, this indicates that the molecular sieve has an MFI crystal structure.

[0082] Its BET specific surface area is 438m². 2 / g, external specific surface area is 56m 2 / g, the silicon / aluminum ratio reaches over 50,000.

[0083] Example 3

[0084] (1) Take a certain amount of waste catalyst C and roast it in an air atmosphere at 650°C for 20 hours in a rotary roasting furnace to burn off the carbon deposits and coke. The catalyst is light gray-white. Then, use a 100-mesh sieve to grind the catalyst in a grinding mill. Repeat once.

[0085] (2) The powder and water were mixed at a mass ratio of 1:3. The mixture was then passed through a colloid mill for grinding, so that 70% of the particles in the final slurry had a diameter of less than 5 μm. The slurry was marked A3 for later use.

[0086] (3) At room temperature, 184 kg of ethanol, 144.4 kg of 22.5% tetrapropylammonium hydroxide solution and 2.02 kg of KOH were poured into a stainless steel reactor and stirred evenly. 32 kg of water was added and stirred for 30 minutes. Then, 240 kg of viscous slurry A3 was added to the stainless steel reactor and stirred evenly at room temperature to form a sol with molar concentrations of TPAOH / SiO2 = 0.16, EtOH / SiO2 = 4, KOH / SiO2 = 0.036, and H2O / SiO2 = 18.

[0087] (4) The above mixture was crystallized at 125℃ for 2 days with a stirring rate of 45 rpm, filtered, washed, dried at 120℃ for 24 hours, and calcined at 550℃ for 5 hours. This yielded a fully silica-1 molecular sieve with an MFI crystal structure. The particle size was 0.15-0.25 μm.

[0088] Its BET specific surface area is 444m². 2 / g, external specific surface area is 57m 2 / g.

[0089] Example 4

[0090] The method is the same as in Example 1, except that in step (3), the amount of KOH added is such that KOH / SiO2 = 0.06.

[0091] All-silica-1 molecular sieves were obtained, with particle sizes of 0.15-0.25 μm and a BET specific surface area of ​​446 m². 2 / g, external specific surface area is 56m 2 / g.

[0092] Example 5

[0093] The method is the same as in Example 1, except that in step (3), the tetrapropylammonium hydroxide used is purchased from Tokyo Chemical Reagents. The tetrapropylammonium hydroxide content is 25wt%, the sodium ion content is 28.5ppm, the bromide ion content is 1.2wt%, the carbonate ion content is 0.2wt%, the APHA color is 30, the potassium ion content is 1.1wt%, the iron ion content is 38ppm, the acetic acid content is 214ppm, and the formic acid and propionic acid content is 26ppm.

[0094] Example 6

[0095] The method is the same as in Example 3, except that in step (2), the slurry is colloid milled to obtain a final slurry with a particle diameter of less than 20 μm, and 50% of the particles being 10 μm. This yields a fully silica-1 molecular sieve with an MFI crystal structure. The particle size is 0.20-0.30 μm.

[0096] Comparative Example 1

[0097] The method is the same as in Example 1, except that step (2) is omitted.

[0098] At room temperature, 92 kg of ethanol, 135.6 kg of 22.5% tetrapropylammonium hydroxide solution and 1.96 kg of KOH were poured into a stainless steel reactor and stirred evenly. 135 kg of water was added and stirred for 30 minutes. Then, an appropriate amount of the powder obtained in step (1) was added and stirred evenly at room temperature to form a sol with molar concentrations of TPAOH / SiO2 = 0.15, EtOH / SiO2 = 2, KOH / SiO2 = 0.035, and H2O / SiO2 = 20.

[0099] The above mixture was crystallized at 120°C for 2 days with a stirring rate of 45 rpm, filtered, washed, dried at 120°C for 24 hours, and calcined at 550°C for 5 hours to obtain the all-silica-1 molecular sieve.

[0100] This molecular sieve has an MFI crystal structure and a BET specific surface area of ​​426 m². 2 / g, external specific surface area is 41m 2 / g, the molecular sieve particle size is 0.2-0.3μm.

[0101] Comparative Example 2

[0102] The method is the same as in Example 1, except that KOH is not added in step (3).

[0103] Step (3): At room temperature, pour 184 kg of ethanol and 135.6 kg of 22.5% tetrapropylammonium hydroxide solution into a stainless steel reactor, add 135 kg of water, stir for 30 minutes, then add slurry A1 into the stainless steel reactor and stir evenly at room temperature to form a sol with molar concentrations of TPAOH / SiO2 = 0.15, EtOH / SiO2 = 4, and H2O / SiO2 = 20.

[0104] (4) The above mixture was crystallized at 120°C for 2 days with a stirring speed of 45 rpm, filtered, washed, dried at 120°C for 24 hours, and calcined at 550°C for 5 hours to obtain the all-silica-1 molecular sieve.

[0105] This molecular sieve has an MFI crystal structure and a BET specific surface area of ​​440 m². 2 / g, external specific surface area is 50m 2 / g.

[0106] Parameter

[0107] 198 g of 22.5% tetrapropylammonium hydroxide solution was poured into a 1000 mL beaker at room temperature and stirred for 30 minutes. 207 g of water was added and stirred for another 30 minutes. Then, 208 g of tetraethyl orthosilicate was added to the 1000 mL beaker and stirred at room temperature for 3–5 hours to hydrolyze the solution until homogeneous, forming a sol with molar concentrations of TPAOH / SiO2 = 0.22, EtOH / SiO2 = 4, and H2O / SiO2 = 20. The mixture was then transferred to a 1000 mL stainless steel reactor and stirred at 45 rpm for crystallization at 100 °C for 3 days. The solution was then filtered, washed, dried at 120 °C for 24 hours, and calcined at 550 °C for 5 hours.

[0108] The all-silica-1 molecular sieve product provided by this invention has a BET specific surface area of ​​436 m². 2 / g, external specific surface area is 55m 2 / g.

[0109] Test Implementation Examples

[0110] This test example is used to illustrate the catalytic reaction results of the all-silica-1 molecular sieve synthesized in the above examples and comparative examples in the gas-phase Beckmann rearrangement reaction.

[0111] The all-silica-1 molecular sieves prepared in the above examples and comparative examples were post-treated according to the nitrogen-containing compound post-treatment method in patent CN102233277A. 9.5 g of all-silica-1 molecular sieve and 95 g of an alkaline buffer solution composed of ammonia and ammonium nitrate (wherein the weight ratio of ammonia to ammonium nitrate aqueous solution was 3:2, and the pH value was 11.35) were added to a pressurized reactor (KCF-100ml magnetically stirred high-pressure reactor, Yantai High-tech Zone Keli Automation Equipment Research Institute) and reacted at 80℃ and 2.3 kg / cm². 2 The catalyst was stirred under pressure for 1 hour, then washed, filtered, and dried to obtain a molecular sieve containing an MFI structure.

[0112] The reaction apparatus was a continuous flow fixed-bed reactor at atmospheric pressure with an inner diameter of 5 mm. The catalyst loading was 0.37 g, and the catalyst particle size was 20-60 mesh. After being loaded into the reaction tube, the catalyst was pretreated for 1 hour at atmospheric pressure and 350°C under a nitrogen atmosphere. The concentration of the feedstock cyclohexanone oxime was 35%, and the weight hourly space velocity (WHSV) was 16 h⁻¹. -1The solvent was ethanol, the reaction temperature was 380℃, the nitrogen flow rate was 2.7 L / h, and the reaction time was 6 hours. The reaction product was collected after cooling with a water circulation system. The product was determined by capillary gas chromatography with a flame ionization detector. The results are shown in Table 2.

[0113] Table 2

[0114]

[0115] The comparison of the above embodiments and comparative examples shows that the molecular sieve synthesized by using waste catalyst as silicon source in the embodiments of the present invention can achieve catalytic activity comparable to that of the molecular sieve prepared in the reference example. It has high conversion rate and selectivity in gas-phase Beckmann rearrangement reaction. This preparation method can effectively utilize waste catalyst, reduce the amount of expensive silicon source and template agent, and improve the economy of all-silicon-1 molecular sieve synthesis.

[0116] 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 all-silica-1 molecular sieves from spent catalysts, characterized in that, The method includes: (1) Carbonization treatment of waste cyclohexanone oxime gas-phase Beckmann rearrangement catalyst; The waste cyclohexanone oxime gas-phase Beckmann rearrangement catalyst contains all-silica-1 molecular sieve; (2) Mix the product obtained in step (1) with water and grind it until the particle diameter in the slurry is less than 20 μm; (3) The slurry, KOH, organic template agent and alcohol are mixed to obtain a colloidal mixture; The composition of the colloidal mixture satisfies the following: the molar ratio of silicon species (calculated as SiO2), KOH, organic template agent, alcohol and water is 1:(0.01-0.1):(0.04-0.15):(3.5-20):(15-45); (4) The colloidal mixture is crystallized, then dried and calcined.

2. The method according to claim 1, characterized in that, The content of all-silica-1 molecular sieve in the waste cyclohexanone oxime gas-phase Beckmann rearrangement catalyst is 50-95 wt%. Preferably, the waste cyclohexanone oxime gas-phase Beckmann rearrangement catalyst further includes a silica binder; Preferably, the amount of carbon deposited in the waste cyclohexanone oxime gas-phase Beckmann rearrangement catalyst is 1-15 wt%.

3. The method according to claim 1 or 2, characterized in that, In step (1), the carbonization process is carried out in an oxygen-containing atmosphere, the temperature of the carbonization process is 550-650℃, and the time is 5-48h. Preferably, the oxygen content in the oxygen-containing atmosphere is 10-100% by volume; Preferably, the method further includes: crushing the product from the charcoal treatment and then passing it through a 100-1000 mesh sieve, preferably a 200-1000 mesh sieve.

4. The method according to any one of claims 1-3, characterized in that, In step (2), the mass ratio of the product obtained in step (1) to water is 1:(0.5-10); Preferably, the particle diameter is less than 10 μm when 90% of the volume of the slurry is ground; preferably, the particle diameter is less than 5 μm when 70% of the volume of the slurry is ground. Preferably, a colloid mill is used for the grinding.

5. The method according to any one of claims 1-4, characterized in that, In step (3), the composition of the colloidal mixture satisfies the following: the molar ratio of silicon species (calculated as SiO2), KOH, organic template agent, alcohol and water is 1:(0.03-0.05):(0.05-0.2):(4-15):(15-30); Preferably, the alcohol is selected from methanol and / or ethanol, and more preferably ethanol; Preferably, no additional silicon source is introduced during the mixing process described in step (3).

6. The method according to any one of claims 1-5, characterized in that, The organic template agent is selected from at least one of aliphatic amine compounds, alcoholic amine compounds, and quaternary ammonium base compounds; the quaternary ammonium base compound is preferably an alkyl quaternary ammonium base compound containing 1-4 carbon atoms, and more preferably tetraethylammonium hydroxide and / or 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.

7. The method according to any one of claims 1-6, characterized in that, The crystallization temperature is 100-150℃, and the time is 0.5-5 days; Preferably, the crystallization temperature is 110-140℃ and the time is 1-3 days.

8. The all-silica-1 molecular sieve obtained by the method for preparing all-silica-1 molecular sieve from waste catalyst as described in any one of claims 1-7.

9. The all-silica-1 molecular sieve according to claim 8, characterized in that, The specific surface area of ​​the all-silica-1 molecular sieve is not less than 400 m². 2 / g, preferably 400-500m 2 / g; Preferably, the external specific surface area of ​​the all-silica-1 molecular sieve is 30-80 m². 2 / g; Preferably, the molar ratio of silicon oxide to aluminum oxide in the all-silica-1 molecular sieve is above 50,000; Preferably, the grain size of the all-silica-1 molecular sieve is 0.1-0.3 μm.

10. The application of the all-silica-1 molecular sieve according to claim 8 or 9 in the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime.

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