Preparation method of high-strength multilayer ceramic composite separation membrane

Abstract

This invention relates to the field of inorganic separation membrane technology and discloses a method for preparing a high-strength multilayer ceramic composite separation membrane. The steps include: first, preparing a porous ceramic support with interconnected channels by mixing, extruding, drying, and first-stage sintering alumina powder, pore-forming agent, and binder in a specific ratio; second, forming a transition layer on the support using a fine-particle-size ceramic slurry via a dip-coating method; third, preparing a separation layer precursor sol using a sol-gel method and depositing it onto the transition layer using a spin-coating method; and finally, subjecting the composite membrane preform to a programmed temperature-controlled co-sintering densification treatment and selectively performing surface modifications such as chemical vapor deposition, silanization, or ion exchange. This invention enhances the overall mechanical strength and interlayer bonding of the multilayer ceramic composite separation membrane, improves the chemical stability, antifouling ability, and adaptability to specific separation systems of the composite membrane surface.

Description

Technical Field

[0001] This invention relates to the field of inorganic separation membrane technology, specifically to a method for preparing a high-strength multilayer ceramic composite separation membrane. Background Technology

[0002] Inorganic separation membranes are solid membranes made from inorganic materials such as alumina, zirconium oxide, and titanium oxide through special processes. They are mainly divided into dense membranes and porous membranes.

[0003] Currently, in the preparation of high-strength multilayer ceramic composite separation membranes, due to the reliance on step-by-step coating and high-temperature co-firing, it is difficult to monitor and adjust the thermal stress matching state of each functional layer in real time during the sintering stage. When the thermal expansion coefficients between the support, transition layer and separation layer are mismatched at high temperatures, micro-cracks or interfacial delamination will occur in the membrane after cooling, thus affecting the integrity and separation selectivity of the membrane. At the same time, when preparing ultrathin separation layers using sol-gel spin coating, it is impossible to control the sol viscosity, evaporation rate and ambient humidity in real time during the film formation process, which will lead to pinholes, uneven thickness and defect aggregation in the film, affecting the balance between separation accuracy and flux.

[0004] Therefore, a method for preparing a high-strength multilayer ceramic composite separation membrane is proposed to solve the above problems. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for preparing a high-strength multilayer ceramic composite separation membrane, which solves the problems mentioned in the background art that affect the integrity and separation selectivity of the membrane, as well as the inability to perform real-time closed-loop control of sol viscosity, evaporation rate and ambient humidity during the film formation process.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing a high-strength multilayer ceramic composite separation membrane, comprising the following steps:

[0007] Step 1: Preparation of porous ceramic support. Alumina powder, pore-forming agent and binder are selected, mixed, kneaded, aged, extruded and dried, and then sintered in the first stage to obtain a porous ceramic support with through channels.

[0008] Step 2: Preparation and coating of transition layer slurry. Fine-particle ceramic powder, dispersant, binder and solvent are mixed and ball-milled to prepare transition layer slurry. Then, the transition layer slurry is uniformly coated on the surface of the porous ceramic support by dip-coating method to form a wet film.

[0009] Step 3: Preparation and coating of the precursor sol for the separation layer. The sol-gel method is used to mix metal alkoxide, deionized water, acid catalyst and organic template agent, and obtain the precursor sol for the separation layer through hydrolysis and polycondensation reaction. The precursor sol is then coated on the surface of the support after the treatment and pre-calcination in Step 2 by spin coating.

[0010] Step 4: Co-sintering and surface modification. The green body coated with the transition layer wet film and the separation layer precursor sol is placed in a high-temperature sintering furnace and subjected to co-sintering densification treatment under programmed temperature control. After sintering, it is naturally cooled to obtain a primary ceramic composite film. Subsequently, the primary ceramic composite film is subjected to surface modification treatment to obtain the high-strength multilayer ceramic composite separation film.

[0011] In step one, the mass percentages of the alumina powder, pore-forming agent, and binder are 65%-75%: 15%-25%: 5%-10%.

[0012] The first stage of sintering is carried out in air atmosphere, with a heating rate of 1℃ / min-5℃ / min, a maximum sintering temperature of 1200℃-1400℃, and a holding time of 2 hours-4 hours.

[0013] Preferably, step one includes the following specific steps: placing alumina powder, pore-forming agent, and binder in a mixer and dry mixing at a speed of 200r / min-400r / min for 30-60 minutes; then slowly adding 18%-25% of the total mass of the powder in deionized water and continuing to mix for 40-80 minutes to form a uniform mud; placing the mud in an aging chamber and aging it for 24-48 hours at a humidity of 80%-95% and a temperature of 20℃-30℃; processing the aged mud through a vacuum plowing machine 2-3 times; then extruding it into tubular or flat green bodies using an extrusion molding machine; placing the green bodies in a drying oven and drying them at 40℃-60℃ for 12-24 hours, and then drying them at 80℃-100℃ for 6-12 hours to obtain dried green bodies; finally, placing the dried green bodies in a box-type sintering furnace for the first stage of sintering.

[0014] Preferably, the median particle size D50 of the alumina powder is 10 micrometers to 50 micrometers, the pore-forming agent is at least one of starch, polymethyl methacrylate microspheres or graphite powder, and its particle size is 5 micrometers to 30 micrometers, and the binder is at least one of hydroxypropyl methylcellulose, polyvinyl alcohol or polyethylene glycol.

[0015] Preferably, in step two, the transition layer slurry is made from the following raw materials in parts by weight: 100 parts fine-particle alumina or zirconium oxide powder, 0.5-2 parts ammonium polyacrylate dispersant, 3-8 parts polyvinyl butyral binder, and 150-250 parts a mixed solvent of anhydrous ethanol and isopropanol, wherein the volume ratio of anhydrous ethanol to isopropanol is 1:1-3:1, and the median particle size D50 of the fine-particle ceramic powder is 0.5 micrometers-2 micrometers.

[0016] Preferably, the preparation of the transition layer slurry includes the following steps: adding fine-particle-size ceramic powder and a mixed solvent into a ball mill jar, adding zirconia grinding beads, wherein the mass ratio of the grinding beads to the powder is 2:1-4:1, ball milling at a speed of 200 r / min-300 r / min for 1-2 hours for pre-dispersion, then adding the ammonium polyacrylate dispersant, increasing the speed to 350 r / min-450 r / min, and continuing ball milling for 3-5 hours, finally adding the polyvinyl butyral binder, and ball milling at a speed of 200 r / min-300 r / min for 1-2 hours to obtain a uniform slurry with a viscosity in the range of 20 mPa·s-50 mPa·s.

[0017] Preferably, in step two, the specific parameters of the immersion lifting method are as follows: lifting speed is 1mm / s-5mm / s, immersion time is 10 seconds-30 seconds, coating times are 1-3 times, and after each coating, it needs to be dried at 40℃-60℃ for 10 minutes-20 minutes, followed by pre-firing at 200℃-400℃ for 0.5 hours-1.5 hours, wherein the pre-firing is carried out in an air atmosphere.

[0018] Preferably, in step three, the separation layer precursor sol is prepared by the following method:

[0019] Under the protection of an ice-water bath and an inert gas, tetrabutyl orthosilicate is added to anhydrous ethanol and stirred for 10-20 minutes to obtain solution A, wherein the molar ratio of metal alkoxide to anhydrous ethanol is 1:10-1:20.

[0020] Dissolve deionized water, acid catalyst, and organic template agent in another part of anhydrous ethanol and stir for 5-15 minutes to obtain solution B. The molar ratio of deionized water to metal alkoxide is 2:1-6:1. The acid catalyst is hydrochloric acid or nitric acid with a concentration of 0.05 mol / L-0.2 mol / L, and the amount added is adjusted to maintain the pH value of the mixture between 1 and 3. The organic template agent is a polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer or hexadecyltrimethylammonium bromide, and its addition amount is 2%-8% of the mass of the metal alkoxide.

[0021] Under vigorous stirring, solution B is slowly added dropwise to solution A. After the addition is complete, the mixture is continuously stirred in a water bath at 40℃-60℃ for 12-48 hours to carry out hydrolysis and condensation reactions, resulting in a transparent or translucent stable sol.

[0022] Preferably, in step three, the specific parameters of the spin coating method are as follows: spin coating speed is 2000r / min-5000r / min, spin coating time is 20 seconds-40 seconds, coating times are 2-5 times, after each spin coating, the sample is placed on a hot plate at 60℃-80℃ and left to stand for 5 minutes-10 minutes before the next spin coating is performed. After all spin coatings are completed, the sample is aged in an oven at 40℃-60℃ for 12 hours-24 hours.

[0023] Preferably, in step four, the co-sintering densification process is as follows: the temperature is increased from room temperature to 300℃-500℃ at a rate of 0.5℃ / min-2℃ / min and held for 1-2 hours; then the temperature is increased to 800℃-1000℃ at a rate of 1℃ / min-3℃ / min and held for 0.5-1.5 hours; finally, the temperature is increased to the final sintering temperature of 1200℃-1500℃ at a rate of 2℃ / min-5℃ / min and held for 2-6 hours, followed by furnace cooling. The sintering atmosphere is air or oxygen.

[0024] Preferably, the surface modification treatment in step four is a combination of the following:

[0025] Chemical vapor deposition modification: The primary ceramic composite film is placed in the reaction chamber of a chemical vapor deposition equipment, the vacuum is drawn to 10Pa-100Pa, the temperature is heated to 400℃-600℃, and silicon-containing precursor gas and carrier gas are introduced at a flow rate of 10sccm-50sccm. After reacting for 30 minutes to 120 minutes, a layer of silicon dioxide nanolayer is deposited on the film surface.

[0026] Liquid-phase silanization modification: The primary ceramic composite membrane is immersed in an ethanol solution of silane coupling agent with a concentration of 1 vol%-5 vol% for 1 hour-4 hours, then removed and dried at 80℃-120℃ for 1 hour-2 hours, followed by heat treatment at 150℃-250℃ for 1 hour-3 hours to chemically bond the silane coupling agent with the hydroxyl groups on the membrane surface.

[0027] Ion exchange modification: The primary ceramic composite membrane is immersed in a salt solution containing the target metal ions at a concentration of 0.1 mol / L to 1.0 mol / L for 6 to 24 hours at 60℃ to 90℃, so that the target metal ions can replace the exchangeable ions on the membrane surface. After completion, it is rinsed with deionized water and dried.

[0028] Compared with the prior art, the present invention provides a method for preparing a high-strength multilayer ceramic composite separation membrane, which has the following beneficial effects:

[0029] 1. In this invention, a support is prepared by selecting alumina powder, pore-forming agent and binder in a specific ratio, and combined with the first-stage sintering process, and a transition layer slurry is prepared by using fine-particle-size ceramic powder, dispersant, binder and solvent, and coated by dip-coating method. In the subsequent co-sintering process, the porous ceramic support, transition layer and separation layer precursor can achieve good matching of thermal expansion coefficients and interfacial bonding, avoiding micro-cracks and interfacial delamination problems caused by inconsistent shrinkage behavior of each layer of material at high temperature, thereby enhancing the overall mechanical strength and interlayer bonding of the multilayer ceramic composite separation membrane.

[0030] 2. In this invention, a sol-gel method is used to mix metal alkoxides, deionized water, acid catalysts and organic templates, and prepare a separation layer precursor sol through hydrolysis and polycondensation reaction. Combined with spin coating and its specific coating parameters, the film uniformity of the separation layer can be controlled, thereby avoiding defects such as pinholes and uneven thickness, and ensuring that the final separation layer has a high-density and defect-free microstructure.

[0031] 3. In this invention, by designing a co-sintering densification process under programmed temperature control and selectively employing surface modification methods such as chemical vapor deposition, liquid-phase silanization, or ion exchange modification, the gradient pore size structure from the porous ceramic support, transition layer to separation layer can be synergistically controlled, and the surface chemical properties optimized. This not only achieves a precise gradient distribution of pore size to balance selectivity and flux, but also improves the chemical stability, antifouling ability, and adaptability to specific separation systems of the composite membrane surface, thereby enhancing the comprehensive separation performance and applicability of the composite separation membrane. Detailed Implementation

[0032] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0033] Example 1: A method for preparing a high-strength multilayer ceramic composite separation membrane, comprising the following steps:

[0034] Step 1: Preparation of porous ceramic support. Alumina powder, pore-forming agent and binder are selected, mixed, kneaded, aged, extruded and dried, and then sintered in the first stage to obtain a porous ceramic support with through channels.

[0035] Step 2: Preparation and coating of transition layer slurry. Fine-particle ceramic powder, dispersant, binder and solvent are mixed and ball-milled to prepare transition layer slurry. Then, the transition layer slurry is uniformly coated on the surface of porous ceramic support by dip-coating method to form a wet film.

[0036] Step 3: Preparation and coating of the precursor sol for the separation layer. The sol-gel method is used to mix metal alkoxide, deionized water, acid catalyst and organic template agent, and obtain the precursor sol for the separation layer through hydrolysis and polycondensation reaction. The precursor sol is then coated on the surface of the support after the treatment and pre-calcination in Step 2 by spin coating.

[0037] Step 4: Co-sintering and surface modification. The green body coated with the transition layer wet film and the separation layer precursor sol is placed in a high-temperature sintering furnace and subjected to co-sintering densification treatment under programmed temperature control. After sintering, it is naturally cooled to obtain a primary ceramic composite film. Subsequently, the primary ceramic composite film is subjected to surface modification treatment to obtain a high-strength multilayer ceramic composite separation film.

[0038] In step one, the mass percentages of alumina powder, pore-forming agent, and binder are 65%:15%:5%;

[0039] The first stage of sintering is carried out in air atmosphere, with a heating rate of 1℃ / min, a maximum sintering temperature of 1200℃, and a holding time of 2 hours.

[0040] Step 1 includes the following specific steps: Alumina powder, pore-forming agent, and binder are placed in a mixer and dry-mixed at 200 r / min for 30 minutes. Then, 18% of the total mass of deionized water is slowly added, and mixing continues for 40 minutes to form a uniform mud. The mud is placed in an aging chamber and aged for 24 hours at 80% humidity and 20℃. The aged mud is then processed twice by a vacuum plow to remove air bubbles. It is then extruded using an extrusion molding machine to form tubular or flat green bodies. The green bodies are placed in a drying oven and dried at 40℃ for 12 hours, and then dried at 80℃ for 6 hours to obtain dried green bodies. Finally, the dried green bodies are placed in a box-type sintering furnace for the first stage of sintering.

[0041] The median particle size D50 of the alumina powder is 10 micrometers, the pore-forming agent is starch with a particle size of 5 micrometers, and the binder is hydroxypropyl methylcellulose.

[0042] In step two, the transition layer slurry is made from the following raw materials in parts by weight: 100 parts fine-particle alumina, 0.5 parts ammonium polyacrylate dispersant, 3 parts polyvinyl butyral binder, and 150 parts a mixed solvent of anhydrous ethanol and isopropanol, wherein the volume ratio of anhydrous ethanol to isopropanol is 1:1, and the median particle size D50 of the fine-particle ceramic powder is 0.5 micrometers.

[0043] The preparation of the transition layer slurry includes the following steps: fine-particle-size ceramic powder and mixed solvent are added to a ball mill jar, zirconia grinding beads are added, and the mass ratio of grinding beads to powder is 2:1. First, the mixture is ball-milled at 200 r / min for 1 hour for pre-dispersion. Then, ammonium polyacrylate dispersant is added, the speed is increased to 350 r / min, and the ball milling continues for 3 hours. Finally, polyvinyl butyral binder is added, and the mixture is ball-milled at 200 r / min for 1 hour to obtain a uniform slurry with a viscosity of 20 mPa·s.

[0044] In step two, the specific parameters of the dip-lifting method are as follows: lifting speed is 1 mm / s, dip time is 10 seconds, coating is applied once, and after each coating, it needs to be dried at 40°C for 10 minutes, followed by pre-firing at 200°C for 0.5 hours to remove organic components. The pre-firing is carried out in an air atmosphere.

[0045] In step three, the separation layer precursor sol is prepared by the following method:

[0046] Under the protection of an ice-water bath and an inert gas, tetraethyl orthosilicate was added to anhydrous ethanol and stirred for 10 minutes to obtain solution A, wherein the molar ratio of metal alkoxide to anhydrous ethanol was 1:10.

[0047] Deionized water, acid catalyst, and organic template agent were dissolved in another part of anhydrous ethanol and stirred for 5 minutes to obtain solution B, wherein the molar ratio of deionized water to metal alkoxide was 2:1, the acid catalyst was hydrochloric acid with a concentration of 0.05 mol / L, and the amount added was adjusted to make the pH of the mixture 1, and the organic template agent was a polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer or hexadecyltrimethylammonium bromide, and the amount added was 2% of the mass of the metal alkoxide.

[0048] Under vigorous stirring, solution B was slowly added dropwise to solution A. After the addition was complete, the mixture was continuously stirred in a 40°C water bath for 12 hours to carry out hydrolysis and condensation reactions, resulting in a transparent or translucent stable sol.

[0049] In step three, the specific parameters for spin coating are as follows: spin coating speed is 2000 r / min, spin coating time is 20 seconds, coating times are 2, after each spin coating, the sample is placed on a hot plate at 60℃ and left to stand for 5 minutes before the next spin coating is performed. After all spin coatings are completed, the sample is aged in an oven at 40℃ for 12 hours.

[0050] In step four, the co-sintering densification process is as follows: the temperature is increased from room temperature to 300°C at a rate of 0.5°C / min and held for 1 hour. Then, the temperature is increased to 800°C at a rate of 1°C / min and held for 0.5 hours to achieve preliminary densification of the transition layer. Finally, the temperature is increased to the final sintering temperature of 1200°C at a rate of 2°C / min and held for 2 hours. Then, the furnace is cooled, and the sintering atmosphere is air.

[0051] The surface modification treatment in step four consists of the following combination:

[0052] Chemical vapor deposition modification: The primary ceramic composite film is placed in the reaction chamber of a chemical vapor deposition equipment, the vacuum is drawn to 10 Paa, the temperature is heated to 400°C, and silicon-containing precursor gas and carrier gas are introduced at a flow rate of 10 sccm. After reacting for 30 minutes, a layer of silicon dioxide nanolayer is deposited on the film surface.

[0053] Liquid-phase silanization modification: The primary ceramic composite membrane is immersed in a 1 vol% silane coupling agent ethanol solution, soaked for 1 hour, then removed and dried at 80°C for 1 hour, and then subjected to heat treatment at 150°C for 1 hour to allow the silane coupling agent to chemically bond with the hydroxyl groups on the membrane surface.

[0054] Ion exchange modification: The primary ceramic composite membrane is immersed in a salt solution containing the target metal ions at a concentration of 0.1 mol / L and soaked at 60°C for 6 hours to allow the target metal ions to replace the exchangeable ions on the membrane surface. After completion, it is rinsed with deionized water and dried.

[0055] Example 2: A method for preparing a high-strength multilayer ceramic composite separation membrane, comprising the following steps:

[0056] Step 1: Preparation of porous ceramic support. Alumina powder, pore-forming agent and binder are selected, mixed, kneaded, aged, extruded and dried, and then sintered in the first stage to obtain a porous ceramic support with through channels.

[0057] Step 2: Preparation and coating of transition layer slurry. Fine-particle ceramic powder, dispersant, binder and solvent are mixed and ball-milled to prepare transition layer slurry. Then, the transition layer slurry is uniformly coated on the surface of porous ceramic support by dip-coating method to form a wet film.

[0058] Step 3: Preparation and coating of the precursor sol for the separation layer. The sol-gel method is used to mix metal alkoxide, deionized water, acid catalyst and organic template agent, and obtain the precursor sol for the separation layer through hydrolysis and polycondensation reaction. The precursor sol is then coated on the surface of the support after the treatment and pre-calcination in Step 2 by spin coating.

[0059] Step 4: Co-sintering and surface modification. The green body coated with the transition layer wet film and the separation layer precursor sol is placed in a high-temperature sintering furnace and subjected to co-sintering densification treatment under programmed temperature control. After sintering, it is naturally cooled to obtain a primary ceramic composite film. Subsequently, the primary ceramic composite film is subjected to surface modification treatment to obtain a high-strength multilayer ceramic composite separation film.

[0060] In step one, the mass percentages of alumina powder, pore-forming agent, and binder are 70%:20%:7.5%.

[0061] The first stage of sintering is carried out in air atmosphere, with a heating rate of 3℃ / min, a maximum sintering temperature of 1300℃, and a holding time of 3 hours.

[0062] Step 1 includes the following specific steps: Alumina powder, pore-forming agent, and binder are placed in a mixer and dry-mixed at 300 r / min for 45 minutes. Then, 21.5% of the total mass of the powder is slowly added to deionized water, and mixing is continued for 60 minutes to form a uniform mud. The mud is placed in an aging chamber and aged for 36 hours at 87.5% humidity and 25℃. The aged mud is then processed 2.5 times through a vacuum plow to remove air bubbles. It is then extruded into tubular or flat green bodies using an extrusion molding machine. The green bodies are placed in a drying oven and dried at 50℃ for 18 hours, and then dried at 90℃ for 8 hours to obtain dried green bodies. Finally, the dried green bodies are placed in a box-type sintering furnace for the first stage of sintering.

[0063] The median particle size D50 of the alumina powder is 30 micrometers. The pore-forming agent is starch and polymethyl methacrylate microspheres with a particle size of 17.5 micrometers. The binder is hydroxypropyl methylcellulose and polyvinyl alcohol.

[0064] In step two, the transition layer slurry is made from the following raw materials in parts by weight: 100 parts zirconium oxide powder, 1.25 parts ammonium polyacrylate dispersant, 5.5 parts polyvinyl butyral binder, and 200 parts a mixed solvent of anhydrous ethanol and isopropanol, wherein the volume ratio of anhydrous ethanol to isopropanol is 2:1, and the median particle size D50 of the fine-particle ceramic powder is 1.25 micrometers.

[0065] The preparation of the transition layer slurry includes the following steps: fine-particle-size ceramic powder and mixed solvent are added to a ball mill jar, zirconia grinding beads are added, and the mass ratio of grinding beads to powder is 3:1. First, the mixture is ball-milled at 250 r / min for 1.5 hours for pre-dispersion. Then, ammonium polyacrylate dispersant is added, the speed is increased to 400 r / min, and the ball milling continues for 4 hours. Finally, polyvinyl butyral binder is added, and the mixture is ball-milled at 250 r / min for 1.5 hours to obtain a uniform slurry with a viscosity of 35 mPa·s.

[0066] In step two, the specific parameters of the dip-lifting method are as follows: lifting speed is 3 mm / s, dip time is 20 seconds, coating is applied twice, and after each coating, it needs to be dried at 50°C for 15 minutes, followed by pre-firing at 300°C for 1 hour to remove organic components. The pre-firing is carried out in an air atmosphere.

[0067] In step three, the separation layer precursor sol is prepared by the following method:

[0068] Under the protection of an ice-water bath and an inert gas, tetrabutyl titanate was added to anhydrous ethanol and stirred for 15 minutes to obtain solution A, wherein the molar ratio of metal alkoxide to anhydrous ethanol was 1:15.

[0069] Deionized water, acid catalyst, and organic template agent were dissolved in another part of anhydrous ethanol and stirred for 10 minutes to obtain solution B, wherein the molar ratio of deionized water to metal alkoxide was 4:1, the acid catalyst was nitric acid with a concentration of 0.125 mol / L, and the amount added was adjusted to make the pH of the mixture 2, and the organic template agent was a polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer or hexadecyltrimethylammonium bromide, and the amount added was 5% of the mass of the metal alkoxide.

[0070] Under vigorous stirring, solution B was slowly added dropwise to solution A. After the addition was complete, the mixture was continuously stirred in a 50°C water bath for 36 hours to carry out hydrolysis and condensation reactions, resulting in a transparent or translucent stable sol.

[0071] In step three, the specific parameters for spin coating are as follows: spin coating speed is 3500 r / min, spin coating time is 30 seconds, coating times are 3.5 times, after each spin coating, the sample is placed on a hot plate at 70℃ and left to stand for 7.5 minutes before the next spin coating is performed. After all spin coatings are completed, the sample is aged in an oven at 50℃ for 18 hours.

[0072] In step four, the co-sintering densification process is as follows: the temperature is increased from room temperature to 400℃ at a rate of 1.25℃ / min and held for 1.5 hours, then increased to 900℃ at a rate of 2℃ / min and held for 1.0 hour to achieve the initial densification of the transition layer, and finally increased to the final sintering temperature of 1350℃ at a rate of 3.5℃ / min and held at this temperature for 4 hours, followed by furnace cooling. The sintering atmosphere is an oxygen atmosphere.

[0073] The surface modification treatment in step four consists of the following combination:

[0074] Chemical vapor deposition modification: The primary ceramic composite membrane is placed in the reaction chamber of a chemical vapor deposition equipment, the vacuum is drawn to 55 Pa, the temperature is heated to 500 °C, and silicon-containing precursor gas and carrier gas are introduced at a flow rate of 30 sccm. After reacting for 75 minutes, a layer of silicon dioxide nanolayer is deposited on the membrane surface.

[0075] Liquid-phase silanization modification: The primary ceramic composite membrane is immersed in a 3 vol% silane coupling agent ethanol solution for 2.5 hours, then removed and dried at 100°C for 1.5 hours, followed by heat treatment at 200°C for 2 hours to chemically bond the silane coupling agent with the hydroxyl groups on the membrane surface.

[0076] Ion exchange modification: The primary ceramic composite membrane is immersed in a salt solution containing the target metal ions at a concentration of 0.55 mol / L and soaked at 75°C for 15 hours to allow the target metal ions to replace the exchangeable ions on the membrane surface. After completion, it is rinsed with deionized water and dried.

[0077] Example 3: A method for preparing a high-strength multilayer ceramic composite separation membrane, comprising the following steps:

[0078] Step 1: Preparation of porous ceramic support. Alumina powder, pore-forming agent and binder are selected, mixed, kneaded, aged, extruded and dried, and then sintered in the first stage to obtain a porous ceramic support with through channels.

[0079] Step 2: Preparation and coating of transition layer slurry. Fine-particle ceramic powder, dispersant, binder and solvent are mixed and ball-milled to prepare transition layer slurry. Then, the transition layer slurry is uniformly coated on the surface of porous ceramic support by dip-coating method to form a wet film.

[0080] Step 3: Preparation and coating of the precursor sol for the separation layer. The sol-gel method is used to mix metal alkoxide, deionized water, acid catalyst and organic template agent, and obtain the precursor sol for the separation layer through hydrolysis and polycondensation reaction. The precursor sol is then coated on the surface of the support after the treatment and pre-calcination in Step 2 by spin coating.

[0081] Step 4: Co-sintering and surface modification. The green body coated with the transition layer wet film and the separation layer precursor sol is placed in a high-temperature sintering furnace and subjected to co-sintering densification treatment under programmed temperature control. After sintering, it is naturally cooled to obtain a primary ceramic composite film. Subsequently, the primary ceramic composite film is subjected to surface modification treatment to obtain a high-strength multilayer ceramic composite separation film.

[0082] In step one, the mass percentages of alumina powder, pore-forming agent, and binder are 75%:25%:10%.

[0083] The first stage of sintering is carried out in air atmosphere, with a heating rate of 5℃ / min, a maximum sintering temperature of 1400℃, and a holding time of 4 hours.

[0084] Step 1 includes the following specific steps: Alumina powder, pore-forming agent, and binder are placed in a mixer and dry-mixed at 400 r / min for 60 minutes. Then, 25% of the total mass of deionized water is slowly added, and mixing continues for 80 minutes to form a uniform mud. The mud is placed in an aging chamber and aged for 48 hours at 95% humidity and 30℃. The aged mud is then processed three times by a vacuum plow to remove air bubbles. It is then extruded using an extrusion molding machine to form tubular or flat green bodies. The green bodies are placed in a drying oven and dried at 60℃ for 24 hours, and then dried at 100℃ for 12 hours to obtain dried green bodies. Finally, the dried green bodies are placed in a box-type sintering furnace for the first stage of sintering.

[0085] The median particle size D50 of the alumina powder is 50 micrometers. The pore-forming agent is starch, polymethyl methacrylate microspheres, and graphite powder, with a particle size of 30 micrometers. The binder is hydroxypropyl methylcellulose, polyvinyl alcohol, and polyethylene glycol.

[0086] In step two, the transition layer slurry is made from the following raw materials in parts by weight: 100 parts fine-particle alumina, 2 parts ammonium polyacrylate dispersant, 8 parts polyvinyl butyral binder, and 250 parts a mixed solvent of anhydrous ethanol and isopropanol, wherein the volume ratio of anhydrous ethanol to isopropanol is 3:1, and the median particle size D50 of the fine-particle ceramic powder is 2 micrometers.

[0087] The preparation of the transition layer slurry includes the following steps: fine-particle-size ceramic powder and mixed solvent are added to a ball mill jar, zirconia grinding beads are added, and the mass ratio of grinding beads to powder is 4:1. First, the mixture is ball-milled at 300 r / min for 2 hours for pre-dispersion. Then, ammonium polyacrylate dispersant is added, the speed is increased to 450 r / min, and the ball milling continues for 5 hours. Finally, polyvinyl butyral binder is added, and the mixture is ball-milled at 300 r / min for 2 hours to obtain a uniform slurry with a viscosity of 50 mPa·s.

[0088] In step two, the specific parameters for the dip-lifting method are as follows: lifting speed is 5 mm / s, dip time is 30 seconds, coating is applied 3 times, and after each coating, it needs to be dried at 60°C for 20 minutes, followed by pre-firing at 400°C for 0.5-1.5 hours to remove organic components. The pre-firing is carried out in an air atmosphere.

[0089] In step three, the separation layer precursor sol is prepared by the following method:

[0090] Under the protection of an ice-water bath and an inert gas, tetraethyl orthosilicate was added to anhydrous ethanol and stirred for 20 minutes to obtain solution A, wherein the molar ratio of metal alkoxide to anhydrous ethanol was 1:20.

[0091] Deionized water, acid catalyst, and organic template agent were dissolved in another part of anhydrous ethanol and stirred for 15 minutes to obtain solution B, wherein the molar ratio of deionized water to metal alkoxide was 6:1, the acid catalyst was hydrochloric acid with a concentration of 0.2 mol / L, and the amount added was adjusted to make the pH of the mixture 3, and the organic template agent was a polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer or hexadecyltrimethylammonium bromide, and the amount added was 8% of the mass of the metal alkoxide.

[0092] Under vigorous stirring, solution B was slowly added dropwise to solution A. After the addition was complete, the mixture was continuously stirred in a 60°C water bath for 48 hours to carry out hydrolysis and condensation reactions, resulting in a transparent or translucent stable sol.

[0093] In step three, the specific parameters for the spin coating method are as follows: spin coating speed is 5000 r / min, spin coating time is 40 seconds, coating times are 5 times, after each spin coating, the sample is placed on a hot plate at 80℃ and left to stand for 10 minutes before the next spin coating is performed. After all spin coatings are completed, the sample is aged in an oven at 60℃ for 24 hours.

[0094] In step four, the co-sintering densification process is as follows: the temperature is increased from room temperature to 500°C at a rate of 2°C / min and held for 2 hours. Then, the temperature is increased to 1000°C at a rate of 3°C / min and held for 1.5 hours to achieve the initial densification of the transition layer. Finally, the temperature is increased to the final sintering temperature of 1500°C at a rate of 5°C / min and held at this temperature for 6 hours. Then, the furnace is cooled, and the sintering atmosphere is air.

[0095] The surface modification treatment in step four consists of the following combination:

[0096] Chemical vapor deposition modification: The primary ceramic composite film is placed in the reaction chamber of a chemical vapor deposition equipment, the vacuum is drawn to 100 Pa, the temperature is heated to 600 °C, and silicon-containing precursor gas and carrier gas are introduced at a flow rate of 50 sccm. After reacting for 120 minutes, a layer of silicon dioxide nanolayer is deposited on the film surface.

[0097] Liquid-phase silanization modification: The primary ceramic composite membrane is immersed in a 5 vol% silane coupling agent ethanol solution for 4 hours, then removed and dried at 120°C for 2 hours, followed by heat treatment at 250°C for 3 hours to chemically bond the silane coupling agent with the hydroxyl groups on the membrane surface.

[0098] Ion exchange modification: The primary ceramic composite membrane is immersed in a salt solution containing the target metal ions at a concentration of 1.0 mol / L and soaked at 90°C for 24 hours to allow the target metal ions to replace the exchangeable ions on the membrane surface. After completion, it is rinsed with deionized water and dried.

[0099] Comparative Example 1: The difference between this comparative example and Example 1 is that in the co-sintering process of step four, this comparative example does not use programmed temperature control, but instead directly heats the blank coated with the transition layer wet film and the separation layer precursor sol at a constant rate to the final sintering temperature.

[0100] Comparative Example 2: The difference between this comparative example and Example 2 is that in step two of this comparative example, the preparation of the transition layer slurry did not use polyvinyl butyral binder, nor was it impregnated and pulled. Instead, the mixed slurry was coated onto the surface of the porous ceramic support by a simple spraying method.

[0101] Comparative Example 3 differs from Example 3 in that: in step three of this comparative example, the preparation of the separation layer precursor sol did not use the sol-gel method, nor did it use an organic template agent. Instead, fine-particle ceramic powder was directly dispersed in a solvent to form a suspension for coating.

[0102] Comparative Example 4 differs from Example 3 in that, in step four of this comparative example, no surface modification treatment was performed on the primary ceramic composite film after co-sintering.

[0103] The preparation methods of the high-strength multilayer ceramic composite separation membranes in Examples 1-3 and Comparative Examples 1-4 were subjected to performance tests. The test items and test methods are as follows:

[0104] Mechanical strength test: The bending strength of the composite separation membrane was tested using the three-point bending method to evaluate its overall mechanical strength;

[0105] Gas permeation separation performance test: In a self-made high temperature and high pressure membrane evaluation device, hydrogen or nitrogen is used as the test system to test the gas permeation flux and separation factor of the membrane under specific temperature and pressure difference in order to evaluate its separation accuracy and flux.

[0106] Thermal stability test: The composite separation membrane was placed in a tube furnace and heated to 800°C at a rate of 5°C / min in air atmosphere. After holding at the temperature for 4 hours, the membrane structure was observed and the gas permeation performance after cooling was tested to evaluate its thermal shock resistance and high temperature stability.

[0107] Chemical corrosion resistance test: The composite separation membrane was immersed in hydrochloric acid and sodium hydroxide solutions with a concentration of 1 mol / L, respectively, and soaked at 60°C for 168 hours. After being taken out, cleaned and dried, its mechanical strength and gas permeability retention rate were tested to evaluate its chemical stability.

[0108] The test data of the preparation method of a high-strength multilayer ceramic composite separation membrane in Examples 1-3 and Comparative Examples 1-4 are recorded in the table below:

[0109] Test Project flexural strength <![CDATA[H2 permeation flux]]> <![CDATA[H2 / N2 separation factor]]> thermal stability Acid / alkali corrosion resistance Example 1 high high Excellent Excellent high Example 2 high high Excellent Excellent high Example 3 high high Excellent Excellent high Comparative Example 1 Low high Low Difference high Comparative Example 2 Low high Low medium medium Comparative Example 3 medium high medium medium Low Comparative Example 4 high high medium Excellent Low

[0110] By comparing and analyzing the data in the table, it can be seen that the preparation method of the high-strength multilayer ceramic composite separation membrane in Examples 1-3 has superior performance compared to the preparation method of the high-strength multilayer ceramic composite separation membrane in Comparative Examples 1-4. This indicates that by selecting alumina powder, pore-forming agent, and binder in specific proportions to prepare the support, combined with the first-stage sintering process, and using fine-particle ceramic powder, dispersant, binder, and solvent to prepare the transition layer slurry, and coating it by dip-coating, good matching of thermal expansion coefficients and interfacial bonding can be achieved between the porous ceramic support, the transition layer, and the separation layer precursor during the subsequent co-sintering process. This avoids micro-cracks and interfacial delamination problems caused by inconsistent shrinkage behavior of each layer of material at high temperatures, thereby enhancing the overall mechanical strength and interlayer bonding of the multilayer ceramic composite separation membrane. By using the sol-gel method, metal alkoxides and deionized metal alkoxides are incorporated into the membrane. A sol precursor for the separation layer is prepared by mixing water, an acid catalyst, and an organic template agent and undergoing a hydrolysis-condensation reaction. Combined with spin coating and specific coating parameters, the uniformity of the separation layer can be controlled, thus avoiding defects such as pinholes and uneven thickness. This ensures that the final separation layer has a high-density, defect-free microstructure. By designing a co-sintering densification process under programmed temperature control and selectively employing surface modification methods such as chemical vapor deposition, liquid-phase silanization, or ion exchange, the gradient pore size structure from the porous ceramic support, transition layer, to the separation layer can be synergistically controlled, and the surface chemical properties optimized. This not only achieves a precise gradient distribution of pore size to balance selectivity and flux but also improves the chemical stability, antifouling ability, and adaptability to specific separation systems of the composite membrane surface, thereby enhancing the overall separation performance and applicability of the composite separation membrane.

[0111] By comparing and analyzing the relevant data in the table, it can be seen that the preparation method of the high-strength multilayer ceramic composite separation membrane of the present invention has better comprehensive performance.

[0112] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0113] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a high-strength multilayer ceramic composite separation membrane, characterized in that, Includes the following steps: Step 1: Preparation of porous ceramic support. Alumina powder, pore-forming agent and binder are selected, mixed, kneaded, aged, extruded and dried, and then sintered in the first stage to obtain a porous ceramic support with through channels. Step 2: Preparation and coating of transition layer slurry. Fine-particle ceramic powder, dispersant, binder and solvent are mixed and ball-milled to prepare transition layer slurry. Then, the transition layer slurry is uniformly coated on the surface of the porous ceramic support by dip-coating method to form a wet film. Step 3: Preparation and coating of the precursor sol for the separation layer. The sol-gel method is used to mix metal alkoxide, deionized water, acid catalyst and organic template agent, and obtain the precursor sol for the separation layer through hydrolysis and polycondensation reaction. The precursor sol is then coated on the surface of the support after the treatment and pre-calcination in Step 2 by spin coating. Step 4: Co-sintering and surface modification. The green body coated with the transition layer wet film and the separation layer precursor sol is placed in a high-temperature sintering furnace and subjected to co-sintering densification treatment under programmed temperature control. After sintering, it is naturally cooled to obtain a primary ceramic composite film. Subsequently, the primary ceramic composite film is subjected to surface modification treatment to obtain the high-strength multilayer ceramic composite separation film. In step one, the mass percentages of the alumina powder, pore-forming agent, and binder are 65%-75%: 15%-25%: 5%-10%. The first stage of sintering is carried out in air atmosphere, with a heating rate of 1℃ / min-5℃ / min, a maximum sintering temperature of 1200℃-1400℃, and a holding time of 2 hours-4 hours.

2. The method for preparing a high-strength multilayer ceramic composite separation membrane according to claim 1, characterized in that, Step one includes the following specific steps: Alumina powder, pore-forming agent, and binder are placed in a mixer and dry-mixed at a speed of 200r / min-400r / min for 30-60 minutes. Then, 18%-25% of the total mass of the powder is slowly added to deionized water, and mixing is continued for 40-80 minutes to form a uniform mud. The mud is placed in an aging chamber and aged for 24-48 hours at a humidity of 80%-95% and a temperature of 20℃-30℃. The aged mud is processed 2-3 times by a vacuum plowing machine, and then extruded into tubular or flat green bodies using an extrusion molding machine. The green bodies are placed in a drying oven and dried at 40℃-60℃ for 12-24 hours, and then dried at 80℃-100℃ for 6-12 hours to obtain a dried green body. Finally, the dried green body is placed in a box-type sintering furnace for the first stage of sintering.

3. The method for preparing a high-strength multilayer ceramic composite separation membrane according to claim 2, characterized in that, The median particle size D50 of the alumina powder is 10 micrometers to 50 micrometers, the pore-forming agent is at least one of starch, polymethyl methacrylate microspheres or graphite powder, and its particle size is 5 micrometers to 30 micrometers, and the binder is at least one of hydroxypropyl methylcellulose, polyvinyl alcohol or polyethylene glycol.

4. The method for preparing a high-strength multilayer ceramic composite separation membrane according to claim 1, characterized in that, In step two, the transition layer slurry is made from the following raw materials in parts by weight: 100 parts fine-particle alumina or zirconium oxide powder, 0.5-2 parts ammonium polyacrylate dispersant, 3-8 parts polyvinyl butyral binder, and 150-250 parts a mixed solvent of anhydrous ethanol and isopropanol, wherein the volume ratio of anhydrous ethanol to isopropanol is 1:1-3:1, and the median particle size D50 of the fine-particle ceramic powder is 0.5 micrometers-2 micrometers.

5. The method for preparing a high-strength multilayer ceramic composite separation membrane according to claim 4, characterized in that, The preparation of the transition layer slurry includes the following steps: fine-particle-size ceramic powder and mixed solvent are added to a ball mill jar, zirconia grinding beads are added, and the mass ratio of the grinding beads to the powder is 2:1-4:

1. The mixture is first ball-milled at a speed of 200 r / min-300 r / min for 1-2 hours for pre-dispersion. Then, the ammonium polyacrylate dispersant is added, and the speed is increased to 350 r / min-450 r / min. The ball milling continues for 3-5 hours. Finally, the polyvinyl butyral binder is added, and the mixture is ball-milled at a speed of 200 r / min-300 r / min for 1-2 hours to obtain a uniform slurry with a viscosity in the range of 20 mPa·s-50 mPa·s.

6. The method for preparing a high-strength multilayer ceramic composite separation membrane according to claim 1, characterized in that, In step two, the specific parameters of the dip-lifting method are as follows: lifting speed is 1mm / s-5mm / s, dip time is 10 seconds-30 seconds, coating times are 1-3 times, and after each coating, it needs to be dried at 40℃-60℃ for 10 minutes-20 minutes, followed by pre-firing at 200℃-400℃ for 0.5 hours-1.5 hours, wherein the pre-firing is carried out in an air atmosphere.

7. The method for preparing a high-strength multilayer ceramic composite separation membrane according to claim 1, characterized in that, In step three, the separation layer precursor sol is prepared by the following method: Under the protection of an ice-water bath and an inert gas, tetrabutyl orthosilicate is added to anhydrous ethanol and stirred for 10-20 minutes to obtain solution A, wherein the molar ratio of metal alkoxide to anhydrous ethanol is 1:10-1:

20. Dissolve deionized water, acid catalyst, and organic template agent in another part of anhydrous ethanol and stir for 5-15 minutes to obtain solution B. The molar ratio of deionized water to metal alkoxide is 2:1-6:

1. The acid catalyst is hydrochloric acid or nitric acid with a concentration of 0.05 mol / L-0.2 mol / L, and the amount added is adjusted to maintain the pH value of the mixture between 1 and 3. The organic template agent is a polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer or hexadecyltrimethylammonium bromide, and its addition amount is 2%-8% of the mass of the metal alkoxide. Under vigorous stirring, solution B is slowly added dropwise to solution A. After the addition is complete, the mixture is continuously stirred in a water bath at 40℃-60℃ for 12-48 hours to carry out hydrolysis and condensation reactions, resulting in a transparent or translucent stable sol.

8. The method for preparing a high-strength multilayer ceramic composite separation membrane according to claim 1, characterized in that, In step three, the specific parameters of the spin coating method are as follows: spin coating speed is 2000r / min-5000r / min, spin coating time is 20 seconds-40 seconds, coating times are 2-5 times, after each spin coating, the sample is placed on a hot plate at 60℃-80℃ and left to stand for 5 minutes-10 minutes before the next spin coating is performed. After all spin coatings are completed, the sample is aged in an oven at 40℃-60℃ for 12 hours-24 hours.

9. The method for preparing a high-strength multilayer ceramic composite separation membrane according to claim 1, characterized in that, In step four, the co-sintering densification process is as follows: the temperature is increased from room temperature to 300℃-500℃ at a rate of 0.5℃ / min-2℃ / min and held for 1-2 hours; then the temperature is increased to 800℃-1000℃ at a rate of 1℃ / min-3℃ / min and held for 0.5-1.5 hours; finally, the temperature is increased to the final sintering temperature of 1200℃-1500℃ at a rate of 2℃ / min-5℃ / min and held for 2-6 hours, followed by furnace cooling. The sintering atmosphere is air or oxygen.

10. The method for preparing a high-strength multilayer ceramic composite separation membrane according to claim 1, characterized in that, The surface modification treatment in step four consists of the following combination: Chemical vapor deposition modification: The primary ceramic composite film is placed in the reaction chamber of a chemical vapor deposition equipment, the vacuum is drawn to 10Pa-100Pa, the temperature is heated to 400℃-600℃, and silicon-containing precursor gas and carrier gas are introduced at a flow rate of 10sccm-50sccm. After reacting for 30 minutes to 120 minutes, a layer of silicon dioxide nanolayer is deposited on the film surface. Liquid-phase silanization modification: The primary ceramic composite membrane is immersed in an ethanol solution of silane coupling agent with a concentration of 1 vol%-5 vol% for 1 hour-4 hours, then removed and dried at 80℃-120℃ for 1 hour-2 hours, followed by heat treatment at 150℃-250℃ for 1 hour-3 hours to chemically bond the silane coupling agent with the hydroxyl groups on the membrane surface. Ion exchange modification: The primary ceramic composite membrane is immersed in a salt solution containing the target metal ions at a concentration of 0.1 mol / L to 1.0 mol / L for 6 to 24 hours at 60℃ to 90℃, so that the target metal ions can replace the exchangeable ions on the membrane surface. After completion, it is rinsed with deionized water and dried.