Recrystallized silicon carbide ceramic nanofiltration membrane as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of membrane separation, and particularly relates to a recrystallized silicon carbide ceramic nanofiltration membrane as well as a preparation method and application thereof. The preparation method comprises the following steps: applying a polycarbosilane solution to a silicon carbide ceramic ultrafiltration body, and carrying out first pyrolysis to obtain a pyrolysis material; a polycarbosilane solution is applied to the pyrolysis material, and then second pyrolysis is carried out; the first pyrolysis process comprises the following steps: heating to 290-310 DEG C from room temperature, and preserving heat; raising the temperature from 290-310 DEG C to 790-810 DEG C, and keeping the temperature; raising the temperature from 790 to 810 DEG C to 1190 to 1210 DEG C, and keeping the temperature; the second pyrolysis comprises first pyrolysis and recrystallization which are carried out in sequence; the recrystallization process comprises the following steps: heating from 1190-1210 DEG C to 1590-1610 DEG C, and preserving heat; the temperature is increased to 2190-2210 DEG C from 1590-1610 DEG C, and heat preservation is conducted. The aperture of the recrystallized silicon carbide ceramic nanofiltration membrane is smaller than 10 nm, and nanofiltration can be achieved.

Description

Technical Field

[0001] This invention relates to the field of membrane separation technology, and in particular to a recrystallized silicon carbide ceramic nanofiltration membrane, its preparation method, and its application. Background Technology

[0002] Membrane filtration precision is categorized into ultrafiltration membranes, nanofiltration membranes, and reverse osmosis membranes, each with its specific application areas and advantages. From the perspective of filtration materials, membranes can be classified into organic and inorganic membranes. Inorganic membranes are further divided into metal membranes, ceramic membranes, and alloy membranes. Ceramic membranes, based on their raw materials, include those made of silicon carbide (SiC), alumina (Al2O3), zirconium oxide (ZrO2), titanium dioxide (TiO2), and silicon dioxide (SiO2).

[0003] Silicon carbide ceramic membranes possess excellent antifouling and washability, making them commonly used as filtration membranes. However, current silicon carbide ceramic membranes typically have pore sizes of 10–100 nm, limiting their application to ultrafiltration. To obtain silicon carbide nanofiltration membranes with pore sizes less than 10 nm, silicon carbide powder with a particle size of 7 nm is required. Due to the high hardness of silicon carbide (green silicon carbide has a Mohs hardness of 9.2, and black silicon carbide has a Mohs hardness of 9.5), it is impossible to produce silicon carbide powder with a particle size of 7 nm, thus hindering the fabrication of silicon carbide nanofiltration membranes. In other words, the filtration precision of existing silicon carbide ceramic membranes remains at the ultrafiltration stage (≥20 nm). Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a recrystallized silicon carbide ceramic nanofiltration membrane, its preparation method, and its application. The recrystallized silicon carbide ceramic nanofiltration membrane obtained by the preparation method provided by this invention has a pore size of less than 10 nm and can be used for nanofiltration.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing a recrystallized silicon carbide ceramic nanofiltration membrane, comprising the following steps: After applying a polycarbosilane solution to a silicon carbide ceramic ultrafiltration body, a first pyrolysis is performed to obtain a pyrolytic material. After applying a polycarbosilane solution to the pyrolysis material, a second pyrolysis is performed to obtain the recrystallized silicon carbide ceramic nanofiltration membrane. The first pyrolysis process is as follows: The temperature is increased from room temperature to 290-310℃ at a rate of 1-5℃ / min and held for 1.5-2.5 hours. The temperature is increased from 290~310℃ to 790~810℃ at a rate of 5~10℃ / min and held for 0.5~1.5h. The temperature is increased from 790~810℃ to 1190~1210℃ at a rate of 2~5℃ / min and held for 3.5~4.5 hours. The process of applying a polycarbosilane solution to the silicon carbide ceramic ultrafiltration body and then performing the first pyrolysis is repeated until the pore size of the pyrolysis material is less than or equal to 1 nm. The second pyrolysis includes sequentially performing a first pyrolysis and recrystallization; The recrystallization process is as follows: The temperature is increased from 1190~1210℃ to 1590~1610℃ at a rate of 5~10℃ / min and held for 1.5~2.5 hours. The temperature is increased from 1590~1610℃ to 2190~2210℃ at a rate of 3~5℃ / min and held for 1~10 hours. The method of applying the polycarbosilane solution is the dip-coating method.

[0006] Preferably, the concentration of the polycarbosilane solution is 2-30 wt%, and the solvent of the polycarbosilane solution includes xylene.

[0007] Preferably, after the impregnation and lifting process, curing is performed; the curing temperature is 40°C and the time is 1 hour; the impregnation and lifting speed is 0.1~10 mm / s.

[0008] Preferably, the preparation method of the silicon carbide ceramic ultrafiltration body includes the following steps: Silicon carbide, cellulose, dextran, vegetable oil, water and glycerol are mixed and then kneaded, extruded, degummed and sintered in sequence to obtain a support. A transition coating is applied to the support, and a second sintering is performed to obtain a microfilter with a support-transition layer structure. An ultrafiltration coating is applied to the transition layer of the microfiltration body, and a third sintering is performed to obtain the silicon carbide ceramic ultrafiltration body.

[0009] Preferably, the silicon carbide, cellulose, dextran, vegetable oil, water, and glycerol constitute the support material; the mass percentage of each component in the support material is 70% silicon carbide, 6% cellulose, 3% dextran, 1% vegetable oil, 19% water, and 1% glycerol. The kneading time is 3-5 hours; the degumming temperature is 140-160℃ and the time is 8-12 hours.

[0010] Preferably, the first sintering process is as follows: The temperature is increased from room temperature by 1-2℃ to 590-610℃ and held for 0.5-1.5 hours. The temperature is increased from 590~610℃ to 1590~1610℃ at a rate of 5~10℃ / min and held for 0.5~1.5h. The temperature is increased from 1590~1610℃ to 2190~2210℃ at a rate of 3~5℃ / min and held for 1.5~2.5 hours. The temperature is increased from 2190~2210℃ to 2440~2460℃ at a rate of 3~5℃ / min and held for 1~3 hours. After the first sintering, the process further includes cooling to room temperature, wherein the cooling rate is 2~5℃ / min.

[0011] Preferably, the transition coating comprises the following components by weight percentage: The composition includes 60% silicon carbide powder, 10% vegetable oil, 25% water, and 5% glycerol; the particle size of the silicon carbide powder is 7 μm. The second sintering process is as follows: The temperature is increased from room temperature to 590-610℃ at a rate of 1-2℃ / min and held for 0.5-1.5 hours. The temperature is increased from 590~610℃ to 1590~1610℃ at a rate of 5~10℃ / min and held for 0.5~1.5h. The temperature is increased from 1590~1610℃ to 2190~2210℃ at a rate of 3~5℃ / min and held for 1~3 hours. After the second sintering, the process further includes cooling to room temperature at a rate of 2-5°C / min.

[0012] Preferably, the ultrafiltration coating comprises the following components by mass percentage: The composition includes 60% silicon carbide powder, 10% vegetable oil, 25% water, and 5% glycerol; the particle size of the silicon carbide powder is 0.7 μm. The third sintering process is as follows: The temperature is increased from room temperature to 590-610℃ at a rate of 1-2℃ / min and held for 0.5-1.5 hours. The temperature is increased from 590~610℃ to 1590~1610℃ at a rate of 5~10℃ / min and held for 0.5~1.5h. The temperature is increased from 1590~1610℃ to 2190~2210℃ at a rate of 3~5℃ / min and held for 0.5~1.5h. After the third sintering, the process further includes cooling to room temperature at a rate of 2-5°C / min.

[0013] The present invention also provides a recrystallized silicon carbide ceramic nanofiltration membrane prepared by the above preparation method, wherein the pore size of the recrystallized silicon carbide ceramic nanofiltration membrane is less than 10 nm.

[0014] The present invention also provides the application of the recrystallized silicon carbide ceramic nanofiltration membrane described in the above technical solution in nanofiltration.

[0015] This invention provides a method for preparing recrystallized silicon carbide ceramic nanofiltration membranes.

[0016] The preparation method of the present invention has the following advantages: 1. Compared with existing recrystallized silicon carbide ceramic membranes, the present invention uses an impregnation-coating method to apply a polycarbosilane solution onto a silicon carbide ceramic ultrafiltration body, followed by a first pyrolysis and a second pyrolysis, which results in better immersion of the silicon carbide membrane layer and a tighter bond.

[0017] 2. Compared with the existing recrystallized silicon carbide ceramic membrane with a filtration accuracy of ≥0.05μm, the silicon carbide ceramic ultrafiltration body of the present invention achieves nanofiltration by impregnating and pulling polycarbosilane solution and sequentially filling the pores through first pyrolysis and second pyrolysis to increase the pore size to below 10nm.

[0018] 3. In this invention, after applying a polycarbosilane solution, a first pyrolysis and a second pyrolysis are performed sequentially. The neck connection is achieved by atomic diffusion on the surface of silicon carbide particles, and recrystallization is realized, thus preparing a fully recrystallized silicon carbide ceramic nanofiltration membrane.

[0019] The present invention also provides a recrystallized silicon carbide ceramic nanofiltration membrane prepared by the above-described technical solution, which has the following advantages: 1. High flux: The unique multi-layer pore structure (the pore size of the recrystallized silicon carbide layer is less than 10nm, the pore size of the ultrafiltration layer is 0.05~0.2μm, the pore size of the transition layer is 0.5~1μm and the pore size of the support is 5~10μm) and high hydrophilicity (water contact angle 0.3°) significantly reduce filtration resistance.

[0020] 2. Corrosion / High Temperature Resistance: It can withstand strong acid and alkali corrosion and high temperature environments (long-term operating temperature > 1000℃), and is suitable for harsh working conditions such as chemical and metallurgical industries.

[0021] 3. High mechanical strength: Excellent thermal shock resistance and mechanical strength, suitable for high-pressure filtration scenarios. Attached Figure Description

[0022] Figure 1 A flowchart illustrating the preparation process of the recrystallized silicon carbide ceramic nanofiltration membrane provided by this invention; Figure 2 The image is a scanning electron microscope (SEM) image of the nanofiltration membrane obtained in Example 1 (×2000). Figure 3 The image is a scanning electron microscope (SEM) image (×2000) of the nanofiltration membrane obtained in Example 2. Figure 4 The image is a scanning electron microscope (SEM) image of the nanofiltration membrane obtained in Example 3 (×2000). Figure 5 The image is a scanning electron microscope (SEM) image of the nanofiltration membrane obtained in Example 4 (×2000). Figure 6 The image shows a scanning electron microscope (SEM) image (×2000) of the nanofiltration membrane obtained in Example 5. Detailed Implementation

[0023] Figure 1 The following is a flowchart illustrating the preparation process of the recrystallized silicon carbide ceramic nanofiltration membrane provided by this invention. Figure 1 The preparation method provided by the present invention will be described in detail.

[0024] This invention provides a method for preparing a recrystallized silicon carbide ceramic nanofiltration membrane, comprising the following steps: After applying a polycarbosilane solution to a silicon carbide ceramic ultrafiltration body, a first pyrolysis is performed to obtain a pyrolytic material. A second pyrolysis is performed after applying a polycarbosilane solution to the pyrolysis material to obtain the recrystallized silicon carbide ceramic nanofiltration membrane.

[0025] Unless otherwise specified, the raw materials used in this invention are preferably commercially available products.

[0026] In this invention, the silicon carbide ceramic ultrafiltration body includes a support, a transition layer attached to the support, and an ultrafiltration layer attached to the transition layer.

[0027] In this invention, the method for preparing the silicon carbide ceramic ultrafiltration body preferably includes the following steps: Silicon carbide, cellulose, dextran, vegetable oil, water and glycerol are mixed and then kneaded, extruded, degummed and sintered in sequence to obtain a support. A transition coating is applied to the support, and a second sintering is performed to obtain a microfilter with a support-transition layer structure. An ultrafiltration coating is applied to the transition layer of the microfiltration body, and a third sintering is performed to obtain the silicon carbide ceramic ultrafiltration body.

[0028] This invention involves mixing silicon carbide, cellulose, dextran, vegetable oil, water, and glycerol, and then sequentially performing kneading, extrusion, degumming, and a first sintering to obtain a support.

[0029] In this invention, the purity of the silicon carbide is preferably 99.8%. In this invention, the silicon carbide is the main raw material used to construct the main body of the over-recrystallized silicon carbide ceramic nanofiltration membrane, improving membrane strength and throughput. In this invention, the cellulose acts as a binding agent, ensuring the membrane does not loosen. In this invention, the dextran acts as a binder, adhering the silicon carbide powder together and filling the gaps between the powder particles. In this invention, the vegetable oil preferably includes one or more of soybean oil, corn oil, and rice bran oil, more preferably rice bran oil, and is used to mix the silicon carbide powder. In this invention, the water is preferably purified water. In this invention, the water is used to mix the silicon carbide powder. In this invention, the purity of the glycerol is preferably 98%, and the glycerol acts as a binder, adhering the silicon carbide powder together and filling the gaps between the powder particles.

[0030] In this invention, silicon carbide, cellulose, dextran, vegetable oil, water and glycerol constitute the support material; the preferred mass percentage of each component in the support material is: silicon carbide 70%, cellulose 6%, dextran 3%, vegetable oil 2%, water 19% and glycerol 1%.

[0031] In this invention, the kneading time is preferably 3 to 5 hours, more preferably 4 hours; the kneading temperature is preferably room temperature, that is, neither additional heating nor additional cooling is required.

[0032] The present invention does not specifically limit the shape of the extrusion; it can be set according to the actual situation.

[0033] In this invention, the degumming temperature is preferably 140~160℃, more preferably 150℃; the time is preferably 8~12h, more preferably 10h.

[0034] In this invention, the first sintering process is preferably as follows: The temperature is increased from room temperature by 1-2℃ to 590-610℃ and held for 0.5-1.5 hours. The temperature is increased from 590~610℃ to 1590~1610℃ at a rate of 5~10℃ / min and held for 0.5~1.5h. The temperature is increased from 1590~1610℃ to 2190~2210℃ at a rate of 3~5℃ / min and held for 1.5~2.5 hours. The temperature is increased from 2190~2210℃ to 2440~2460℃ at a rate of 3~5℃ / min and held for 1~3 hours. The first sintering process is further preferably: The temperature was increased from room temperature by 1-2℃ to 600℃ and held for 1 hour. The temperature was increased from 600℃ to 1600℃ at a rate of 5~10℃ / min and held for 1 hour. The temperature was increased from 1600℃ to 2200℃ at a rate of 3~5℃ / min and held for 2 hours. The temperature was increased from 2200℃ to 2450℃ at a rate of 3~5℃ / min and held for 1 hour.

[0035] In this invention, the temperature is raised from room temperature to 590-610°C at a rate of 1-2°C and held for 0.5-1.5 hours. This process removes the binder (dextran and glycerol) and solvent. The first heating rate is preferably controlled at 1-2°C / min to prevent the film from cracking.

[0036] In this invention, the temperature is increased from 590~610℃ to 1590~1610℃ at a rate of 5~10℃ / min and held for 0.5~1.5h; this process can activate the particle surface.

[0037] In this invention, the temperature is increased from 1590~1610℃ to 2190~2210℃ at a rate of 3~5℃ / min and held for 1.5~2.5h; during this process, the SiC surface evaporates and condenses, a neck is formed, and oxidation is prevented.

[0038] In this invention, the temperature is increased from 2190~2210℃ to 2440~2460℃ at a rate of 3~5℃ / min and held for 1~3 hours. This process can achieve densification and promote grain growth, so that the grain size is within a suitable range and the strength is improved.

[0039] After the first sintering, the present invention preferably further includes cooling to room temperature, wherein the cooling rate is preferably 2~5°C / min. In the present invention, this process can prevent thermal stress cracking.

[0040] In this invention, the first sintering is preferably carried out under a vacuum or protective atmosphere, wherein the protective atmosphere is preferably argon.

[0041] In this invention, the aperture of the support is preferably 5~10μm.

[0042] In this invention, the raw material of the support is completely converted into recrystallized silicon carbide after being kneaded, extruded, degummed and sintered for the first time.

[0043] After obtaining the support, the present invention applies a transition coating to the support and performs a second sintering to obtain a microfilter with a support-transition layer structure.

[0044] In this invention, the transition coating preferably comprises the following components by weight percentage: The composition comprises 60% silicon carbide powder, 10% vegetable oil, 25% water, and 5% glycerol. In this invention, the particle size of the silicon carbide powder is preferably 7 μm.

[0045] In this invention, the second sintering process is preferably as follows: The temperature is increased from room temperature to 590-610℃ at a rate of 1-2℃ / min and held for 0.5-1.5 hours. The temperature is increased from 590~610℃ to 1590~1610℃ at a rate of 5~10℃ / min and held for 0.5~1.5h. The temperature is increased from 1590~1610℃ to 2190~2210℃ at a rate of 3~5℃ / min and held for 1~3 hours. The second sintering process is further preferably: The temperature was increased from room temperature to 600℃ at a rate of 1~2℃ / min and held for 1 hour. The temperature was increased from 600℃ to 1600℃ at a rate of 5~10℃ / min and held for 1 hour. Increase the temperature from 1600℃ to 2200℃ at a rate of 3~5℃ / min and hold for 1~3 hours.

[0046] In this invention, the temperature is increased from room temperature to 590-610°C at a rate of 1-2°C / min and held for 0.5-1.5 hours. This process can remove the binder / solvent and prevent the film from cracking.

[0047] In this invention, the temperature is increased from 590~610℃ to 1590~1610℃ at a rate of 5~10℃ / min and held for 0.5~1.5h, which can activate the particle surface.

[0048] In this invention, the temperature is increased from 1590~1610℃ to 2190~2210℃ at a rate of 3~5℃ / min and held for 1~3h. This process can promote grain growth and form a dense film.

[0049] After the second sintering, the present invention preferably further includes cooling to room temperature, wherein the cooling rate is preferably 2~5°C / min. In the present invention, this process can prevent thermal stress cracking.

[0050] In this invention, the second sintering is preferably carried out under a vacuum or protective atmosphere, preferably argon.

[0051] In this invention, the pore size of the microfilter is preferably 0.5~1μm.

[0052] After obtaining a microfilter with a support-transition layer structure, the present invention applies an ultrafiltration coating to the transition layer of the microfilter and performs a third sintering to obtain the silicon carbide ceramic ultrafilter.

[0053] In this invention, the ultrafiltration coating preferably comprises the following components by weight percentage: 60% silicon carbide powder, 10% vegetable oil, 25% water, and 5% glycerol. In this invention, the particle size of the silicon carbide powder is preferably 0.7 μm.

[0054] In this invention, the third sintering process is preferably as follows: The temperature is increased from room temperature to 590-610℃ at a rate of 1-2℃ / min and held for 0.5-1.5 hours. The temperature is increased from 590~610℃ to 1590~1610℃ at a rate of 5~10℃ / min and held for 0.5~1.5h. The temperature is increased from 1590~1610℃ to 2190~2210℃ at a rate of 3~5℃ / min and held for 0.5~1.5h. The third sintering process is further preferably: The temperature was increased from room temperature to 600℃ at a rate of 1~2℃ / min and held for 1 hour. The temperature was increased from 600℃ to 1600℃ at a rate of 5~10℃ / min and held for 1 hour. The temperature is increased from 1600℃ to 2200℃ at a rate of 3~5℃ / min and held for 0.5~1.5h.

[0055] In this invention, the temperature is increased from room temperature to 590-610°C at a rate of 1-2°C / min and held for 0.5-1.5 hours. This process can remove the binder / solvent and prevent the film from cracking.

[0056] In this invention, the temperature is increased from 590~610℃ to 1590~1610℃ at a rate of 5~10℃ / min and held for 0.5~1.5h, which can activate the particle surface.

[0057] In this invention, the temperature is increased from 1590~1610℃ to 2190~2210℃ at a rate of 3~5℃ / min and held for 0.5~1.5h. During this process, grain growth can be promoted to form a dense film layer.

[0058] After the third sintering, the present invention further includes cooling to room temperature, wherein the cooling rate is preferably 2~5℃ / min.

[0059] In this invention, the third sintering is preferably carried out under a vacuum or protective atmosphere, preferably argon.

[0060] In this invention, the pore size of the silicon carbide ceramic ultrafiltration body is preferably 0.05~0.2μm.

[0061] After obtaining the silicon carbide ceramic ultrafiltration body, the present invention applies a polycarbosilane solution to the silicon carbide ceramic ultrafiltration body and then performs a first pyrolysis to obtain a pyrolytic material.

[0062] In this invention, the concentration of the polycarbosilane solution is 2-30 wt%, specifically preferably 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, or 30 wt%. In this invention, the solvent of the polycarbosilane solution preferably includes xylene. In this invention, the preparation of the polycarbosilane solution is preferably carried out under an argon atmosphere, wherein the oxygen content of the argon atmosphere is preferably <1 ppm, and the water content is preferably <1 ppm.

[0063] In this invention, the polycarbosilane solution is applied by dip-lifting, and after dip-lifting, it is preferably cured; the curing temperature is preferably 40°C, and the curing time is preferably 1 hour; the dip-lifting speed is preferably 0.1~10 mm / s.

[0064] In this invention, the first pyrolysis process is as follows: The temperature is increased from room temperature to 290-310℃ at a rate of 1-5℃ / min and held for 1.5-2.5 hours. The temperature is increased from 290~310℃ to 790~810℃ at a rate of 5~10℃ / min and held for 0.5~1.5 hours. The temperature is increased from 790~810℃ to 1190~1210℃ at a rate of 2~5℃ / min and held for 3.5~4.5 hours. The preferred process for the first pyrolysis is: The temperature was increased from room temperature to 300℃ at a rate of 1~5℃ / min and held for 2 hours. The temperature was increased from 300℃ to 800℃ at a rate of 5~10℃ / min and held for 1 hour. The temperature was increased from 800℃ to 1200℃ at a rate of 2~5℃ / min and held for 4 hours.

[0065] In this invention, the temperature is increased from room temperature to 290-310°C at a rate of 1-5°C / min and held for 1.5-2.5 hours. This process can evaporate the solvent and promote further cross-linking.

[0066] In this invention, the temperature is increased from 290~310℃ to 790~810℃ at a rate of 5~10℃ / min and held for 0.5~1.5h. During this process, polycarbosilane (PCS) is pyrolyzed to generate amorphous SiC (α-SiC) and a small amount of free carbon.

[0067] In this invention, the temperature is increased from 790~810℃ to 1190~1210℃ at a rate of 2~5℃ / min and held for 3.5~4.5h. During this process, β-SiC is initially crystallized to generate α-SiC nanocrystals.

[0068] In this invention, the first pyrolysis is preferably carried out under a protective atmosphere, which is preferably argon gas, and the oxygen content and water content in the argon gas are preferably <1 ppm.

[0069] After the first pyrolysis, the present invention preferably further includes furnace cooling to room temperature.

[0070] In this invention, the process of applying a polycarbosilane solution to a silicon carbide ceramic ultrafiltration body and then performing a first pyrolysis is repeated until the pore size of the pyrolysis material is less than or equal to 1 nm.

[0071] In this invention, the pore size of the pyrolysis material is less than or equal to 1 nm.

[0072] This invention rationally controls the heating rate of the first pyrolysis, which can improve the ceramic yield and maintain the integrity of the film.

[0073] After obtaining the pyrolysis material, the present invention applies a polycarbosilane solution to the pyrolysis material and performs a second pyrolysis to obtain the recrystallized silicon carbide ceramic nanofiltration membrane.

[0074] In this invention, the concentration and application method of the polycarbosilane solution are preferably consistent with the above-described technical solution, and will not be repeated here.

[0075] In this invention, the second pyrolysis includes sequentially performing a first pyrolysis and recrystallization; The recrystallization process is as follows: The temperature is increased from 1190~1210℃ to 1590~1610℃ at a rate of 5~10℃ / min and held for 1.5~2.5 hours. The temperature is increased from 1590~1610℃ to 2190~2210℃ at a rate of 3~5℃ / min and held for 1~10 hours. The preferred recrystallization process is as follows: The temperature was increased from 1200℃ to 1600℃ at a rate of 5~10℃ / min and held for 2 hours. The temperature is increased from 1600℃ to 2200℃ at a rate of 3~5℃ / min and held for 1~10 hours.

[0076] In this invention, the second pyrolysis process specifically includes: The temperature is increased from room temperature to 290-310℃ at a rate of 1-5℃ / min and held for 1.5-2.5 hours. The temperature is increased from 290~310℃ to 790~810℃ at a rate of 5~10℃ / min and held for 0.5~1.5 hours. The temperature is increased from 790~810℃ to 1190~1210℃ at a rate of 2~5℃ / min and held for 3.5~4.5 hours. The temperature is increased from 1190~1210℃ to 1590~1610℃ at a rate of 5~10℃ / min and held for 1.5~2.5 hours. The temperature is increased from 1590~1610℃ to 2190~2210℃ at a rate of 3~5℃ / min and held for 1~10 hours. The preferred specific process for the second pyrolysis is as follows: The temperature was increased from room temperature to 300℃ at a rate of 1~5℃ / min and held for 2 hours. The temperature was increased from 300℃ to 800℃ at a rate of 5~10℃ / min and held for 1 hour. The temperature was increased from 800℃ to 1200℃ at a rate of 2~5℃ / min and held for 4 hours. The temperature was increased from 1200℃ to 1600℃ at a rate of 5~10℃ / min and held for 2 hours. The temperature is increased from 1600℃ to 2200℃ at a rate of 3~5℃ / min and held for 1~10 hours.

[0077] After the second pyrolysis, the present invention preferably further includes furnace cooling to room temperature.

[0078] In this invention, the second pyrolysis is preferably carried out under a vacuum or a protective atmosphere, preferably argon.

[0079] In this invention, during the second pyrolysis process, an evaporation-condensation mechanism exists, specifically: SiC surface atoms evaporate at high temperatures and condense at the particle neck, driving material migration. It also promotes grain growth: β-SiC grains gradually grow (40~50 nm), porosity decreases to obtain smaller pore sizes, and a continuous ceramic phase is formed; furthermore, it enables the densification of the film layer.

[0080] The present invention also provides a recrystallized silicon carbide ceramic nanofiltration membrane prepared by the preparation method described above, wherein the pore size of the recrystallized silicon carbide ceramic nanofiltration membrane is less than 10 nm.

[0081] In this invention, the recrystallized silicon carbide ceramic nanofiltration membrane can be used as a nanofiltration membrane.

[0082] The present invention also provides the application of the recrystallized silicon carbide ceramic nanofiltration membrane in nanofiltration.

[0083] In this invention, the nanofiltration system is capable of retaining divalent and higher ions, as well as small molecule organic matter; the divalent and higher ions preferably include Ca. 2+ Mg 2+ or SO4 2- In this invention, the small molecule organic compounds preferably include dyes and pesticides.

[0084] In this invention, the recrystallized silicon carbide ceramic nanofiltration membrane is further preferably capable of being used for water softening, dye desalination, pharmaceutical concentration, or seawater desalination.

[0085] In this invention, when the recrystallized silicon carbide ceramic nanofiltration membrane is used for water softening, it can remove Ca from the water. 2+ Mg 2+ .

[0086] In this invention, the recrystallized silicon carbide ceramic nanofiltration membrane is used for seawater desalination, wherein the seawater is preferably low in salinity.

[0087] The following detailed description, in conjunction with embodiments, illustrates the recrystallized silicon carbide ceramic nanofiltration membrane, its preparation method, and its applications provided by the present invention. However, these descriptions should not be construed as limiting the scope of protection of the present invention.

[0088] Example 1 The preparation steps for recrystallized silicon carbide ceramic nanofiltration membranes are as follows: Step 1, Preparation of the support: The raw materials are mixed according to the following mass percentages: 70% silicon carbide, 6% cellulose, 3% dextran, 1% vegetable oil (specifically rice bran oil), 19% water and 1% glycerol. The mixture is then subjected to kneading (room temperature, 4h), extrusion, degumming (150℃, 10h) and first sintering. The mixture is cooled to room temperature at a cooling rate of 2~5℃ / min to obtain the support. The filter pore size of the obtained support is 10μm.

[0089] The first sintering process is as follows: The temperature was increased from room temperature to 600℃ at a rate of 1~2℃ / min and held for 1 hour. The temperature was increased from 600℃ to 1600℃ at a rate of 5~10℃ / min and held for 1 hour. The temperature was increased from 1600℃ to 2200℃ at a rate of 3~5℃ / min and held for 2 hours. Heat from 2200℃ to 2450℃ at a rate of 3~5℃ / min and hold for 3 hours; The first sintering is carried out in argon gas.

[0090] Step 2: Preparation of microfilters with a support / transition layer structure Silicon carbide powder (7μm particle size), vegetable oil, water and glycerol were mixed in a mass ratio of 60:10:25:5 to obtain a transition coating.

[0091] The transition coating was applied to the support, and a second sintering was performed to obtain a transition film with a pore size of 1 μm.

[0092] The second sintering process is as follows: The temperature was increased from room temperature to 600℃ at a rate of 1~2℃ / min and held for 1 hour. The temperature was increased from 600℃ to 1600℃ at a rate of 5~10℃ / min and held for 1 hour. The temperature was increased from 1600℃ to 2200℃ at a rate of 3~5℃ / min and held for 2 hours. The temperature was reduced from 2200℃ to room temperature at a cooling rate of 2~5℃ / min; The second sintering is carried out in argon gas.

[0093] Step 3: Preparation of silicon carbide ceramic ultrafiltration body with support-transition layer-ultrafiltration layer Silicon carbide powder (0.7 μm particle size), vegetable oil, water and glycerol were mixed in a mass ratio of 60:10:25:5 to obtain an ultrafiltration coating.

[0094] The ultrafiltration coating was applied to the transition layer, and a third sintering was performed to obtain a silicon carbide ceramic ultrafiltration body with a pore size of 0.05 μm.

[0095] The third sintering process is as follows: The temperature was increased from room temperature to 600℃ at a rate of 1~2℃ / min and held for 1 hour. The temperature was increased from 600℃ to 1600℃ at a rate of 5~10℃ / min and held for 1 hour. The temperature was increased from 1600℃ to 2200℃ at a rate of 3~5℃ / min and held for 1 hour. The temperature was reduced from 2200℃ to room temperature at a cooling rate of 2~5℃ / min; The third sintering is carried out in argon gas.

[0096] Step 4: Under the protection of clean argon (oxygen < 1 ppm, water < 1 ppm), dissolve polycarbosilane in xylene to form a polycarbosilane solution (concentration 5 wt%).

[0097] A polycarbosilane solution was coated onto a silicon carbide ceramic ultrafiltration body using an impregnation-coating method at a speed of 10 mm / s. After coating, the material was cured at 40°C for 1 hour, followed by a first pyrolysis.

[0098] The first pyrolysis process is as follows: The temperature was increased from room temperature to 300℃ at a rate of 1~5℃ / min and held for 2 hours. The temperature was increased from 300℃ to 800℃ at a rate of 5~10℃ / min and held for 1 hour. The temperature was increased from 800℃ to 1200℃ at a rate of 2~5℃ / min and held for 4 hours. The furnace temperature was lowered from 1200℃ to room temperature. The atmosphere for the first pyrolysis is argon.

[0099] Repeat step 4 twice to obtain pyrolysis material.

[0100] Step 5, Second pyrolysis A polycarbosilane solution was coated onto the pyrolytic material using an dip-coating method at a speed of 10 mm / s. After coating, the material was cured at 40°C for 1 hour, followed by a second pyrolysis.

[0101] The temperature was increased from room temperature to 300℃ at a rate of 1~5℃ / min and held for 2 hours. The temperature was increased from 300℃ to 800℃ at a rate of 5~10℃ / min and held for 1 hour. The temperature was increased from 800℃ to 1200℃ at a rate of 2~5℃ / min and held for 4 hours. The temperature was increased from 1200℃ to 1600℃ at a rate of 5~10℃ / min and held for 2 hours. Heat from 1600℃ to 2200℃ at a rate of 3~5℃ / min and hold for 2 hours; then cool to room temperature in the furnace. The atmosphere for the second pyrolysis is argon.

[0102] Example 2 The difference from Example 1 is that in step 4, the concentration of the polycarbosilane solution is 10 wt%, and the rest is the same as in Example 1.

[0103] Example 3 The difference from Example 1 is that in step 4, the concentration of the polycarbosilane solution is 20 wt%, and the rest is the same as in Example 1.

[0104] Example 4 The difference from Example 2 is that in step 4, the number of times "step 4" is repeated is 5 times, and the rest is the same as in Example 1.

[0105] Example 5 The difference from Example 3 is that in step 4, the number of times "step 4" is repeated is 5 times, and the rest is the same as in Example 1.

[0106] Performance testing (1) Flux and aperture The pure water flux of the recrystallized silicon carbide ceramic nanofiltration membrane was determined by gravimetric method, and the pore size was determined by BSD-PB bubble pressure method membrane pore size analyzer. The results are shown in Table 1.

[0107] Table 1 shows the pure water flux and pore size of the recrystallized silicon carbide ceramic nanofiltration membrane (transmembrane pressure: 0.1 MPa).

[0108] (2) Abrasion resistance test The test was conducted according to ASTM G65 (dry sand rubber wheel method) and ASTM G133 (reciprocating sliding wear) standards, with a load of 50N and abrasives of 120 mesh SiC sand (dry sand method) or Al2O3 balls (sliding method).

[0109] Table 2 shows the comparative test data of the wear resistance of the recrystallized silicon carbide ceramic nanofiltration membrane obtained in Example 1 and the commercially available ordinary silicon carbide ceramic membrane as a function of time under room temperature (25°C).

[0110] Table 2 Abrasion resistance data

[0111] As can be seen from Table 2, the recrystallized silicon carbide ceramic nanofiltration membrane obtained by the present invention exhibits advantages in long-term wear (fatigue wear resistance).

[0112] (3) Hydrofluoric acid corrosion resistance test The corrosion comparison test data of the recrystallized silicon carbide ceramic nanofiltration membrane obtained in Example 1 and the commercially available ordinary silicon carbide ceramic membrane over time under the conditions of room temperature (25℃) and 10% hydrofluoric acid (HF) are shown in Tables 3 and 4.

[0113] Table 3 Results of hydrofluoric acid corrosion resistance

[0114] As can be seen from Table 3, the obtained recrystallized silicon carbide ceramic nanofiltration membrane has excellent resistance to hydrofluoric acid corrosion.

[0115] Table 4 Comparison of corrosion rates between 10%HF and 20%HF

[0116] As can be seen from Table 4, the concentration has a negligible effect on recrystallized silicon carbide ceramic nanofiltration membranes due to their purely chemical corrosion mechanism.

[0117] (4) High temperature resistance test Thermal conductivity was measured using the laser flare method according to ASTM E1461, and the results are shown in Table 5.

[0118] Table 5 Thermal Properties

[0119] (5) Thermal shock resistance test The results are shown in Table 6.

[0120] Table 6 Comparison of Thermal Shock Resistance

[0121] (6) Mechanical performance testing The flexural strength of the material was tested using ASTM C1161, and the results were as follows: The flexural strength of the recrystallized silicon carbide ceramic nanofiltration membrane obtained in Example 1 was 105 ± 10 MPa.

[0122] Figures 2-6 The images shown are scanning electron microscope (SEM) images (×2000) of the nanofiltration membranes obtained in Examples 1-6, in sequence. Figures 2-6 It can be seen that the nanofiltration membranes obtained in Examples 1 to 5 become increasingly dense.

[0123] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a recrystallized silicon carbide ceramic nanofiltration membrane, characterized in that, Includes the following steps: After applying a polycarbosilane solution to a silicon carbide ceramic ultrafiltration body, a first pyrolysis is performed to obtain a pyrolytic material. After applying a polycarbosilane solution to the pyrolysis material, a second pyrolysis is performed to obtain the recrystallized silicon carbide ceramic nanofiltration membrane. The first pyrolysis process is as follows: The temperature is increased from room temperature to 290-310℃ at a rate of 1-5℃ / min and held for 1.5-2.5 hours. The temperature is increased from 290~310℃ to 790~810℃ at a rate of 5~10℃ / min and held for 0.5~1.5h. The temperature is increased from 790~810℃ to 1190~1210℃ at a rate of 2~5℃ / min and held for 3.5~4.5 hours. The process of applying a polycarbosilane solution to the silicon carbide ceramic ultrafiltration body and then performing the first pyrolysis is repeated until the pore size of the pyrolysis material is less than or equal to 1 nm. The second pyrolysis includes sequentially performing a first pyrolysis and recrystallization; The recrystallization process is as follows: The temperature is increased from 1190~1210℃ to 1590~1610℃ at a rate of 5~10℃ / min and held for 1.5~2.5 hours. The temperature is increased from 1590~1610℃ to 2190~2210℃ at a rate of 3~5℃ / min and held for 1~10 hours. The method of applying the polycarbosilane solution is the dip-coating method.

2. The preparation method according to claim 1, characterized in that, The concentration of the polycarbosilane solution is 2-30 wt%, and the solvent of the polycarbosilane solution includes xylene.

3. The preparation method according to claim 1 or 2, characterized in that, After the impregnation and lifting process, the material is cured; the curing temperature is 40℃ and the time is 1 hour; the impregnation and lifting speed is 0.1~10mm / s.

4. The preparation method according to claim 1, characterized in that, The preparation method of the silicon carbide ceramic ultrafiltration body includes the following steps: Silicon carbide, cellulose, dextran, vegetable oil, water and glycerol are mixed and then kneaded, extruded, degummed and sintered in sequence to obtain a support. A transition coating is applied to the support, followed by a second sintering process to obtain a microfilter with a support-transition layer structure. An ultrafiltration coating is applied to the transition layer of the microfiltration body, and a third sintering is performed to obtain the silicon carbide ceramic ultrafiltration body.

5. The preparation method according to claim 4, characterized in that, The support material consists of silicon carbide, cellulose, dextran, vegetable oil, water, and glycerol; the mass percentage of each component in the support material is 70% silicon carbide, 6% cellulose, 3% dextran, 1% vegetable oil, 19% water, and 1% glycerol. The kneading time is 3-5 hours; the degumming temperature is 140-160℃ and the time is 8-12 hours.

6. The preparation method according to claim 4, characterized in that, The first sintering process is as follows: The temperature is increased from room temperature by 1-2℃ to 590-610℃ and held for 0.5-1.5 hours. The temperature is increased from 590~610℃ to 1590~1610℃ at a rate of 5~10℃ / min and held for 0.5~1.5h. The temperature is increased from 1590~1610℃ to 2190~2210℃ at a rate of 3~5℃ / min and held for 1.5~2.5 hours. The temperature is increased from 2190~2210℃ to 2440~2460℃ at a rate of 3~5℃ / min and held for 1~3 hours. After the first sintering, the process further includes cooling to room temperature, wherein the cooling rate is 2~5℃ / min.

7. The preparation method according to claim 4, characterized in that, The transition coating comprises the following components by weight percentage: The composition includes 60% silicon carbide powder, 10% vegetable oil, 25% water, and 5% glycerol; the particle size of the silicon carbide powder is 7 μm. The second sintering process is as follows: The temperature is increased from room temperature to 590-610℃ at a rate of 1-2℃ / min and held for 0.5-1.5 hours. The temperature is increased from 590~610℃ to 1590~1610℃ at a rate of 5~10℃ / min and held for 0.5~1.5h. The temperature is increased from 1590~1610℃ to 2190~2210℃ at a rate of 3~5℃ / min and held for 1~3 hours. After the second sintering, the process further includes cooling to room temperature at a rate of 2-5°C / min.

8. The preparation method according to claim 4, characterized in that, The ultrafiltration coating comprises the following components by mass percentage: The composition includes 60% silicon carbide powder, 10% vegetable oil, 25% water, and 5% glycerol; the particle size of the silicon carbide powder is 0.7 μm. The third sintering process is as follows: The temperature is increased from room temperature to 590-610℃ at a rate of 1-2℃ / min and held for 0.5-1.5 hours. The temperature is increased from 590~610℃ to 1590~1610℃ at a rate of 5~10℃ / min and held for 0.5~1.5h. The temperature was increased from 1590~1610℃ to 2190~2210℃ at a rate of 3~5℃ / min and held for 0.5~1.5h. After the third sintering, the process further includes cooling to room temperature at a rate of 2-5°C / min.

9. The recrystallized silicon carbide ceramic nanofiltration membrane prepared by the preparation method according to any one of claims 1 to 8, characterized in that, The pore size of the recrystallized silicon carbide ceramic nanofiltration membrane is less than 10 nm.

10. The application of the recrystallized silicon carbide ceramic nanofiltration membrane according to claim 9 in nanofiltration.

Images