A recrystallized silicon carbide ceramic nanofiltration membrane, a preparation method and application thereof

Abstract

The application belongs to the technical field of membrane separation, and particularly relates to a recrystallized silicon carbide ceramic nanofiltration membrane and a preparation method and application thereof. The application comprises the following steps: applying a polycarbosilane solution on a silicon carbide ceramic ultrafiltration body to perform first pyrolysis, and obtaining a pyrolysis material; applying the polycarbosilane solution on the pyrolysis material to perform second pyrolysis, and obtaining the recrystallized silicon carbide ceramic nanofiltration membrane; the first pyrolysis process comprises the following steps: heating from room temperature to 290-310 DEG C and keeping warm; heating from 290-310 DEG C to 790-810 DEG C and keeping warm; heating from 790-810 DEG C to 1190-1210 DEG C and keeping warm; the second pyrolysis comprises sequentially performing the first pyrolysis and recrystallization; the recrystallization process comprises the following steps: heating from 1190-1210 DEG C to 1590-1610 DEG C and keeping warm; heating from 1590-1610 DEG C to 2190-2210 DEG C and keeping warm. The recrystallized silicon carbide ceramic nanofiltration membrane obtained by the application has a pore size of less than 10 nm, and can realize nanofiltration.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of membrane separation technology, in particular to a recrystallized silicon carbide ceramic nanofiltration membrane and a preparation method and application thereof. BACKGROUND

[0002] The filtration accuracy of the membrane is divided into: ultrafiltration membrane, nanofiltration membrane, reverse osmosis membrane, etc. Each type of filtration membrane has its specific application field and advantage. From the aspect of filtration material, it is classified into: organic membrane and inorganic membrane. The inorganic membrane is further divided into: metal membrane, ceramic membrane and alloy membrane. Among them, the ceramic membrane is divided into: silicon carbide (SiC), aluminum oxide (Al2O3), zirconium oxide (ZrO2), titanium oxide (TiO2) and silicon dioxide (SiO2) ceramic membranes from the aspect of raw materials.

[0003] The silicon carbide ceramic membrane has excellent anti-pollution and cleaning resistance, so it is often used as a filtration membrane. However, the current silicon carbide ceramic membrane has a pore size of 10-100 nm, which can only be used as an ultrafiltration membrane. If a silicon carbide nanofiltration membrane with a pore size less than 10 nm is needed, a silicon carbide powder with a particle size of 7 nm is needed. Due to the high hardness of silicon carbide (the Mohs hardness of green silicon carbide is 9.2, and the Mohs hardness of black silicon carbide is 9.5), it is impossible to prepare a silicon carbide powder with a particle size of 7 nm, and thus it is impossible to prepare a silicon carbide nanofiltration membrane. That is, the filtration accuracy of the existing silicon carbide ceramic membrane is limited to the ultrafiltration stage (≥20 nm). SUMMARY

[0004] Therefore, the present application aims to provide a recrystallized silicon carbide ceramic nanofiltration membrane and a preparation method and application thereof. The recrystallized silicon carbide ceramic nanofiltration membrane prepared by the preparation method has a pore size less than 10 nm and can be used for nanofiltration.

[0005] In order to achieve the above-mentioned application purposes, the present application provides the following technical solutions:

[0006] The present application provides a preparation method of a recrystallized silicon carbide ceramic nanofiltration membrane, comprising the following steps:

[0007] After applying a polycarbosilane solution on the silicon carbide ceramic ultrafiltration body, a first pyrolysis is performed to obtain a pyrolysis material;

[0008] After applying a polycarbosilane solution on the pyrolysis material, a second pyrolysis is performed to obtain the recrystallized silicon carbide ceramic nanofiltration membrane;

[0009] The process of the first pyrolysis is:

[0010] From room temperature to 290-310℃ at a rate of 1-5℃ / min, and keep for 1.5-2.5h;

[0011] heated from 290-310℃ to 790-810℃ at a rate of 5-10℃ / min and kept for 0.5-1.5h;

[0012] heated from 790-810℃ to 1190-1210℃ at a rate of 2-5℃ / min and kept for 3.5-4.5h;

[0013] the process of the first pyrolysis after applying the polycarbosilane solution on the silicon carbide ceramic ultrafiltration body is repeated until the pore size of the pyrolysis material is less than or equal to 1nm;

[0014] the second pyrolysis comprises sequentially performing the first pyrolysis and recrystallization;

[0015] the process of the recrystallization is:

[0016] heated from 1190-1210℃ to 1590-1610℃ at a rate of 5-10℃ / min and kept for 1.5-2.5h;

[0017] heated from 1590-1610℃ to 2190-2210℃ at a rate of 3-5℃ / min and kept for 1-10h;

[0018] the polycarbosilane solution is applied by dip-coating method.

[0019] Preferably, the concentration of the polycarbosilane solution is 2-30wt%, and the solvent of the polycarbosilane solution comprises xylene.

[0020] Preferably, after the dip-coating, solidification is performed; the temperature of the solidification is 40℃, and the time is 1h; the speed of the dip-coating is 0.1-10mm / s.

[0021] Preferably, the preparation method of the silicon carbide ceramic ultrafiltration body comprises the following steps:

[0022] mixing silicon carbide, cellulose, dextran, vegetable oil, water and glycerol, and sequentially performing mud refining, extrusion, degumming and first sintering to obtain a support body;

[0023] applying a transition coating on the support body, and performing second sintering to obtain a microfiltration body with a support body-transition layer structure;

[0024] applying an ultrafiltration coating on the transition layer of the microfiltration body, and performing third sintering to obtain the silicon carbide ceramic ultrafiltration body.

[0025] Preferably, the silicon carbide, cellulose, dextran, vegetable oil, water and glycerol constitute a support body raw material; the mass percentage of each component in the support body raw material is 70% of silicon carbide, 6% of cellulose, 3% of dextran, 1% of vegetable oil, 19% of water and 1% of glycerol;

[0026] The time of the mud practice is 3-5h; the temperature of the degumming is 140-160℃, and the time is 8-12h.

[0027] Preferably, the process of the first sintering is:

[0028] from room temperature to 590-610℃ at 1-2℃ / min, and keep for 0.5-1.5h;

[0029] from 590-610℃ to 1590-1610℃ at 5-10℃ / min, and keep for 0.5-1.5h;

[0030] from 1590-1610℃ to 2190-2210℃ at 3-5℃ / min, and keep for 1.5-2.5h;

[0031] from 2190-2210℃ to 2440-2460℃ at 3-5℃ / min, and keep for 1-3h;

[0032] After the first sintering, it further includes cooling to room temperature, and the cooling rate is 2-5℃ / min.

[0033] Preferably, the transition coating includes the following components with mass percentage:

[0034] silicon carbide powder 60%, vegetable oil 10%, water 25% and glycerol 5%; the particle size of the silicon carbide powder is 7μm;

[0035] The process of the second sintering is:

[0036] from room temperature to 590-610℃ at 1-2℃ / min, and keep for 0.5-1.5h;

[0037] from 590-610℃ to 1590-1610℃ at 5-10℃ / min, and keep for 0.5-1.5h;

[0038] from 1590-1610℃ to 2190-2210℃ at 3-5℃ / min, and keep for 1-3h;

[0039] After the second sintering, it further includes cooling to room temperature, and the cooling rate is 2-5℃ / min.

[0040] Preferably, the ultrafiltration coating includes the following components with mass percentage:

[0041] silicon carbide powder 60%, vegetable oil 10%, water 25% and glycerol 5%; the particle size of the silicon carbide powder is 0.7μm;

[0042] The process of the third sintering is:

[0043] Rising from room temperature to 590-610 DEG C at 1-2 DEG C / min, and holding for 0.5-1.5 h;

[0044] Rising from 590-610 DEG C to 1590-1610 DEG C at 5-10 DEG C / min, and holding for 0.5-1.5 h;

[0045] Rising from 1590-1610 DEG C to 2190-2210 DEG C at 3-5 DEG C / min, and holding for 0.5-1.5 h;

[0046] After the third sintering, the method further comprises cooling to room temperature, and the cooling rate is 2-5 DEG C / min.

[0047] The application further provides the recrystallized silicon carbide ceramic nanofiltration membrane prepared by the preparation method.

[0048] The application further provides the application of the recrystallized silicon carbide ceramic nanofiltration membrane in nanofiltration.

[0049] The application provides a preparation method of a recrystallized silicon carbide ceramic nanofiltration membrane.

[0050] The preparation method has the following advantages:

[0051] 1. Compared with the existing recrystallized silicon carbide ceramic membrane, the polycarbosilane solution is applied to the silicon carbide ceramic ultrafiltration body by the dip-coating method in the application, and then the first pyrolysis and the second pyrolysis are performed, so that the silicon carbide membrane layer has better immersion and is more closely combined.

[0052] 2. Compared with the existing recrystallized silicon carbide ceramic membrane with a filtration precision of greater than or equal to 0.05 microns, the silicon carbide ceramic ultrafiltration body in the application fills the pores by sequentially performing the first pyrolysis and the second pyrolysis after the polycarbosilane solution is applied, so that the pore size is increased to less than 10 nm, and nanofiltration is achieved.

[0053] 3. After the polycarbosilane solution is applied, the first pyrolysis and the second pyrolysis are sequentially performed in the application, the neck connection is realized by using the atomic diffusion of the surface of the silicon carbide particles, and recrystallization is realized, that is, a completely recrystallized silicon carbide ceramic nanofiltration membrane is prepared.

[0054] The application further provides the recrystallized silicon carbide ceramic nanofiltration membrane prepared by the preparation method, and the recrystallized silicon carbide ceramic nanofiltration membrane has the following advantages:

[0055] 1. High flux: the unique multi-layer pore size structure (the pore size of the recrystallized silicon carbide layer is less than 10 nm, the pore size of the ultrafiltration layer is 0.05-0.2 microns, the pore size of the transition layer is 0.5-1 micron, and the pore size of the support body is 5-10 microns) and high hydrophilicity (water contact angle 0.3°) significantly reduce the filtration resistance.

[0056] 2. Corrosion resistance / high temperature: can resist strong acid and strong base corrosion and high temperature environment (long-term use temperature > 1000℃), suitable for harsh working conditions in chemical industry, metallurgy and other fields.

[0057] 3. High mechanical strength: excellent thermal shock resistance and mechanical strength, suitable for high pressure filtration scenarios. BRIEF DESCRIPTION OF DRAWINGS

[0058] Figure 1 A preparation flowchart of the recrystallized silicon carbide ceramic nanofiltration membrane provided by the present application is provided.

[0059] Figure 2 A scanning electron microscope picture (x2000) of the nanofiltration membrane obtained in Example 1 is provided.

[0060] Figure 3 A scanning electron microscope picture (x2000) of the nanofiltration membrane obtained in Example 2 is provided.

[0061] Figure 4 A scanning electron microscope picture (x2000) of the nanofiltration membrane obtained in Example 3 is provided.

[0062] Figure 5 A scanning electron microscope picture (x2000) of the nanofiltration membrane obtained in Example 4 is provided.

[0063] Figure 6 A scanning electron microscope picture (x2000) of the nanofiltration membrane obtained in Example 5 is provided. DETAILED DESCRIPTION

[0064] Figure 1 A preparation flowchart of the recrystallized silicon carbide ceramic nanofiltration membrane provided by the present application is provided, and the following will be described in detail. Figure 1 The preparation method provided by the present application will be described in detail.

[0065] The present application provides a preparation method of a recrystallized silicon carbide ceramic nanofiltration membrane, comprising the following steps:

[0066] After applying a polycarbosilane solution on the silicon carbide ceramic ultrafiltration body, a first pyrolysis is performed to obtain a pyrolysis material;

[0067] After applying a polycarbosilane solution on the pyrolysis material, a second pyrolysis is performed to obtain the recrystallized silicon carbide ceramic nanofiltration membrane.

[0068] Unless otherwise specified, the raw materials used in the present application are preferably commercially available products.

[0069] In the present application, the silicon carbide ceramic ultrafiltration body comprises a support body, a transition layer attached to the support body, and an ultrafiltration layer attached to the transition layer.

[0070] In the present application, the preparation method of the silicon carbide ceramic ultrafiltration body preferably comprises the following steps:

[0071] The silicon carbide, cellulose, dextran, vegetable oil, water and glycerol are mixed, and the mud is practiced, extruded, degreased and first sintered in sequence to obtain a support body;

[0072] The transition coating is applied on the support body, and the second sintering is performed to obtain a microfiltration body with a support body-transition layer structure;

[0073] The ultrafiltration coating is applied on the transition layer of the microfiltration body, and the third sintering is performed to obtain the silicon carbide ceramic ultrafiltration body.

[0074] In the present application, the silicon carbide, cellulose, dextran, vegetable oil, water and glycerol are mixed, and the mud is practiced, extruded, degreased and first sintered in sequence to obtain a support body.

[0075] In the present application, the purity of the silicon carbide is preferably 99.8%. In the present application, the silicon carbide is the main raw material for constructing the main body of the over-recrystallized silicon carbide ceramic nanofiltration membrane, improving the membrane body strength and the membrane body throughput. In the present application, the cellulose functions to form a binding force to ensure that the membrane body will not be loose. In the present application, the dextran functions as an adhesive to bond the silicon carbide powder together and fill the gaps between the silicon carbide powder. In the present application, the vegetable oil preferably includes one or more of soybean oil, corn oil and rice oil, and is further preferably rice oil, which is used for mixing the silicon carbide powder. In the present application, the water is preferably pure water. In the present application, the water is used for mixing the silicon carbide powder. In the present application, the purity of the glycerol is preferably 98%, which functions as an adhesive to bond the silicon carbide powder together and fill the gaps between the silicon carbide powder.

[0076] In the present application, the silicon carbide, cellulose, dextran, vegetable oil, water and glycerol constitute the support body raw material; the mass percentage of each component in the support body raw material is preferably: 70% of silicon carbide, 6% of cellulose, 3% of dextran, 2% of vegetable oil, 19% of water and 1% of glycerol.

[0077] In the present application, the time of the mud practicing is preferably 3-5h, and is further preferably 4h; the temperature of the mud practicing is preferably room temperature, i.e. neither additional heating nor additional cooling is needed.

[0078] In the present application, the shape of the extrusion is not specifically limited, and can be set according to the actual situation.

[0079] In the present application, the temperature of the degreasing is preferably 140-160℃, and is further preferably 150℃; the time is preferably 8-12h, and is further preferably 10h. In the present application, the temperature of the degreasing is preferably 140-160℃, and is further preferably 150℃; the time is preferably 8-12h, and is further preferably 10h.

[0080] In the present application, the first sintering process is preferably:

[0081] from room temperature to 590-610℃ at a rate of 1-2℃ / min, and holding for 0.5-1.5h;

[0082] from 590-610℃ to 1590-1610℃ at a rate of 5-10℃ / min, and holding for 0.5-1.5h;

[0083] from 1590-1610℃ to 2190-2210℃ at a rate of 3-5℃ / min, and holding for 1.5-2.5h;

[0084] from 2190-2210℃ to 2440-2460℃ at a rate of 3-5℃ / min, and holding for 1-3h;

[0085] The first sintering process is further preferably:

[0086] from room temperature to 600℃ at a rate of 1-2℃ / min, and holding for 1h;

[0087] from 600℃ to 1600℃ at a rate of 5-10℃ / min, and holding for 1h;

[0088] from 1600℃ to 2200℃ at a rate of 3-5℃ / min, and holding for 2h;

[0089] from 2200℃ to 2450℃ at a rate of 3-5℃ / min, and holding for 1h.

[0090] In the present application, from room temperature to 590-610℃ at a rate of 1-2℃ / min, and holding for 0.5-1.5h; this process can remove the binder (dextran and glycerol) and solvent; the first heating rate is preferably controlled at 1-2℃ / min to prevent the film layer from cracking.

[0091] In the present application, from 590-610℃ to 1590-1610℃ at a rate of 5-10℃ / min, and holding for 0.5-1.5h; this process can activate the surface of the particles.

[0092] In the present application, from 1590-1610℃ to 2190-2210℃ at a rate of 3-5℃ / min, and holding for 1.5-2.5h; in this process, SiC surface evaporates and condenses, neck formation occurs; and oxidation can be prevented.

[0093] In the present application, from 2190-2210℃ to 2440-2460℃ at a rate of 3-5℃ / min, and holding for 1-3h; this process can achieve densification, and promote grain growth, so that the grain size is in an appropriate size, and the strength is improved.

[0094] After the first sintering, the application preferably further comprises cooling to room temperature, and the cooling rate is preferably 2-5℃ / min. In the application, the process can prevent thermal stress cracks.

[0095] In the application, the first sintering is preferably performed under vacuum or a protective atmosphere, and the protective atmosphere is preferably argon.

[0096] In the application, the pore size of the support is preferably 5-10μm.

[0097] In the application, after the support raw material is refined, extruded, degummed and first sintered, it is all converted into recrystallized silicon carbide.

[0098] After the support is obtained, the application applies a transition coating on the support, and performs second sintering to obtain a microfiltration body with a support-transition layer structure.

[0099] In the application, the transition coating preferably comprises the following components by mass percentage:

[0100] Silicon carbide powder 60%, vegetable oil 10%, water 25% and glycerol 5%. In the application, the particle size of the silicon carbide powder is preferably 7μm.

[0101] In the application, the process of the second sintering is preferably as follows:

[0102] Raising the temperature from room temperature to 590-610℃ at a rate of 1-2℃ / min and maintaining for 0.5-1.5h;

[0103] Raising the temperature from 590-610℃ to 1590-1610℃ at a rate of 5-10℃ / min and maintaining for 0.5-1.5h;

[0104] Raising the temperature from 1590-1610℃ to 2190-2210℃ at a rate of 3-5℃ / min and maintaining for 1-3h;

[0105] The process of the second sintering is further preferably as follows:

[0106] Raising the temperature from room temperature to 600℃ at a rate of 1-2℃ / min and maintaining for 1h;

[0107] Raising the temperature from 600℃ to 1600℃ at a rate of 5-10℃ / min and maintaining for 1h;

[0108] Raising the temperature from 1600℃ to 2200℃ at a rate of 3-5℃ / min and maintaining for 1-3h.

[0109] In the application, raising the temperature from room temperature to 590-610℃ at a rate of 1-2℃ / min and maintaining for 0.5-1.5h can remove the binder / solvent and prevent film layer cracking.

[0110] In the present application, the process of heating from 590-610℃ to 1590-1610℃ at a rate of 5-10℃ / min for 0.5-1.5h can activate the surface of the particles.

[0111] In the present application, the process of heating from 1590-1610℃ to 2190-2210℃ at a rate of 3-5℃ / min for 1-3h can promote the growth of the crystal grains and form a densified film layer.

[0112] After the second sintering, the present application preferably further comprises cooling to room temperature, and the cooling rate is preferably 2-5℃ / min. In the present application, the process can prevent thermal stress cracks.

[0113] In the present application, the second sintering is preferably performed in vacuum or a protective atmosphere, and the protective atmosphere is preferably argon.

[0114] In the present application, the pore size of the microfiltration body is preferably 0.5-1μm.

[0115] After obtaining the microfiltration body with a support-transition layer structure, the present application applies an ultrafiltration coating to the transition layer of the microfiltration body, performs a third sintering, and obtains the silicon carbide ceramic ultrafiltration body.

[0116] In the present application, the ultrafiltration coating preferably comprises the following components in mass percentage: 60% of silicon carbide powder, 10% of vegetable oil, 25% of water, and 5% of glycerol. In the present application, the particle size of the silicon carbide powder is preferably 0.7μm.

[0117] In the present application, the process of the third sintering is preferably as follows:

[0118] heating from room temperature to 590-610℃ at a rate of 1-2℃ / min for 0.5-1.5h;

[0119] heating from 590-610℃ to 1590-1610℃ at a rate of 5-10℃ / min for 0.5-1.5h;

[0120] heating from 1590-1610℃ to 2190-2210℃ at a rate of 3-5℃ / min for 0.5-1.5h;

[0121] The process of the third sintering is further preferably as follows:

[0122] heating from room temperature to 600℃ at a rate of 1-2℃ / min for 1h;

[0123] heating from 600℃ to 1600℃ at a rate of 5-10℃ / min for 1h;

[0124] heating from 1600℃ to 2200℃ at a rate of 3-5℃ / min for 0.5-1.5h.

[0125] In the present application, the temperature is raised from room temperature to 590-610℃ at a rate of 1-2℃ / min and kept for 0.5-1.5h, which can remove the binder / solvent and prevent the film layer from cracking.

[0126] In the present application, the temperature is raised from 590-610℃ to 1590-1610℃ at a rate of 5-10℃ / min and kept for 0.5-1.5h, which can activate the surface of the particles.

[0127] In the present application, the temperature is raised from 1590-1610℃ to 2190-2210℃ at a rate of 3-5℃ / min and kept for 0.5-1.5h, which can promote the growth of the crystal grains and form a densified film layer.

[0128] After the third sintering, the present application further comprises cooling to room temperature, and the cooling rate is preferably 2-5℃ / min.

[0129] In the present application, the third sintering is preferably carried out in vacuum or a protective atmosphere, and the protective atmosphere is preferably argon.

[0130] In the present application, the pore size of the silicon carbide ceramic ultrafilter is preferably 0.05-0.2μm.

[0131] After obtaining the silicon carbide ceramic ultrafilter, the present application applies a polycarbosilane solution on the silicon carbide ceramic ultrafilter and then carries out first pyrolysis to obtain a pyrolyzed material.

[0132] In the present application, the concentration of the polycarbosilane solution is 2-30wt%, and is particularly preferably 5wt%, 10wt%, 15wt%, 20wt%, 25wt% or 30wt%. In the present application, the solvent of the polycarbosilane solution preferably comprises xylene. In the present application, the preparation of the polycarbosilane solution is preferably carried out in an argon atmosphere, and the oxygen content of the argon atmosphere is preferably <1ppm, and the water content is preferably <1ppm.

[0133] In the present application, the polycarbosilane solution is applied by dip coating, and after the dip coating, solidification is preferably carried out; the temperature of the solidification is preferably 40℃, and the time is preferably 1h; the speed of the dip coating is preferably 0.1-10mm / s.

[0134] In the present application, the first pyrolysis is carried out by:

[0135] raising the temperature from room temperature to 290-310℃ at a rate of 1-5℃ / min and keeping for 1.5-2.5h;

[0136] raising the temperature from 290-310℃ to 790-810℃ at a rate of 5-10℃ / min and keeping for 0.5-1.5h;

[0137] heating from 790~810℃ to 1190~1210℃ at a rate of 2~5℃ / min, and holding for 3.5~4.5h;

[0138] The first pyrolysis process is preferably:

[0139] heating from room temperature to 300℃ at a rate of 1~5℃ / min, and holding for 2h;

[0140] heating from 300℃ to 800℃ at a rate of 5~10℃ / min, and holding for 1h;

[0141] heating from 800℃ to 1200℃ at a rate of 2~5℃ / min, and holding for 4h.

[0142] In the present application, heating from room temperature to 290~310℃ at a rate of 1~5℃ / min, and holding for 1.5~2.5h, which can volatilize the solvent and promote further cross-linking.

[0143] In the present application, heating from 290~310℃ to 790~810℃ at a rate of 5~10℃ / min, and holding for 0.5~1.5h, which can pyrolyze the PCS to generate amorphous SiC (α-SiC) and a small amount of free carbon.

[0144] In the present application, heating from 790~810℃ to 1190~1210℃ at a rate of 2~5℃ / min, and holding for 3.5~4.5h, which can preliminarily crystallize the β-SiC to generate α-SiC nanocrystals.

[0145] In the present application, the first pyrolysis is preferably carried out in a protective atmosphere, which is preferably argon, and the oxygen content in the argon is preferably <1ppm, and the water content is preferably <1ppm.

[0146] After the first pyrolysis, the present application preferably further comprises cooling to room temperature in the furnace.

[0147] In the present application, the process of applying a PCS solution on the silicon carbide ceramic ultrafiltration body and then performing the first pyrolysis is repeated until the pore size of the pyrolyzed material is less than or equal to 1nm.

[0148] In the present application, the pore size of the pyrolyzed material is less than or equal to 1nm.

[0149] The present application can improve the ceramic yield and maintain the integrity of the membrane body by reasonably controlling the heating rate of the first pyrolysis.

[0150] After obtaining the pyrolyzed material, the present application applies a PCS solution on the pyrolyzed material and then performs the second pyrolysis to obtain the recrystallized silicon carbide ceramic nanofiltration membrane.

[0151] In the present application, the concentration and application method of the polycarbosilane solution are preferably consistent with the above technical solution, and will not be repeated here.

[0152] In the present application, the second pyrolysis comprises sequentially performing first pyrolysis and recrystallization;

[0153] The process of the recrystallization is:

[0154] heating from 1200℃ to 1600℃ at a rate of 5-10℃ / min and holding for 2h;

[0155] heating from 1600℃ to 2200℃ at a rate of 3-5℃ / min and holding for 1-10h.

[0156] The process of the recrystallization is preferably:

[0157] heating from 1200℃ to 1600℃ at a rate of 5-10℃ / min and holding for 2h;

[0158] heating from 1600℃ to 2200℃ at a rate of 3-5℃ / min and holding for 1-10h.

[0159] In the present application, the process of the second pyrolysis is specifically:

[0160] heating from room temperature to 290-310℃ at a rate of 1-5℃ / min and holding for 1.5-2.5h;

[0161] heating from 290-310℃ to 790-810℃ at a rate of 5-10℃ / min and holding for 0.5-1.5h;

[0162] heating from 790-810℃ to 1190-1210℃ at a rate of 2-5℃ / min and holding for 3.5-4.5h;

[0163] heating from 1190-1210℃ to 1590-1610℃ at a rate of 5-10℃ / min and holding for 1.5-2.5h;

[0164] heating from 1590-1610℃ to 2190-2210℃ at a rate of 3-5℃ / min and holding for 1-10h;

[0165] The process of the second pyrolysis is specifically preferably:

[0166] heating from room temperature to 300℃ at a rate of 1-5℃ / min and holding for 2h;

[0167] heating from 300℃ to 800℃ at a rate of 5-10℃ / min and holding for 1h;

[0168] heating from 800℃ to 1200℃ at a rate of 2-5℃ / min and holding for 4h;

[0169] The temperature was increased from 1200℃ to 1600℃ at a rate of 5~10℃ / min and held for 2 hours.

[0170] The temperature is increased from 1600℃ to 2200℃ at a rate of 3~5℃ / min and held for 1~10 hours.

[0171] After the second pyrolysis, the present invention preferably further includes furnace cooling to room temperature.

[0172] In this invention, the second pyrolysis is preferably carried out under a vacuum or a protective atmosphere, preferably argon.

[0173] 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.

[0174] 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.

[0175] In this invention, the recrystallized silicon carbide ceramic nanofiltration membrane can be used as a nanofiltration membrane.

[0176] The present invention also provides the application of the recrystallized silicon carbide ceramic nanofiltration membrane in nanofiltration.

[0177] 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.

[0178] 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.

[0179] 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+ .

[0180] In this invention, the recrystallized silicon carbide ceramic nanofiltration membrane is used for seawater desalination, wherein the seawater is preferably low in salinity.

[0181] The recrystallized silicon carbide ceramic nanofiltration membrane provided by the present application, the preparation method and application thereof will be described in detail below in combination with examples, but they cannot be understood as limiting the protection scope of the present application.

[0182] Example 1

[0183] The preparation of the recrystallized silicon carbide ceramic nanofiltration membrane includes the following steps:

[0184] Step 1, preparation of the support: the raw materials are mixed according to the following mass percentage: silicon carbide 70%, cellulose 6%, dextran 3%, vegetable oil (specific type: rice oil) 1%, water 19% and glycerol 1%, and then the following steps are performed in sequence: mud refining (room temperature, 4h), extrusion, degumming (150℃, 10h) and first sintering, and then the temperature is lowered to room temperature at a cooling rate of 2-5℃ / min, to obtain the support, and the filtration pore size of the obtained support is 10μm.

[0185] The process of the first sintering is as follows:

[0186] heated from room temperature to 600℃ at a rate of 1-2℃ / min and kept for 1h;

[0187] heated from 600℃ to 1600℃ at a rate of 5-10℃ / min and kept for 1h;

[0188] heated from 1600℃ to 2200℃ at a rate of 3-5℃ / min and kept for 2h;

[0189] heated from 2200℃ to 2450℃ at a rate of 3-5℃ / min and kept for 3h;

[0190] The first sintering is performed in argon.

[0191] Step 2, preparation of the microfiltration body with support / transition layer structure

[0192] The silicon carbide powder (particle size 7μm), vegetable oil, water and glycerol are mixed according to the mass ratio of 60:10:25:5 to obtain the transition coating.

[0193] The transition coating is coated on the support, and the second sintering is performed to obtain the transition membrane with a pore size of 1μm.

[0194] The process of the second sintering is as follows:

[0195] heated from room temperature to 600℃ at a rate of 1-2℃ / min and kept for 1h;

[0196] heated from 600℃ to 1600℃ at a rate of 5-10℃ / min and kept for 1h;

[0197] heated from 1600℃ to 2200℃ at a rate of 3-5℃ / min and kept for 2h;

[0198] cooling at a rate of 2~5℃ / min from 2200℃ to room temperature;

[0199] The second sintering is performed in argon.

[0200] Step 3, preparation of silicon carbide ceramic ultrafiltration body with support-transition layer-ultrafiltration layer

[0201] The silicon carbide powder (particle size 0.7μm), vegetable oil, water and glycerol are mixed in a mass ratio of 60:10:25:5 to obtain an ultrafiltration coating.

[0202] The ultrafiltration coating is coated on the transition layer, and the third sintering is performed to obtain a silicon carbide ceramic ultrafiltration body with a pore size of 0.05μm.

[0203] The third sintering process is as follows:

[0204] heating at a rate of 1~2℃ / min from room temperature to 600℃ for 1h;

[0205] heating at a rate of 5~10℃ / min from 600℃ to 1600℃ for 1h;

[0206] heating at a rate of 3~5℃ / min from 1600℃ to 2200℃ for 1h;

[0207] cooling at a rate of 2~5℃ / min from 2200℃ to room temperature;

[0208] The third sintering is performed in argon.

[0209] Step 4, polycarbosilane is dissolved in xylene to form a polycarbosilane solution (concentration 5wt%) under the protection of clean argon (oxygen <1ppm, water <1ppm).

[0210] The polycarbosilane solution is coated on the silicon carbide ceramic ultrafiltration body by dip-coating at a speed of 10mm / s, and after coating, it is cured at 40℃ for 1h, and then the first pyrolysis is performed.

[0211] The first pyrolysis process is as follows:

[0212] heating at a rate of 1~5℃ / min from room temperature to 300℃ for 2h;

[0213] heating at a rate of 5~10℃ / min from 300℃ to 800℃ for 1h;

[0214] heating at a rate of 2~5℃ / min from 800℃ to 1200℃ for 4h;

[0215] cooling in the furnace from 1200℃ to room temperature;

[0216] The first pyrolysis is performed in argon.

[0217] Step 4 was repeated 2 times to obtain the pyrolyzed material.

[0218] Step 5, second pyrolysis

[0219] The polycarbosilane solution was coated on the pyrolyzed material by dip-coating method at a speed of 10 mm / s, and after coating, it was cured at 40℃ for 1 h, and then the second pyrolysis was performed.

[0220] Ramp from room temperature to 300℃ at 1-5℃ / min and keep for 2 h;

[0221] Ramp from 300℃ to 800℃ at 5-10℃ / min and keep for 1 h;

[0222] Ramp from 800℃ to 1200℃ at 2-5℃ / min and keep for 4 h;

[0223] Ramp from 1200℃ to 1600℃ at 5-10℃ / min and keep for 2 h;

[0224] Ramp from 1600℃ to 2200℃ at 3-5℃ / min and keep for 2 h; cool down to room temperature in the furnace;

[0225] The atmosphere of the second pyrolysis was argon.

[0226] Example 2

[0227] The difference from Example 1 is that the concentration of the polycarbosilane solution in Step 4 is 10 wt%, and the others are the same as Example 1.

[0228] Example 3

[0229] The difference from Example 1 is that the concentration of the polycarbosilane solution in Step 4 is 20 wt%, and the others are the same as Example 1.

[0230] Example 4

[0231] The difference from Example 2 is that the number of times of repeating Step 4 in Step 4 is 5 times, and the others are the same as Example 1.

[0232] Example 5

[0233] The difference from Example 3 is that the number of times of repeating Step 4 in Step 4 is 5 times, and the others are the same as Example 1.

[0234] Performance test

[0235] (1) Flux and pore size

[0236] The pure water flux of the obtained 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, and the results are shown in Table 1.

[0237] Pure water flux and pore size of the recrystallized silicon carbide ceramic nanofiltration membrane obtained in Table 1 (transmembrane pressure: 0.1 MPa)

[0238]

[0239] (2) Abrasion resistance test

[0240] The test is based on ASTM G65 (dry sand rubber wheel method) and ASTM G133 (reciprocating sliding wear) standards, with a load of 50 N, and the abrasive is 120 mesh SiC sand (dry sand method) or Al2O3 ball (sliding method).

[0241] The comparative test data of the abrasion resistance of the recrystallized silicon carbide ceramic nanofiltration membrane obtained in Example 1 and the commercially available ordinary silicon carbide ceramic membrane at room temperature (25°C) with time are shown in Table 2.

[0242] Table 2 Abrasion resistance data

[0243]

[0244] As can be seen from Table 2, the recrystallized silicon carbide ceramic nanofiltration membrane obtained in the application exhibits advantages in long-term wear (anti-fatigue wear).

[0245] (3) Hydrofluoric acid corrosion resistance test

[0246] The comparative test data of the corrosion of the recrystallized silicon carbide ceramic nanofiltration membrane obtained in Example 1 and the commercially available ordinary silicon carbide ceramic membrane at room temperature (25°C) with time under the condition of 10% hydrofluoric acid (HF) are shown in Table 3 and Table 4.

[0247] Table 3 Hydrofluoric acid corrosion resistance results

[0248]

[0249] As can be seen from Table 3, the recrystallized silicon carbide ceramic nanofiltration membrane obtained has excellent hydrofluoric acid corrosion resistance.

[0250] Table 4 Comparison of corrosion rates of 10% HF and 20% HF

[0251]

[0252] As can be seen from Table 4, the recrystallized silicon carbide ceramic nanofiltration membrane has weak concentration effect due to the pure chemical corrosion mechanism.

[0253] (4) High temperature resistance test

[0254] The thermal properties were determined by laser flash method, and the results are shown in Table 5.

[0255] Table 5 Thermal properties

[0256]

[0257] (5) Thermal shock resistance test

[0258] The results are shown in Table 6.

[0259] Table 6 Comparison of thermal shock resistance performance

[0260]

[0261] (6) Mechanical property test

[0262] The flexural strength of the material was tested by ASTM C1161, and the result was that the flexural strength of the recrystallized silicon carbide ceramic nanofiltration membrane obtained in Example 1 was 105±10 MPa.

[0263] Figures 2-6 The scanning electron microscope pictures (×2000) of the nanofiltration membranes obtained in Examples 1-6 are shown in order; from Figures 2-6 It can be seen that the nanofiltration membranes obtained in Examples 1-5 are more and more dense.

[0264] The above only describes the preferred embodiments of the present application, and it should be noted that for those skilled in the art, without departing from the principles of the present application, a number of improvements and refinements can be made, and these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. A method for preparing a recrystallized silicon carbide ceramic nanofiltration membrane, characterized by, The method comprises the following steps: a first pyrolysis is performed after a polycarbosilane solution is applied on a silicon carbide ceramic ultrafiltration body to obtain a pyrolysis material; a second pyrolysis is performed after a polycarbosilane solution is applied on the pyrolysis material to obtain the recrystallized silicon carbide ceramic nanofiltration membrane; the first pyrolysis comprises the following steps: the temperature is increased from room temperature to 290-310℃ at a rate of 1-5℃ / min and is kept for 1.5-2.5h; the temperature is increased from 290-310℃ to 790-810℃ at a rate of 5-10℃ / min and is kept for 0.5-1.5h; the temperature is increased from 790-810℃ to 1190-1210℃ at a rate of 2-5℃ / min and is kept for 3.5-4.5h; the process of the first pyrolysis after a polycarbosilane solution is applied on a silicon carbide ceramic ultrafiltration body is repeated until the pore size of the pyrolysis material is less than or equal to 1nm; the second pyrolysis comprises a first pyrolysis and a recrystallization performed in sequence; the recrystallization comprises the following steps: the temperature is increased from 1190-1210℃ to 1590-1610℃ at a rate of 5-10℃ / min and is kept for 1.5-2.5h; the temperature is increased from 1590-1610℃ to 2190-2210℃ at a rate of 3-5℃ / min and is kept for 1-10h; the polycarbosilane solution is applied by a dip-coating method.

2. The production method according to claim 1, characterized by, The concentration of the polycarbosilane solution is 2-30wt%, and the solvent of the polycarbosilane solution comprises dimethylbenzene.

3. The production method according to claim 1 or 2, characterized by, After the dip-coating, solidification is performed; the temperature of the solidification is 40℃, and the time of the solidification is 1h; the speed of the dip-coating is 0.1-10mm / s.

4. The production method according to claim 1, characterized by, The preparation method of the silicon carbide ceramic ultrafiltration body comprises the following steps: a support body is obtained by mixing silicon carbide, cellulose, dextran, vegetable oil, water and glycerol, and sequentially performing mud refining, extrusion, degumming and first sintering; a transition coating is applied on the support body, and second sintering is performed to obtain a microfiltration body with a support body-transition layer structure; an ultrafiltration coating is applied on the transition layer of the microfiltration body, and third sintering is performed to obtain the silicon carbide ceramic ultrafiltration body.

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

6. The preparation method according to claim 4, characterized in that, The first sintering comprises the following steps: the temperature is increased from room temperature to 590-610℃ at a rate of 1-2℃ / min and is kept for 0.5-1.5h; the temperature is increased from 590-610℃ to 1590-1610℃ at a rate of 5-10℃ / min and is kept for 0.5-1.5h; the temperature is increased from 1590-1610℃ to 2190-2210℃ at a rate of 3-5℃ / min and is kept for 1.5-2.5h; the temperature is increased from 2190-2210℃ to 2440-2460℃ at a rate of 3-5℃ / min and is kept for 1-3h; After the first sintering, cooling to room temperature is further included, and 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 with the following mass percentages: Silicon carbide powder 60%, vegetable oil 10%, water 25% and glycerol 5%; the particle size of the silicon carbide powder is 7 μm; The process of the second sintering is: from room temperature to 590-610℃ at a rate of 1-2℃ / min, and then kept for 0.5-1.5h; from 590-610℃ to 1590-1610℃ at a rate of 5-10℃ / min, and then kept for 0.5-1.5h; from 1590-1610℃ to 2190-2210℃ at a rate of 3-5℃ / min, and then kept for 1-3h; After the second sintering, it further includes cooling to room temperature, and the cooling rate is 2-5℃ / min.

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

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

10. Use of the recrystallized silicon carbide ceramic nanofiltration membrane of claim 9 in nanofiltration.

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