Silicon carbide ceramic membrane has the characteristics of high chemical stability, good thermal shock resistance, strong hydrophilicity, large membrane flux, high mechanical strength, concentrated pore size distribution, and good pore structure gradient. Compared with traditional membrane materials, silicon carbide ceramic membrane can effectively separate suspended particles and oil droplets in water during water treatment without being affected by the quality of water supply. It is also considered to be stable and durable because it can effectively reduce downtime and installation costs. A new type of separation membrane that is expected to replace various inorganic membranes.
Application advantages of silicon carbide ceramic membrane
With the increasingly stringent requirements of various governments on wastewater discharge and crude oil recovery, silicon carbide ceramic membranes have shown greater advantages in industrial applications. In recent years, commercial silicon carbide ceramic membranes represented by liqtech have begun to emerge in high-temperature gas-solid separation and industrial wastewater treatment.
Silicon carbide has excellent thermal conductivity, chemical inertness, fracture toughness and acid and alkali resistance. It has a large membrane flux and is very efficient for water treatment. Similarly, it has a very wide range of applications in high temperature environments, biomedicine, and food.
Silicon carbide ceramic membrane has obvious advantages in the application of oil-water separation, because compared with polymer membranes, although the hydrophilicity and pollution resistance of the membrane can be improved by blending modification, the flux of the membrane is still relatively low, and The flux will decrease more after washing. Silicon carbide ceramic membrane has the advantages of large membrane flux, strong cleanability, good separation effect and long service life.
Silicon carbide ceramic membrane not only has the advantages of high temperature and pressure resistance, chemical corrosion resistance, and high chemical stability of general inorganic membranes, but also has high mechanical strength, strong thermal shock resistance, high porosity, and large specific surface area. It can be used for high temperature dust removal And other fields.
Method for preparing silicon carbide ceramic membrane
Different from the more mature oxide ceramic membranes, silicon carbide ceramic membranes are slightly inferior in terms of membrane preparation due to the particularity of their materials. The existing preparation techniques include particle accumulation method, carbothermic reduction method, polymer cracking method and Chemical vapor deposition method, etc.
Particle packing method
The particle accumulation method is the solid particle sintering method. This method is derived from the preparation of porous ceramics. It is a common method for preparing ceramic membranes. Large particles are doped with small particles, and the small particles are easily sintered. The particles form a connection, and the ideal situation is the neck bonding between the large particles, leaving a large number of through holes, while maintaining good mechanical properties.
When using the particle accumulation method to make silicon carbide film, the slurry method is often used to generate the film layer by using the capillary effect. After preparing a stable suspension slurry, the slurry is contacted with the surface of the support, the medium flows into the support, and the raw materials are dispersed in the medium. It is concentrated and deposited on the surface of the support to form a particle layer, which is then dried and fired to form a finished product.
This method has simple procedures, low equipment requirements, is suitable for industrialized mass production, has good mechanical properties, but has relatively low porosity. Since the porosity and mechanical properties are inversely related, it is possible to choose between the two by adjusting the process parameters.
Carbothermic reduction reaction sintering method
Carbothermal reduction reaction sintering mainly uses a suitable amount of silicon source and carbon as raw materials to be uniformly mixed, uniformly coated on the support, and then the carbothermal reduction reaction is carried out in an argon atmosphere or vacuum environmental protection, using silicon dioxide as the silicon source For example, the main reactions are:
Carbothermal reduction reaction sintering to prepare silicon carbide ceramic membranes uses carbon sources and silicon sources that are mostly organic, and sol-gel method is often used to form the film. However, the sol-gel method for silicon carbide film has harsh film formation conditions and is prone to defects. Difficulties such as low rate, so there are few specific applications.
The carbothermic reduction reaction sintering materials are diverse and the reaction temperature is low. If it can solve the problems of harsh conditions and low yield in the film forming stage, it has the potential to compete with the particle accumulation method in the industrial production of silicon carbide ceramic films.
Polymer cracking
The polymer cracking method uses a ceramic precursor to dissolve or melt it and coat it on the support, and then undergo high-temperature cracking to form inorganic ceramics. It is a relatively common method for preparing non-oxide inorganic ceramics abroad.
Taking polycarbosilane as an example, when heated to 550℃~800℃ in an inert atmosphere, the Si-H bond and CH bond in its molecular structure are broken to produce a large amount of free hydrogen and generate hydrogen gas, and the part containing methyl group accepts free hydrogen. The methyl boundary produces CH4, and the remaining hydrogen atoms above 800°C continue to be converted into free hydrogen to decompose, begin to form Si-C bonds, and finally form β-SiC.
The silicon carbide film prepared by the polymer cracking method has the advantages of convenient film formation, controllable thickness, and simple process. Compared with the particle accumulation method, the heating temperature is lower (about 1000°C), but the raw material cost is relatively high.
At present, large-scale production of silicon carbide ceramic membranes for filtration uses the particle accumulation method and polymer cracking method. The finished products produced by the particle accumulation method are mostly microfiltration membranes. The application range is limited. Compared with other membrane materials, there is no decisive advantage. Further development.
The polymer pyrolysis method is relatively mature, the thickness is stable but difficult to control, and the pore size is small, and the film formation rate is good, and further improvement is needed. Although the carbothermic reduction method has a small film-forming pore size, the film-forming rate is not high and the effect needs to be improved.
In addition to the above methods, there are chemical vapor deposition methods that have strong controllability, high density, and small pore diameters. However, the cost is relatively high, the process is complicated, and the throughput is slightly insufficient. The prepared silicon carbide ceramic film is mostly used in the semiconductor industry and gas phase separation, and its application in other directions needs further development.