China Powder Network News With the rapid development of industry, the ecological environment has also changed, and water pollution has become more and more serious. Under the call of General Secretary Xi Jinping that "lucid waters and lush mountains are invaluable assets", water governance has become a national plan for building an ecological civilization circle. Ceramic membrane technology plays an important role in modern water treatment because of its high efficiency and energy saving.
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Silicon carbide ceramic membrane is a new type of non-oxide inorganic membrane, which not only has the characteristics of high mechanical strength, concentrated pore size distribution, good thermal shock resistance, long service life, etc., but also has advantages in membrane flux, high temperature stability, and strong acid resistance. Strong alkali has outstanding advantages, and it is a beneficial attempt to use it in the treatment of heavy metal wastewater. Silicon carbide (SiC) ceramic membrane separation technology is considered to be one of the most rapidly developing membrane separation technologies in recent years.
Image source: Dijie Film official website
1 What is a silicon carbide ceramic membrane?
Silicon carbide ceramic membrane (SIC) is formed by recrystallization technology through high temperature sintering. Its separation layer, transition layer and porous support layer are all made of SiC material, and its filtration precision is mostly microfiltration and ultrafiltration. According to the different membrane structure, it is generally divided into tubular membrane and flat membrane. The tubular membrane is composed of a separation layer, a transition layer and a supporting layer, and the flat membrane is composed of a separation layer and a supporting layer.
The SIC membrane filtration separation system mostly adopts the form of "cross-flow filtration" to separate the liquid. The raw material liquid flows at high speed in the membrane tube, and the clear permeate containing small molecular components is driven by the pressure to pass through the dense layer of the membrane outward in a vertical direction to it. , the turbid concentrated liquid containing macromolecular components is intercepted, so as to achieve the purpose of clarifying, separating, concentrating and purifying the fluid.
2 Why choose silicon carbide ceramic membrane?
Silicon carbide ceramic membrane has the following advantages:
♦Good chemical stability, resistant to strong acid and alkali and all organic solvents;
♦Good thermal stability, thermal shock - stable operation under high temperature conditions;
♦ High open porosity and large flux;
♦Good hydrophilic and oleophobic properties - can efficiently separate oil and water;
♦The film has high bonding strength and good wear resistance.
Comparison table of the advantages and properties of SiC film and other films
3 Preparation method of silicon carbide ceramic film
The existing preparation technologies of silicon carbide ceramic film include: particle stacking method, carbothermal reduction method, polymer cracking method and chemical vapor deposition method.
3.1 Particle packing method
The particle stacking method is the solid-state particle sintering method. This method is derived from the preparation method of porous ceramics. It is a common method for preparing ceramic membranes. Small particles are doped into large particles. Connections are formed between particles, and the ideal situation is neck bonding between large particles, leaving a large number of through holes, while maintaining good mechanical properties.
Process flow chart of particle stacking method
3.2 Carbothermal reduction reaction sintering method
Carbothermal reduction reaction sintering mainly uses an appropriate amount of silicon source and carbon as raw materials to be uniformly mixed, uniformly coated on the support, and then carbothermic reduction reaction is carried out in an argon atmosphere or vacuum environmental protection.
Carbothermal reduction sintering process flow chart
The carbon source silicon source used in the preparation of silicon carbide ceramic film by carbothermic reduction reaction sintering is mostly organic, and the sol-gel method is often used to form the film. The rate is not high and difficult, so there are few specific applications.
The carbothermic reduction reaction has various sintering raw materials and low reaction temperature. 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 stacking method in the industrial production of silicon carbide ceramic films.
3.3 Polymer cracking method
The polymer cracking method uses a ceramic precursor to dissolve or melt and coat it on the support, and then undergo high temperature cracking to form inorganic ceramics. It is a relatively common preparation method of non-oxide inorganic ceramics abroad.
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 cost of raw materials is relatively high.
3.4 Chemical Vapor Deposition
The film layer obtained by chemical vapor deposition method has strong controllability, high density and small pore size, but its cost is high, the process is complicated, and the flux is slightly insufficient. At present, the silicon carbide ceramic film obtained by chemical vapor deposition method is mostly used for semiconductors. Industry and gas phase separation, applications in other directions have yet to be further developed.
4 Application of silicon carbide ceramic membrane separation technology
4.1 Separation of oil and water
SiC ceramic membrane separation technology is the most widely used in oil-water separation. The types of oily water involved include industrial processing cleaning oily sewage, ship bilge oily sewage, oily sewage in the petroleum industry and solid fuel thermal processing industry. Depending on the pore size of the SiC ceramic membrane (usually 0.01~10 μm), the types of oil pollution it treats can include slick oil, emulsified oil and even dissolved oil. The SiC ceramic membrane separation technology not only makes the overall separation system more compact, but also reduces the use of chemicals compared to current technologies used to treat oil and gas exploration wastewater.
4.2 Water purification
Because of its high structural stability and selectivity, SiC ceramic ultrafiltration membrane can also be used to purify water and separate suspended solids, bacteria and other impurities in water. Generally, the filtration precision of SiC ceramic membrane is microfiltration and ultrafiltration. In the water treatment process, it is generally configured as a secondary or even tertiary finishing process, which can effectively separate suspended solids, tiny solid particles, bacteria, etc. The research on SiC ceramic membrane separation technology in water purification still needs to be deepened, and the expandable application fields also need to be further explored.
4.3 Gas dust removal and purification
In recent years, the application research of SiC ceramic membrane in gas dust removal and purification has also emerged, and SiC ceramic membrane is expected to make great achievements in the field of gas separation.
5Conclusion
With the increasing emphasis on environmental protection at home and abroad, the support needs of countries for high-performance filtration and separation technology are becoming more and more urgent, creating an opportunity for the development and application of SiC ceramic membrane separation technology. In the future, it is still necessary to invest a lot of resources to solve the problems of immature membrane production and preparation technology and imperfect application research, so that SiC ceramic membrane separation technology can truly be applied and benefit the people.
Reference source:
[1] The official website of Hubei Dijie Membrane Technology Co., Ltd.
[2] Xu Zhengwei. Study on the treatment of heavy metal wastewater by silicon carbide ceramic membrane. Wuhan Engineering University. 2018.
【3】Yu Yanzi, et al. Research progress on the application of porous silicon carbide ceramic membrane separation technology. 2021.
(Edited by China Powder Network/Xingyao)
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