1. Classification of ceramic membrane
Ceramic membrane is a kind of inorganic porous membrane made of ceramic material as a medium with separation function. It is based on the principle of "sieving" and uses the pressure difference as the driving force to achieve the physical separation of liquid and solid.
(1) According to the difference of module form, it can be divided into:
1. Sheet type
2. Tube type
3. Multi-channel honeycomb type
(2) According to the size of the membrane pore size, it can be divided into:
Microfiltration membrane (MF: 0.5 ~ 10μm): It is suitable for the separation of gas-solid and liquid-solid phases. It can remove the colloidal solid particles in the micron or sub-micron range through the microfiltration membrane. , No medium falling off.
Ultrafiltration membrane (UF: 0.01 ~ 0.5μm): It can be used for the separation and purification of dairy products, biological products, fruit wine juice, etc. It is generally operated at room temperature, and the rapidly developing MBR membrane reactor is currently processing industrial wastewater Has been widely used.
Nanofiltration membrane (NF: 0.5 ~ 10nm): Because of the nanometer-sized membrane pore size, and the membrane surface is usually charged, it can be used for the separation of small molecules, divalent salts, free acids and other substances.
2. Application examples of ceramic membrane in chemical technology
(1) Treatment of industrial wastewater
Industrial wastewater generally has particularities such as acidity and alkalinity, and contains organic solvents. Traditional organic membranes are usually difficult to adapt to such harsh and complex conditions; and ceramic membranes can fully and stably operate in these extreme environments for a long time due to the advantages of their materials. For example, oily wastewater such as oilfield produced water, wastewater from petrochemical plants, metal surface cleaning wastewater, and emulsified wastewater. These oily wastewaters are difficult to handle by conventional methods. The hydrophilic and oleophobic properties of ceramic membranes are required to effectively remove oil from industrial wastewater. The removal rate of alumina ceramic membrane in the treatment of emulsified oil wastewater can reach more than 99%. If the two treatment processes of microfiltration and nanofiltration are added, the removal rate of oil can be increased to more than 99.5%, and the superiority is very significant.
After CNOOC Tianjin Chemical Research and Design Institute modified the surface of the porous ceramic membrane with super-hydrophilic and oleophobic properties, a functional ceramic ultrafiltration membrane with strong anti-pollution was formed. The surface tension can be used to form a dynamic water film on the membrane surface to reduce particulate contamination Plugging holes and surface oil pollution, while effectively preventing the growth of microorganisms on the membrane surface. This ceramic membrane is more resistant to pollution than ordinary ceramic membranes, and the chemical cleaning cycle is three times that of ordinary ones. It is expected to break through the current bottleneck of China's offshore low-permeability oilfield development technology.
In addition to oil-containing wastewater, paper pulp industry wastewater is the main source of COD (chemical oxygen demand) pollution. Compared with traditional treatment methods, the retention rate of COD and lignin by ceramic membrane ultrafiltration technology is 49.4% and respectively. 90%, can also realize the direct recovery and reuse of permeate.
(2) Separation and purification of carbon quantum dots
Carbon quantum dots (CQDs) are a new type of carbon nanomaterials with good optical properties, photoelectric conversion, high biological and compatibility, and low cytotoxicity. They are used in photoelectric equipment, ion detection, nanosensors, biological The fields of imaging and catalysts have broad application prospects. And ensuring that carbon quantum dots have a narrow size distribution is an important way to ensure their luminous purity.
The methods of carbon quantum dot purification are commonly used in dialysis, centrifugation, electrophoresis, chromatography, and filtration. However, there are cumbersome operations, low separation efficiency, and difficulty in achieving continuous operation, and ceramic membrane separation technology can solve these problems (currently Mainly this part of the application is mainly concentrated in ultrafiltration and microfiltration). After the ultra-fine and micro-filtration treatment of carbon quantum dot feed solution, large particles of impurities can be effectively trapped by the membrane, and carbon quantum dots and some small molecular impurities will pass through the membrane material together. However, after removing large particles of impurities, it is still necessary to remove small molecule impurities in the carbon quantum dot feed solution in combination with dialysis and other methods.
(3) Applied in the production process of cyclohexanone oxime
Caprolactam is an important raw material for synthetic fibers and engineering plastics. Cyclohexanone oxime is an intermediate for producing caprolactam, and up to 90% of caprolactam products are produced by rearrangement. At present, the processes for producing cyclohexanone oxime in industry all have shortcomings such as many intermediate steps, complicated processes, many by-products and three wastes. Therefore, it is of great significance to improve the existing processes. Among them, the new process of preparing cyclohexanone oxime from titanium silicon-1 molecular sieve (TS-1) catalyzed cyclohexanone ammoximation attracted the most attention from the industry. This process has the characteristics of mild reaction conditions, high selectivity, less by-products, low energy consumption and low pollution, and has entered the stage of industrial application. However, in the process of producing cyclohexanone oxime with titanium silicon-1 molecular sieve (TS-1) as a catalyst, the catalyst will be seriously lost due to the small particle size of the catalyst. The ceramic membrane filtration process is coupled with the cyclohexanone oxime reaction process, and the titanium silicon molecular sieve catalyst is retained through the ceramic membrane to form a new membrane catalysis integration new process, which can not only effectively solve the problem of catalyst recycling, but also shorten the process flow To improve the continuity of the process.
(4) Used for purification treatment of coal tar
Coal tar is an important liquid product obtained by coal during underflow and gasification. Some components contained in it are difficult to obtain from other raw materials, so coal tar occupies an important position in the field of chemical raw materials. However, the directly extracted coal tar contains a lot of toxic compounds, and the toxic gas generated when used directly as a crude fuel will cause serious pollution, so the pretreatment process is indispensable in the process of coal tar processing. Ceramic membrane ultrafiltration technology has the advantages of strong acid and alkali resistance, high mechanical strength, uniform pore size distribution, good temperature resistance, and long service life. The use of inorganic ceramic membranes in coal tar filtration can be good for coal tar. The impurities are separated. The removal rate of heavy metals, ash and moisture can reach 90%. It also has good removal effects on impurities such as salt and chlorine. The removal rate of salt reaches 83.59%, the removal rate of chlorine reaches 65.82% Can be greatly improved.