CRM Membrane for Silica Sol Production

Silica sol is a dispersion of nano-scale silica particles in water or solvent. Since the SiO2 in the silica sol contains a large amount of water and hydroxyl groups, the silica sol can also be expressed as mSiO2.nH2O. There are different ways to prepare silica sol. The most commonly used methods are ion exchange, silicon powder one-step hydrolysis, and silane hydrolysis.  The basic principle is to remove sodium ions that are easily soluble in water.Various silica sols having particle sizes of 10-60 nm can be prepared by these methods. From the different pH values ​​exhibited by colloidal silica, silica sol is divided into alkaline silica sol and acidic silica sol. They are all important fine chemical products with different important uses: for example, alkaline silica sol is used in precision casting, exterior wall coatings, etc.; acidic silica sol is used in color picture tubes, colloidal lead-acid batteries, and imported from abroad Application of electrostatic flocking technology, etc.

The concentration process  is the most important step in the production of colloidal silica. To produce high-concentration, low-viscosity, and stable silica sol products, to a large extent depends on the method of concentration. The concentration stage of silica sol production is a process link that consumes a lot of energy and has a long cycle. The traditional method of concentration generally adopts the distillation method to dehydrate, and evaporates the water under reduced pressure, so as to obtain the silica sol of the required concentration. Due to the phase change in the evaporation process, the energy consumption is relatively high.

Ultrafiltration membrane method is a more advanced method of concentrated preparation of silica sol. Ultrafiltration membranes are different from traditional dead-end filtration. The filter pore size of ultrafiltration membrane elements is generally smaller than the particle diameter of silica sol. During the cross-flow dynamic filtration process, only water and soluble salts are allowed to pass, and sol particles are not allowed to pass. Since the filtration process is carried out at room temperature and low pressure, there is no phase change, and the filtration efficiency is very high. While removing the water in the dilute sol, it can also remove a small amount of ions or soluble substances. Therefore, the ultrafiltration membrane concentration process has low energy consumption, short cycle, simple operation, and low equipment investment, which is an effective way to reduce product costs and improve the quality of silica sol products.

The silica sol concentration process can be divided into organic membrane and inorganic membrane according to the different ultrafiltration membrane materials used. The organic ultrafiltration membrane is made of polyphenol or polyethersulfone, with small pore size, which can trap sol particles well, and the equipment investment is small; however, due to the high temperature during the filtration process, it will be washed under high flow rate and a certain viscosity of the sol solution for a long time. , The membrane layer is easily damaged by impact and causes glue leakage. The membrane element needs to be replaced frequently during operation, which has high maintenance costs and poor reliability. CRM ceramic membrane ultrafiltration membrane is made of alumina sintered at a high temperature of 1700 degrees Celsius. The pore size is small, rejection of small particles is high, and it has excellent characteristics such as high temperature resistance and mechanical erosion resistance. It is very suitable for high temperature and high multiple concentration of silica sol solution. It has good reliability, easy maintenance and simple equipment. CRM ceramic ultrafiltration membranes have been successfully and widely used in the production process of silica sol in various countries.