Brief introduction of structure and principle of ultrafiltration membrane

In industrial application, there is a new type of chemical unit operation, which is used to separate large and small polymer colloids or suspended particles from the solution in the process of ultrafiltration. It is called ultrafiltration membrane. This is a kind of asymmetric membrane type with pressure as driving force and pore diameter of 1-100nm. Its density is about 10 / cm, and the operating pressure difference is 100-1000kpa. It is widely used to remove colloidal particles and macromolecules. It can separate the solution with concentration less than 10%.

Ultrafiltration membrane can be used in separation, concentration and purification of biological products, pharmaceutical products and food industry; at the same time, it can also be used in blood treatment, wastewater treatment and terminal treatment device in ultra pure water preparation. In addition, the successful application of ultrafiltration membrane in China lies in the concentration and purification of Chinese herbal medicine. With the progress of technology, the screening function of ultrafiltration membrane will be better improved and strengthened, and its contribution to social progress will be greater and greater.

The structure of ultrafiltration membrane can be divided into symmetry and asymmetry. The former is isotropic and has no cortex, and the pores in all directions are the same, which belongs to deep filtering; the latter has a denser surface layer and a bottom layer with finger like structure, the thickness of the surface layer is 0.1 μ m or less, and has well arranged micropores, and the thickness of the bottom layer is 200-250 μ m, which belongs to surface filtering. The industrial ultrafiltration membrane is generally asymmetric. Membrane materials of ultrafiltration membrane mainly include cellulose and its derivatives, polycarbonate, polyvinyl chloride, polyvinylidene fluoride, polysulfone, polyacrylonitrile, polyamide, polysulfonamide, sulfonated polysulfone, cross chain polyvinyl alcohol, modified acrylic polymer, etc.

In the process of ultrafiltration membrane screening, the pressure difference on both sides of the membrane is used as the driving force, and the ultrafiltration membrane is used as the filtering medium. Under a certain pressure, when the original solution flows through the membrane surface, many tiny pores on the surface of the ultrafiltration membrane only allow water and small molecular substances to pass through and become the permeate, while the substances in the original solution whose volume is larger than the micropores on the membrane surface are trapped on the inlet side of the membrane and become the concentrate. Therefore, the purpose of purification, separation and concentration of the original solution is realized. There are about 6 billion 0.01 micron micropores on the wall of each meter long ultrafiltration membrane. The pore diameter only allows water molecules, beneficial minerals and trace elements in the water to pass through, and the volume of bacteria is more than 0.02 micron. Therefore, bacteria, as well as colloids, rust, suspended solids, sediment, macromolecular organics, which are much larger than bacteria, can be trapped by ultrafiltration membrane, thus realizing purification process.