Ultrafiltration (UF) is also a membrane separation process driven by pressure difference. Ultrafiltration is generally considered to be a sieve separation process. Driven by the pressure difference, the solvent and small solute particles in the raw material liquid pass through the membrane from the high-pressure feed liquid side to the low-pressure side. The resulting liquid is generally called filtrate or permeate, and the large particle group Separated by the membrane, it increases the concentration in the remaining filter liquid, and achieves the purposes of solution purification, separation and concentration. The water treatment center took the lead in successfully developing this technology in China in the 1980s.
Ultrafiltration membranes used cellulose acetate membrane materials in the early stage, and later used polysulfone, polyethersulfone, polyacrylonitrile, polyvinyl chloride, polyvinylidene fluoride, vinyl chloride alcohol and other inorganic membrane materials. The pore size of the membrane is about 0.002 to 0.1 μm, and the molecular weight cutoff is about 500 to 500,000. Its operating pressure is around 0.07-0.7MPa.
(1) There is no phase change in the process, and it can be carried out at normal temperature and low pressure, so the energy consumption is low;
(2) There is no qualitative change in the process of concentration and separation, which is suitable for the treatment of heat-sensitive materials;
(3) It can classify and separate substances with different molecular weights;
(4) No impurities fall off the ultrafiltration membrane during use, ensuring the purity of the ultrafiltrate.