Ultrafiltration is an advanced membrane separation technology。Ultrafiltration membrane can effectively remove particles, colloids, bacteria, heat sources and organic matter in water, and is suitable for various production processes for the purpose of separation, concentration and purification。Ultrafiltration is one of the membrane separation technologies driven by pressure。For the purpose of separation of large and small molecules, the membrane pore size is between 20-1000A°。Hollow fiber ultrafilter (membrane) has the advantages of high filling density per unit of soluble, small footprint and so on。In the process of ultrafiltration, the water depth liquid flows through the membrane surface under pressure, and the deep agent (water) and small molecule solute permeable membrane smaller than the membrane hole become the purification liquid (filter liquid), and the solute and solute group larger than the membrane hole are trapped and discharged with the water flow to become the deep shrinkage liquid。
The ultrafiltration process is dynamic filtration, and the separation is completed in the flow state。The solute is only deposited on the membrane surface, the ultrafiltration rate attenuates to a certain extent and tends to equilibrium, and can be restored by cleaning。Ultrafiltration originated in 1748，Schmidt uses cotton film or celluloid to filter the solution，When a certain amount of pressure is applied，Solution (water) through the membrane，Proteins, colloids and other substances are trapped，Its filtration accuracy far exceeds that of filter paper，So he came up with the term ultrafiltration，1896年，Martin made the first artificial ultrafiltration membrane，It was in the 1960s，The concept of molecular scale is proposed，It was the beginning of modern ultrafiltration，The 1970s and 1980s were a period of rapid development，After the 1990s, it began to mature。China's research on this technology is late, in the 1970s is still in the research period, in the late 1980s, it entered the stage of industrial production and application。Ultrafiltration device like reverse osmosis device, there are plate, tube type (internal pressure tube type and external pressure tube bundle type), roll type, hollow fiber type and other forms。Concentration polarization is a natural phenomenon in membrane separation process. How to minimize this phenomenon is one of the important issues in ultrafiltration technology。
The current measures are:
(1) Increase the water flow velocity on the membrane surface to reduce the thickness of the boundary layer, and make the trapped solute taken away by the water in time;
② Take physical or chemical washing measures。
