The water to be filtered enters the ultrafiltration membrane tube, and under the action of the water pressure difference between the two sides of the membrane, the pores on the membrane surface are dense to 0.0 1, so that small molecular beneficial substances penetrate into the other end of the water outlet and become purified water. Unqualified substances or substances with large molecular weight that cannot pass through will remain on one side of the membrane. So as to achieve the purposes of solution purification, separation and concentration.
In fact, the principle of ultrafiltration membrane is not complicated. During ultrafiltration, the trapped impurities will stay on the membrane surface, resulting in concentration polarization. When the impurity concentration on the membrane surface reaches a certain level, a layer will be formed, which will make the water permeability of the membrane drop sharply and affect the application of ultrafiltration to a certain extent. Therefore, it is necessary to study and determine the best process and operating conditions to minimize the influence of concentration polarization and make ultrafiltration a reliable reverse osmosis pretreatment method.
Structure of ultrafiltration membrane:
The structure of ultrafiltration membrane can be divided into symmetrical type and asymmetrical type. The former is isotropic, has no cortex, and has the same pores in all directions, which belongs to deep filtration; The latter has a dense surface layer and a fingerlike bottom layer, the thickness of the surface layer is below 0. 1 micron, and there are ordered micropores, and the thickness of the bottom layer is 200 ~ 250 microns, which belongs to surface filtration. Ultrafiltration membranes used in industry are generally asymmetric membranes. The membrane materials of ultrafiltration membrane mainly include cellulose and its derivatives, polycarbonate, polyvinyl chloride, polyvinylidene fluoride, polysulfone, polyacrylonitrile, polyamide, polysulfone amide, sulfonated polysulfone, crosslinked polyvinyl alcohol, modified acrylic polymer and so on.
Ultrafiltration membranes can also be divided into plate-frame type, tube type, roll type and hollow fiber type.