Filtration and Membrane Filter

The filtration includes two methods: positive pressure and negative pressure filtration. The two kinds of methods can both make the solvent and the solute of smaller molecules pass through the filtration membrane with certain pore size, while the solute of larger molecules cannot pass through, so as to dehydrate, desalinate and concentrate the macromolecule materials, which will intercept the bacteria and parasites in order to achieve the purpose of sterilization, bacteria collection or increase the detection rate.

According to the size of separated substances, the membrane filtration technology is divided into microfiltration (MF), ultrafiltration (UF), reverse osmosis (RO) and nanofiltration (NF), etc.

Most of the filter membranes are made of high molecular materials, including cellulose ester, regenerated cellulose, polyamide, polyvinyl alcohol derivative, polyacrylonitrile, polypropylene, polyethylene, polyvinyl chloride, acrylonitrile/vinyl chloride copolymer, polycarbonate, polytetrafluoroethylene, polyvinylidene fluoride, etc.

The pore size of the membrane is expressed in μm, mainly including 0.025, 0.03, 0.05, 0.08, 0.1, 0.22, 0.3, 0.45, 0.6, 0.8, 1.0, 2.0, 3.0, 5.0, etc.

The main components of the membrane are including flat membrane, foldable membrane, tubular membrane, roll-type, and hollow fiber.

Cellulose Ester Materials is a standard membrane filter, characterized in good pore-forming performance, good hydrophobicity, easy availability of materials and low cost. And the pore size specification of the membrane is of a wide variety. The temperature range of the film is very wide. It is suitable for resistant to acid and base, but not suitable for ketone, ester, strong acid and alkali liquid filtration.

Fluorine-containing materials, such as PVDF and PTFE, provide excellent chemical stability and are suitable for use at high temperatures. In particular, PTFE film, its operating temperature is -40 to 260 degrees Celsius, can be resistant to strong acid, strong alkali and a variety of organic solvents. Because of its hydrophobicity, it can be used to filter steam and all kinds of corrosive liquids.

Polycarbonate and Polyester Materials are mainly used in the preparation of nuclear pore micro-porous membranes. The pore size of the nuclear pore membrane is very uniform, and the general thickness is 5 ≤ 15 um. Because the thin filtration speed is the same as that of the above membranes, but the fabrication process is more complex and the price of the film is higher.

According to its application, the filter membrane can be divided into hydrophilic and hydrophobic. The hydrophilic membrane filter, such as cellulose acetate membrane (CAM), is suitable for filtration of particles and bacteria in aqueous solution and protein electrophoresis. The hydrophobic membrane filter, such as polytetrafluoroethylene membrane (PTFE), is suitable for filtration of organic solvents, acids, and bases.

In the pharmaceutical industry of our country, the microfiltration, which means the pore diameter of the membrane is less than 0.22 μm, has been used to remove bacteria and pyrogen again. Ultrafiltration is also used to remove pyrogen in antibiotics. This method is a kind of pyrogen removal method certified by the Food and Drug Administration of the United States.

Its principle is to use the ultrafiltration membrane with the pore diameter smaller than the molecular weight of pyrogen to cut off the pyrogen and let the material pass through. This method has the advantages of simple equipment operation, non-polluting material, high yield, good quality, and low labor intensity，which can be widely used in the production of injection, raw materials, water for injection and other products.