Composite membrane

The composite film is mainly composed of the above two kinds of materials, it is a very thin dense layer and porous support layer composite. Porous support layer, also known as the base film, from the enhanced mechanical strength of the role; dense layer, also known as the epidermis, from the role of desalination, it is also known as desalination layer. Desalination layer thickness is generally 50nm, the thinnest of 30nm.
An asymmetric membrane made of a single material has the following disadvantages:
1, there is a compacted transition layer between the dense layer and the support layer.
2, the skin layer thickness of the thinnest limit of 100nm, it is difficult to reduce the membrane thickness to reduce the push pressure.
3, desalination rate and permeable rate of mutual restraint, because the same kind of material is difficult to both desalination and support both excellent.
The composite film solves the above problems, and can select materials with high desalination property and high mechanical strength for the requirements of the dense layer and the support layer, respectively. So that the dense layer of the composite membrane can be made thin, which is good for reducing the dragging pressure. At the same time, the transition zone is eliminated, and the anti-compaction property is good.
Polysulfone is the most commonly used material for the base film, followed by polypropylene and polyacrylonitrile. Because the polysulfone cheap and easy to get a simple film, mechanical strength, good compression resistance, chemical stability, non-toxic, can be biodegradable.
In order to further enhance the strength of the porous support layer, a polyester nonwoven fabric is often used.
The material of the desalting layer is mainly aromatic polyamide. In addition, piperazine amide, propylene-alkyl polyamide and condensation of urea, furfuryl alcohol and three hydroxyethyl isocyanate, m-phenylenediamine and trimesoyl chloride and so on. (1) high desalination rate at high flow rates; (2) high mechanical strength and service life; (3) ability to function at lower operating pressures; (4) tolerance to chemical or biochemical effects ; (5) by the pH value, temperature and other factors less; (6) film source of raw materials easy, simple processing, low cost.
Reverse osmosis membrane structure, there are two kinds of asymmetric membrane and homogeneous membrane. Currently used membrane material mainly cellulose acetate and aromatic polyamides. Its components are hollow fiber type, roll type, frame type and tube type. Can be used for separation, concentration, purification and other chemical unit operation, mainly for pure water preparation and water treatment industry.