According to the different pore size, filter membrane is mainly divided into reverse osmosis membrane, microfiltration membrane, nanofiltration membrane and ultrafiltration membrane. Membrane filtration technology in the environment, medicine, chemical, food and other fields have been widely used, the technology in the process of separation filtration processing conditions is mild, easy to realize mechanization, automatic operation, is a relatively green, energy saving technology. At present, the common membrane filtration methods include microfiltration, ultrafiltration, nanofiltration, reverse osmosis, electrodialysis, etc. The characteristics of membrane separation: no phase transition occurs in the process of membrane separation, so the efficiency of energy conversion is high. The membrane separation process is carried out at room temperature because it is especially suitable for heat sensitive materials; Simple device, simple operation, easy to control and maintenance, and high separation efficiency.