Preparation And Application Of Monovalent Cation Exchange Membrane

Along with water resources gradually reducing, sea water desalination and reuse of waste water have raised great concern all over the world. With the development of science and technology, membrane separation is thought to be one of the most advanced potential technology. Electrodialysis is one of the most important branch of membrane separation, which has been widely used in various fields. But when it is used in practical applications, it still has some flaws, such as the permeation of multivalent ions. The existence of these ions may reduce the current efficiency, increase the consumption of power, and even cause the melting of the membranes. However, the application of monovalent cation exchange membrane can solve this problem easily.In this article, chemical modification and electro-deposition method were taken to modify the membrane. The obtained membrane was applied in concentrated seawater to compare advantages and disadvantages of the membranes.In the method of chemical modification, the surfactant N,N-dimethyl-N-2-propenyl-2-propene-1-ammonium chloride-2-propenam-ide(poly-quaternium-7, PQ7) is used to modificate the cation exchange membranes. A series of electrodialysis experiments were conducted to evaluate the monovalent selectivity. The leakage of Zn2+ was decreased and the leakage of Ca2+ and Mg2+ were both decreased while the membranes were used in concentrated seawater. The obtained results indicated that the membrane had an excellent performance, particularly with respect to selectivity.The chitosan/aniline copolymer was used as modified material. The electrolyte was transferred and deposited on the surface of the membrane at the existence of electrostatic field. The glutaraldehyde was used as crosslinker. From the analysis of SEM and FTIR, the copolymer was addicted on the surface of the membrane.The electrodialysis experiments showed that the leakage of Ca2+ reduced about 23.5% while the leakage of Mg2+ redused 50.1%. The experiments revealed that when the content of aniline was about 0.3-0.5, the membrane has the highest selectivity. The resistance of the membrane revealed that althorough the resistance increased with deposition time, but the resistance did not have a significant increase after modification.These two kinds of methods can provide some information and lay a foundation for further survey on monovalent membranes.