Development of a chlorine-resistant polyamide reverse osmosis membrane

The chlorine resistance of polyamides synthesized using various diamines and acid chlorides was investigated. The retention ratio of molecular weight and the polymer weight loss after the immersion in chlorine solution were used as the evaluation for chlorine resistance. The influence of the diamine chemical structures on the chlorine resistance is discussed. After screening 17 diamines, N,N'-dimethyl-m-phenylenediamine (N,N'-DMMPD) was selected in the preparation of the reverse osmosis polyamide membrane. The membrane prepared from N,N'-DMMPD and 1,3,5-benzenetricarbonyl trichloride (TMC) showed much higher chlorine resistance than commercial polyamide and cellulose acetate RO membranes. The use of mixture of TMC and isophthaloyl dichloride (IPC) in the preparation of the polyamide membrane brought about further improvement in the chlorine resistance. The solute rejection hardly changed after the immersion in aqueous sodium hypochlorite solution (200 ppm) at 40°C for 96 h.