Preparation of macroreticular-type oleophilic anion exchange resin membrane and its permselectivity to halides and thiocyanate

Macroreticular-type oleophilic anion exchange resin membranes containing high-molecular-weight ammonium ions such as tri-n-octylbenzylammonium and tri-n-dodecylbenzylammonium as fixed site were freshly prepared. These membranes were wetted well with water-immiscible organic solvents even in aqueous surroundings. The properties of the membrane, i.e. porosity, water and organic solvent content, capacity and conductivity were determined. The permselectivity of the membrane impregnated with nitrobenzene or o-nitrophenyloctylether to halide and thiocyanate ions was evaluated by measurement of bi-ionic membrane potential and electrodialysis. p]The sequence of the permselectivity was Cl^? < Br^? < I^? < SCN^?, and was consistent with the Hofmeister anion series. The value of the permselectivity was 10–100 times larger than that of usual hydrophilic anion exchange membranes. It was found that the permselectivity of the present membrane was strongly dependent on the separation factor, which was in turn affected by the hydrophobicity of the membrane. The effect of the ion association between fixed ion-exchange site and counter ion on the specific conductance of the membrane was also discussed.