Developement of New Polymer Membranes for Separation

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Cationic exchange membranes were prepared with 2,3-epithiopropyl methacrylate(ETMA)-methacrylic acid(MAc),ETMA-2-phosphoethyl methacrylate(MP), and ETMA-2-acrylamide-2-methylpropane sulfonic acid(tertiary butyl acrylamide sulfonic acid) (TBAS) copolymers. Transporrt of alkali metal ions through the membranes was investigated by using the system containing acid(left side) and alkali or alkali earth metal ions(right side). All these copolymer membranes transported alkali metal ions from the right side to left side against their concentration gradient. In order to obtain the membrane with high ability of transport of metal ions against its concentration gradient, it was necessary to (1) increase the content of carrier such as carboxyl group, phosphoric acid group or sulfonic groups in the membrane in the composition range at which the membrane can be used without breaking because of high swelling, (2) make the membrane dense for <H^+> and <OH^-> not to diffuse simply through the membrane by the concentration gradient, and (3) depress the diffusion of anion such as <Cl^-> into the membrane. The transport of alkali metal ions through the ETMA-MP and ETMA-TBAS copolymer membrane is higher than that through the ETMA-MAc copolymer membrane. The transport rate, transport fraction of alkali metal ions , and the selective transport between alkali metal ions through the ETMA-MAc copolymer membrane could be increased by using the copolymer membranes irradiated with ultra violet light, because the physical and chemical structure of the membrane made of ETMA-MAc copolymer can be easily be changed by irradiation with ultra violet light. The transport in this system, where one side of the membrane in a cell was acidic and the other alkaline, was influenced significantly by the initial <H^+> concentration on the acidic side.