Selective Transport and Counter Transport of Na⁺ and K⁺ through Poly (3-vinyl-1, 4-butyrolactoneco-acrylonitrile) Membrane

Abstract

When a mixed solution of KOH and NaOH and a solution of HCl were placed across a membrane of lactone-containing polymer, poly (3-vinyl-1, 4-butyrolactone-co-acrylonitrile), the selective transport of Na⁺ and K⁺ was observed. The transport behavior was much affected by the H⁺ concentration and the selectivity (K⁺/Na⁺) varied above and below unity. The selectivity was larger than unity at a higher H⁺ concentration, and smaller than unity at a moderate H⁺ concentration. When a solution of HCl was added into one side of NaOH solutions (same concentrations) which were separated with the membrane, Na⁺ was concentrated in the HCl side and H⁺ was counter-transported. It was suggested that the degree of ring-opening of lactone moiety in the membrane (chemical factor) and the lyophilicity or the hydrophilicity of the membrane (physical factor) control the selectivity. A proton-pump mechanism was considered for the concentration of Na⁺.