Shiro Takashima

Permeability of mono-carboxylate ions across an anion exchange membrane

Abstract Transport numbers of several aliphatic and aromatic carboxylate ions across an anion exchange membrane were determined on the basis of the transport number of the co-ions across the membrane in electrodialysis. Also, the specific conductivity and water content of each carboxylate ionic-form membrane were measured. The transport number of lower aliphatic carboxylate ions decreases slowly with increasing molecular weight, but it decreases markedly where the carbon number is over five. In particular, the transport number of caprylate or of caprate ions is below 0.5, and these ionic-form membranes apparently lose the characteristics of an anion exchange membrane. For aromatic carboxylate ions, the benzoate ion a higher transport number, but p- or O-hydroxybenzoate ions only about 0.6. The specific conductivity and water content of each carboxylate ion having a lower transport number are very small compared with other carboxylate ions of higher transport number. This suggests that the hydration number and the activity of ions with a lower transport number are small in anion exchange membranes.