Transport properties of ion-exchange membranes in the presence of surface active agents

Abstract

Transport properties of ion-exchange membranes in the presence of various surface-active agents were observed. Measurements were carried out by the following two methods: (1) electrodialysis using a cation exchange membrane which has been adsorbed or ion exchanged with hexadecyl pyridinium chloride; (2) electrodialysis of a mixed salt solution containing surface-active agents using anion or cation exchange membranes. The transport properties measured in this report were: the relative transport number of two ionic species with the same sign ( P M 2 M 1 ), the current efficiency, the voltage drop by electric resistance of the membrane during the electrodialysis, and the current-voltage curve. P M 2 M 1 of cation exchange membranes was changed remarkably by adsorption of or ion exchange with the cationic surface-active agent above a certain concentration, but was not changed by adsorption of a nonionic or anionic surface-active agent. Similarly, P M 2 M 1 of anion exchange membrane changed remarkably by adsorption of or ion exchange with an anionic surface-active agent. The cation exchange membrane in the presence of cationic surface-active agents and the anion exchange membrane in the presence of anionic surface-active agents were preferentially permeable to monovalent ions over multivalent ions. The current-voltage curves were characteristic of a bipolar ion-exchange membrane. These membranes were preferentially permeable to monovalent ions because the electrostatic repulsion force between the multivalent ions and the surface charge of the membrane is larger than that between the monovalent ion and the surface charge of the membrane. The current efficiency of cation exchange membrane decreased slightly with an increase in the amount of dodecyl pyridinium chloride adsorbed or ion exchanged. However, the current efficiency decreased or increased depending on the species of surface-active agent and ion-exchange membrane. The voltage drop due to the electrical resistance of the cation exchange membrane increased as the electrodialysis proceeded and also as the concentration of cationic surface-active agent was increased.