Interactions between large organic cations and cation exchange membranes

Interactions between cation exchange membranes and large organic cations have been studied; namely (1) adsorption and electrodialytic desorption of cationic surface active agents, and (2) change in transport properties of the membranes by adsorption.N-dodecyl pyridyl compounds, such as N-dodecyl pyridinium bromide (C₁₂-Py), N-dodecyl dipyridyl bromide (C₁₂-Dipy) and N-dodecyl tripyridyl bromide (C₁₂-Tripy) were used for the adsorption and electrodialytic desorption; and for the study on the change in transport properties of membranes, N-dodecyl pyridinium chloride, C₁₂-Py, C₁₂-Dipy, C₁₂-Tripy and hexadecyl trimethylammonium chloride were used. It was confirmed that the higher the molecular weight of the cation the longer the time required to reach adsorption equilibrium, and that the amount of adsorption exceeded the ion-exchange capacity of the membrane. After equilibrium was attained, electrodialytic desorption from the membranes was difficult.The adsorption or ion-exchange of large organic cations was effective to the permselectivity of the cation exchange membrane to the sodium ion in electrodialysis of a solution of sodium chloride and calcium chloride. The relationship between the permselectivity and the properties of the cations was examined.