Study of Ion Transport across Amphoteric Ion Exchange Membrane. II. Transport of Symmetric Tetraalkylammonium Chlorides

Abstract

Abstract Transport characteristics of NH4Cl, (CH3)4NCl (TMA–Cl), (C2H5)4NCl (TEA–Cl), (n-C3H7)4NCl (TPA–Cl), and (n-C4H9)4NCl (TBA–Cl) across homogeneous type amphoteric ion exchange membrane (1.0-PA-29, Kanegafuchi Chem. Ind.) were studied. Membrane potentials and conductances of the concentration cell systems were measured to calculate the membrane permeabilities which represent a measure of ionic permselectivity. Membrane potential changed considerably with cationic species and the membrane tended to behave more anionic selectively with increasing bulkiness of cations. The cationic permeabilities calculated from electrochemical data were PNH4>PTMA>PTEA>PTPA>PTBA. Membrane permeabilities to chloride ions, PCl, were greater than those to cations in all the systems studied and it was interesting that PCl values and their dependencies on external electrolyte concentration were almost unchanged irrespective of the difference in cationic species. The present experiment was designed in order to examine the effects of ionic size on the transport processes across homogeneous type amphoteric ion exchange membrane. The obtained results indicated that the hydrated radius of permeant ion is an important factor to control the ionic transport processes and to reveal the potentiometric selectivity in these systems. It was suggested that the ion transport across homogeneous type amphoteric ion exchange membrane is strongly affected by hydrodynamic properties of permeant ion, but scarcely influenced by ionic charges of which effects are well known to be exclusive in the uniform cation and anion exchange membranes.