Investigation of the transport properties of a quaternary ammonium anion exchange membrane. Part 1.—Application of irreversible thermodynamics to the chloride form

Abstract

A detailed study of the transport properties of the chloride form of a strong base quaternary ammonium anion exchange membrane has been completed. Experimental determination of isotope diffusion coefficients and electrical, salt diffusion, and osmotic properties has been made. From these data a complete irreversible thermodynamic analysis of the system in 0.1 and 1.0 mol dm–3 sodium chloride solutions has been obtained.Using primarily the frictional coefficient treatment, it is shown that the kinetic interaction between membrane ions and fixed charge contributes to a very large degree in reducing ion mobility, but that this contribution is large primarily because the membrane has very large internal ionic molality and not due to ion association. Equally, although there is considerable evidence for water structure enforcement around quaternary ammonium ions in aqueous solution, there is no evidence for this effect in the membrane. Water-to-water friction is similar to that obtained in other membrane studies on cation exchangers and to aqueous electrolyte solutions. The terminal hydroxyl groups on the quaternary ammonium fixed charges of the A104 membrane may do much to modify the unique solvation of alkyl substituted analogues. Pressure permeability and osmotic coefficients obtained by calculation indicate that the membrane is almost ideally semi-permeable with a reflection coefficient, σ, of 0.99 and 0.97 in 0.1 and 1.0 mol dm–3 salt solutions, respectively, and has a very low salt permeability.