High normality ion exchange membranes containing entrapped

Abstract

Anionic and cationic exchange materials including membranes are beneficiated by a method involving swelling the ion exchange material in the presence of an electrically neutral Reagent A and then contacting the swollen material with a similarly electrically-neutral Reagent B selected to interact with A forming in situ in the ion exchange pathways of the ion exchange material a chemical substance or substances which ionize the membrane to form bulky multicharge entrapped ions of the same electrical sign as the covalently-bonded ion sites of the membrane material. The entrapped ions are electrostatically retained most tenaciously in the ion exchange channels of the membrane even when extracted with water or solvents and even when the membrane is put under electric stress as when current at high densities pass through the membrane in electrolytic chlorine processes, in dialysis cells, and the like. As compared to existing membranes having a concentration of covalently-bonded ion sites averaging about 0.05 to 0.1 N, beneficiated membranes may be made having a critical electrolyte concentration between about 0.25 and about 10 N. Beneficiated membranes at about 0.5 to 10 N or higher reject ions of the same electric charge at ion concentrations well above those at which the original ion exchange material is effective. Outstanding properties of such beneficiated membranes are very high in transfer rates, low electrical resistivities, very high permselectivities allowing them to function under very high ion concentrations, and high resistance to penetration or fouling by nonionized salts, all without loss of the basic physical and chemical integrity of the original membrane. Beneficiated cation exchange membranes are especially useful in the electrolytic generation of chlorine.