Transport of Ions and Water in Sulfonated Polysulfone Membranes

Ion-exchange type, charged membranes were amongst the first materials recognized to be suitable for desalting water by reverse osmosis (R.O.) ( 1 ). However, subsequent to the development of neutral, asymmetric cellulose acetate membranes ( 2 ), they were paid relatively little attention. The first step toward the attainment of a charged equivalent of a conventional asymmetric R.O. membrane was the development of thin-film composites of sulphonated polyphenylene- oxide) ( 3, 4 ). These membranes showed some promise, but did not give sufficiently high rejection of concentrated salt solutions to be considered practical for seawater desalting. Sulphonated polysulphone (SPS) membranes, on the other hand, have been shown to have excellent salt rejections and water fluxes ( 5 - 7 ) which are maintained even for feeds of very high salt concentration. In fact, both the magnitude of the salt rejections cited and their independence of feed concentration are remarkably non-characteristic of the behaviour of any charged membrane heretofore examined. Utilizing