Morphology and Reverse Osmosis Properties of Sulfonated 2,6-Dimethyl Polyphenylene Oxide Membranes

Abstract

It is well known that ion exchange membranes are permselective and will pass water while rejecting dissolved salts under pressure. This is the case with the cation exchange membranes of sulfonated polyphenylene oxide (PPO), in which the anchored negative sulfonate ions repulse like charges (anions in solution) and, in order that electrical neutrality be preserved, cations must also remain behind. The advantage of using sulfonated PPO for reverse osmosis application compared to other commercially available ion exchange membranes, such as those discussed by Spiegler[l] and Merten et al.[2], is that it can be solvent cast as a thin (0.1 to 0.2 mil) unsupported membrane having excellent chemical and physical stability with good flux and rejection characteristics. Water contents are adjusted easily to give the desired permeability by controlling the ion exchange capacity of the sulfonated polymer. Techniques have also been developed for adjusting the water content of a sulfonated PPO membrane with a given ion exchange capacity. This work shows that for certain feeds sulfonated PPO may be comparable or superior to cellulose acetate.