Effect of ethanol–water mixture as gelation medium during formation of cellulose acetate reverse osmosis membranes

Abstract

AbstractBy using ethanol–water mixtures in a wide range of alcohol concentrations and temperatures, cellulose acetate membranes with a wide range of surface porosities can be obtained. Two different casting solution compositions were used, involving cellulose acetate, acetone, and aqueous magnesium perchlorate (composition I) or formamide (composition II). All reverse osmosis experiments were carried out at 250 psig using a 3500 ppm NaCl–H2O feed solution at laboratory temperature. The effective area of film surface was 12 cm2 in all cases. With composition I, with pure water gelation medium at 0°C, the resulting membrane gave a solute separation of 5% and product rate of 220 g/hr, whereas with 95% alcohol as gelation medium, the resulting membrane gave a solute separation of ∼1% and product rate of 1240 g/hr under otherwise identical experimental conditions. With composition II membranes, the maximum product rate of 360 g/hr with the corresponding minimum solute separation of ∼1% was obtained with 71.2% alcohol–water gelation medium at 0°C. Increase in the temperature of the gelation medium in the range 12° −25°C tends to increase the average size of pores on the membrane surface. These results offer a basis for the development of cellulose acetate ultrafiltration membranes.