TRANSPORT CHARACTERISTICS OF POROUS CELLULOSE ACETATE MEMBRANES FOR REVERSE OSMOSIS SEPARATION OF SUCROSE IN AQUEOUS SOLUTIONS

Analysis of the reverse osmosis separation data for the system sucrose-water using a number of Loeb-Sourirajan type porous cellulose acetate membranes shows that the solute transport parameter, DAM/Kδ, for sucrose decreases with increase in its boundary concentration, XA2. The plot of log DAM/Kδ vs. XA2 is a straight line, and this relationship is independent of the combination of feed concentration and flow rate used. The slope of the above straight line is a function of the operating pressure, and at a given operating pressure is essentially the same for all the membranes tested. For every film, a unique relationship exists between DAM/Kδ for sodium chloride and the extrapolated value of DAM/Kδ for sucrose at XA2 = 0, giving rise to a new method of expressing membrane selectivity on a relative scale. The predictability of membrane performance for the reverse osmosis separation of sucrose in aqueous solution and the effect of membrane compaction on solute separation, from the initial specifications of the film given in terms of the pure water permeability constant and DAM/Kδ for sodium chloride, are illustrated and discussed. © 1968, American Chemical Society. All rights reserved.