THE EFFECTS OF MOLECULAR WIDTH ON PERMEATION OF ORGANIC SOLUTE THROUGH CELLULOSE-ACETATE REVERSE-OSMOSIS MEMBRANES

In order to examine the effects of molecular shape on the permeation of organic solute through a cellulose acetate reverse osmosis membrane the molecular length and width parameters were computed by modification of the STERIMOL parameters, where the orientation of the solute at the surface of cellulose acetate was considered. The orientation of the organic compound was estimated based on the interpretation of the retention mechanism in liquid chromatography with cellulose acetate as the stationary phase. The molecular width was recognized to be a useful descriptor of the effective molecular size from the following facts: the molecular width estimated in this study was correlated linearly with the Stokes radius in an aqueous solution system and corresponded very well to the distance parameter (D) developed empirically as the apparent molecular size in the pores of a cellulose acetate membrane by Matsuura et al. [ Ind. Eng. Chem., Process Des. Dev., 23 (1984) 673]. In the case of bulky compounds (molecular width > ca. 3 X 10(-10) m), however, the values of the parameter D were significantly larger than the molecular width. The results suggested the influence of the microcavities in the pores of cellulose acetate membranes.