Transport Parameters in a Porous Cellulose Acetate Membrane

The transport parameters of a cellulose acetate membrane prepared from a mixture of cellulose acetate, formamide, and acetone, 25:25:50 by weight, were studied. The membrane consists of a thin, porous layer, the skin, in series with a thick, highly porous layer, the coarse support. In the skin the diffusional permeability coefficient, ω, of a number of small amides and alcohols depends critically upon the partition coefficient, K(s), the size of the molecule, and the apparent hydrogen-bonding ability, N(s), of the solute. These observations are in general agreement with our earlier conclusions on the properties of nonporous membranes. On the other hand, the corrected reflection coefficient, σ', is not a very sensitive function of either N(s) or K(s) taken separately. The correlation between σ' and molecular diameter is reasonably good; however, it is much improved when both N(s) and K(s) are taken into consideration. Isotope interaction was also studied in the present preparation and was found to provide only a small (5–8%) contribution to the diffusional permeability coefficient of ethylene glycol. The contribution of solute-water friction was found to be less than 24% of the total solute friction.