EFFECT OF CRYSTALLINITY AND SWELLING ON THE PERMEABILITY AND SELECTIVITY OF POLYMER MEMBRANES

The conventional equations describing mass transport through membranes predict proportionality between flux and driving force. Experimental results inconsistent with this prediction are usually attributed to a concentration dependency of the diffusion coefficients of the species involved. It has been found that, in addition to this effect, simplifications in the models and the neglect of crystallinity and swelling of the membrane material contribute to the deviations. A simplified procedure is proposed for calculating membrane separation of multicomponent mixtures, which is based on the assumption of an exponential concentration gradient inside the membrane in accordance with reported experimental observations. The exponential form, which differs for each composition and set of conditions, can be calculated from the boundary conditions of the membrane.