TRANSPORT-PROPERTIES OF POLY(VINYL ALCOHOL) MEMBRANES OF DIFFERENT DEGREES OF CRYSTALLINITY .1. PERVAPORATION RESULTS

Dense poly (vinyl alcohol) (PVA) membranes of different crystallinitie s were prepared and studied in pervaporation of water-ethanol mixtures . High selectivities to water were obtained with all types of membrane s. Permeation fluxes increase exponentially with the water content in the liquid mixture. At a given water content, the membrane permeabilit y decreases drastically when its crystallinity increases. When the per vaporation temperature increases, the permeation flux increases accord ing to the Arrheniuslike law, with a permeation activation energy that depends strongly on the crystallinity of the membrane. A permeation m odel, in which the volume fraction of amorphous polymer intervenes in both the sorption and the diffusion laws, was proposed and validated b y the experimental data. With the obtained values of the parameters, t he permeation flux can be calculated for membranes of a given crystall inity at any temperature and composition of the water-alcohol mixture.