Mass transport of aliphatic alcohols and esters through hydrophobic pervaporation membranes

Mass transport in pervaporation of multi-component mixtures of homologous series of alcohols and esters through composite pervaporation membranes has been investigated. Pervaporation experiments were performed in a concentration range relevant for aroma recovery, using a membrane with an active layer of poly(octyl)methylsiloxane (POMS) caste on a porous polyetherimide (PEI) support. The fluxes, selectivities and average diffusion coefficients were determined for each compound studied and were related to the properties of the permeating molecule. The reduction in the selectivity of the higher homologues of the alcohol series with increase in feed concentration was explained by a decrease in diffusion coefficient with respect to feed concentration. There was evidence of a tendency towards aggregation of water molecules, lower homologues of alcohol series and the first two homologues of the ester series, which resulted in a decrease in diffusivity for the polar, lower homologues in both series.