Pervaporation of aqueous ester solutions through hydrophobic poly(ether-block-amide) copolymer membranes

Abstract

The pervaporation of three ethyl esters (aroma model compounds) in aqueous solutions was studied with poly(ether-block-amide) copolymer (PEBA) membranes of different compositions. The ester flux increases linearly with the ether-unit (tetramethylene oxide) content. The slope of the increase changes from a low to a higher value at 50 wt% polyether content. This behavior is explained by a change in the membrane structure from a continuous polyamide matrix structure to a polyether matrix one. The ester flux from saturated aqueous solutions increases from butyrate to propionate, then to acetate. This order differs from that of the poly(dimethylsiloxane) (PDMS) membrane whose flux was highest for butyrate and lowest for propionate ester. The PEBA membrane permeability and selectivity to the esters increase significantly with the polyether content. However, the best PEBA membrane had lower flux and selectivity to esters in aqueous solutions than the PDMS membrane. The activation energy for ester permeation was always lower than that for water permeation; its value was the highest for the PEBA membrane with the highest polyamide content.