Separation of water-ethanol mixtures by pervaporation through composite membranes prepared by concentrated emulsion polymerization: Improvement of the permeation rate with a porogen

Abstract

The sorption and pervaporation characteristics of hydrophilic-hydrophobic composite membranes are investigated for the water-ethanol mixture. The membranes have been prepared using a concentrated emulsion as precursor. In this emulsion, an aqueous solution of sodium acrylate (SA), N,N′-methylene-bisacrylamide and an initiator constitutes the dispersed phase, and a mixture containing styrene, butylacrylate, hexane and an initiator the continuous phase. The polymerization of this emulsion generates a composite which is used to prepare a membrane in which hydrophilic cells are separated by hydrophobic films. The porogen (hexane) does not participate in the polymerization process and was introduced in the continuous phase of the emulsion in order to generate pores in the films and thus to increase the permeation rate through the membrane. It was found that with increasing SA content of the membrane, both the equilibrium swelling ratio S e and the equilibrium sorption selectivity α s increase monotonically; there is a slight decrease of α s but almost no change of S e with increasing amount of porogen (hexane). The permeation rate Q increases and the separation factor α p decreases with increasing contents of SA and porogen in the emulsion. The best performance, hence the highest value of α p Q, was 67 kg/m 2-hr. The prepared membranes have not changed their pervaporation characteristics after 250 hr of operation.