Hydrophobic polydimethylsiloxane thin-film composite membranes for the efficient pervaporative desalination of seawater and brines

Abstract

The pervaporative desalination of synthetic seawater and brines was studied to explore the water flux and salt rejection of a thin-film composite (TFC) membrane made of polydimethylsiloxane (PDMS) dip-coated on porous polysulfone support. Despite the hydrophobic nature of rubbery PDMS, we demonstrate that nonporous TFC membranes exhibit remarkable pervaporative desalination performance as evidenced by very high water permeance and 99.8 ± 0.2% NaCl rejection. For comparison, two commercial hydrophilic polyamide thin-film composite membranes designed for reverse osmosis (RO) were also tested in pervaporation mode. At the highest temperature explored (85 °C) the PDMS thin-film composite membrane produced an outstanding pure water flux of ∼70 kg m−2 h−1, which was 2.6 times higher than that of the best commercial RO membrane tested in this work. Although the presence of salt in the feed water reduced water flux to 36 kg m−2 h−1 (at a brine sodium chloride concentration of 70,000 ppm and 85 °C), the hydrophobic PDMS composite membrane performed among the best compared with previously reported hydrophilic TFC polymer membranes.