Thermoresponsive copolymer-based draw solution for seawater desalination in a combined process of forward osmosis and membrane distillation

A thermoresponsive copolymer, poly(sodium styrene-4-sulfonate-co-n-isopropylacrylamide) (PSSS-PNIPAM), is employed as a draw solute in forward osmosis (FO) for seawater desalination. When PSSS-PNIPAM is dissolved in water to form a draw solution, PSSS as a strong polyelectrolyte generates a high osmotic pressure and extracts water from seawater in an FO process. A water flux of 4 LMH has been attained with simulated seawater as the feed solution. The draw solution is then regenerated with membrane distillation (MD) at a temperature above the low critical solution temperature (LCST) of PNIPAM, which agglomerates and leads to decreased osmotic pressure of the solution and thus higher water vapor pressure. The combined FO-MD process with PSSS-PNIPAM as the draw solute should be promising not only for seawater desalination, but also for other membrane-involved separation processes in wastewater treatment and protein or medicine enrichment. (C) 2014 Elsevier B.V. All rights reserved.