Exploration of oligomeric sodium carboxylates as novel draw solutes for forward osmosis

Abstract

FO technology has attracted growing attention in water treatment and desalination applications recently. The development of a suitable draw solute with high performance and low cost is therefore in high demand to facilitate practical FO applications. In this study, two oligomeric carboxylates — poly maleic acid sodium (PMAS) and poly(itaconate-co-acrylate) sodium [P(IA-co-AA)] with controllable molecular weights of 400–1000Da, are synthesized via one-step polymerization and employed as novel draw solutes for FO applications. The successful synthesis is confirmed via by various characterization techniques. The osmotic pressure, relative viscosity and FO performance of PMAS and P(IA-co-AA) draw solutions with different concentrations are studied systematically. Two types of FO membranes are employed, and their performance is compared using PMAS draw solution. With 0.5mol/kg PMAS draw solution and DI water feed solution, high water fluxes of 30.6 and 62.4LMH can be achieved using HTI-TFC and homemade PSf-TFC membrane in the FO tests, respectively. 0.5mol/kg PMAS draw solution is further studied for the desalination of 0.6mol/kg NaCl solution via FO, with a water flux of 6.63LMH obtained. The diluted PMAS solution after FO test can be recovered by nanofiltration with a high rejection rate. The excellent performance and available recovery route of the developed oligomeric carboxylates imply their great potential as promising draw solutes for FO applications.