Effect of the Molecular Weights of Thermoresponsive Polyalkylene Glycol Draw Solutes on Forward Osmosis Performance

Abstract In recent years, the forward osmosis (FO) process has been used as an alternative water purification technique. To achieve the FO process, one of the most important factors is the development of a draw solution (DS) that exhibits a high osmotic pressure and low solute leakage. In this study, poly(propylene glycol-ran-ethylene glycol) monobutyl ethers (PAGBs) with Mw = 278–3911 g/mol were studied and compared as thermoresponsive draw solutes for FO. All PAGBs exhibited phase separations with a lower critical solution temperature (LCST) between 42 and 53 °C. The osmotic pressure curve profiles differed among the tested PAGBs. Both the FO water flux Jw and reverse DS flux Js decreased with increasing molecular weights of PAGBs. The FO performance was measured by calculating Js/Jw. The value of Js decreased more drastically with increasing molecular weights of PAGBs than Jw. PAGBs with Mw range of 1810–3911 g/mol had the lowest Js/Jw ratio and were suitable as draw solutes for FO. These experimental results were confirmed by numerical calculations. Thermoresponsive DSs such as PAGBs may simplify the regeneration of DSs in FO systems.