Forward Osmosis Desalination Using Thermoresponsive Hydrogels as Draw Agents; An Experimental Study

Hydrogel polymers have been the subject of many studies, due to their fascinating ability to alternate between being hydrophilic and hydrophobic, upon the application of appropriate stimuli. In particular, thermo-responsive hydrogels such as N-Isopropylacrylamide (NIPAM), which possess a unique lower critical solution temperature (LCST) of 32°C, have been leveraged for membrane-based processes such as using NIPAM as a draw agent for forward osmosis (FO) desalination. The low LCST temperature of NIPAM ensures that fresh water can be recovered, at a modest energy cost as compared to other thermally based desalination processes which require water recovery at higher temperatures. This work studies by experimentation, key process parameters involved in desalination by FO using NIPAM and a copolymer of NIPAM and Sodium Acrylate (NIPAM-SA). It encompasses synthesis of the hydrogels, development of experiments to effectively characterize synthesized products, and the measuring of FO performance for the individual hydrogels. FO performance was measured using single layers of NIPAM and NIPAM-SA respectively. The values of permeation flux obtained were compared to relevant published literature and it was found to be within reasonable range. Furthermore, a conceptual design for future large-scale implementation of this technology is proposed. It is proposed that perhaps more effort should focus on physical processes that have the ability to increase the low permeation flux of hydrogel driven FO desalination systems, rather than development of novel classes of hydrogels