Forward osmosis with membrane distillation using tetrabutylphosphonium based LCST-type ionic liquid as osmotic agent for seawater desalination.
Junzhe QUAN1, Sanskrita MADHUKAILYA1, Leila MOURA1, John HOLBREY1
1Queen's University Belfast QUILL, Belfast, United Kingdom
Access to pure water is becoming a global challenge due to many environmental and societal reasons. Since traditional seawater desalination is highly energy intensive (either through multistage flash evaporation approaches or via reverse osmosis) there is a significant interest in developing desalination technologies with reduced energy demands. Forward Osmosis (FO) is one such example, however FO requires a high?performance draw fluid to extract water across a membrane and from which purified water can be subsequently recovered. This regeneration process represents the largest energy consumption component in FO processes, and the development of efficient draw fluids that can use low grade and environmentally friendly energy such as solar or waste heat for regeneration is a critical component of research.
Ionic liquids that exhibit lower critical solution temperature (LCST) behavior have been proposed as potential thermally switchable draw fluids for water desalination, these include tetrabutylphosphonium arylsulfonates ([P4444][tol-SO3]) and CO2-switchable solvent. We have examined the performance of series of known, and new, tetrabutylphosphonium and tetrabutylammonium-based ionic liquids as draw fluids in a laboratory-scale FO cell. The prospects, and possible deficiencies, of these ionic liquids as FO osmotic agents have been evaluated interms of capacity, osmotic pressure, and effects of ionic liquid and electrolyte composition on critical behaviour and are reported here.