Characterizations of Thermo-Responsive Alkyl Imidazolium Perchlorates for Forward Osmosis Membrane Process

抄録

The forward osmosis （FO） process uses a spontaneous water permeation phenomenon driven by an osmotic pressure difference between a feed solution （FS） and a draw solution （DS） through a semipermeable membrane. Hence, it is assumed that seawater desalination and feed solution concentration using FO processes can be conducted at low energy and cost. It is crucial to develop an optimal DS for the FO process before it can be put into practical use. The DS must have the following characteristics: （1） Develops higher osmotic pressure than FS, （2） Easy to regenerate and recover, （3） Low leakage, and （4） Low viscosity. Particularly, we propose low-grade waste heat to reduce energy consumption during DS regeneration and chose a temperature phase transition type DS that separates into water and solute components based on thermal response. In this study, we synthesized six alkyl imidazolium type ionic liquids （ILs） having perchlorate anion （［ClO₄］）, phase transition characteristics, and osmotic pressure, and the consequent FO performance was examined. The synthesized ILs, 1-ethyl-3-propylimidazolium perchlorate ［Im （2.0.3）］［ClO₄］ and 1,2-dimethyl-3-propylimidazolium perchlorate ［Im （1.1.3）］［ClO₄］, showed an upper critical solution temperature type phase transition in the temperature range of 25 ℃ to 50 ℃. The FO test confirms that pure water can be derived from saltwater using the osmotic pressure of DS. In comparison to other synthesized ILs, ［Im （1.1.3）］［ClO₄］ showed higher performance in phase diagrams and osmotic pressure.