Using UCST Ionic Liquid as a Draw Solute in Forward Osmosis to Treat High-Salinity Water

• Published in: Environmental science & technology Vol. 50; no. 2; pp. 1039 - 1045
• Main Authors: Zhong, Yujiang, Feng, Xiaoshuang, Chen, Wei, Wang, Xinbo, Huang, Kuo-Wei, Gnanou, Yves, Lai, Zhiping
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 19.01.2016
• Subjects: ambient temperature; betaine; Heating; ionic liquids; Ionic Liquids - chemistry; Ions; Osmosis; Salinity; Solubility; solutes; Solutions - chemistry; Spectrophotometry, Ultraviolet; Temperature; Temperature effects; thermal stability; Ultraviolet radiation; ultraviolet-visible spectroscopy; Water - chemistry; Water Purification - methods; water salinity
• ISSN: 0013-936X; 1520-5851; 1520-5851
• DOI: 10.1021/acs.est.5b03747

The concept of using a thermoresponsive ionic liquid (IL) with an upper critical solution temperature (UCST) as a draw solute in forward osmosis (FO) was successfully demonstrated here experimentally. A 3.2 M solution of protonated betaine bis­(trifluoromethylsulfonyl)­imide ([Hbet]­[Tf2N]) was obtained by heating and maintaining the temperature above 56 °C. This solution successfully drew water from high-salinity water up to 3.0 M through FO. When the IL solution cooled to room temperature, it spontaneously separated into a water-rich phase and an IL-rich phase: the water-rich phase was the produced water that contained a low IL concentration, and the IL-rich phase could be used directly as the draw solution in the next cycle of the FO process. The thermal stability, thermal-responsive solubility, and UV–vis absorption spectra of the IL were also studied in detail.