HyLITE · Hydrophobic Ionic Liquid Technologies

Hydrophobic Ionic Liquid Technologies

Over the past twenty years hydrophobic ionic liquids with little, or no vapour pressure have been developed as alternatives to volatile organic compounds solvents VOCs for use in chemical and materials separation processes from water. Applications include removal of organic compounds and metal ions for purification and pollution remediation, separation of radioactive nuclei for waste management, biotransformation and liquid chromatography for analytical and preparative synthesis. However, while many successes while many successful applications of hydrophobic ionic liquids have been demonstrated at a laboratory scale, with the exception of analytical chromatography, commercial applications have not followed. The main reason for this is because most hydrophobic ionic liquids contain complex (and expensive) perfluorinated anions that may have significant negative environmental impacts, for example generation of bio-persistant non-degradable products or, when decomposition takes place during use, formation of hydrofluoric acid. The aim of this project was to investigate how new hydrophobic ionic liquids, for application in ionic liquid-water separations processes, in which the liquid/liquid separations could be produced that incorporate favourable performance characteristics, but remove the need for using fluorinated components. The research program examined synthetic strategies to prepare a library of ionic liquids, and then characterised their co-miscibility with water - the key selection criteria for a hydrophobic material - using this to iteratively improve properties. New ionic liquids based on a family of phenyl-5-tetrazolate anions have been developed which exhibit the relatively rare behaviour in ionic liquids of having a lower critical solubility temperature (LCST) with water. That is, they are completely miscible with water at low temperatures and, on heating, separate into two phases (see attached image from the first publication on these materials from 2017 in the journal ChemPhysChem., DOI: 10.1002/cphc.201700942). The critical temperature and miscibility ranges can be controlled by modification of the tetrazolate anions enabling temperature responsive separations to be achieved.

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