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Ionic liquids separated from mixtures by CO2

Carbon dioxide gas could be used as an "antisolvent" to remove traces of ionic liquids from organic and aqueous solutions. The group recently showed that CO2 can be used to separate mixtures of methanol and the ionic liquid 3-butyl-1-methylimidazolium hexafluorophosphate. Applying CO2 pressure to the solution results in the formation of two liquid phases, one rich in the ionic liquid and the other in methanol. The latter can be induced to merge with the CO2 to form a supercritical fluid phase that contains no detectable ionic liquid. "The method could provide a way of removing ionic liquid contaminants from liquid organic product phases or organic liquid extracts containing a reaction product," AUTHOR suggests. The group has also shown that CO2 can be used to remove small amounts of ionic liquids from aqueous solutions. "This is important, as many ionic liquids are completely miscible with water and have the potential to enter the environment through aqueous waste streams," AUTHOR says. Preliminary ecotoxicity studies at Org. on Daphnia magna, a small crustacean that is used as a standard test organism, indicate that the ecotoxicity of dialkylimidazolium salts is similar to that of benzene or dichloromethane and may therefore be a major issue for potential applications associated with these types of ionic liquids



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