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Environment

Ionic Liquids

Contrary to assumption, ionic liquids can be distilled without decomposition

by Michael Freemantle
February 20, 2006 | A version of this story appeared in Volume 84, Issue 8

The widely held assumption that low-melting-point salts, known as ionic liquids, cannot be distilled because they have no measurable vapor pressure has been shown to be unfounded. An international team of researchers led by Luís P. N. Rebelo, professor of chemical and biological technology at the New University of Lisbon, in Portugal, has shown that many ionic liquids can be distilled at low pressure without decomposition (Nature 2006, 439, 831).

The research team demonstrated that selected families of ionic liquids, such as bis[(trifluoromethyl)sulfonyl]amide salts, can be vaporized under vacuum at 200-300 oC and then recondensed at lower temperatures.

"At lower temperatures, the ionic liquids exert undetectable pressure in the gas phase and will therefore keep their environmentally friendly status because they do not pollute the atmosphere," Rebelo tells C&EN. The team also distilled binary mixtures of ionic liquids and demonstrated significant enrichment of one component in the distillate and the other component in the residue.

"The possibility of separating two ionic liquids by distillation will, in particular, unlock the door" to new ways of manufacturing ionic liquids and regenerating spent ionic liquids from technical processes, comments Peter Wasserscheid, a chemistry professor at the University of Erlangen, in Germany, in the same issue of Nature.

Rebelo observes that ionic liquids can now potentially participate in gas-phase processes from which they have previously been excluded. "We anticipate an explosion of studies aimed at revealing the ionic liquids' gas-phase structure," he says.

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