In the search for less hazardous manufacturing solvents, researchers at the Universities of Notre Dame and Pittsburgh report in the May 6, 1999, issue of Nature a new process to separate problematic chemicals from ionic liquids.

It is the vapor pressure of traditional solvents that generally make them hazardous, explains Joan F. Brennecke, professor of chemical engineering at the University of Notre Dame and principal investigator of the study. Because the solvents evaporate easily into the air, factory workers may inhale them. Additionally, the solvents add to damage of the earth's atmosphere, because organic solvents eventually will oxidize and create carbon dioxide, a green house gas with potential impact on global warming.

In recent years, ionic liquids have emerged as possible "green" solvents -- that is, environmentally benign -- largely because they have no measurable vapor pressure. They do not evaporate

Ionic liquids are liquid salts -- not salt dissolved in a liquid, but a salt that exists in liquid form at room temperature. As salts, they have a plus charge and a negative charge. They don't occur naturally, but are manufactured, and there are dozens of various ionic liquids.

And ionic liquids are potentially good solvents, Brennecke says. "People are now showing that you can do all kinds of reactions in them, and many reactions must be done in a solvent. But once the reaction is complete, we need to get the chemical product out of the ionic liquid in pure form."

This has posed a problem in certain cases. Water soluable compounds can be extracted with water, and distillation can be used to remove chemicals with high vapor pressures. "But you would need very high temperatures to distill larger compounds that have low vapor pressures," Brennecke says. "This isn't practical."

In addition there are many chemicals that would break down, or decompose, when heated. Many
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Contact: Joan Brennecke
Joan.Brennecke.1@nd.edu
219-631-5847
University of Notre Dame
6-May-1999