Dreamlike liquids for the (almost) impossible

Oeiras, 11.04.13

It's almost like magic. You put together two solids to come up with a liquid that can dissolve what other liquids cannot. In their search for better and better solvents, researchers from the Molecular Thermodynamics Lab tested a new type of compounds to solve one of the oldest engineering problems in chemistry: separating liquid mixtures impossible to separate by traditional vapour distillation. The results are promising and have just been published in Green Chemistry.

When boiling liquid mixtures, one of the components will usually turn first into vapour, while the other(s) stay behind. But in azeotropic mixtures, vapour and liquid always have the same composition, no matter what, so processes like distillation are useless. While some solvents can help separate these mixtures, chemists are on the look for better, cheaper, greener candidates. But some of the attractive candidates have a tiny problem: they are solid.

In this work, researchers were able to create a liquid mixture out of a specific solid salt (choline chloride) by adding one of three natural organic acids that are also solids. All these materials are cheap, non-toxic, completely biodegradable, and biocompatible. It is enough to mix, heat and stir. The results are highly promising liquids, efficient and selective in the separation of ethanol-heptane mixtures, with the additional benefit of producing a liquid end product that can be recovered and reused.
 

Original Article

Green Chem., 2013, Advance Article DOI: 10.1039/C3GC37030E

Deep eutectic solvents as extraction media for azeotropic mixtures

Filipe S. Oliveira , Ana B. Pereiro , Luís P. N. Rebelo and Isabel M. Marrucho