Use of ionic liquids in extraction

Abstract

In order to separate liquid mixtures, common distillation is not always suitable, especially if relative volatility of the mixture components is close to or equals unity, thus avoiding separation based on the vapor enrichment by more volatile component. To overcome this limitation of distillation, several alternatives were suggested including pressure swing and extraction distillation. Another, principally different, separation method used for the liquid mixtures separation is liquid-liquid extraction. Separation efficiency of this method is closely related to the basic extraction solvent characteristics, capacity and selectivity. In order to minimize costs connected with extraction, new extraction solvents are developed, among which ionic liquids show high potential due to their tunable properties. Here, efficiency of traditional extraction solvent, benzene, was compared to that of tetradecyltrihexylphosphonium bis(trifluoromethylsulfonyl)imide ionic liquid in separation of ethanol from its aqueous solution. The comparison was assessed on the base of results of a counter-current extractor simulation. Further, some economic aspects of this separation procedure were discussed. Optimum consumption of extraction solvent was identified taking into account alcohol-to-water molar (mass) ratio in the final extract as optimization criterion.