Comparison of Ionic Liquids to Conventional Organic Solvents for Extraction of Aromatics from Aliphatics

Commonly used solvents for separation of aromatics from aliphatics using liquid-liquid extraction are reviewed in terms of their physical properties and separation performance. The experimental liquid-liquid measurements for conventional solvents are contrasted with the phase behavior when using an ionic liquid as the extracting component. For comparison purposes, ternary systems of heptane + toluene + extraction solvent are used as representative mixtures, where sulfolane is the main organic extraction solvent discussed. Since ionic liquid properties are drastically changed by changing the anion, comparisons are performed for 1-ethyl-3-methylimidazolium based ionic liquids using different anions. Ionic liquids containing cyano-substituted and bis(trifluoromethylsulfonyl)imide anions provide good selectivities and distribution ratios. On the basis of the phase behavior and capacities, as well as their relatively low viscosities, they appear to be competitive alternatives to organic solvents.