Bis{(trifluoromethyl)sulfonyl}amide ionic liquids as solvents for the extraction of aromatic hydrocarbons from their mixtures with alkanes: effect of the nature of the cation

Abstract

The liquid–liquid equilibria of two ternary systems comprising hexane, benzene and a bis{(trifluoromethyl)sulfonyl}amide ionic liquid, [A][NTf₂] (where A = cation), have been determined at 40 °C. Specifically, the cations of the ionic liquids investigated are 1-ethylpyridinium, [C₂py]⁺, and (2-hydroxyethyl)trimethylammonium, [N_{1 1 1}(C₂OH)]⁺. The effectiveness of each ionic liquid as solvent for the separation of benzene from its mixtures with hexane was evaluated, and compared to that of 1-ethyl-3-methylimidazolium bis{(trifluoromethyl)sulfonyl}amide, [C₂mim][NTf₂], as well as of trihexyl(tetradecyl)phosphonium bis{(trifluoromethyl)sulfonyl}amide, [P_{6 6 6 14}][NTf₂]. It was observed that the ammonium ionic liquid leads to higher selectivities in a certain range of global compositions, but it presents lower distribution ratios. No significant difference was observed between the pyridinium and the imidazolium ionic liquids. It was concluded that these ionic liquids can be envisioned as potential alternatives for the replacement of conventional organic solvents currently used for the separation of aromatic and aliphatic hydrocarbons. The liquid–liquid equilibrium data were acceptably correlated by means of the ‘Non-Random Two-Liquid’ (NRTL) equation.