1-Ethyl-3-methylimidazolium bis{(trifluoromethyl)sulfonyl}amide as solvent for the separation of aromatic and aliphatic hydrocarbons by liquid extraction – extension to C7- and C8-fractions

Abstract

The ionic liquid 1-ethyl-3-methylimidazolium bis{(trifluoromethyl)sulfonyl}amide ([C₂mim][NTf₂]) was tested as solvent for the separation of aromatic and aliphatic hydrocarbons containing 7 or 8 carbon atoms (the C₇- and C₈-fractions). The liquid–liquid equilibria (LLE) of the ternary systems (heptane + toluene + [C₂mim][NTf₂]) and (octane + ethylbenzene + [C₂mim][NTf₂]), at 25 °C, were experimentally determined. The performance of the ionic liquid as the solvent in such systems was evaluated by means of the calculation of the solute distribution ratio and the selectivity. The results were compared to those previously reported for the extraction of benzene from its mixtures with hexane by using the same ionic liquid, therefore analysing the influence of the size of the hydrocarbons. It was found that the ionic liquid is also good for the extraction of C₇- and C₈-fraction aromatic compounds, just a greater amount of ionic liquid being needed to perform an equivalently efficient separation than for the C₆-fraction. It is also discussed how [C₂mim][NTf₂] performs comparably better than the conventional solvent sulfolane. The original ‘Non-Random Two-Liquid’ (NRTL) equation was used to adequately correlate the experimental LLE data.