Selective extraction of toluene from n-heptane using [emim][SCN] and [bmim][SCN] ionic liquids as solvents

• LLE for {n-heptane + toluene + [emim][SCN] or [bmim][SCN]} at 313.2 K were measured.
• LLE data were successfully correlated to the NRTL model.
• Di and α2,1 were compared to those of sulfolane and other highly selective ILs.
• [emim][SCN] and [bmim][SCN] showed higher selectivities than sulfolane.
• Physical properties of [emim][SCN] were suitable to be applied at industrial scale.

Among the ionic liquids (ILs) studied so far in the liquid–liquid extraction of aromatic hydrocarbons, only a few of them have shown aromatic distribution ratios and aromatic/aliphatic selectivities considerably higher than those of conventional organic solvents, such as sulfolane. Moreover, these ILs had high dynamic viscosities that could limit their application at industrial scale. In this work, we have studied the performance of 1-ethyl-3-methylimidazolium thiocyanate ([emim][SCN]) and 1-butyl-3-methylimidazolium thiocyanate ([bmim][SCN]) ILs in the liquid–liquid extraction of toluene from n-heptane at 313.2 K. Densities, dynamic viscosities, and surface tensions of the ILs were also measured to evaluate their suitability as aromatic extraction solvents. In spite of the high selectivities and toluene distribution ratios of [bmim][SCN], its high dynamic viscosity could imply an important drawback. By contrast, the [emim][SCN] shown toluene/n-heptane selectivities three times higher of the sulfolane values and also substantially higher than those of other promising ILs. Futhermore, densities, viscosities, and surface tensions of [emim][SCN] were also appropriate to consider this IL as an alternative to organic solvents.

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