Separation of toluene from n-heptane by liquid–liquid extraction using binary mixtures of [bpy][BF4] and [4bmpy][Tf2N] ionic liquids as solvent

Highlights: ► Binary mixtures of ionic liquids as extraction solvents of aromatics. ► [4bmpy][Tf2N] shows higher capacity but lower selectivity than sulfolane. ► [bpy][BF4] shows lower capacity but higher selectivity than sulfolane. ► Mixed {[4bmpy][Tf2N] + [bpy][BF4]} improves both extractive properties. - Abstract: The use of binary mixture of ionic liquids N-butylpyridinium tetrafluoroborate ([bpy][BF4]), and 1-butyl-4-methylpyridinium bis(trifluoromethylsulfonyl)imide ([4bmpy][Tf2N]) in the liquid–liquid extraction of toluene from n-heptane has been investigated at 313.2 K and atmospheric pressure. The experimental capacity of extraction and selectivity for this binary mixture has proved to be intermediate to those corresponding to the pure ionic liquids, and they can be predicted using a logarithmic–linear model of solubility. Furthermore, the results showed that the use of binary mixture of {[bpy][BF4] + [4bmpy][Tf2N]} at a mole solvent composition around 0.7 for [bpy][BF4] improves both the capacity of extraction of toluene and the selectivity with respect to those of sulfolane, the organic solvent taken as a benchmark. Thus, this mixed ionic liquid could be likely to be used in the extraction of aromatic from aliphatic in replacement to sulfolane.