Liquid–liquid extraction of toluene from n-heptane using binary mixtures of N-butylpyridinium tetrafluoroborate and N-butylpyridinium bis(trifluoromethylsulfonyl)imide ionic liquids

Liquid–liquid extraction of toluene from heptane using binary mixtures of the ionic liquids N-butylpyridinium bis(trifluoromethylsulfonyl)imide ([bpy][Tf2N]) and N-butylpyridinium tetrafluoroborate ([bpy][BF4]) have been investigated at 313.2 K and atmospheric pressure. On the basis of the experimental liquid–liquid equilibrium data for the pseudoternary system n-heptane + toluene + mixed ionic liquids, the values of the distribution ratio and selectivity were calculated and compared to those for the pure ionic liquids, for sulfolane, and those predicted by an ideal mixing rule. The results showed that the use of binary mixture of {[bpy][BF4] + [bpy][Tf2N]} at a mole solvent composition of 0.7 for [bpy][BF4] improves both the distribution ratio of toluene and the selectivity with respect to those of sulfolane. Thus, this mixed ionic liquid could be considered an environmentally benign alternative solvent for the aromatic extraction process.

► Ionic liquids as extraction solvents for aromatics.
► High capacity and selectivity are required.
► [bpy]Tf2N shows higher capacity but lower selectivity than sulfolane.
► [bpy]BF4 shows lower capacity but higher selectivity than sulfolane.
► Mixed [bpy]Tf2N + [bpy]BF4 shows both higher capacity and selectivity than sulfolane.