Liquid–Liquid Extraction of Toluene from n-Heptane with [emim][FSI], [emim][Tf2N], [emim][BETI], [emim][DCA], and [emim][TCM]

Abstract

Ionic liquids (ILs) (e.g., 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([emim][Tf₂N])) have been widely investigated as solvents for liquid–liquid extraction of aromatics from aliphatics. Here, we present new liquid–liquid equilibrium (LLE) data with n-heptane and toluene at 295.0 K for two similar ILs, 1-ethyl-3-methylimidazolium bis(pentafluoroethylsulfonyl)imide ([emim][BETI]) and 1-ethyl-3-methylimidazolium bis(fluoromethylsulfonyl)imide ([emim][FSI]), where the two −CF₃ groups in the [Tf₂N]⁻ anion have been replaced with −C₂F₅ groups ([BETI]⁻) and -F groups ([FSI]⁻). We include NRTL model predictions based on parameters fit to binary data. In comparison to [emim][Tf₂N], [emim][BETI] has poorer selectivity toward toluene over n-heptane and poorer distribution ratios, but [emim][FSI] has significantly improved values, primarily from reduced n-heptane capacity. In addition, we present LLE data for two previously studied ILs with exceptionally high toluene/heptane selectivities, [emim][DCA] and [emim][TCM]. Our data for [emim][DCA] agree extremely well with one of the two data sets in the literature, providing clarification on the literature inconsistency. Unfortunately, the literature value of the solubility of toluene in [emim][TCM] is significantly overestimated, which affects the ternary system tie lines at high toluene content. Nonetheless, [emim][TCM] is an excellent IL for toluene extraction from heptane, having selectivities and distribution ratios comparable to or slightly better than those of [emim][FSI].