Tetrathiocyanatocobaltate and bis(trifluoromethylsulfonyl)imide-based ionic liquids as mass agents in the separation of cyclohexane and cyclohexene mixtures by homogeneous extractive distillation

In this work, the suitability of two tetrathiocyanatocobaltate-based ionic liquids, namely bis(1-ethyl-3-methylimidazolium) tetrathiocyanatocobaltate ([emim]2[Co(SCN)(4)]) and bis(1-butyl-3-methylimidazolium) tetrathiocyanatocobaltate ([bmim](2)[Co(SCN)(4)]), and two bis(trifluoromethylsulfonyl)imide-based ionic liquids, namely 1-ethyl-4-methylpyridinium bis(trifluoromethylsulfonyl)imide ([4empy][Tf2N]) and 1-butyl-4-methylpyridinium bis(trifluoromethylsulfonyl)imide ([4bmpy][Tf2N]), as mass separating agents to separate cyclohexane and cyclohexene mixtures by homogeneous extractive distillation was analysed. Isothermal vapour-liquid equilibria (VLE) for the binary systems {cyclohexane or cyclohexene + ionic liquid} and the ternary systems {cyclohexane + cyclohexene + ionic liquid} were determined at 323.2, 363.2 and 403.2 K by headspace-gas chromatography (HS-GC). All the ternary systems were studied with a solvent-to-feed ratio on mass basis of 10. In addition, solvent-to-feed ratios on mass basis of 8 and 6 were evaluated for the ternary systems containing [Tf2N]-based ionic liquids. The Non-Random Two Liquids (NRTL) model was used to describe the experimental VLE data accurately. The values of cyclohexane/cyclohexene relative volatilities provided by the four ionic liquids enhanced those obtained with conventional mass agents such as ethylene glycol. The highest relative volatilities were obtained with the [Co(SCN)(4)]-based ionic liquids. However, taking into account the viscosity and thermal stability of the four ionic liquids studied here, the [4empy][Tf2N] was considered the most promising alternative from an extractive distillation approach. (C) 2021 Elsevier Ltd.

Automated summary

This study analyzed the suitability of four ionic liquids for separating cyclohexane and cyclohexene mixtures, with tetrathiocyanatocobaltate-based ionic liquids showing the highest relative volatilities and bis(trifluoromethylsulfonyl)imide-based ionic liquids being the most promising in terms of viscosity and thermal stability. The Non-Random Two Liquids (NRTL) model accurately described the experimental vapor-liquid equilibria data for the systems studied.