COSMO-RS-Based Ionic-Liquid Selection for Extractive Distillation Processes

A solvent selection methodology for extractive distillation processes is applied to identify promising ionic liquid (IL) solvents for the following separation cases: methylcyclohexane/toluene, 1-hexene/n-hexane, and ethanol/water. Thermodynamic and phase stability analyses are done in order to understand the strong interactions between the solutes and ILs (solvents) and vice versa. The solvent preselection is done with COSMOtherm software (version C2.1, release 01.11a). Selectivities and activity coefficients at infinite dilution are predicted. Variations in the IL structure (in the cations and anions) and their effect on the solubility and selectivity are theoretically studied and experimentally confirmed. Suitable Its are selected by experimentation at finite dilution (real solutions). A suitable IL for the separation of 1-hexene from n-hexane yielding a better performance than the conventional solvent N-methyl-2-pyrrolidone (NMP) was not found. Tetracyanoborate-based ILs seem to be promising solvents for the extractive distillation of toluene from methylcyclohexane as a replacement of the conventional solvent NMP. For the separation of ethanol from water, the ILs 1-ethyl-3-methyl-imidazolium acetate and 1-ethyl-3-methyl-imidazolium dicyanamide (due to its thermal stability) seem to be suitable candidates and possible replacements of ethylene glycol, which is used as a conventional solvent for the separation of this mixture.