Simplified COSMO-SAC-based phase equilibria predictions for extractive distillation of toluene-heptane mixtures using ionic liquids

A comparative study of isobaric Vapor-Liquid-Liquid Equilibria (VLLE) prediction using the COnductor like Screening MOdel Segment Activity Coefficient (COSMO-SAC) model was performed on nine Ionic Liquids (ILs) and their extractive properties were evaluated for the separation of toluene/1-heptane mixtures using IL-based extractive distillation. For better insights into the IL-hydrocarbon mixture behavior, the ILs were classified on the basis of their constituent cations, i.e. as having imidazolium moiety or pyridinium moiety. A-priori activity coefficient calculation for each phase was performed by the COSMO-SAC method. Compositions of liquid phases were determined by the Liquid-Liquid flash relation of Rachford-Rice and the vapor-phase compositions were obtained by the modified Raoult's Law formulation. Reasonable description of phase behavior of IL-aromatic-aliphatic mixtures was obtained at temperatures 323 K and 363 K. The overall root mean square deviation (rmsd) considering all 104 datasets and 936 data points was found to be 6.83%, which is satisfactory given that our simplified method is also predictive in nature. For ascertaining the robustness of our algorithm, it was compared with the Genetic Algorithm (GA) based GA-NRTL and GA-UNIQUAC models to correlate the experimental VLLE data.