Computer-aided design and process evaluation of ionic liquids for n-hexane-methylcyclopentane extractive distillation

Ionic liquids (ILs) are highly attractive entrainers for separating close-boiling alkane-cycloalkane mixtures in extractive distillation processes while studies on this particular topic are still scarce. This work employs computer-aided molecular design (CAMD) and process simulation to identify suitable ILs for the extractive distillation of n-hexane-methylcyclopentane, a representative alkane-cycloalkane mixture. A large number of experimental data on the infinite dilution activity coefficient of methylcyclopentane and vapor-liquid equilibria of relevant systems are collected from literature to validate the reliability of the employed UNIFAC-IL model, which is the basis of CAMD and process simulation. Combining the UNIFAC-IL model and two group contribution models of IL physical properties, a mixed integer nonlinear programming (MINLP) problem is then formulated for the CAMD of ILs. The top IL candidates pre-identified from MINLP-CAMD are further introduced into Aspen Plus for process simulation and evaluation. By comparing their process performances with the benchmark solvent N-methyl-2-pyrrolidinone, 1-nonyl-imidazolium thiocyanate ([C9Im][SCN]) is consequently identified as the optimal entrainer.