Multilevel Comparison of Ionic Liquid Separation of a Methanol/Methyl Acetate/Water Mixture

This paper aimed to investigate whether ionic liquids (ILs) with excellent phase equilibrium abilities were also economically superior at the process level. Comprehensive comparisons of seven different types of ILs for the separation of a methanol/methyl acetate/water mixture were performed from molecular, phase equilibrium, to the process level. The validated NRTL model was used for phase equilibria and process simulation and COSMO-based sigma profiles for mechanism analysis. Energy consumption, energy cost, and total annual cost (TAC) were carried out to quantify process performances. Heat pump-assisted IL-extractive distillation processes were proposed. The results indicated that the heat pump-assisted schemes saved the TAC up to 51.2%. The process economic performances of 1-ethyl-3-methylimidazolium acetate ([EMIM][Ac]), 1-hexyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium methylsulfate, and 1-ethyl-3-methylimidazolium thiocyanate were equally well, while that of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide was the worst at all levels. The TAC savings of the [EMIM][Ac] process ranged from 3.4 to 48.2% compared with the latter six ILs. The order of performance of ILs in terms of relative volatility or binary phase diagram was nearly the same as the process level, while using the minimum amount of ILs required to break azeotropes as an indicator was of a different order.