Ionic liquids as entrainer in extractive distillation for effectively separating 1-propanol–water azeotropic mixture

Economically separating 1-propanol (NPA) from water is an emergent issue for producing pharmaceutical intermediates such as n-propyl acetate, n-propylamine and so on. In this work, fourionic liquids (ILs) 1-ethyl-3-methylimidazolium thiocyanate ([EMIM][SCN]), 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]), 1,3-dimethylimidazolium methylsulfate ([MMIM][MS]), 1,3-dimethylimidazolium dimethylphosphate ([MMIM][DMP]) were introduced as potential entrainers for separating NPA–water azeotropic mixture. The results show that [MMIM][MS] is the most suitable entrainer compared with other ILs from the analysis of vapor–liquid equilibrium and relative volatilities. The extractive distillation process with the entrainer regeneration system of flash tank and stripper was employed and optimized by the two-step optimization method. The results show that total annual cost and energy consumption per product flow rate were reduced by 39.79% and 60.47% compared with literature. In addition, the efficiency indicator of extractive section, efficiency indicator of per tray in extractive section, carbon dioxide emissions were also selected as the evaluation index for selection of operating parameters and calculated for different cases. The CO2 emissions of the optimal design can be reduced by 60.98% from environmental aspect.