Ionic-liquid based separation of azeotropic mixtures

Abstract

y A methodology for screening of ionic liquids (ILs) as entrainers and for design of ILs -based separation processes in various homogeneous binary azeotropic mixtures is presented through two case studies: ethanol + water and isopropanol + water. ILs as entrainers were screened based on a combination of criteria such as stability, toxicity, environmental impacts, their miscibility in the target solute component (water) and their Hildebrand solubility parameter group contribution. The best candidates for the aqueous systems were selected, namelyl- Ethyl- 3 -Methylimidazolium Ethylsulfate [C2MIM][EtSO4], l-Ethyl- 3 –Methylimidazolium Dicyanamide [C2MIM][N(CN)2], l- Ethyl- 3 -Methylimidazolium Acetate [C2MIM][Ac], and 1,3 -Dimethylimidazolium Dimethyl phosphate [C1MIM][DMP]. Extractive distillation with a solvent recovery was simulated in Pro II simulator to evaluate the energy requirement to obtain 99.8 % mol purity of alcohol. Based on minimum energy requirement of each IL entrainer, [C1MIM][DMP] was chosen as the final candidate for the ethanol + water, given an energy savings of 22 % compared to the conventional solvent (Ethyleneglycol). The design flexibility for a zeotropic separation process with the same ILs entrainer, product purity, and designed parameters was investigated for the isopropanol + water azeotrope. [C1MIM][DMP] was excluded since the extraction with [C1MIM][DMP] could not give 99.8 % mol purity of the alcohol with a reasonable number of theoretical stages. By fixing all design parameters with the same [C2MIM][N(CN)2] as entrainer, anincrease in size of alcohol from ethanol to isopropanol gives a lower overall energy consumption because the isopropanol + water had a weaker in teraction than the ethanol + water leading to the easier to extract water from isopropanol than extracting of water from ethanol.