Ionic liquids (ILs) have received much attention in the last two decades. One of the important applications is to use this relatively new class of compounds for the separation of azeotropic mixtures via extractive distillation. In this paper, overall extractive distillation processes of two azeotropic separation systems using a favorable ionic liquid as entrainer are rigorously developed. The optimized design flowsheets are compared with the conventional processes using an industrial entrainer. The two ionic liquid extractive distillation systems include separating acetone and methanol using 1,3-dimethylimidazolium dimethylphosphate ([MMIM][DMP]) as entrainer and another system of separating isopropyl alcohol and water using 1-ethyl-3-methylimidazolium acetate ([EMIM][OAC]) as entrainer. The potential drawbacks of using an ionic liquid in the extractive distillation systems are given in the paper. It is found that the degradation temperature and high normal boiling point temperature of the ionic liquids in these two systems require the IL processes to use high vacuum operating conditions, thus making them only economically comparable to the conventional processes.

Cyclohexanol is an important precursor in synthesizing intermediates of Nylons and also plasticizers. In this paper, a plantwide reactive-distillation process for the production of cyclohexanol by direct hydration of cyclohexene with water has been studied. Design with excess water is needed to economically increase conversion of cyclohexene to 99.9%. The optimal design of the proposed flowsheet also makes use of the natural liquid–liquid splitting of the binary cyclohexanol–water azeotrope. Realistic fresh cyclohexene feed with impurity of cyclohexane was also considered. This inert is designed to leave the system in the organic outlet stream of a decanter on top of the reactive-distillation column. The reboiler duty requirement of the proposed design flowsheet is compared with existing processes in open literature. It is found that significant energy savings can be realized by using this design.