Energetic aspects of imidazolium-based ionic liquid regeneration from aqueous solutions

Abstract

Separation processes are common in chemical industry. Higher prices of energies and environmental threats led to increased interest in the design of new and the optimization of real technologies. As an example, the effort to replace conventional solvents in extractive distillation and liquid extraction can be used. In the last years, ionic liquids have emerged as suitable alternative solvents. The presented work deals with the separation of a tert-butyl alcohol–water mixture by extractive distillation using a methylimidazolium-based ionic liquid (1-ethyl-3-methylimidazolium bromide, [EMim]Br). For the ionic liquid regeneration from its aqueous solution (bottom product from the extractive distillation column working at atmospheric pressure), an alternative separation method, evaporation at reduced pressure, was assumed. Two case studies of ionic liquid (IL) regeneration were evaluated. In the first case, pressure of the liquid bottom stream was reduced by passing through a throttle valve and the created vapor–liquid stream entered an evaporator in which the extraction solvent is pre-concentrated to be re-used in the extractive distillation column. In the second case, after the pressure reduction in the throttle valve, the vapor phase (pure water steam) was separated in a phase separator, and the stream entering the evaporator was the concentrated liquid mixture of [EMim]Br with water. Both regeneration procedures were analyzed for the heat and cooling consumption duty and compared to that corresponding to IL regeneration by distillation.