Vapor liquid equilibrium prediction of methanol-ionic liquid systems using UNIFAC model to select alternative working fluids of absorption cycle

The purpose of this paper is to study the working fluids in absorption cycle containing methanol (CH3OH) as the refrigerant and the imidazolium ionic liquid (IL) as the absorbent. The UNIFAC model was implemented to correlate the published experimental vapor liquid equilibrium data of CH3OH-IL working fluids and 14 new group interaction parameters between CH3OH and ILs were obtained. Method reliability and applicability were evaluated by calculating the vapor pressures of five CH3OH-IL working fluids. The ILs contained 1-methyl-3-methylimidazolium dimethylphosphate ([Dmim][DMP]), 1-ethyl-3-methylimidazolium ethyl sulfate ([Emim][ES]), 1-ethyl-3-methylimidazolium diethylphosphate ([Emim][DEP]), 1-butyl-3-methylimidazolium dibutylphosphate ([Bmim][DBP]), and 1-ethyl-3-ethylimidazolium diethylphosphate ([Eeim][DEP]). The average absolute relative deviations for the vapor pressures between the calculated results and the experimental data were 0.91%, 1.67%, 0.66%, 0.75%, and 2.1%, respectively. Then, the CH3OH-IL systems without experimental data were predicted. Comparisons of the vapor pressure and excess Gibbs function of the studied CH3OH-IL systems, CH3OH-[Hmim][DEP] (1-hexyl-3-methylimidazolium diethylphosphate) system, as an alternative working fluid, was found to have potential to improve the absorption cycle performance upon more research work.