Separation of the Methanol-Ethanol-Water Mixture Using Ionic Liquid

Vapor pressure data for the binary systems (water/methanol/ethanol + 1-ethyl-3-methylimidazolium acetate ([EMIM](+)[Ac](-))) and the ternary systems (methanol + water + [EMIM](+)[Ac](-), ethanol + water + [EMIM](+)[Ac](-), and methanol + ethanol + [EMIM](+)[Ac](-)) were measured by a modified equilibrium still. For the above systems, the maximum average relative deviation between experimental data and the UNIFAC-Lei model predicted values was 7%, confirming the prediction accuracy of the UNIFAC-Lei model. Thus, this model was further used to predict the isobaric vapor-liquid equilibrium (VLE) data at 101.3 kPa for the methanol + water + [EMIM](+)[Ac](-), ethanol + water + [EMIM](+)[Ac](-), and methanol + ethanol + [EMIM](+)[Ac](-) systems at a fixed mole fraction of ionic liquid (IL) (x(IL) = 0.2). It was demonstrated that the ionic liquid [EMIM](+)[Ac](-) was an appropriate entrainer to separate the methanol-ethanol-water mixture. On this basis, the extractive distillation process was simulated using the rigorous equilibrium (EQ) stage model. The results showed that the entrainer consumption, the heat duty of total reboilers, and the heat duty of total condensers decrease by 25, 6, and 6%, respectively, when [EMIM](+)[Ac](-) replaces the conventional entrainer ethylene glycol (EG). Furthermore, the sigma-profiles and excess enthalpies obtained by the COSMO-RS model provided theoretical insights into the separation mechanism at the molecular level.