A study on the liquid–liquid equilibrium of 1-alkyl-3-methylimidazolium dialkylphosphate with methanol and dimethyl carbonate

Abstract

Methanol and dimethyl carbonate (DMC) mixture is present in the industrial manufacturing process of DMC, which is made from the catalytic oxidative carbonylation of methanol. The separation of methanol and DMC is important but difficult due to the formation of an azeotropic mixture. This work has been focused on a study of phosphoric-based ionic liquids (ILs) as green solvents for the separation of methanol and DMC in the extraction process. The knowledge of liquid–liquid equilibrium (LLE) of this mixture is essential for the design of the extraction separation process. For this reason, LLE data for the ternary systems {methanol+DMC+1-methyl-3-methylimidazolium dimethylphosphate ([MMIM][DMP])} and {methanol+DMC+1-ethyl-3-methylimidazolium diethylphosphate ([EMIM][DEP])} were measured at T=(298.2 and 313.2)K and atmospheric pressure. The solute distribution ratio and selectivity of the methanol, derived from the tie-lines data, were calculated and analyzed in order to evaluate the capacity of the studied ILs as solvents in liquid extraction process. The experimental results show that the values of selectivity for the studied ILs follow this order: [MMIM][DMP]>[EMIM][DEP]. Finally, the experimental LLE data for the studied ternary systems were compared with the calculated values obtained by means of the non-random two liquid (NRTL) model. The NRTL model was verified to accurately correlate the experimental LLE data.