Abstract

High pressure carbon dioxide was dissolved in ionic liquid+toluene mixtures to obtain the conditions of pressure and composition where a liquid-liquid phase split occurs at constant temperature. Ionic liquids (ILs) with four different cations paired with the bis(trifluoromethylsulfonyl)imide ([Tf2N](-)) anion were selected: 1-hexyl-3-methylimidazolium ([hmim](+)), 1-hexyl-3-methylpyridinium ([hmpy](+)), triethyloctylphosphonium ([P-2228](+)), and tetradecyltrihexylphosphonium ([P-66614](+)). The solubility of CO2 was measured in the liquid mixtures at temperatures between 298 and 333 K and at pressures up to 8 MPa, or until the second liquid phase appeared, for initial liquid phase compositions of 0.30, 0.50, and 0.70 mole fraction of IL. Ternary isotherms were compared with the binary solubility of CO2 in each IL and pure toluene. The lowest pressure for separating toluene in a second liquid phase was achieved by decreasing the temperature of the system, increasing the amount of toluene in the initial liquid mixture and using [hmim][Tf2N]. (c) 2015 American Institute of Chemical Engineers AIChE J, 61: 2968-2976, 2015