Prediction of ionic liquid solubilities in supercritical CO2 + co-solvent systems using Peng–Robinson equation of state with accurate critical temperature

Abstract

Supercritical fluid deposition (SCFD) using supercritical carbon dioxide (CO2) to impregnate substrates with ionic liquids (ILs) has attracted considerable attention for the preparation of porous-supported ILs. Because ILs are generally insoluble in pure CO2, it is essential to estimate the solubilities of ILs in supercritical CO2 + co-solvent systems for developing the SCFD process. In this study, a methodology was developed to predict the solubility of ILs in supercritical CO2 with co-solvents using the corresponding binary phase-equilibrium data. For the prediction, the binary interaction parameters for the Peng–Robinson equation of state (PR-EoS) were determined using the correlations to each phase-equilibrium system (i.e., IL + CO2, CO2 + co-solvent, and IL + co-solvent). The predictive model using the PR-EoS, which included a re-determined critical temperature as a pure component parameter of ILs, could reproduce the effects of the temperature, pressure, and co-solvent concentration on the IL solubilities in the supercritical fluid phase without any fitting parameters for the ternary systems. The average absolute relative deviations based on the logarithmic scale for the predictions were <23 %, indicating that the methodology was acceptable for describing the IL solubilities in the supercritical CO2 + co-solvent system.