Ionic liquid structural effects on solute partitioning in biphasic ionic liquid and supercritical carbon dioxide systems

An overview of measurements of partition coefficient measurements reported in the literature is given. New infinite dilution partition coefficients for aromatic components (benzyl alcohol, phenol, acetophenone, and chlorobenzene) between ionic liquid phase and supercritical CO2 phase are reported as determined with a chromatographic technique. Three types of solutes and six types of ionic liquids were studied. Infinite dilution partition coefficients became larger according to [bmim][Tf2N], [bmim][PF6], [bmim][BF4], [bmim][Cl]. For the case of benzyl alcohol, the weight basis partition coefficient had its highest value (0.180) in [bmim][Tf2N] at 333.2 K and 20 MPa and its lowest value (0–0.003) in [bmim][Cl] at 333.2 K and at pressures from 12 to 16 MPa. The values of the infinitely dilute partition coefficients were not sensitive to the alkyl chain length of the ionic liquids [emim][PF6], [bmim][PF6], and [hmim][PF6] and could be correlated with the Sanchez–Lacombe equation of state. Trends of the infinite dilution partition coefficients for the same cation, [bmim] for the anions studied seemed to correlate with the charge per surface area of the anion.