Measurement of infinite dilution partition coefficients of isomeric benzene derivatives in [bmim][Tf₂N]-CO₂ biphasic system and correlation with the ePC-SAFT equation of state

Infinite dilution partition coefficients of isomeric benzene derivatives in the [bmim][Tf₂N] (1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide)-CO₂ biphasic system were measured with a supercritical fluid chromatography technique at pressures of 6–15 MPa and at temperatures of 313–353 K. The partition coefficients of o-cresol were always larger than those of m and p-cresol, while those of o-xylene were always smaller than those of m and p-xylene for all temperatures and pressures. The partition coefficients of the solutes in the ionic liquid-CO₂ systems were found to be in the order of their vapor pressure in accordance with previous reports. The partition coefficient data were correlated with the ePC-SAFT (electrolytes perturbed-chain statistical associating fluid theory) equations and with the empirical LSER (Linear Solvation Energy Relationship)-δ model. The overall average relative deviation (ARD) of the ePC-SAFT equation using interaction parameters between ionic liquid and solute as fitting parameters was 8.2% and compared well with the LSER-δ model (7.5%). In one approach to improve the prediction capability of the ePC-SAFT equation, literature data of infinite dilution activity coefficients of toluene in the [bmim][Tf₂N]-toluene biphasic system at atmospheric pressure were used to determine ePC-SAFT interaction parameters between [bmim][Tf₂N] and toluene. Although this approach improved the ePC-SAFT description of the [bmim][Tf₂N]–CO₂–toluene system, the correlation was qualitative at high pressure and can be attributed to CO₂ in the liquid phase that affects [bmim][Tf₂N]-toluene interactions.