(102c) Infinite Dilution Partition Coefficients of Naphthalene and Benzene in the [Bmim][Pf6]-Co2 System

Ionic liquids are molten organic salts that have very low vapor pressure, are nonflammable, and can dissolve many organic and inorganic substances. Ionic liquids used with supercritical CO2 have many potential applications in environmental and chemical fields such as desulfurization, absorption and syntheses. However, many of these applications require phase partitioning data of organic solutes with ionic liquids and CO2 and these data are lacking. In this work, infinite dilution partition coefficients Kinf of naphthalene and benzene in the 1-butyl-3-methylimidazorium hexafluorophosphate ([bmim][PF6]) + carbon dioxide system were measured at pressures up to 15 MPa with a chromatographic technique, where Kinf was defined as the weight ratio of solute in the CO2 phase to that in the ionic liquid phase. The ionic liquid, [bmim][PF6], was used as the stationary phase in a packed column and CO2 was used as the mobile phase. Detection of solutes was by UV/vis spectroscopy. Columns were prepared with support materials (chromosorb W AW) that were coated with ionic liquid using dichloromethane solvent and rotary evaporator. Measured partition coefficients of naphthalene in [bmim][PF6] + CO2 compared well with capillary column data of Planeta and Roth (2004). The Kinf values of benzene increased with increasing pressure, which can be attributed to the increase in CO2 density and the probable expanded liquid state of [bmim][PF6]. The measured Kinf of benzene in [bmim][PF6] + CO2 were one order of magnitude higher than those of naphthalene over most of the pressures (5 to 15 MPa) and temperatures (313 to 333 K) studied. The Sanchez - Lacombe EOS (SL EOS) was chosen to correlate the data, since it has been successfully applied to nonvolatile compounds such as polymers and its parameters can be related to molecular characteristics of the fluid. To apply the SL EOS, parameters were determined from PVT data. For a ternary system, there are three possible binary interaction parameters. The solute-CO2 and [bmim][PF6]-CO2 binary interaction parameters were determined by fitting available phase equilibria data. The solute-ionic liquid binary interaction parameter was determined by fitting the partition coefficient data. Calculation results showed that the equation could represent experimental data well. From the results, we concluded that the infinite dilution partition coefficients could be reliably measured with a packed column chromatographic technique and the Sanchez-Lacombe EOS could be applied to correlate the data. The Sanchez-Lacombe equation can be used to estimate partition coefficients at other conditions and can be possibly applied to other organic solute + ionic liquid + supercritical fluid systems.