Infinite dilution partition coefficients of benzene derivative compounds in supercritical carbon dioxide + ionic liquid systems: 1-butyl-3-methylimidazolium chloride [bmim][Cl], 1-butyl-3-methylimidazolium acetate [bmim][Ac] and 1-butyl-3-methylimidazolium octylsulfate [bmim][OcSO4

Abstract

Infinite dilution partition coefficients of benzene and benzene derivative compounds (chlorobenzene, bromobenzene, toluene, ethylbenzene, benzaldehyde, benzyl alcohol and phenol) between supercritical carbon dioxide and ionic liquids (1-butyl-3-methylimidazolium chloride [bmim][Cl], 1-butyl-3-methylimidazolium acetate [bmim][Ac] and 1-butyl-3-methylimidazolium octylsulfate [bmim][OcSO4]) were measured with a packed-column chromatographic technique. The Sanchez–Lacombe equation of state was used to correlate the data and could describe the qualitative changes of the infinite dilution partition coefficients over a wide range of temperatures (313–352K) and pressures (5–15MPa). A linear solvation energy relationship (LSER) model, LSER-δ, was developed for compressible phases that uses solute, solvent and ionic liquid solubility parameters. Partition coefficients were generally in the order of solute volatility with the exception of hydrogen bonding solutes. LSER solute volume (McGowan's volume, V) and solute dipolarity/polarizability (S) greatly affected the partition coefficient values. It was found that the McGowan's volume can be considered as a function of the CO2 solubility parameter, which may be helpful in extending LSER theory to supercritical fluid systems. Both models could describe the partition coefficient well and were useful in understanding some of the interactions of the solute with the supercritical CO2 and ionic liquid phases.