Pure component pressure-volume-temperature (pVT) data for five imidazolium-based ionic liquids, 1-ethyl-were measured with a bellows type apparatus. High-pressure densities of ionic liquids showed smooth trends with temperature and pressure variations except for [emim][PF 6 ] which exhibited a solid phase transition at temperatures below 352.7 K and which solidified at 100 MPa at 352.7 K. Solid densities were measured and were about 6.3 % higher than those of the liquid. Isothermal compressibilities and thermal expansion coefficients were calculated from the Tait equation that was fit to the pVT data. Isothermal compressibilities increased with alkyl chain length which is probably related to the ionic liquid free volume.

Pressure-density-temperature (pFT) data for three types of ionic liquid, [emim] and [bmim][Cl], were measured with a bellows type dilatometer at temperatures up to 452 K and at pressures up to 200 MPa. The Tait equation could correlate the density data as a function of temperature and pressure to within an average relative deviation (ARD) of 0.014 %. The thermal expansion coefficients and the isothermal compressibilities were estimated with the Tait equation, and their variations with temperature and pressure, dR p /dT and dk T /dp, were found to be negative. Lattice type equations of state were applied to correlate the data. The densities could be correlated to within an ARD of 0.21 % and 0.067 %, for the Sanchez-Lacombe equation of state and the ε-modified Sanchez-Lacombe equation of state, respectively. The equation-of-state parameters determined should be useful in estimating the properties of mixtures and in estimating the phase equilibria of binary and multicomponent systems.

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Ionic liquids combined with supercritical fluid technology hold great promise as working solvents for developing compact processes. Ionic liquids, which are organic molten salts, typically have extremely low volatility and high functionality, but possess high viscosities, surface tensions and low diffusion coefficients, which can limit their applicability. CO 2 , on the other hand, especially in its supercritical state, is a green solvent that can be used advantageously when combined with the ionic liquid to provide viscosity and surface tension reduction and to promote mass transfer. The solubility of CO 2 in the ionic liquid is key to estimating the important physical properties that include partition coefficients, viscosities, densities, interfacial tensions, thermal conductivities and heat capacities needed in contactor design. In this work, we examine a subset of available high pressure pure component ionic liquid PVT data and high pressure CO 2 -ionic liquid solubility data and report new correlations for CO 2 -ionic liquid systems with equations of state that have some industrial applications including: (1) general, (2) fuel desulfurization, (3) CO 2 capture, and (4) chiral separation. New measurements of solubility data for the CO 2 and 1-butyl-3-methylimidazolium octyl sulfate, [bmim][OcSO 4 ] system are reported and correlated. In the correlation of the CO 2 ionic liquid phase behavior, the Peng-Robinson and the Sanchez-Lacombe equations of state were considered and are compared. It is shown that excellent correlation of CO 2 solubility can be obtained with either equation and they share some common characteristics regarding interaction parameters. In the Sanchez-Lacombe equation, parameters that are derived from the supercritical region were found to be important for obtaining good correlation of the CO 2 -ionic liquid solubility data.