(386g) High-Pressure Transport Properties and Phase Equilibria of Imidazolium Ionic Liquids with CO2 and R-134a

Ionic liquids (ILs) and compressed gases are found in a number of proposed processes in extractions, reactions, and engineering applications. This investigation presents experimental and modeling results of the phase behavior, phase equilibria, viscosity and diffusivity of imidazolium ionic liquids with compressed carbon dioxide and 1,1,1,2-tetrafluoroethane (R-134a). Both gases are very soluble in ionic liquids. However with R-134a, all of the ionic liquids studied have regions in temperature and pressure of miscibility and criticality exist at certain temperatures and pressures; Type V systems from the classification scheme of Scott-van Konynenburg. CO₂ has no known regions of miscibility with ionic liquids (possibly Type III). This has important ramifications on potential applications. The presence of the dissolved gases significantly increases the mass transport properties of ionic liquids. While ILs often have higher ambient viscosity than common organic solvents, mixtures of ILs with the gases can decrease the viscosity by 80+%. This decrease in viscosity increases the self-diffusivity of the gases. Effects of the structure of the cation and anion were measured and compared for both thermodynamic and transport properties.