(215c) Transport Properties of Imidazolium Ionic Liquids Saturated with Compressed Gases

The inherent characteristics of ionic liquids allow for their potential utilization in a myriad of engineering applications, such as reaction media, extractive distillation, pre- and post-combustion, CO₂ capture, lubrication, refrigeration, etc. Many of the aforementioned engineering applications involve biphasic systems of ionic liquids and compressed gases. To properly characterize and design such systems, thermodynamic phase equilibrium data as well as transport property data is needed. Transport data for biphasic ionic liquid and gas systems in the literature is less abundant than solubility data. Here, the liquid thermal conductivity, viscosity, density, and self-diffusivity of gas-saturated ionic liquids are measured over various temperatures and pressures ranging up to 125 ⁰C and 200 bar. Systems investigated and reported herein include various imidazolium based ionic liquids coupled with carbon dioxide as well as several hydrofluorocarbon (HFC) gases. Investigated systems have shown a relatively significant decrease in viscosity even with just a slight increase in dissolved gas composition. This in turn, results in an increase in self-diffusion. However, for the thermal conductivity of the systems investigated, an increase of gas composition has shown a much more moderate to negligible effect even to high compositions. For CO₂/IL systems, the thermal conductivity of the system is generally dominated by that of the pure ionic liquid across a large composition range where most of the changes are due to hydrostatic effects. For HFC gases, composition effects are more pronounced with a moderate decrease in the thermal conductivity of the IL phase. The qualitative behavior of thermal conductivity seems more dependent on the relative polarity of the dissolved component. The observed behavior for all systems investigated indicates that simple composition-based mixing rules for mixture properties based upon pure component properties would not be appropriate.