Ionic Liquids and Supercritical CO2

Ionic liquids (ILs) are organic salts that have melting points around room temperature. They have received tremendous attention recently due to their low volatility and subsequent potential to reduce air pollution if used as replacements for volatile organic solvents. As a result, they have the potential to be used in a wide variety of chemical processing applications, including as solvents for reactions, gas separations, extractive distillation, lubrication, heat transfer, and polymer processing. Physical properties and the phase behavior of ionic liquids with a wide range of compounds are important in evaluating ILs for many of these applications. One area of particular interest in our research at the University of Notre Dame is the interaction of ionic liquids with high pressure or supercritical CO2. We will discuss three aspects of ionic liquid/CO2 systems. First, we will show the phase behavior of CO2 with ionic liquids and how the solubility of the gas in the liquid is influenced by the choice and structure of the cation and the anion. Second, we will show how supercritical CO2 can be used to extract solutes from ionic liquids. Third, we will demonstrate how lower pressure gaseous carbon dioxide can cause a phase separation in organic and aqueous solutions containing ILs. Finally, we will touch on the implications of the interesting phase behavior that we have found for CO2/ionic liquid mixtures.