(309c) From Supercritical Fluids to Ionic Liquids

One of the keys to efficient and selective separation processes is the ability to tune the power of the solvent and its interactions with the species being recovered. This places the emphasis on the design of materials used to facilitate the separation. Materials design for separations provides an alternative to energy-driven separations like distillation. Supercritical fluids and ionic liquids are two classes of materials that afford this tunability. Supercritical fluids, like carbon dioxide, can be tuned by varying temperature and pressure, which can exquisitely tune the density, and correspondingly, the solvent power of the fluid. Supercritical fluids can also be tuned by additions of small amounts of cosolvent that ‘cluster’ around dissolved solutes. We will show how both of these techniques have been used to facilitate separations using supercritical fluids. Ionic liquids can be tuned by careful choice of cation, anion and substituents. They allow the design of solvents with multiple functionalities, ranging from polar to nonpolar, that can be extended into reversible reactions. We will give examples of the design of ionic liquids for a variety of separation processes.