(216a) “Smart” Solvents for Extractions and Purifications

Conventional solvent removal in chemical processing involves distillations and extractions. An environmentally and potentially economically superior method will entail having it undergo an abrupt change in properties to facilitate the separation. We discuss here such ?smart? solvents, where some stimulus ? heat, light, pH, etc. ? causes a significant discontinuity in solvent properties. These will be compared to tunable solvents, such as supercritical fluids, nearcritical fluids, and gas-expanded liquids, where a small change in property yields a much larger (but continuous) change in property. In both cases it is virtually mandatory to have such changes be reversible to permit solvent recycle and reuse.

We present here two different types of smart solvents we have developed and used: reversible ionic liquids and ?volatile? DMSO substitutes. In the former case, CO2 is added to a precursor (amidine, guanidine, or amine) to form an ionic liquid at room temperature; the processes are reversed by sparging an inert gas or by heat. In the latter case we discuss piperylene sulfone, with solvent properties very close to DMSO, but with the removal built in. Just above 100°C, piperylene sulfone breaks down into two gaseous molecules which can be cooled and recombined for recycle. Examples are presented describing the application of these smart solvents to the extraction of alkanes from oil shale and the post-reaction purification of synthesis products, including catalyst recycle.