(662a) Provoking Phase Changes for Extractive Separations
Conventional extraction involves heterogeneous systems with fixed distribution coefficients. We exploit novel solvent systems to change phase behavior at will to give (or remove) homogeneity and to adjust distribution coefficients. Our new solvents have phase changes ?built in? that will enable the use to go from a miscible system to an immiscible one with a very good separation. We report here two classes of such solvents using CO2 as the miscibility switch ? gas expanded liquids (GXLs) and reversible ionic liquids (RevILs). Normally a mixed solvent would carry with its use the disadvantage of the downstream separation for reuse, but with CO2 this step becomes no more than a facile pressure release. The GXLs operate because of the limitless solubility CO2 of in most organics and its relative immiscibility in water. A miscible aqueous/organic mixture becomes immiscible at a few tens of bars of CO2. Examples shown include isomer separations, recovery of phase transfer catalysts, and the combination of homogeneous reactions with heterogeneous separations for the recycle of homogeneous catalysts.. RevILs are formed when CO2 is bubbled at ambient conditions through a precursor, such as a relatively nonpolar liquid amadine, guanidine, or amine. Nonpolar compounds such as alkanes are completely miscible with the precursor, yet nearly completely immiscible with the RevIL. Such a phase change leads to a plethora of opportunities for separations, ranging from CO2 capture from stack gases and harvesting of oil sands to additional methods for combining homogeneous reactions with heterogeneous separations. The overriding message of this work is that devising and controlling phase changes creates new sustainable separations.