For any chemical process there must be both a reaction and a separation. Conventionally these are often designed separately, but we have combined them with a series of novel, benign, tunable solvents to create a paradigm for sustainable development – benign solvents and improved performance.

Tunable solvent systems offer distinct advantages for coupling reaction and separation processes for sustainable technology. We have taken a systems approach to the synthesis problem, using novel solvent systems to achieve homogeneous reactions and heterogeneous separations, with the goal of developing more benign processes with economic advantages. Our group is a synergistic combination of chemistry and engineering, and we have used primarily water and carbon dioxide to alter reaction conditions to increase selectivity, eliminate waste, recycle catalysts, and to achieve facile separations.

Supercritical fluids are a classic tunable solvent, where the use of benign CO2 permits both improved mass transfer and facile recycle of catalysts. Examples are shown of tuning both rates and selectivity, as well as for recycling catalysts. Another example is nearcritical (250-300ºC) water, which dissolves both ions and nonpolar organics, and which dissociates readily to promote both acid and base catalysis. Further, we use gas-expanded liquids, where the addition of CO2 to an organic is used to tune or alter phase behavior. We show techniques of making biphasic reactions monophasic for reaction and biphasic for catalyst recycle. Further we demonstrate the application of gas-expanded liquids to recycle phase transfer catalysts by CO2 assisted aqueous extraction. Finally we show the use of organic-aqueous tunable solvents for biocatalyzed reactions.