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Presidential Green Chemistry Challenge: 2004 Academic Award

Professors Charles A. Eckert and Charles L. Liotta of the Georgia Institute of Technology


Benign Tunable Solvents Coupling Reaction and Separation Processes


Innovation and Benefits: Professors Eckert and Liotta found ways to replace conventional organic solvents with benign solvents, such as supercritical carbon dioxide (CO2) or water "tuned" by carefully selecting both temperature and pressure. These methods combine reactions and separations, improving efficiency and reducing waste in a variety of industrial applications.

Summary of Technology: For any chemical process, there must be both a reaction and a separation. Generally, the same solvent is used for both but is optimized only for the reaction. The separation typically involves 60–80 percent of the cost, however, and almost always has a large environmental impact. Conventional reactions and separations are often designed separately, but Professors Charles A. Eckert and Charles L. Liotta have combined them with a series of novel, benign, tunable solvents to create a paradigm for sustainable development: benign solvents and improved performance.

Supercritical carbon dioxide (CO2), nearcritical water, and CO2-expanded liquids are tunable benign solvents that offer exceptional opportunities as replacement solvents. They generally exhibit better solvent properties than gases and better transport properties than liquids. They offer substantial property changes with small variations in thermodynamic conditions, such as temperature, pressure, and composition. They also provide wide-ranging environmental advantages, from human health to pollution prevention and waste minimization. Professors Eckert, Liotta, and their team have combined reactions with separations in a synergistic manner to use benign solvents, minimize waste, and improve performance.

These researchers have used supercritical CO2 to tune reaction equilibria and rates, improve selectivities, and eliminate waste. They were the first to use supercritical CO2 with phase transfer catalysts to separate products cleanly and economically. Their method allows them to recycle their catalysts effectively. They have demonstrated the feasibility of a variety of phase transfer catalysts on reactions of importance in the chemical and pharmaceutical industries, including chiral syntheses. They have carried out a wide variety of synthetic reactions in nearcritical water, replacing conventional organic solvents. This includes acid- and base-catalysis using the enhanced dissociation of nearcritical water, negating the need for any added acid or base and eliminating subsequent neutralization and salt disposal. They have used CO2 to expand organic fluids to make it easier to recycle homogeneous catalysts, including phase transfer catalysts, chiral catalysts, and enzymes. Finally, they have used tunable benign solvents to design syntheses that minimize waste by recycling and demonstrate commercial feasibility by process economics.

The team of Eckert and Liotta has combined state-of-the-art chemistry with engineering know-how, generating support from industrial sponsors to facilitate technology transfer. They have worked with a wide variety of government and industrial partners to identify the environmental and commercial opportunities available with these novel solvents; their interactions have facilitated the technology transfer necessary to implement their advances.

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