Environmentally benign chemical processing using supercritical carbon dioxide and near-critical water

The chemical industry is under increasing pressure to improve conventional processes to make them more environmentally benign while maintaining the same level of productivity and expense. Near-critical water (NCW) and supercritical carbon dioxide (scCO₂) are both environmentally benign media with the potential to help in the transition of the chemical industry to clean processing by reducing or eliminating the use of hazardous chemicals as well as the volume of industrial waste production. This is made possible due to the extraordinary and highly tunable physical and chemical properties of these media. Manipulation of temperature, pressure, and cosolvent additions allow for the optimization of equilibria, reaction rates, yields, and selectivities. This tunability also leads to processing opportunities, particularly in terms of facile separations. A novel epoxidation technique using ScCO₂ and H₂O₂ was developed that does not require the addition of any activating peroxy acid or metallic catalysts and furthermore does not use an organic solvent. This was made possible through the in situ formation of peroxycarbonic acid, the active species in the synthesis of epoxides.; Investigations were also performed to elucidate the capabilities of near-critical water (250–350°C) to serve as a medium for organic synthesis. In this NCW region, the properties of water are vastly different from those at low temperatures allowing acid and base catalyzed reactions to be performed in a homogeneous system without the addition of acids or bases or the use of an organic solvent. This is very important to the chemical industry since it can significantly reduce the production of waste salts associated with acid and base neutralizations. The ability to perform base catalysis in NCW is demonstrated for the first time through investigations of the Claisen-Schmidt reaction, which has distinct acid and base catalyzed products. Studies of various base catalyzed reactions, including the butyrladehyde self-condensation reaction and the condensation of acetone with benzaldehyde, were also investigated. In addition to these studies, acid catalyzed Friedel-Crafts acylations, which involve the formation of carbon-carbon bonds to aromatics, were investigated in NCW. All of these reactions are very important to the chemical industry and are used in the production of pharmaceuticals, polymers, and various other commodity and specialty chemicals.