Transport and Phase-Transfer Catalysis in Gas-Expanded Liquids

Abstract

Gas-expanded liquids (GXL) are a new and benign class of liquid solvents that are intermediate in physical properties between normal liquids and supercritical fluids and therefore may offer advantages in separations, reactions, and advanced materials. Phase-transfer catalysis (PTC) is a powerful tool in chemistry that facilitates interaction and reaction between two or more species present in immiscible phases and offers the ability to eliminate the use of frequently expensive, environmentally undesirable, and difficult to remove polar, aprotic solvents. The work presented here seeks to further characterize the transport properties of GXLs and apply these new solvents to PTC systems, which could result in both greener chemistry and improved process economics. The transport properties of GXL are characterized by the measurement of diffusivities by the Taylor-Aris dispersion method and calculation of solvent viscosity based on those measurements. The measurement of these bulk properties is part of a larger effort to probe the effect of changes in the local structure surrounding a solute on the solution behavior. The two technologies of PTC and GXL are combined when the distribution of a phase-transfer catalyst between GXL and aqueous phases is measured and compared to changes in the kinetics of a reaction performed in the same system. The results show that increased reaction rates and more efficient catalyst recovery are possible with GXL solvents.