Green chemical processes with supercritical fluids: Properties, materials, separations and energy

In this work, an overview of the properties of supercritical fluids is given on using water and carbon dioxide for developing green chemical processes. Present industrial processes and emerging technologies that use supercritical fluids are highlighted. Supercritical fluids are being used in transcritical cycles for heat transfer due to their favorable thermophysical properties and their environmental compatibility. Supercritical water is being proposed as a reaction solvent for zinc silicate industrial phosphors, since it allows production of luminescent materials at low temperatures (400 °C) and with less energy than industrial solid-state methods that require high temperatures (1200 °C). Supercritical CO2–ionic liquid systems have much potential as biphasic systems for reactions and separations, however, when used for chiral separations, the selectivity of these systems is not well understood yet. The use of supercritical CO2 for viscosity reduction in ionic liquid reaction systems seems to be a favorable research area with conversion of d-fructose to 5-hydroxymethylfurfural in high yields (>90%) being an example. Systems to convert biomass to energy by direct oxidation in supercritical water are under development. Many opportunities exist for developing green chemical processes with supercritical fluids.