Supercritical Fluids

Abstract

A supercritical fluid is a gas that is pressurized and heated to a compressed fluid state, which is above both the critical pressure and the temperature. In this state, density and subsequently solvent strength and transport properties are highly adjustable by modest changes in temperature and pressure. Complex phase behavior and interactions with materials occurring in this state can be examined experimentally and described by molecular thermodynamics. Carbon dioxide and water are two substances used frequently as supercritical fluids. Carbon dioxide, which may be used independently or in the presence of various cosolvents, is used because of its environmentally benign nature and low cost. Water is used because of its efficiency in destroying hazardous aqueous pollutants and hydrothermal synthesis.Numerous supercritical fluid processes have been commercialized, including coffee and tea decaffeination, supercritical water oxidation, and supercritical fluid chromatography. Process research and development involving supercritical fluids are progressing in many diverse areas, including extraction, membrane filtration, polymerization, particle formation, cleaning and drying, and applications in microelectronic engineering.