1. 1. Introduction
1. 2. Properties and fundamentals of supercritical fluids
1. 2.1. Solvent strength.
1. 2.2. Phase behavior
1. 2.3. Extraction with supercritical fluids
1. 2.4. Polymers and supercritical fluids
1. 2.5. Biocatalysis and supercritical fluids
1. 2.6. Dispersions in supercritical fluids
1. 3. Applications and commercial processes of supercritical fluids
1. 3.1. Supercritical Fluid Chromatography
1. 3.2. Fractionation
1. 3.3. Reactions
1. 3.4. Applications in the material and polymer industry
1. 3.5. Food applications
1. 3.6. Pharmaceutical applications
1. 3.7. Environmental applications




A fluid heated to above the critical temperature and compressed to above the critical pressure is known as a supercritical fluid. Frequently the term, compressed liquid, is used to indicate a supercritical fluid, a near-critical fluid, an expanded liquid or a highly compressed gas. The phenomena and behavior of supercritical fluids has been the subject of research right from 1800’s.

Two supercritical fluids are of particular interest, carbon dioxide and water. Carbon dioxide has a low critical temperature of 304 K and a moderate critical pressure of 73 bar. It is non-flammable, non-toxic and environmentally friendly. It is often used to replace toxic freons and certain organic solvents. Further, it is miscible with a variety of organic solvents and is readily recovered after processing. It is also a small and linear molecule and thus diffuses faster than conventional liquid solvents.

Water has a critical temperature of 647 K and a critical pressure of 220 bar due to its high polarity. The character of water at supercritical conditions changes from one that supports only ionic species at ambient conditions to one that dissolves paraffins, aromatics, gases and salts. Due to this unique property, research has been carried out on supercritical water for reaction and separation processes to treat toxic wastewater. Further, the dielectric constant of water changes from about 78 at room temperature and atmospheric pressure to roughly 6 at critical conditions, enabling control of reactions that depend on the dielectric constant of the medium.

Supercritical fluids such as water and carbon dioxide are substances that are compatible with the earth's environment. However, several other supercritical fluids can be used, but the final choice would depend on the specific application and additional factors such as safety, flammability, phase behavior and solubility at the operating conditions and the cost of the fluid. In the following sections, a brief outline of the properties, fundamentals and applications of supercritical fluids is provided.

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