Supercritical fluid is defined as a substance at a temperature and pressure above its critical point where the liquid and gas phases do not exist. (1)

Critical point: The point of highest temperature and pressure at which the substance can exist as gas and liquid in equilibrium. (2) It can diffuse through solids like gases and dissolves materials like liquids. (1)

Supercritical fluids present in a mixture are completely miscible when the mixture is above its critical point. Supercritical fluid does not have any surface tension as they do not posses any liquid gas boundary. (1) The phenomenon of super critical fluids can be explained with the help of phase diagram of carbon dioxide. (2) The critical temperature and pressure for carbon dioxide are 304.1k and 72.8 atm respectively.(1) Above this temperature and pressure, CO₂ exist as a supercritical fluid.

APPLICATIONS :( 1)

• Supercritical fluid extraction: it is the process of separating two components by using super critical fluid as a solvent Dry cleaning: in dry cleaning instead of perchloroethylene super critical carbon dioxide can be used.
• Super critical fluid chromatography: it is mainly used for the analysis and purification of thermally labile molecules and for separation of chiral molecules.
• Impregnation and dyeing.
• Nano and micro particle formations: supercritical fluids can form small particles by exceeding the saturation point of solute.
• Supercritical drying: it is a method of drying without surface tension effects
• Supercritical water oxidation: this process uses supercritical water to oxidize harmful waste, eliminates production of toxic combustion products that produce on burning.
• Supercritical fluid deposition: supercritical fluids are used to deposit nanostructured films and nano particles on metal surfaces.
• Refrigeration: supercritical carbon dioxide is used as refrigerant.
• Generation of pharmaceutical co crystals. Supercritical water power generation.
• Biodiesel production.
• Super critical carbon dioxide also has antimicrobial activity.

REFERENCES:

1. http://en.wikipedia.org/wiki/Supercritical_fluid
2. Http://www1.chem.leeds.ac.uk//People/CMR/whatarescf.html http://en.wikipedia.org/wiki/Supercritical_fluid_extraction
3. http://chemeng.iisc.ernet.in/giridhar/rect.html
4. http://www.nottingham.ac.uk/supercritical/scintro.html
5. http://www.kobelco.co.jp/p108/p14/sfe01.htm
6. http://en.wikipedia.org/wiki/Supercritical_fluid_chromatography