Supercritical carbon dioxide

This video shows the property of carbon dioxide to go into a supercritical state with increasing temperature

Supercritical carbon dioxide (sCO
₂) is a fluid state of carbon dioxide where it is held at or above its critical temperature and critical pressure.

Carbon dioxide usually behaves as a gas in air at standard temperature and pressure (STP), or as a solid called dry ice when cooled and/or pressurised sufficiently. If the temperature and pressure are both increased from STP to be at or above the critical point for carbon dioxide, it can adopt properties midway between a gas and a liquid. More specifically, it behaves as a supercritical fluid above its critical temperature (304.128 K, 30.9780 °C, 87.7604 °F)^[1] and critical pressure (7.3773 MPa, 72.808 atm, 1,070.0 psi, 73.773 bar),^[1] expanding to fill its container like a gas but with a density like that of a liquid.

Supercritical CO
₂ is becoming an important commercial and industrial solvent due to its role in chemical extraction, in addition to its relatively low toxicity and environmental impact. The relatively low temperature of the process and the stability of CO
₂ also allows compounds to be extracted with little damage or denaturing. In addition, the solubility of many extracted compounds in CO
₂ varies with pressure,^[2] permitting selective extractions.

^ ^a ^b Span, Roland; Wagner, Wolfgang (1996). "A New Equation of State for Carbon Dioxide Covering the Fluid Region from the Triple-Point Temperature to 1100 K at Pressures up to 800 MPa". Journal of Physical and Chemical Reference Data. 25 (6): 1509–1596. Bibcode:1996JPCRD..25.1509S. doi:10.1063/1.555991.
^ Discovery - Can Chemistry Save The World? - BBC World Service

[spanWagner-1] Span, Roland; Wagner, Wolfgang (1996). "A New Equation of State for Carbon Dioxide Covering the Fluid Region from the Triple-Point Temperature to 1100 K at Pressures up to 800 MPa". Journal of Physical and Chemical Reference Data. 25 (6): 1509–1596. Bibcode:1996JPCRD..25.1509S. doi:10.1063/1.555991.

[2] Discovery - Can Chemistry Save The World? - BBC World Service

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