Supercritical carbon dioxide

Supercritical carbon dioxide (sCO2) is a fluid state of carbon dioxide where it is held at or above its critical temperature and critical pressure.

Overview

Carbon dioxide usually behaves as a gas in air at standard temperature and pressure (STP), or as a solid called dry ice when frozen. 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 (31.1°C) and critical pressure (72.9 atm), expanding to fill its container like a gas but with a density like that of a liquid.

Properties

The density of supercritical carbon dioxide is similar to that of a liquid, and it can dissolve substances like a liquid solvent. Its viscosity is much lower than that of a liquid, and its diffusivity is much higher, which can be advantageous in applications such as extraction. The surface tension of supercritical carbon dioxide is zero, which allows it to penetrate porous solids like a gas.

Applications

Supercritical carbon dioxide is used in various industrial applications. It is used in decaffeination of coffee, extraction of natural products, and in particle physics and power generation. It is also used in the foaming of polymers and the production of aerogel, in the fractionation of essential oils, in the sterilization of medical instruments, and in enhanced oil recovery in the petroleum industry.

Environmental Impact

Supercritical carbon dioxide is considered a more environmentally friendly solvent compared to traditional organic solvents. It is non-toxic, non-flammable, and can be recycled and reused, reducing the amount of waste generated in industrial processes.

See Also

• Supercritical fluid
• Carbon dioxide
• Critical point (thermodynamics)