scCO2

Supercritical carbon dioxide, or scCO2, is carbon dioxide held above its critical temperature (31.1°C) and critical pressure (73.8 bar), where it behaves as a single phase with properties of both a gas and a liquid. In this state, CO2 has liquid-like density but gas-like diffusivity and viscosity, enabling it to permeate solids and dissolve certain solutes.

The solvent strength of scCO2 increases with density and can be tuned by adjusting pressure and temperature. It is largely nonpolar and excellent for extracting fats, oils, waxes, and many natural products. Polar compounds may require co-solvents such as small amounts of alcohol to boost solubility.

Common applications include decaffeination of coffee and tea, extraction of essential oils, SFC (supercritical fluid chromatography), polymer impregnation and foaming, and environmentally friendly dry-cleaning-like cleaning. It offers high selectivity and minimal residue compared with conventional organic solvents.

Advantages include low toxicity relative to many organic solvents, non-flammability, and simple removal by depressurization. Disadvantages include the need for specialized high-pressure equipment, limited solubility for many polar compounds, and higher costs for scale-up. Use often requires modifiers or process optimization.

Safety considerations focus on the hazards of elevated pressures and reduced-oxygen environments. CO2 itself is not toxic in typical occupational exposure but can cause asphyxiation in confined spaces; equipment must be rated for high pressure and include proper relief, venting, and depressurization steps.