What is a Supercritical Fluid, Anyway?

We learned in elementary school about water, gas, liquid, and plasma states, but there is another – Supercritical!

Carbon dioxide is in its supercritical fluid state when both the temperature and pressure equal or exceed the critical point of 31°C and 73 atm (see diagram). In its supercritical state, CO₂ has both gas-like and liquid-like qualities, and it is this dual characteristic of supercritical fluids that provides the ideal conditions for extracting compounds with a high degree of recovery in a short period of time.

By controlling or regulating pressure and temperature, the density, or solvent strength, of supercritical fluids can be altered to simulate organic solvents ranging from chloroform to methylene chloride to hexane. This dissolving power can be applied to purify, extract, fractionate, infuse, and recrystallize a wide array of materials.

Because CO₂ is non-polar, a polar organic co-solvent (or modifier) can be added to the supercritical fluid for processing polar compounds. By controlling the level of pressure/temperature/modifier, supercritical CO₂ can dissolve a broad range of compounds, both polar and non-polar.

To see some of the uses for supercritical fluids, visit the Applied Separations website, and view the presentation on our YouTube channel.

https://www.youtube.com/watch?v=5G4zZ3hNr2U