What is supercritical CO2 and how does it differ from liquid and gaseous CO2.
Q.1 (f) What is supercritical CO2 and how does it differ from liquid and gaseous CO2.
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Supercritical CO2 (scCO2) is CO2 held above its critical temperature (Tc = 31.1 °C) and critical pressure (Pc = 72.8 atm ≈ 7.38 MPa). Above this point there is no separate liquid or gas phase, only a single fluid phase with properties between those of a liquid and a gas. It is a green solvent: non-toxic, non-flammable, cheap, recyclable and easily removed by releasing the pressure.
| Property | Gaseous CO2 | Supercritical CO2 | Liquid CO2 |
|---|---|---|---|
| Conditions | Below Pc (or above Tc at low P) | T > 31.1 °C and P > 72.8 atm | Below Tc, under pressure |
| Density | Very low | Liquid-like, and can be tuned with P and T | High |
| Viscosity and diffusivity | Low viscosity, high diffusivity | Gas-like: low viscosity, high diffusivity | Higher viscosity, low diffusivity |
| Solvent power | Negligible | Good, and adjustable | Moderate |
| Surface tension | – | Zero, so it penetrates pores easily | Present |
Uses of scCO2: decaffeination of coffee, extraction of essential oils, dry cleaning, polymerisation reactions.
Doubtly AI
· 25 Oct 2026
AI-verified · Oct 2026
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