Supercritical Fluid
Definition and meaning of Supercritical Fluid in chemistry.
A supercritical fluid is a substance that exists at temperatures and pressures above its critical point, where the distinction between liquid and gas phases disappears and the substance forms a single phase with properties intermediate between liquid and gas.
In more detail
Every pure substance has a characteristic critical temperature (Tc) and critical pressure (Pc) above which no distinct liquid-gas phase boundary exists. A supercritical fluid uniquely combines the high density and exceptional solvating power of liquids with the low viscosity and high diffusivity of gases, making it a remarkable solvent. Supercritical CO2 forms above 31°C and 73.8 bar, while water becomes supercritical above 374°C and 218 atm. These unusual properties enable selective extraction and purification in food, pharmaceutical, and cosmetic industries.
Key facts
| Field | Physical Chemistry |
|---|---|
| Critical point | Temperature and pressure above which liquid and gas phases merge into one phase |
| Supercritical CO<sub>2</sub> | Critical temperature 31°C, critical pressure 73.8 bar; used in food and pharmaceutical extraction |
| Properties | Density of liquids with diffusivity of gases; exceptional solvent for nonpolar compounds |
Supercritical carbon dioxide is used industrially to decaffeinate coffee and extract essential oils and flavoring compounds from plants; the dissolved compounds are easily recovered by reducing the pressure, causing the CO2 to return to its gaseous state and evaporate.
Frequently asked questions
What is a critical point?
The critical point (Tc, Pc) is the specific temperature and pressure at which the distinction between liquid and gas phases vanishes; beyond this point, there is only one fluid phase.
Why is supercritical CO2 preferred for extraction?
It is non-toxic, non-flammable, leaves no residue, easily removed by depressurization, and selectively extracts target compounds while leaving others behind.