Supercritical fluids, in particular CO2, are used for their unique liquid-to-gas properties beyond their critical point.
These fluids are used in a wide range of industries for innovative, environmentally-friendly processes :
- They offer significant advantages in terms of solubility and diffusion, facilitating more efficient industrial processes.
- They are used for various types of unit operations such as extraction, purification, cleaning and chemical synthesis.
Find out more about the use of supercritical fluids !
What does “supercritical” mean ?
Every pure compound has a critical point corresponding to a given pressure and temperature. When the pure compound is subjected to a pressure and temperature higher than its critical point, it is in a so-called “supercritical” phase.
Its behavior is intermediate between the liquid and gaseous states, with specific properties : a high density like liquids, a diffusivity coefficient intermediate between liquids and gases, and low viscosity (like gases).
The liquid-gas equilibrium curve is interrupted at the critical point, ensuring a continuum of physico-chemical properties.
The term supercritical fluid is used when a fluid is heated above its critical temperature and compressed above its critical pressure. This behavior of matter was first observed in 1822 by a French engineer and physicist, Charles Cagniard de La Tour. It was later used under the term supercritical fluid by Irish chemist Thomas Andrews.

Supercritical fluids: how does it work ?
What's the point ?
A step toward sustainable chemistry
Supercritical fluids (SCFs) are considered a breakthrough in the field of green chemistry because of their ability to replace conventional petrochemical solvents in various industrial applications .
They offer a cleaner, greener alternative while still retaining the advantages of liquids and gases.
For example, supercritical fluids can be used to extract active compounds from vegetal materials in a more efficient and environmentally-friendly way than conventional methods.
Moreover, their low viscosity and high diffusivity can help reduce energy consumption and minimize waste in these processes. Supercritical fluids are therefore seen as a step towards a more sustainable and environmentally-friendly chemistry.
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Answers to popular beliefs
What is supercritical CO2 ?
The most widely used supercritical fluid is CO2 (carbon dioxide). In its supercritical phase, it has the advantage of being a totally neutral, non-toxic, non-polluting and non-flammable “green” solvent. It can be used at temperatures close to ambient (its critical temperature is 31°C) and at high pressures (its critical pressure is 74 bar), which are easily achievable with today's technologies. Moreover, CO2 is widely available at high purity and low cost.
Where does CO2 come from?
The CO2 used in supercritical processes is a by-product of industry, recycled through a clean technology.
Raw gas is captured in the flows emitted by factories manufacturing certain products or power generation plants.
Through the purification and liquefaction stages, the “waste” CO2 is transformed into a raw material in several fields of activity such as :
- food industry
- energy recovery
- microalgae and biofuel production
- organic synthesis and biocatalysis
and, of course, supercritical processes .

Deuxième vie du CO2 avant la valorisation dans nos équipements
What is subcritical and supercritical water ?
Water's critical point is much higher than that of CO2, but its applications are promising, and some of them are in the process of being industrialized.
Water in its supercritical phase (Pressure > 221 bar; Temperature > 374°C) precipitates inorganic compounds and becomes a solvent for organic matter. Processes using supercritical water are also known as hydrothermal processes.
Water in its subcritical phase (Pressure: 15 to 100 bar; Temperature: 150 to 250°C) can solubilize specific hydrophobic compounds and can therefore be used to extract plant products.
For waste treatment, the process using subcritical water is also known as wet oxidation.
Other supercritical fluids
In addition to water and carbon dioxide, compounds such as ethane and propane are also used in their supercritical phase for certain applications (extraction, chemical reactions, etc.).
