Estrazione con fluidi supercritici (EFS)
Above 31 °C and 74 bar, CO₂ stops being a liquid or a gas and becomes something more useful: a dense fluid with the solvent power of a liquid and the diffusivity of a gas. It penetrates a packed bed of biomass the way a gas does, dissolves what it finds the way a liquid does, and leaves the matrix the moment pressure drops. That combination is why supercritical CO₂ has become the reference technology for botanical, food and pharmaceutical extraction.
Where liquid CO₂ is selective by nature, supercritical CO₂ is selective by design. Its density, and with it its solvent power, is set by pressure and temperature. At 100 bar and 40 °C it behaves like a light solvent, taking volatiles and essential-oil fractions. At 250 bar it reaches oils, oleoresins and lipids. At 300 bar and above it extracts waxes, pigments and the heaviest components of the matrix. The same vessel, the same solvent, a different extract at each setting: this is what makes multi-step extraction possible, collecting several fractions in sequence from a single charge, from the lightest volatiles to the heaviest resins, each one concentrated on its own.
The advantages follow directly from the physics. Extraction is fast and complete, because low viscosity and high diffusivity overcome mass-transfer resistance even in dense or oily matrices. Separation is instantaneous and solvent-free: a pressure drop in the separator precipitates the extract and returns CO₂ to the circuit, with no evaporation step, no residual solvent, no thermal stress on the product. Working temperatures stay between 35 and 65 °C, low enough to protect most active compounds. And a co-solvent such as ethanol, dosed at a few percent, extends the reach to polar molecules that pure CO₂ would leave behind.
Here is the detail that matters. Those parameters are only available if the plant is built for them. Pressure rating decides which fractions you can reach; the number of separators in cascade decides how many you can collect separately; pump capacity and heat-exchange sizing decide how fast the cycle runs and how stable the conditions stay. A system designed for one extract at one pressure will run that recipe well and nothing else. A system designed for supercritical extraction in the full sense gives you the whole map of pressure and temperature to work with, and with the right drain design, liquid CO₂ operation on the same vessels.
Supercritical CO₂ is not a single process but a family of them. Choosing it means choosing equipment that lets you explore it.
