Supercritical CO2 extraction process depends by its particularly is “geometrically variable”. A supercritical fluid is any compound at a temperature and pressure above its Critical Point.
It can diffuse through solids like a gas, and it can dissolve materials like a liquid. For any pure compound, there is a transition state called “critical” state: for temperatures below the critical temperature Tc two phases – liquid and vapor - coexist; for temperature above Tc, there is only one phase: supercritical fluid. Solubility is a function of pressure and temperature:
- Solubility Increases with increasing pressure at constant temperature.
- Solubility May Increase, or Decrease, when temperatures are raised at constant pressure.
Solubility is related to density. Higher Density, Higher Solubility. This is true from the theoretical point of view, but when applied to singular compound we may see different results, as shown in the graphs below.
The supercritical fluid density always increases with the pressure at fixed temperature, while always decrease increasing temperature at fixed pressure. Solubility depends on a particular pair of values (pressure/temperature). These values are strictly connected with the solubility of each single compound. Extraction with supercritical fluids operating conditions are chosen to obtain the selective extraction of compounds of interest, reducing to a minimum the co-extraction of undesired compounds. The selection of the operating conditions depends on the Specific Compound or compound family to be extracted.