After the extraction process, the mixture composed of CO2 and solutes leaves the extraction vessel(s) and it is directed to the separation vessels. By varying the pressure, flow and temperature of these vessels, it is possible to induce the selective precipitation of different chemical compounds as a function of their different saturation conditions in the supercritical fluid.
First of all, the mixture is directed into separator S1 and here, with the use of a lamination valve, the pressure goes down and (due to the Joule-Thomson Effect) the gas that was rapidly expanded during the depressurization process cools because the molecules get the energy using their specific heats, also the temperature of gaseous CO2 drops dramatically, and two important effects are observed:
- Solvent properties of CO2 changes immediately: Density of the fluid is reduced ten-fold and the expansion of the CO2 changes the speed of the CO2 from centimeters per second to meters per second.
- All compounds dissolved in the CO2 immediately fall out of solution because the fluid changed its status from supercritical to gaseous and it has become a weak solvent.
S1 is a heated gravimetric separator. This design is particularly effective for the heaviest compounds of the extract. The gravimetric separator works by gravitational force. But this isn’t enough to completely clean up the CO2, in fact other lighter solutes are not separated from the solvent in S1. For this reason there are two additional separators, S2 and S3.
S2 is a heated cyclonic separator. While S1 works using gravity, S2 works using centrifugal force. The fluid moves very quickly creating a vortex inside the vessel. The fluid continues to spin and the particles of extract begin to separate, moving toward the walls of the separator and sliding to the bottom. The temperature of the walls determines which compound will be condensed. Generally, essential oils, like hydrocarbon terpenes, can be found in this separator, as they are lipid-soluble compounds, while oxygenated terpenoids, and sterols travel to separator S3 dissolved in the water micro drops — they are polar compounds and the condensation point (because of heating) is too high to condense them in separator S2.
S3 is a cooled cyclonic separator. Micro droplets of water will condense and collect in this separator along with hydrophilic/oxygenated terpenes and other volatile substances due to their low condensation point.