Part 3: Distillation Methods—CO2 Processing

Carbon dioxide (CO₂) extraction is a modern technique for collecting essential oils by using CO₂ as a solvent. Although the equipment needed for this method is costly, the overall process is fast and efficient compared to steam distillation while producing comparatively high quality yields.

CO₂ is a gas with the unique ability to reach a supercritical state at a relatively low temperature and pressure. A supercritical state is achieved when the CO₂ is neither completely gas nor completely liquid, but has properties of both phases. This unique property allows even the most heat sensitive oils to be collected by CO₂ in a pure, high quality yield. First, the CO₂ gas is heated and pressurized. The compressed and warmed CO₂ gas changes into its supercritical phase and becomes an excellent solvent. Similar to other solvent extractions, the supercritical CO₂ is added to plant material to remove the essential oil. Once the resulting mixture has been filtered to remove any leftover plant material, the pressure and heat of the system is reduced. As the system returns to atmospheric pressure and temperature, the unique properties of CO₂ cause it to return to its gaseous state, evaporate out of the oil, and leave a pure essential oil product behind.

Although the process of CO₂ extraction is costly, there are many benefits. Not only does this method eliminate the possibility of leaving residual solvent behind, it also prevents changing the chemical structure or aroma of the oil that can be caused by other solvents. CO₂ is non-combustible, colorless, tasteless, and odorless, making it an excellent solvent for collecting essential oils.

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