What is 'supercritical'?
Supercritical carbon dioxide is a fluid form of carbon dioxide obtained where it is held at or above its critical temperature and critical pressure (87.98 F and 1073 psi, respectively).
The near-liquid density of supercritical fluid increases the interactions between the substrate and the CO2. The gas-like property of the supercritical fluid gives it excellent mass transfer capabilities.
These features make supercritical CO2 an amazing solvent for extraction, as it can be passed through a solid organic matrix to pick up desired extractants. As a gas, CO2 loses its solvency power, facilitating separation from the solute.
By changing extraction pressure and temperature, the solvent power and selectivity of supercritical CO2 can be changed to optimize an extraction for a species of interest.
Subcritical solvents are of interest when extracting yields with increased volumes of terpenoids, flavonoids, and other such volatiles.
Subcritical carbon dioxide runs at milder extraction parameters than other solvents, targeting those volatile compounds.
Follow a subcritical run with a supercritical extraction to completely scrub the matrix of any remaining valuable compounds and achieve a full-spectrum extraction.
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Supercritical CO2 is non-toxic and non-flammable, reducing concern of combustion/explosion during operation of the system. CO2 extracts are free from residual solvent and require minimal post-processing.
It is more environmentally responsible to use CO2 as an extraction solvent. Carbon dioxide is produced as a natural organic waste from fermentation and respiration. It can be captured for use without the need for synthesis and processing, which can be harmful to our environment and create additional costs.
Moreover, in the event that solvent leaching occurs, CO2 is harmless and will not negatively affect our environment.
CO2 retains solvency power as either a liquid (subcritical) or supercritical fluid.
At subcritical parameters it is possible to remove extractants that are thermolabile, resulting in more aromatic extracts. Extracts obtained from CO2 most closely resemble the natural starting material, which is the goal of essential oil extraction.
By changing extraction pressure and temperature of supercritical CO2, its solubility and selectivity for a species of interest can be changed to optimize an extraction. CO2 displays exceptional extractant selectability over a wide range of pressure, from 300 psi upwards.
In this same way, it is even possible in CO2 extraction to refuse undesired compounds such as chlorophyll.