“Supercritical Fluid Extraction” is the method of separating one component (extract) from another (cannabis) using supercritical fluids such as CO2.
Super-critical fluid extraction (SFE) uses the strange properties of gases that have been compressed beyond their “critical point.” Carbon dioxide (CO2) is the most frequently used gas because its critical point can be reached at around 90 °F, cool enough that delicate plant terpenes and cannabinoids don’t get deactivated. Furthermore, the shape of the CO2 molecule allows it to act as a non-polar solvent, in the same way butane or hexane are non-polar. Polarity plays a major role in the many different final products that can be created. A supercritical fluid behaves both like a liquid and a gas; it diffuses through solids like a gas but dissolves compounds like a liquid. The fluid has almost no surface tension, so it easily penetrates the cuticle of cannabis’ trichomes dissolving all the oils in its path. The dissolving powers of CO2 change with different pressures; this allows the extractor to use different vessels at different pressures to separate different components. Playing with the pressure allows complete separation of terpenes and cannabinoids, and everything in between. Super-critical carbon dioxide runs through an extraction vessel at a certain temperature and pressure, after gathering the available terpenes, waxes and cannabinoids the solution passes to a separator vessel (under different conditions of temperature and pressure) that can be used to change the composition of the extract. After the extraction is complete, a drop in pressure allows the CO2 to easily evaporate and be recovered. CO2 produces sanitized extracts with a higher terpene content and less wax than typical BHO extractions. Whereas BHO might have anywhere between 0.5 % to 3.5 % terpenes, CO2 oil for consumption generally has around 8 -10 % terpenes by mass. Besides the advantages that SFE offers as far as selectivity (the ability to choose extracts with different components from the same starting material), CO2 is also a “green solvent” unlike butane or hexane, which are petroleum derivatives.