Supercritical CO2 extraction (SFE) (1/2)

Supercritical CO2 extraction (SFE) (1/2)

CannabiGold oils are obtained by supercritical carbon dioxide extraction (SFE) technique. The abbreviation SFE stands for Supercritical Fluid Extraction and means exactly this – extraction with fluids in supercritical state. “Fluid”, hence (at least theoretically) any substance can be converted to supercritical fluid state. In practice, for most substances obtaining such state requires such extreme pressure and temperatures that only a few of them, including carbon dioxide, are viable for SFE procedures.

Supercritical state is nothing less but the fourth state of matter. Everyone knows and remembers from school the three basic ones – gaseous, liquid and solid. The fourth one is rarely mentioned. Probably because it is not observed under “normal” pressure and temperature conditions and requires a sophisticated apparatus to be obtained. In any case, grossly simplifying, it is the state between gaseous and <liquidic?>. Such liquid shares with gases their great penetration qualities, and at the same time is a great solvent – as liquids are; it is safe to say that supercritical fluids combine the advantages of gas and liquid and therefore make for a great [2].

It is fairly easy to turn carbon dioxide supercritical, as it “only” requires the temperature of above 31 ° C… and the pressure above 74 bar (for comparison – 1 bar equals the atmospheric pressure). This is CO2’s huge advantage, not the only one, though. Its performance in extraxtion can be listed as a second one – once it has fulfilled its purpose, CO2 is extracted back into the gas after the extraction, and spills itself out of the extract, leaving no trace. In effect, unlike like in extrction with liquid solvents, supercritical CO2 extraction does not require the tedious process of evaporating the solvent itself, a process often resulting in lowering the final product’s quality [4]. Furthermore, CO2 is not toxic to humans, which can not be said of liquid solvents.

It also contains no impurities and rudiments that are always present in liquid organic solvents (such as petroleum ether or alcohols) and which always remain and even accumulate in extracts, even after distilling the solvent. This quality is especially important – it must be borne in mind that huge quantities of solvents are used for the extraction -up to 20 liters of solvent is needed per kilogram of dry matter. In consequence, if, for example, 20 liters of solvent has been used, even such of a high purity of 99.5%, 100 g of God knows what kind of impurities still remain in it. Even if only a small fracture of them remain in the final extract it is still too much.

For another example let me comment on one aspect of ethanol extraction. Not everyone knows it, but one of the typical impurities in anhydrous ethanol is benzene. As it is cancerogenic, benzene itself is rarely used for extraction, but is used in the production of many organic solvents used in laboratory and industrial extraction, and therefore in many of solvents benzene residua can be present in (not only in ethanol but also in methanol, isopropanol, hexane or acetone). For this reason, the pharmaceutical industry is obliged to measure benzene levels in drugs which required ethanol and other solvents to produce [5]. One can only guess how many manufacturers of CBD preparations that use extraction with anhydrous ethanol, test the level of benzene in their products…

Extracts obtained using CO2 are extremely clean. Supercritical CO2 extraction does not extract from the plant many contaminants from that typical liquid solvents do [6]. It is especially important as cannabis is known for its ability to recultivate and purify the soil on which it grows – this means nothing else that they accumulate heavy metals in themselves (even if grown in uncontaminated regions). Luckily, CO2 does not have the ability to extract metals, therefore the extract will be free of them even if the plant was polluted. Supercritical CO2 extraction also guarantees a microbiological purity [2] – under high pressure and in high CO2 concentrations, all microorganisms present in the plant material perish, so provided the hygiene is maintained during the next stages of production (such as packaging or any additional process, if applicable), the product will be microbiologically safe.

Dr inż. Beata Plutowska

References:

[1] Capuzzo A., Maffei M.E., Occhipinti A. Supercritical fluid extraction of plant flavors and fragrances. Molecules 18 (2013) 7194-7238.
[2] Perrut M. What is a supercritical fluid? http://www.separex.fr/download/category/1-supercritical-fluids-and-applications.html
[3] Brunner G. Supercritical fluids: technology and application to food processing. Journal of Food Engineering 67 (2005) 21-33.
[4] Reverchon E., De Marco I. Supercritical fluid extraction and fractionation of natural matter. Journal of Supercritical Fluids 38 (2006) 146-166.
[5] Vicente N. CEP submission: How to prepare a new aplication? 2010 EDQM, Council fo Europe
[6] Xu L., Zhan X., Zeng Z., Chen R., Li H., Xie T., Wang S. Recent advances on supercritical fluid extraction of essential oils. African Journal of Pharmacy and Pharmacology 5 (2011) 1196-1211.