Supercritical CO2 extraction (SFE) (2/2)

Supercritical CO2 extraction (SFE) (2/2)

Supercritical CO2 extraction technique guarantees natural composition of the extract and does not cause degradation of its precious ingredients. This is possible, first and foremost, due to the fact that this technique does not involve the use of high temperatures that are often required for solvent extraction (especially when crude, amateurish methods such as distillation or solvent evaporation of solvent by heating it are at play), so no thermal degradation will occur [1]. Thermal degradation will result in more than just a change of extract’s color from golden (which is natural for cannabinoids) to brown or even black. What really happens is invisible – and truly disaterous – oxidation, isomerization or polymerisation processes that the elevated temperatures induces can cause the decay of many valuable components of the extract. Even worse, these processes can often turn beneficial ingredients into harmful ones. Terpenes can serve as an example – once oxidated they can acquire irritant, allergic and pro-inflammatory properties [2]. Of course, the SFE process can also be carried out at higher temperatures (which in this case means any above 31 ° C), but even then oxidation processes will not be initiated due to the simple fact that there is no oxygen present in the system , just pure and completely inert carbon dioxide.

SFE can be counted among the green technologies, meaning that it is environmentally friendly. First of all, unlike solvent extraction, it does not generate toxic waste that getting into the water, soil and air pollutes the environment. Moreover, the instalation design allows for carbon dioxide to circulate in closed circuit, so even the consumption of this crucial ingredient is minimized in the process [3].

SFE is part of a whole range of innovative tehnologies that involve the use of supercritical fluids. Thanks to such techniques’ many advantages they have been recently finding use in an increasing number of industries, including grocery and pharmaceuticals. This has happened partially due to the fact that, apart from its applications in extraction and separation techniques, supercritical CO2 can be also used as the perfect medium for conducting various types of reactions, micronization, crystallization, impregnation and many others, my personal favorite being supercritical fluid chromatography (SFC).

The figure above shows a simplified diagram of the basic supercritical CO2 extraction system.

In the simplest version of a supercritical extraction system, liquid carbon dioxide (storaged, for example, in a cylinder or a tank) is supplied to a pump that generates the desired presure in the extractor containing the plant material. At the same time, the extractor is heated to the predetermined, above-critical temperature. Once the carbon dioxide reaches the supercritical state, the extraction process begins. Carbon dioxide circulates and everything it “draws” out of the plant material in the extractor is thrown into the separator – a tank behind the extractor. This is possible because the conditions in the separator are different than in the extractor chamber and the CO2 from the supercritical state suddenly turns back into a gas. As gases possess no extraction capacity, any substances that have just been extracted by the carbon dioxide in its supercritical state are ‘precipitated’ <wytrącone?> during its transition to the gaseous state. The cycle concludes with transition from gas back to liquid state in the <refrigerator-chłodziarka przemysłowa>. Liquid carbon dioxide returns to the pump, then to the extractor and the separator and so on, over and over until everything is extracted out of the plant material. Of course, the scheme above demonstrates only the basic principle of the technology, depending on the specific technological solutions used, SFE installations can be much more complex and serve multiple purposes [5].

Setting the optimal conditions for the extractions is an experiment itself. This is a very empirical and somewhat intuitive technique, and experts that have mastered it are well aware of how often the supercritical state eludes theoretical assumptions. This is due to many reasons. First and foremost – the complexity of the materials to be extracted and the interactions between them. Besides, there is no such thing as one supercritical state, identical for all the conditions and techniques at use. Any combination of temperature and pressure above supercritical threshold (and many other conditions, which I will not be mentioning here in order not to complicate things even further) will result with supercritical fluid of a slightly different extraction capacity. This can be seen, though, as one of the many advantages of this technique, as the composition of extract obtained can be manipulated by adjusting the extraction conditions[6]. In the CannabiGold production process we use all the possibilities the SFE technique grants and therefore we have developed separate production processes for each extract. In other words, this means that the 5% proof extract is produced in a slightly different way than, for example, the 20% product, and is not just obtainded (as is often the case with commercially available formulations) by simply diluting the more concentrated paste produced under random conditions.

Dr inż. Beata Plutowska

References:

[1] Sovova H., Stateva R.P. Supercritical fluid extraction from vegetable materials. Rev Chem Eng 27 (2011) 79-156.
[2] Turek C., Stintzing F. C. Stability of essentail oils: a review. Comprehensive Reviews in Food Science and Food Safety 12 (2013) 40-53.
[3] de Melo M.M.R., Silvestre A.J.D., Silva C.M. Supercritical fluid extraction of vegetable matrices: Applications, trends and future perspectives of a convincing green technology. The Journal of Supercritical Fluids 92 (2014) 115-176.
[4] Marentis R., Hsu J.T. Supercritical fluid extraction of nutraceutical products. 4th Brazilian Meeting on Supercritical Fluids EBFS 2001
[5] Pourmortazavi S.M., Hajimirsadeghi S.S. Supercritical fluid extraction in plant essential and volatile oil analysis. Journal of Chromatography A 1163 (2007) 2-24.
[6] Reverchon E. Supercritical fluid extraction and fractionation of essential oils and related products. Journal of Supercritical Fluids 10 (1997) 1-37.