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Supercritical Fluid Extraction

The cannabis/hemp industry is constantly growing and evolving as harsher restrictions and regulations are lifted and people are able to study the plant more in-depth resulting in new methods and developments for extractions being found. One of these extractions that is considered more economically viable as well as environmentally friendly is supercritical fluid extraction (SFE) using carbon dioxide (CO2). This article aims to clarify what a supercritical fluid extraction is, how efficient it is at extracting cannabinoids, and why CO2 is the better solvent to use.

What is a Supercritical Fluid?

The critical point is a region of the phase diagram located at the intersection of the critical pressure and critical temperature (figure 1). At temperatures and pressures above the critical point the phase boundary between the liquid phase and gas phase disappears and the fluid takes on properties that can be described as a mixture between gasses and liquids (1). Once a substance reaches its critical point, it is called a supercritical fluid (2). Due to the physical properties of supercritical fluids, they make for very interesting extraction solvents that are selective and produce a high yield of concentrated extract.

Figure 1. Phase Diagram for Carbon Dioxide. The three common phases (solid, liquid, gas) are shown, along with the supercritical region above the critical point. The critical temperature for CO2 is 31℃, and the critical pressure is 1,070 psi (74 bar). Above this point, the gas and liquid phases converge into a single uniform phase that is tunable with temperature and pressure.

How Does Supercritical Extraction Work?

Supercritical fluids exhibit both qualities of liquids and gasses which make them excellent at extracting various cannabinoids. CO2 is a great solvent to use with SFE due to it being cheap, reusable, environmentally friendly, and it has a low critical point (3). The low temperature needed for CO2 to become supercritical (31℃) is excellent for keeping the sample integrity intact with little to no degradation. The gas properties of supercritical CO2 allow it to permeate through plant material, while the liquid properties allow it to extract the cannabinoids with ease and specificity (4). While CO2 is the go-to solvent for SFE, another potentially interesting solvent for SFE is water. Similarly to CO2, water is a cheap, reusable, and green solvent; however, the critical temperature for water (374℃ and 220 bar) can degrade the plant material, and extract undesirable compounds such as sugars and other plant constituents into the extract (5).

The general set-up of a CO2-based supercritical fluid extraction system is shown in figure 2 below:

Figure 2. Schematic of a supercritical fluid extraction system utilizing carbon dioxide

If we follow the diagram from left to right, CO2 is pressurized and heated/cooled to the desired temperature depending on the extraction method using the CO2 Pump and fluid heat exchangers. Once the CO2 is preconditioned it flows through the extraction vessel where it mixes with the plant material and dissolves and extracts out the cannabinoids and terpenes. Pressure relief is controlled by depressurization through a series of back pressure regulators. As the CO2 decompresses from a supercritical fluid back into a gas, the CO2 solvent loses all ability to dissolve the cannabinoids and terpenes and the extract precipitates and is collected in the cyclone separators. This leaves behind a high concentrate extract with little to no residual solvent in the extract.

How Effective are Supercritical Extractions?

Multiple studies have shown that SFE is very effective at extracting relatively non-polar compounds from natural products. In this study (6), SFE was compared to a liquid soxhlet extraction (7) and saw that the SFE had a higher extraction rate and can get an even higher yield if assisted with other methods or solvents. Other solvents can increase the efficiency when added along with supercritical CO2 during the extraction process such as when ethanol is added as a co-solvent, it can increase the yield to around 92% (8). There are many variables that can influence the yield, such as temperature, pressure, flow rate of CO2, and even the time of the extraction process; this study found that a high yield of CBD is dependent on the flow rate of CO2, while a high yield of THC is dependent on both flow rate and total extraction time (9). Even with the current research that is available, it only begins to scratch the surface of how to extract cannabinoids with high efficiency using supercritical fluids.

Once an extract is obtained, further remediation can be performed before having the extract tested for potency or the extract can be tested as is for confirmation that the extract is what you’re looking for. Here at Ionization Labs, our Cannabinoid Testing Services are able to test the potency of whatever extract obtained from a supercritical fluid extraction with ease. You can get verified and accurate results in as little as 24 hours! Any comments or questions about testing can be directed to [email protected] or call us at 737-231-0772.

References:

[1] Critical Point

[2] Supercritical fluid

[3] How do supercritical fluids work?

[4] Overview of Supercritical Extraction

[5] Extraction by Subcritical and Supercritical Water, Methanol, Ethanol and Their Mixtures

[6] Supercritical CO2 extraction of hemp (Cannabis sativa L.) seed oil

[7] 7.6: Classifying Separation Techniques

[8] Supercritical carbon dioxide extraction of cannabinoids from Cannabis sativa L.

[9] Utilisation of Design of Experiments Approach to Optimise Supercritical Fluid Extraction of Medicinal Cannabis