According to the U.S. Agriculture Improvement Act of 2018 (aka the 2018 Farm Bill), hemp is defined as cannabis containing not more than 0.3% THC by dry weight. Hemp production is growing rapidly around the world due to the massive growth in CBD products on the market. Several methods are available for extracting hemp oil from the cannabis plant. Hemp oil contains CBD, other cannabinoids, and terpenes (the compounds which provide cannabis its distinct aroma). The two most commonly used techniques to extract hemp oil are ethanol extraction and supercritical carbon dioxide (CO2) extraction. However, hydrocarbon extraction is also sometimes used. No solvent is perfect for cannabis extraction in every way as each technique has its pros and cons.
Hydrocarbon Extraction
Hydrocarbons are organic compounds consisting of carbon and hydrogen. They are formed from the compression of plant material and animal remains over a long period of time. Hydrocarbons can be removed from porous rocks such as limestone and sandstone where they concentrate.
The most common hydrocarbons used for extraction are butane and propane. These hydrocarbons are fast and effective in pulling out the desired cannabinoids and terpenes. The extract is then further refined and if performed correctly, very little or no hydrocarbon residue remains.
Both butane and propane have low boiling points. So, removing these solvents from the extract can be done without disturbing temperature-sensitive terpenes. Propane extracts slightly different ratios of cannabinoids and terpenes than butane. For this reason, it’s common for a blend of propane and butane to be used in hydrocarbon extraction.
Unfortunately for extraction purposes, propane and butane are highly combustible. Explosions could result if these solvents are not handled properly. In addition, poor extraction techniques with hydrocarbons can lead to harmful toxins remaining in the extracted oil.
Supercritical CO2 Extraction
Supercritical CO2 is a more common method to extract hemp oil from the cannabis plant. The term “supercritical” refers to the point at which CO2 has properties of both a liquid and a gas. Carbon dioxide is a gas at standard pressure and temperature. However, when heated above 88° F (critical temperature) and 1,071 psi (critical pressure), it demonstrates properties of both a liquid and a gas.
At this point, a chamber containing the cannabis plant material is filled with this supercritical CO2. Cannabinoids and terpenes then dissolve into the carbon dioxide. Next, the solution passes through a separator where the pressure is lower, and hemp oil extract is left behind.
One of the advantages of utilizing supercritical CO2 is that the process doesn’t leave behind a toxic solvent. Also, by adjusting the temperature and pressure, the process can be fine-tuned to extract specific cannabinoids and terpenes from the cannabis plant.
That said, supercritical CO2 extraction is a more time-consuming process than other methods. Additionally, waxes and plant lipids (fats) are more abundantly extracted using supercritical CO2 compared to other methods. Ethanol (alcohol) is then needed to remove the waxes and lipids (a process known as winterization). Furthermore, supercritical CO2 extraction requires relatively high amounts of energy consumption, especially compared to ethanol extraction.
Ethanol Extraction
The U.S. Food and Drug Administration (FDA) classifies ethanol as “Generally Regarded as Safe,” or GRAS. This means it is considered by experts to be safe for human consumption. Ethanol is created by fermentation of a variety of plant starches or sugars, then later distilled. For this reason, advocates believe it’s the best method to maintain the ratio of natural compounds throughout the extraction process.
Unlike other solvents used in hemp oil extraction, ethanol also extracts water soluble compounds like chlorophyll (the green pigment in plants). Chlorophyll contains vitamins and antioxidants, which have their own health benefits. However, it tends to give hemp oil a “grassy” taste and is therefore removed from the finished product. So initially in the process, both ethanol and the cannabis plant material are chilled to approximately -40° F. This significantly reduces the extraction of unwanted compounds like chlorophyll. Next, the plant material is soaked in the cold ethanol for several minutes and the liquid part is removed. Then, the ethanol is evaporated away, leaving the hemp oil extract. Finally, post-processing equipment including filtration, distillation, and chromatography can be used to refine the oil into the desired distillate.
Another benefit of this technique is that it has no risk of leaving toxic, residual chemicals in the final extract. Furthermore, ethanol enables the extraction of a full spectrum of cannabinoids and terpenes (also called whole plant extract).
Conclusion
Several extraction techniques are commonly used to remove the beneficial compounds of cannabis from the plant. Some techniques require safety equipment. The extraction process must also be performed correctly in order to produce a product safe for humans and pets. Some techniques are more expensive, more time-consuming, and require more energy than others. However, different methods of cannabis extraction serve different purposes for isolating specific, desired compounds. No matter the method used though, proper analytical testing of the final product should be independently performed and clearly reported.
References:
Grijo D et al; Supercritical Extraction Strategies Using CO2 and Ethanol to Obtain Cannabinoid Compounds from Cannabis Hybrid Flowers; Journal of CO2 Utilization; 2018 Dec; 28: 174 – 180.
Rovetto L et al; Supercritical carbon dioxide extraction of cannabinoids from Cannabis
sativa L; The Journal of Supercritical Fluids; 2017 Mar; 129: 16 – 27.
https://www.cannabistech.com/articles/co2-extraction-supercritical-vs-subcritical/
https://www.chemengonline.com/supercritical-co2-a-green-solvent/?printmode=1
https://www.leafly.com/news/industry/ethanol-cannabis-extraction
This content is for informational purposes only. It is not intended to take the place of medical advice or treatment from a personal physician. All readers of this content should consult their physician or qualified healthcare professional regarding specific health questions, especially those taking prescription or over-the-counter medications. CannaGlobe does not take responsibility for possible health consequences of any person reading and/or following this informational content.
