How CBD Extraction Works
By Jillian Jastrzembski
Have you ever wondered how manufacturers are able to pull cannabidiol (CBD) out of cannabis? How do they separate it from the hundreds of other compounds that are in there?
To fully appreciate the headache that is botanical extraction, imagine you’ve made a vegetable soup. It’s already pureed and ready to go when you find out that the onions have been recalled. How do you get the onions out of the soup? You don’t, you throw it out. For scientists, that’s not an option.
In this article, we’re talking about the process of pulling CBD from cannabis. Why is this necessary, and what exactly makes it so challenging? What ingenious methods have scientists developed to extract CBD from cannabis?
Why extract CBD?
Cannabidiol, or CBD, is a potent bioactive compound found in the cannabis plant. Cannabis has a plethora of bioactive compounds, the most famous of which are a class of over 100 compounds called cannabinoids. Among these, CBD and THC are the best-studied.
While THC is the compound that is responsible for the psychotropic effects of cannabis, CBD is coveted for its therapeutic effects. Early research suggests that CBD possesses potent anti-inflammatory, anti-oxidant, and immunomodulatory effects. Thanks to these properties, CBD is of interest for the treatment of insomnia, mood disorders, chronic disease, and overall well-being.
The only way researchers can discern all of this is by separating CBD from the rest of cannabis. That way, they know which effects are coming very CBD versus the other components of the plant.
Few therapeutic benefits have been reported from THC, the other prominent cannabinoid in cannabis. In fact, THC is associated with increased risk of psychosis, anxiety, and other psychological disorders.
So the question then becomes, how to get CBD alone in a room?
There are two arenas of CBD extraction and they both present their own challenges:
- CBD extraction for research purposes
- CBD extraction for medicinal and commercial purposes
Challenges to CBD Extraction
Some of the challenges of CBD extraction include:
- Lipophilic nature of CBD
- Complicated matrix
- Thermally labile compounds
- Finding safe solvents, or ensuring removal of toxic solvents
- Finding green extraction methods
People have been performing botanical extractions for thousands of years. Traditionally, it was common for herbalists to macerate plant parts in water and either heat the mixture or allow it to soak for an extended period of time.
This doesn’t work well for CBD because CBD is a lipophilic compound and water is a polar solvent. That’s why most homemade cannabis extracts are made in ethanol or oil.
But that still doesn’t solve the problem of how to separate CBD from all the structurally similar compounds in cannabis. For example, THC and other, lesser-known cannabinoids have a remarkably similar structure. In fact, it is fairly simple to convert CBD to THC through cyclization.
Which brings up another challenge – the bioactive compounds in cannabis can easily decompose or derivatize when exposed to heat, pressure, or extended storage. CBD and THC themselves are not even naturally present in cannabis. Instead, they take the form of their carboxylic acid derivatives, CBDA and THCA. Those compounds must be decarboxylated to produce the biological effects of cannabis.
Because the desired compound, CBD, is lipophilic, finding non-toxic solvents becomes more challenging. In an analytical research setting, it is appropriate to use high-toxicity solvents such as carbon tetrachloride, benzene, or chlorinated chemicals. However, for medical applications, it is important to switch to slightly less toxic solvents that can either be fully removed following extraction, such as hexane and methanol. Ideally, and particularly for medical purposes, we would use low-toxicity solvents that are safe in residual quantities, such as ethanol and ethyl acetate.
To add one last challenge, it is becoming increasingly important to choose green solvents and find environmentally sustainable extraction techniques.
With these obstacles in mind, let’s take a look at how extraction chemists are able to extract a specific compound from an incredibly complex matrix.
How CBD Extraction works
Extraction chemists have parameters they can play around with to help them optimize CBD extraction. These include things like: herb pretreatment, the chemical nature of the solvent, temperature, and pressure.
As we mentioned, it is common practice to macerate plants in a solvent to enhance the extractability of bioactive compounds. The idea is that if you break up the plant cell structures, you allow the compounds more opportunity to interact with the solvent. In the case of CBD, macerating the herb isn’t actually helpful. That’s because the majority of cannabinoids are located in the trichome, so breaking up the herb just releases more undesired compounds that can get in the way.
The solvent is chosen to have a high affinity for the desired compound. If the solvent has a similar polarity to the compound, they are more likely to “get along” – meaning that the solvent will be able to pull the compound out of the plant matrix and ideally away from other compounds. The most popular solvent choices for CBD extraction are ethanol, methanol, ether, and chloroform.
Heating an extraction solution can help to improve the solubility of the desired compound in the solvent. However, it also increases the risk of thermal degradation, or chemical reactions that produce new compounds. That’s why long processing times are often required for successful extraction.
One promising method for extraction of pharmaceutical compounds, including CBD, is called supercritical fluid extraction, or SFE. Carbon dioxide can be used as a supercritical fluid, by increasing its temperature and pressure beyond a critical point. Using supercritical carbon dioxide is a relatively cheap and green way to extract cannabinoids. The carbon dioxide must be used in combination with a cosolvent that is both fully miscible with carbon dioxide, and has the appropriate polarity for CBD extraction. To further isolate CBD from other chemicals in cannabis, scientists must also employ separation methods such as chromatography. Another tool is to use activated carbon, an absorbent material that can aid in the removal of impurities. This is especially useful in the removal of chlorophyll from CBD extracts.
Summary
CBD extraction is a complicated problem, but is nonetheless essential for both research and medical purposes. Some challenges associated with CBD extraction include the complicated matrix of the cannabis plant, the thermal lability of the desired compound, and the choice of non-toxic green solvents. One promising method for efficient, green CBD extraction is the use of super critical fluids, such as carbon dioxide, along with an appropriate co-solvent.
References
Ramirez, Cristina Lujan, Maria Alejandra Fanovich, and Maria Sandra Churio. “Cannabinoids: Extraction methods, analysis, and physicochemical characterization.” Studies in natural products chemistry 61 (2019): 143-173.
Song, Yu‐Xiang, et al. “Meta‐analysis and review of cannabinoids extraction and purification techniques.” The Canadian Journal of Chemical Engineering 101.6 (2023): 3108-3131.
