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If you know cannabis, you know extracts are a crucial segment of the industry. The essential oil of cannabis - a concentrate of all the active pharmaceutical ingredients in the plant - is a dynamic substance that can be turned into numerous forms for consumption. Extracts can take the shape of tinctures, transdermal patches, tablets, drink powders, suppositories and oral tablets, not to mention the commonly-used vaporizing and dabbing oils.

But how do we get the most valuable constituent botanicals from the cannabis plant to create the highest quality extract? That’s where super-critical extraction comes in.

To get the definition out of the way, a super-critical fluid is a substance pressurized and heated to a point where there is no difference between the liquid and gaseous phases. That means that it can slip into the smallest spaces between particles and carry a high concentration of solutes.

 “Super-critical carbon dioxide is the solvent of choice if the user would like to separate cannabis components into predetermined product pipelines during the extraction phase of manufacturing,” says Mark June-Wells, principal consultant at Sativum Consulting Group.1

One of the key features of this type of extraction process is that, while other solvents such as hydrocarbons and ethanol are more adept at freeing plant material of their cannabinoids and terpenes, super-critical extraction “has the unique ability to target specific fractions in the parent (plant) material or separate solutes. Those processes are possible because SCCO2 density is dependent on pressure and temperature parameters.”2

This method can get complicated, so June-Wells breaks down two possible approaches: He says the first way is to use pressure and temperature gradients during the extraction process to target specific solutes in the cannabis plant.  “Each solute of interest (e.g. acid form cannabinoids, neutral form cannabinoids, terpenes, etc.) has a specific solubility in super-critical carbon dioxide that is a function of carbon dioxide density.  This is called the cross-over phenomenon (i.e. cross over from low solubility to high solubility in carbon dioxide),” he says. 

The other approach to separation is to harness the cross-over phenomenon in the opposite direction.  This is called retrograde solubility and the idea is to use high pressure (or high density) super-critical carbon dioxide during the extraction process which squeezes all solutes from the main material, then undergo sequential depressurization, in which all products are extracted simultaneously.

“The result is that components are deposited as they lose their solubility in super-critical carbon dioxide during that process.  Either approach will allow you to separate acid form cannabinoids, neutral forms, and terpenes from each other,” June-Wells notes.

When it comes to drawbacks of super-critical extraction, June-Wells highlights two red flags cannabis users should be aware of: This process often extracts a large amount of fatty acids and pigments from the parent material, which must be removed before the final product is ready. Also, “...extraction times are generally longer than those associated with other solvents,” he warns.

Interested extractors should realize there is a relatively large cost for the technology featuring this process, including high-pressure extraction tanks and pumps.

  1. Via interview conducted September 13, 2018
  2. http://www.cannabisbusinesstimes.com/article/your-guide-to-supercritical-extraction/

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