A Primer on CO2 Extraction

Noel Palmer, Ph.D.

Chief Scientist, Evolab

There are many methods that can be used to isolate and concentrate the cannabinoids, terpenes and other compounds in cannabis.  Traditional methods might be described as physical separations – where hash and kief are produced. Cannabinoid concentrations in these forms typically ranges from 20-60% (wt/wt) depending on the quality of the starting material and the method being used.  In these concentrates, plant material is also found in the final product – making these concentrates less desirable for infused products, including vapor cartridges.

Recent advances and trends in cannabis extractions have gone down the path of chemical separations – in which a solvent is used to dissolve and isolate the cannabinoids.  Many solvents can be successfully used – however varying  state laws often dictate what is permissible.  In most states, chemical solvents that have been approved include alcohols (ethanol and isopropyl alcohol), hydrocarbons (butane and propane) and CO2.  While perfectly safe in highly controlled laboratory environments, ‘amateur extractors’ working with hydrocarbons in their basements and garages are notorious for causing explosions and generating sub-par concentrates, which is part of why these extraction processes have developed a bad reputation.

In chemistry, we often talk about chemicals and solvents in terms of their polarity – or their ability to respond to a magnetic field.  Some chemicals are highly polar (i.e. water) and some chemicals are highly non-polar (i.e. butane).   When describing how a particular solvent will dissolve a chemical – there is a rule of thumb that ‘like dissolves like’.  Meaning, a non-polar solvent will dissolve a non-polar chemical. 

Cannabinoids are considered to be non-polar, thus using a non-polar solvent is most appropriate. Logic suggests however, that a non-polar solvent will not selectively dissolve cannabinoids – rather a non-polar solvent will dissolve all non-polar compounds, which might include pesticides, herbicides or aflatoxins. As a result, a cannabis concentrate will contain cannabinoids up to 90%+ wt/wt – but any other non-polar constituents may also be concentrated.  

Most states have set tolerances for residual solvents in a final product.  In Colorado, a level of 5000ppm has been established for butane.   While butane has been approved by the FDA at certain levels in food items, butane has not been evaluated for its safety in smoking or vaporizing devices. These levels set by Colorado for Health Safety may be appropriate – however it is our opinion that more research is needed in this regard to prove public safety.  

At Evolab, we believe that no residual solvents should exist in a cannabis concentrate, so we avoid them altogether. 

When Evolab was first established, the team began by exploring the current state of the art in processing technology. At the time, this largely consisted of relatively crude extraction processes using hydrocarbon solvents or antiquated approaches like cold water extraction that were highly inefficient. However, CO2 extraction technologies had begun to become increasingly common in the herbal and pharmaceutical industries for many reasons. 

Through significant research and development, Evolab created the cannabis industry’s first CO2 extraction solution that not only preserves terpenes and flavonoids, but also allows for the extraction of the entire profile of any plant. Furthermore, this approach provides the unique ability to extract only the terpenes if desired, which led to the first product line featuring pure cannabis terpene profiles —FreshTerps™.

So how does it actually work?

Liquid CO2 is the starting point for all CO2 extractions. From this liquid state, we increase the temperature and pressure until the fluid becomes supercritical — which simply means that it can express properties of a gas and a liquid at the same time.

This supercritical property is ideal for cannabis extraction because it does not cause damage or denaturing. Furthermore, because solubility in CO2 varies with pressure, supercritical CO2 can be used to extract specific compounds, rather than pulling out all compounds. To make  oil, supercritical CO2 is passed through cannabis material. The CO2 pulls out cannabinoids, terpenes, flavonoids, as well as waste products like waxes and chlorophyll. Depending on the conditions used in a CO2 extraction system, the cannabinoids may be extracted as acidic compounds (e.g. THCA, CBDA, CBGA, CBCA) - or neutral cannabinoids (e.g. THC, CBD, CBG, CBC). 

This material is then passed through a separator to be broken down into its constituent parts. Terpenes and cannabinoids are collected, while the supercritical CO2 is pumped into a condenser to be turned back into a liquid and recycled. What about residual CO2 in the extract? It simply evaporates at room temperature.

Over the years since the creation of that first Evolab machine, we’ve continued to refine our extraction technology and processes, establishing a reputation as the preferred processor for many growers across Colorado.

Graham Sorkin