The full CO2 extraction process begins with high quality, ground up cannabis or hemp. The plant material needs to be as dry as possible to avoid water in the extract – CO2 and water do not like to mix and it will reduce the yield. Some of our customers use freeze dryers to remove as much water as possible.
The material should be decarboxylated before the run to get a greater yield.
What is Decarboxylation?
Decarboxylation (or decarbing) is the process of heating the plant material to activate the acid components, for example, THCa (the acid form of tetrahydrocannabinol) to THC. THC has psychoactive tendencies, while THCa does not. This means THC will make you high, while THCa will not. This makes THCa an ideal medication for children and anyone who does not want the high.
The CO2 Extraction process, explained
There are four basic stages in CO2 extraction with an Apeks system: Filling, Pressurizing, Extracting, Recovering. Let’s explore each in detail:
Once the system is loaded with plant material, the operator makes final safety checks, prompted by the system. He or she will select required parameters – subcritical or supercritical. Our customers have perfected their parameters and since the systems are fully automatic, the results are consistent from run to run. Once the “start” button is pressed, the system begins to fill with CO2. The operator can walk away at this point since the machine will run until it reaches the required parameters, then go into recovery. Full automation means that no manual intervention is required during a run.
The system begins to pressurize. The diaphragm compressor pumps the flow of CO2 from the cylinders into the Extraction vessel, where the plant material is loaded. The plant material is ground up, to a coffee ground-like consistency. This particle size is optimal for the CO2 to pull as much oil as possible. Any smaller and it might be pulled into filters, causing clogs, and any larger, the CO2 won’t be able to pull as efficiently.
Once the system is up to pressure, it begins to extract. CO2 acts as a solvent when under certain pressure and temperature, and as it runs over the plant material, it extracts essential oils and carries it along in the stream. At subcritical parameters, the CO2 is still a gas (see CO2 Phase diagram below) but as it gets into higher pressures it changes to a murky liquid state.
The extraction phase continues for as long as the operator has dictated. It could be half an hour, or it could be several hours. The CO2 will flow in a loop over the material many times, extracting everything as it goes. Of course, at some point, there’s a point of diminishing returns when there is little oil left and it’s not worth continuing.
Once the run is complete, the CO2 is recovered back to the cylinders. The recovery rate is 95% in Apeks systems.
During the extraction phase, the CO2 stream flows through to the Separator vessel and passes through an orifice. The orifice causes the flow to depressurize, which means the oil drops out of the stream, into a collection cup. Apeks systems are excellent at fractionating because CO2 is highly tunable.
Does CO2 extraction remove terpenes?
Yes, CO2 can extract terpenes and many of our customers have an Apeks system just for terpenes, while they use an ethanol system to pull everything else.
What is Fractionation?
Fractionation is the ability to extract different components of the plant material, for example, terpenes, cannabinoids, and crude oil. This is done using different parameters – subcritical or supercritical.
Four separate fractions from a single run from an Apeks Duplex® system – image courtesy of our customer Marie Riggs of Kentucky
The various phases of extraction
What are Terpenes?
Terpenes are the smells and flavonoids of the plant. These compounds do not contain cannabinoids but are still highly sought after and offer additional benefits for patients. Terpenes are fragile and harmed by exposure to heat, so it’s important to extract them early before they are thermally degraded.
What is Subcritical CO2 extraction?
Subcritical is low pressure/low temperature, typically below 1083psi and 88F. Terpenes are extracted early in the subcritical phase – in some of our systems, as quickly as 15 minutes, but others take a little longer.
What is Supercritical CO2 extraction?
Supercritical is anything above 1083psi and 88F. This is an extremely powerful state that will strip everything out of the plant, including fats, waxes and lipids which are not needed for ingestible products. These are removed after post processing and one method of refining is Winterization.
What is Winterization?
This is a refining step after extraction. The fats, waxes, and lipids contained in the crude oil need to be removed. The oil looks sludgy and thick. Below is another image from our customer in Kentucky showing a terpene pull (left), subcritical pull (middle) and supercritical (right).
The fats and waxes can be removed from the extract by mixing ethanol into it, then deep freezing it overnight. The fully homogenized mixture is then passed through a filter paper, which captures the fats, waxes and lipids. Once clean of those components, the ethanol is removed using a rotary evaporator, which heats the oil/ethanol mixture. The ethanol boils at a different temperature to the oil so it’s distilled out into a collection cup, and can be used again.
Are there other Post Processing Techniques?
Absolutely! Winterization is one option but there are others. In addition, the winterized oil can be distilled even further, separating individual compounds out to create isolates.
What are Isolates?
Isolates are isolated compounds. The cannabis plant is comprised of many different compounds, the most well-known being THC (Tetrahydrocannabinol) which is what makes you high. THCa (the acid version) will not make you high but if heat is added (a process called Decarboxylation), the acid form is activated and it is converted to THC. Another popular compound is CBD (Cannabidiol), which is also found in cannabis and hemp. Hemp usually has higher levels of CBD than cannabis but cultivators are breeding high CBD cannabis as we speak.
What does CO2 extracted CBD mean?
CO2 won’t isolate a particular compound as it’s extracted. However, the particular compounds can be isolated after extraction using a refining method like short path distillation (there are other methods, this is just one). Short path works on the same principle as the Winterization process in the oil mixture is heated and since each compound has a different boiling point, it boils off separately and is collected in vessels. It’s a scientific method and requires training to make sure the process is done correctly.
CO2 extraction is one method of extracting essential oils from plants. There are others, like butane/propane, ethanol/alcohol, as well as non-solvent methods like bubble bath and ice water hash extraction. Our sister company Delta Separations manufactures the VTS-50: Vortex Trichome Separator, which works like a large washing machine to gently remove trichomes from cannabis.