How Does CO₂ Extraction Work and What is it Used For?

Apeks Supercritical systems use CO2 (carbon dioxide) to extract oils from botanical material, specifically cannabis and hemp. Our systems can be run using subcritical or supercritical parameters. Subcritical is low pressure/low temperature, while supercritical is high pressure/high temperature. Refer to the phase diagram to understand the various phases of the process.

CO2 is a strong solvent that can extract essential oils from botanical materials. It’s also used as a solvent in dry cleaning – it will remove dirt without harming the clothes. In the same way, it does not harm the plant when it passes through it, despite being at high pressure and high temperature. During the subcritical phase, the CO2 is a gas, and it is pumped through the plant, extracting the oil as it passes through the plant. Then it moves into another vessel, via an orifice and in doing so, it depressurizes, which forces the oil to drop out of the CO2 stream, into a collection cup. During the first few minutes of the run, operators can harvest terpenes, which are the smells and flavonoids from the plant. These are highly sought after and have their own medicinal properties, although they are not cannabinoids. The cannabinoids are extracted during the rest of the subcritical run, and the supercritical run after that.

When CO2 hits supercritical parameters, it converts from a gas to a liquid, and becomes an even more powerful solvent than at subcritical parameters. During this phase, it will extract not only the essential oils, but also fats, waxes, and lipids, which are typically not required. That means some post processing is needed, to remove these undesirable components.

Apeks Supercritical systems are closed loop systems, so the way extraction works is in a loop. The CO2 runs over the plant material, extracting the oil, then into the separation vessel, and the oil is collected in the collection cup. The CO2 flow continues its journey and flows over the plant material multiple times. At the end of the run, 95% of the CO2 is recovered, and can be used for future runs.

Let’s take a closer look at the phases.

What is Subcritical CO2 extraction?

Subcritical is when the temperature is lower than 88F and the pressure is under 1083 psi. Refer to the red box in the CO2 phase diagram below – those are subcritical parameters.

During the subcritical phase, the more volatile oils are extracted. The terpenes are considered to be volatile – they are destroyed if too much pressure or heat is applied so the tunability of CO2 is perfect to extract these oils – the operator knows exactly the terpene run is done, and can pause the run, harvest the terpenes and set them aside. This extract will not need any further processing and can be used as is but it does not contain any cannabinoids. The operator will then continue the run to extract the rest of the oils at subcritical parameters. The subcritically extracted oil will need some post processing work to remove unwanted components but not quite as much as supercritical oil.

How does supercritical fluid extraction work?

Supercritical parameters result in the CO2 changing from a gas to a sludgy liquid state. It’s not completely liquid but is more like a milky substance, but in this phase, it becomes a very powerful solvent and will remove everything from the plant material, including fats, waxes, and lipids which are not usually desirable. These will need to be removed in post processing refinement. There are a few methods to choose from, one of which is winterization.

What is winterization?

Winterization is when the extract is mixed with food-grade ethanol and placed in a deep freezer overnight. The mixture is then run through a filter to remove the fats, waxes, and lipids. After that, the oil/ethanol mixture is warmed in a rotary evaporator, and the ethanol evaporates out because it has a different boiling point than the oil. The recovered ethanol can be reused in a future winterization process.

How do you make a supercritical CO2 extractor?

Apeks Supercritical systems have been developed over more than 20 years. The systems conform to a variety of industry standards for safety and quality. Other companies may sell CO2 extractors, but do not manufacture them – they simply import the parts and assemble them. Apeks systems are manufactured on site in our Johnstown, Ohio facilities using high quality raw materials. We have a team of engineers who ensure that standards are met and that the systems won’t blow up because of the pressure. Quality and safety is extremely important but one thing that CO2 operators do not need to worry about: the volatility of the solvent. CO2 is an inert gas that won’t explode or catch fire, in fact, it’s the main component in fire extinguishers. Other solvents like butane, propane and ethanol are considered volatile and require special safety equipment. But that does not necessarily make CO2 a “better” solvent.

Is CO2 extraction better?

The answer to this question is another question: “What are you trying to make?” The end product determines the best extraction process. The chart below shows which solvent is best for each end product. Operators should consider what they want to produce before deciding on an extraction system. Many laboratories have more than one type of extraction system, allowing them the versatility of different methods. CO2 is usually considered to a be pure extraction because the solvent simply bubbles out of the extract and dissipates. There is nothing of the solvent left behind in the extraction, whereas hydrocarbons (butane/propane) may leave a trace behind.

Companies also need to consider equipment and peripheral equipment cost. CO2 systems only require a CO2 monitor in case of leaks. Hydrocarbons and ethanol extraction systems require special C1D1 equipment, which is effectively a bomb shelter. The whole laboratory is designed to prevent sparks which could ignite the solvent and cause a massive explosion. The peripheral equipment can sometimes cost as much as the extractor, and in certain regions is not even allowed due to safety concerns.

Does CO2 extraction kill mold?

While CO2 does kill mold during the extraction process, we recommend not using moldy source material! Also, testing before and after extraction is recommended and, in some states, required. The reason it’s requested both before and after is because a) contaminated material shouldn’t be extracted and b) if there was an undetectable amount of contamination in the plant material, it will be concentrated after extraction and could cause harm.

What is supercritical CO2 used for?

The Apeks Supercritical CO2 extraction systems are mostly used to extract oil from cannabis and hemp. However, they can be used for other botanical material, provided it’s dry. That’s key – CO2 extraction doesn’t work well with water, which is why it is not recommended for Live Resin (see chart above) because of the high water content.

CO2 extraction systems might be expensive, but the return on investment is usually fairly quick because of the high price of good quality concentrates. In the cannabis and hemp markets, pure oils are highly sought after and since they are designed for human consumption, it is important that there are no contaminants or residual solvent particles.

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