Supercritical CO2 extraction of CBD: the process in numbers
Supercritical CO2 extraction uses carbon dioxide brought above 31.0 °C and 73.8 bar. In that state it dissolves cannabinoids and terpenes as a liquid would, and it returns to a gas once the pressure falls, so no solvent stays in the extract. The pressure setting determines what is extracted: in a 2022 study, light terpenes came out around 130 bar and CBD around 285 bar.
Key takeaways
- CO2 reaches its critical point at 31.0 °C and 73.8 bar; beyond it, the fluid is neither liquid nor gas.
- Yields in a study on industrial hemp varied from 0.75 to 8.83% with pressure and temperature.
- The raw extract is mostly CBDA, the acid form, and only heating turns it into CBD.
- The European Union authorises CO2, ethanol and butane alike as food extraction solvents.
- Extracting a flower concentrates its THC too, so an extract can go over 0.30% from a plant that was under it.
What "supercritical" means
Every pure substance has a critical point: a temperature and pressure past which its liquid and gas phases become indistinguishable. The NIST tables place the critical point of carbon dioxide at 304.18 K and 73.80 bar, which is 31.0 °C. Its triple point, where solid, liquid and gas coexist, is at −56.6 °C and 5.18 bar.
Beyond that point, CO2 is a supercritical fluid. Its density comes close to a liquid's, so it can dissolve weakly polar molecules such as cannabinoids, while it moves through plant material almost as a gas does. The pressure sets its density, and with it the fluid's dissolving power.
The process, step by step
A CO2 extraction unit works as a loop:
- Preparation: the plant material (flowers, leaves, threshing residues) is dried, then ground to give the fluid more surface.
- Extraction: compressed, heated CO2 passes through the vessel containing the material and picks up cannabinoids, terpenes and waxes.
- Separation: in a second vessel the pressure falls, the CO2 turns back into a gas and loses its dissolving power, and the extract settles.
- Recycling: the gas is condensed again and returned to the extraction vessel.
A Croatian team's study, published in 2022 in Pharmaceuticals, gives orders of magnitude. The researchers extracted industrial hemp inflorescences for 30 minutes at a CO2 flow of 1.4 kg per hour. Their separator ran at 15 bar and 25 °C, where CO2 is a gas and the extract falls to the bottom. The paper also notes that other work obtained better yields by adding a little ethanol to the CO2 as a co-solvent.
Pressure and temperature decide what comes out
Supercritical CO2 extracts compounds selectively. The authors of the 2022 study varied pressure and temperature, then analysed each extract by chromatography.
| Optimal setting measured | Target compounds |
|---|---|
| 131.2 bar | Monoterpenes (myrcene, pinenes, limonene) |
| 284.78 bar | CBD |
| 319.7 bar | Sesquiterpenes (beta-caryophyllene, etc.) |
| 60 °C | Optimal temperature for all responses studied |
Depending on the setting, yield varied from 0.75 to 8.83% of the plant mass. At 320 bar and 40 °C, the extract held 305.8 µg of CBDA per milligram, about 31% of its mass. Most of the CBD is thus in acid form, because the process does not get hot enough to convert it. A heating step, decarboxylation, follows; our guide to decarboxylation methods describes it.
Volatile terpenes come out at low pressure and heavier molecules at high pressure. Two extracts both labelled "CO2" can thus have quite different profiles, depending on the setting. Our article on hemp terpenes describes these families of molecules.
CO2, ethanol, butane: what the rules say
The "solvent-free" claim deserves a caveat. Under Directive 2009/32/EC on food extraction solvents, propane, butane, ethyl acetate, ethanol, carbon dioxide, acetone and nitrous oxide are allowed for all uses, subject to good manufacturing practice. Hexane is permitted only for specific uses, with residue limits such as 1 mg/kg in an oil.
For medicines, the ICH Q3C guideline on residual solvents, adopted by the European Medicines Agency, places ethanol in class 3, the least toxic, and accepts up to 5,000 ppm, or 0.5%, with no justification needed. Hexane is in class 2, with a limit of 290 ppm.
| Process | EU food status | Residue to check |
|---|---|---|
| Supercritical CO2 | Authorised for all uses | None: the CO2 leaves as a gas |
| Ethanol | Authorised for all uses | Residual ethanol, ICH class 3 (0.5%) |
| Butane, propane | Authorised for all uses | Residual hydrocarbons, to be measured |
| Hexane | Restricted uses | ICH class 2, 290 ppm |
| Sieving, heat press | No solvent | No solvent; see rosin |
Since the law treats these solvents alike, the real advantage of CO2 is physical: it leaves nothing in the extract to measure. With other processes, a serious certificate of analysis includes a residual solvent test, and our article on solvents in CBD hash explains how to read it.
What extraction does not change: the THC threshold
The French order of 30 December 2021 caps Δ⁹-THC at 0.30% in authorised hemp varieties and in the extracts and products made from them, whatever the extraction method.
A quick calculation shows why the extract needs testing. Start from a flower at 0.2% total THC and an extraction yield of 8%. If all the THC passes into the extract, it reaches 0.2 ÷ 0.08, or 2.5%, more than eight times the threshold. The raw extract must then be purified or diluted, in an oil for example, until the finished product falls back under 0.30%.
On the finished product, the laboratory therefore checks THC, CBD and the other cannabinoids, plus residual solvents depending on the process. Testing methods are described on the laboratory page. For the steps that follow (dilution, carrier oil, spectrum), see how a CBD oil is made and the range of CBD oils.
Frequently asked questions
No. Once the pressure falls, CO2 becomes a gas again and escapes from the extract. The separator in the 2022 study ran at 15 bar and 25 °C, conditions in which CO2 is a gas.
Extraction runs at moderate temperatures, 40 to 60 °C in the 2022 study, which is too low to decarboxylate the acid forms. The richest extract in that study contained about 31% CBDA.
CO2 leaves no residue and allows compounds to be separated by pressure. Ethanol is still an authorised solvent of low toxicity, and quality depends mainly on purification and on testing the finished product.
Yes, because extraction concentrates all the cannabinoids. At an 8% yield, a flower with 0.2% THC gives a raw extract at 2.5%, and the finished product must be brought back under 0.30%.
Written by the Phytogrammes team
Each journal article draws on cited primary sources: ANSM, EFSA, EUR-Lex and peer-reviewed publications. Product profiles are distinguished from documented laboratory results. Our approach.
Article published on . CBD is not a medicine.