How supercritical CO2 pulls oil from hemp

Above 31.1 °C and about 73.8 bar, carbon dioxide becomes a supercritical fluid that flows like a gas but dissolves oils like a liquid solvent. A pump pushes it through a vessel packed with ground hemp, where it picks up cannabinoids and terpenes, then a valve drops the pressure in a separator so the CO2 lets go of the oil and loops back to be reused.

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Liquefy and pumpCO2 from storage is chilled to a liquid so the pump can push it efficiently, then pumped up to the working pressure.
Heat past the critical pointA heat exchanger warms the high pressure CO2 above 31.1 °C. Above both the critical temperature and pressure it is neither gas nor liquid but a dense supercritical fluid.
Dissolve the oilThe fluid seeps through ground hemp in a thick walled pressure vessel and dissolves cannabinoids, terpenes and some waxes. Higher pressure packs the CO2 denser and makes it a stronger solvent.
Drop the pressureA valve lets the pressure fall into a separator. The CO2 thins out, can no longer hold the oil, and the extract drops to the bottom to be drained.
Below the critical pointAt 70 bar and 40 °C the CO2 is just a gas and the separator barely fills. This is why extractors run well above the critical point.

Density is the dial

Near its critical point, a small change in pressure or temperature changes CO2 density a lot, and density largely sets how much oil it can carry. The density readout uses the Peng Robinson equation of state, a standard engineering model that is typically within about 10 percent of measured CO2 data in this range. NIST lists the critical point at about 304.1 K and 73.8 bar.

The solvating power readout is a simplified Chrastil style index: density relative to a reference raised to the fifth power, times a temperature term. The exponent and temperature constant are illustrative, not fitted to hemp, so read it as a direction rather than a yield.

Try it: hold pressure at 150 bar and raise the temperature from 35 to 80 °C. Solvating power falls because the CO2 gets thinner. Now repeat at 350 bar and it rises instead, because warmer oils evaporate into the dense fluid more easily. Researchers call this the crossover effect.

Why processors choose CO2

CO2 leaves no solvent residue and is not flammable, and running separators at different pressures lets operators split terpenes from heavier cannabinoids. The costs are high pressure equipment, slower throughput than ethanol, and a crude oil that usually still needs winterization to remove waxes.

Vessels are rated pressure equipment with relief valves, and CO2 rooms use oxygen and CO2 monitors because a leak can displace breathable air. Licensed processors handle only hemp at or below 0.3 percent delta 9 THC on a dry weight basis under the USDA program, or cannabis under state licenses.

Sources

Supercritical Carbon Dioxide Technology for Recovering Valuable Phytochemicals from Cannabis sativa L. and Valorization of Its Biomass for Food ApplicationsMolecules, via PubMed Central (NIH)
Carbon dioxide: Phase change dataNIST Chemistry WebBook
Industrial Hemp Research: Cannabis Analysis, Extraction and PurificationNorth Carolina A&T State University, Biological Engineering

How to cite this model

Avid Solutions International. (2026, November 11). How supercritical CO2 pulls oil from hemp [Interactive 3D model]. Avid Field Lab. https://avidsolutionsintl.com/explore/supercritical-co2-extraction

Last updated November 11, 2026

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