Found this, thought I would share..
Supercritical CO2 Extraction 101
Warning: The following description may seem a little complicated if you’re not an industrial chemist or if you’re not already high enough while you read this.
CO2 extraction machines essentially freeze and compress CO2 gas into a “supercritical” cold liquid state. “What does it mean to be in a supercritical state?” We’re glad you asked.
Carbon dioxide (CO2) usually behaves as a gas at standard temperature and pressure (i.e., in places where humans can survive without special equipment). That gas can be changed to a solid without much effort. This solid state is known as dry ice. These are the two most-common phases of CO2 that appear outside a lab.
With special equipment (i.e., in a lab), you can change CO2 gas into a liquid by increasing the pressure to 75 pounds per square inch and keeping the temperature below -69 ℉. Brrr! This liquid CO2 is the starting point for our CO2 extraction.
From this liquid state, we’re going to increase the temperature and pressure past a certain point. We won’t get into the numbers here because it becomes super complicated. Just know that when you increase the temperature and pressure of liquid CO2, the fluid becomes supercritical.
This means that it can adopt properties midway between a gas and a liquid at the same time. Mind blown, right? A supercritical fluid can fill a container like a gas while still maintaining its density like a liquid.
This supercritical property of CO2 is great for chemical extraction because it is “gentler” than other compounds and won’t cause damage or denaturing (making unfit for consumption). And because the solubility in CO2 varies with pressure, supercritical CO2 can be used to extract selected compounds (rather than a combination of all compounds) with just a few small adjustments.
So now that you have a passing understanding of what supercritical CO2 is, we can turn our attention to how it’s used to make cannabis extracts.
As you can see in the diagram above, you start with liquid CO2 (top left corner). You raise the pressure of the liquid CO2 via a compressor (top middle), and then raise the temperature via a heater (top right).
The supercritical CO2 is then passed through some high-grade pot contained in an extractor (bottom right corner). It’s at this point that the CO2 pulls all of the essential trichomes and terpene oils and/or waxes out of the plant material.
This solution (the supercritical CO2 containing all the ganja good stuff) is then passed through a separator (bottom middle) where it is broken down into its constituent parts.
The trichomes, terpenes, and other goodies are sent to a collection receptacle (“Extract” on the diagram above) while the supercritical CO2 is passed through a condenser (bottom left), where it is turned back into a liquid. This liquid is then sent to the storage tank where it can be used to restart the process.
And if you’re wondering about residual CO2 left over in the extract, don’t worry. Decreasing the pressure on the CO2 after the extraction process is complete allows the liquid CO2 molecules to turn back into a gas and evaporate into the atmosphere.
This is probably the simplest part of the whole procedure: just leave the extracts out at room temperature.
This is the same chemical reaction that causes a soda pop to go flat after it’s opened and warms up. Some industrial supercritical machines can even simplify this process by recapturing, recycling and reusing the CO2 gases that are given off when extraction is complete.