Supercritical CO2 Details

Supercritical CO2 has so many advantages it is now used world wide to extract oils from a huge variety of materials. Well known applications are the extraction of caffeine from coffee and tea. Other less known applications use CO2 superfluid extraction (SFE) to reduce the fat content in cheese and extract fish oil. Unlike other extraction methods, CO2 is tunable to focus the extraction on a particular oil.

The strength of CO2's ability to target particular oils is based on molecular polarity. Every atom acts like a little bar magnet with poles at each end. Put several atoms together in a molecule, and this magnetism combines differently for each molecule. This means that each unique molecule will have its own level of polarity or non-polarity depending on how the atoms stack up.

Non-polar solvents most easily dissolve non-polar oils, and polar more easily dissolves polar. This is known in the science world as "like dissolves like". CO2 heated to above 90 degrees Fahrenheit and 1000 pounds per square inch pressure is considered supercritical. Supercritical CO2 will act as a solvent that dissolves oils. CO2 is widely used as a solvent because increasing the pressure and temperature of supercritical CO2 actually adjusts the polarity of the CO2 molecule.

How easily supercritical CO2 dissolves a given oil depends on how well matched the CO2's polarity is to the polarity of the target molecule. CO2 is normally non-polar but under increasing pressure and temperature in the supercritical state, it becomes more polar. Hence you can adjust the polarity of the CO2 solvent to match the polarity of the target molecule!

With the right combination of pressures and temperatures, the supercritical CO2 will most easily dissolve the closest matching oil. It will also still dissolve other oils but at a slower rate. Terpenes, for example, are the flavor and aroma molecules. They are most easily dissolved at around 1500 psi and 110 degrees Fahrenheit. Above 2500 psi you start matching the more active oils. There is, however, a dead zone from around 2000-2200 psi known as the 'solubility cross over point'. This pressure range should be avoided.

Successful CO2 extraction is more than just getting the extraction device. It requires an appropriate recipe of temperatures and pressures to focus on your desired oils. In the same way buying a great oven does not guarantee a great cake, you still need a good recipe. Virtually all commercial plant species have been studied under supercritical CO2 extraction, and there are many papers published with this information. The focus of practically every paper is to determine the best temperature and pressure profile to maximize extraction efficiency. Google scholar is a great place to start in researching for your own application.