Supercritical carbon dioxide is a fluid state of carbon dioxide where it is held at or above its critical temperature and critical pressure.
Carbon dioxide behaves as a gas at ambient temperature and pressure conditions and behaves as a solid when frozen. If the temperature and pressure are increased from ambient conditions to be above the critical point for CO2, it adopts properties between that of a gas and liquid.
More specifically, it behaves as a supercritical fluid above its critical temperature 31.10 °C and critical pressure of 73.9 bar expanding to fill its container like a gas but with a density like that of a liquid.
In this state, carbon dioxide exhibits solvating properties of a liquid and the diffusivity of a gas. This makes it a powerful medium for extraction of natural oils from organic materials.
Supercritical Fluid Extraction of solids, is generally operated in batch mode on milled materials (or pellets, granulates), with food grade carbon dioxide as solvent. The equipment consists of two or more extractors operating above the CO2 critical pressure, and two separators where the extract and the CO2 are separated prior to the CO2 being recycled.
The supercritical CO2 extraction process consists of first raising the temperature and pressure of the carbon dioxide gas till it reaches super critical state. This is done using a high pressure pump and a heater. The organic raw material is loaded into the extractors through which the super critical CO2 passes. Based on the components present in the raw materials, and the pressure-temperature settings, the supercritical CO2 extracts the oils from the raw materials and passes through a series of pressure regulator valves to enter the separators. The two separator pressures are controlled individually to separate the different components of the extract. Once the extracted oil is separated from the CO2 which escapes in the form of a gas, the oil is collected in collection vessels while the extract free Carbon dioxide is recycled by condensing and storing in the CO2 tank in the liquid form. This CO2 is then reused and the entire cycle is repeated for the duration of the batch.