When a gas such a carbon dioxide is compressed and heated, its physical properties change and it is referred to as a supercritical fluid. Under these conditions, it has the solvating power of a liquid and the diffusivity of a gas. In short, it has the properties of both a gas and a liquid. This enables supercritical fluids to work extremely well as a processing media for a wide variety of chemical, biological, and polymer extraction.
Near liquid densities increase the probability of interactions between the carbon dioxide and the substrate, similar to a liquid solvent. The gas-like diffusivities of supercritical fluids are typically one to two orders of magnitude greater than liquids, allowing for exceptional mass transfer properties. Moreover, near zero surface tension as well as low viscosities similar to gases, allow supercritical fluids to easily penetrate a microporous matrix material to extract desired compounds. The synergistic combination of density, viscosity, surface tension, diffusivity, and pressure and temperature dependence, allow supercritical fluids to have exceptional extraction capabilities.
Another powerful aspect of supercritical fluid extraction (SFE) is the ability to precisely control which component(s) in a complex matrix are extracted and which ones are left behind. This is accomplished through precise control of several key parameters such a temperature, pressure, flow rates and processing time. Yields from SFE are typically much greater than those of extractions performed by traditional techniques. Product purity is high, and decomposition of material almost never occurs due to the relatively mild processing temperatures.