Supercritical fluid extraction refers to the process of separating the extractant from the matrix by utilizing the supercritical fluids as the extracting solvent. The extraction is typically done from the solid matrix although the extraction can also be done from the liquids. The superficial fluid extraction can be applied as a sample preparation step for the analytical reasons. This article discusses how the extraction of carbon dioxide is done unless stated otherwise.
Advantages of supercritical fluid extraction
You can change the properties of the supercritical fluid by altering the temperature and pressure as this will allow what is referred to as selective extraction. For instance, the volatile oils can be extracted with low pressures from the plants. The liquid extraction can also be used for the removal of the lipids.
Lipids can be removed by making use of pure carbon dioxide at high temperatures. The phospholipids, on the other hand, are removed by adding ethanol. This is the same principle that is used in the extraction of the unsaturated fatty acids and polyphenols from the wine wastes.
The extraction is done through a biological process called diffusion which refers to the movement of water molecules from the point of high concentration to a low concentration. The solvent is critical in this case as it is what makes it possible for the two mixtures to be separated. The solvent can easily penetrate through because of the negligible viscosities and lack of surface tension. The supercritical fluid extraction will take between ten and sixty minutes unlike the use of an organic liquid which takes hours. The supercritical extract will be one of the final products.
The system that is used for extraction must have a pump for the carbon dioxide, a collecting vessel, and a pressure cell which will help in containing the sample. The liquid will then be pumped to the heating zone whereby it will be heated to the supercritical conditions.
After being heated, it will pass through the extraction vessel where it will rapidly dissolve the material that is being extracted because it will firstly dissolve in the material that is being extracted. The stuff that is dissolved will be swept into a separator at low temperature before it settles out. After this is done, the carbon dioxide can then be cooled and recompressed before it is released into the atmosphere.
Typically, the carbon dioxide is pumped like a liquid. This is usually below 41 degrees Fahrenheit with a pressure of about 50 bar being applied. The solvent is then injected as a liquid since it is not compressible.