A supercritical fluid is a substance heated above its critical point, with properties of both a liquid and a gas. Carbon dioxide is often used as a supercritical fluid due to its critical temperature and pressure. It can be used in various industries, including food and pharmaceuticals, to extract compounds without leaving chemical residue.
A supercritical fluid is a substance that has been heated above its critical point. The critical point of a substance is the point at which critical pressure and critical temperature coexist, allowing the substance to exist in its liquid and gaseous forms at equilibrium. The result of ingesting a substance beyond this point is that a fluid has the dissolving properties of a liquid, but the diffusing properties of a gas. This means it can dissolve substances such as a liquid while expanding to fill a container such as a gas. These unique properties allow it to be used in different industries.
When a substance is taken above its critical point, it becomes a supercritical fluid. For a fluid to become supercritical, a person must know the critical temperature and critical pressure. Normally, a high temperature gas can be transformed into a liquid by adding pressure, and a high pressure liquid can be transformed into a gas by adding heat. Critical pressure is the pressure above which a substance cannot exist as a gas despite high temperature. Similarly, the critical temperature is the point above which a substance cannot be liquid despite high pressure.
An interesting phenomenon occurs when a substance is heated above the critical temperature and placed under a pressure above the critical one. The substance can be neither a liquid nor a gas. Rather, it has the properties of both. The lines between the phases of matter practically disappear and the fluid changes its properties. The new supercritical fluid has properties of both a liquid and a gas.
One supercritical fluid that is often used is carbon dioxide. It is a good substance to make into a supercritical fluid because its critical temperature is 87.8°F (31°C) and its critical pressure is 73 atmospheres (about 55,480 mm Hg). Once it is a supercritical fluid, the properties of carbon dioxide can be altered with changes in temperature and pressure. For example, manipulating pressure can change the substances that will dissolve in the fluid. Since carbon dioxide is a non-polar molecule, modifiers can be added to increase its ability to dissolve polar molecules.
Some supercritical fluids can be used to extract a greater amount of a desired substance in a shorter period of time. These and other properties allow it to be used in a wide range of industries. The food and pharmaceutical industries, for example, can use the fluid to extract certain compounds from food. Using a supercritical fluid, such as carbon dioxide, a scientist can extract fatty acids, oils and antioxidants without leaving any chemical residue on the extract. Supercritical carbon dioxide also has a relatively low temperature, so it can be used where a chemical cannot be exposed to high heat.
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