The fractional distillation of air is a process by which the substances in air are separated, evaporated and measured as they condense at different temperatures. Fractionally distilling air in this way makes it easier to understand the chemical makeup of air and to separate it into nitrogen and oxygen. After being separated, these elements can be used separately for many different reasons.
Fractional distillation is a method of separating substances that can be applied to many different chemicals, such as crude oil. However, one of its most popular applications is in the separation of nitrogen and oxygen from a quantity of air.
In order to perform fractional distillation on air, the air must first be liquefied and filtered for dust. This involves cooling it to a very low temperature. Then, this liquefied air is put into an apparatus called a fractionating column. The temperature rises slightly, and the nitrogen rises to the top of the column, where it is piped off separately from the oxygen. The oxygen pools at the bottom of the column and can be collected on its own as well. Because there are sometimes trace amounts of argon in the oxygen, it can be run through a second fractionating column to further separate it from the argon.