This is a multi-step process that takes advantage of the different boiling points of the gases. The process uses repeated cooling and heating to create a temperature difference that causes the gases to condense and then vaporise at different rates.
After the air is compressed and cooled, the process typically starts by cooling the mixture to a certain temperature, which creates two liquids: a top layer containing mostly nitrogen and a bottom layer contenant almost pure oxygen.
The top layer of liquid nitrogen is then sent to a distillation column where it is further separated into pure nitrogen gas and a small amount of oxygen and other gases.
To remove the remaining oxygen from the bottom layer of liquid oxygen, it is sent to a separate column where it is heated and then condensed. This process yields pure oxygen gas, with any remaining impurities (such as nitrogen) being removed in a final step known as 'purification'.
This fractional distillation process is used by BOC to separate the various gases in the atmosphere to create medical-grade oxygen, industrial gases, and other gas products. The efficiency of this process means it is widely used in industrial and medical applications, especially where highly pure oxygen is required.
