How is nitrogen separated from liquefied air by fractional distillation?

Commercial production of nitrogen is primarily achieved through the fractional distillation of liquefied air. This process relies on the different boiling points of the components found in air to separate them.12

The procedure generally follows these steps:

• Preparation: Air is filtered to remove particulates, and moisture and carbon dioxide are removed by absorption in alkali.3
• Liquefaction: The air is compressed and cooled through multiple expansion and compression cycles until it reaches a liquid state at approximately −196 °C.3
• Distillation: The liquid air is allowed to warm gradually. Because nitrogen has a lower boiling point (−195.8 °C) than oxygen, it is more volatile and vaporizes first.13
• Separation: As the mixture warms, the light rare gases and nitrogen distill off as vapors, leaving behind the liquid oxygen, which has a higher boiling point.3

Through repeated condensation and revaporization in a fractionating column, the components are separated based on their specific volatilities, allowing for the collection of pure nitrogen.2