Question

(a) Explain how, nitrogen , oxygen and argon gases are separated from air.
(b) Draw a flow diagram of the processes involved in obtaining gases like nitrogen, oxygen and argon from air.

Answer 1

(a) Nitrogen, oxygen and argon are separated from air by fractional distillation. Following are the steps followed to separate these gases from air:
• Air is first filtered to remove the dust particles, spores etc. Subsequently water vapours and carbon dioxide are removed.
• Air is subjected to high pressure and then cooled. This air is then allowed to expand in a chamber which causes further cooling of the air.
• This process is repeated to cool the air further. Ultimately, the air becomes so cold that it turns into a liquid.
• This liquid air is then fed into a fractionating column from its bottom end and is cooled slowly.
• Liquid nitrogen boils off first to nitrogen gas as the boiling point of nitrogen is lowest at -196°C.
• Liquid argon boils off at a boiling point of -186°C.
• Liquid oxygen boils off last as it has highest boiling point among all three (around -183°C).

Fig. Separation of major gases of air