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Question
Explain how, nitrogen , oxygen and argon gases are separated from air.
Solution
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).
Figure 84. Separation of the major gases of air.
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