How is nitrogen gas turned into a liquid?

Nitrogen is an abundantly found element in the earth’s atmosphere constituting around 78% by volume. It is colorless, odorless and inert gas. The element is extensively used in wide range of industries and is called as the largest industrial gas. Besides gaseous nitrogen (LIN), there are many important applications for liquid nitrogen gas as well.  Liquid nitrogen is nitrogen liquefied at cryogenic temperature with a boiling point of (-195.79%). LIN is generated by cryogenic distillation of atmospheric air in a nitrogen gas plant.  Liquid nitrogen is dense so could be easily transported as a source of dry nitrogen. 

It is interesting to know how nitrogen gas is turned into liquid nitrogen. It is done in an air separation plant.  Atmospheric air is let into the air separation unit where it is compressed and is sent to a cleanup system where impurities like carbon dioxide, hydrocarbons and moisture. After being cleaned, the air is passes through heat exchangers where it is cooled to cryogenic temperatures. Now, the air is directed into the high pressure distillation column where it is physically separated into vaporous nitrogen at the top of the distillation column and oxygen at the bottom of the column. Nitrogen is withdrawn from the column and sent to a low pressure column where it is distilled till it meets commercial specifications.

Liquid nitrogen has got numerous medical and industrial applications.  LIN finds applications in removal of warts and actinic keratosis.  Biological specimens including semen, blood samples, etc, are preserved using liquid.  It is used for storage for preserving human and animal cells at cryogenic temperatures for research. Liquid nitrogen is studied in detail under a scientific study called cryogenics.  Other important applications of liquid nitrogen include immersion, freezing, and transportation of food products. LIN is also important as a coolant and is used as a component in cooling baths for carrying out low temperature reactions in chemistry.

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