Liquid nitrogen is simply the element nitrogen in liquid state. Nitrogen is a gas at room temperature, it is the largest component of air, but it turns into a liquid at an extremely low temperature. Nitrogen has a boiling point of approximately -196 °C (-321 °F) and it freezes at -210 °C (-346 °F), which means that liquid nitrogen can only exist between these temperatures. Liquid nitrogen is used for a number of applications such as storing cells, blood and other biological materials at extremely low temperatures, removing unwanted skin lesions, as a coolant, and many more. Let’s find out how liquid nitrogen is produced.
How is liquid nitrogen made?
The first step in producing liquid nitrogen is called air separation. The most common method for separating air is called cryonic distillation. In this process the air is filtered and an air compressor is used to compress the air to high pressure. This air is then passed through a special sieve to remove carbon dioxide and water vapor. The high pressure gas is then cooled back to room temperature and then allowed to expand. The expanding air cools upon expansion and allows the oxygen, nitrogen and argon to be removed separately. The nitrogen is compressed again until a liquid is produced.
Liquid nitrogen can also be easily made from nitrogen gas without using compression. The gas is pumped into a dewar, a special flask invented by James Dewar, which is used to store the nitrogen. This flask is then cooled with a special cooler called a cryocooler and the gas becomes a liquid.
Did you know?
Liquid nitrogen must be handled very carefully. Even brief contact with human skin will lead to cold burns (frostbite). In October 2012 an English teenager had her stomach removed after drinking a cocktail made with liquid nitrogen.
Liquid nitrogen also expands rapidly when boiling and this can lead to a drop in the available oxygen if working in an enclosed space. In 1999 a laboratory assistant died of asphyxiation caused by a liquid nitrogen spill in a storage room.