Separation of Air - How is Air Separated?

Air is a mixture of many different gases. 
These different gases are very useful.
But they must be separated from each other before we can use them.

Air separation process

Air is first changed from a gas to a liquid.
It is compressed, which means it is squeezed into a smaller space, and then cooled to about - 310 °F (-190 °C).
Then the liquid air passes into a tower called a fractionating column. 
The tower is warmer at the bottom and cooler at the top.
The liquid begins to evaporate, turning into gas.
Some gases evaporate at a lower temperature.
Helium and neon collect at the top of the tower.
Nitrogen evaporates next, leaving liquid oxygen at the bottom of the tower.
Separating gases in this way is called fractional distillation.

Gases from the air are used in many different ways.
People with breathing problems cannot take in enough oxygen. They are given special air with extra oxygen added to it.
Fuels cannot burn without oxygen.
A gas called acetylene burns in pure oxygen to give a very hot flame. The flame can melt metals and cut through them.
In sewage plants, oxygen is used to help change harmful substances into harmless ones.
Liquid nitrogen is very cold and is used to freeze foods quickly. It can also freeze liquids in damaged pipes so that the pipes can be repaired.
Substances do not burn in nitrogen, so it is also used inside light bulbs to keep the filament from burning away. In oil tankers, it can prevent fires and explosions.
Plants need nitrogen, so many farmers put fertilizers containing nitrogen compounds into the soil.

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