Fractional distillation of air.
| Many gases are obtained in
commercial quantities through a process known as fractional distillation
of liquefied air. Air is filtered to remove dust and other solids, water
vapour and carbon dioxide. Water vapour and carbon dioxide are removed because
they solidify at low temperatures and this would block the flow of liquid
air through the pumps and pipes. As the dry air free of carbon dioxide is
compressed to 200 times atmospheric pressure it becomes warm. Heat is removed
by a network of pipes carrying liquid nitrogen. The cold, compressed air
is then allowed to expand rapidly thus cooling even further to the point
where most of the air is liquefied.
The gas mixture is then purified by fractional distillation. Dense oxygen is captured as liquid as it sinks while nitrogen gas escapes from the top and is collected.