How is air separated?

Answer 1

Cryogenic distillation

• Air is separated through a process known as cryogenic distillation. The process works through various steps to separate elements from the air, one by one, through a series of columns. This process can be applied to many instances where there is a need to remove certain elements or by-products from more complex compounds.

Purification

• The first step in cryogenic distillation requires taking large volumes of air from the atmosphere. The air is compressed to approximately 94 psi where it is then cooled. As it cools, water vapor is condensed and removed. The air, still under pressure, is then passed through a filter known as a molecular sieve. This will remove compounds such as carbon dioxide and any residual water vapor.

Splitting the Air Stream

• The now completely pure air is split between two columns. The smaller air column is cooled further by increasing the pressure and then allowing the air to decompress to pressures close to the natural atmosphere. This super chilled air is passed into the cryogenic section and will provide the extremely cold temperatures needed for separation.

Initial Separation

• The chilled, decompressed air is passed through the main air column in a series of heat exchangers. The main air column is rapidly cooled and oxygen, as it has the highest boiling point, begins to condense to a liquid at the bottom of the tank. The remaining gas, composed of nitrogen and argon, remain above as vapor. The crude oxygen is then filtered out, cooled, and cycled through the same process of cryogenic distillation to further purify it for commercial sale.

Final separation

• The nitrogen and argon vapors are siphoned out and raised to atmospheric pressure. They are then introduced into a low pressure column. The sudden expansion of pressure causes the temperature of the gases to rapidly drop. The result is a separation of the two as they have different boiling points. The lighter nitrogen will remain completely gaseous at the top of the tank while the argon will collect toward the bottom as vapor. Like the oxygen, the two gases can now be removed and further purified.

Answer 2

No. Not so in most of the cases.