Air separation

Cryogenic air separation units (ASUs) are built to provide nitrogen or oxygen and often co-produce argon.

[1] Pure gases can be separated from air by first cooling it until it liquefies, then selectively distilling the components at their various boiling temperatures.

This process was pioneered by Carl von Linde in the early 20th century and is still used today to produce high purity gases.

To achieve the low distillation temperatures, an air separation unit requires a refrigeration cycle that operates by means of the Joule–Thomson effect.

The size of compressor is much reduced over a liquefaction plant, and portable oxygen concentrators are made in this manner to provide oxygen-enriched air for medical purposes.

[citation needed] Membrane gas separation is used to provide oxygen-poor and nitrogen-rich gases instead of air to fill the fuel tanks of jet liners, thus greatly reducing the chances of accidental fires and explosions.

Conversely, membrane gas separation is currently used to provide oxygen-enriched air to pilots flying at great altitudes in aircraft without pressurized cabins.