How Is Oxygen Produced Industrially?

The short answer

Industrial oxygen is extracted from atmospheric air, which is about 21% oxygen, 78% nitrogen and 1% argon. There are two commercial routes.

Cryogenic air separation cools air until it liquefies, then distils it into its components — producing high purity oxygen (99.5%+) plus nitrogen and argon as saleable products, at large scale. Pressure swing adsorption (PSA) passes compressed air through a zeolite molecular sieve that holds nitrogen back and lets oxygen through, producing 93 – 95% oxygen at small to medium scale, generated on site.

Neither creates oxygen. Both are separation processes — the oxygen was always in the air.

Cryogenic air separation, step by step

1. 1
   1 · Filtration and compression

   Air is drawn in, filtered of dust and compressed. This is the largest single energy cost in the whole process.
2. 2
   2 · Pre-purification

   Water vapour, carbon dioxide and hydrocarbons are removed on molecular sieve beds. This is safety-critical: any hydrocarbon carried forward concentrates in the liquid oxygen, where it becomes a serious explosion hazard.
3. 3
   3 · Heat exchange

   The clean air is cooled against the cold product streams leaving the plant, recovering refrigeration rather than wasting it.
4. 4
   4 · Expansion and liquefaction

   Further cooling by expansion takes the air to around −185 °C, where it liquefies.
5. 5
   5 · Distillation

   The liquid air is fractionated in a distillation column. The components boil at different temperatures — nitrogen at −195.8 °C, argon at −185.8 °C, oxygen at −183.0 °C — so they separate by boiling point, exactly as in any distillation.
6. 6
   6 · Product take-off

   Oxygen is drawn off as liquid for storage and tanker delivery, or vaporised and compressed into cylinders. Nitrogen and argon are recovered from the same column as saleable products.

That ten-degree spread between the three boiling points is the entire basis of the process — and the reason argon is a by-product of oxygen production rather than something obtained separately.

PSA: adsorption instead of cold

A PSA oxygen plant uses no refrigeration at all. Compressed air passes through a bed of zeolite molecular sieve, which adsorbs nitrogen preferentially and lets oxygen through as product gas.

Because the bed saturates, PSA plants run in pairs. One tower produces oxygen while the other is depressurised to release the captured nitrogen to atmosphere; the towers then swap, typically on a cycle of under a minute. The swing between adsorption and regeneration pressure is what gives the process its name.

The practical ceiling is around 93 – 95% oxygen, with the remainder mostly argon — which the sieve does not separate well from oxygen. For flame cutting, furnace enrichment, effluent treatment and aquaculture that is entirely adequate.

Choosing between them

The decision usually turns on two questions: does your process genuinely need more than 95%, and is consumption steady enough to justify owning a plant? Below roughly a cylinder bank a week, delivered cylinders are simpler and cheaper. Well above that, on-site generation generally costs less per cubic metre and removes the delivery dependency.

How medical oxygen is produced

Medical oxygen comes from the same cryogenic process. What differs is everything after the column: batch testing against the pharmacopoeial monograph, release documentation, retained samples, a dedicated controlled cylinder fleet, and licensed filling premises.

Medical PSA installations also exist, particularly for hospital pipelines, but they are a distinct equipment specification with their own validation, continuous monitoring and alarm requirements — not an industrial PSA plant with a different label.

The hydrocarbon rule in air separation

One detail deserves emphasis, because it is where cryogenic plants have historically failed catastrophically. Hydrocarbons in the incoming air — from nearby traffic, solvent use or a plant flare — are not very soluble in liquid oxygen, and acetylene in particular precipitates as a solid below about −195 °C.

Solid hydrocarbon accumulating in a liquid oxygen bath is an explosion waiting for a trigger. This is why pre-purification is treated as safety equipment rather than a quality step, and why air-intake siting is a serious engineering decision rather than a convenience.