Oxygen: Production route
Giant cold boxes or small sieve units
What this tab covers How it is made: the main production routes or, for product families, the main product types and technologies, compared on share of supply, inputs per tonne, plant scale, yield, co-products and unit cost.Oxygen is separated from air, never synthesised. Large users need cryogenic ASUs, which make oxygen, nitrogen and argon together and can deliver liquid. Smaller users, hospitals and remote sites use pressure or vacuum swing adsorption (PSA/VPSA), which makes 90-95% oxygen without cryogenics. Electrolysers for green hydrogen also release 8 t of oxygen per t of hydrogen, a by-product that could matter locally. The choice depends on volume, purity and whether liquid or argon is needed.
Routes compared
| Route | Share of supply | Inputs per tonne | Typical scale | Yield | Co-products | Unit cost |
|---|---|---|---|---|---|---|
| Cryogenic air separation (ASU) | most of world oxygen (indicative) | about 200-300 kWh per t gaseous O2; about 600-1,000 kWh per t liquid O2 (indicative) | single trains up to about 5,000 t O2 a day; INOX Air Products' six Indian ASUs (2017 plan) totalled 1,200 t a day of liquid | oxygen recovery over 95% (indicative) | about 3.3 t nitrogen and up to about 55 kg argon per t oxygen (basis: air composition by mass) | India contract price 8.11 US cents per Nm3 (about $57/t) ex-works, cash cost 3.5-4.0 cents per Nm3 (May 2023) |
| Pressure or vacuum swing adsorption (PSA/VPSA) | small share of volume; most hospital and small-industrial capacity (indicative) | about 250-400 kWh per t O2 (indicative) | 1-300 t a day; India's 2021 PSA programme averaged about 1.5 t a day per plant | 90-95% purity | nitrogen-rich vent | not published |
| Membrane separation | negligible | not published | small | 25-40% oxygen | nitrogen-rich retentate | not published |
| By-product of electrolysis | negligible (2 GW electrolysis installed, 2024) | free by-product | a 100 MW electrolyser gives about 40-70 kt O2 a year depending on load factor (indicative) | very high purity after drying | hydrogen is the main product | near zero marginal cost |
How each route works
Cryogenic air separation (ASU)Compressed, purified air is cooled against product streams in a heat exchanger, expanded and distilled in a double column. Oxygen collects at the bottom, nitrogen at the top and an argon side-stream is drawn off. Plants run continuously and can store liquid for peak demand.
Lowest cost at scale and makes liquid and argon; high capex and slow to start.
Intratec (May 2023); process-worldwide (2017); Thunder Said Energy (2023); indicative energy Pressure or vacuum swing adsorption (PSA/VPSA)Air passes through zeolite beds that adsorb nitrogen; oxygen of 90-95% purity passes through. Beds cycle between adsorption and regeneration. Units are modular and start in minutes.
Cheap and quick for small volumes; no liquid or argon, lower purity.
Deccan Herald citing Government of India (2021); indicative energy Membrane separationPolymer membranes let oxygen permeate faster than nitrogen, giving oxygen-enriched air of about 25-40%. Used for combustion enrichment and small medical concentrators.
Simple; cannot make high purity.
industry practice (indicative) By-product of electrolysisWater electrolysers make 8 t of oxygen per t of hydrogen. Most is vented today; some projects plan to sell it to hospitals, steel or wastewater plants.
Could cut ASU demand near large hydrogen hubs.
IEA GHR 2025; stoichiometry Unit economics are indicative ranges from the sources named; costs move with feedstock and energy prices, plant size and region.