Nitrogen gas: Production route
Three ways to pull nitrogen out of air
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.Industrial nitrogen comes from air by three routes. Cryogenic ASUs make high-purity nitrogen at large scale along with oxygen and argon, and are the only route to liquid. PSA units use carbon molecular sieves to adsorb oxygen and deliver 95-99.999% nitrogen on site. Membrane units give 95-99.5% nitrogen cheaply for small flows. For ammonia, gas-based plants add air in a secondary reformer so that the oxygen is burned and nitrogen remains. The choice is set by volume, purity and need for liquid.
Routes compared
| Route | Share of supply | Inputs per tonne | Typical scale | Yield | Co-products | Unit cost |
|---|---|---|---|---|---|---|
| Cryogenic air separation | most high-purity and liquid nitrogen (indicative) | about 100-200 kWh per t gaseous N2; about 400-700 kWh per t liquid (indicative) | single trains up to several thousand t a day | over 99.999% purity possible | oxygen and argon | India contract price 5.69 US cents per Nm3 (about $45/t), cash cost 3.6-3.9 cents per Nm3 (June 2023) |
| Pressure swing adsorption (PSA) | large share of on-site small and medium supply (indicative) | about 200-400 kWh per t N2 at 99.5-99.9% (indicative) | 10-3,000 Nm3 an hour | 95-99.999% | oxygen-enriched vent | not published |
| Membrane separation | small (indicative) | about 300-500 kWh per t N2 (indicative) | 1-1,000 Nm3 an hour | 95-99.5% | oxygen-enriched permeate | not published |
| Secondary reforming with air (ammonia plants) | most feedstock nitrogen in gas-based ammonia, which is just over 70% of ammonia (IEA 2021) | included in ammonia plant energy | world-scale ammonia trains 1.1-1.3 Mt NH3 a year | not applicable | none separate | included in ammonia cost |
How each route works
Cryogenic air separationAir is compressed, purified and distilled at about -195 C. Nitrogen is the overhead product. Plants built mainly for nitrogen make little oxygen; plants built for oxygen produce surplus nitrogen that is often vented.
Lowest cost at scale and makes liquid; high capex.
Intratec (June 2023); energy indicative Pressure swing adsorption (PSA)Carbon molecular sieve beds adsorb oxygen faster than nitrogen; two beds alternate. Purity is set by cycle time and bed size.
Cheap and quick to install; no liquid; energy rises sharply with purity.
indicative Membrane separationHollow-fibre polymer membranes let oxygen, water and CO2 permeate faster than nitrogen. Used for tyre inflation, offshore and small inerting.
Simple, no moving parts; limited purity.
indicative Secondary reforming with air (ammonia plants)In gas-based ammonia plants, air is fed to a secondary reformer; its oxygen burns some hydrogen and methane, leaving nitrogen in the right ratio for synthesis. No separate nitrogen plant is needed.
Cheapest feedstock nitrogen; tied to the reformer.
IEA Ammonia Technology Roadmap (2021); nitrogen tile Unit economics are indicative ranges from the sources named; costs move with feedstock and energy prices, plant size and region.