Nitric acid

Ammonia oxidised to a strong oxidising acid; the route to ammonium nitrate fertiliser and explosives, and a large, cheaply avoidable source of nitrous oxide.

Commodity chemicals · Acids & alkalis · No. 2

• Single chemical
• Feedstock: Minerals and salts
• about 65.5 Mt HNO3 a year (100% basis)
• 1.8 t CO₂e per t
• HS 280800

Half the world's nitric acid plants still leak a potent greenhouse gas that costs as little as $1 a tonne to stop.

Chart: Illustration: Nitric acid

Where it comes from

Chart: Map of where it comes from

In the Ostwald process ammonia is burnt over platinum-rhodium gauze at about 850-950 C, and the nitrogen oxides are absorbed in water to give 55-68% acid.

Three things to know

1. Ammonia makes up 80-90% of nitric acid's cash cost, so cheap gas decides who can produce it profitably.
2. An unabated plant emits about 5-9 kg of nitrous oxide per tonne, equal to 1.4-2.5 t of CO₂.
3. Most acid never leaves its site: under about 2% of output is traded, because ammonium nitrate ships far more easily.

The journey

1. 1 AmmoniaAbout 0.28 t per tonne of acid
2. 2 OxidationBurnt over platinum-rhodium gauze near 900 C
3. 3 AbsorptionNitrogen oxides absorbed into 55-68% acid
4. 4 Tail gasCatalysts strip N2O, expander recovers energy
5. 5 NeutralisationMixed with ammonia into ammonium nitrate
6. 6 End useFertiliser, mining explosives, nylon, polyurethane

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