Nitric acid

Raw materials

1. Ammonia

2. Oxygen

Process

Ostwald Process

Ammonia is converted to nitric acid in two stages.

1. Ammonia is oxidized by heating with oxygen in the presence of a catalyst such as platinum with 10% rhodium to form nitric oxide and water with typical conditions of (which contribute to an overall yield of about 96%) pressure between 4-10 atm and temperature of 900 °C. This step is strongly exothermic, making it a useful heat source once initiated:

4 NH₃ (g) + 5 O₂ (g) → 4 NO (g) + 6 H₂O (g) (ΔH = −905.2 kJ)

2. Stage two (combining two reaction steps) is carried out in the presence of water in an absorption apparatus. Initially nitric oxide is oxidized again to yield nitrogen dioxide:

2 NO (g) + O₂ (g) → 2 NO₂ (g) (ΔH = −114 kJ/mol)

This gas is then readily absorbed by the water, yielding the desired product (nitric acid, albeit in a dilute form), while reducing a portion of it back to nitric oxide:

3 NO₂ (g) + H₂O (l) → 2 HNO₃ (aq) + NO (g) (ΔH = −117 kJ/mol)

The NO is recycled, and the acid is concentrated to the required strength by distillation.

Product

Nitric acid

Used for

Rocket fuel, chemical reagent, woodworking (artificially age pine and maple)

Production facility

Port Lincoln, SA

Export

Gaborone, Botswana