Manufacture of dilute nitric acid

Nitric acid production involves two stages: -

1. The oxidation of ammonia
2. The absorption of gases with water
diagram: flow diagram for nitric acid production












diagram: comparing methods for controlling emissions












Total emissions from nitric acid plants can be reduced to very low levels.

Dinitrogen Monoxide

Dinitrogen monoxide (N2O, nitrous oxide) is also formed at the ammonia oxidation stage, and this can be difficult to remove. Careful control of conditions will reduce the amount formed, but some will inevitably be produced.

Several methods for the removal are being piloted, and are likely to be in use in the near future. This is important because dinitrogen monoxide is a significant greenhouse gas.
Methods being tried include:

  • Using an additional catalyst at the ammonia oxidation stage to decompose dinitrogen monoxide
  • Catalytic reduction of dinitrogen monoxide in the tail gas using ammonia

It is expected that application of these methods will achieve a reduction of N2O emission in the region of 80 - 90%.

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