Manufacturing of nitric acid by Ostwald process
Step 1 — Primary oxidation (formation of nitric acid)
Oxidation of ammonia is carried out in a catalyst chamber in which ammonia and oxygen 1:8 by volume are introduced. The temperature of chamber is about 700'C. This chamber contains a platinum gauze which serves as catalyst.
Oxidization of ammonia is reversible and exothermic process. ammonia is converted into nitric oxide (NO).
4NH3 + 5O2 - - - >4NO + 6H2O
Step 2 — Secondary oxidation (formation of nitrogen dioxide)
Nitric oxide gas obtained by the oxidation of ammonia is very hot. In order to reduce its temperature, it is passed through a heat exchanger where the temperature of nitric oxide is reduces to 200'C. Nitric oxide after cooling is transferred to another oxidizing tower where at about 50'C it is oxidized to nitrogen dioxide (NO2).
2NO + O2 ----> 2 NO2
Step 3 — Absorption of NO2 (formation of HNO3)
Nitrogen dioxide from secondary oxidation chamber is introduced into a special absorption tower. NO2 gas passed through the tower and water is showered over it. By the absorption, nitric acid is obtained.
3NO2 + H2O - - - -> 2HNO3 + NO
Nitric acid so obtain is very dilute. It is recycled in absorption tower so that more and more NO2 get absorbed. HNO3 after recycle becomes about 68 per cent concentrated.
Step 4 — Concentration:
In order to increase the concentration of HNO3, vapors of HNO3 are passed over concentrated H2SO4. Being a dehydrating agent, H2SO4 absorbs water from HNO3 and concentrated HNO3 is obtained.
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