Nitric Acid Process

Process control in the production of nitric acid

Nitric acid (HNO3), also known as aqua fortis or spirit of nitre, is used for the production of ammonium nitrate, which is used in fertilizers. Nitric acid is also a key component in the manufacture of adipic acid and terephatalic acid. Other applications include explosives, mine leaching and stainless steel pickling. Nitric acid production can be composed of one or two processes depending on the required final concentration.

Nitric acid is often produced by high-temperature catalytic oxidation of ammonia. This process consists of three main steps: ammonia oxidation, nitric oxide oxidation and absorption.

The most common catalyst is composed of about 90% platinum and 10% rhodium (by weight). The catalyst is formed in the wire gauze and inserted into the converter. The exothermic reaction proceeds to a nitric oxide yield of about 93-98 %. The nitric oxide is then cooled to certain temperatures and at defined pressure. The next reaction is highly dependent on temperature and pressure.

After cooling down, the nitrogen dioxide/nitrogen tetroxide mixture enters an absorption column. After the absorption, acid concentration is typically between 55-65 % by weight. 

Vaisala Polaris™ process refractometer is used to control the absorption process and get a stable nitric acid concentration value.

Learn the details of the nitric acid process from the application note.

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