Being one of the four most important inorganic acids in the world as well as identified as one of the top ten chemical manufactured in the US, nitric acid production is an intricate and elaborate process but one which has been refined over years of research and practice.

Nitric acid is a colorless liquid which is (1) a strong oxidizing agent, having the ability to dissolve most metals except platinum and gold, (2) a potent acid due to the high concentration of hydrogen ions, and (3) a good source of fixed nitrogen necessary for the manufacture of nitrate containing fertilizers.

The process of producing nitric acid employs two methods, one producing weak nitric acid and high-strength (concentration) nitric acid.

Weak Nitric Acid Production

Weak nitric acid has 50-70% concentrated and it is produced in greater volume than the concentrated form mainly because of its industrial applications. This is typically produced using the high temperature catalytic oxidation of ammonia. It follows a three step process beginning with ammonia oxidation to nitric oxide followed by oxidation of nitric oxide into nitrogen dioxide and finally absorption of nitrogen dioxide in water.

In the first step of this process, a catalyst is applied and the most common catalyst used is a combination of 90 percent platinum and 10 percent rhodium gauze assembled into squares of fine wire. Heat is released from this reaction and the resulting nitric oxide is then oxidized by making it react with oxygen using condensation and pressure.

The final step involves introduction of deionized water. Nitric acid concentration now depends on the pressure, temperature, and number of absorption stages as well as the concentration of nitrogen oxides entering the absorber. The rate of the nitric dioxide absorption is controlled by three factors: (1) oxidation of nitrogen oxide in the gas phase, (2) the physical distribution of the reacting oxides from the gas phase to the liquid phase, and (3) the chemical reaction that takes place in the liquid phase.

High Strength (Concentration) Nitric Acid Production

High strength nitric acid has 95-99% percent concentration which is obtained by extractive distillation of weak nitric acid. The distillation employs a dehydrating agent, usually 60% sulfuric acid. The dehydrating agent is fed into the chamber with the weak nitric acid at atmospheric pressure resulting to vapors of 99 percent nitric acid with trace amounts of nitrogen dioxide and oxygen. The vapor then goes through a condenser to cool it down and separate oxygen and nitrogen oxides byproducts. Resulting nitric acid is now in concentrated form.

The trace amounts of oxides of nitrogen are converted to weak nitric acid when it reacts with air. Other gases are also released and emitted from the absorption chamber. It is important to note the amount of released oxides of nitrogen since these are indicators of the efficacy of the acid formation as well as the absorption chamber design. Increased emissions of nitrogen oxides are signs of problems in structural, mechanical problems, or both.

It might all sound complicated to a layman, and it is. However, people who work at manufacturing plants which produce nitric acid in both its forms are properly trained at handling the ins and outs of the processes.

Nitric acid production is a very delicate process however we can always look for better ways to make production more effective but not forgetting the hazards this chemical poses to both humans and the environment. So it is very important that proper safety procedures and training are given to those who are directly working with nitric acid. Also, structural and mechanical designs must be made to specifications, maintained regularly and monitored for possible leaks and damages.