NITRIC ACID

Nitric acid (HNO₃) is a highly toxic and corrosive acid. Pure nitric acid is colourless and concentrated solutions have a yellow-brown colour due to dissolved nitrogen dioxide.  Nitric acid is miscible in water and distillation of it gives an azeotrope of 68.4% nitric acid. Nitric acid is produced by using ammonia (NH₃), air and water as feedstock.

Process Overview

There is one nitric acid plant located on the Point Lisas Industrial Estate. It is produced in Methanol Holdings Trinidad Limited A-U-M Complex and the plant has a production capacity 532,000 metric tonnes (MT) per year of nitric acid. The A-U-M complex was commissioned in 2010 and process technology used to produce nitric acid is Uhde technology from Germany.

The production of nitric acid takes place in three stages:

1. Ammonia oxidation
2. Nitric Oxide Oxidation
3. Absorption of nitrogen dioxide to nitric acid

The production process is briefly described in the flow chart:

The process starts with liquid ammonia being vapourized and preheated as well as a stream of air is filtered and compressed. A mixture of air and ammonia consisting of 90% air and 10% ammonia enters the Ammonia Oxidation Reactor. In the reactor, ammonia is oxidized to nitric oxide (NO).

4NH₃ + 5O₂ → 4NO + 6H₂O

Subsequently the nitric oxide downstream the reactor oxidizes to nitrogen dioxide (NO₂) via the chemical reaction as the gases are cooled in a condenser.

2NO + O₂ → 2NO₂

The resulting gas/liquid mixture from the condenser is a weak nitric acid and nitrogen dioxide gas is fed to the Absorber column. Process water is fed to the top of the column. The non-dissolved nitrogen oxide gases (NOx) are absorbed into the weak acid to form nitric acid at a concentration of approximately 60%.

3NO₂ + H₂O → 2HNO₃ + NO 

The nitric acid produced in the absorber contains dissolved nitrogen oxides which are physically stripped off in a stripper and returned to the absorber using bleaching air. The nitric acid is pumped from the bottom of the stripper to the nitric acid storage tank.

The nitrogen oxides gases (tailgas) released are treated with ammonia before being released to the atmosphere via the chemical reactions to produce nitrogen (N₂) and water vapour:

6NO₂ + 8NH₃ → 7N₂ 12H₂O

6NO + 4NH₃ → 5N₂ + 6H₂O

Uses of Nitric Acid

It is estimated that 80% of the nitric acid produced worldwide is used as an intermediate in the production of nitrogenous fertilizers where about 65% is used to make ammonia nitrate, and the remaining 20% used in the explosive, plastics and chemical industries. These alternative uses of nitric acid include:

• Silver and gold separation
• Military munitions
• Photoengraving
• Acidulation of phosphate rock
• Steel and brass pickling
• Production of nitrobenzene, dinitrotoluenes, and other chemical intermediates, which can be utilized in the manufacture of explosives

Product Description

Please refer to link for a more detail description of the nitric acid process:

http://www.uhde.eu/competence/technologies/nitrates/182/overview.html

Nitric Acid is corrosive and highly toxic acid. A Material Safety and Data Sheet (MSDS) for nitric acid can be found at this link:

www.sciencelab.com/msds.php?msdsId=9926241