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Manufacture of nitric acid

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Manufacture of nitric acid Overview: The manufacture of nitric acid is a three-stage process each having distinct reaction: a) Ammonia oxidation 4NH3 + 5O2 4NO + 6H2O ?H = - 900 kJmol-1 b) Nitric oxide oxidation 2NO + O2 2NO2 ?H = - 115 kJmol-1 2NO2 N2O4 ?H = - 58 kJmol-1 c) Dinitrogen tetroxide absorption 3N2O4 + 2H2O 4HNO3 + 2NO ?H = - 103 kJmol-1 Industrial Production of Nitric Acid Nitric acid is produced by 2 methods. 1. The first method involves oxidation, condensation, and absorption and yields a weak nitric acid with concentrations ranging from 30 to 70 percent nitric acid. 2. The second method combines dehydrating, bleaching, condensing, and absorption and produces a high-strength nitric acid from a weak nitric acid. High-strength nitric acid contains more than 90 percent nitric acid. Weak Nitric Acid Production This is done by the high-temperature catalytic oxidation of ammonia as shown in Figure. ...read more.


Both liquids flow countercurrent to the nitrogen dioxide/dimer gas mixture. Oxidation takes place in the free space between the trays, while absorption occurs on the trays. The exothermic reaction occurs as follows: 3N2O4 + 2H2O 4HNO3 + 2NO ?H = - 103 kJmol-1 A secondary air stream is introduced into the column to re-oxidize the NO that is formed in Reaction. This secondary air also removes NO from the product acid. This results in yield of 30 to 70 percent nitric acid, which depend upon factors such as temperature, pressure, number of absorption stages, and concentration of nitrogen oxides entering the absorber. High-Strength Nitric Acid Production: * A high-strength nitric acid (98 to 99 percent concentration) can be obtained by concentrating the weak nitric acid using extractive distillation. The distillation process is carried out in the presence of a dehydrating agent (Concentrated sulfuric acid 60 %). * The nitric acid concentration process consists of feeding strong sulfuric acid and 55 to 65 percent nitric acid to the top of a packed dehydrating column at atmospheric pressure. ...read more.


* Repeated exposure to high levels produces adverse effects on lung and teeth. * Nitric acid is harmful to aquatic life. Critical Evaluation of the manufacturing process: Large-scale manufacturing involves various issues such as cost and economies, safety and environmental issues. The environmental impact of the process and the byproducts has to be weighed carefully and newer more environmental friendly processes have to be designed. Running the process at optimum temperature and pressure using an appropriate catalyst can bring down the cost of the manufacturing. This is evident from both Haber process as well as for the synthesis of Nitric acid. It is important that emission levels are checked under permissible limits for any chemical process. Various products and by products shall be handled carefully with adequate safety measures adopted while manufacturing as well as during transport and storage. The benefits of Haber process and Manufacturing process of nitric acid far outweigh the hazards and therefore must be continued, however new research should be carried out to make the process as smooth, easy, economic and hazard free as possible. ...read more.

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