Help
Add this page to your book
Show book (0 pages)
Suggest pagesOstwald process
The Ostwald process is a chemical process for producing nitric acid, which was developed by Wilhelm Ostwald (patented 1902). It is a mainstay of the modern chemical industry. Historically and practically it is closely associated with the Haber process, which provides the requisite raw material, ammonia.
[edit] Description
Ammonia is converted to nitric acid in two stages. It is oxidized (in a sense "burnt") by heating with oxygen in the presence of a catalyst such as platinum with 10% rhodium, to form nitric oxide and water. This step is strongly exothermic, making it a useful heat source once initiated:[1]
- 4 NH3 (g) + 5 O2 (g) → 4 NO (g) + 6 H2O (g) (ΔH = −905.2 kJ)
Stage two (combining two reaction steps) is carried out in the presence of water in an absorption apparatus. Initially nitric oxide is oxidized again to yield nitrogen dioxide:[1]
- 2 NO (g) + O2 (g) → 2 NO2 (g) (ΔH = −114 kJ/mol)
This gas is then readily absorbed by the water, yielding the desired product (nitric acid, albeit in a dilute form), while reducing a portion of it back to nitric oxide:[1]
- 3 NO2 (g) + H2O (l) → 2 HNO3 (aq) + NO (g) (ΔH = −117 kJ/mol)
The NO is recycled, and the acid is concentrated to the required strength by distillation.
Alternatively, if the last step is carried out in air:
- 4 NO2 (g) + O2 (g) + 2 H2O (l) → 4 HNO3 (aq)
Typical conditions for the first stage, which contribute to an overall yield of about 96%, are:
- pressure between 4 and 10 atmospheres (approx. 400-1010 kPa or 60-145 psig) and
- temperature is about 1173 K (approx. 900 °C or 1652 °F.).
A complication that needs to be taken into consideration involves a side-reaction in the first step that reverts the nitric oxide back to N2:
- 4 NH3 + 6 NO → 5 N2 + 6 H2O
This is a secondary reaction that is minimised by reducing the time the gas mixtures are in contact with the catalyst.[2]
[edit] References
- ^ a b c Alan V. Jones; M. Clemmet; A. Higton; E. Golding (1999). Alan V. Jones. ed. Access to chemistry. Royal Society of Chemistry. p. 250. ISBN 0854045643.
- ^ Harry Boyer Weiser (2007). Inorganic Colloid Chemistry -: The Colloidal Elements. Read Books. p. 254. ISBN 1406713031.
- GB 190200698, Ostwald, Wilhelm, "Improvements in the Manufacture of Nitric Acid and Nitrogen Oxides", published January 9, 1902, issued March 20, 1902
- GB 190208300, Ostwald, Wilhelm, "Improvements in and relating to the Manufacture of Nitric Acid and Oxides of Nitrogen", published December 18, 1902, issued February 26, 1903
[edit] External links
- Physics Daily
- Nitrogen & Phosphorus (General Chemistry course), Purdue University
- Drake, G; "Processes for the Manufacture of Nitric Acid" (1963), International Fertiliser Society
- Manufacturing Nitrates: the Ostwald process Carlton Comprehensive High School; Prince Albert; Saskatchewan, Canada.
