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Ostwald process
The Ostwald process is a chemical process used for making nitric acid (HNO3). The Ostwald process is a mainstay of the modern chemical industry, and it provides the main raw material for the most common type of fertilizer production. Historically and practically, the Ostwald process is closely associated with the Haber process, which provides the requisite raw material, ammonia (NH3). This method is preferred over other methods of nitric acid production, in that it is less expensive and more efficient.
Ammonia is converted to nitric acid in 2 stages.
The Ostwald process begins with burning ammonia. Ammonia burns in oxygen at temperature about 900 °C (1,650 °F) and pressure up to 8 standard atmospheres (810 kPa) in the presence of a catalyst such as platinum gauze, alloyed with 10% rhodium to increase its strength and nitric oxide yield, platinum metal on fused silica wool, copper or nickel to form nitric oxide (nitrogen(II) oxide) and water (as steam). This reaction is strongly exothermic, making it a useful heat source once initiated:
A number of side reactions compete with the formation of nitric oxide. Some reactions convert the ammonia to N2, such as:
This is a secondary reaction that is minimised by reducing the time the gas mixtures are in contact with the catalyst. Another side reaction produces nitrous oxide:
The platinum and rhodium catalyst is frequently replaced due to decomposition as a result of the extreme conditions which it operates under, leading to a form of degradation called cauliflowering. The exact mechanism of this process is unknown, the main theories being physical degradation by hydrogen atoms penetrating the platinum-rhodium lattice, or by metal atom transport from the centre of the metal to the surface.
The nitric oxide (NO) formed in the prior catalysed reaction is then cooled down from around 900˚C to roughly 250˚C to be further oxidised to nitrogen dioxide (NO2) by the reaction:
2NO + O2 → 2NO2 (ΔH = -114.2 kJ/mol)
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Ostwald process
The Ostwald process is a chemical process used for making nitric acid (HNO3). The Ostwald process is a mainstay of the modern chemical industry, and it provides the main raw material for the most common type of fertilizer production. Historically and practically, the Ostwald process is closely associated with the Haber process, which provides the requisite raw material, ammonia (NH3). This method is preferred over other methods of nitric acid production, in that it is less expensive and more efficient.
Ammonia is converted to nitric acid in 2 stages.
The Ostwald process begins with burning ammonia. Ammonia burns in oxygen at temperature about 900 °C (1,650 °F) and pressure up to 8 standard atmospheres (810 kPa) in the presence of a catalyst such as platinum gauze, alloyed with 10% rhodium to increase its strength and nitric oxide yield, platinum metal on fused silica wool, copper or nickel to form nitric oxide (nitrogen(II) oxide) and water (as steam). This reaction is strongly exothermic, making it a useful heat source once initiated:
A number of side reactions compete with the formation of nitric oxide. Some reactions convert the ammonia to N2, such as:
This is a secondary reaction that is minimised by reducing the time the gas mixtures are in contact with the catalyst. Another side reaction produces nitrous oxide:
The platinum and rhodium catalyst is frequently replaced due to decomposition as a result of the extreme conditions which it operates under, leading to a form of degradation called cauliflowering. The exact mechanism of this process is unknown, the main theories being physical degradation by hydrogen atoms penetrating the platinum-rhodium lattice, or by metal atom transport from the centre of the metal to the surface.
The nitric oxide (NO) formed in the prior catalysed reaction is then cooled down from around 900˚C to roughly 250˚C to be further oxidised to nitrogen dioxide (NO2) by the reaction:
2NO + O2 → 2NO2 (ΔH = -114.2 kJ/mol)