Production Methods Summary

The demand and the desire to fix nitrogen to make explosives, as well as fertilisers, led to the development of chemical processes to produce ammonia, nitric acid and nitrates from the distillation of coal and the by-products of other industrial chemical processes.

Early processes (1900 - 1920) were the Arc Process and the Cyanamid Process, both highly energy intensive and uncompetitive relative to the later Haber-Bosch process.

Alternative Catalysts
In 1992, M.W. Kellog and the Ocelot Ammonia Company started ammonia production using a new ruthenium catalyst deposited on an active carbon support. It is referred to as the Kellog Advanced Ammonia Process (KAAP). This new technology can be retro-fitted to existing ammonia plants and operates at lower temperatures and pressures, giving considerable savings in both money and energy. Typically, a pressure of 40 atmospheres can be used, instead of 100 - 250 atmospheres. The newer catalyst is more expensive, but this is outweighed by other cost reductions.

In 2000, scientists at the Danish company Haldor - Topsøe announced the discovery of a new commercially viable catalyst for the Haber reaction. These involve ternary nitrides such as Fe3Mo3N; Co3Mo3N and Ni2Mo3N. These compounds, with caesium promoters, appear to have catalytic activities 2 or 3 times greater than present commercial iron based catalysts at the same operating conditions. They are also considerably cheaper than ruthenium based catalysts of the KAAP process. The same Haldor - Topsøe team have produced ruthenium catalysts with Barium promoters that are 2.5 times more active than current ruthenium catalysts.

diagram: chemical equation
diagram: nitrogenase enzyme

Taking a Leaf from Nature
Atmospheric nitrogen is "fixed" at normal temperatures and pressures by several natural organisms. The enzyme nitrogenase is responsible for this. Nitrogenase contains clusters of iron, molybdenum and sulphur (Fe/Mo/S). Several artificial clusters have been made that show catalytic activity, and may lead eventually to ammonia synthesis at room temperature and normal atmospheric pressure.

The Breakthrough
Although nitrogen gas is readily and cheaply available from air, it proved very difficult to break the nitrogen triple bond. It was not until 1909, after considerable effort worldwide, that Fritz Haber managed to fix nitrogen from the air, by reacting it with hydrogen. The secret was in the catalyst used and Haber and Carl Bosch systematically tested some 20,000 catalysts, before succeeding with some iron ore from Kiruna in Sweden. By chance, this ore contained trace amounts of alkali metal compounds and the catalyst used today in the Haber- Bosch process, iron oxide with potassium hydroxide promoter, is not so very different to that discovered by Haber and Bosch.
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For further details on use of enzyme-based catalysis, see the catalysis site.

image: catalyst surface

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