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Ammonia is produced by combining hydrogen and nitrogen gas using iron as a catalyst. The process, known as the Haber process, was developed by Fritz Haber in the early 1900s. Hydrogen is usually sourced from natural gas and the temperature and pressure used are high. Nitrogen fixation is an alternative process that uses microorganisms to produce ammonia from nitrogen gas in the air.
Ammonia synthesis is the production of ammonia from the combination of hydrogen and nitrogen gas. Most of the ammonia produced is used as a fertilizer, although it can be used for other purposes, such as making explosives. The process was developed in Germany in the early 1900s.
The atmosphere is filled with nitrogen, but it is unreactive and generally does not combine with other elements. The basic strategy for producing ammonia, NH3, is to combine hydrogen gas, H2, with nitrogen gas, N2, at high temperature and high pressure. Chemically, this is a difficult reaction, so it requires an agent to speed up the process.
A catalyst is a compound that causes a reaction to proceed faster. In the synthesis of ammonia, the catalyst used is generally iron. The type of iron used is reduced magnetite ore. There are other chemicals that can be used as catalysts, but iron is the most common.
The source of hydrogen gas is usually natural gas, also known as methane, CH4. This describes the basic process of ammonia synthesis. Many other steps take place in an ammonia synthesis plant. The sulfur compounds are first removed from natural gas by reacting with zinc oxide, which is transformed into zinc sulfide. This leaves the methane free, which goes through many other transformations to generate hydrogen gas.
The temperature used is approximately 1482° F (400° C). The pressure used is lower than the optimum for the reaction. For safety reasons, a pressure of about 200 atmospheres (atm) is used. Yield is around 10-20% under these conditions. When the mixture leaves the reactor, it is cooled so that the ammonia becomes liquid. The heat is captured and reused to reheat the incoming gases.
This ammonia synthesis method is known as the Haber process, because it was created by the German chemist Fritz Haber, who developed the conditions for the chemical reaction. He developed it during a shortage of nitrogen-containing fertilizers in the early 1900s and because Germany needed explosives for World War I. Currently, ammonia is produced on a large scale all over the world.
An alternative way to produce the hydrogen for the reaction is through the electrolysis of water. Electrolysis uses electricity to break down compounds. In this case, the water is decomposed into hydrogen and oxygen. This was done in conjunction with the production of electricity from hydroelectric power plants. As early as 1911, the electrolysis of water was used to supply hydrogen for the synthesis of ammonia.
Some microorganisms are able to use nitrogen gas from the air to produce ammonia. This process is called nitrogen fixation. In this case the catalysts are complex enzymes called nitrogenases. The bacteria that carry out this process live on the roots of legumes, such as pea plants. Nitrogen fixation has significantly improved the nutritional status of many soils.
