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Haber process


Haber process
From Wikipedia, the free encyclopedia
The Haber process, also called the Haber–Bosch process, is the reaction of nitrogen and hydrogen, over an iron substrate, to produce ammonia.[1][2][3] The Haber process is important because ammonia is difficult to produce on an industrial scale. Even though 78.1% of the air we breathe is nitrogen, the gas is relativelyunreactive because nitrogen molecules are held together by strong triple bonds. It was not until the early 20th century that this method was developed to harness the atmospheric abundance of nitrogen to create ammonia, which can then be oxidized to make the nitrates and nitrites essential for the production of nitrate fertilizer and munitions.

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1 History 2 Theprocess o 2.1 Synthesis gas preparation o 2.2 Ammonia synthesis 3 Reaction Rate and Equilibrium 4 Catalysts 5 Economic and environmental aspects 6 See also 7 References 8 External links

The process was first patented by Fritz Haber. In 1910 Carl Bosch, while working for chemical company BASF, successfully commercialized the process and secured further patents. Haber and Bosch were laterawarded Nobel prizes, in 1918 and 1931 respectively, for their work in overcoming the chemical and engineering problems posed by the use of large-scale high-pressure technology. Ammonia was first manufactured using the Haber process on an industrial scale in Germany during World War I to meet the high demand for ammonium nitrate (for use in explosives) at a time when supply of Chile saltpetre fromChile could not be guaranteed because this industry was then almost 100% in British hands. It has been suggested that without this process, Germany would almost certainly have run out of explosives by 1916, thereby ending the war.

The process
The bulk of the chemical technology consists in getting the hydrogen from methane or natural gas using heterogeneous catalysis and then reacting it withthe atmospheric nitrogen.

Haber process


Synthesis gas preparation
First, the methane is cleaned, mainly to remove sulfur impurities that would poison the catalysts. This is done by turning sulfur into hydrogen sulfide: CH3SH + H2 → CH4 + H2S and then reacting with zinc oxide to form zinc sulfide: H2S + ZnO → ZnS + H2O The clean methane is then reacted with steam over a catalyst ofnickel oxide. This is called steam reforming: CH4 + H2O → CO + 3H2 Secondary reforming then takes place with the addition of air to convert the methane that did not react during steam reforming. The Carbon Monoxide (CO) is also a catalyst poisoning, which would interact with the Iron catalyst, forming an Iron compound, thus affecting the reaction. The air added during this step also serves as anitrogen source for ammonia synthesis: CH4 + 1/2O2 → CO + 2H2 CH4 + 2O2 → CO2 + 2H2O Then occur two’’shifts’’ which convert CO to CO2 by reaction with steam, one at high temperature, then one at low temperature: CO + H2O → CO2 + H2 high temperature → the catalyst here is a mixture of iron, chromium and copper CO + H2O → CO2 + H2 low temperature → the catalyst here is a mixture of copper, zinc andaluminium Then the carbon dioxide is removed by reaction with potassium carbonate. K2CO3 + H2O + CO2→ 2KHCO3 The gas mixture is now passed into a methanator which converts any remaining CO2 into methane for recycling: CO2 + 4H2 → CH4 + 2H2O We now have a gas mixture containing nitrogen and hydrogen in the correct ratio of 1:3.

Haber process


Ammonia synthesis
The final stage is thecrucial synthesis of ammonia using promoted magnetite, iron oxide, as the catalyst: N2(g) + 3H2(g) → 2NH3(g), ΔHo = -92.4 kJ/mol This is done at 150 - 250 atmospheres (atm) and between 300 and 550 °C, passing the gases over four beds of catalyst, with cooling between each pass to maintain a reasonable equilibrium constant. On each pass only about 15% conversion occurs, but any unreacted gases will...
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