The Haber process, also called the Haber-Bosch process, is the method of manufacturing ammonia from nitrogen and hydrogen using iron as a catalyst, under conditions of optimum temperature and pressure. This process was developed by the German chemist Fritz Haber in 1909, and was later expanded to an industrial scale by Carl Bosch. They were awarded the Nobel Prize in 1918 for overcoming the technical barriers involved in the use of high-pressure technology on an industrial scale.
Ammonia is very important to industry, as it is essential for the manufacture of most nitrogen-containing fertilizers and ammunition. It is synthesized by combing one volume of nitrogen with three volumes of hydrogen in the presence of porous iron as a catalyst. This is carried out under an optimum temperature of 1022°F (550°C) and a pressure of 2175 to 3626 psi (15 to 25 MPa) respectively. Though osmium and uranium were initially used as the catalysts for the Haber process, they were later replaced by iron, as it is a much cheaper alternative.
The hydrogen for the reaction is generally obtained by reacting methane or natural gas with steam in the presence of nickel oxide as a catalyst. The element is then made to pass over beds of iron oxide, along with nitrogen gas from the atmosphere. As the reaction is very slow under room temperature, the temperature is increased to accelerate the process. This reaction is an exothermic, or heat releasing, reaction, so an increase in the temperature will only favor the reverse reaction, leading to further reduction of the product.
This is in accordance to Le Chatlier’s principle, which states that any change in concentration, temperature, volume, or partial pressure to a system in equilibrium will cause the equilibrium to shift, in order to counteract the imposed change. In simpler terms, if the temperature of the reaction is increased to speed up the production of ammonia, it will lead to a further breakdown of the produced ammonia into nitrogen and hydrogen. Since the catalyst can function effectively only around 752°F (400°C), the temperature has to be maintained between 752° and 1022°F (300° and 550°C).
To increase the formation of ammonia, very high pressure is applied. Even under these conditions, only about 15% of ammonia is obtained in each pass. By repeated recycling of the unreacted gas, it is possible to get a recovery of almost 98%. The Haber process is used in the manufacture of nearly 100 million tons of fertilizer every year.