Realization of ammonia synthesis under high pressure

2 Realization of ammonia synthesis under high pressure 

The amount of ammonia formed in a single-pass is too little so that it is impossible to achieve the production in commercial scale. Therefore, Haber proposed to place the reactor in a closed system and circulate the gas mixture after flowing through the catalyst. This great idea provides foundation for industrial ammonia synthesis and numerous other synthesis reactions at high pressures in organic chemistry area. 

In 1908, Haber et al. was awarded a patent on ammonia synthesis from its elements by using high pressure circulating method, in which ammonia was condensed and separated continuously and N2-H2 mixture was recycled under high pressures, as shown in Fig. 1.4. 

Although iron catalysts were already used in ammonia synthesis at that time, excellent industrial catalysts had not been found yet. Haber energetically screened about 20,000 catalysts. In the March of 1909, he found that osmium exhibits excellent activity in ammonia synthesis. He obtained 8% ammonia concentration on 

However, osmium is a very rare resource and osmium oxide volatilize easily. Therefore, it was necessary to develop cheaper catalysts with excellent performances for ammonia synthesis. Since then, Haber identified that uranium is active for ammonia synthesis. However, in 1912, he was appointed as the director of Institute of Physical Chemistry and Electrochemistry in the Kaiser Wilhelm Institute, indicating the end of the research activity of Haber in the field of ammonia synthesis. Since then, Bosch and Mittasch became the principal researchers in BASF to continue the industrialization process for the ammonia synthesis. Bosch was the leader of the whole research group, and Mittasch became the main investigator for the exploration of catalysts. 

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