We begin our new series breaking down key innovations in agriculture with the Haber-Bosch process, which enabled large-scale agriculture worldwide.
Ammonia – a compound of nitrogen and hydrogen – is therefore a key ingredient in fertilisers, allowing farmers to replenish the soil with nitrogen at will. As well as fertilisers, ammonia is used in pharmaceuticals, plastics, refrigerants, explosives, and in numerous industrial processes.
But how is it made? At the turn of the 20th Century, ammonia was mostly mined from deposits of niter (also known as saltpetre – the mineral form of potassium nitrate), but the known reserves would not satisfy predicted demands. Researchers had to find alternative sources.
Fritz Haber (left) and Carl Bosch (right) created and commercialised the process.
Atmospheric nitrogen, which makes up almost 80% of air, was the obvious feedstock – its supply, to all intents and purposes, being infinite. But reacting atmospheric nitrogen, which is exceptionally stable owing to its strong triple bonds, posed a challenge for chemists globally.
In 1905, German chemist Fritz Haber cracked the riddle of fixing nitrogen from air. Using high pressure and an iron catalyst, Haber was able to directly react nitrogen and hydrogen gas to create liquid ammonia.
His process was soon scaled up by BASF chemist and engineer Carl Bosch, becoming known as the Haber-Bosch process, and this would lead to the mass production of agricultural fertilisers and a phenomenal increase in the growth of crops for human consumption.
The Haber-Bosch process is conducted at a high pressure of 200 atmospheres and reaction temperatures of 450°C. It also requires a large feedstock of natural gas, and there is a global research and development effort to replace the process with a more sustainable alternative – just as the Haber-Bosch process replaced niter mining over a century ago.