Haber–Bosch fertiliser helps feed half the world

Person: Fritz Haber
Lived: 1868–1934
Field: Chemistry
From: German

The story

In the nineteenth century, demand for nitrogen fertiliser grew rapidly. Most of it came from mined nitrate deposits, above all in Chile, and from guano gathered on tropical islands. By 1900 these reserves were thought insufficient to meet future needs. Nitrogen makes up about 78 percent of the air, but it is so stable that turning it into a usable compound had defeated chemists for decades.

In the summer of 1909 Fritz Haber, a Jewish-born professor at Karlsruhe, and his assistant Robert Le Rossignol demonstrated a tabletop machine that produced ammonia from nitrogen and hydrogen, drop by drop, at about 125 millilitres an hour. The chemical company BASF bought the process and assigned its chemist and engineer Carl Bosch to scale it up. Haber's apparatus used rare osmium as a catalyst, but in 1909 the BASF researcher Alwin Mittasch found a far cheaper iron-based catalyst that is still used today. Bosch solved the engineering problems of working continuously at high pressure, including reactor walls that cracked under hydrogen.

Industrial production began in 1913 at BASF's plant in Oppau, reaching 20 tonnes a day the following year. The Haber–Bosch process, considered by many one of the most important technological advances of the twentieth century, made nitrogen fertiliser mass-producible. Farmers could grow far more food on the same land. Haber received the Nobel Prize in Chemistry for 1918, and Bosch received the 1931 prize for his work on high-pressure chemistry.

Today the world produces more than 100 million tonnes of synthetic nitrogen fertiliser a year. About a third of annual global food production uses ammonia from the Haber–Bosch process, and this food is estimated to support nearly half the world's population. One estimate suggests that, at 1900 crop yields, the harvest of the year 2000 would have needed nearly four times as much farmland, close to half of all ice-free land on Earth.

The principle of controlling catalytic reactions at high pressure and temperature also led to further industrial processes, including Mittasch's synthesis of methyl alcohol and the production of nitric acid. For this work Haber has been called one of the most important industrial chemists in history. In his Nobel acceptance speech he noted modestly that nitrogen-fixing bacteria still used methods that chemists did not yet know how to imitate.

Why it matters

Synthetic nitrogen fertiliser has helped feed billions of people who could not otherwise have been fed, while sparing vast areas of land from the plough.

About Fritz Haber

Nobel chemist whose ammonia synthesis made the fertilisers that feed billions, who also led Germany’s WWI poison-gas programme, and who was driven out by the Nazis.

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Fritz Haber

1868–1934 · Chemistry

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