Haber-Bosch Process (1909): Making Fertiliser and Bread from Air

The Haber-Bosch process is the industrial method of making ammonia from the nitrogen in the air. In July 1909 the German chemist Fritz Haber demonstrated a working laboratory apparatus at Karlsruhe, and over the next four years Carl Bosch of the chemical firm BASF turned it into a giant industrial process. Its cheap fertiliser now helps feed billions of people, but it also supplied explosives for war.

Background: the nitrogen problem

Plants need nitrogen to grow. Although air is about 78 percent nitrogen, the gas is very unreactive, and most crops cannot use it directly. Farmers had long relied on manure, crop rotation with legumes such as clover and beans, and imported natural fertilisers.

By the late 19th century the main imported sources were guano, the accumulated droppings of seabirds, and sodium nitrate mined in the Atacama Desert of Chile, known as Chile saltpetre. Both were finite. In a famous address to the British Association in 1898, the chemist William Crookes warned that the world’s growing population would face a wheat shortage unless chemists learned to “fix” nitrogen from the air.

Nitrates were also vital for explosives and gunpowder. For a country like Germany, which depended on imports carried by sea, this was a strategic weakness as well as an agricultural one.

Haber’s breakthrough

Fritz Haber (1868–1934) was a professor of physical chemistry at the Technische Hochschule in Karlsruhe. From about 1904 he studied the reaction between nitrogen and hydrogen that forms ammonia. The reaction yields very little ammonia at ordinary pressures, and at high temperatures the ammonia breaks down again.

Haber and his English assistant Robert Le Rossignol tackled the problem by working at very high pressure, around 200 atmospheres, at about 500 to 600 °C, with a catalyst to speed the reaction. Their apparatus recirculated the unreacted gases so that they could pass over the catalyst again, and removed the ammonia as it formed. Haber filed a patent in October 1908.

In early July 1909 Haber demonstrated the tabletop apparatus to representatives of BASF, including the catalyst chemist Alwin Mittasch. Using a rare osmium catalyst, it produced liquid ammonia continuously for several hours, at a rate usually given as roughly 80 grams (about 125 millilitres) per hour. BASF agreed to develop the process.

Bosch scales it up

Turning a small glass-and-steel laboratory device into a factory was an enormous engineering task, and it was led by Carl Bosch (1874–1940), a chemist and engineer at BASF.

Three problems stood out:

• The catalyst. Osmium and uranium, which Haber had used, were rare and costly. Mittasch’s team tested thousands of materials in many thousands of experiments and found that cheap iron, with small amounts of added compounds, worked well.
• The reactors. At high pressure and temperature, hydrogen seeped into ordinary steel and made it brittle, causing early reactors to burst. Bosch solved this with a double-walled design, a soft-iron inner lining inside a strong steel outer shell, with small holes to let hydrogen escape.
• The gases. The plant needed large, steady supplies of pure hydrogen and nitrogen, as well as compressors and pumps that could run safely at high pressure.

The first industrial plant opened at Oppau, near BASF’s headquarters in Ludwigshafen, in September 1913.

The First World War

When war broke out in 1914, the British naval blockade cut Germany off from Chilean nitrate. Ammonia from the Haber-Bosch process could be oxidised to nitric acid, a key raw material for explosives, so BASF expanded production for the German war effort. A second, larger plant was built at Leuna, near Merseburg, and began production in 1917.

Many historians argue that synthetic nitrogen helped Germany continue fighting far longer than its pre-war nitrate stocks would have allowed. Haber himself became deeply involved in the war. He directed Germany’s chemical weapons programme and oversaw the first large-scale chlorine gas attack at the Second Battle of Ypres in April 1915. His wife, the chemist Clara Immerwahr, took her own life in May 1915; her motives are debated, but her opposition to his war work is often cited.

Key people

• Fritz Haber developed the high-pressure synthesis and won the 1918 Nobel Prize in Chemistry, awarded in 1919, a choice that was controversial because of his gas warfare. Although he had converted to Christianity and served Germany loyally, he was of Jewish origin and left the country in 1933 after the Nazis came to power. He died in Basel, Switzerland, in January 1934. In the 1920s he had also spent years on an unsuccessful project to extract gold from seawater, hoping to help Germany pay its war reparations.
• Carl Bosch led the industrial development and later became head of the chemical conglomerate IG Farben. He shared the 1931 Nobel Prize in Chemistry with Friedrich Bergius.
• Robert Le Rossignol built much of the laboratory apparatus with Haber.
• Alwin Mittasch led the search that found the iron-based catalyst still used, in improved form, today.

Consequences and legacy

After the war the process spread around the world. The Treaty of Versailles and the occupation of the Rhineland gave the Allies a close look at the German plants, and Britain, France, the United States and others soon built their own. Chile’s nitrate industry, which had once supplied most of the world’s fixed nitrogen and paid for much of the Chilean state, went into steep decline in the 1920s and 1930s as cheaper synthetic nitrogen took over the market. Cheap synthetic nitrogen fertiliser became one of the foundations of modern farming and, combined with new crop varieties after 1945, of the large rises in crop yields of the 20th century.

The scale today is vast. Ammonia production is estimated to use around 1 to 2 percent of the world’s energy and is a significant source of carbon dioxide emissions, mainly because the hydrogen is usually made from natural gas or coal. Researchers such as Vaclav Smil estimate that without synthetic fertiliser the world could feed only about half of its current population.

The process also has environmental costs. Excess nitrogen washes from fields into rivers and seas, feeding algal blooms and “dead zones” with little oxygen, and fertiliser releases nitrous oxide, a greenhouse gas. Like Alfred Nobel’s dynamite, the Haber-Bosch process shows how one chemical discovery can serve both peaceful and destructive purposes.

By the numbers

Timeline

• 1898: William Crookes warns of a coming shortage of nitrogen for wheat growing.
• 1908, October: Fritz Haber files his patent for high-pressure ammonia synthesis.
• 1909, July: Haber and Le Rossignol demonstrate continuous ammonia production to BASF.
• 1910: Alwin Mittasch’s team begins large-scale testing of catalysts at BASF.
• 1913, September: The first Haber-Bosch plant starts production at Oppau.
• 1915, 22 April: Chlorine gas, released under Haber’s direction, is used at Ypres.
• 1917: The large Leuna plant begins producing ammonia.
• 1919: Haber receives the Nobel Prize in Chemistry for 1918.
• 1931: Carl Bosch shares the Nobel Prize in Chemistry with Friedrich Bergius.

Why it matters

The Haber-Bosch process freed farming from the limits of natural nitrogen. It made it possible to grow food for a world population that rose from under 2 billion in 1913 to more than 8 billion today, while also arming armies and putting new pressure on the environment. Few inventions have touched so many lives so directly.