The Haber Process in War and Peace

By James Patton

Many have heard of the brilliant German chemist Fritz Haber (1868–1934), infamously remembered as the Father of Chemical Warfare due to his work developing and deploying weaponized chlorine, phosgene and diphosgene, and considered by some to be a quintessential "mad scientist." However, gas was actually his second-most important contribution to WWI. For what was vicariously his most important contribution, Haber received the Nobel Prize for Chemistry in 1918.

Fritz Haber

In 1909 Haber first demonstrated the Haber Process (also called the Haber-Bosch Process) by which he successfully synthesized ammonia, which is a precursor to the synthesis of nitrates and nitrates, which form the basis for both fertilizers and explosives. With the major natural sources of these substances denied to the Central Powers by the Royal Navy’s blockade, without the synthetic ammonia they would have quickly run out of ammunition, making the Haber Process probably the single most important factor that prolonged and intensified the war, so that it could be a horrific disaster.  

Born to a Jewish family in Breslau, Prussia, Haber’s father ran his family’s chemical works, making dyes, paints, and drugs. Haber received his doctorate from the Frederick Wilhelm University in Berlin in 1891. After a brief stint in the family business, he agreed to convert to Lutheranism to get a position in the laboratory of Hans Bunte (1848–1925) at the Technical Institute of Karlsruhe (Baden), and in 1898 he received a royal appointment to the faculty there. During this time he married the brilliant Clara Immerwahr (1870–1915), one of the first women to hold a doctorate in chemistry.

While at Karlsruhe Haber became interested in the work of his French colleague Henri Louis Le Chatelier (1850–1936), who in 1894 postulated the principle that bears his name, which he stated as:

When any system at equilibrium is subjected to change in concentration, temperature, volume, or pressure, the system readjusts itself to counteract the effect of the applied change and a new equilibrium is established.

To physical chemists this meant that chemical reactions could be reversible. Haber was particularly interested in producing ammonia (NH₃) from gaseous nitrogen and hydrogen. Ammonia is found in nature, a waste byproduct of living organisms and previous research had successfully decomposed natural ammonia into elemental nitrogen and hydrogen. Pursuant to Le Chatelier’s Principle, Haber reasoned that the process could be reversed, and on an industrial scale. If he was right the result would be a significant find because natural ammonia was scarce. 

Haber’s desired chemical reaction is expressed thus: N₂ + 3H₂  → 2NH₃

Sounds simple, but the process proved to be complicated, involving a pressure vessel and a metal catalyst, originally osmium (Os), which is the densest element and not abundant. Later research by Carl Bosch (1874–1940) of BASF led to the satisfactory substitution of iron compounds, particularly magnetite (Fe3O4), which dramatically reduced the production cost. Years later, Bosch shared a Nobel for Chemistry in 1931. 

Haber on Right in the Laboratory

There are six steps to the process, which occur as the pressure and temperature are increased (adsorbed means accumulated on the surface of the catalyst, akin to freezing rain adhering to a car window):

1. N2 (g) → N2 (adsorbed)
2.  N2 (adsorbed) → 2 N (adsorbed)
3.  H2 (g) → H2 (adsorbed)
4.  H2 (adsorbed) → 2 H (adsorbed)
5.  N (adsorbed) + 3 H(adsorbed)→ NH3 (adsorbed)
6. NH3 (adsorbed) → NH3 (g)

The process requires pressure at 2,200 to 3,600 psi and a temperature of 750 to 930°F. In this environment, the mixture of 3 parts hydrogen gas to 1 part nitrogen gas is repeatedly passed over the catalyst. On each cycle about 15% conversion occurs until 97% conversion is attained. 

The Haber Process is not just a footnote in history. It remains vitally important to humanity, as ammonia-based fertilizers are used everywhere to increase and improve crop yields and start "Green Revolutions." Without these chemicals half of us would starve.