Ammonia Synthesis: Green Revolution The air in the atmosphere is 78% nitrogen, but free nitrogen N 2 cannot be utilized by

3.1.2 Ammonia Synthesis: Green Revolution The air in the atmosphere is 78% nitrogen, but free nitrogen N 2 cannot be utilized by

plants and animals. N 2 has to be “fixed” or converted with a great deal of energy into

a water-soluble chemical compound, such as nitrogen oxide NO or ammonia NH 3 . Fixed nitrogen needed by plants is provided by nature from the energy of lightning, which fixes atmospheric nitrogen in the form of nitric oxide, as well as from the legume nodule bacteria that fix nitrogen from air by consuming energy from sugar.

The recommended daily protein need per person is 0.8 g/kg or 6 g of nitrogen contained in 56 g of protein for a 70 kg person. The world population today is

6.5 billion, so we would need 14 million tons of fixed nitrogen per year to supply enough plant food for human consumption. The actual requirement is much higher because of meat’s higher nitrogen requirement: when we feed soya bean to cattle,

1 g of beef nitrogen requires the consumption of 10 g of soya bean nitrogen. The ancient society with a static population and locally grown food was a self- sustained society: the plants obtained their nitrogen and phosphorous from the soil, the minerals were consumed by humans and animals through the plants, and then the min- erals were returned to fertilize the soil in the form of urine and dung. Modern society poses a new set of problems, leading to a society that is not self-sustained in food minerals: (i) a growing world population requires increased crop size, and (ii) dung from cities is treated in sewage plants and discharged into rivers and oceans, but not returned to the farms. Thus, there is a need for supplemental inorganic fertilizers and nitrogen, or else there would be insufficient food to feed the growing population.

Nitrate deposits were discovered in South America in 1809, which resulted from the millions of years of guano deposited by sea birds that had fed on the fish

89 from the cold rich waters of the Humboldt Current. The location of these deposits is

3.1 FOOD

called the Atacama Desert, which is one of the most arid regions of the world with almost no rainfall each year; so this rich deposit was not washed away to the sea.

The deposits are in the form of saltpeter or NaNO 3 .

This supply of nitrate deposits was so important that the War of the Pacific (1879–1883) was fought between Chile and the joint forces of Peru and Bolivia to control these mines. These nitrate mines were a source of enormous profit to Chile for many decades, as British firms would ship the saltpeter to Europe to fertilize farms and to make gunpowder. But these mines were depleting the age-old deposits at a rate of one half million ton per year, which could not provide unlimited quantit- ies and ultimately the mines would be exhausted.

This situation was compounded by even greater concerns. Fixed nitrogen is also the basis of explosives such as black gunpowder, nitroglycerine, and TNT, which were used in excavation and in warfare. In the early twentieth century, Germany was dependent on a fleet of ships traveling every year from the mines in northern Chile, sailing south past the Cape of Horn, and steaming up past Africa and England to reach the German port of Hamburg to deliver the precious nitrate. In case of a war with England, this route would be cut off by the superior British navy, so that Germany would be brought to its knees without its fertilizer or bombs.

Thomas Malthus said in 1800 that mankind is always trying to find balance in the race between a growing population that requires more food and improving methods to grow more food. In 1893, Sir William Crookes predicted the ultimate starvation of a large portion of the world population due to the exhaustion of these Chilean nitrate deposits. This prediction provoked discussions and research attempts to fix the atmospheric nitrogen.

In 1900, the world was struggling to feed 1.5 billion people, and there were only a few inadequate processes for fixing nitrogen. The electric arc process could fix nitrogen in imitation of atmospheric lightning, but it formed nitric oxide at a

yield of less than 1%. It proceeded by the chemical reaction of N 2 þ O 2 ¼ 2NO. The process was in commercial operation in Norway by 1905, thanks to Norway’s large and inexpensive hydroelectric power. Another nitrogen fixation process was the cyanamide process, which was also in operation in Italy at that time. Both of these processes were inefficient and not economical, as they required high- temperature reactions at enormous costs of power. Many scientists began to work on nitrogen fixation in their laboratories, including two German Nobel Prize winning chemists, Wilhelm Ostwald and Walter Nernst.

A future Nobel Prize winner from Germany, Fritz Haber was born in Breslau in 1868. Haber was the son of a Jewish chemical wholesale merchant in natural dyes, paints, lacquers, and other chemicals and drugs. He showed an early interest in languages, music, theater, and literature. Haber studied at the University of Berlin, then at Heidelberg under Professor Bunsen, earning a doctor of philosophy in 1891. In 1892, he converted to Christianity, which was a time of few opportunities for Jews. Haber received an appointment at the Karlsruhe Technical Institute as an assistant in Chemical and Fuel Technology, where he taught dye and textile printing.

In 1901, he met and married Clara Immerwahr who was also from a Jewish family, and who also had earned a doctorate in chemistry. The following year, he