"Ammonia … deserves the top position as our most important material. As explained in the previous chapter, without its use as the dominant nitrogen fertilizer (directly or as feedstock for the synthesis of other nitrogenous compounds), it would be impossible to feed at least 40 percent and up to 50 percent of today's nearly 8 billion people. Simply restated: in 2020, nearly 4 billion people would not have been alive without synthetic ammonia. No comparable existential constraints apply to plastics or steel, nor to the cement that is required to make concrete (nor, as already noted, to silicon).
"Ammonia is a simple inorganic compound of one nitrogen and three hydrogens (NH3), which means that nitrogen makes up 82 percent of its mass. At atmospheric pressure it is an invisible gas with a characteristic pungent smell of unflushed toilets or decomposing animal manure. Inhaling it in low concentrations causes headaches, nausea, and vomiting; higher concentrations irritate the eyes, nose, mouth, throat, and lungs; and inhalation of very high concentrations can be instantly fatal. In contrast, ammonium (NH4, ammonium ion), formed by the dissolution of ammonia in water, is non-toxic and does not easily penetrate cell membranes.
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| First reactor at the Oppau plant in 1913 |
"Synthesizing this simple molecule was surprisingly challenging. The history of inventions includes famous cases of accidental discoveries; in this chapter on materials, the story of Teflon might be the most apposite example. In 1938, Roy Plunkett, a chemist at DuPont, and his assistant Jack Rebok formulated tetrafluoroethylene as a new refrigerant compound. After storing it in refrigerated cylinders, they found that the compound underwent unexpected polymerization, turning into polytetrafluoroethylene, a white, waxy, slippery powder. After the Second World War, Teflon became one of the best-known synthetic materials, and perhaps the only one that made it into political jargon (we have Teflon presidents, but seemingly no Bakelite presidents -- though there was an Iron Lady).
"The synthesis of ammonia from its elements belongs to the opposite class of discoveries -- those with a clearly defined goal pursued by some of the best -- qualified scientists and eventually reached by a persevering researcher. The need for this breakthrough was obvious. Between 1850 and 1900 the total population of the industrializing countries of Europe and North America grew from 300 million to 500 million, and rapid urbanization helped to drive a dietary transition from a barely adequate grain-dominated supply to generally higher food energy intakes containing more animal products and sugar. Yields remained stagnant but the dietary shift was supported by an unprecedented expansion of cropland: between 1850 and 1900, about 200 million hectares of North and South American, Russian, and Australian grasslands were converted to grain fields.
"Maturing agronomic science made it clear that the only way to secure adequate food for the larger populations of the 20th century was to raise yields by increasing the supply of nitrogen and phosphorus, two key plant macronutrients. The mining of phosphates (first in North Carolina and then in Florida) and their treatment by acids opened the way to a reliable supply of phosphatic fertilizers. But, there was no comparably assured source of nitrogen. The mining of guano (accumulated bird droppings, moderately rich in nitrogen) on dry tropical islands had quickly exhausted the richest deposits, and the rising imports of Chilean nitrates (the country has extensive sodium nitrate layers in its arid northern regions) were insufficient to meet future global demand.
"The challenge was to ensure that humanity could secure enough nitrogen to sustain its expanding numbers. The need was explained in 1898 in the clearest possible manner by William Crookes, chemist and physicist, to the British Association for the Advancement of Science, in his presidential address dedicated to the so-called wheat problem. He warned that 'all civilized nations stand in deadly peril of not having enough to eat,' but he saw the way out: science coming to the rescue, tapping the practically unlimited mass of nitrogen in the atmosphere (present as the unreactive molecule N2) and converting it into compounds assimilable by plants. He rightly concluded that this challenge 'differs materially from other chemical discoveries which are in the air, so to speak, but are not yet matured. The fixation of nitrogen is vital to the progress of civilized humanity. Other discoveries minister to our increased intellectual comfort, luxury, or convenience; they serve to make life easier, to hasten the acquisition of wealth, or to save time, health, or worry. The fixation of nitrogen is a question of the not far-distant future.'
"Crookes's vision was realized just 10 years after his address. The synthesis of ammonia from its elements, nitrogen and hydrogen, was pursued by a number of highly qualified chemists (including Wilhelm Ostwald, a Nobel Prize winner in chemistry in 1909), but in 1908 Fritz Haber -- at that time professor of physical chemistry and electrochemistry at the Technische Hochschule in Karlsruhe -- working with his English assistant Robert Le Rossignol and supported by BASF, Germany's (and the world's) leading chemical enterprise, was the first researcher to succeed. His solution relied on using an iron catalyst (a compound that increases the rate of a chemical reaction without altering its own composition) and deploying unprecedented reaction pressure.
"It was a no smaller challenge to scale up Haber's experimental success to a commercial enterprise. Under the leadership of Carl Bosch, an expert in chemical as well as metallurgical engineering who joined BASF in 1899, success was achieved in just four years. The world's first ammonia synthesis plant began to operate at Oppau in September 1913, and the term 'Haber-Bosch process' has endured ever since.
"Within a year, the Oppau plant's ammonia was diverted to make the nitrate needed to produce explosives for the German army. A new, much larger, ammonia factory was completed in 1917 in Leuna, but it did little to prevent Germany's defeat. The postwar expansion of ammonia synthesis proceeded despite the economic crisis of the 1930s, and continued during the Second World War, but by 1950 synthetic ammonia was still far less common than animal manures.
"The next two decades saw an eightfold increase of ammonia production to just over 30 million tons a year as synthetic fertilizer enabled the Green Revolution (starting during the 1960s) -- the adoption of new superior wheat and rice varieties that, when supplied with adequate nitrogen, produced unprecedented yields. The key innovations behind this rise were the use of natural gas as the source of hydrogen, and the introduction of efficient centrifugal compressors and better catalysts."
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