They also create acid rain, which makes soils more acidic, disrupting ecosystems, and threatening biodiversity. When nitrogen compounds run off into rivers, they likewise promote the growth of some organisms more than others. The results include ocean "dead zones", where blooms of algae near the surface block out sunlight and kill the fish below.
The Haber-Bosch process is not the only cause of these problems, but it is a major one, and it is not going away. Demand for fertiliser is projected to double in the coming century. In truth, scientists still do not fully understand the long-term impact on the environment of converting so much stable, inert nitrogen from the air into various other, highly reactive chemical compounds.
One result is already clear: plenty of food for lots more people. If you look at a graph of global population, you will see it shoot upwards just as Haber-Bosch fertilisers start being widely applied. Again, Haber-Bosch was not the only reason for the spike in food yields. New varieties of crops like wheat and rice also played their part. Still, if we farmed with the best techniques available in Fritz Haber's time, the earth would support about four billion people.
Our current population is around seven and a half billion, and growing. Back in , as Haber triumphantly demonstrated his ammonia process, he could hardly have imagined how transformative his work would be. On one side of the ledger, food to feed billions more human souls; on the other, a sustainability crisis that will need more genius to solve. For Haber himself, the consequences of his work were not what he expected. As a young man, he converted from Judaism to Christianity, aching to be accepted as a German patriot.
When the Nazis took power in the s, however, none of this outweighed his Jewish roots. Stripped of his job and kicked out of the country, Haber died, in a Swiss hotel, a broken man. In the future, will farming be fully automated? Fifty years later, industrialized nations were challenged with how to feed their growing populations and Great Britain was importing the majority of its wheat. In , William Crooks, president for the British Association for the Advancement of Science, called for chemistry researchers to find solutions to aid in the manufacture of N fertilizers to help solve the coming food crisis.
The solution soon came from German scientist Fritz Haber, who discovered in that the chemical reaction of N and hydrogen-produced ammonia—the main component in nitrogen-based fertilizers. Ammonia production depended on high temperatures and pressures, as discovered by Haber. Without the Haber-Bosch process we would only be able to produce around two-thirds the amount of food we do today. Haber initially attempted to produce nitric oxide with the help of electric discharges, mimicking natural processes during a thunderstorm.
But the yield was so low and the process so onerous that Haber dismissed it as impractical. Haber next investigated high-temperature synthesis, with some success, and even succeeded in producing a small amount of nitrogen in Better catalysts or higher pressure were needed, but high-pressure synthesis was in its infancy and suitable equipment scarce.
Indeed, Le Chatelier, who was the first to suggest fixing nitrogen under high pressure, gave up after a particularly hefty laboratory explosion. It was not until that Haber, working with his student Robert le Rossignol, decided to tackle the high-pressure route.
It was a good choice. These were supply of raw materials, ie of the gases hydrogen and nitrogen, at a lower price than hitherto possible; the manufacture of effective and stable catalysts; and lastly the construction of the apparatus.
Neither did any of the other known hydrogen production processes, which were either too expensive or produced hydrogen with too many impurities. He was looking for examples to illustrate his theory finally published in and considered that Haber and van Oort's results would be a good test. But his law conflicted with the experimentally derived data - the percentages quoted were too high - and so he decided to investigate the equilibrium reaction himself.
Nernst chose to work at atm. This, he reasoned, would make the ammonia concentrations more accurately measurable. He reported his successful synthesis in Thus, as Haber's biographer J. Coates says: 'Nernst was the first to synthesise ammonia under pressure'. In Nernst informed Haber of his experimental results and this provoked Haber now working with Channel Islander Robert Le Rossignol to take up the challenge again.
In Nernst published the data from his pressure reactions and, a few months later, Haber published his work on the extent of the conversions, again working at 1 atm pressure. His results were about 50 per cent higher than Nernst's when converted to the same pressure. Nernst responded robustly, and in public, perceiving Haber to be in error. Coates takes up the story:. Without delay, therefore, he and Le Rossignol began a new and decisive determination of the equilibrium, this time under a pressure of 30 atm.
This work published in also fully confirmed their earlier work at 1 atm'. Such conditions were just about achievable at that time with available compressors, but only on the lab bench. Effective catalysts uranium, osmium and specially treated iron were developed with this small-scale apparatus and the results announced in Soon a pilot scale was producing a few hundred millilitres of liquid ammonia per hour, with very little expenditure of energy.
In July BASF representative Dr Carl Bosch saw the plant in action and noted both its potential and the fact that the engineering difficulties inherent in scaling it up to produce tonnage amounts of product would not be insurmountable. He took the process to his Ludwigshafen laboratories for development and the rest is history.
The construction of a plant at Oppau, near Ludwigshafen was started in and became operational in September , soon producing tonnes NH 3 per year. Germany's increasing needs for ammonia and the nitrates derived from it led to the building of a large plant at Leuna, near Merseburg, and located in the lignite coalfields of central Germany. Its initial capacity was 33, tonnes NH 3 per year and, by the end of World War I this had expanded to an annual production of , tonnes of ammonia.
The Haber-Bosch process was important because it addressed two quite different concerns that arose at the beginning of the 20th century. The importance of fixed nitrogen nitrogen compounds as a fertiliser, especially for cereals, had been grasped. Initially the demand was met from various sources in Nature, ranging from the coprolite fossilised dung beds of Cambridgeshire to the guano bird dung beds found on islands off Peru.
By the end of the 19th century, these had been largely superseded by native sodium nitrate Chile saltpetre mined in the arid Atacama desert. At the same time, the military were developing high explosive shells, filled with picric acid trinitrophenol in Britain and trinitrotoluene TNT in Germany. This increased demand for nitric acid could be met by oxidising ammonia to nitric acid using oxygen gas, using the Ostwald process, but the supplies of ammonia from gasworks and coke production was limited.
The output from Oppau alone was simply not enough to meet the demand. In April , however, BASF completed the construction of the huge Haber-Bosch plant at Leuna, which was able to supply enough ammonia to meet the demands for explosives but not to cover Germany's need for fertilisers. Near starvation was one of the causes of Germany's defeat in If the political ramifications of the Haber-Bosch process are a matter of debate, there is no doubt about its technological and industrial impact. The construction of high-pressure equipment led to the development of a process to make oil from coal.
Such were the financial costs of this hydrogenation process on top of the already heavy costs of the Haber-Bosch process that it accelerated the amalgamation of the major German chemical companies to form IG Farben in This brought about the formation a year later of Imperial Chemical Industries ICI with a mission to develop its own high-pressure chemistry.
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