History of the Haber process

For several centuries, farmers knew that certain nutrients were essential for plant growth. In different parts of the world, farmers developed different methods of fertilizing the farmland. In China, human waste was scattered in rice fields. Justus von Liebig (1803 – 1873), German chemist and founder of industrial agriculture, claimed that England had "stolen" 3.5 million skeletons from Europe to obtain phosphorus for fertilizer. In Paris, as many as one million tons of horse dung was collected annually to fertilize city gardens. Throughout the nineteenth century, bison bones from the American West were brought back to East Coast factories for the production of phosphorus and phosphate fertilizer.

File:Bison skull pile edit.jpg

From the 1820s to the 1860s, the Chincha Islands of Peru were exploited for their high quality guano deposits, which they exported to the United States, France and the United Kingdom. The guano-boom increased economic activity in Peru considerably for a few decades until all 12.5 million tons of guano deposits were exhausted.Hager 2008, pp. 31–34Smil 2001, p. 42

Research was initiated to find alternative sources of fertilizer. The Atacama Desert, at that time part of Peru, was home to significant amounts of saltpeter (sodium nitrate). At the time of the discovery of these deposits, the saltpeter had limited agricultural use. Then chemists successfully developed a process to purify the saltpeter in order to produce gunpowder. The saltpeter was also converted into nitric acid, the precursor of powerful explosives, such as nitroglycerine and dynamite. As exports from this region increased, tensions between Peru and its neighbors increased as well.Hager 2008, pp. 38–43

In 1879, Bolivia, Chile, and Peru went to war over possession of Atacama Desert, the so-called "Saltpeter War". Bolivian forces were quickly defeated by the Chileans. In 1881, Chile defeated Peru and seized control of nitrate exploitation in the Atacama Desert. Consumption of Chilean saltpeter for agriculture quickly grew and Chileans standard of living rose significantly.

Technological developments in Europe brought an end to these days. In the twentieth century, the minerals from this region "contribute[d] minimally to global nitrogen supply."{{cite news|url=http://minerals.usgs.gov/minerals/pubs/commodity/nitrogen/480303.pdf|title=Nitrogen (Fixed)—Ammonia|author=Kramer, Deborah A.|journal=U.S. Geological Survey|date=January 2003|page=119}}

In the late nineteenth century, chemists, including William Crookes, President of the British Association for the Advancement of Science in 1898,Hager 2008, pp. 3-4{{cite web|url=http://www.todayinsci.com/C/Crookes_William/CrookesWilliam-Quotations.htm|title=Sir William Crookes Quotes - Dictionary of Science Quotations and Scientist Quotes|work=Today in Science History|year=2007|access-date=22 April 2009}} predicted that the demand for nitrogen compounds, either in the form of fertilizer or explosives, would exceed supply in the near future.{{cite book|title=1918 Nobel Laureate. Fritz Haber 1868-1934|volume=Nobel Laureates in Chemistry, 1901-1902|author=Laylin, James|date=30 October 1993|publisher=American Chemical Society|page=[https://archive.org/details/isbn_9780841226906/page/118 118]|isbn=0-8412-2690-3|url=https://archive.org/details/isbn_9780841226906/page/118}}

Following the work by Claude Louis Berthollet published in 1784, chemists knew ammonia to be a nitrogen compound.{{cite book|title=Encyclopédie internationale des sciences et des techniques|author1=Auger, Pierre |author2=Grmek, Mirko D.|publisher=Presses de la cité|year=1969|location=Verona, Italy|page=434|language=fr}} Early attempts to synthesize ammonia were performed in 1795 by Georg Friedrich Hildebrandt. Several others were made during the nineteenth century.Smil 2001, p. 62

In the 1870s, ammonia was an unwanted byproduct of making manufactured gas. Its importance emerged later, and in the 1900s the industry modified their facilities to produce it from coke. Still, production could not meet demand.Haber 1920, pp. 328–329

In 1900, Chile, with its deposits of saltpeter, produced two-thirds of all fertilizer on the planet.Wisniak 2002, p. 161 However, these deposits rapidly diminished, the industry was dominated by an oligopoly and the cost of saltpeter rose constantly. To ensure food security for Europe's growing population, it was essential that a new economical and reliable method of obtaining ammonia be developed.{{cite book|title=Chimie 534|last1=Bachand|first1=Luc|last2=Petit|first2=Guy|last3=Vanier|first3=Philippe|publisher=LIDEC|year=1996|location=Montreal|page=315|isbn=2-7608-3587-1|language=fr}}

Issues of food security were particularly acute in Germany.Smil 2001, p. 48 Its soil was poor and the country lacked an empire. A major consumer of Chilean saltpeter, Germany saltpeter imports totaled 350,000 tonnes in 1900. Twelve years later, it imported 900,000 tonnes. The United States was in much better position due to the Guano Islands Act.Hager 2008, p. 52{{cite web|url=http://www.tacitus.nu/historical-atlas/population/germany.htm|title=Population of Europe|work=Historical Atlas|access-date=6 April 2009}}{{cite book|title=Histoire des États-Unis|author=Binoche, Jacques|publisher=Ellipses Marketing|year=2003|page=256|isbn=978-2-7298-1451-9|language=fr}}

In the years between 1890 and 1900, chemistry advanced on several fronts, and more scientists attempted to fix atmospheric nitrogen. In 1895, German chemists Adolf Frank and Nikodem Caro succeeded in reacting calcium carbide with dinitrogen to obtain calcium cyanamide, a chemical compound used as a fertilizer. Industrialization of the Frank-Caro process began in 1905. By 1918, there were 35 synthesis sites fixing 325,000 tonnes of nitrogen annually. However, the Cyanamide process consumed large amounts of electrical power and was more labor-intensive than the Haber process.Hager 2008, pp. 137–143 Today, cyanamide is used primarily as a herbicide.{{cite web|url=http://www.degussa-history.com/geschichte/en/inventions/calcium_cyanamide/|title=Rich harvest, healthy environment. Calcium cyanamide|access-date=18 July 2008}}

Wilhelm Ostwald, considered one of the best German chemists of the early twentieth century, attempted to synthesize ammonia in 1900 using an invention. He interested BASF, who asked Carl Bosch, a recently hired chemist, to validate the device.

In 1901, Henry Le Chatelier managed to synthesize ammonia from air. After obtaining a patent, he claimed it was possible to obtain better performance by increasing the pressure. When one of his assistants was killed following the accidental explosion of a device, Le Chatelier decided to end his research.Wisniak 2002, p. 163

In 1905, Norwegian physicist Kristian Birkeland, funded by engineer and industrialist Samuel Eyde, developed the Birkeland–Eyde process which fixes atmospheric nitrogen as nitrogen oxides.{{cite news|url=http://www.larecherche.fr/content/impression/article?id=12535|title=Kristian Birkeland, prophète électromagnétique|author=Witkowski, Nicolas|journal=La Recherche|access-date=4 March 2009|language=fr|archive-date=29 September 2011|archive-url=https://web.archive.org/web/20110929202108/http://www.larecherche.fr/content/impression/article?id=12535|url-status=dead}} The Birkeland–Eyde process requires a considerable amount of electricity, constraining possible site location; fortunately, Norway possessed several sites capable of meeting these needs. Norsk Hydro was founded 2 December 1905 to commercialize the new process.{{cite web|url=http://fert.yara.fr/fr/about_us/history/index.html|title=Yara - Historique|access-date=4 March 2009|language=fr|archive-url=https://web.archive.org/web/20090211115040/http://fert.yara.fr/fr/about_us/history/index.html|archive-date=11 February 2009|url-status=dead}} In 1911, the Norsk Hydro facility was consuming 50,000 kW, the next year, consumption doubled to 100,000 kW.{{cite journal|journal=The Journal of Industrial and Engineering Chemistry|title=Mineral Wastes: The Chemists' Opportunity|volume=4|issue=1|date=Feb 1912|page=127|doi=10.1021/ie50038a013|last1=Parsons|first1=Chas. L.|url=https://zenodo.org/record/1428714}} By 1913, Norsk Hydro's facilities were producing 12,000 tonnes of nitrogen, about 5 percent of the volume extracted from coke at the time.Smil 2001, pp. 54–55

Similar processes were developed at the time. Schönherr, an employee of BASF, worked on a nitrogen fixation process beginning in 1905. In 1919, Schönherr's Badische process was employed at Norsk Hydro facilities.{{cite book|title=Intermediate Text Book of Chemistry|url=https://archive.org/details/intermediatetex00smitgoog|author=Smith, Alexander|year = 1919|page=[https://archive.org/details/intermediatetex00smitgoog/page/n336 320]}} That same year, the Pauling process was used in Germany and the United States.

All these methods were quickly supplanted by the less-expensive Haber process.

In 1905, German chemist Fritz Haber published Thermodynamik technischer Gasreaktionen (The Thermodynamics of Technical Gas Reactions), a book more concerned about the industrial application of chemistry than to its theoretical study. In it, Haber inserted the results of his study of the equilibrium equation of ammonia:

:{{chem|N|2}} (g) + 3 {{chem|H|2}} (g) {{eqm}} 2 {{chem|NH|3}} (g) - ΔH

At 1000 °C in the presence of an iron catalyst, "small" amounts of ammonia were produced from dinitrogen and dihydrogen gas.{{Cite book|title=Great Chemists|author=Faber, Eduard|year=1961|publisher=Interscience Publishers|location=New York|page=1305}} These results discouraged his further pursuit in this direction.Travis 1993 However, in 1907, spurred by a scientific rivalry between Haber and Walther Nernst, nitrogen fixation became Haber's first priority.Smil 2001, pp. 68–74 A few years later, Haber used results published by Nernst on the chemical equilibrium of ammonia and his own familiarity with high pressure chemistry and the liquefaction of air, to develop a new nitrogen fixation process.Haber 1920, pp. 336–337 He had no precise information on the parameters to impose on the system,Hager 2008, p. 81, 91 but at the conclusion of his research, he was able to establish that an effective ammonia production system must:Haber 1920, p. 337-338Smil 2001, p. 79In modern chemical manuals, the authors explain Haber's choices by relying on Le Chatelier's principle. However, at the start of the 20th century, Haber ignored this principle. (See for example Haber 1920, p. 339).

• operate at high pressure (on the order of 20 MPaThis was the maximum pressure Haber could obtain with his equipment. Travis 1993);
• implement one or more catalystsIn Fritz Haber's speech upon receiving his Nobel prize in chemistry, the texts mentions "catalysts" (plural), though it is more probable that the synthesis used only one catalyst at a time. (see Haber 1920, p. 337 for more details) to accelerate the synthesis of ammonia;
• operate at a high temperature (between 500 °C and 600 °C) to obtain the best efficiency in the presence of the catalyst;
• since about 5% of the N₂ and H₂ molecules react with each passage in the chemical reactor:
• separate the ammonia from the other molecules by liquefaction,
• withdraw ammonia continuously,
• inject the N₂ and H₂ that did not react into the chemical reactor again;
• recycle the heat produced.

To overcome the problems associated with high pressure, Haber called upon the talents of Robert Le Rossignol, who designed the equipment necessary for the success of the process.Smil 2001, p.78-79 Early in 1909, Haber discovered that osmium could serve as a catalyst. Later, he established that uranium could also act as a catalyst.Jayant M. Modak, "Haber Process for Ammonia Synthesis", Resonance, 2002. [http://www.ias.ac.in/resonance/Volumes/16/12/1159-1167.pdf read online] [http://archive.wikiwix.com/cache/?url=http%3A%2F%2Fwww.ias.ac.in%2Fresonance%2FVolumes%2F16%2F12%2F1159-1167.pdf archive] [PDF] Haber also obtained good results with iron, nickel, manganese and calcium.Haber 1920, pp. 333–335 In the chemical equation shown above, the direct reaction is exothermic. This heat can be used to heat the reagents before they enter the chemical reactor.In the literature on high-temperature chemical processes, the term "furnace" can replace "chemical reactor." Haber's team developed a system that recycles the heat produced.Hager 2008, p. 91

In March 1909, Haber demonstrated to his laboratory colleagues that he had finally found a process capable of fixing atmospheric dinitrogen sufficient to consider its industrialization.Hager 2008, p.92

While BASF took out a patent on the Haber process,BASF had requested a patent in Germany in 1908: see patent [http://v3.espacenet.com/textdoc?locale=fr_V3&DB=EPODOC&F=0&IDX=DE235421%7CDE 235 421] [http://archive.wikiwix.com/cache/20190623162405/http://v3.espacenet.com/textdoc?locale=fr_V3] Verfahren zur synthetischen Darstellung von Ammoniak aus den Elementen, requested October 13, 1908, approved June 8, 1911 August Bernthsen, director of research at BASF, doubted the utility of it. He did not believe that BASF wanted to engage in such a project.Nobel Foundation, [http://nobelprize.org/nobel_prizes/chemistry/laureates/1931/bosch-bio.html Carl Bosch - Biography] [http://archive.wikiwix.com/cache/20110224031212/http://nobelprize.org/nobel_prizes/chemistry/laureates/1931/bosch-bio.html archive], 1931 (accessed March 3, 2009) According to Bernthsen, no industrial device was capable of withstanding such high pressure and temperature for a long enough period to pay off the investment. In addition, it appeared to him that the catalytic potential of osmium could disappear with use, which required its regular replacement despite the metal being scarce on Earth.Hager 2008, pp. 92–93.

However, Carl Engler, a chemist and university professor, wrote to BASF President Heinrich von Brunck to convince him to talk to Haber. Von Brunck, along with Bernthsen and Carl Bosch, went to Haber's laboratory to determine whether BASF should engage in industrialization of the process. When Bernthsen learned that he needed devices capable of supporting at least 100 atm (about 10 MPa), he exclaimed, "One hundred atmospheres! Just yesterday an autoclave at seven atmospheres exploded on us!"Hager 2008, p. 93. Before deciding, von Brunck asked for Bosch's advice.

The latter had already worked in metallurgy, and his father had installed a mechanical workshop at home where the young Carl had learned to handle different tools. He had been working for several years on nitrogen fixation, without having obtained any significant results.Bosch had experience with metallic cyanide and nitride. In 1907, he started an experimental site producing cyanide from barium. He knew that processes that used electric arc furnaces, such as the Birkeland–Eyde process, required huge amounts of electricity, making them economically nonviable outside Norway. To continue to grow, BASF had to find a more economical method of fixing.Hager 2008, pp. 93–97 Bosch said, "I think it can work. I know exactly what the steel industry can do. We should risk it."Hager 2008, p. 97

In July 1909, BASF employees came to check on Haber's success again: the laboratory equipment fixed the nitrogen from the air, in the form of liquid ammonia, at a rate of about 250 milliliters every two hours.Hager 2008, p. 99Certain authors specify the mass of ammonia. One must simply perform the necessary conversion. For example, in Smil 2001, p. 81, the author mentions 80 g of NH₃ per hour, which gives 160 g for two hours. At 0 °C and 191.3 kPa, liquid ammonia has a density of 0.6386 g/cm³. BASF decided to industrialize the process, although it was associated with Norsk Hydro to operate the Schönherr process.Hager 2008, p. 88 Carl Bosch, future head of industrialization of the process, reported that the key factor that prompted BASF to embark on this path was the improvement of the efficiency of the catalyst.Bosch 1931, p. 197{{Reflist|group=note}}

At the time, high-pressure chemistry was a new field of knowledge, making its industrialisation all the more difficult. However, BASF had developed an industrial process for synthesizing indigo dye. This development took 15 years of work, but paid off, as this process made BASF an industrial giant.{{harvsp|Hager|2008|p=82-86}}

File:Carl_Bosch.jpg published by the Nobel Foundation around 1931,{{cite web|access-date=3 March 2009 |date=1931 |language=en |publisher=Fondation Nobel |title=Carl Bosch - Biography |url=http://nobelprize.org/nobel_prizes/chemistry/laureates/1931/bosch-bio.html}} but taken around the end of the 1920.{{harvsp|Smil|2001|p=224}}]]

In his speech before accepting his Nobel prize in chemistry in 1931, Carl Bosch claimed that, before ammonia could be synthesized industrially, three major obstacles needed to be overcome:{{harvsp|Bosch|1931|p=198}}

1. Obtain hydrogen and nitrogen gas at a lower cost than what was commonly available at the time,
2. Manufacture efficient and stable catalysts,
3. Building the apparatus.

At the time Bosch began the development of this industrial process in 1909, it was possible to obtain a sufficiently pure gas mixture of hydrogen and nitrogen in the right proportions. However, there was no source capable of supplying an industrial plant at sufficiently low cost. Developing an economical source was essential as, according to Bosch, the cost of ammonia production was mostly dependent on the cost of hydrogen.

Bosch and his colleagues succeeded in developing a catalytic chemical process cable of supplying hydrogen to BASF's facilities,{{Harvard citation no brackets|Bosch|1931|p=198}} consequently providing a substitute to the chlor-alkali process.{{Harvard citation no brackets|Smil|2001|p=97}} In the 21st century, the bulk of required hydrogen is produced from methane using heterogeneous catalysts, which requires considerably less energy than other methods.{{Cite web |last=Nexant |year=2007 |title=Ammonia Process Overview |url=http://www.chemsystems.com/about/cs/news/items/PERP%200506%20S11%20Ammonia.cfm |access-date=17 September 2009 |publisher=Nexant |language=en}}

File:Alwin_Mittasch_1902_retuschiert.jpg

When the industrialisation project started, Bosch rejected osmium as a catalyst, due its rarity. He also rejected uranium because it easily reacts with oxygen and water, both present in air,ref>{{Harvard citation no brackets|Hager|2008|p=105}}

Bosch assigned Alwin Mittasch to search for a stable and inexpensive catalyst. Together with his colleagues, they studied practically all the elements of the periodic table to find the best catalyst. In September 1909, they discovered an iron-based compound that exhibited interesting properties. The impurities in the compound had a catalytic effect, but Mittasch did not know the exact arrangement. After two years of work, they discovered a catalyst, also iron-based, significantly less expensive and more stable than osmium.{{Harvard citation no brackets|Hager|2008|p=101, 105-108}} When he stopped his search for an ideal catalyst in 1920, Mittasch estimated that he had tested about 20,000 compounds.{{Harvard citation no brackets|Hager|2008|p=111}}{{Harvard citation no brackets|Travis|1993}} His efforts ushered in a new era in chemistry: chemists recognized the importance of promoters, impurities that increase the catalytic effect tenfold.{{Harvard citation no brackets|Hager|2008|p=107}}

According to Bosch, all iron-based catalysts used in 1931 were used in ammonia synthesis. He also mentioned that molybdenum had excellent catalytic properties.{{Harvard citation no brackets|Bosch|1931|p=198}}

Bosch's team also had to conceive industrial apparatus capable of working under the new conditions of the time: pressures of the order of 20 MPa and temperatures in the order of 600 °C. According to Bosch, there was no other equivalent in industry (Linde's liquefaction process, of physical nature, was the closest thing). To meet their needs, they had to set up a manufacturing workshop from scratch.{{Harvard citation no brackets|Bosch|1931|p=199}} Bosch and his colleagues replicated Haber's prototype to conduct their experiments. This apparatus could not operate on an industrial scale. They conceived new devices, and 24 of these were put into continuous operation for years.

File:Krupp_gun.jpg in the 1880s as published by Scientific American in 1887.{{Cite journal |date=18 June 1887 |title=The New Krupp Guns |url=//www.gutenberg.org/files/11662/11662-h/11662-h.htm#17 |journal=Scientific American Supplement |language=en |volume=XXIII |issue=598 |page=Fig. 1 |access-date=8 July 2009}}]]

When Bosch believed his team had gained sufficient experience with benchtop devices, he had two larger chemical reactors built. Each was 2.44 meters high and had a wall thickness exceeding 2.5 centimeters. These cylinders were built by the best German gun manufacturer of the time: Krupp.{{Harvard citation no brackets|Hager|2008|p=116}}

During their experiments, they discovered that the supposedly strong alloys lost their elasticity under these operating conditions. Bosch spontaneously believed that chemical corrosion caused by nitrogen was responsible for this phenomenon. To confirm his suspicions, he used a novelty in the industrial setting of the time: metallographic analysis. It revealed that hydrogen at high pressure and temperature was responsible: it penetrated the steel walls of the reactor and weakened them by forming a new alloy.{{Harvard citation no brackets|Bosch|1931|p=200, 203-204 et 206-207}}

They attempted to solve this problem by reducing the temperature of the reactor, but the catalyst only worked at temperatures above 400 °C. They covered the inner reactor walls with thermal insulators, but hydrogen diffused easily through these materials, and, is an excellent thermal conductor at high pressures. They also tried various steels that were commercially available at the time, without success.{{Harvard citation no brackets|Bosch|1931|p=208}}

The program was in jeopardy, and six months after the problem first appeared, there were still no viable and permanent solutions. Finally, it was Bosch that found one: separating the two functions offered by the reactor shell. The reactor shell serves to (1) maintain internal pressure, and (2) prevent the diffusion of the gaseous mixture outside of the reactor. A reactor with two walls, nested together like Russian dolls, makes it possible to separate both functions. Hydrogen diffuse across the inner walls and sees its pressure greatly reduced on the other side, where it is much less likely to corrode the interior shell. To facilitate the flow of hydrogen, the exterior walls are engraved with small gutters on their inner faces. On the other hand, it was possible for hydrogen to accumulate between the two walls. Bosch wondered how to prevent the risk of explosions caused by such pockets. The solution came to him when he realized that hydrogen could escape through the outside walls without significantly reducing the pressure in the reactor. He had small holes driller in the outer surface.{{Harvard citation no brackets|Hager|2008|p=120-121}} Bosch claimed that this solution was still in use in 1931.{{Harvard citation no brackets|Bosch|1931|p=208-209}} It was also possible to reduce corrosion by circulating nitrogen gas between the two walls.{{Harvard citation no brackets|Bosch|1931|p=211}}{{Harvard citation no brackets|Travis|1993}}.

Several members of Bosch's team were veterans of the era where BASF had created various dye synthesis processes, including indigo. They knew that the development of an industrial process could take years, and so were not particularly disappointed when problems arose. However, the program moved forward regularly, which maintained the morale of the employees.{{sfn|Hager|2008|p=115}}

At the time, there was no industrial pump capable of delivering pressures in the order of 20 MPa. Linde's liquefaction process, for example, used air pumps, but they were too small. Additionally, air leaks were tolerated. In the Haber-Bosch process, hydrogen leaks were not permissible due to the risk of explosion. Additionally, any leaks increase the cost of ammonia production. After several years of work, employees under Bosch's orders managed to put into operation sealed pumps of about 2240 kW that could operate continuously for 6 months before requiring maintenance, something that had not yet been achieved.{{Harvard citation no brackets|Bosch|1931|p=221-222}}

While Bosch and his team experimented to create new apparatus, some exploded under pressure. They would then perform an "autopsy" of the debris to determine what had caused the rupture. This allowed them to design stronger, more reliable devices.{{harvsp|Hager|2008|p=107}} To maintain the physical integrity of the production devices, the production system had to be quickly halted in case of breakage. They developed a set of instruments designed to continuously monitor the evolution of chemical reactions, another novelty at the time.{{harvsp|Bosch|1931|p=222}} According to Bosch, the production site had to operate continuously and smoothly, and any stoppage at any point lead to a complete shut down and it would take several hours before it could restart, making production less profitable

It was finally on May 7, 1911, in Oppau, Germany, that the construction of BASF's first industrial synthesis site officially began. Bosch supervised the project, ensuring its smooth running. On site, workers assembled compressors the size of locomotives, chemical reactors four times larger than those commonly used elsewhere in the chemical industry, a mini-factory to extract nitrogen from the air and purify it before injecting it into the reactors, kilometers of tubing, a complete electrical system including generators, a port shipping system attached to a marshalling yard, a laboratory operated by 180 researchers assisted by a thousand assistants, as well as housing for more than 10,000 workers<.ref>{{Harvard citation no brackets|Hager|2008|p=129}}

File:Ammoniak-Reaktor_1913_Oppau.jpg

The company was able to produce ammonia industrially from 1913. The Oppau site started production on September 9. In the same year, it was able to produce up to 30 tons of ammonia per day{{cite journal|lang=en|title=Haber Process for Ammonia Synthesis|first=Jayant M.|last=Modak|date=2002|journal=Resonance|url=http://www.ias.ac.in/resonance/Volumes/16/12/1159-1167.pdf|format=pdf|access-date=1 March 2009}} In 1914, the plant produced 8700 tons of ammonia, which was used to supply a neighboring unit, which produced 36000 tons of ammonium sulfate.ref>{{cite book |last1=Rival |first1=Michel |title=Les Apprentis Sorciers: Haber, Von Braun, Teller |date=1998 |publisher=Seuil |isbn=978-2-02-021515-2 |page=44}}

The Oppau site was not only an increasingly important source of revenue for BASF, as its steadily growing production was completely sold out, it also served as a laboratory. The site offered the opportunity to develop the emerging technology of high-pressure chemistry. Bosch ad his colleagues encountered problems never seen before, but could explore different approaches without worrying about the costs associated with their development.{{Harvard citation no brackets|Hager|2008|p=131}}

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• {{cite book |language=en

| title = Enriching the Earth: Fritz Haber, Carl Bosch, and the Transformation of World Food Production

|last1= Smil |first1=Vaclav |author-link1=Vaclav Smil

|publisher = MIT Press

|year = 2001

|pages =358

|isbn = 978-0-262-69313-4

}}

• {{cite book|language=en|author-link3=Ernst Homburg|title=Determinants in the Evolution of the European Chemical Industry, 1900-1939: New Technologies, Political Frameworks, Markets and Companies (Chemists and Chemistry)|last1=Travis|first1=Anthony S.|last2=Schröter|first2=Harm G.|last3=Homburg|first3=Ernst|last4=Morris|first4=Peter J. T.|publisher=Springer|year=1998|pages=300|isbn=978-0792348900}}
• {{cite book | language=en

| title = Ullmann's Agrochemicals

| last1= Wiley-VCH

| publisher = Wiley-VCH

| year = 2007

| location = United States

|pages =932

|url = https://books.google.com/books?id=3bgUxSKZVmQC&q=%22Ullmann%27s+Agrochemicals%22+Schoenherr+BASF&pg=PA154

| isbn = 978-3527316045

}}

• {{cite journal|journal=Proceedings of the Indian National Science Academy|language=en|last1=Wisniak|first1=Jaime|title=Fritz Haber - a Conflicting Chemist|volume=37|number=2|year=2002|pages=153–173|issn=0019-5235|url=https://www.researchgate.net/publication/236235556}}

{{History of chemistry}}

Category:History of chemistry

Category:Fritz Haber