In 1908, Fritz Haber entered into a contractual agreement with BASF to develop, on the basis of his discovery, an industrial-scale, high pressure synthesis of ammonia (Haber 1971, pp. 92–97), (Stoltzenberg 1994, pp. 144–170), (Szöllösi-Janze 1998b, pp. 171–181). BASF was no stranger to daunting challenges: the production of indigo had taken a full 17 years to develop. In addition, there was now Nernst’s theoretical description of ammonia synthesis which assured the company that Haber’s determination of the equilibrium of ammonia was correct (Haberditzl 1960; Suhling 1972). The bet paid off. On July 2, 1909, Haber and Le Rossignol delivered a working laboratory scale apparatus for the continuous production of ammonia. At that point, two main hurdles separated Haber and BASF from an industrial solution. First, a completely new high pressure system was needed to withstand enormous working pressures and temperatures. Second, suitable catalysts needed to be found that were both economical and effective. The experimentally successful osmium from the incandescent light bulb industry provided a laboratory scale solution, but the worldwide supply amounted to only several dozen kilograms, making it, like the costly uranium, a poor fit for industrial production.

The efforts to overcome the engineering challenges were led by Carl Bosch (Bosch 1932), (von Nagel 1991, pp. 26–33), (Holdermann 1960, pp. 65–102). The extreme conditions for the continual production of ammonia required constant reassessment of the use of raw materials and energy. Looking back in 1933, Bosch succinctly stated the demands of large scale ammonia synthesis (Bosch 1933),

It is not enough to master the process in the laboratory. Rather, the production of hydrogen and the appropriate design of the reaction chambers must be solved in a technical and economical manner along with the viability and stability of the catalysts and other materials.Footnote 1

One of the main difficulties was to produce a large enough quantity of the nitrogen-hydrogen gas mixture that was to be converted into ammonia. Nitrogen could be produced in a straightforward way via air separation, but the production and purity of hydrogen had a larger effect on the synthesis of ammonia. In the end, several different methods were employed, the most suitable of which was the catalytic conversion of carbon monoxide and steam to carbon dioxide and hydrogen based on the water gas shift reaction, but with a novel iron oxide-chromium oxide catalyst (von Nagel 1991, pp. 34–37). Hydrogen was to be produced from air, coal, coke, and water in “the largest gas production facilities ever built (Bosch 1933).”Footnote 2 They would eventually reach rates of ∼1 Million m3/hr. A corresponding quantity of nitrogen needed to be produced and, along with the hydrogen, cleaned of carbon monoxide, hydrogen sulfide (which poisoned the catalysts), and other contaminants. These processes ran at the unprecedented pressure of 200 atmospheres and proper materials were needed to withstand the resulting forces and high heat while allowing thermal conduction to regulate temperature.

The challenges for the synthesis of ammonia itself proved even more severe. Bosch, starting from Haber’s laboratory apparatus, designed reaction tubes to withstand longer production times. The first tubes, however, burst after only about 80 hours of use. The walls of the tubes were made of carbon steel (carbonaceous perlite dispersed in pure iron) and the hydrogen inside the reaction space had defused into the walls where decarbonization of the perlite led to the formation of methane. The result was a brittle alloy (iron hydride). The working conditions under high pressure and above 400 ∘C meant that degradation was inevitable after hours or days, no matter the material used (of those available at the time). Bosch’s proposed solution was to separate the converter into two functional parts: one to withstand the high working pressures and one to provide a gas-tight seal. The special construction could be achieved by a converter consisting of a thin, soft steal inner lining, surrounded by a pressure-bearing steel mantle with perforations (Bosch holes). The hydrogen could diffuse through the soft steel (which would become brittle but remain intact) and escape through the holes in the mantle without compromising its structural integrity. The inner lining could be replaced as needed. Another challenge was the temperature. The hydrogenation processes had to be held within narrow temperature limits, making temperature control essential. To avoid excessive temperature gradients and conserve energy, a heat exchange system was developed, similar to those used by Ostwald and Haber, that took heat from the exothermic chemical reactions and warmed the incoming gases. The functionality of the system was vital: if the reaction drifted outside of the temperature limits, secondary reactions could release more heat, leading to a chain reaction and drastic material damage (Bosch 1932, pp. 200–221), (von Nagel 1991, pp. 26–33). Bosch was able to overcoming these and other hurdles and began the industrial scale production of hydrogen and ammonia (Fig. 7.1). The experience later helped him with the hydrogenation of carbon monoxide to methanol, and of coal, crude oil, and tar to gasoline—processes that became the backbone of the modern high-pressure catalytic industry.

Fig. 7.1
figure 1figure 1

This page: installation of a high-pressure contact reactor in 1920. Opposite page: A high-pressure contact oven in 1943. Comparison with Haber and Le Rossignol’s laboratory apparatus in Fig. 12.1 of Part II, Chap. 12 illustrates the challenge of sheer magnitude faced by Carl Bosch and Alwin Mittasch. Source: BASF SE, Corporate History, Ludwigshafen

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Of equal importance were the catalysts for hydrogen production and for ammonia synthesis. Bosch followed these developments closely as the production facilities were planned in tandem with catalyst research; the efficacy of the catalyst determined the working temperature and pressure as well as the volume of the reaction chambers. The catalyst research itself was carried out in a separate department of BASF under the leadership of Alwin Mittasch, also a student of Ostwald’s. He planned and executed a gigantic experimental program to investigate and test thousands of different contact materials (Mittasch 1951, pp. 91–121), (von Nagel 1991, pp. 23–25). BASF had the added benefit of extensive experience in sulfuric acid production (Knietsch’s contact process) and in ammonia synthesis via the multi-step process (barium cyanide and titanium nitride), and through direct synthesis during the previous cooperation with Ostwald. This background pertained not only to catalyst materials, but also to specific knowledge about additives and catalyst poisoning. In only a few years, over 20,000 materials and material mixtures were tested on an industrial scale, including iron and other elements in the iron group such as osmium, uranium, manganese, cobalt, and nickel—an inconceivable undertaking in an academic setting. Their suitability was assessed on the basis of physical structure as well as on the ability of additives to activate or poison the catalyst. Using up to 20 high pressure ovens at a time, the BASF ammonia laboratory could test 50 to 100 different materials every week. Soon the result was clear: a highly porous iron catalyst with alumina and alkali additives was the best compromise between efficacy and cost. The interweaving of laboratory structure, financial assets of the industry, and academia produced the innovation. Physical chemistry played an important role, but not during every practical step. Modern scientific concepts were employed in tandem with the centuries-old strategy of trial and error. Mittasch, as had been done in the 1800s, made skilled use of the empirical method. There was no way to find appropriate catalysts except to manufacture and test each possibility.

Fritz Haber also reminds us of the importance of experience and experimental courage in opening new avenues of research. He and Mittasch had placed great importance on the use of pure substances in the laboratory. In a letter to the board of BASF in 1910, Haber wrote (Haber 1910d),

Iron, first used by Ostwald and which we also tried hundreds of times in a pure form, finally worked in an impure state.Footnote 3

The impurity was, of course, targeted rather than random. Mittasch’s insight into the role of additives, activation, and poisoning as well as the physical structure of catalysts went further than the development of high pressure synthesis itself. With Mittasch, catalytic chemistry became a technical tool, especially in the later application of the power of mixed-material catalysts to the field of hydrocarbon chemistry. This progress led to the emergence of petroleum chemistry and the formation of the material basis of the twentieth century. The molecule became the building block of the chemical industry and could be paired in any combination with a particular catalyst to achieve the desired result. However, the development of catalytic chemistry was not self-evident as BASF opened the first ammonia synthesis plant in Oppau in 1913. Just one year later the First World War began and threw the nitrogen market into a tumult. Suddenly, the nitrogen sources in South America were no longer accessible to the Central Powers and the only alternative was to boost internal industrial capacities. In Germany, giant ammonia production facilities were built at Leuna. Haber, Bosch, and Mittasch’s synthesis method, which a short time before had been insignificant, was propelled into the forefront of a worldwide industry. The necessities of war changed Germany from a nitrogen importing nation into a net exporter (Stoltzenberg 1994, pp. 186–189), (Szöllösi-Janze 1998b, pp. 185–191, 274–316).

Paradoxically, even as Germany was losing World War I, the Haber-Bosch-Mittasch process decisively brought its local nitrogen industry to the world market. After the end of the war in 1919, price controls for nitrogen had to be implemented for the protection of the agricultural industry because modern farming methods had grown entirely dependent on synthetic sources of fertilizer (Schwarte 1920, pp. 542–551), (Szöllösi-Janze 2000, pp. 91–121). Such was the unprecedented control humans had gained over the nitrogen cycle.

The long march across two centuries toward agricultural optimization came to a close in the early 1920s. Or was it more of an overshoot?