THE EFFECT OF THE HABER PROCESS ON FERTILIZERS

Raymond Zmaczynski (email)

Chicago, IL

The Haber Process for the synthesis of ammonia (NH3) gas from its elements nitrogen (N2) and hydrogen (H2) is discussed in almost every high school chemistry text as an excellent example of chemical equilibrium. Very little, if anything, is said in most chemistry texts about the effects of this process on the course of history and on society. However, the effects of the Haber Process are important to the history of fertilizers and, to a lesser extent, the history of explosives.

Natural fertilizers such as manures and ground animal bones have been known since ancient times. The ideas of crop rotation, letting soil lie fallow, and planting certain crops to enrich the soil are also very old. The modern study of plants, soils, and the chemical requirements for growth was not established until the 1840's in Europe. The first production of fertilizers from inorganic chemical sources also begins at this time.

Scientific study established three elements as necessary in large quantities for plant growth: potassium (K), phosphorus (P), and nitrogen (N). These inorganic fertilizer elements were all originally mineral deposits. From the 1840's to the present day various deposits of phosphate rocks and potash have been found to provide adequate sources of the elements phosphorus and potassium. The process and techniques of fertilizer preparation and production have changed but the chemical reaction and concepts that are involved continue to remain basically the same.

Such was not the case with nitrogen where only one source, Chile saltpeter (NaNO3), accounted for more than 60% of the world's supply for most of the 19th century. Other sources of nitrogen such as guano were discovered periodically, but were usually depleted within a few years. Ammonia and nitrates were also produced from the destructive distillation of coal and as industrial by-products of other chemical processes.

As world population increased, so did the use of fertilizers. Using fertilizer with a high nitrogen content provided good crop yield, but caused some scientists in the 1890's to begin to worry about the depletion of the sources of nitrogen for chemical fertilizer. Since plants could not directly convert atmospheric nitrogen to soluble nitrogen compounds, mankind had to search for a solution.

The early 20th century produced three methods to "fix" nitrogen, that is, convert it from an inactive gas in the air to nitrogen compounds that would be further reacted to produce fertilizers or used directly. Two methods, the electric arc process and the cyanamid process never proved important in making fertilizer in the United States though they were of some importance through the first part of this century. The third process, the Haber Process, has made a lasting impression on chemical technology and fertilizers.

The full name for the process is the Haber-Bosch Process. Fritz Haber and Karl Bosch of Germany developed the process in the early years of this century, before World War I. The effort was a joint one between German industry and the German University. While the reaction between nitrogen gas and hydrogen gas to produce ammonia gas had been known for many years, the yields were very small and the reaction very slow. Haber and Bosch and their coworkers determined the conditions necessary (high temperatures and very high pressures) and the catalysts necessary (a variety were found, the cheapest and most effective being oxides of iron with traces of oxides of other common elements). German industry also developed the high pressure equipment necessary to run the process By 1913 a chemical plant was operating in Germany, producing ammonia by means of the Haber-Bosch process.

World War I started in 1914. Early in the war, naval battles were fought off the coast of Chile and in the South Atlantic between the British and the Germans. These battles enabled the Germans to transport some nitrates to Germany but eventually these naval battles and others established the British control of the sea.

Many historians and scientists think that Germany would have run out of nitrates by early 1916 if it had not been for German scientific discoveries and their industrial technology. One reason that the war lasted until late 1918 was German use of the Haber- Bosch process to make ammonia and the Ostwald Process to convert ammonia into nitric acid and nitrates. With these processes the Germans could and did make fertilizers and explosives without relying on a foreign source of chemicals and the naval power necessary to transport these chemicals to Germany. Fertilizers and explosives could be made from readily available natural resources-- air, water, and coal. The Allies, however, were dependent almost exclusively on the Chilean nitrates. During the war the price of the Chilean nitrates rose dramatically because the cartel controlling the supply of nitrates was dominated by German nationals and their sympathizers. Eventually American diplomacy provided a way for the Allies to have a ready supply of nitrates with a nice profit for the Chileans.

British and American efforts to produce ammonia using the Haber-Bosch Process during World War I failed even though several attempts were made and patents for the process were available. The failure was due to a lack of knowledge and ability in building and maintaining the high pressure equipment needed to carry out the reaction and a lack of knowledge about the chemistry of the catalysts needed. The German patents omitted many vital technical details, particularly those concerning the preparation of the required catalysts.

In the 1920's, the first ammonia producing plants based on the Haber-Bosch Process were built in the United States and in Europe outside of Germany. In some cases the needed information was obtained by industrial spying; in other cases the needed processes similar to the Haber-Bosch Process but requiring different catalysts and different temperature and pressure conditions were developed. Attempts by the Chilean nitrate mine owners and some European chemical manufacturers to form a cartel to control supply and price of ammonia nitrates were made during the 1920's and 1930's but were unsuccessful. In the 1920's there was a general consolidation of smaller chemical companies into larger ones which seemed to provide cheaper and more efficient methods of producing ammonia. In the 1930's, American agriculture developed methods for adding ammonia directly to the soil as fertilizers. In addition, better processes of carrying on the chemical reaction continued to be developed. Although ammonia from these plants was still more expensive to use in fertilizers than some that came from by-products of other reactions, the advent of World War II increased demand and led to still cheaper and more efficient methods.

The use of ammonia in fertilizer has made it the second most important chemical in the United States. It is the most important source of nitrogen in fertilizers today. The use of fertilizers today is over 400% greater than it was in 1940. Because of increased demand and increased population, the demand for nitrogen based fertilizers will continue to be high. The fertilizer industry is considered a mature industry but a growing and changing one. Current research is directed more toward improving techniques and methods of production and in lowering costs rather than toward the discovery of a new and different way of producing fertilizers.

The Haber-Bosch and the Ostwald processes did increase the amount and availability of explosives produced but they did not substantially change the techniques and basic chemical reactions that Nobel and others developed in the late 19th century. More importantly, the Haber-Bosch Process has changed the way nitrogen fertilizers are produced and used and has increased the availability and use of fertilizers. It is an important part of the "Green Revolution" of the 20th century.
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