Ammonia
Ammonia (NH3) is one of the most familiar compounds of nitrogen and hydrogen as well as one of the world's most valuable industrial and agricultural chemicals. Under ordinary conditions, ammonia is a colorless gas with a sharp odor that stings the nose. If inhaled in great enough concentrations, it can cause suffocation and death. In nature the gas is often found dissolved in water (ammonium hydroxide). Released during the decomposition of proteins from plants and animals, ammonia and other nitrogen compounds enter the soil when plants and animals decay. Plants need these compounds to make proteins and other nutrients. Ammonia's pungent odor contributes to the distinctive smell of barns, zoos, and other animal enclosures since it is also found in animal wastes, such as urine. The compound can also be found in certain mineral deposits that contain ammonium salts (compounds of ammonia and various acids).
During the Middle Ages, alchemists produced ammonium hydroxide (ammonia water), which they called "spirits of hartshorn," by distilling the horns and hoofs of oxen. In the 1770s, Joseph Priestley developed a new laboratory method that enabled him to collect gases that normally dissolve in water. Using this method, Priestley isolated ammonia gas for the first time in 1774. Although Carl Wilhelm Scheele showed that the gas contains nitrogen, it was Claude Berthollet who discovered the exact composition of ammonia in 1785.
People have known for hundreds of years that organic materials containing ammonia are good fertilizers. During the 1800s, scientists learned that plants can flourish without organic fertilizers as long as ammonium salts or other nitrogen sources are supplied. Although most plants depend on fertilizers for their nitrogen, certain plants called legumes--which include beans, peas, clover, and alfalfa--can replenish the soil's nitrogen by extracting it from the air. Actually, this feat is performed by bacteria that live on the roots of legumes. These "nitrogen-fixing" bacteria convert nitrogen from the air into ammonia, which is then converted by other bacteria into nitrogen compounds that can be used by plants.
For most of human history, scientists did not need to worry about synthesizing ammonia because natural sources were sufficient to meet demand. Large quantities, for instance, were produced from Chile saltpeter (sodium nitrate, or NaNO 3), which was mined in South America. However, in 1898 William Crookes predicted that the world would soon run short of Chile saltpeter and the growing world population would go hungry without nitrogenous fertilizers to increase crop yields. Crookes's warning spurred the search for an alternative source of ammonia.
In 1908, German chemist Fritz Haber (1868-1934) developed a process for synthesizing ammonia by combining atmospheric nitrogen with hydrogen. In 1913, German chemist Carl Bosch (1874-1940) further developed Haber's process, making it practical for commercial ammonia production. A research scientist for a large German chemical company, Bosch was given the task of bringing Haber 's laboratory process up to industrial scale. Bosch met the challenge of successfully designing a reactor that could withstand extremely high pressures and the corrosive effects of hydrogen gas. Soon after, the newly developed process was used by the Germans to produce synthetic ammonia for ammunition when their supply of saltpeter was cut off during World War I. Both Haber and Bosch received Nobel Prizes for their work on ammonia synthesis. Haber received the award in 1918, and Bosch shared the prize in 1931 with Friedrich Bergius (1884-1949). Today, the Haber-Bosch process is used to manufacture thousands of tons of ammonia.
Ammonia has come to be nearly indispensable in agriculture, industry and the marketplace. Compounds of ammonia are used throughout the world as a crop fertilizer. Ammonia and its salts are used extensively in soldering processes as well as in the manufacture of many chemicals, plastics, vitamins and drugs. Because liquefied ammonia absorbs a large amount of heat from its surroundings when it vaporizes, it has been used as a refrigerant. Ammonia is also used to produce nitric acid (HNO 3), a necessary ingredient of such explosives as TNT (trinitrotoluene) and nitroglycerin. The textile industry uses ammonia to produce nylon, rayon, and other synthetic fibers, and aqueous ammonia serves as a popular household cleaning fluid.
In the early 1990s a new reduced energy process method was developed to manufacture ammonia using a ruthenium based catalyst whose activity is as much as 20 times greater than traditional catalysts.
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