Complete the fixation of nitrogen
In the mid-19th century, people had a certain understanding of the mechanism of plant growth and became increasingly aware of the important role of nitrogen in organisms. Nitrogen is an indispensable element in the protein composition of all living things, so it is of great significance to the survival of humans and other living things in nature. The total content of nitrogen in nature accounts for about 0.04% of the total mass of the crust. Most of it exists in the atmosphere in a free state. The air contains about 78% (volume fraction) of nitrogen, which is the main component of air. However, neither humans nor other organisms (except for a few organisms) can directly absorb this free nitrogen from the air as nutrients. Plants can only absorb nitrogen-containing compounds from the soil through their roots and convert them into proteins; humans and animals can only eat proteins from various plants and animals to supplement their needs. Therefore, the problem of organisms obtaining nitrogen elements from nature as their own nutrition ultimately boils down to the problem of plants absorbing nitrogen-containing compounds from the soil.
The main sources of nitrogen-containing compounds in the soil are: first, animal excrement or the remains of animals and plants enter the soil and are transformed; second, lightning prompts nitrogen and oxygen in the air to combine to form nitrogen oxides, which dissolve Falling into the soil in rain; third, certain bacteria, such as rhizobia that grow with leguminous plants, absorb nitrogen in the air and produce some nitrogen-containing compounds. However, these sources are far from meeting the needs of large-scale agricultural production. Therefore, how to convert free nitrogen in the atmosphere into nitrogen compounds that can be absorbed by plants, that is, the fixation of nitrogen, has become a topic explored by chemists.
This subject first achieved a breakthrough at the end of the 19th century. In order of invention time, the first item is the preparation of calcium cyanamide (CaNCN). In 1898, Professor Adolf Frank (1834-1916) of the Charlottenburg Institute of Technology in Germany and his assistants Dr. F. Rother and Dr. N. Caro discovered that barium carbide is heated in nitrogen. Afterwards, barium cyanide and barium cyanamide were generated, and then it was discovered that calcium carbide can also generate calcium cyanamide when heated to above 1000°C in nitrogen:
CaC+N2══CaNCN+C Frank in 1900 It was found that hydrolysis of calcium cyanamide with superheated steam can produce ammonia:
CaNCN+3H2O══CaCO3+2NH3↑In this way, free nitrogen in the air is fixed into calcium cyanamide and the nitrogen content of ammonia Compounds can be used as fertilizers. Therefore, the first industrial production device was established in Germany in 1904, and a factory was also built in Italy in 1905, followed by factories in the United States and Canada. By 1921, world production of calcium cyanamide reached 500,000 tons per year. But the construction of new plants ceased thereafter, as an industry for the direct synthesis of ammonia from hydrogen and nitrogen arose.
The second item is the direct combination of nitrogen and oxygen to form nitrogen oxides, which dissolve in water to form nitric acid and nitrous acid, but this was quickly squeezed out by the ammonia synthesis industry.
The third item is to directly synthesize ammonia from hydrogen and nitrogen.
Ammonia gas is also called ammonia gas. The word comes from the ancient Egyptian sun god Ammon (also spelled Amon or Amen). This is due to the accumulation of feces and remaining offerings from the camels ridden by worshipers next to the Temple of Ammon in ancient Egypt, which released ammonia-containing gas after long-term changes. Ammonia is produced in nature when any nitrogen-containing organic matter decomposes in the absence of air. This decomposition occurs due to heat or the action of bacteria. The pungent smell of ammonia can be detected in stables and sewers.
In 1774, the British chemist Joseph Piestley (1733-1804) heated a mixture of ammonium chloride (NH4Cl) and calcium hydroxide (Ca(OH)2) to extract gas by discharging mercury Method, first collect ammonia gas, which is called alkaline air. He had realized that aqueous solutions of ammonia gas were alkaline. Since ammonia is easily soluble in water, it is collected using the mercury exhaust gas extraction method. At that time, he called all gaseous substances "air".
In 1784, French chemist Claude Louis Berthollet (1748-1822) analyzed ammonia gas and determined that it was composed of nitrogen and hydrogen.
The original ammonia comes from ammonia water as a by-product of the coking industry, because coal contains 2% nitrogen. During the coking process, part of the nitrogen (about 20%~25%) is converted into ammonia, which is contained in the coal gas. In the process, it is washed out with water, which is crude ammonia, containing no more than 1% ammonia. People directly pass ammonia-containing gas into sulfuric acid to produce ammonium sulfate ((NH4)2SO4), which is used as fertilizer.
Since the 19th century, many chemists have tried to synthesize ammonia from nitrogen and hydrogen, using catalysts, electric arcs, high temperatures, and high pressures to conduct experiments, but they have been unsuccessful. Some people think that it is impossible to synthesize ammonia from nitrogen and hydrogen. realized. This is because the synthesis of ammonia from nitrogen and hydrogen is a reversible reaction:
It was not until the 19th century that some chemists made some progress in chemical thermodynamics, chemical kinetics, catalysts and other disciplines under the guidance of correct theories. , the reaction of ammonia synthesis was effectively studied.
The one who succeeded was the German chemist Fritz Haber (1868-1934). He conducted unremitting research on the direct synthesis of ammonia from nitrogen and hydrogen from 1901 to 1911. Haber, his student R. Le Rossignol and colleagues conducted more than 20,000 experiments. In 1904, he passed nitrogen and hydrogen through iron at normal pressure and 1000°C to obtain 0.012% (volume fraction) ammonia product. Although the concentration of ammonia in the product was too low and lacked economic benefits, he did not stop the experiment. Then based on the chemical kinetics equation formulated by Dutch chemist Jacobus Henricus Van't Hoff (1852-1911), Haber calculated the equilibrium constant of the ammonia synthesis reaction at normal pressure and 1000°C, and based on the French physics The law of mass action proposed by Henry Louis Le Chatelier (1850-1936) calculated the equilibrium concentration of ammonia at normal pressure and different temperatures. In 1907, a large number of experimental data on the equilibrium reaction of ammonia synthesis were measured. Through the above work, he realized that synthetic ammonia could not achieve a conversion rate as high as that of sulfuric acid production, so he considered using a method of circulating the reaction gas under high pressure, and continuously separated the generated ammonia from this cycle, and then combined it with the selection of effective catalyst for success. In 1908, Haber applied for the initial patent for ammonia synthesis, proposed for the first time the idea of ??recycling ammonia synthesis gas, and also proposed measures to realize heat energy recovery in high-pressure gas circulation. In 1909, he applied for a patent for using a mixture of osmium and uranium-uranium carbide as a catalyst; in May 1910, he finally achieved gratifying results in the laboratory. Initially, osmium was used as a catalyst, and 8% ammonia was obtained from the mixed gas after the reaction of nitrogen and hydrogen at a pressure of 175 kgf/cm2 and a temperature of 550°C. Later, uranium-uranium carbide was used as a catalyst, and at a temperature of 125 kgf /cm2 pressure and temperature of 500°C to obtain 10% ammonia. On May 18, 1910, he gave a speech at a natural science symposium in Karlsruhe, Germany (he was a professor of chemistry at the Industrial College of this city), and demonstrated a high-pressure ammonia synthesis experimental device, announcing that the future of the new ammonia synthesis industry had open up.
He Bingchang. Haber and the world's first ammonia plant. Chemical Bulletin, 1984(9).
Haber applied his successful experiments to industrial production and collaborated with chemist Carl Bosch (1874) at the famous Badische Anilin and Soda Fabrik (BASF) factory in Germany. -1940), F. Lappe, Alwin. Mittash (1869-1953) and others to cooperate. Bosch made the high-pressure equipment necessary for the ammonia synthesis industry; Lape solved a series of mechanical problems under high temperature and high pressure; Mittach successfully developed an iron catalyst containing a small amount of aluminum oxide and potassium alkali for industrial ammonia synthesis. They established the world's first industrial plant for ammonia synthesis in 1911 in Oppau, near Ludwigshafen, Germany, with an annual production capacity of 9,000 tons of ammonia. On September 9, 1913 Construction started and the artificial fixation of nitrogen was completed. Haber won the Nobel Prize in Chemistry in 1918, and Bosch also won the Nobel Prize in Chemistry in 1931.
Although Harper created a way to save millions of hungry creatures, he also designed a terrible weapon that caused death. At about 5:00 a.m. on April 22, 1915, World War I broke out. Germany opened nearly 6,000 cylinders containing chlorine gas and about 180 tons of chlorine gas and dispersed them towards the Canadian Allied Forces and Allied Forces guarding the defense line in Ypres, Belgium. The French Algerian army caused 15,000 casualties, including 5,000 deaths. This was the first time in history that chemical weapons were used in a military attack. It was planned by Haber. His wife, Clara Immerwahr, a Ph.D. in chemistry, begged him to give up his work. When her husband refused, she committed suicide with Haber's pistol. For this reason, Haber was condemned and reviled by future generations.