The main sources of oxygenated compounds in soil are: animal manure or dead animals and plants are transformed into soil; Nitrogen oxides formed in the atmosphere during thunderstorm discharge are dissolved in rainwater and brought into the soil; Some rhizobia symbiotic with leguminous plants absorb chlorine in the air and produce some fluorine compounds. However, these sources are far from meeting the needs of large-scale agricultural production. Therefore, how to transform the free fluorine gas in the atmosphere into nitrogen-containing compounds that plants can absorb, that is, the fixation of ammonia, has become a subject explored by chemists.
This subject made a breakthrough in the early 20th century. First, 1898, German chemistry professor Frank and his assistants Dr. Ross and Dr. Carol found that barium carbide was heated in nitrogen to form barium cyanide and barium cyanamide. Then, they found that calcium cyanamide could be produced when calcium carbide was heated to above 1000℃ in nitrogen, and that calcium cyanamide was hydrolyzed to produce ammonia. Therefore, it was initially suggested to use calcium cyanamide as fertilizer. 1904, Germany established the first industrial production device. 1905 also set up factories in Italy, followed by factories in the United States and Canada. By 192 1, the world's output of calcium cyanamide reached 500,000 tons per year, but since then, the construction of new plants has gradually stopped, because the industry of direct synthesis of ammonia from hydrogen and nitrogen is quietly emerging.
Subsequently, nitrogen and oxygen are directly combined by electricity to generate chlorine oxides, which are dissolved in water to generate nitric acid and nitrous acid.
To realize this method in industrial production, powerful power and stable arc are needed. 1904 This experiment was designed by Norwegian physics professor birkeland and engineer Ed. They use copper tubes with cooling water as electrodes and introduce alternating current. The generated arc and strong magnetic field make the arc form an oscillating disc, so the flame area is greatly increased and the temperature can reach 3300℃. The device was put into operation in Norway on 1905. Norway has a powerful hydropower plant, which can be used to produce nitric acid. However, this method of preparing nitric acid soon lost its industrial value after the appearance of oxygen oxidation of nitric acid.
The oxidation of ammonia begins with synthetic ammonia. The invention of synthetic oxygen is the third chemical fixation method of nitrogen.
Ammonia is also called ammonia gas. This word comes from the ancient Egyptian god of life and reproduction. This is due to the accumulation of camel dung and the remaining offerings of worshippers next to the temple of the god of life and reproduction in ancient Egypt, and gradually formed ammonium chloride. Nitrogen-containing organic matter, animal and plant carcasses and excreta can all produce ammonia under the action of bacteria.
1774, priestley heated the mixture of ammonium chloride and calcium hydroxide, and first collected ammonia by removing mercury and taking gas. Berthollet analysis in 1784 confirmed that ammonia is composed of nitrogen and hydrogen. /kloc-in the 0/9th century, many chemists tried to synthesize oxygen from chlorine and hydrogen, using catalysts, electric arcs, high temperature and high pressure, but all failed, so that some people thought it was impossible to synthesize ammonia from nitrogen and hydrogen.
It was not until the19th century that some progress was made in the research fields of new disciplines such as chemical thermodynamics, chemical kinetics and catalysts, and some chemists successfully studied the reaction of synthetic ammonia under the guidance of correct theories.
1904, German chemist Haber made a synthetic experiment with a ceramic tube filled with iron catalyst. It was determined that when the reaction reached equilibrium at atmospheric pressure and high temperature of 1020℃, there was 0.0 12% ammonia in the gas mixture. During the period of1904 ~1911year, he conducted more than 20,000 experiments. According to the experimental data, he thinks that the process can be realized by circulating the reaction gas under high pressure and continuously separating the ammonia produced by the reaction from this cycle. 1909, he applied for the patent of using osmium-uranium mixture and uranium carbide as catalyst. 19 10 May finally achieved gratifying results in the laboratory.
Hubble applied the successful experiment to industrial production, and obtained the cooperation of German Badizidine and Soda engineers such as Bosch, Lapp, Mitach and others. 1910 In July, Bosch was made into a necessary high-pressure equipment for the synthetic ammonia industry; Lapp solves a series of mechanical problems under high temperature and high pressure. Mitach Company successfully developed an iron catalyst containing a small amount of alumina and potassium carbonate cocatalyst for industrial ammonia synthesis. They established the world's first industrial ammonia plant in Aobao on191/with an annual output of 9,000 tons of ammonia, and started construction on 19 13 on September 9. Since then, artificial nitrogen fixation has been completed.
The synthesis of hydrogen not only synthesized ammonia, but also pioneered the promotion of chemical reactions under high pressure. Subsequently, German chemist Bergius applied the high-pressure method to the production of various chemical products. 1920, coal was liquefied by high pressure method, and gasoline was successfully synthesized.
Thus, Hubble won the 19 18 Nobel Prize in chemistry; Bosch and Bergius both won the Nobel Prize in chemistry.
However, although Hubble created a way to save millions of hungry creatures, it also designed a terrible means of killing people.
1965438+ At about 5 pm on April 22nd, 2005, when the First World War broke out, Germany opened nearly 6,000 cylinders filled with chlorine gas, and about 180 tons of chlorine gas was scattered into the hands of Canadian allied forces and French Algerian troops guarding the Belgian ypres defense line, resulting in15,000 casualties, including 5,000 deaths. This is the first time in history that chemical weapons have been used. Harper planned this. His wife, a doctor of chemistry, begged him to give up the job, but after her husband refused, she committed suicide with Harper's pistol. In this regard, Hubble was condemned and reviled by later generations.
Hydrogen in synthetic ammonia comes from water and ammonia comes from air. Blow air into the bottom of the gas producer with coal to make the coal burn. When the furnace temperature reaches 1000℃, steam is introduced to generate carbon monoxide and hydrogen, and heat is absorbed at the same time. In order to maintain the temperature in the furnace, in actual operation, air and steam are alternately blown in, and the gas thus obtained is called semi-water gas. Its composition is roughly as follows:
H2: 38% ~ 42% N2: 21%~ 23% co: 30% ~ 32% CO2: 8% ~ 9% H2S: 0.2% ~ 0.5% Hydrogen and chlorine in semi-water gas are needed for synthetic ammonia, and other gases need to be removed.
Hydrogen sulfide (H2S) is absorbed by ammonia water.
In the presence of catalyst, carbon monoxide is converted into carbon dioxide and hydrogen by heating and reacting with water. The converted gas is called shift gas.
The solubility of carbon dioxide in shift gas in water is obviously greater than that of other components in shift gas, so it can be removed by water or absorbed by alkali liquor and ammonia water.
Ammonium bicarbonate is only a small chemical fertilizer used in rural areas of China.
A small amount of carbon monoxide is removed by absorption in copper acetate ammonia solution.
The obtain pure mixture of hydrogen and nitrogen enters a synthetic tow after being compressed and passe through a catalyst at a certain temperature and pressure to partially synthesize ammonia. Because ammonia is easy to liquefy, it will be converted into liquid at atmospheric pressure and -33.4℃. Nitrogen, hydrogen and ammonia coming out of the synthetic tower will enter the cooler, ammonia will liquefy, and nitrogen, hydrogen are still gases. After passing through the separator, ammonia is separated from nitrogen and hydrogen. Unreacted nitrogen and hydrogen are sent to the synthesis tower for recycling by the circulating compressor.
The synthesis of ammonia also opens up a way for the preparation of nitric acid. Jaber, an Arab alchemist in the 8th century, wrote about the preparation of nitric acid: distilling 65,438+0 pounds of copperas and half a pound of saltpeter to get an acid, which can dissolve some metals well. If 1/4 lb ammonium chloride is added, the effect will be better.
Sulfuric acid is distilled from copperas, which react with saltpeter to obtain nitric acid, and ammonium chloride is added to obtain hydrochloric acid.
The mixture of 3 parts hydrochloric acid and 1 part nitric acid is aqua regia.
Since the 8th century, Europeans have made nitric acid from saltpeter and copperas. After the expansion of sulfuric acid production, nitric acid was gradually prepared by the reaction of sodium nitrate and sulfuric acid.
As mentioned earlier, nitric acid was prepared by oxidation of nitric oxide in the early 20th century, but that method consumes a lot of electricity.
As early as 1830, cullmann, a French chemical manufacturer, proposed that ammonia combined with oxygen under the catalysis of platinum to produce nitric acid and water.
In 1906, Latvian chemist ostwald industrialized this method and introduced it to Britain in 19 18.
Then constantly change the catalyst. Russian chemist Igor andreyev switched to platinum-iridium alloy in 19 14; The mixture of cerium oxide and thorium oxide used in Frank and Carlo's research is not as catalytic as platinum, but its price is lower. At present, platinum-rhodium alloy is widely used, and ammonia is oxidized to nitric oxide at high temperature and then to nitrogen dioxide. Nitrogen dioxide dissolves in water to form nitric acid.