Atmospheric nitrogen fixation - Fixation of atmospheric nitrogen

This refers to the synthesis of various nitrogen compounds from nitrogen in the air. Before the development of the modern chemical industry, Chilean saltpeter was the only nitrogen resource, and ammonia was obtained as a by-product of coal dry distillation. However, as the uses of nitrogen compounds, including ammonia, increased, it became increasingly difficult to rely on natural resources, and by the end of the 19th century, there was a need to utilize the nitrogen that exists in inexhaustible quantities in the atmosphere. Thus, from the end of the 19th century to the beginning of the 20th century, various methods were devised, and the airborne nitrogen fixation industry emerged.

Methods for fixing nitrogen in the air can be classified according to the method of fixation: (1) the lime nitrogen method, (2) the electric arc method, and (3) the ammonia synthesis method. (1) is a method in which calcium carbonate reacts with nitrogen to obtain calcium carbonate. Ammonia production from calcium carbonate was also carried out industrially in the past, but is now limited to the production of calcium carbonate due to the development of the ammonia synthesis industry. (2) is a method in which air is passed through an electric arc furnace, where nitrogen and oxygen react directly to produce nitrogen oxide, which is cooled and further oxidized to produce nitrogen dioxide, which is then absorbed into water to produce nitric acid. It was industrialized in Norway, but it consumed a large amount of electricity and was not economically viable, so it has now been replaced by the ammonia oxidation method. (3) is a method in which ammonia is synthesized from nitrogen and hydrogen through a high-temperature, high-pressure reaction in the presence of a catalyst whose main component is iron oxide. The ammonia synthesis method has grown in close association with the fertilizer industry, but has made great strides with the development of the organic synthetic chemical industry.

Products derived from ammonia include chemical fertilizers such as ammonium sulfate, ammonium nitrate, ammonium chloride, ammonium phosphate, and urea, as well as dyes, explosives, celluloid, pharmaceuticals, and cyanides, and are closely related to the nitric acid industry, nitrogen fertilizer industry, dye industry, and pharmaceutical industry.

In addition to these industrial methods, nitrogen assimilation, the process of converting free nitrogen into nitrogen compounds that are easily biologically available, is called nitrogen fixation.

[Tsuyoshi Arakawa]

"Inorganic Industrial Chemistry" edited by Jiro Shiokawa (1980, Kagaku Dojin)

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

空気中の窒素から、種々の窒素化合物を合成することをさす。近代化学工業の発展以前は、窒素資源としてはチリ硝石が唯一のものであり、アンモニアは石炭を乾留する際の副産物として得ていた。しかしアンモニアをはじめとして窒素化合物の用途が増加するにつれて天然資源に頼ることがしだいに困難となり、19世紀末には大気中に無尽蔵に存在する窒素の利用の必要に迫られた。こうして19世紀末から20世紀初頭にかけて種々の方法が考案され空中窒素固定工業が出現した。

　空中窒素固定法をその固定の様式から分類すると、(1)石灰窒素法、(2)電弧法、(3)アンモニア合成法、に分けられる。(1)は炭化カルシウムと窒素とを反応させて石灰窒素を得る方法で、石灰窒素からのアンモニア製造も以前工業的に実施されていたが、現在はアンモニア合成工業の発達により石灰窒素の製造までにとどまっている。(2)は電弧炉中に空気を通じ、窒素と酸素を直接反応させ酸化窒素とし、これを冷却しさらに酸化して二酸化窒素を得、水に吸収させて硝酸をつくるものである。ノルウェーで工業化されたが、多量の電力を消費し経済的に成立せず、現在ではアンモニア酸化法に切り替わった。(3)は窒素と水素から酸化鉄を主成分とする触媒の存在下、高温高圧反応によってアンモニアを合成する方法である。アンモニア合成法は、肥料工業と密着して伸びてきたが、有機合成化学工業の発展とともに飛躍的に発展した。

　アンモニアからの誘導品としては、硫安、硝安、塩安、リン安、尿素などの化学肥料が、また、染料、爆薬、セルロイド、医薬品、シアン化物などがあり、硝酸工業、窒素肥料工業、染料工業、医薬品工業と深い関連がある。

　なお、これらの工業的な方法のほかに、遊離窒素を生物学的に利用しやすい窒素化合物に変える窒素同化は窒素固定といわれる。

［荒川　剛］

『塩川二朗編『無機工業化学』（1980・化学同人）』

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