Birkeland–Eyde process

The Birkeland–Eyde process was one of the competing industrial processes in the beginning of nitrogen based fertilizer production. It was developed by Norwegian industrialist and scientist Kristian Birkeland along with his business partner Sam Eyde in 1903, based on a method used by Henry Cavendish in 1784. This process was used to fix atmospheric nitrogen (N₂) into nitric acid (HNO₃), one of several chemical processes generally referred to as nitrogen fixation. The resultant nitric acid was then used as a source of nitrate (NO₃⁻) in the reaction

HNO₃ → H⁺ + NO₃⁻

which may take place in the presence of water or another proton acceptor.

A factory based on the process was built in Rjukan and Notodden in Norway, combined with the building of large hydroelectric power facilities.

The Birkeland–Eyde process is relatively inefficient in terms of energy consumption. Therefore, in the 1910s and 1920s, it was gradually replaced in Norway by a combination of the Haber process and the Ostwald process. The Haber process produces ammonia (NH₃) from molecular nitrogen (N₂) and hydrogen (H₂), the latter usually but not necessarily produced by steam reforming methane (CH₄) gas in current practice. The ammonia from the Haber process is then converted into nitric acid (HNO₃) in the Ostwald process.

An electrical arc was formed between two coaxial electrodes, and through the use of a strong magnetic field, was spread out into a thin disc. The plasma temperature in the disc was in excess of 3000°C. Air was blown through this arc, causing some of the nitrogen to react with oxygen forming nitric oxide. By carefully controlling the energy of the arc and the velocity of the air stream, yields of up to 4% nitric oxide were obtained. The process is extremely energy intensive. Birkeland used a nearby hydroelectric power station for the electricity as this process demanded about 15 MWh/Ton of nitric acid. The same reaction is carried out by lightning, providing a natural source for converting atmospheric nitrogen to soluble nitrates.

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