View source for Birkeland–Eyde process

{{Short description|Nitrogen fixation process using electrical arcs}}
[[File:Birkeland-Eyde lysbue.JPG|thumb|Reactor used in Rjukan from 1916 to 1940 having a capacity of 3000&nbsp;kW (outside [[Norwegian Museum of Science and Technology]])]]
The '''Birkeland–Eyde process''' was one of the competing industrial processes in the beginning of [[Nitrogen fertilizer|nitrogen-based fertilizer]] production. It is a multi-step [[nitrogen fixation]] reaction that uses electrical arcs to react atmospheric [[nitrogen]] (N<sub>2</sub>) with oxygen (O<sub>2</sub>), ultimately producing [[nitric acid]] (HNO<sub>3</sub>) with water.<ref>{{cite journal|last1=Remsen|first1=I.|last2=Renoup|first2=H.|title=The Oxidation of Atmospheric Nitrogen with Reference to the Manufacture of Nitrates and Nitric Acid|journal=American Chemical Journal|date=1906|volume=35|pages=358–367|url=https://archive.org/download/americanchemical351906balt/americanchemical351906balt_bw.pdf|accessdate=1 February 2019}}</ref>  The resultant nitric acid was then used as a source of [[nitrate]] (NO<sub>3</sub><sup>−</sup>) in the reaction <chem display=inline>HNO3 + H2O -> H3O+ + NO3-</chem> which may take place in the presence of water or another [[proton acceptor]].

It was developed by Norwegian industrialist and scientist [[Kristian Birkeland]] along with his business partner [[Sam Eyde]] in 1903,<ref>{{cite journal| title= The Manufacture of Nitrates from the Atmosphere by the Electric Arc—Birkeland-Eyde Process| first=Sam | last=Eyde | journal= Journal of the Royal Society of Arts| volume= 57| issue = 2949 | year= 1909| pages= 568–576 | jstor=41338647}}</ref> based on a method used by [[Henry Cavendish]] in 1784.<ref>{{cite journal |last1=Cavendish |first1=Henry |title=Experiments on air |journal=Philosophical Transactions of the Royal Society of London |date=1785 |volume=75 |pages=372–384 |url=https://archive.org/details/philtrans03761202/mode/2up}}</ref><ref>{{cite book
| title = The development of modern chemistry
| author = Aaron John Ihde
| publisher = Courier Dover Publications
| year = 1984
| isbn = 0-486-64235-6
| page = 678
}}</ref> A factory based on the process was built in [[Rjukan]] and [[Notodden]] in Norway, combined with the building of large [[hydroelectric power]] facilities.<ref>{{cite book
| title = The world's greatest fix: a history of nitrogen and agriculture
| url = https://archive.org/details/worldsgreatestfi0000leig
| url-access = registration
| author = G. J. Leigh
| publisher = Oxford University Press US
| year = 2004
| isbn = 0-19-516582-9
| pages = [https://archive.org/details/worldsgreatestfi0000leig/page/134 134–139]
}}</ref><ref name="Birkeland1906">{{cite journal|last1= Birkeland|first1 =Kr.|title=On the oxidation of atmospheric nitrogen in electric arcs|journal=Transactions of the Faraday Society|volume=2| issue=December|year=1906|pages=98|issn=0014-7672|doi=10.1039/tf9060200098|url =https://zenodo.org/record/1429765}}</ref>

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 (NH<sub>3</sub>) from molecular nitrogen (N<sub>2</sub>) and hydrogen (H<sub>2</sub>), the latter usually but not necessarily produced by [[steam reforming]] methane (CH<sub>4</sub>) gas in current practice. The ammonia from the Haber process is then converted into [[nitric acid]] (HNO<sub>3</sub>) in the [[Ostwald process]].<ref>{{cite book
| title = A short history of twentieth-century technology c. 1900-c. 1950
| author1 = Trevor Illtyd Williams
| author2 = Thomas Kingston Derry
| publisher = Oxford University Press
| year = 1982
| isbn = 0-19-858159-9
| pages = 134–135
}}</ref>

==The process==
[[File:Birkeland-Eyde Plasma Disc.png|thumb|Diagram of the production of a plasma disc using water-cooled electrodes and an electromagnet]]
[[File:Rjukan electric arc furnace.jpg|thumb|One type of reactor used at Rjukan from 1912 to 1940 now located in a park in Rjukan]]
[[File:Såheim Rjukan II.jpg|thumb|Reactor Building II behind the [[Såheim Hydroelectric Power Station]] in which 35 Birkeland-Eyde reactors were installed requiring 3000&nbsp;kW each]]

An [[electrical arc]] was formed between two coaxial water-cooled copper tube electrodes powered by a [[high voltage]] alternating current of 5&nbsp;kV at 50&nbsp;Hz. A strong static magnetic field generated by a nearby [[electromagnet]] spreads the arc into a thin disc by the [[Lorentz force]]. This setup is based on an experiment by [[Julius Plücker]] who in 1861 showed how to create a disc of sparks by placing the ends of a U-shaped electromagnet around a spark gap so that the gap between them was perpendicular to the gap between the electrodes, and which was later replicated similarly by [[Walther Nernst]] and others.<ref>{{cite journal |last1=Plücker |title=Ueber die Einwirkung des Magnets auf die elektrische Entladung |journal=Annalen der Physik und Chemie |date=1861 |volume=113 |pages=249–280 |url=https://babel.hathitrust.org/cgi/pt?id=umn.31951d00326552p&view=1up&seq=264&skin=2021 |trans-title=On the effect of the magnet on the electric discharge |language=German}}  From p. 255:  ''" … die Curven, welche dieselbe durchziehen, soweit die Schätzung des Auges reicht, genau die Form von  Kreisbogen an[nehmen], die sämmtlich auf der die beiden Spitzen des Entladers verbindenden geraden Linie, als gemeinschaftlicher, senkrecht stehen."''  ( … the curves which [the luminous discharges] traverse, assume — as far as the eye can judge — exactly the form of circular arcs, all of which stand perpendicular to the same straight line that joins the two points of the electrodes.)</ref><ref name="Word1921">{{cite book |title=Technology of Cellulose Esters |last=Worden |first=Edward Chauncey |publisher=D. Van Nostrand Company |volume=1:2 |year=1921 |page=[https://archive.org/details/dli.bengal.10689.5914/page/n324 870] |url=https://archive.org/details/dli.bengal.10689.5914}}</ref> The plasma temperature in the disc was in excess of 3000&nbsp;°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 approximately 4–5% nitric oxide were obtained at 3000&nbsp;°C and less at lower temperatures.<ref name="Mell1918">{{cite book |title=Modern Inorganic Chemistry |last1=Mellor |first1=J. W. |publisher=Longmans, Green and Co. |year=1918 |page=[https://archive.org/details/cu31924055328623/page/n532 509] |url=https://archive.org/details/cu31924055328623}}</ref><ref name="Geof1915">{{cite book |title=Industrial Nitrogen Compounds and Explosives |author1=Martin, Geoffrey |author2=Barbour, William |publisher=Crosby Lockwood and Son |year=1915 |page=[https://archive.org/details/IndustrialNitrogenCompoundsAndExplosives/page/n24 21] |url=https://archive.org/details/IndustrialNitrogenCompoundsAndExplosives}}</ref> The process is extremely energy intensive. Birkeland used a nearby hydroelectric power station for the electricity as this process demanded about 15&nbsp;MWh per ton of nitric acid, yielding approximately 60&nbsp;g per kWh. The same reaction is carried out by lightning, providing a natural source for converting atmospheric nitrogen to soluble nitrates.<ref>{{cite book
| title = Nitrogen fixation at the millennium
| author1 = Karl Fisher
| author2 = William E. Newton
| editor = G. J. Leigh
| publisher = Elsevier
| year = 2002
| isbn = 0-444-50965-8
| pages = 2–3
}}</ref>

:<chem>N2 + O2 -> 2NO</chem>

The hot nitric oxide is cooled and combines with atmospheric oxygen to produce [[nitrogen dioxide]]. The time this process takes depends on the concentration of NO in the air. At 1% it takes about 180 seconds and at 6% about 40 seconds to achieve 90% conversion.<ref name="webb1923">{{cite book |title=Absorption of Nitrous Gases |first=H. W. |last=Webb |year=1923 |publisher=Edward Arnold & Co. |page=[https://archive.org/details/Absorption_of_Nitrous_Gases/page/n24 20] |url=https://archive.org/details/Absorption_of_Nitrous_Gases}}</ref>

:<chem>2 NO + O2 -> 2 NO2</chem>

This nitrogen dioxide is then dissolved in water to give rise to nitric acid, which is then purified and concentrated by [[fractional distillation]].<ref>{{cite book
| title = Industrial Chemical Process Design
| author = Douglas Erwin
| publisher = McGraw-Hill
| year = 2002
| isbn = 0-07-137621-6
| page = 613
}}</ref>

:<chem>3 NO2 + H2O -> 2 HNO3 + NO</chem>

The design of the absorption process was critical to the efficiency of the whole system. The nitrogen dioxide was absorbed into water in a series of [[Packed bed#Packed column|packed column]] or [[plate column]] absorption towers each four stories tall to produce approximately 40–50% nitric acid. The first towers bubbled the nitrogen dioxide through water and non-reactive quartz fragments. Once the first tower reached final concentration, the nitric acid was moved to a granite storage container, and liquid from the next water tower replaced it. That movement process continued to the last water tower which was replenished with fresh water. About 20% of the produced oxides of nitrogen remained unreacted so the final towers contained an alkaline solution of [[Lime (material)|lime]] to convert the remaining oxides to [[calcium nitrate]] (also known as Norwegian saltpeter) except approximately 2% which were released into the air.<ref name="Knox1914">{{cite book |last=Knox |first=Joseph |title=The Fixation of Atmospheric Nitrogen |publisher=D. Van Nostrand Company |year=1914 |pages=[https://archive.org/details/fixationatmosph00knoxgoog/page/n56 45]-50 |url=https://archive.org/details/fixationatmosph00knoxgoog}}</ref>

==References==
{{reflist|2}}

{{DEFAULTSORT:Birkeland-Eyde process}}
[[Category:Name reactions]]
[[Category:Chemical processes]]
[[Category:Science and technology in Norway]]
[[Category:Norwegian inventions]]