Birkeland–Eyde process

<h2 id="the-process">The process</h2>

An <a href="/facts/Electrical_arc/1hUPPAG0">electrical arc</a> was formed between two coaxial water-cooled copper tube electrodes powered by a <a href="/facts/High_voltage/lUy99k3E">high voltage</a> alternating current of 5 kV at 50 Hz. A strong static magnetic field generated by a nearby <a href="/facts/Electromagnet/3YMYtSMX">electromagnet</a> spreads the arc into a thin disc by the <a href="/facts/Lorentz_force/aq1Rc3SS">Lorentz force</a>. This setup is based on an experiment by <a href="/facts/Julius_Pl%25C3%25BCcker/QgoMT64G">Julius Plücker</a> 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 <a href="/facts/Walther_Nernst/B2bYwpQp">Walther Nernst</a> and others.<a class="footnote-ref" id="fnref:8" href="#fn:8">8</a><a class="footnote-ref" id="fnref:9" href="#fn:9">9</a> 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 <a href="/facts/Nitric_oxide/UvhdvDzp">nitric oxide</a>. 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 °C and less at lower temperatures.<a class="footnote-ref" id="fnref:10" href="#fn:10">10</a><a class="footnote-ref" id="fnref:11" href="#fn:11">11</a> The process is extremely energy intensive. Birkeland used a nearby hydroelectric power station for the electricity as this process demanded about 15 MWh per ton of nitric acid, yielding approximately 60 g per kWh. The same reaction is carried out by lightning, providing a natural source for converting atmospheric nitrogen to soluble nitrates.<a class="footnote-ref" id="fnref:12" href="#fn:12">12</a>

N
            
              2
            
            
              
            
          
          +
          
            O
            
              2
            
            
              
            
          
          ⟶
          2
          
          NO
        
      
    
    {\displaystyle {\ce {N2 + O2 -> 2NO}}}

The hot nitric oxide is cooled and combines with atmospheric oxygen to produce <a href="/facts/Nitrogen_dioxide/FoLvApPI">nitrogen dioxide</a>. 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.<a class="footnote-ref" id="fnref:13" href="#fn:13">13</a>

2
          
          NO
          +
          
            O
            
              2
            
            
              
            
          
          ⟶
          2
          
          
            NO
            
              2
            
            
              
            
          
        
      
    
    {\displaystyle {\ce {2 NO + O2 -> 2 NO2}}}

This nitrogen dioxide is then dissolved in water to give rise to nitric acid, which is then purified and concentrated by <a href="/facts/Fractional_distillation/DdNf0k8I">fractional distillation</a>.<a class="footnote-ref" id="fnref:14" href="#fn:14">14</a>

3
          
          
            NO
            
              2
            
            
              
            
          
          +
          
            H
            
              2
            
            
              
            
          
          O
          ⟶
          2
          
          
            HNO
            
              3
            
            
              
            
          
          +
          NO
        
      
    
    {\displaystyle {\ce {3 NO2 + H2O -> 2 HNO3 + NO}}}

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 <a href="/facts/Packed_bed/7WuekCYT">packed column</a> or <a href="/facts/Plate_column/vSh39E0p">plate column</a> 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 <a href="/facts/Lime_(material)/uMcVXGBM">lime</a> to convert the remaining oxides to <a href="/facts/Calcium_nitrate/t4aY1BqH">calcium nitrate</a> (also known as Norwegian saltpeter) except approximately 2% which were released into the air.<a class="footnote-ref" id="fnref:15" href="#fn:15">15</a>

<h2 id="references">References</h2>

<ol>
<li id="fn:1">Remsen, I.; Renoup, H. (1906). "The Oxidation of Atmospheric Nitrogen with Reference to the Manufacture of Nitrates and Nitric Acid" (PDF). American Chemical Journal. 35: 358–367. Retrieved 1 February 2019. <a href="https://archive.org/download/americanchemical351906balt/americanchemical351906balt_bw.pdf" target="_blank">https://archive.org/download/americanchemical351906balt/americanchemical351906balt_bw.pdf</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></li>
<li id="fn:2">Eyde, Sam (1909). "The Manufacture of Nitrates from the Atmosphere by the Electric Arc—Birkeland-Eyde Process". Journal of the Royal Society of Arts. 57 (2949): 568–576. JSTOR 41338647. <a href="/wiki/JSTOR_(identifier)" target="_blank">/wiki/JSTOR_(identifier)</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></li>
<li id="fn:3">Cavendish, Henry (1785). "Experiments on air". Philosophical Transactions of the Royal Society of London. 75: 372–384. <a href="https://archive.org/details/philtrans03761202/mode/2up" target="_blank">https://archive.org/details/philtrans03761202/mode/2up</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></li>
<li id="fn:4">Aaron John Ihde (1984). The development of modern chemistry. Courier Dover Publications. p. 678. ISBN 0-486-64235-6. <a href="0-486-64235-6" target="_blank">0-486-64235-6</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></li>
<li id="fn:5">G. J. Leigh (2004). The world's greatest fix: a history of nitrogen and agriculture. Oxford University Press US. pp. 134–139. ISBN 0-19-516582-9. <a href="0-19-516582-9" target="_blank">0-19-516582-9</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></li>
<li id="fn:6">Birkeland, Kr. (1906). "On the oxidation of atmospheric nitrogen in electric arcs". Transactions of the Faraday Society. 2 (December): 98. doi:10.1039/tf9060200098. ISSN 0014-7672. <a href="https://zenodo.org/record/1429765" target="_blank">https://zenodo.org/record/1429765</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></li>
<li id="fn:7">Trevor Illtyd Williams; Thomas Kingston Derry (1982). A short history of twentieth-century technology c. 1900-c. 1950. Oxford University Press. pp. 134–135. ISBN 0-19-858159-9. <a href="0-19-858159-9" target="_blank">0-19-858159-9</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></li>
<li id="fn:8">Plücker (1861). "Ueber die Einwirkung des Magnets auf die elektrische Entladung" [On the effect of the magnet on the electric discharge]. Annalen der Physik und Chemie (in German). 113: 249–280. 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.) <a href="https://babel.hathitrust.org/cgi/pt?id=umn.31951d00326552p&view=1up&seq=264&skin=2021" target="_blank">https://babel.hathitrust.org/cgi/pt?id=umn.31951d00326552p&view=1up&seq=264&skin=2021</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></li>
<li id="fn:9">Worden, Edward Chauncey (1921). Technology of Cellulose Esters. Vol. 1:2. D. Van Nostrand Company. p. 870. <a href="https://archive.org/details/dli.bengal.10689.5914" target="_blank">https://archive.org/details/dli.bengal.10689.5914</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></li>
<li id="fn:10">Mellor, J. W. (1918). Modern Inorganic Chemistry. Longmans, Green and Co. p. 509. <a href="https://archive.org/details/cu31924055328623" target="_blank">https://archive.org/details/cu31924055328623</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></li>
<li id="fn:11">Martin, Geoffrey; Barbour, William (1915). Industrial Nitrogen Compounds and Explosives. Crosby Lockwood and Son. p. 21. <a href="https://archive.org/details/IndustrialNitrogenCompoundsAndExplosives" target="_blank">https://archive.org/details/IndustrialNitrogenCompoundsAndExplosives</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></li>
<li id="fn:12">Karl Fisher; William E. Newton (2002). G. J. Leigh (ed.). Nitrogen fixation at the millennium. Elsevier. pp. 2–3. ISBN 0-444-50965-8. <a href="0-444-50965-8" target="_blank">0-444-50965-8</a> <a href="#fnref:12" class="footnote-back-ref">↩</a></li>
<li id="fn:13">Webb, H. W. (1923). Absorption of Nitrous Gases. Edward Arnold & Co. p. 20. <a href="https://archive.org/details/Absorption_of_Nitrous_Gases" target="_blank">https://archive.org/details/Absorption_of_Nitrous_Gases</a> <a href="#fnref:13" class="footnote-back-ref">↩</a></li>
<li id="fn:14">Douglas Erwin (2002). Industrial Chemical Process Design. McGraw-Hill. p. 613. ISBN 0-07-137621-6. <a href="0-07-137621-6" target="_blank">0-07-137621-6</a> <a href="#fnref:14" class="footnote-back-ref">↩</a></li>
<li id="fn:15">Knox, Joseph (1914). The Fixation of Atmospheric Nitrogen. D. Van Nostrand Company. pp. 45-50. <a href="https://archive.org/details/fixationatmosph00knoxgoog" target="_blank">https://archive.org/details/fixationatmosph00knoxgoog</a> <a href="#fnref:15" class="footnote-back-ref">↩</a></li>
</ol>

Birkeland–Eyde process open-in-new

Birkeland–Eyde process