
The Birkeland–Eyde process was one of the competing industrial processes in the beginning of
nitrogen-based fertilizer production. It is a multi-step
nitrogen fixation
Nitrogen fixation is a chemical process by which molecular dinitrogen () is converted into ammonia (). It occurs both biologically and abiological nitrogen fixation, abiologically in chemical industry, chemical industries. Biological nitrogen ...
reaction that uses electrical arcs to react atmospheric
nitrogen
Nitrogen is a chemical element; it has Symbol (chemistry), symbol N and atomic number 7. Nitrogen is a Nonmetal (chemistry), nonmetal and the lightest member of pnictogen, group 15 of the periodic table, often called the Pnictogen, pnictogens. ...
(N
2) with oxygen (O
2), ultimately producing
nitric acid
Nitric acid is an inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but samples tend to acquire a yellow cast over time due to decomposition into nitrogen oxide, oxides of nitrogen. Most com ...
(HNO
3) with water. The resultant nitric acid was then used as a source of
nitrate
Nitrate is a polyatomic ion with the chemical formula . salt (chemistry), Salts containing this ion are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are solubility, soluble in wa ...
(NO
3−) in the reaction
HNO3 + H2O -> H3O+ + NO3- which may take place in the presence of water or another
proton acceptor.
It was developed by Norwegian industrialist and scientist
Kristian Birkeland
Kristian Olaf Bernhard Birkeland (born 13 December 1867 – 15 June 1917) was a Norway, Norwegian space physics, space physicist, inventor, and professor of physics at the University of Oslo, Royal Fredriks University in Oslo. He is best remembe ...
along with his business partner
Sam Eyde in 1903, based on a method used by
Henry Cavendish
Henry Cavendish ( ; 10 October 1731 – 24 February 1810) was an English experimental and theoretical chemist and physicist. He is noted for his discovery of hydrogen, which he termed "inflammable air". He described the density of inflammable a ...
in 1784. A factory based on the process was built in
Rjukan
Rjukan () is a List of towns and cities in Norway, town in Tinn Municipality in Telemark county, Norway. The town is also the administrative centre of Tinn Municipality. The town is located in the Vestfjorddalen valley, between the lakes Møsvatn ...
and
Notodden
is a municipality in Telemark county, Norway. It is located in the traditional district of Aust-Telemark. The administrative centre of the municipality is the town of Notodden. Other population centres include the villages of Bolkesjø, G ...
in Norway, combined with the building of large
hydroelectric power
Hydroelectricity, or hydroelectric power, is Electricity generation, electricity generated from hydropower (water power). Hydropower supplies 15% of the world's electricity, almost 4,210 TWh in 2023, which is more than all other Renewable energ ...
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
The Haber process, also called the Haber–Bosch process, is the main industrial procedure for the ammonia production, production of ammonia. It converts atmospheric nitrogen (N2) to ammonia (NH3) by a reaction with hydrogen (H2) using finely di ...
and the
Ostwald process
The Ostwald process is a chemical process used for making nitric acid (HNO3). The Ostwald process is a mainstay of the modern chemical industry, and it provides the main raw material for the most common type of fertilizer production. Historically a ...
. The Haber process produces ammonia (NH
3) from molecular nitrogen (N
2) and hydrogen (H
2), the latter usually but not necessarily produced by
steam reforming
Steam reforming or steam methane reforming (SMR) is a method for producing syngas (hydrogen and carbon monoxide) by reaction of hydrocarbons with water. Commonly, natural gas is the feedstock. The main purpose of this technology is often hydrogen ...
methane (CH
4) gas in current practice. The ammonia from the Haber process is then converted into
nitric acid
Nitric acid is an inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but samples tend to acquire a yellow cast over time due to decomposition into nitrogen oxide, oxides of nitrogen. Most com ...
(HNO
3) in the
Ostwald process
The Ostwald process is a chemical process used for making nitric acid (HNO3). The Ostwald process is a mainstay of the modern chemical industry, and it provides the main raw material for the most common type of fertilizer production. Historically a ...
.
The process

An
electrical arc
An electric arc (or arc discharge) is an electrical breakdown of a gas that produces a prolonged electrical discharge. The current through a normally nonconductive medium such as air produces a plasma, which may produce visible light. An a ...
was formed between two coaxial water-cooled copper tube electrodes powered by a
high voltage
High voltage electricity refers to electrical potential large enough to cause injury or damage. In certain industries, ''high voltage'' refers to voltage above a certain threshold. Equipment and conductors that carry high voltage warrant sp ...
alternating current of 5 kV at 50 Hz. A strong static magnetic field generated by a nearby
electromagnet
An electromagnet is a type of magnet in which the magnetic field is produced by an electric current. Electromagnets usually consist of wire (likely copper) wound into a electromagnetic coil, coil. A current through the wire creates a magnetic ...
spreads the arc into a thin disc by the
Lorentz force
In electromagnetism, the Lorentz force is the force exerted on a charged particle by electric and magnetic fields. It determines how charged particles move in electromagnetic environments and underlies many physical phenomena, from the operation ...
. This setup is based on an experiment by
Julius Plücker
Julius Plücker (16 June 1801 – 22 May 1868) was a German mathematician and physicist. He made fundamental contributions to the field of analytical geometry and was a pioneer in the investigations of cathode rays that led eventually to the di ...
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
Walther Hermann Nernst (; 25 June 1864 – 18 November 1941) was a German physical chemist known for his work in thermodynamics, physical chemistry, electrochemistry, and solid-state physics. His formulation of the Nernst heat theorem helped ...
and others.
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
Nitric oxide (nitrogen oxide, nitrogen monooxide, or nitrogen monoxide) is a colorless gas with the formula . It is one of the principal oxides of nitrogen. Nitric oxide is a free radical: it has an unpaired electron, which is sometimes den ...
. 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.
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.
:
N2 + O2 -> 2NO
The hot nitric oxide is cooled and combines with atmospheric oxygen to produce
nitrogen dioxide
Nitrogen dioxide is a chemical compound with the formula . One of several nitrogen oxides, nitrogen dioxide is a reddish-brown gas. It is a paramagnetic, bent molecule with C2v point group symmetry. Industrially, is an intermediate in the s ...
. 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.
:
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
fractional distillation
Fractional distillation is the separation of a mixture into its component parts, or fractions. Chemical compounds are separated by heating them to a temperature at which one or more fractions of the mixture will vaporize. It uses distillation ...
.
:
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
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 to convert the remaining oxides to
calcium nitrate
Calcium nitrate are inorganic compounds with the formula Ca(NO3)2(H2O)x. The anhydrous compound, which is rarely encountered, absorbs moisture from the air to give the tetrahydrate. Both anhydrous and hydrated forms are colourless salts. Hydrated ...
(also known as Norwegian saltpeter) except approximately 2% which were released into the air.
References
{{DEFAULTSORT:Birkeland-Eyde process
Name reactions
Chemical processes
Science and technology in Norway
Norwegian inventions