The Birkeland–Eyde process was developed by Norwegian industrialist and scientist Kristian Birkeland

Kristian Birkeland

Kristian Olaf Birkeland was a Norwegian scientist. He is best remembered as the person who first elucidated the nature of the Aurora borealis. In order to fund his research on the aurorae, he invented the electromagnetic cannon and the Birkeland-Eyde process of fixing nitrogen from the air...

 along with his business partner Sam Eyde

Sam Eyde

Samuel Eyde was a Norwegian engineer and industrialist, the founder of Norsk Hydro and Elkem.-Biography:Sam Eyde was the son of a shipowner, and studied engineering in Berlin where he graduated in 1891. He started his career in Hamburg, working with the railways where he planned new lines, bridges...

 in 1903, based on a method used by Henry Cavendish

Henry Cavendish

Henry Cavendish FRS was a British scientist noted for his discovery of hydrogen or what he called "inflammable air". He described the density of inflammable air, which formed water on combustion, in a 1766 paper "On Factitious Airs". Antoine Lavoisier later reproduced Cavendish's experiment and...

 in 1784. This process was used to fix atmospheric nitrogen

Nitrogen

Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...

 which was in turn used to produce nitric acid

Nitric acid

Nitric acid , also known as aqua fortis and spirit of nitre, is a highly corrosive and toxic strong acid.Colorless when pure, older samples tend to acquire a yellow cast due to the accumulation of oxides of nitrogen. If the solution contains more than 86% nitric acid, it is referred to as fuming...

, used for production of synthetic fertilizer. A factory based on the process was built in Rjukan

Rjukan

Rjukan is a town and the administrative center of Tinn municipality in Telemark . It is situated in Vestfjorddalen, between Møsvatn and Tinnsjå, and got its name after Rjukanfossen west of the town. The Tinn municipality council granted township status for Rjukan in 1996. The town has 3 386...

 and Notodden

Notodden

is a town and municipality in Telemark county, Norway. It is part of the traditional region of Øst-Telemark. The administrative centre of the municipality is the town of Notodden....

 in Norway, combined with the building of large hydroelectric power facilities. The process is inefficient in terms of energy usage, and is today replaced by the Ostwald process

Ostwald process

The Ostwald process is a chemical process for producing nitric acid, which was developed by Wilhelm Ostwald . It is a mainstay of the modern chemical industry. Historically and practically it is closely associated with the Haber process, which provides the requisite raw material,...

, that produces nitrous acid from ammonia (usually from the Haber process

Haber process

The Haber process, also called the Haber–Bosch process, is the nitrogen fixation reaction of nitrogen gas and hydrogen gas, over an enriched iron or ruthenium catalyst, which is used to industrially produce ammonia....

) instead of air.

The 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

Nitric oxide

Nitric oxide, also known as nitrogen monoxide, is a diatomic molecule with chemical formula NO. It is a free radical and is an important intermediate in the chemical industry...

. 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 oxygen to soluble nitrates.

+ → 2 NO

The hot nitric oxide is cooled and combines with atmospheric oxygen to produce nitrogen dioxide

Nitrogen dioxide

Nitrogen dioxide is the chemical compound with the formula it is one of several nitrogen oxides. is an intermediate in the industrial synthesis of nitric acid, millions of tons of which are produced each year. This reddish-brown toxic gas has a characteristic sharp, biting odor and is a prominent...

.

2 NO + → 2

This nitrogen dioxide is then dissolved in water to give rise to nitric acid, which is then purified by fractional distillation

Fractional distillation

Fractional distillation is the separation of a mixture into its component parts, or fractions, such as in separating chemical compounds by their boiling point by heating them to a temperature at which several fractions of the compound will evaporate. It is a special type of distillation...

.

3 + → 2 + NO