Nitrogen

1 Nitrogen as an inert

The Nitrogen molecule N2 has extraordinary properties and plays a key role in the history of life and the biological environment on earth.

With a boiling point of -196oC and a dissociation temperature of more than 2000oC it is often used as an inert gas with close to noble gas properties. Simultaneously the nitrogen atom N is the key component and limiting factor in the formation and existence of life.

Model of N2 molecule

78% of the atmosphere consists of Nitrogen and 21% is Oxygen.  The rest is mainly noble gasses, 1%, and 400 ppm of CO2.  Nitrogen is without taste or smell, and is not poisonous, but still being the single gas causing more fatalities in the industry than any other gas.  Nitrogen is used as an intert gas for purging and keeping tanks and equipment in an atmosphere free of oxygen. When a human is exposed to an oxygen depleted atmosphere for only a few inhalations, asphyxiation occurs with no pre-warning. Instant loss of consciousness and subsequent brain damage and death will occur if aspiration of oxygen containing air is not initiated immediately.

The inert property of Nitrogen is crucial for maintaining a stable atmosphere on earth.  If the reaction between Oxygen and Nitrogen had taken place at any measurable rate, the oceans would have been Nitric Acid.  The biological activity in the ocean is consuming the reactive Nitrate (Nitric Acid) much faster than the chemical reaction is able to produce it.  The same biological activity is not able to cope with the excess CO2 being released.

2 Nitrogen in life

Before the green plants emerged on earth, the atmosphere was lacking oxygen.

The oxygen was bound in the form of minerals, water and carbon-dioxide.  The atmosphere consisted of molecular nitrogen and carbon-dioxide.  Chemically bound nitrogen was present in the form of ammonia together with other nutrient salts.

In this reducing environment, the first primitive forms of life have occurred.  As life developed into green plants which were using the photosynthesis, the atmosphere changed from being reducing to become oxidising, containing free oxygen.  The oxidising atmosphere was developed around 3 bill years ago.  This is confirmed by analysing the rock being formed in these periods.

The first primitive life was exploiting the chemically available nutrient salts and ammonia, which was thermodynamically available in the absence of oxygen.  With the development of the photosynthesis, a green revolution took place in the form of green algae blooming in the ocean.

The competition for carbon-dioxide and nutrients was fierce, and the first global lack of chemically available nitrogen has probably occurred.

This situation again opened for nitrogen fixation from blue-green algae like “cyanobacter”.  It is likely that the photosynthesis and nitrogen fixation was developed in parallel.

3 Role and availability of nutrients

The next global lack of chemically bound nitrogen occurred when man was unable to grow enough food to cover its need for proteins, nutrients and energy.

Our ancient cultures grew up around the river deltas like the Nile, Euphrates and Tigris and Indus.  Outside these naturally fertilised areas, large and sustainable societies were hard to establish.  The slash and burn technique was utilised in prehistoric times.  In the pre-industrial times the farmers were limited to using manure and organic waste as fertilisers.

The understanding of the role of nutrients in the growth mechanism of crops was explained and fully understood in 1840 by Liebig.  The scientific proof of the mechanism was done with isotope tracing of the molecules in the 1965.  The plant can only take up fully mineralized nutrients like NH3, NO3, PO4, K, SO4, etc.

The natural sources for nitrogen were mainly Chilean nitrates and the fast exploited Guano. The industrial production of Nitrogen fertiliser was mainly coming from ammonia taken out as a by-product from coke production, and made into ammonium sulphate. In 1898 Sir William Crook predicted also an exhaustion of the Chile nitrates and the coming of a severe starvation around 1931.

To solve the nitrogen deficiency therefore became a challenge for the chemical industry, which was developing fast at this time. The solution several scientists in leading industrial countries were looking for was to take NO gas out of thin air by means of an electric arc.  The electric arc was known to be able to “burn” the air and make NO gas, which was further oxidised to NO2.

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