For
all living organisms, nitrogen (N) is one of the building blocks of the amino acids which make
up proteins and enable metabolic function. More specifically, in plants, N is
involved in the production of chlorophyll – the green pigment that makes
photosynthesis possible and enables the conversion of solar energy into the
chemical energy that is essential to the survival of plants.
Plants can acquire N through the uptake of ammonium (NH4+)
or nitrate (NO3-) in soils and water, with species
preferring one form to the other depending on their N uptake mechanisms and
adaptations.
These two main compounds are made available in soils thanks to the process of
nitrogen fixation. Nitrogen fixation, defined as the combination of atmospheric
nitrogen (N2) with other elements to form more reactive compounds
that plants can uptake from their root systems, may occur in two different
ways: when lightning strikes, providing sufficient energy for a reaction
between nitrogen and oxygen to produce nitrogen oxide and nitrogen dioxide; and
when diazotrophic soil bacteria fix nitrogen into ammonia, nitrites, and
nitrates, while often forming a symbiotic relationship with the plant. The
latter provides most of the “fixed nitrogen” in soils.
The fixed N then provides the basis of the entire N cycle which benefits all
living organisms on the planet.
As a result of the increasing need for food
production, contemporary agricultural practices favour the use of products
which increase soil nutrient content, so that crops can access sufficient
nutrients and grow fast, big and nutritious. N-fertilisers are designed to
increase the content of immobilised N in the soil in the form of ammonium or
nitrate (and sometimes nitrites). Fertilisers, including nitrogen fertilisers, have
become ubiquitous. According to the IPCC, their use has risen by 800% since the
1960s.
Further increase is expected in the next years, and decades, with the global
N-fertiliser market projected to amount to around $125 billion by the end of
2022.
In this article we look at the production pathways for
the manufacture of ammonia destined for N-fertilisers. We compare conventional
fossil-derived ammonia and sustainably produced “green ammonia”, and their
respective markets. We also look at the use of “green ammonia” as a potential
biofuel for maritime shipping.
To read the rest of the article, please click here.