Ammonia, you Toxic Chemical…

This blog post is written for Sciencegeist’s #ToxicCarnival

Ah Nitrogen (N2), thank you for helping me run my oxygen-sensitive reactions, you are 78% of the earth’s atmosphere, and when fixed you provide us with food. The last example that I am talking about is the Haber-Bosch process of taking inert N2 and converting it into reactive ammonia (NH3) that we put into fertilizer.

Fritz Haber and his synthetic process of fixing nitrogen is very relevant to our discussion of “toxic chemicals” because ultimately his process was discovered because Germany needed nitrates for making explosives during WWI.  Here is a great example of how a chemical and the ability to mass produce a chemical can be for good and bad. When asked about the duality of his discovery Haber said this:

“The interest of a wider circle has its source in the recognition that ammonia synthesis on a large scale represents a useful…way to satisfy an economic need. This practical usefulness was not the preconceived goal of my experiments. I was not in doubt that my laboratory work could furnish no more than a scientific statement of the foundations and a knowledge of the experimental equipment, and that much had to be added to this result in order to attain economic success on an industrial scale.”

Ammonia in fertilizer is one of the most important chemicals used today. The hydrogenation of nitrogen is catalyzed by a heterogeneous iron oxide catalyst at over 300 C and around 15 – 20 MPa.  This is a very energy intensive process using about 1.2% of the world’s energy. Yet, the massive production of ammonia through the Haber-Bosch process allows for the global food supply to keep up with the demands of human population growth. And in general, reactive forms of nitrogen not only provides the necessary nutrients for feeding the world, it is also responsible for providing us with the precursors for industrial goods such as cleaners, antiseptics, and nylon.

However we are beginning to see the detrimental effects to our environment such as ozone depletion in our excessive use of these reactive nitrogen reagents in fertilizer and the burning of fossil fuels. Yet, it is slightly more complicated than making overarching regulatory decisions to decrease reactive nitrogen use.  For example nitrogen that has leached into the ecosystem has enhanced plant growth in wetlands and riparian restoration and in turn account for substantial carbon sequestration and slowing of global warming. Another compounding factor of nitrogen management is that N2O slows decomposition and the release of CH4, but itself also contributes to the breakdown of the ozone. (reference)

So how can we better manage the nitrogen cycle? Nitrogen played a significant role during Haber’s lifetime and it is again an important element to understanding how we have changed its ecosystem, and make better decisions on how to manage it and take advantage of its benefits.

Further reading:
http://www.nature.com/scientificamerican/journal/v302/n2/full/scientificamerican0210-64.html
http://www.npr.org/programs/morning/features/2002/jul/fritzhaber/
Great plot of the production of ammonia over the last decade: http://en.wikipedia.org/wiki/Ammonia#Synthesis_and_production
http://www.nature.com/ngeo/journal/v1/n10/full/ngeo325.html

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