Monday, May 18, 2015

Review of Enriching the Earth: Fritz Haber, Carl Bosch, and the Transformation of World Food Production by Vaclav Smil

Very typical of Vaclav Smil, we have Enriching the Earth, about the Haber-Bosch invention of synthetic nitrogen fertilizer, which was once the "holy grail of synthetic inorganic chemistry." He calls it the most important invention ever because the fixation of nonreactive, atmospheric, molecular nitrogen into usable form is alone what has allowed the world to swell to seven billion people.

Leibig's law of the minimum says that plant growth is limited by whatever substance is present in the soil in the least adequate amount. Many times, this is nitrogen, which is why most of the world's civilizations independently discovered intercropping of legumes in order to add nitrogen to soil, as early as 12,000 years ago.

Liebeg described agriculture's principle objective as "the production of digestible nitrogen," and as a 19th century chemist noted, "every vital phenomenon is due to some change in a nitrogen compound and indeed in the nitrogen atom of that compound".

But nitrogen was very scarce for humanity, because plants cannot use atmospheric nitrogen, and the only technology for increasing soil nitrogen was the symbiotic nitrogen fixing bacteria associated with legumes. The result was that the nitrogen cycle had to be kept very tight, with nitrogen wastes being returned to the soil, and even going so far as to harvest nitrogen-rich seabird guano from islands off the coasts of South America. There was federal legislation enacted in 1856, the Guano Islands Act:

"Whenever any citizen of the United States discovers a deposit of guano on any island, rock, or key, not within the lawful jurisdiction of any other Government, and not occupied by the citizens of any other Government, and takes peaceable possession thereof, and occupies the same, such island, rock, or key may, at the discretion of the President, be considered as appertaining to the United States."
In 1910, Fritz Haber developed a process for making ammonia (which can be used for fertilizer, or to make explosives) that would scale. The reaction N2 + 3 H2 → 2 NH3 uses an iron-based catalyst and extremely high temperature and pressure, which together overcome the strong triple bond holding the molecular nitrogen together.

The hydrogen for the reaction generally comes from natural gas, although if you have surplus electricity from wind or hydro or solar, you could make it by electrolysis of water. But apparently less than 5% of world natural gas production is used to make fertilizer, so there is no immediate need to worry about alternate supplies.

Depending on your theory of simultaneous invention, many people may owe their existence to Norman Borlaug and to Fritz Haber.

Another funny thing to think about is that given the ubiquity of nitrogen fertilizer in agriculture, and that the human body is 3% nitrogen by mass, everyone is carrying around a hefty slug of nitrogen atoms that streamed over a catalyst at an ammonia plant!


Some other Vaclav Smil books look interesting.
Prime Movers of Globalization: The History and Impact of Diesel Engines and Gas Turbines
Energy Transitions: History, Requirements, Prospects
Energy in Nature and Society: General Energetics of Complex Systems

No comments: