Friday, October 9, 2020

"Turning air into bread"

Since I have been, and will be, going on about ammonia as a carrier for hydrogen 

NH3 - ammonia - three hydrogens attached to a nitrogen:

about fertilizer and guano, about Yara and Norsk Hydro and Birkeland and explosives, I thought it time to add another post to ouyr nitrogen mini-library.
From the cheerfully optimistic The Roots of Progress:

I recently finished The Alchemy of Air, by Thomas Hager. It’s the story of the Haber-Bosch process, the lives of the men who created it, and its consequences for world agriculture and for Germany during the World Wars.
What is the Haber-Bosch process? It’s what keeps billions of people in the modern world from starving to death. In Hager’s phrase: it turns air into bread.

Some background. Plants, like all living organisms, need to take in nutrients for metabolism. For animals, the macronutrients needed are large, complex molecules: proteins, carbohydrates, fats. But for plants they are elements: nitrogen, phosphorus and potassium (NPK). Nitrogen is needed in the largest quantities.

Nitrogen is all around us: it constitutes about four-fifths of the atmosphere. But plants can’t use atmospheric nitrogen. Nitrogen gas, N2, consists of two atoms held together by a triple covalent bond. The strength of this bond renders nitrogen mostly inert: it doesn’t react with much. To use it in chemical processes, plants need other nitrogen-containing molecules. These substances are known as “fixed” nitrogen; the process of turning nitrogen gas into usable form is called fixation.

In nature, nitrogen fixation is performed by bacteria. Some of these bacteria live in the soil; some live in a symbiotic relationship on the roots of certain plants, such as peas and other legumes.
Nitrogen availability is one of the top factors in plant growth and therefore in agriculture. The more fixed nitrogen is in the soil, the more crops can grow. Unfortunately, when you farm a plot of land, natural processes don’t replace the nitrogen as fast as it is depleted.
Pre-industrial farmers had no chemistry or advanced biology to guide them, but they knew that soil would lose its fertility over the years, and they had learned a few tricks. One was fertilization with natural substances, particularly animal waste, which contains nitrogen. Another was crop rotation: planting peas, for instance, would replace some of the nitrogen in the soil, thanks to those nitrogen-fixing bacteria on their roots.

But these techniques could only go so far. As the world population increased in the 19th century, more and more farmland was needed. Famine was staved off, for a time, by the opening of the prairies of the New World, but those resources were finite. The world needed fertilizer.
An island off the coast of Peru where it almost never rains had accumulated untold centuries of—don’t laugh—seagull droppings, some of the world’s best known natural fertilizer. An industry was made out of mining guano on these islands, where it was piled several stories high, and shipping it all over the world. When that ran out after a couple decades, attention turned inland to the Atacama Desert, where, with no rainfall and no life, unusual minerals grew in crystals on the rocks. The crystals included salitre, or Chilean saltpeter, a nitrogen salt that could be made into fertilizer.
It could be made into something else important, too: gunpowder. It turns out that nitrogen is a crucial component not only of fertilizer, but also of explosives. Needing it both to feed and to arm their people, every country considered saltpeter a strategic commodity. Peru, Chile and Bolivia went to war over the saltpeter resources of the Atacama in the late 1800s (Bolivia, at the time, had a small strip of land in the desert, running to the ocean; it lost that strip in the war and has remained landlocked ever since).

By the end of the 19th century, as population continued to soar, it was clear that the Chilean saltpeter would run out within decades, just as the guano had. Sir William Crookes, head of the British Academy of Sciences, warned that the world was heading for mass famine, a true Malthusian catastrophe, unless we discovered a way to synthesize fertilizer. And he called on the chemists of the world to do it.

Nearby, in Germany, other scientists were thinking the same thing. Germany was highly dependent on salt shipped halfway around the world from Chile. But Germany did not have the world’s best navy. If—God forbid—Germany were ever to be at war with England (!), they would quickly blockade Germany and deprive it of nitrogen. Germany would have no food and no bombs—not a good look, in wartime.

The prospect of synthesizing fixed nitrogen was tantalizing. After all, the nitrogen itself is abundant in the atmosphere. A product such as ammonia, NH3, could be made from that and hydrogen, which of course is present in water. All you need is a way to put them together in the right combination.
The problem, again, is that triple covalent bond. Owing to the strength of that bond, it takes very high temperatures to rip N2 apart. More troublesome is that ammonia is by comparison a weak molecule. So at temperatures high enough to separate the nitrogen atoms, the ammonia basically burns up.

Fritz Haber was the chemist who solved the fundamental problem. He found that increasing the pressure of the gases allowed him to decrease the temperature. At very high pressures, he could start to get an appreciable amount of ammonia. By introducing the right catalyst, he could increase the production to levels that were within reach of a viable industrial process.

Carl Bosch was the industrialist at the German chemical company BASF who led the team that figured out how to turn this into a profitable process, at scale. The challenges were enormous. To start with, the pressures required by the process were immense, around 200 atmospheres. The required temperatures, too, were very high. No one had ever done industrial chemistry in that regime before, and Bosch’s team had to invent almost everything from scratch, pioneering an entirely new subfield of high-pressure industrial chemistry. Their furnaces kept exploding—not only from the pressure itself, but because hydrogen was eating away at the steel walls of the container, as it forced into them. No material was strong enough and inexpensive enough to serve as the container wall. Finally Bosch came up with an ingenious system in which the furnaces had an inner lining of material to protect the steel, which would be replaced on a regular basis.

A further challenge was the catalyst: Haber had used osmium, an extremely rare metal. BASF bought up the entire world’s supply, but it wasn’t enough to produce the quantities they needed. They experimented with thousands of other materials, finally settling on a catalyst with an iron base combined with other elements....


Roots of Progress homepage
Roots of Progress post list (current through October 9)

Previously on our friend, nitrogen:
"How Making One Chemical Created the Modern World"
"Can We Grow One of the World's Largest Food Crops Without Fertilizer?"
The Adventures of a Nitrogen Atom
This Could Be A Big Deal: Norway's Yara and the Australian Nitrogen Economy
Shipping: "UK Department of Transport recommends launch of ammonia / hydrogen powered vessels within 5-15 years"
Ammonia, it's what everyone is talking about.
And if your crowd isn't, you'll be the best-informed next-gen energy storage/transport-medium connoisseur at the Thursday afternoon salon!

The $100M Synthetic Biology Bet From Bayer and Ginko Bioworks (YAR:Oslo; CF)
"Saudi Arabia Sends Blue Ammonia to Japan in World-First Shipment"
Nitrogen Upgraded, Potash Target Lowered; Ununquadium Decayed (AGU, CF; TRA; POT)
That Time A Dozen Norwegians Stopped the Nazis From Developing the Atom Bomb and Possibly Saved Europe