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Chemists unlock secret to making green ammonia from renewable energy in refrigerator-size reactors 

The new, efficient technique could slash agricultural and transportation carbon emissions and be rolled out in communities and on individual farms
June 17, 2021

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A hundred years ago, ammonia helped revolutionize agriculture and feed the world’s growing population. Ammonia is the main ingredient of fertilizers, and half of the world’s food production today relies on it. But the important chemical bears an enormous carbon footprint. Producing a metric ton of ammonia emits nearly twice as much carbon dioxide.

Researchers from Monash University in Australia hope to reduce that footprint with a new process that could speed up the production of environmentally friendly green ammonia, which is made using water and renewable energy.

The breakthrough, reported in the journal Science, could cut the carbon emissions of fertilizers, and also transport. The shipping industry is looking at ammonia as a zero-carbon fuel to slash the greenhouse gas emissions of international shipping. “Green ammonia is seen as a very important fuel and renewable energy carrier if cost effective production methods can be developed,” says Douglas MacFarlane, a professor of chemistry at Monash who led the work.

The world produces about 180 million metric tons of ammonia every year, over 80 percent of which goes to fertilizer production. Nearly all this ammonia is made using an energy-hungry technique called the Haber–Bosch process, which reacts hydrogen and atmospheric nitrogen. The process requires high temperatures and pressures, and can only be done efficiently in large reactors. Plus, it relies on fossil fuels to both generate hydrogen and power the reactor.

To cut ammonia’s carbon footprint, scientists and chemical companies have been trying to instead use renewable energy for the power and to split water for hydrogen. This green ammonia process has so far been inefficient and slow, relegated mostly to the laboratory and able to make very small amounts of ammonia.

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MacFarlane and his colleagues used special chemicals known as phosphonium salts to speed up the electrochemical process that reduces nitrogen. The process gives ammonia directly at room temperature and normal pressures using air, water, and renewable energy.

The process could also enable farmers and communities to make ammonia at small scale using renewable energy in reactors as small as a refrigerator, the researchers say.

“This research has raised the ammonia reaction into the realms that are considered genuinely practical,” MacFarlane says. “This paves the way for scale up engineering effort to begin and is encouraging investors to support this technology.”

The team aims to have a device that can produce 0.1 kg of ammonia per day by the end of next year, he adds, and a 1 metric ton per day unit by 2025. They are scaling up the technology through a new spin out company, Jupiter Ionics.

Source: Bryan H. R. Suryanto et al. Nitrogen reduction to ammonia at high efficiency and rates based on a phosphonium proton shuttle. Science, 2021.

Image: Roadsidepictures




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