Researchers in the US have developed a new way to make clean ammonia that could be 60% cheaper than using green hydrogen to decarbonise NH3 production.
Currently, ammonia is produced by combining hydrogen gas with nitrogen from the air in the Haber-Bosch process, which is extremely energy intensive due to the high temperature and pressure needed to crack N2 molecules into ions.
As such, most of the focus on reducing emissions from NH3, particularly for use in fertilisers and other chemicals, has been to decarbonise the hydrogen feedstock — today made predominantly from fossil gas or coal — by producing green H2 from renewables-powered electrolysis.
However, a research team at the University of Illinois Chicago (UIC) has designed a new process of lithium-mediated ammonia synthesis (LMAS) that can run at low temperatures, which combines nitrogen gas and a hydrogen-donating fluid such as ethanol with a charged lithium electrode.
Nitrogen atoms “stick” to the lithium before combining with hydrogen to form NH3 molecules, they say.
From there, both the lithium catalyst and unused hydrogen ions are regenerated in each cycle, meaning this method does not result in the by-production of large quantities of H2 gas — one of the stumbling blocks of similar electrochemical ammonia production methods.
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LMAS could only cost $450 per tonne of NH3 if scaled up — 60% cheaper than other green ammonia production pathways, according to the research team’s lead Meenesh Singh.
Market intelligence agency S&P’s most recent monthly average prices for grey ammonia ranged from $299 to $475 per tonne, depending on where it was produced, while a tonne of green NH3 made from renewable hydrogen was calculated to cost between $750 and $888.
“The lithium-based approach can actually be found in any organic chemistry textbook. It’s very well-known” Singh said. “But making this cycle run efficiently and selectively enough to meet economically feasible targets was our contribution.”
Ethanol is currently mass-produced around the world fairly cheaply from biomass, mainly corn and sugar cane, but it can also be made from non-food matter, such as straw, switchgrass and corn stover (the husks, leaves and stalks left over once corn is harvested).
But the UIC researchers have not stated the expected lifecycle emissions footprint of LMAS compared to other green ammonia production methods.
Ammonia is used today for the production of fertilisers and chemicals, and is being lined up as a major clean shipping fuel in the years to come.
Dr. Thomas Hughes is a UK-based scientist and science communicator who makes complex topics accessible to readers. His articles explore breakthroughs in various scientific disciplines, from space exploration to cutting-edge research.
