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University of Illinois Chicago engineers have updated an ammonia production process that consists of orchestrating a “symphony” of lithium, nitrogen and hydrogen atoms to make the substance environmentally friendlier.
In a paper published in the journal ACS Applied Materials & Interfaces, the scientists point out that ammonia -a nitrogen-based chemical used in fertilizer, dyes, explosives and many other products-ranks second only to cement in terms of carbon emissions, due to the high temperatures and energy needed to manufacture it.
Their new process, however, combines nitrogen gas and a hydrogen-donating fluid such as ethanol with a charged lithium electrode and instead of cracking apart nitrogen gas molecules with high temperature and pressure, nitrogen atoms stick to the lithium, then combine with hydrogen to make the ammonia molecule.
The technique, called lithium-mediated ammonia synthesis, works at low temperatures and it’s also regenerative, restoring the original materials with each cycle of ammonia production.
“There are two loops that happen. One is the regeneration of the hydrogen source and the second is the regeneration of the lithium,” head researcher Meenesh Singh said in a media statement. “There is a symphony in this reaction, due to the cyclic process. What we did was understand this symphony in a better way and try to modulate it in a very efficient way, so that we can create a resonance and make it move faster.”
The process is the latest innovation from Singh’s lab in the quest for cleaner ammonia. Previously, his group developed methods to synthesize the chemical using sunlight and wastewater and created an electrified copper mesh screen that reduces the amount of energy needed to make ammonia.
Their latest advance is built on a reaction that has been known to scientists for nearly a century.
“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.”
Those targets include high energy efficiency and low cost. If scaled up, the process would produce ammonia at roughly $450 per ton, which is 60% cheaper than prior lithium-based approaches and other proposed green methods.
But selectivity is also important, as many attempts to make ammonia production cleaner have ended up creating large quantities of unwanted hydrogen gas instead.
The Singh group’s results are among the first to achieve selectivity and energy use levels that could meet Department of Energy standards for industrial-scale ammonia production.
The researcher also said the process, which can be performed in a modular reactor, could be made even greener by powering it with electricity from solar panels or other renewable sources and feeding the reaction with air and water.
The technique could also help meet another energy goal — the use of hydrogen as fuel. Reaching that goal has been stymied by the difficulties of transporting the highly combustible liquid.
“You want hydrogen to be generated, transported and delivered to hydrogen pumping stations, where hydrogen can be fed to the cars. But it’s very dangerous,” Singh said. “Ammonia could function as a carrier of hydrogen. It’s very cheap and safe to transport, and at the destination, you can convert ammonia back to hydrogen.”
The scientist and his team are now partnering with the General Ammonia Co. to pilot and scale up their lithium-mediated ammonia synthesis process at a plant in the Chicago area.
