The low-temperature regenerative method saves energy and produces conventional chemicals efficiently. Among the many chemicals we use every day, ammonia is one of the most harmful to the atmosphere. The nitrogen-based chemical, used in fertilizers, paints, explosives and many other products, ranks second after cement in terms of carbon emissions due to the high temperatures and energy required for its production.

But by improving a well-known electrochemical reaction and arranging a “symphony” of lithium, nitrogen and hydrogen atoms, engineers led by Minesh Singh of the University of Illinois at Chicago have developed a new process for producing ammonia that meets various environmental requirements. targets.

The process, called lithium-assisted ammonia synthesis, combines nitrogen gas and a hydrogen-donating liquid such as ethanol with a charged lithium electrode. Instead of breaking down nitrogen gas molecules under high temperature and pressure, the nitrogen atoms stick to the lithium and then combine with hydrogen to form an ammonia molecule.

The reaction takes place at low temperatures and is also regenerative; Starting materials are recovered in each cycle of ammonia production.

Science through process

“There are two cycles going on. One is hydrogen source regeneration, the other is lithium regeneration,” said Singh, UIC associate professor of chemical engineering. “There’s a certain symphony to this reaction because of the cyclic process. What we’re doing is understanding the symphony better and trying to modulate it very efficiently so that it resonates and moves faster.”

The process described in the published article on the cover ACS Applied Materials and Interfacesis Singh’s lab’s latest innovation in the search for purer ammonia. His group previously 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 produce ammonia.

Their latest advances are built on a not-so-new reaction. Scientists have known this for almost a century.

“The lithium-based approach can actually be found in any organic chemistry textbook. It is very well known,” said Singh, “but it was our contribution to make this cycle efficient and selective enough to achieve cost-effective targets.”

These goals include high energy efficiency and low cost. If scaled up, the process would produce ammonia at around $450 per tonne, which would be 60% cheaper than previous lithium-based approaches and other proposed green methods, Singh said. But selectivity is also important because many attempts to make ammonia production cleaner have resulted in the production of too much unwanted hydrogen gas.

Environmental advantages and potential of using hydrogen fuel

Singh’s group’s results are among the first to reach levels of selectivity and energy use that could meet Department of Energy standards for industrial ammonia production. Singh also said the process, which can be done 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 process could also help achieve another energy goal, the use of hydrogen as a fuel. The difficulty of transporting a flammable liquid prevented this goal from being achieved.

“You want the hydrogen to be produced, transported and delivered to hydrogen pump stations where the hydrogen can be fed into the vehicle. But this is very dangerous,” said Singh. “Ammonia can act as a hydrogen carrier. “It’s very cheap and safe to transport, and you can convert the ammonia back into hydrogen at the destination.”

Scientists are currently working with General Ammonia Co. to pilot and scale the lithium-assisted ammonia synthesis process at a facility in the Chicago area. It works with. UIC’s Office of Technology Management has filed a patent for the process.