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Pathway Toward Cleaner Ammonia Synthesis

Among the various chemicals used daily, ammonia is one of the most harmful to the environment. Due to the high temperatures and energy required to create it, the nitrogen-based chemical used in fertilizer, dyes, explosives, and many other products emits the second most carbon dioxide after cement.

Lithium (black tiles) mediates the conversion of nitrogen (blue blocks) and hydrogen (white blocks) to ammonia. Image Credit: Meenesh Singh of UIC and Crystal Price and Joseph Gauthier of Texas Tech University)
Lithium (black tiles) mediates the conversion of nitrogen (blue blocks) and hydrogen (white blocks) to ammonia. Image Credit: Meenesh Singh of UIC and Crystal Price and Joseph Gauthier of Texas Tech University)

However, by expanding on a well-known electrochemical reaction and orchestrating a “symphony” of lithium, nitrogen, and hydrogen atoms, the University of Illinois Chicago researchers led by Meenesh Singh have invented a novel ammonia production method that achieves key green targets.

The method, known as lithium-mediated ammonia synthesis, involves combining nitrogen gas and a hydrogen-donating fluid like ethanol with a charged lithium electrode. Instead of breaking apart nitrogen gas molecules at high temperatures and pressures, nitrogen atoms adhere to lithium and mix with hydrogen to form the ammonia molecule.

The reaction operates at low temperatures and is regenerative, recovering the original components after each ammonia generation cycle.

There are two loops that happen. One is regeneration of the hydrogen source and second is the regeneration of the lithium. 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.

Meenesh Singh, Associate Professor, University of Illinois Chicago

The technique, reported in a study published in ACS Applied Materials & Interfaces and featured on the cover, is Singh's lab’s most recent invention in the hunt for cleaner ammonia. Previously, his research discovered ways for synthesizing the chemical from sunlight and wastewater and an electrified copper mesh screen that minimizes the energy required to produce ammonia.

Their latest advancement is based on a reaction that is not new. Scientists have known about it for almost a century.

Singh added, “The lithium-based approach can actually be found in any organic chemistry textbook. It is very well-known. But making this cycle run efficiently and selectively enough to meet economically feasible targets was our contribution.

These objectives include excellent energy efficiency and minimal costs. According to Singh, if the process is scaled up, it will produce ammonia for about $450 per ton, 60% less than previous lithium-based techniques and other potential green alternatives.

However, selectivity is vital since numerous attempts to clean up ammonia production have resulted in enormous amounts of undesired hydrogen gas.

The Singh group’s findings are among the first to attain selectivity and energy consumption levels that match Department of Energy guidelines for industrial-scale ammonia production.

Singh further stated that the process, which can be carried out in a modular reactor, can be made even more environmentally friendly by using energy generated by solar panels or other renewable sources and fostering the reaction with air and water.

The method might also aid in meeting another energy goal: using hydrogen as a fuel. The difficulty of transporting the highly combustible liquid has hampered progress toward this goal.

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. Ammonia could function as a carrier of hydrogen. It is very cheap and safe to transport, and at the destination you can convert ammonia back to hydrogen,” Singh further added.

Currently, the scientists are working with General Ammonia Co. to test and scale up their lithium-mediated ammonia synthesis method in a plant in the Chicago region. UIC’s Office of Technology Management has submitted a patent application for the procedure.

Grants from General Ammonia Co supported the study. The study’s co-authors are Nishithan C. Kani and Ishita Goyal of UIC, Joseph A. Gauthier of Texas Tech University, and Windom Shields and Mitchell Shields of General Ammonia Co.

Journal Reference:

Kani, N. C., et. al. (2024) Pathway toward Scalable Energy-Efficient Li-Mediated Ammonia Synthesis. ACS Applied Materials & Interfaces. doi:10.1021/acsami.3c19499

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