Engineers at Rice University have created a novel reactor design that has the potential to reduce water pollution and decarbonize the production of ammonia. Despite being essential to maintaining food production for the world's expanding population, ammonia contributes 1.4 % of carbon dioxide emissions and 2 % of global energy consumption.
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In a study featured in Nature Catalysis, a team of engineers from Rice University, led by Haotian Wang, unveiled a novel reactor system designed to transform nitrates—commonly found as pollutants in industrial wastewater and agricultural runoff—into ammonia. Ammonia is a crucial chemical utilized not only in fertilizers but also across various industrial and commercial applications, including household cleaners, plastics, explosives, and even fuel.
Ammonia ranks among the most extensively produced chemicals globally, with annual demand exceeding 180 million tons. The traditional method for producing ammonia is the Haber-Bosch process, which involves a high-temperature, high-pressure reaction between hydrogen and nitrogen, relying heavily on large-scale centralized infrastructure. An alternative method to this is electrochemical synthesis, where electricity is used to drive the necessary chemical reactions.
Electrochemistry can occur at room temperature, is more amenable to scalable formats for different infrastructure systems, and can be powered by decentralized renewable energy. However, the current challenge for this technology is that large quantities of additive chemicals are required during the electrochemical conversion process. The reactor we developed uses recyclable ions and a three-chamber system to improve the reaction’s efficiency.
Feng-Yang Chen, Graduate Student and Study Lead Author, Department of Chemical and Biomolecular Engineering, Rice University
A major breakthrough in this process was the introduction of a porous solid electrolyte, which removed the need for high concentrations of supporting electrolytes—a challenge that has previously hindered sustainable nitrate-to-ammonia conversion. Additionally, using renewable energy to power this process could make ammonia production essentially carbon neutral.
We conducted experiments where we flowed nitrate-contaminated water through this reactor and measured the amount of ammonia produced and the purity of the treated water. We discovered that our novel reactor system could turn nitrate-contaminated water into pure ammonia and clean water very efficiently, without the need for extra chemicals. In simple terms, you put wastewater in, and you get pure ammonia and purified water out.
Feng-Yang Chen, Graduate Student and Study Lead Author, Department of Chemical and Biomolecular Engineering, Rice University
The new reactor system enables an electrochemical pathway for converting nitrates to ammonia, effectively bypassing the need for denitrification. Denitrification is the process used by wastewater treatment plants to remove nitrates from contaminated water, which are then used in the Haber-Bosch process. By avoiding both traditional denitrification and the Haber-Bosch process, this innovative approach also offers an efficient method for water decontamination.
Nitrate is one of the priority pollutants that most frequently violates drinking water standards, and it is a is a significant concern in growing cities as farmland with nitrate-contaminated groundwater supplies is converted to urban development.
Pedro Alvarez, George R. Brown Professor, Civil and Environmental Engineering, Rice University
Pedro Alvarez, who is also the Director of the Nanosystems Engineering Research Center for Nanotechnology-Enabled Water Treatment (NEWT) and the Water Technologies Entrepreneurship and Research (WaTER) Institute at Rice, continued, “Conventional nitrate removal in drinking water treatment involves ion exchange or membrane filtration by reverse osmosis, which generates brines and transfers the nitrate problem from one phase to another.”
“Professor Wang’s innovation is very timely and important, as it offers a solution that eliminates nitrate toxicity and associated liability without the need to add treatment chemicals,” said Alvarez.
The impact of this work goes beyond just ammonia production. The reactor design and the accompanying techno-economic assessment provide valuable insights that could guide further research into other sustainable chemical processes. This has the potential to revolutionize how industries tackle environmental challenges.
“Our findings suggest a new, greener method of addressing both water pollution and ammonia production, which could influence how industries and communities handle these challenges. If we want to decarbonize the grid and reach net-zero goals by 2050, there is an urgent need to develop alternative ways to produce ammonia sustainably,” added said Wang, Associate Professor of Chemical and Biomolecular Engineering, Materials Science and Nanoengineering, and Chemistry at Rice.
Journal Reference:
Chen, F., et al. (2024) Electrochemical nitrate reduction to ammonia with cation shuttling in a solid electrolyte reactor. Nature Catalysis. doi.org/10.1038/s41929-024-01200-w