New research finds that producing the fertilizer urea using electrified synthesis could both denitrify wastewater while enabling low-carbon-intensity urea production, according to a press release from Northwestern University.
The process, which includes converting carbon dioxide and waste nitrogen by using a hybrid catalyst made of zinc and copper, could benefit water treatment facilities by reducing their carbon footprint and supplying a potential revenue stream.
Agriculture relies on synthetic nitrogen fertilizer, which is made using energy- and carbon-intensive processes and creates nitrate-containing runoff. Researchers have long sought solutions to reduce emissions from the industry that accounts for 3% of energy consumption each year.
The findings were published Sept. 11 in the journal Nature Catalysis.
“It’s estimated that synthetic nitrogen fertilizer supports half of the global population,” said Ted Sargent, a corresponding author on the paper and professor at Northwester University. “A chief priority of decarbonization efforts is to increase quality of life on Earth, while simultaneously decreasing society’s net CO2 intensity. Figuring out how to use renewable electricity to power chemical processes is a big opportunity on this score.”
Yuting Luo, the paper’s first author, a post-doctoral fellow in the Sargent Group and a Banting Postdoctoral Researcher, said a deep dive into historical references helped identify what would become their catalyst. Typically, chemists use alloys or more complicated materials to trigger reactions, limiting them to favor a single reaction step at a time.
“It’s quite uncommon to put two catalysts together that cooperate in a relay mode,” Luo said. “The catalyst is the real magic here.”
The team saw references dating back to the 1970s that implied pure metals — like zinc and copper — can be useful in processes involving carbon dioxide and nitrogen conversion.
These preliminary experiments, which the Sargent lab went on to replicate, converted relatively little of the initial ingredients into the desired product (the team found about a 20-30% conversion efficiency to urea).
Renewable energy sources tip the scales
Creating change within industries requires careful cost-benefit analyses that definitively prove a new production route will ultimately pay off in both energy and cost savings. That’s where chemical engineering professor Jennifer Dunn’s research came in. Chayse Lavallais, a fourth-year Ph.D. student in the Dunn lab, helped the team conduct a thorough life-cycle analysis, carefully including each energy input and output in a variety of scenarios.
“Using an average U.S. grid, the energy emissions are about the same,” Lavallais said. “But when you go to renewable sources, several factors lower energy emissions, including CO2 sequestration and carbon credits stored in end-use polymers. In a water treatment facility, if it adds emissions or energy, they’re not encouraged to use the technology. We saw this doesn’t impact the daily operational costs significantly, and there’s potential to sell the product.”
They found the conversion efficiency would need to reach 70% to be practical.
There’s a way to go before the process can be commercialized, the researchers said. Primarily, the reaction as it stands does not account for impurities found in a water treatment context. They also hope to increase the amount of time their process can operate.
The paper, “Selective electrochemical synthesis of urea from nitrate and CO2 via relay catalysis on hybrid catalysts,” was funded by the Banting Postdoctoral Fellowships Program (grant number 01353-000).
