MIT researchers propose hybrid approach to cut ammonia production emissions

Scientists at MIT have developed a novel method to dramatically reduce greenhouse gas emissions from ammonia production by combining two existing low-carbon manufacturing approaches into a single integrated facility.

The hybrid system, which pairs “blue” and “green” ammonia production methods side-by-side, could slash emissions by up to 63 percent compared to current leading low-emission techniques, according to research published in the journal Energy & Fuels.

Ammonia ranks among the world’s most widely produced chemicals, primarily used as fertilizer to feed the global population. However, its manufacture generates roughly 20 percent of all greenhouse gases from the entire chemical industry due to the high heat and pressure required in traditional production processes.

“Ammonia has the most carbon dioxide emissions of any kind of chemical,” said William H. Green, director of the MIT Energy Initiative and the Hoyt C. Hottel Professor in Chemical Engineering. “It’s a very important chemical because its use as a fertilizer is crucial to being able to feed the world’s population.”

A marriage of two technologies

The researchers’ key insight was recognizing that blue and green ammonia facilities could complement each other when built adjacent to one another.

Green ammonia plants use renewable electricity to split water through electrolysis, producing hydrogen without burning fossil fuels. This process generates substantial amounts of leftover oxygen that typically goes to waste.

Blue ammonia facilities, meanwhile, capture and sequester their carbon dioxide emissions underground. Their production method, called autothermal reforming, requires a source of pure oxygen—exactly what the neighboring green plant would be venting.

“Putting them next to each other turns out to have significant economic value,” Green explained.

Bridging to a cleaner future

The hybrid approach could serve as a crucial stepping stone toward an eventual future dominated by green ammonia, the cleanest production method. However, that transition remains decades away due to economic constraints.

“Right now, it’s nowhere close, except in very special situations,” Green said of green ammonia’s current competitiveness. The combined plants “could be a really appealing concept, and maybe a good way to start the industry.”

Growing demand is making the challenge more urgent. Population growth and rising wealth are driving increased fertilizer needs, while ammonia is also emerging as a promising zero-carbon fuel for cargo ships and heavy trucks—sectors that are difficult to decarbonize.

“People think that the most likely market of that type would be for shipping,” Green noted, explaining that ammonia’s toxicity and odor make it better suited for high-volume use in remote locations like the open ocean.

Industry response

Kevin van Geem, a professor at Ghent University’s Center for Sustainable Chemistry who was not involved in the research, called the work “rigorous” and said it “provides a credible and balanced view of the trade-offs.”

“Given the scale of global ammonia production, such a reduction could have a highly impactful effect on decarbonizing one of the most emissions-intensive chemical industries,” van Geem said.

Green acknowledged that while the team’s detailed technical and economic analysis shows great promise, practical challenges remain. “No one has ever built one,” he said. “Surely when people build the first one, they’ll find funny little things that need some attention.”

The research team has filed for a patent on the integrated process. The work was supported by IHI Japan through the MIT Energy Initiative and the Martin Family Society of Fellows for Sustainability.

Co-authors include MIT graduate student Sayandeep Biswas, MITEI Director of Research Randall Field, postdoc Angiras Menon, and research lead Guiyan Zang.