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A Stanford team puts carbon-free fertilizer to the test

Researchers are developing a solar-based fertilizer production that could one day replace a decades-old process that consumes energy and causes greenhouse gas emission.

soil in a large, tilled field on a sunny day with clouds in the sky

Ammonia fertilizers help feed the world. Could a new process produce these crop-boosting chemicals sustainably? | Photo by Zbynek Burival on Unsplash

The mid-September harvest was a moment of truth for Stanford University PhD candidate in mechanical engineering Nico Pinkowski and his colleagues.

They were gathering their tomato crop on a farm in California’s Central Valley. Soon, the entrepreneurs would know how well their new device for making fertilizer on site from only air, water and renewable electricity had performed.

This growing season Pinkowski and his team conducted the first field test of their device, which produces nitric acid fertilizer. They worked on a small plot on California State University, Fresno’s research farm in the middle of the city, surrounded by businesses, subdivisions and the campus. The results are promising. The team’s crop yielded a quantity of tomatoes in line with the control crop while using one-third of the fertilizer. Their successful test puts the team one step closer to their goal of making fossil-free fertilizer a reality.

“Our objective is to decarbonize the fertilizer industry,” said Pinkowski. “It’s a pretty moonshot thing.”

“Bosch Squasher”

The current fertilizer industry uses the hundred-year-old Haber-Bosch process to combine nitrogen in the air with hydrogen to make to ammonia fertilizer. Since the process was developed, synthetic fertilizer has revolutionized agriculture, supported global population growth and become a massive industry.

“It’s feeding billions of people,” said Thomas Jaramillo, associate professor of chemical engineering and photon science at Stanford and advisor to the project. “It’s wonderful, but we see opportunities to make it more sustainable.”

Ammonia fertilizer production is very energy intensive and relies on fossil fuels. It accounts for about one percent of total global energy use. Much of this energy use and resulting greenhouse gas emissions come from using natural gas as a feedstock to make ammonia.

The process also requires heat and extremely high pressure, and therefore “makes the most sense in a really big facility,” said Pinkowski. This resulted in a centralized industry. There are only about 150 to 200 such factories globally — and 4 billion acres of farmland.

The research and development team seeks to change this equation and has named their system the “Bosch Squasher.” Their device consists of a solar array providing renewable energy, a reactor and two 55-gallon drums. It uses normal pressure, which means carbon-free fertilizer can be produced right on the farm.

“We want to shift the focus from factories to the field,” said Pinkowski.

Pinkowski and others have launched a new company, Nitricity, building technology out of the co-founders’ backyards and shipping it to the farm in Fresno. Their technology offers on-site fertilizer production, which allows farmers to have more control over how their crops grow, including how often they apply fertilizer and what type they use. This can help reduce runoff.

“Most ammonia that goes into the ground doesn’t end up inside the crop. It runs off into rivers, lakes and streams, causing environmental problems,” explained Jaramillo.

Farmers tend to apply commercial fertilizer in batches a few times a year. Knowing some will run off, they apply extra fertilizer to make sure their plants get enough nutrients. The new technology would allow them to fertilize their plants more frequently, use less fertilizer and reduce runoff.

“You time the delivery exactly with the need,” said Jaramillo.

Up all night

In addition to Pinkowski, the team includes Joshua McEnaney (postdoctoral scholar), Brian Rohr (PhD, chemical engineering) and Jay Schwalbe (PhD, chemical engineering). McEnaney, Rohr and Schwalbe did research in the SUNCAT Center for Interface Science & Catalysis, led by Jaramillo.

Getting their pilot project up and running wasn’t easy.

“When things break, we are up all night making sure it all works when the sun hits the panels in the morning,” said Pinkowski. “We’re basically living under our solar array.” Over the course of the growing season, the team made their device three to four times more energy efficient, Pinkowski estimates.

The technology shows promise, according to Charles Hillyer, director of the Center for Irrigation Technology, but “it’s got to be practical.”

If it works, Hillyer thinks farmers would have powerful economic and environmental incentives to use this technology. Fertilizer is a significant expense for farmers and a significant source of their carbon emissions.

“Farmers care deeply about being good stewards to the land,” said Hillyer. “They understand that being carbon negative is the best way to do that, but they must balance sustainability with the economic realities of farming. This new tool could change that equation for farmers.”

What’s next?

After science and engineering comes economics. According to Jaramillo, the next step will be cost reduction.

“It would be too much to ask for any technology to compete head-to-head against Haber Bosch in cost effectiveness right now,” said Jaramillo, “but hopefully the technology in the field can establish a trajectory to get it to some level of competitiveness.”

Stanford’s ecosystem of support for R&D in sustainability has bolstered such a trajectory. The team first connected through the Precourt Institute for Energy’s Stanford Climate Ventures course. Stanford’s TomKat Center for Sustainable Energy chose the team for its 2019-20 Innovation Transfer Program for a related project, and this spring the team won the Stanford BASES 100K Challenge. The team also won a StartX student-in-residence fellowship. Support from other universities has been crucial as well, including MIT, Caltech and Fresno State. Together, this support enabled the team’s early research and this summer’s pilot project, according to Pinkowski. In addition, the team was chosen by the U.S. Department of Energy supported Cyclotron Road for participation in its R&D program.

The team plans to release a full report of its research findings in October. In the meantime, they plan to celebrate — and use their tomato crop — with a salsa party.

“Our next step is to get something on a commercial farm,” said Pinkowski. The team is in the process of lining up a commercial farm for a larger test next year.

Stanford has no financial interest in the technology underlying this project.