Pulling cleaner fertilizer out of thin air

The last time you scrubbed a streaky window or polished a porcelain appliance, you probably used a chemical called ammonia.

Also known as ammonium hydroxide when mixed with water, ammonia is more than a common household cleaner. More than 170 million metric tons of it are produced globally every year, with most of it ending up as fertilizer for corn, cotton and soybeans.

UIC researchers are scaling up a system for farmers to produce ammonia in their own backyards. The method, which uses renewable electricity and Earth's natural resources, appears in the journal PNAS.

"So many people around the world need food. Farmers need fertilizer to grow food faster," said project lead Meenesh Singh, a chemical engineering professor at the UIC College of Engineering. "I hope our project can help provide on-demand fertilizers to farmers, people and communities facing food scarcity."

Ammonia's main ingredients are nitrogen - the atmosphere's most frequent flyer - and hydrogen. It's usually produced by smashing the elements together under high temperatures and high pressure in what's called the Haber-Bosch process.

While muscular enough to meet the world's growing ammonia demand, the Haber-Bosch process is energy-intensive and responsible for 1-3% of global carbon dioxide emissions.

Singh wanted to reduce ammonia's environmental impact, which means turning down the heat on hydrogen and nitrogen's high-pressure union. Previously, he'd tried using lithium, but obtaining enough of the metal wasn't feasible.

This time, Singh tried cooling the reaction with a more abundant mineral: calcium, which binds with nitrogen to form calcium nitride. He combined the calcium nitride with hydrogen atoms to create ammonia without emitting any carbon dioxide.

Unlike the Haber-Bosch process, this reaction can take place at room temperature. If nitrogen and hydrogen gas are in good supply, ethanol can maintain the production of ammonia. Singh said his "holy grail" is finding a way to start with water, not hydrogen gas, making do-it-yourself ammonia production even easier.

Physically, this looks like a 1-square centimeter, lab-scale reactor that produces about 1 gram of ammonia per day - about the weight of a jellybean. It's a proof-of-concept and not supposed to be a commercial-size operation yet, Singh said.

"This method could enable distributed ammonia production in smaller-scale devices, reducing reliance on large, centralized plants."

Modest though it is, this model represents the most scaled-up version in the field so far, Singh said. And, like the crops it's destined to service, it will grow. First to 100 square centimeters, and up and up to, eventually, a square meter. Currently, Singh's team is scaling up the reactor in collaboration with General Ammonia, Co. to produce 11 pounds of ammonia per day.

"Every step forward is a step toward wider industrial use," Singh said. "We're taking things one step at a time."

Additional UIC coauthors include Ishita Goyal, Hasiya Najmin Isa, Vamsi Vikram Gande and Rohit Chauhan.

The scientists are partnering with the General Ammonia Co. to pilot and scale up their calcium-mediated ammonia synthesis process in the Chicago area. UIC's Office of Technology Management has filed a patent for the process.