New reactor could decarbonise ammonia production

In a study published in Nature Catalysis, Rice engineers led by Haotian Wang described the development of a new reactor system that converts nitrates into ammonia, a chemical used in fertilisers and a range of industrial and commercial products.

Ammonia is one of the most widely produced chemicals globally, with worldwide demand surpassing 180 million tons annually.

The main way to make ammonia is the Haber-Bosch process, a chemical reaction that synthesises ammonia (NH3) from nitrogen (N2) and hydrogen (H2) gases that occurs under high temperature and pressure conditions and is dependent on large-scale centralised infrastructure.

One alternative to this process is electrochemical synthesis, which uses electricity to drive chemical reactions.

In a statement, Feng-Yang Chen, a Rice graduate student and lead author, said: “Electrochemistry can occur at room temperature, is more amenable to scalable formats for different infrastructure systems, and has the capacity to be powered by decentralised 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.”

According to Rice, a key innovation is in the use of a porous solid electrolyte, which reportedly eliminates the need for high concentrations of supporting electrolytes, which has been an issue that has hampered previous attempts to convert nitrates to ammonia sustainably. Additionally, powering the conversion process with renewable energy would effectively render ammonia production 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,” said Chen, who is pursuing a doctoral degree in chemical and biomolecular engineering under Wang’s supervision. “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.”

The new reactor system makes possible an electrochemical nitrate-to-ammonia conversion pathway that would eliminate the need for denitrification, the process by which wastewater treatment plants remove nitrates from contaminated water, generating nitrogen that gets fed into the Haber-Bosch process. In addition to bypassing the traditional denitrification and Haber-Bosch routes, this approach provides an effective way of decontaminating water.