Ammonia production goes green: Biomethane approach offers net-zero emissions

December 16, 2024 by Leiden University

Collected at: https://phys.org/news/2024-12-ammonia-production-green-biomethane-approach.html

Using biomethane to produce ammonia, a crucial chemical in agriculture, could drastically reduce the climate impact of the process. In a study published in One Earth, researcher Robert Istrate shows it’s even possible to make ammonia production net-zero or carbon negative.

Ammonia is a chemical more essential than many realize. It forms the basis of synthetic fertilizers used in agriculture worldwide, meaning billions of people depend on it. Unfortunately, ammonia production comes with a significant drawback: its substantial carbon footprint that contributes to the climate crisis.

Ammonia is made from nitrogen and hydrogen, with the hydrogen typically derived from natural gas. “Natural gas contains both carbon and hydrogen, but you only need the hydrogen for ammonia. As a result, a lot of carbon is released during the production process,” Istrate explains.

One potential solution to reduce ammonia’s climate impact is to produce hydrogen through electrolysis, using renewable energy. “But that’s an expensive option,” Istrate says, “and it’s not very well established yet.” As a result, only a small fraction of ammonia is currently produced this way.

Biomethane has the same chemical structure as natural gas

Istrate, an environmental engineer, proposed an alternative idea. While exploring ways to decarbonize chemical processes, he noticed the advantages of biomethane for producing ammonia.

Biomethane has the same chemical structure as natural gas (CH₄), “which means existing ammonia production facilities can be used.” However, the two have a crucial difference: natural gas is a fossil fuel, while biomethane is derived from biomass, such as food waste or agricultural residues.

When biomethane is used, the carbon released into the atmosphere was recently captured during biomass growth via photosynthesis: in plants as they grew. “That achieves a balance,” Istrate explains. In contrast, using natural gas releases extra CO₂ into the atmosphere, CO₂ that has been stored underground for millions of years.

Capturing the carbon and storing it permanently

“This already represents an advantage over natural gas,” Istrate says. But there’s more. “If, instead of emitting this carbon, you capture and store it permanently, then you can start thinking about net-zero emissions or even carbon negativity.” In other words, ammonia production could actively remove CO₂ from the atmosphere.

Capturing the carbon doesn’t require much extra effort because separating CO₂ is inherent to the biomethane and ammonia production processes. “That’s a key advantage of ammonia. It already requires separating the CO₂“, Istrate notes. “So no new technologies need to be developed for that.”

In his research, Istrate compared the full lifecycle of conventional ammonia production methods, electrolysis, and biomethane-based production. He found that when ammonia is produced entirely from biomethane combined with carbon capture and storage (CCS), the process can indeed become carbon negative.

What about a ‘more realistic’ scenario?

The researcher also examined a more realistic scenario where natural gas is blended with biomethane. He concluded that to achieve carbon neutrality, on average, 44% biomethane must be blended with 56% natural gas, while capturing the released carbon.

According to the study, biomethane can be economically competitive—at least when the cost of achieving carbon neutrality via CO₂ removal is factored into all scenarios. A significant reason is the high gas prices, partly driven by the Russian invasion of Ukraine. And Direct Air Carbon Capture and Storage (DACCS), an alternative to removing CO₂ directly from the air, is expensive and inefficient.

“You don’t need complex technology like DACCS. There are often simpler solutions that can have an immediate impact,” Istrate says. Introducing biomethane into ammonia production could be one of these “simple solutions.”

More information: Robert Istrate et al, One-tenth of the EU’s sustainable biomethane coupled with carbon capture and storage can enable net-zero ammonia production, One Earth (2024). DOI: 10.1016/j.oneear.2024.11.005

Journal information: One Earth