Novel Solution Yields Net-Zero Emission Ammonia

Ammonia is a chemical more essential than many realise. It forms the basis of synthetic fertilisers 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 decarbonise 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.

'The key advantage of ammonia is that it already requires seperating the CO₂.'

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 percent biomethane must be blended with 56 percent 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 remove 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'.