UC Berkeley researchers develop MOFs to green up ammonia production

16 January 2023 | Muriel Cozier

‘We’ve put forward a new way of thinking about how you can use metal-organic frameworks in the context of ammonia capture for a modified Haber-Bosch process.

Researchers at the University of California Berkeley, US, have designed and synthesised metal-organic frameworks (MOFs) that bind and release ammonia at moderate temperatures and pressures, which they say could lead to a less energy-intensive production process for ammonia.

The researchers explain that industrial production of ammonia is one of the world’s largest chemical markets, but also one of the most energy-intensive. The reaction to produce ammonia requires temperatures in the region of 300-500oC, while cooling the gas to a liquid requires temperatures of -20oC.

Publishing their work in the journal Nature, the researchers report that their MOFs bind and release ammonia at moderate pressures and temperatures of around 175oC. Because the MOF does not bind to any of the reactants, the capture and release of ammonia can be achieved with smaller temperature swings. The researchers say that this development could lead to the production of greener ammonia for greener fertiliser and opens up the possibility of producing fertiliser at smaller facilities closer to farms.

Professor Benjamin Snyder, UC Berkeley Postdoctoral Fellow, who led the research said: ‘The dream here would be enabling a technology where a farmer in some economically disadvantaged area of the world now has much more ready access to the ammonia that they need to grow their crops. To be clear, our material hasn’t gone and solved that problem outright. But we’ve put forward a new way of thinking about how you can use metal-organic frameworks in the context of ammonia capture for a modified Haber-Bosch process. I think this study represents a really important conceptual advance in that direction.’

Synder added that a significant amount of research is taking place to make the Haber-Bosch process more sustainable. But removing ammonia from the mixture after the reaction has remained difficult. Attempts to use other MOFs have resulted in failure as they have disintegrated in the presence of ammonia, and other porous materials such as zeolites are unable to absorb and release large quantities of ammonia.

Snyder added: ‘The benefit of our MOFs is that we’ve discovered that they can be rationally tuned, which means that if you end up locking in on a certain set of reaction conditions in a specific process, we can modify the MOFs performance parameters – the temperature that you use and the pressure that you use for this adsorbent – to closely match up with the specific application.’

SCI’s Fine Chemicals Group and IChemE’s Catalysis and Engineering Group will be hosting the Factories for the Future event on 28 March 2023. Find out how manufacturing plants will need to evolve as the world moves toward net zero.

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