With the growing population, climate action has become increasingly critical and is a major challenge to modern industry. When it comes to supporting a growing global population, food production is key. Approximately 50% of the planet’s food production depends on applying fertilizers that contain ammonia – a chemical harmful to the environment.
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Current production methods use outdated energy-intensive processes, such as the Haber-Bosch process. Such processes consume around 1% of the world’s fossil fuels while producing large amounts of CO2 gas, contributing to around 1% of global greenhouse gas emissions.1 Therefore, developing greener ways to produce this is vital.
Now, a group of researchers at the University of California, Berkeley, has made significant progress in producing “green” ammonia and, in turn, making “greener” fertilizers. The team’s research was recently published in the journal Nature, where the team describes its strategy for developing energy-efficient ammonia adsorbents.
This work is of fundamental importance because it reveals a new cooperative mechanism for selective gas capture… We are optimistic that the mechanism will extend to other molecules of industrial significance that have a strong affinity for binding metals.
Jeffrey Long, C. Judson King Distinguished Professor, UC Berkeley
Creating Greener Processes
Good fertilization makes for better plant nutrition, promotes plant growth, and boosts the quality of crops while preserving and even enhancing soil fertility. Thus, with the aim to ensure and boost the health of plants and crops, it is integral to ensure that the environment does not suffer in the long term.
Led by UC Berkeley postdoctoral fellow Benjamin Snyder, Long and his team set out to improve the main method of ammonia production, the aforementioned Haber-Bosch process, which typically uses methane as a fuel and feedstock for hydrogen.
Hydrogen is one of the major reactants required for the process and requires extreme conditions and releases a great deal of CO2.
However, to help combat these extremes and to establish a more environmentally-friendly method, the UC Berkeley team has designed a method for synthesizing metal-organic frameworks (MOFs) that bind and release ammonia at less extreme temperatures, saving energy.
A big challenge to decarbonizing fertilizer production is finding a material where you can capture and then release very large quantities of ammonia, ideally with a minimal input of energy... You don’t want to have to put a lot of heat in your material to force the ammonia to come off, and likewise, when the ammonia absorbs, you don’t want that to generate a lot of waste heat.
Benjamin Snyder, Postdoctoral Fellow, UC Berkeley
Innovative Metal-Organic Frameworks
Researchers have been working tirelessly to help make the conventional Haber-Bosch process more sustainable. However, unlike others, Snyder’s approach makes use of a relatively new set of MOFs that use copper atoms that are linked by cyclohexanedicarboxylate organic molecules to create the rigid and highly porous MOF structure.
In addition, at relatively low temperatures, the polymer strands appeared to give up their bound ammonia rather easily, meaning that the material has the potential to be restored to its initial porous, rigid MOF structure.
The UC Berkeley team also found that they were able to tune the MOFs, making them highly adaptable across a range of conditions, increasing their application potential. This would also pave the way to enabling production at smaller facilities rather than large industrial plants, which means the new process could be employed in remote parts of the world.
The dream here would be enabling a technology where a farmer in some economically disadvantaged areas of the world now has much more ready access to the ammonia that they need to grow their crops.
Benjamin Snyder, Postdoctoral Fellow, UC Berkeley
Despite researchers across the world working on several innovations that accommodate a catalyst and reactor design for a more sustainable modified Haber Bosch process, Snyder’s approach is unique.
“Where we come in is, after you’ve made the ammonia, our materials are what you would try to use to separate and capture the ammonia under these new reaction conditions,” Snyder explained.
While there remains a significant amount of work to be done to fully address the impact that ammonia production has on the environment, the UC Berkeley team has encouraged new ways of using MOFs in a modified Haber-Bosch process, representing a move towards green ammonia production for greener fertilizers.
References and Further Reading
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Sanders, R. (2023) A big step toward 'green' Ammonia and a 'greener' fertilizer, Berkeley News. Available at: https://news.berkeley.edu/2023/01/11/a-big-step-toward-green-ammonia-and-a-greener-fertilizer/
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Snyder, B.E. et al. (2023) “A ligand insertion mechanism for cooperative NH3 capture in metal–organic frameworks,” Nature, 613(7943), pp. 287–291. Available at: https://www.nature.com/articles/s41586-022-05409-2
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