We need fertilizer to grow food on industrial scales. And yet, this product is one of the most emissions-intensive aspects of farming. It’s a catch-22 situation that researchers have been trying to solve for some time. Now, a team of Australian and Chinese scientists say they have the answer: a way to make ammonia, the key ingredient in fertilizer, without the high heat and intense pressure that gives conventional fertilizer its huge footprint.
Most synthetic ammonia today is produced using the Haber-Bosch process, which laid the foundation for the Green Revolution and industrial agriculture in the 1950s. This method works by drawing on abundant nitrogen in the air; it’s a substance that forms about 78% of earth’s atmosphere.
But nitrogen is made up of two atoms powerfully fused together by three bonds. Those can only be broken apart—to form ammonia—under intensive pressures, which requires huge amounts of energy to work. In fact conventional ammonia-production requires temperatures of over 400°C, which produces a striking 2.4 tonnes of CO2 per tonne of ammonia—a huge figure that accounts for 2% of global emission each year. This energy-intensive process uses up 5% of worldwide gas reserves annually.
“With increasing awareness of climate change, there is a growing demand for low carbon-emitting alternatives that do not heavily rely on fossil fuels,” write the researchers in their new study. It’s a challenge they’ve been working on for some time: this new research builds on previous work where they managed to produce ammonia more efficiently—but they say their new study takes that to a whole new level.
It comes down to an extremely sophisticated grasp of chemistry, paired with a few key ingredients: lasers, water, and air. First the researchers used a pulsing laser to zap the air and make plasma, which can best be understood as highly-activated air. Using this process, they were able to turn the abundant nitrogen into nitrate, a compound made from nitrogen and oxygen. Crucially, the type of nitrate they produced is unstable, and only has one bond which is easier to crack. This means less energy is required to break it.
The experiment isn’t over yet. To make ammonia—NH3—nitrate needs to ditch its one oxygen atom and substitute it with a hydrogen, which the researchers did by interfacing it with water.
That in itself is revelatory. But the real discovery in all of this, the researchers say, is that they’ve managed to rapidly scale up this process, by using the laser to blast the air at a rate of nanoseconds, which actually forms tiny parcels of nitrate, which can then in turn diffuse into the water more efficiently to produce large amounts of ammonia. In fact, this process produced almost 40 times more ammonia when compared to the conventional Haber-Bosch process, and at a sliver of the energy cost.
Interestingly, the technique the researchers had explored in previous papers worked well enough to get them a deal with an Australian company which has since built a prototype and will be deploying it soon to start making fertilizer for Australian farms. Now, their new discovery promises greater energy efficiency that will amp up the green credentials of this new invention.
It comes at a critical time, not just because of the climate impact of farming, but for other reasons that make conventional ammonia an increasingly unsustainable resource: “Ammonia-based fertilizers are in critically short supply due to international supply chain disruptions and geopolitical issues, which impact our food security and production costs,” the researchers say
An added boon is that this technology doesn’t require the vast infrastructure that conventional fertilizer production does, and so, production can be decentralized to farms. That cuts out another source of emissions from the transport that’s typically required to ferry fertilizer across the globe.
As the team said about their previous research: “If we can make it locally to use locally, and make it as we need it, then there’s a huge benefit to society as well as the health of the planet.”
Jalili et. al. “Sustainable ammonia production via nanosecond-pulsed plasma oxidation and electrocatalytic reduction.” Applied Catalysis B: Environmental. 2023.
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