Ammonia has enormous potential as a fuel of the future, but most current production methods make it a dirty source of energy. Yet a new method from MIT that would derive the compound using the Earth's rocks and natural heat cleans it up considerably.
Currently, ammonia is the second-most produced chemical in the world, where about 80% of it is used as agricultural fertilizer. However, current ammonia-production methods chew up about 2% of the world's fossil fuel energy and release about 1% of worldwide manmade greenhouse gas emissions. Put another way, for each ton of ammonia produced, about 2.4 tons of carbon dioxide (CO2) are released.
Still, the compound, which is a combination of nitrogen and hydrogen, has enormous potential in the power sector as it can store more than 20 times as much energy by weight as current lithium batteries. It can also be burned cleanly if managed correctly. So green ammonia production could go a long way toward both servicing our energy needs, and reducing carbon emissions.
Progress toward this goal has been accelerating lately. In August of last year, three Danish energy companies brought the world's first green ammonia plant online, which is said to be capable of producing 5,000 tons of the chemical every year using only solar and wind power. In 2026, the world's first clean ammonia-powered container ship is slated to launch in Norway. These projects join the world's first zero-emissions ammonia-electric semi and the first ammonia-powered tractor in demonstrating the fuel's green potential.
Now MIT researchers have added to the potential of clean ammonia by authoring a study in which they demonstrate how to produce the chemical without the introduction of any outside energy and with zero CO2 emissions.
Aha moment
The idea, says study senior author Iwnetim Abate, came from a well in Mali, West Africa. First spotted in the 1980s, the unusual well was found to be full of hydrogen gas streams. It was determined that the gas was coming from a reaction deep below the Earth's surface between chemicals in the rock and the water.
“It was an ‘aha’ moment,” says Abate. “We may be able to use Earth as a factory, harnessing its heat and pressure to produce valuable chemicals like ammonia in a cleaner manner.”
To find out, Abate and his team built a model system that allowed them to inject nitrogen-enhanced water into synthetic iron-rich minerals, mimicking those that are found beneath the Earth's surface. Sure enough, the process yielded ammonia without producing any CO2 or requiring any outside energy to encourage the chemical process.
Then, they replaced the synthetic iron with olivine, an iron-rich rock found in nature. In this case, they also added a copper catalyst and heated the system up to 300 °C (572 °F) to mimic the temperatures found miles beneath the Earth's surface. They found that the nitrogen in the water reacted with the iron to create clean hydrogen, which in turn reacted with the nitrogen to create ammonia. The process yielded 1.8 kg (4 lb) of ammonia per ton of olivine.
“These rocks are all over the world, so the method could be adapted very widely across the globe,” said Abate, adding that “there’s a whole other level of complexity that we’ll need to work through.”
That complexity consists of the problems that might arise when you drill deep into the Earth, inject nitrogen-enhanced water, and deal with the ways in which the liquids and gases produced interact with bedrock.
Still, Abate remains hopeful that his team's proof-of-concept work could open another pathway to producing green ammonia and hopes to test the system in the real world within a year or two. He even says the system could take advantage of the nitrogen found in wastewater to operate.
“This is a significant breakthrough for the future of sustainable development,” says Geoffrey Ellis, a geologist at the U.S. Geological Survey, who was not associated with the study. “While there is clearly more work that needs to be done to validate this at the pilot stage and to get this to the commercial scale, the concept that has been demonstrated is truly transformative. The approach of engineering a system to optimize the natural process of nitrate reduction by iron is ingenious and will likely lead to further innovations along these lines.”
The research group has applied for a patent for its discovery.
The study has been published in the journal Joule.
Source: MIT
