Forget massive steel tanks—some scientists want to make chemicals with the help of rocks deep beneath Earth’s surface.
New research shows that ammonia, a chemical crucial for fertilizer, can be produced from rocks at temperatures and pressures that are common in the subsurface. The research was published today in Joule, and MIT Technology Review can exclusively report that a new company, called Addis Energy, was founded to commercialize the process.
Ammonia is used in most fertilizers and is a vital part of our modern food system. It’s also being considered for use as a green fuel in industries like transoceanic shipping. The problem is that current processes used to make ammonia require a lot of energy and produce huge amounts of the greenhouse gases that cause climate change—over 1% of the global total. The new study finds that the planet’s internal conditions can be used to produce ammonia in a much cleaner process.
“Earth can be a factory for chemical production,” says Iwnetim Abate, an MIT professor and author of the new study.
This idea could be a major change for the chemical industry, which today relies on huge facilities running reactions at extremely high temperatures and pressures to make ammonia.
The key ingredients for ammonia production are sources of nitrogen and hydrogen. Much of the focus on cleaner production methods currently lies in finding new ways to make hydrogen, since that chemical makes up the bulk of ammonia’s climate footprint, says Patrick Molloy, a principal at the nonprofit research agency Rocky Mountain Institute.
Recently, researchers and companies have located naturally occurring deposits of hydrogen underground. Iron-rich rocks tend to drive reactions that produce the gas, and these natural deposits could provide a source of low-cost, low-emissions hydrogen.
While geologic hydrogen is still in its infancy as an industry, some researchers are hoping to help the process along by stimulating production of hydrogen underground. With the right rocks, heat, and a catalyst, you can produce hydrogen cheaply and without emitting large amounts of climate pollution.
Hydrogen can be difficult to transport, though, so Abate was interested in going one step further by letting the conditions underground do the hard work in powering chemical reactions that transform hydrogen and nitrogen into ammonia. “As you dig, you get heat and pressure for free,” he says.
To test out how this might work, Abate and his team crushed up iron-rich minerals and added nitrates (a nitrogen source), water (a hydrogen source), and a catalyst to help reactions along in a small reactor in the lab. They found that even at relatively low temperatures and pressures, they could make ammonia in a matter of hours. If the process were scaled up, the researchers estimate, one well could produce 40,000 tons of ammonia per day.
While the reactions tend to go faster at high temperature and pressure, the researchers found that ammonia production could be an economically viable process even at 130 °C (266 °F) and a little over two atmospheres of pressure, conditions that would be accessible at depths reachable with existing drilling technology.
While the reactions work in the lab, there’s a lot of work to do to determine whether, and how, the process might actually work in the field. One thing the team will need to figure out is how to keep reactions going, because in the reaction that forms ammonia, the surface of the iron-rich rocks will be oxidized, leaving them in a state where they can’t keep reacting. But Abate says the team is working on controlling how thick the unusable layer of rock is, and its composition, so the chemical reactions can continue.
To commercialize this work, Abate is cofounding a company called Addis Energy with $4.25 million in pre-seed funds from investors including Engine Ventures. His cofounders include Michael Alexander and Charlie Mitchell (who have both spent time in the oil and gas industry) and Yet-Ming Chiang, an MIT professor and serial entrepreneur. The company will work on scaling up the research, including finding potential sites with the geological conditions to produce ammonia underground.
The good news for scale-up efforts is that much of the necessary technology already exists in oil and gas operations, says Alexander, Addis’s CEO. A field-deployed system will involve drilling, pumping fluid down into the ground, and extracting other fluids from beneath the surface, all very common operations in that industry. “There’s novel chemistry that’s wrapped in an oil and gas package,” he says.
The team will also work on refining cost estimates for the process and gaining a better understanding of safety and sustainability, Abate says. Ammonia is a toxic industrial chemical, but it’s common enough for there to be established procedures for handling, storing, and transporting it, says RMI’s Molloy.
Judging from the researchers’ early estimates, ammonia produced with this method could cost up to $0.55 per kilogram. That’s more than ammonia produced with fossil fuels today ($0.40/kg), but the technique would likely be less expensive than other low-emissions methods of producing the chemical. Tweaks to the process, including using nitrogen from the air instead of nitrates, could help cut costs further, even as low as $0.20/kg.
New approaches to making ammonia could be crucial for climate efforts. “It’s a chemical that’s essential to our way of life,” says Karthish Manthiram, a professor at Caltech who studies electrochemistry, including alternative ammonia production methods.
The team’s research appears to be designed with scalability in mind from the outset, and using Earth itself as a reactor is the kind of thinking needed to accelerate the long-term journey to sustainable chemical production, Manthiram adds.
While the company focuses on scale-up efforts, there’s plenty of fundamental work left for Abate and other labs to do to understand what’s going on during the reactions at the atomic level, particularly at the interface between the rocks and the reacting fluid.
Research in the lab is exciting, but it’s only the first step, Abate says. The next one is seeing if this actually works in the field.
