Researchers have discovered a novel method for removing carbon dioxide from the ocean. It could be used by ships that would travel, or at offshore drilling platforms or aquaculture fish farms. Credit: Researchers
A novel technique for decommissioning greenhouse gases from the ocean might be more efficient than existing methods for decommissioning them from the atmosphere.
Researchers around the world have spent years looking for ways to remove carbon dioxide effectively from the atmosphere. The ocean, however, is the world's number one "sink" for carbon dioxide from the atmosphere, which absorbs some 30 to 40 percent of human activity.
Another promising technique for reducing CO2 emissions has emerged recently, one that may one day lead to overall net negative emissions. However, unlike air capture systems, the concept has yet to be widely used.
T. Alan Hatton and Kripa Varanasi, MIT faculty members, and graduate students Michael Nitzsche, Simon Rufer, and Jack Lake have proposed a truly efficient and inexpensive removal mechanism.
Hatton, a professor of chemical engineering at Ralph Landau University, says the membranes are expensive, and chemicals are required to drive the whole electrode reactions at either end of the stack, increasing the expense and complexity of the processes.
This rendering illustrates how the new technique might be extended to ships and offshore platforms.
The research involved a membrane-free electrochemical cell system that first acidifies the water and returns it to the sea before regenerating it during alkalization.
According to Varanasi, a professor of mechanical engineering, this removal of carbon dioxide and the reinjection of alkaline water may begin to gradually reverse, at least locally, the acidification of the oceans caused by carbon dioxide buildup, which has endangered coral reefs and shellfish.
Varanasi cautions that he isn't capable of treating all of the planet's emissions. However, reinjection may be performed in places such as fish farms, which tend to acidify the water, thus this might be a feasible strategy.
The captured CO2 may be used as a transportation fuel or as a specialty chemical once it is removed from the water. “No matter what, a significant portion of the captured CO2 will need to be buried underground.”
According to Varanasi, the goal would be to integrate existing or planned infrastructure that already processes seawater, such as desalination facilities. There, the carbon dioxide removal could be a straightforward add-on to existing processes, which already replenish vast quantities of water to the sea.
"With desalination plants, you're already pumping all of the water, so why not co-locate there?" Varanasi asks. "All of the capital costs associated with the way you move the water, and the permitting, all of which could already be taken care of."
Ships that travel water might also benefit from the new feature, which could help reduce ship traffic's significant contribution to overall emissions. "This could help shipping companies offset some of their emissions and transform ships into ocean scrubbers," Varanasi says.
The system might be deployed on offshore drilling platforms or aquaculture farms as well. Eventually, it may lead to the deployment of free-standing carbon removal plants scattered around the world.
Hatton believes that direct air-capture systems are more efficient than air capture systems because the concentration of carbon dioxide in seawater is more than 100 times greater than in air. In direct air-capture systems, however, it is first necessary to capture and concentrate the gas before recovering it. "The capture step has already been done for you,," says the author, potentially simplifying the entire process and reducing the footprint requirements.
Hatton says that substantial progress has been made on these issues, but that it is still too early to report on them. The system might be ready for a practical demonstration project within two years.
"Our life and existence are defined by the carbon dioxide problem," Varanasi says. "So clearly, we need all the help we can get."
Seoni Kim, Michael Nitzsche, Jack R. Lake, Kripa Kiran Varanasi, and T. Alan Hatton, in Energy & Environmental Science, do I: 10.1039/D2EE03804H
ARPA-E provided funding for this research.