CLIMATEWIRE | There's a growing consensus among climate scientists that in order to avoid the worst effects of global warming, humanity has to find a way to sequester carbon dioxide — and most efforts to date have focused on removing CO2 from the atmosphere.
But two ongoing efforts — including one from the Massachusetts Institute of Technology — have turned to the oceans, rather than the air. And if successful, the scientists say the process could significantly cut the cost of using carbon capture to fight global warming.
One big reason? “In oceans, the capture step has already kind of been done for you," said T. Alan Hatton, a professor of chemical engineering and a leader of the MIT team, which published a report on their process this month in the journal Energy & Environmental Science.
That’s because the oceans are the Earth’s main “carbon sink,” sucking 30 to 40 percent of the greenhouse gas out of the atmosphere.
“Moreover, the density of the greenhouse gas in the oceans is more than 100 times greater than it is in the air,” Hatton added. “Which means the volumes of material that need to be handled in ocean capture are much smaller than in air capture operations, further simplifying the whole process.”
The MIT report describes a two-step “electrochemical” process that draws CO2 out of the seawater. The first step uses electricity to temporarily acidify the water, which encourages the removal of CO2. A second step removes the acidity and collects the CO2.
Kripa Varanasi, a professor of mechanical engineering and co-author of the MIT report, said in an interview that the MIT approach cuts energy costs and expensive membranes used to collect CO2 to the point where merchant ships that run on diesel power could collect enough CO2 to offset their emissions.
Other ships “could become the scrubber of the oceans,” he said — a step that might also appeal to small nations whose incomes rely on tourism, aquaculture and fishing industries that otherwise might be severely damaged by warming waters brought by climate change.
MIT is one of the two leading U.S. efforts to explore the ocean CO2 removal process. Earlier this month, Captura Corp. — a company that was spun out of the California Institute of Technology — released a press release that marked the start of its first pilot plant near Newport Beach, Calif., that is being designed to remove CO2 from the Pacific Ocean.
The company uses a process that relies on electrolysis and membranes to remove CO2 from seawater. It has received financial support from Saudi Arabian Oil Co., which believes its large collection of water desalination plants can be used for CO2 removal. It also was awarded a $1 million grant from a carbon removal XPRIZE competition being financed through a $100 million gift from billionaire Elon Musk.
Hatton said the MIT effort, which started later than Cal Tech’s, hopes to join the contest once it finishes its technology research within the next year. “Hopefully it will be just as good, if not better,” he said, noting that MIT’s research started with a grant from the Department of Energy’s Advanced Research Projects Agency-Energy two years ago.
The XPRIZE, billed as the largest incentive prize in history, is designed to spur global competition among companies, governments and investors who can find effective ways to remove 10 billion metric tons of CO2 annually by 2050.
The ultimate winners of the XPRIZE will be announced on Earth Day in 2025. The most promising removal technology will receive $50 million, and the next three contestants will split $30 million.
What it means to the MIT effort is that the ultimate CO2 collection efforts must be very large. The planners there are thinking of making CO2 into fuels such as ethanol or products such as concrete.
But underground geologic storage areas, such as depleted oil reservoirs, are likely to get most of the ocean-derived CO2, Hatton said.
“You’re not going to be able to use all of it as a feedstock. You’ll run out of markets.” So, as he put it, “a significant amount of the captured CO2 will need to be buried underground.”
Reprinted from E&E News with permission from POLITICO, LLC. Copyright 2023. E&E News provides essential news for energy and environment professionals.