This is another in our series of stories identifying new technologies and actions that can slow climate change, reduce its impacts or help communities cope with a rapidly changing world.
Carbon dioxide traps heat in the atmosphere, which warms our planet. But lately, excess levels of that gas have been making much of our world too toasty. Many climate solutions focus on reducing how much of that gas makes its way into the air. Some engineers instead look to mop up what’s already there. Arup SenGupta is one of them.
“Why don’t you take carbon dioxide out of the atmosphere?” asks this environmental engineer. He works at Lehigh University in Bethlehem, Penn.
SenGupta is part of a team that recently invented a system that works a bit like a water filter. But instead of removing pollution from water, it takes carbon dioxide (CO2) out of the air. When air flows through the filter, the CO2 gets trapped. Other gases pass through. The researchers described their process March 8 in Science Advances.
To clean out the filter, pass ocean water through it. This process converts the trapped CO2 into a compound called sodium bicarbonate. It’s the same stuff as baking soda. This compound dissolves and can be safely released into the ocean. Now the filter is ready to use again.
“If you remove 50 tons of CO2 from the atmosphere and put [the sodium bicarbonate] in the ocean, it doesn’t change the ocean chemistry at all,” SenGupta says. Do it enough, however, and it might even prove a bit beneficial. Sodium bicarbonate is alkaline. It can help offset ocean acidification, another problem linked to climate change.
The Intergovernmental Panel on Climate Change, or IPCC, is a global group focused on the climate. For the past 150 years, atmospheric levels of CO2 have been steadily rising. To avoid catastrophic climate change, the IPCC has called for bringing those levels down by 2050.
That strategy should include removing CO2 from the air and storing it, says Katie Lebling. She studies CO2-removal strategies at the World Resources Institute (WRI). This nonprofit group in Washington, D.C., is working to develop climate solutions.
“Carbon dioxide removal is a critical part of meeting our climate goals,” says Lebling. “We not only need to stop adding more, but also need to actively remove CO2 that’s already in the air.”
Just the latest in CO2-filtering tech
Already, filters remove CO2 from some sources, such as coal-fired power plants. Another air-filtering technology is described as “direct air capture,” or DAC. Right now, 18 DAC facilities operate in the United States, Europe and Canada. These plants are expensive and only capture a small share of the CO2 in air. That’s partly because the CO2 molecules in air are widely spread out.
“Direct capture is a way, I believe, we should work on,” SenGupta says. “But the technology is not there yet” to be able to address the problem on a large scale.
He thinks his group’s new tech could in theory help — and be used anywhere. It’s not just for power-plant chimneys. “You could go to the Himalayas and remove CO2,” he says. Or “you can go offshore in the middle of the Atlantic and remove CO2.”
SenGupta’s previous work had focused on water cleanups. But during the pandemic, he and his team began thinking about our warming world. From previous work, these engineers knew about materials that remove contaminants like arsenic and ammonia from water.
“We wanted to find something [for the air],” he recalls, “which takes out only CO2.”
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Over two years, they investigated ways to absorb CO2 from air. They tested many absorbent materials. In the end, a filter design using copper attached to a material called a polymer worked best.
The testing process began by blowing air through the copper and polymer filter. The researchers compared how much CO2 went in to how much came out. That let them determine when the filter was full. In their lab tests, the new material pulled CO2 from the air just as well as the filters now used on smokestacks.
The team “reset” the filter by pouring ocean water through it. (A lab assistant who lived near the New Jersey shore collected it in large plastic drums and brought it to the lab.) The captured CO2 flushed out as sodium bicarbonate.
However, lab tests don’t always guarantee success in the real world.
The tech might not be easy to scale up. The new process requires large amounts of other chemicals to work. Trapping one ton of CO2, for example, requires a ton of a caustic compound called sodium hydroxide. (It’s better known as lye.) And the reaction produces a strong acid called hydrochloric acid. SenGupta says that acid could be used in other industrial applications, such as making microelectronics. But it would have to be stored properly for other uses.
If SenGupta’s idea is going to work, chemists will need to think about all the materials that go in and come out. But he thinks it will be worth the effort to remove CO2. “We’re now talking to different scientists who can hopefully be helpful” in solving these other problems, he reports.
Lebling, at WRI, says there’s a lot of interest in using the ocean to store carbon safely. “It is a potential option for carbon removal, in part for the vast space it provides,” she says. “At the same time,” she adds, “it presents a host of unknowns.” Some have to do with how efficiently the sea can hold carbon. Others relate to possible ecological impacts. Before these approaches can be safely used, she says, scientists need to know how storing carbon in the ocean will affect the environment.
This is one in a series presenting news on technology and innovation, made possible with generous support from the Lemelson Foundation.