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An engineering researcher at Lehigh University has developed a novel way to capture carbon dioxide from the air and store it in the ocean.
The approach uses a copper-containing polymeric filter and essentially converts CO2 into sodium bicarbonate (aka baking soda) that can be released into the ocean with minimal environmental impacts.
The new hybrid material, or filter, is called DeCarbonHIX, which stands for decarbonization through hybrid ion exchange material.
In a paper published in the journal Science Advances, lead researcher Arup Sengupta explains that the new system demonstrated a 300% increase in the amount of carbon captured compared with existing direct air capture methods.
“The climate crisis is an international problem,” Sengupta said in a media statement. “And I believe we have a responsibility to build direct air capture technology in a way that it can be implemented by people and countries around the world. Anyone who can operate a cell phone should be able to operate this process. This is not technology for making money. It’s for saving the world.”
DeCarbonHIX was the outcome of an ongoing CO2-driven wastewater desalination project funded by the Bureau of Reclamation under the jurisdiction of the US Department of the Interior. Sengupta and his students were on the lookout for a reliable supply of CO2 even in remote places. That quest led the way to the field of direct air capture, or DAC, and the creation of DeCarbonHIX.
The researcher explained that there are three ways to reduce CO2. The first—government action—can reduce emissions, but that won’t address what’s already in the air.
The second way is removing it from point sources, places like chimneys and stacks where carbon dioxide is being emitted in huge amounts.
“The good thing about that is you can remove it at very high concentrations, but it only targets emissions from specific sources,” Sengupta said.
The newest method is called direct air capture, which, he said, “allows you to remove CO2 from anywhere, even your own backyard.”
With DAC, chemical processes remove CO2 from the atmosphere, after which it’s typically stored underground. However, the technology is limited by its capacity. It can’t capture enough CO2 to overcome the energy cost of running the process.
“If you’re capturing carbon dioxide from a chimney at a plant, the amount of CO2 in the air can be upwards of 100,000 parts per million,” the scientist noted. “At that concentration, it’s easy to remove. But generally speaking, the CO2 level in the air is around 400 parts per million. That’s very high from a climate change point of view, but for removal purposes, we consider that ultra-dilute. Current filter materials just can’t collect enough of it.”
Another challenge with DAC involves storage. After the CO2 is captured, it’s dissolved, put under pressure, liquified, and typically stored miles underground. A DAC operation must then be located in an area with enough geological storage—and stability. A country like Japan, for instance, can’t pump CO2 underground because the area is prone to earthquakes.
Sengupta’s DAC method overcomes both the capture problem and the issue of storage.
For the capture problem, he developed DeCarbonHIX—a mechanically strong, chemically stable sorbent (a material used to absorb liquids or gasses)—that contains copper.
“The copper changes an intrinsic property of the parent polymer material and enhances the capturing capacity by 300%,” he said. “We showed that for direct air capture from air with 400 parts per million of CO2, we achieve capacity, meaning capacity is no longer a function of how much carbon dioxide is in the air. The filter will get saturated completely at any concentration, which means you can perform DAC in your backyard, in the middle of the desert, or in the middle of the ocean.”
The ocean is Sengupta’s solution to the storage problem. His DAC process starts with air blowing through the filter to capture CO2. Once the filter is saturated with gas molecules (determined by measuring the amount of gas going into the filter versus coming out of it), seawater is passed through the filter. The seawater converts carbon dioxide to sodium bicarbonate. The dissolved sodium bicarbonate is then released directly into the ocean.
“And it has no adverse impact on the ocean whatsoever,” he said. “It doesn’t change the salinity at all.”
In fact, he believes that sodium bicarbonate, which is slightly alkaline, may improve the health of the ocean. That’s because elevated levels of CO2 in the atmosphere have gradually reduced the pH of the ocean, causing acidification.
“Sodium bicarbonate may reverse that lowering of pH,” he said.
The researcher pointed out that, like existing DAC processes, DeCarbonHIX can also be desorbed with hot water or steam, and pure CO2 can be recovered, compressed, and stored underground in geological storage.
“In reality, this new filter material offers a dual mode of desorption and sequestration,” Sengupta said.
