A textile filter paves the way for eco-friendly carbon capture technology
"Innovation happens when two disciplines of science that normally don't intersect come together. If you've a foot in both of those worlds, you'll notice something obvious - that won't come easily to the others," Sonja Salmon, an associate professor of textile engineering, chemistry, and science at NC State, tells IE in an interview.
Salmon is referring to her expertise in textile engineering and biochemistry. Recently, Salmon and Jialong Shen, a postdoctoral research scholar at NC State, created a seemingly simple textile-based filter that can capture carbon dioxide emissions.
An eco-friendly one at that.
The researchers chose a piece of cotton cloth, known for its versatile properties, and a naturally-occurring enzyme called carbonic anhydrase to create the fabric, whose special property is simply removing carbon dioxide molecules from a gas mixture.
Their findings were published in the journal ACS Sustainable Chemical Engineering earlier this month.
Their choice of weapon? Cotton
It is a known fact that carbon dioxide levels today are some of the highest that has been seen in the past 800,000 years. According to the National Oceanic and Atmospheric Administration, the fossil fuels that people burn for energy are primarily responsible for the current high concentrations of CO2.
"I've been working in this field since 2005. At the time, global CO2 emissions were only 24 billion tonnes per year. Now they are greater than 35 billion tonnes per year. Humans crave energy, and we are throwing away the byproduct of that need for energy — which is carbon dioxide — away in the air and not collecting it. We can't see or smell it. It's very invisible to us, but it's causing a very big problem for our planet, and we need to do something about that," says Salmon.
Their solution was the filter.
"One thing that we already know about cotton is that it absorbs and transports water and moisture well," she says.
Cotton can also be used to spread the water out into a thin film, creating a very high contact area for the gas. "When carbon dioxide gas molecules have to be removed from gas mixtures, the molecule has to come in contact with something - hence the big surface area," explains Salmon.
Carbon capture within our bodies?
The researchers chose to model their technology on a reaction occurring within our bodies.
Carbonic anhydrase is an enzyme found in abundance in all mammalian tissues, as well as plants, algae, and bacteria. The carbonic anhydrase aids in the conversion of CO2 and water into bicarbonate (HCO3-) and protons (H+) (and back again). This process is vital for life and central to respiration, digestion, and the regulation of cellular pH levels.
According to the researchers, their "textile filters with enzyme attached work like a mix between an air filter and a water filter that carry out a chemical reaction at the same time."
"There are conventional carbon capture systems working today that are used in the oil and gas industry - to purify methane, natural gas mostly. When natural gas is taken out of the ground, it's often mixed with carbon dioxide. So, the technology for separating carbon dioxide from gases has already existed for decades," explains Salmon.
However, most previous systems released CO2 back into the atmosphere. Whereas the idea behind using these filters is to trap the gas instead, capture it, and it could then be put underground or turned into valuable products.
"Our technology uses textiles and enzymes to capture the CO2 molecules in a very efficient manner," says Salmon.
Capturing carbon dioxide for useful purposes
To create the filter, the enzyme was attached to a piece of two-layer cotton fabric by 'dunking' the fabric in a solution containing chitosan, which acts like glue. The material traps the enzyme, which then sticks to the fabric, according to a press release.
A series of experiments were then conducted to see how efficiently the filter would separate carbon dioxide from a mixture of carbon dioxide and nitrogen, simulating levels that equaled those emitted by power plants.
The fabric was rolled into a spiral and shoved into a tube. The researchers pushed the gas through the tube, along with a water-based solution. As the CO2 reacted with the water and the enzyme in the solution, it turned into bicarbonate and dripped down the filter and the tube. Then, they captured the bicarbonate solution and routed it out. It could then be used to create more energy or react with calcium to form limestone.
When the researchers pushed air through the filter at a rate of four liters per minute, they could pull out 52.3 percent of carbon dioxide with a single-stacked filter and 81.7 percent with a double-stacked filter.
Translating into real-world applications
While the initial results are exciting, the filter still needs to be tested using the faster air flow rates found in commercial power plants. A full-scale filtration system would need to process more than 10 million liters of flue gas per minute.
"To tackle this huge problem [Carbon emissions], we were sure that the technology [the one they're working on] should have to be scaled up very quickly," Shen tells IE.
While several carbon capture technologies rely on complex materials, Salmon and Shen chose cotton, which is readily available and can survive repeated washing, drying, and storing cycles. "Our technology can be easily scaled up using existing textile manufacturing infrastructure," says Shen.
The researchers are already looking at real-world applications - power plants. "The problem with currently-used technologies is that it involves a lot of energy to regenerate the solvent, which is expensive," says Shen. The team intends to use solvents with low regeneration energy, a "cost-effective method that can be deployed at scale."
Their research has been modeled on current technology. 'The beauty of our design — the filter — is that it could drop into existing equipment at power plants," says Salmon.
Can the modified fabric be worn someday? Could a shirt help in battling climate change?
"That's more futuristic," says Salmon. "Our technology helps capture the gas molecules that have to be stored somewhere. So, our system is meant for something stationary. Unfortunately, it isn't something that you could stick on the back of your car or wear around right now. But again, with innovation, there will be new ways to think about using it," she adds.
Next in the pipeline
The project received funding from the U.S. Department of Energy, through a collaboration with Dr. Min Zhang at the National Renewable Energy Laboratory and Dr. Jesse Thompson at the University of Kentucky’s Center for Applied Energy Research. They were supported by Novozymes, who supplied enzymes for the work.
"Together with our collaborators, we have done some scale-up, and hopefully, there will be a publication later this year about that work. Frankly, we think the technology works well enough already to think about trying to deploy them on a larger scale. But that means having partnerships with commercial opportunities. We're now starting to talk to folks about that and look forward to making progress," says Salmon.
Over the past few years, many concepts for fighting climate change have been developed. However, many of these do not make it past the proof-of-concept stage.
Salmon states the energy penalty might have something to do with that.
"There's an energy requirement for any carbon capture system. Because you're fighting to grab gas molecules out of the air and pull them into a more concentrated form, and that goes against the natural laws of thermodynamics. So you have to pay an energy penalty for it," Salmon says. In other words, you need to expend some energy in order to fuel the carbon capture and storage technology.
The size of that energy penalty so far has been a limiting factor.
"There's also the perception that we've been throwing CO2 away for free and now have to pay for it — that stands as an obstacle. But, people need to understand that unless we pay for it our planet is in trouble," adds Salmon.
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