The team at North Carolina State University found that they could filter carbon dioxide from air and gas mixtures at ‘promising rates’ using the filter, which combines cotton fabric and an enzyme called carbonic anhydrase — one of nature’s tools for speeding chemical reactions.
Whilst the filter would need to be scaled up in size significantly for reducing emissions from biomass, coal or natural gas power plants, researchers believe their design would make that step easier compared with other proposed solutions.
“With this technology, we want to stop carbon dioxide emissions at the source, and power plants are the main source of carbon dioxide emissions right now,” said the study’s lead author Jialong Shen, postdoctoral research scholar at NC State.
The centrepiece of the team’s design for a proposed textile-based chemical filter is the naturally occurring carbonic anhydrase, which can speed up a reaction in which carbon dioxide and water will turn into bicarbonate. The enzyme plays an important role in the human body, transporting carbon dioxide so it can be exhaled.
“We borrowed this wonderful enzyme in our process to speed up the carbon dioxide uptake in an aqueous solution,” Shen said.
To create the filter, researchers attached the enzyme to a two-layer cotton fabric by dunking the fabric in a solution containing chitosan, which physically traps the enzyme, causing it to stick to the fabric.
They then ran a series of experiments to see how well their filter would separate carbon dioxide from an air mixture of carbon dioxide and nitrogen, simulating levels emitted by power plants. They rolled the fabric into a spiral so that it could be placed into a tube, then pushed the gas through the tube along with a water-based solution.
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As the carbon dioxide reacted with the water in the solution and the enzyme, it turned into bicarbonate and dripped down the filter and the tube. They then captured the bicarbonate solution and routed it out.
According to researchers, when they pushed air through the filter at a rate of four litres per minute, they could pull out 52.3 per cent of carbon dioxide with a single-stacked filter, and 81.7 per cent with a double-stacked filter.
Whilst findings are promising, the team said, they need to test the filter against the faster flow air rates that are used in commercial power plants. For comparison, a full-scale operation would need to process more than ten million litres of flue gas per minute. The researchers are working with collaborators to test at a bigger scale and to compare their technology to other comparable technologies under the study.
Researchers also tested how well the filter would work after five cycles of washing, drying and storing, finding that it could maintain a high level of performance.
“The enzyme can be maintained at a lower temperature for a very long time and it’s going to be durable,” said Shen. “The fabric provides physical support and structure for it, while providing a large surface area for it to react with the carbon dioxide.”
The team is also exploring how to recycle the liquid after it exits the filter, as well as the process of turning the bicarbonate back into carbon dioxide so it can be stored and disposed of, or used for other commercial purposes.
“We want to regenerate the water solution we use with the filter so we can use it over and over,” said Sonja Salmon, study co-author and associate professor of textile engineering, chemistry and science at NC State. “That side of the process needs more work, to make the regeneration energy of the solvent as low as possible.”
Researchers hope their system could help drive down cost to help boost adoption of new technologies that require less energy than existing commercialised tech.
“There are a lot of different ways to capture carbon dioxide,” Shen said. “The current standard in the commercial setting uses a reaction that is so fast, so robust, and that binds the carbon dioxide so well, that you can’t easily get the carbon dioxide out. You have to use very high temperatures, which means a lot of energy consumption. That makes your process more expensive.”
