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Capture of airborne carbon dioxide at any concentration made possible

Image credit: Mr.siwabud Veerapaisarn | Dreamstime.com

Researchers from the Massachusetts Institute of Technology (MIT) have developed a new technology to capture carbon dioxide from a stream of air at any concentration level – a tool that could be significant in the battle against climate change.

The US researchers said that while most methods of removing carbon dioxide from a stream of gas required higher concentrations – such as those found in the flue emissions from fossil fuel-based power plants – the new method could suck out the gas even when it was present in very low concentrations.

According to the researchers, the new method is significantly less energy-intensive and expensive. They added that the method could even suck out the greenhouse gas at the roughly 400 parts per million currently found in the atmosphere.

In a study, published in the journal Energy and Environmental Science, the researchers described the device as a large, specialised battery with a stack of electrodes that absorbed carbon dioxide from the air passing over its surface as it was being charged up, then released the gas as it was being discharged.

The team said the device alternated between charging and discharging cycles. During the charging cycle, they said that fresh air was fed into the system and concentrated carbon dioxide was blown out during the discharging.

Also, as the battery charges, an electrochemical reaction takes place at the surface of each of a stack of electrodes. These electrodes are coated with a compound known as polyanthraquinone, which is composited with carbon nanotubes.

The study noted that the electrodes have a natural affinity for carbon dioxide and readily react with its molecules in the airstream or feed gas, even when it is present at very low concentrations.

Sahag Voskian and T. Alan Hatton

A flow of air or flue gas (blue) containing carbon dioxide (red) enters the system from the left. As it passes between the thin battery electrode plates, carbon dioxide attaches to the charged plates while the cleaned airstream passes on through and exits at right.

Image credit: Diagram on method by MIT

When the battery is discharged, however, the team said that the process ejects a stream of pure carbon dioxide, also providing a part of the power needed for the whole system. They also added that the device operates at room temperature and normal air pressure.

“The greatest advantage of this technology over most other carbon capture or carbon-absorbing technologies is the binary nature of the adsorbent’s affinity to carbon dioxide,” said study co-author Sahag Voskian, MIT.

Voskian said that the electrode material, by its nature, “has either a high affinity or no affinity whatsoever,” depending on the battery’s state of charging or discharging.

“This binary affinity allows capture of carbon dioxide from any concentration, including 400 parts per million, and allows its release into any carrier stream, including 100 per cent CO2,” Voskian added.

According to the researchers, the pure carbon dioxide stream could be compressed and injected underground for long-term disposal or even made into fuel through a series of chemical and electrochemical processes.

Voskian said that the new system is energy efficient compared to existing methods, consistently using around one gigajoule of energy per tonne of carbon dioxide captured. He added that other existing methods have energy consumption which varies between 1 to 10 gigajoules per tonne, depending on the inlet carbon dioxide concentration.

In September this year, the UK’s offshore oil and gas industry outlined how it intends to cut carbon emissions from its operations and has pushed for greater use of carbon capture technologies to offset emissions from its production.

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