The carbon capture technique, developed at the Massachusetts Institute of Technology, can work with any concentration, down to the roughly 400 parts per million currently found in air.
Air passes through a stack of charged electrochemical plates, which absorb the carbon dioxide as the electrodes charge up, and then releases the gas as it is being discharged. In operation, the device would simply alternate between charging and discharging, with fresh air blown through the system during the charging cycle, and then the pure, concentrated carbon dioxide being blown out during the discharging.
The electrodes are coated with a compound called polyanthraquinone, which is built with carbon nanotubes, which react with the carbon dioxide its molecules in the air. The whole system 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 researcher Sahag Voskian. The means the electrode either has 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 percent CO2,” he said.
The battery-based carbon capture technique is also energy efficient, using 1GJ of energy per tonne of carbon dioxide captured. Other methods have energy consumption which vary between 1 to 10 GJ per tonne, depending on the carbon dioxide concentration, says Voskian.
The captured carbon dioxide can be used for a range of applications, from soft-drink bottling plants or to feed plants in greenhouses. Alternatively, 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.
“All of this is at ambient conditions — there’s no need for thermal, pressure, or chemical input,” he said.
Next: Building the carbon capture technology
“It’s just these very thin sheets, with both surfaces active, that can be stacked in a box and connected to a source of electricity,” said Voskian.
“In my laboratories, we have been striving to develop new technologies to tackle a range of environmental issues that avoid the need for thermal energy sources, changes in system pressure, or addition of chemicals to complete the separation and release cycles,” said his supervisor, Alan Hatton, the Ralph Landau Professor of Chemical Engineering at MIT. “This carbon capture technology is a clear demonstration of the power of electrochemical approaches that require only small swings in voltage to drive the separations.”
In the lab, the team has proven the system can withstand at least 7,000 charging-discharging cycles, with a 30 percent loss in efficiency over that time. The researchers estimate that they can readily improve that to 20,000 to 50,000 cycles. The electrodes themselves can be manufactured by standard chemical processing methods in roll-to-roll production systems.
“We have developed very cost-effective techniques,” said Voskian, at a cost of a few tens of dollars per square meter of electrode. The spinoff company, Verdox, aims to develop a pilot-scale plant within the next few years, he says.
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