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Electro-swing adsorption separates CO2 from mixed gases at any concentration

By Scott Jenkins |

Effectively separating carbon dioxide from combustion exhaust or directly from air is essential for realizing net reductions in greenhouse-gas emissions, but existing technologies for CO2 capture (such as CO2-scrubbing with amines), involve parasitic energy losses, which make carbon-capture economics unfavorable. To address this, researchers from the laboratory of T. Alan Hatton at the Massachusetts Institute of Technology (MIT; Cambridge, Mass.; www.mit.edu) Department of Chemical Engineering have demonstrated the first voltage-dependent separation of CO2 from mixed-gas using electro-swing adsorption (ESA).

MIT’s device is an electrochemical cell that selectively captures CO2 when current is applied in one direction, and releases CO2 when the current is reversed. The ESA system takes advantage of the fact that the molecule quinone, in its two reduced forms, reacts with CO2 in a nucleophilic addition, but has no affinity for CO2 in its oxidized form, explains Sahag Voskian, a post-doctoral researcher at MIT. “It is this binary nature of the affinity of quinone to CO2 at its different oxidation states which makes this system unique,” Voskian notes.

The researchers synthesized cathode material by polymerizing quinone and suspending the polyquinone in a solution of dispersed carbon nanotubes (CNTs). The polyquinone-CNT “ink” is used to dip-coat the cathode, Voskian says, and a ferrocene-CNT anode allows for reversible charge-discharge of the cell (that is, capture and release of the CO2). Ionic liquids serve as electrolytes to complete the circuit.

A series of five-layer electrode sheets are arranged in parallel such that the CO2-containing mixed gas flows through the channels between the stationary stacks (diagram). The cell architecture is designed to maximize contact between the gas and the high-surface-area electrodes.

The device works at ambient conditions on a wide range of CO2 concentrations in the feed gas, from parts-per-million (ppm)-level CO2 to 100% CO2, and can be controlled to release pure CO2 for other applications or for long-term underground disposal, Voskian says.

Voskian and Hatton, along with Brian Baynes, founded a company to develop prototypes for the device, optimize the electrode manufacturing process and eventually build a pilot plant.

electro-swing adsorption

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