Science & Society

MIT engineers build up a new approach to expel carbon dioxide from the air

A new method for expelling carbon dioxide from a stream of air could give a significant tool in the fight against climate change. The new system can take a shot at the gas at for all intents and purposes at any concentration level, even down to the approximately 400 parts per million right now found in the atmosphere.

Most strategies for expelling carbon dioxide from a stream of gas require higher concentrations, for example, those found in the flue emissions from fossil fuel-based power plants. A few varieties have been built up that can work with the low focuses found in air, however, the new technique is fundamentally less energy-intensive and costly, the specialists state.

The procedure, in light of passing air through a stack of charged electrochemical plates, is depicted in a new paper in the journal Energy and Environmental Science, by MIT postdoc Sahag Voskian, who built up the work during his Ph.D., and T. Alan Hatton, the Ralph Landau Professor of Chemical Engineering.

The gadget is essentially an enormous, particular battery that ingests carbon dioxide from the air (or different gas stream) ignoring its electrodes as it is being charged up, and afterward releases the gas as it is being discharged. In operation, the gadget would just alternate between charging and discharging, with fresh air or feed gas being blown through the system during the charging cycle, and afterward the pure, concentrated carbon dioxide being extinguished during the discharging.

As the battery charges, an electrochemical reaction happens at the surface of each of a stack of electrodes. These are covered with a compound called polyanthraquinone, which is composited with carbon nanotubes. The electrodes have a natural affinity for carbon dioxide and promptly respond with its molecules in the airstream or feed gas, in any event, when it is available at very low concentrations. The reverse reaction happens when the battery is discharged — during which the gadget can give some portion of the power required for the entire system — and in the process ejects a stream of pure carbon dioxide. The entire system works 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,” clarifies Voskian. As such, the electrode material, by its nature, “has either a high affinity or no affinity whatsoever,” contingent upon the battery’s state of charging or discharging. Different reactions utilized for carbon capture require intermediate chemical processing steps or the input of critical energy, for example, heat, or pressure differences.

“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,” Voskian says. That is, as any gas moves through the stack of these flat electrochemical cells, during the discharge step the caught carbon dioxide will be carried alongside it. For instance, if the ideal end-product is pure carbon dioxide to be utilized in the carbonation of beverages, at that point a stream of the pure gas can be blown through the plates. The caught gas is then released from the plates and joins the stream.

In some soft-drink bottling plants, fossil fuel is burned to create the carbon dioxide expected to give the drinks their fizz. Likewise, a few ranchers burn natural gas to produce carbon dioxide to encourage their plants in greenhouses. The new system could dispose of that requirement for fossil fuels in these applications, and in the process really be taking the greenhouse gas right out of the air, Voskian says. Then again, 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 procedures.

The procedure this system utilizes for catching and discharging carbon dioxide “is revolutionary” he says. “All of this is at ambient conditions — there’s no need for thermal, pressure, or chemical input. 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.”

“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,” Hatton says. “This carbon dioxide capture technology is a clear demonstration of the power of electrochemical approaches that require only small swings in voltage to drive the separations.”

In a working plant — for instance, in a power plant where exhaust gas is being produced persistently — two sets of such stacks of the electrochemical cells could be set up side by side to work in parallel, with flue gas being directed first at one set for carbon capture, at that point redirected to the second set while the first set goes into its discharge cycle. By alternating back and forth, the system could always be both catching and discharging the gas. In the lab, the team has demonstrated the system can withstand at least 7,000 charging-discharging cycles, with a 30 percent misfortune in efficiency over that time. The scientists gauge that they can promptly improve that to 20,000 to 50,000 cycles.

The electrodes themselves can be manufactured by standard chemical processing strategies. While today this is done in a laboratory setting, it very well may be adapted so that eventually they could be made in large quantities through a roll-to-roll manufacturing process like a newspaper printing press, Voskian says. “We have developed very cost-effective techniques,” he says, estimating that it could be created for something like several dollars for every square meter of the electrode.

Contrasted with other existing carbon capture technologies, this system is quite an energy proficient, utilizing around one gigajoule of energy for each ton of carbon dioxide caught, reliably. Other existing strategies have energy consumption which varies between 1 to 10 gigajoules per ton, contingent upon the inlet carbon dioxide concentration, Voskian says.

The specialists have set up an organization called Verdox to commercialize the procedure, and want to build up a pilot-scale plant within the next few years, he says. What’s more, the system is anything but difficult to scale up, he says: “If you want more capacity, you just need to make more electrodes.”

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