Green Machine: Sucking carbon dioxide out of the air

Think of it as a chemical vacuum cleaner for sucking greenhouse gases out of the air.

Air capture, in which carbon dioxide is removed from the atmosphere, has been touted as a potentially promising way to tackle climate change. That's because unlike carbon capture from power plant flue gases, the technology has the potential to reduce existing CO₂ levels, rather than simply slowing the rate of increase.

To demonstrate that the technology works, Christopher Jones at the Georgia Institute of Technology in Atlanta tested a CO₂ absorbent based on amines - the chemicals predominantly used in power plant carbon capture trials - on gases with CO₂ concentrations similar to those found in ambient air.

He found the material was able to repeatedly extract CO₂ from the gas without being degraded, which will be vital if the technology is to be used economically on a wide-scale.

However, unlike the liquid amines typically used in power plant carbon capture, which consume large amounts of energy as they must be heated to very high temperatures to re-release their stored CO2, Jones' team has developed a new class of the material called hyperbranched aminosilica, in which the amine is held on a solid porous silica substrate.

Solid amines release the stored CO2 when heated to just 110 degrees Celsius - much lower than the temperatures required by the water-based liquid amine solutions - reducing the amount of energy required by 75 per cent.

This also means the energy needed could be supplied by widely available sources such as waste heat from industrial plants, says Peter Eisenberger of air capture company, based in New York. The energy could also be supplied by renewable sources such as solar power, he says. The captured CO2 could then be fed to algae, which absorb the gas to produce biofuel and biochar.

Jones is working with the company to test a pilot air capture plant in Menlo Park, California, which is absorbing 2 tonnes of CO2 from the atmosphere each day. A commercial plant could absorb 1 million tonnes of CO2 per day, says Eisenberger.

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