Chemical 'sponge' could filter CO2 from the air
12:37 03 October 2007
NewScientist.com news service
Catherine Brahic

Sucking carbon dioxide out of the atmosphere could provide a last-ditch solution to climate change, according to calculations performed by a US scientist.

Frank Zeman at Columbia University in New York, US, believes CO2 could be efficiently extracted from the atmosphere using a relatively simple chemical process, before being buried underground.

This would help reduce the build-up of greenhouse gases in the atmosphere – a phenomenon that is widely blamed for global warming.

Carbon capture and storage (CCS) is currently being explored as a way to reduce CO2 emissions from large industrial plants. The idea is to isolate – or "scrub" – the gas from factory exhaust before it is released into the atmosphere. But Zeman believes CCS could also offer a way to soak up CO2 that has already been emitted into the atmosphere.

Unlike factories and power plants, cars, planes and homes each emit relatively small amounts of CO2. Cumulatively, however, their effect mounts up.

Transportation, for instance, accounts for about 15% of global emissions. But because these dispersed emissions get diluted with other gases in the atmosphere, isolating them is thought to require much more energy than extracting them from flue gasses where they are more concentrated.

Earth Prize
Removing CO2 from the atmosphere is the subject of a prize announced earlier in 2007 by British entrepreneur Richard Branson. Branson pledged to award $25 million to anyone who can develop a scheme for removing at least one billion tonnes of the gas from the atmosphere every year, for a decade.

So, together with Klaus Lackner, a former colleague at Columbia University, Zeman devised a new way of scrubbing CO2 from air. He has also performed calculations, published in Environmental Science & Technology, which suggest that the new method is efficient enough to justify its use.

The process involves pumping air from the atmosphere through a chamber containing sodium hydroxide, which reacts with the CO2 to form sodium carbonate. This carbon-containing solution is then mixed with lime to precipitate powdered calcium carbonate – a naturally occurring form of which is limestone. Finally, the "limestone" is heated in a kiln releasing pure CO2 for storage.

Zeman calculates that one carbon atom would need to be expended as fuel – to pump air and heat the process – in order to capture four carbon atoms from air.

Jon Gibbins, an expert on energy technology at Imperial College in the UK concedes that carbon capture from air could be a desirable last-ditch solution, but is concerned that it could also provide justification for continuing to burn fossil fuels.

Electricity switch
Gibbins believes it makes more sense to use fossil fuels to generate electricity, capture the CO2 at the power plant, and use the resulting electricity to power cars and trains.

"Is it better to burn fossil fuels and capture the carbon dioxide from air, or to decarbonise the power first and put that into transport?" he says. "If we bite bullet and move on to electricity then we can use electricity from anywhere, including renewable sources," he says.

Christian Koerner of the Institute of Basel in Switzerland adds that there are other ways to slow the build-up of CO2 in the atmosphere, such as simply making cars more fuel efficient.

Zeman claims that his process does not use any more energy than decarbonising emissions straight from power plants. But Gibbins points out that much of Zeman's process is run on electricity, while carbon capture at power plants relies on heat that would otherwise be wasted.

Zeman says he has no plans to enter Branson’s Earth Challenge. Lackner, meanwhile, has set up a private company called Global Research Technologies to explore the possibilities of scrubbing CO2 from air.

Journal reference: Environmental Science & Technology (DOI: 10.1021/es070874m)