A novel synthetic material that is a thousand times more efficient than trees at capturing carbon dioxide from the atmosphere was presented by Klaus Lackner, director of Arizona State University's new Center for Negative Carbon Emissions, at a meeting of the American Physical Society in Maryland last Sunday. According to Lackner, the amount of carbon dioxide in the atmosphere has reached the point where simply reducing emissions will not be enough to tackle climate change. Referring to recent environmental reports, Lackner emphasized the need for prolonged periods of carbon capture and storage – also known as "negative carbon emission".

Trees and other biological matter are natural sinks of carbon dioxide but they do not trap it permanently and the amount of land required is prohibitive. "There is no practical solution that doesn't include large periods of negative emission," said Lackner, who added that "we need means that are faster than just growing a tree." During the past few years, Lackner and his colleagues have developed a synthetic membrane that can capture carbon dioxide from the air passing through it. The membrane consists of an "ion-exchange" resin – positive anions in the resin attract carbon dioxide, with a maximum load of one carbon-dioxide molecule for every positive charge. This process is moisture sensitive, such that the resin absorbs carbon dioxide in dry air and releases it again in humid air. As a result, this material works best in warm, dry climates.

Show and tell

Lackner plans to install corrugated collecting panels incorporating the membrane material on the roof of the Center for Negative Carbon Emissions this summer. The researchers hope that this public installation will demonstrate the economic feasibility and efficiency of a new technology that can address the issue of climate change, and help shift the debate from reduced carbon emissions to negative carbon emissions.

To keep costs low, the first step – capturing the carbon from the air – is free. "We made it cheap by being passive. We can't afford to be blowing air around," said Lackner. The resin itself is readily available and can be mass-produced, because it is already widely used to soften and purify water. The collectors trap between 10 and 50% of the total carbon dioxide that passes through. Compared with the amount of carbon dioxide that a typical tree collects during the course of its lifetime, these panels are a thousand times more efficient.

"I believe we have reached a point where it is really paramount for substantive public research and development of direct air capture," said Lackner. "The Center for Negative Carbon Emissions cannot do it alone."

Post trappings

Lackner estimated that about a hundred-million shipping-container-sized collectors would be needed to deal with the world's current level of carbon emissions. As these collectors would typically become saturated within an hour, Lackner envisions a possible "ski-lift" approach where saturated panels are taken away to a humid environment to release their carbon dioxide and then recycled back to the dry air for more carbon capture.

The question also remains of what to do with the carbon dioxide once it is trapped. Burying it is one option, which is something Lackner said is likely, given the sheer quantity of carbon that must be captured. His centre is also testing ways to recycle the carbon dioxide and sell it to industries that could use it to make products such as fire extinguishers, fizzy drinks and carbon-dioxide-enhanced greenhouses, and even synthetic fuel oil.

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