(September 5) Alongside green energy production, capturing carbon emissions at the source is another avenue in the fight against climate change. New materials and treatments are regularly improving carbon capture efficiency, and now scientists have developed an efficient low-cost technique that makes use of an ultra-thin membrane, like a bubble, to filter CO2 out of flue gas.
The researchers, from Sandia National Laboratories and the University of New Mexico, call their creation a CO2 Memzyme – a membrane full of enzymes. With a liquid layer 10 times thinner than a soap bubble, CO2 diffuses through this membrane and is captured and dissolved, while allowing nitrogen and oxygen to pass through. Bubbles are notoriously fragile, though, so to prevent breaks or leakage, the team bolstered theirs with a silica-based support of nanopores, made up of a relatively thick layer that repels water, and a thin layer that attracts it.
Scientists have developed a thin, bubble-like membrane which could help filter CO2 out of flue gas.
Enzymes were added to the liquid layer to help speed up the C02 dissolution process. The team used carbonic anhydrase, an enzyme found in human muscles, blood and lungs that helps the body process and remove carbon dioxide, and found that it increased the rate that the CO2 dissolved by a factor of 10 million. With the nanopores forming an unusual environment for the enzymes, the researchers ran molecular simulations to figure out how the carbonic anhydrase was behaving in the cramped conditions and see how they might improve its performance.
The simulations showed that although the nanopores aren't much bigger than the enzymes themselves, several of them could cram into the space and work together to help process the CO2. The nanopore structure helped protect the enzymes as well, meaning they could stay dissolved and active in much higher concentrations than usual, and do so for months on end, at temperatures as high as 140° F (60° C).
Altogether, the team claims their design is 10 to 100 times more selective for CO2 over nitrogen in passing flue gas than existing carbon capture membranes, and it performs 100 times faster. At the other end, the CO2 that's produced is 99 percent pure, which can be used in a variety of ways, like manufacturing concrete or producing biofuel from bacteria and algae.
Sandia National Laboratories researcher Susan Rempe peers through bubbles. Credit: Randy Montoya
While the team is currently seeking out partners to help scale the technology up for use in power plants, lab tests have shown promise.
"If we applied it to a single coal-fired power plant, then over one year we could avoid CO2 emissions equivalent to planting 63 million trees and letting them grow for 10 years," says Rempe.
The team received a patent for the Memzyme technology earlier this year and, although it's still early days, say it could be the first to meet the Department of Energy's national clean energy goal of having technology that can capture 90 percent of carbon emissions at a cost of US$40 per ton by 2025.