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Environment

Bird-Inspired Filter Captures Carbon

ACS Meeting News: Microchannel material based on avian anatomy might one day help remove CO2 from smokestacks

by Lauren K. Wolf
September 16, 2013 | A version of this story appeared in Volume 91, Issue 37

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Credit: Courtesy of Aaron Esser-Kahn
Polymeric filters arranged in a square (top electron microscope image) capture CO2 faster than filters packed in a hexagon.
Electron microscope images show that polymer-based carbon capture filters in a “double square” pattern (bottom) snag more carbon dioxide from a gas stream than do those with a “hexagonal” pattern (top).
Credit: Courtesy of Aaron Esser-Kahn
Polymeric filters arranged in a square (top electron microscope image) capture CO2 faster than filters packed in a hexagon.

To reduce emissions of the greenhouse gas carbon dioxide, factories and power plants can filter their flue gas by passing it through a column filled with a solution of a CO2-trapping compound such as monoethanolamine (MEA). This technique isn’t very efficient, so researchers have been looking for alternative technologies. One research team, led by Aaron P. Esser-Kahn of the University of California, Irvine, has developed a carbon capture material inspired by one of nature’s most efficient membranes: a bird’s lungs. To fly efficiently, birds have evolved intricate structures in their lungs to rapidly exchange CO2 for oxygen, Esser-Kahn said. His team produced its bird-lung mimics by stretching polylactic acid fibers of two different diameters between brass plates. The researchers then filled a mold around the fibers with polydimethylsiloxane. After the polymer set, the team heated the assembly to degrade the fibers and leave behind microchannels of two sizes. When the researchers filled the small-diameter channels with MEA and passed CO2 through the larger ones, they observed the gas diffuse through the filter and react with MEA. Surprisingly, CO2 transferred most rapidly when the channels were packed in a “double square” pattern—a geometric pattern not observed in nature—rather than a hexagonal pattern that more closely simulates a bird’s airways.

 

Schematic shows that in order to make a microvascular carbon capture filter, researchers first stretch ultrathin polylactic acid (PLA) fibers across brass plates. Then they fill and polymerize the space around them with polydimethylsiloxane. Applying heat and a vacuum to the assembly degrades and evaporates the PLA, leaving behind microchannels.
Credit: Courtesy of Aaron Esser-Kahn

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