filtering system to remove carbon dioxide from electric power station smokestacks before the main greenhouse gas can billow into the atmosphere and contribute to global climate change.
With climate change now a major concern, many power plants rely on CO2 capture and sequestration methods to reduce their greenhouse gas emissions. Speaking at a symposium, “CO2 Separation and Capture,” Aaron P. Esser-Kahn, Ph.D., said he envisions new CO2-capture units with arrays of tubes made from porous membranes fitted side-by-side, much like blood vessels in a natural lung. Once fabricated to be highly efficient and scalable to various sizes by repeating units, these units can then be “plugged” into power plants and vehicles, not unlike catalytic converters, he explained.
To capture the most CO2, the Esser-Kahn group from the University of California, Irvine, first had to figure out the best pattern to pack two sets of different-sized tubes –– one for waste emissions and the other a CO2-absorbing liquid –– into the unit. “The goal is to cram as much surface area into the smallest space possible,” said Esser-Kahn.
They studied the way blood vessels are packed in the avian lung and the fish swim bladder. Birds need to exchange CO2 for oxygen rapidly, as they burn a lot of energy in flight, while fish need to control the amount of gas in their swim bladder effectively to move up and down in the water. “We’re trying to learn from nature,” said Esser-Kahn, adding that the avian lung and fish swim bladder are biologically well-suited systems for exchanging gases.
But the blood vessels in the avian lung and fish swim bladder are packed in different patterns. The avian lung consists of a hexagonal pattern where three large tubes form the vertices of a triangle and a small tube sits in the gap, while the fish swim bladder has a squarer pattern where a large and small tube alternate between vertices of a square. It turned out that this tube-packing challenge is a well-studied mathematical problem with nine unique solutions, or patterns, Esser-Kahn said.
Now, scientists can conduct further research to improve CO2-capture units’ efficiencies by adjusting the sizes of the tubes, thicknesses of the tube walls and membrane materials that make up the tube walls. “Biological systems spent an incredible amount of time and effort moving towards optimization,” said Esser-Kahn. “What we have is the first step in a longer process.”
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