Issue Date: November 1, 2010
Carbon Capture By Solids
By combining experimental and computational methods to examine an amine-functionalized metal-organic-framework (MOF) compound, researchers in Canada have identified the chemical nature of carbon dioxide-binding sites in that porous crystalline material (Science 2010, 330, 650). The study reveals molecular-level details of nitrogen-CO2 interactions, which are central to commercial CO2-scrubbing systems. The findings could lead to advances in carbon-capture technology.
Carbon cleanup in industrial settings today is often carried out by flowing flue gases through a column containing an aqueous solution of amine compounds such as monoethanolamine to selectively extract CO2 from the exhaust stream. The CO2-enriched solution is then typically heated to above 100 °C to remove the CO2 and regenerate the amine solution.
Technology based on those processes is well established. Nevertheless, various shortcomings, such as the corrosive nature of the solutions and the high energy input required to regenerate them, leave room for improvement.
Solid adsorbents might offer viable alternatives, especially because some MOF compounds exhibit the capacity to take up exceptionally high quantities of CO2. That feature has motivated researchers to synthesize large numbers of these compounds, including ones with amine moieties, in hopes of pushing CO2 uptake even higher.
In the new work, a team led by chemists Ramanathan Vaidhyanathan and George K. H. Shimizu of the University of Calgary and Tom K. Woo of the University of Ottawa used crystallography and computational techniques to sort out subtle details of CO2 binding in an amine-functionalized zinc-based triazole oxalate compound. Among other findings, the group determined the geometry of the amine-CO2-binding site in the MOF. The researchers found that cooperative binding of CO2 in the form of dimers and suitable pore size are collectively responsible for the material’s high uptake of the gas.
“This study reveals for the first time the specific interactions that hold CO2 in the pores of amine-functionalized MOFs,” says Omar M. Yaghi of the University of California, Los Angeles. “This is a significant step toward understanding what makes for a good CO2-capture material.”
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