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.”