Adsorbent breaks CO2 barrier

April 15, 2008

Amine-modified silicas have posed a trade-off between carbon dioxide removal ability and robustness. However, a new variant provides both high capacity and reusability, say researchers at Georgia Tech, Atlanta. The material is produced via a simple one-step process, and its raw materials are relatively inexpensive, adds Christopher Jones, a professor in the School of Chemical and Biomolecular Engineering.

The hyperbranched aminosilica (HAS) adsorbs 2 to 3 mmole of CO2/g of adsorbent at temperatures from 25°C to 75°C, the range likely for commercial use. This is up to five times better than the performance of other amine adsorbents reported in the literature.

Laboratory tests in a fixed bed showed that the adsorbent maintained constant performance (within the limits of experimental error) over 12 adsorption/desorption cycles, notes Jones.

The material can clean up flue gases but also may be good for capturing CO2 from other sources and for removing SOX, he adds.

The key to the material’s performance and robustness is the creation of a covalent chemical bond between branched multiple layer organic adsorbent and the silica support. Other amine-modified silicas that rely on physical linkage provide high capacity but can’t be reused. Materials with chemical bonds can be reused but don’t provide as high capacity because they are limited to an amine monolayer. The synthesis approach developed at Georgia Tech yields multiple amine layers with branches on both the surface and within the pores of the silica, and thus provides significantly greater capacity to capture CO2. Fine-tuning the ratio of types of binding sites may provide even more capacity, notes Jones.

Piloting could begin within a year, he reckons, if the researchers opt to stay with a fixed bed. However, such beds might not be optimal for exposing flue gases to the adsorbent on an industrial scale, Jones says. So, it may make sense to develop a better process and test it simultaneously with the adsorbent, although this would delay piloting, he adds. Discussions with potential partners have already started.

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