New chemical combination could improve carbon capture.

Current methods for C[O.sub.2] capture from flue gases are energy-intensive, and consequently too expensive for most applications. A new solvent/amine system developed at Saint Mary's University could change that.

The standard practice is to bubble the gas through a solution of about 20 per cent monoethanolamine (MEA) in water. C[O.sub.2] dissolves and forms an adduct with the MEA--this releases a proton which must be accepted by a second MEA molecule. The solution is then heated to release gaseous C[O.sub.2] and regenerate the MEA. "The problem with these MEA/water catch-and-release systems is that they have a very high heat capacity," says Jason Clyburne, professor of chemistry at Saint Mary's University. "The catch is very good, but the release is very costly." As a result, it is currently only useful in high-value applications, such as purification of natural gas; for economical greenhouse gas mitigation the cost needs to be reduced significantly.

Clyburne and his team surveyed many alternatives, both for the capture molecule and the solvents. In a paper published in Industrial and Engineering Chemistry Research, they point out that diethylenetriamine (DETA) is similar to MEA, but is much less volatile and contains multiple amine groups. This means it doesn't require a second molecule to accept a proton, and can be used in a 1:1 ratio to capture C[O.sub.2], rather than the 2:1 ratio required by MEA. As for the solvent, the team tested various compounds that would be non-volatile, robust under process conditions, and have a lower heat capacity than water. Several ionic liquids were investigated, but in the end a similar performance at much lower cost could be obtained with a commercially-available polymeric solvent.

The new solvent/amine system is undergoing testing, but so far indications are that it will release C[O.sub.2] at significantly lower energies than traditional MEA/water systems. Clyburne has filed a patent application and is collaborating with GreenCentre Canada, a green chemistry commercialization centre in Kingston, Ont., to bring the discovery to market. "My gut feeling is it won't take very long," says Clyburne.

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