Scubalike technology could suck carbon dioxide from smokestacks

The technology that allows submariners to breathe underwater could someday allow the rest of us to breathe cooler air. Researchers have found a way to suck planet-warming carbon dioxide (CO 2 ) from industrial smokestacks using a chemical technique similar to one scuba divers and submarines use to “rebreathe” CO 2 -rich exhalations.

The team’s technique “has tremendous potential,” says Kristin Bowman-James, a chemist at the University of Kansas in Lawrence.

The advance relies on a class of organic chemicals called bis(imino guanidines), or BIGs. These chemicals were first discovered more than a century ago, but researchers recently found that they’re really good at binding to negatively charged ions, says Radu Custelcean, a chemist at Oak Ridge National Laboratory in Tennessee. He and his colleagues harness that binding ability to capture CO 2 .

First, the team dissolves a particular BIG in water, where the substance helps break down H 2 O molecules into positively charged protons (H+) and negatively charged hydroxide (OH–) ions. The BIG molecules snatch free-floating protons and take on a positive charge. Those BIG ions then react with negatively charged bicarbonate (HCO 3 –) ions that form when CO 2 -rich gas bubbles through the solution, Custelcean says. Because the resulting substance doesn’t readily dissolve, it crystallizes and can be separated from the solution.

Those crystals can then be heated to drive off CO 2 so it can be collected and stored, rather than emitted to the atmosphere, Custelcean says. The team’s lab tests suggest that process can occur at the relatively low temperature of 120°C. So, the researchers report today in Chem , capturing and recovering CO 2 from industrial exhaust using their technique takes about 24% less energy than a process commonly used in smokestack “scrubbers.” Once CO 2 has been driven from the crystals, the BIG can be redissolved in the solution, making it available to capture even more CO 2 .

The particular BIG used by Custelcean’s team sits at what Amar Flood, an organic chemist at Indiana University in Bloomington who was not involved with the work, calls a “magic sweet spot.” Its affinity for bicarbonate ions allows the crystal-forming reaction to readily occur, but the weak hydrogen bonding within the crystal also makes it relatively easy to recover the CO 2 .