Soda lime is a solid off-white mixture of calcium and sodium hydroxides used in scuba rebreathers, submarines, anesthesia, and other closed breathing environments to prevent the poisonous accumulation of CO2 gas. The mixture acts as a sorbent (a substance that collects other molecules), turning into calcium carbonate (limestone) as it amasses CO2. The ORNL team's CO2 scrubber works in essentially the same way to treat the CO2-rich flue gas released by coal-burning power plants -- although advancing carbon-capture technology was not always their objective.
"We initially stumbled into this research by accident," says senior author Radu Custelcean, a research scientist at ORNL.
Custelcean - Team - Class - Compounds - Bis-iminoguanidines
Custelcean and his team recently "rediscovered" a class of organic compounds called bis-iminoguanidines (BIGs), which were first reported by German scientists at the turn of the 20th century and recently noted for their ability to selectively bind anions (negatively charged ions). The team members realized that the compounds' ability to bind and separate anions could be applied to bicarbonate anions, leading them to develop a CO2-separation cycle using an aqueous BIG solution. With their carbon-capture method, flue gas is bubbled through the solution, causing CO2 molecules to stick to the BIG sorbent and crystallize into a sort of organic limestone. This solid can then be filtered out of the solution and heated at 120 degrees C to release the CO2 so it can be sent to permanent storage. The solid sorbent can then be dissolved in water and reused in the process indefinitely.
State-of-the-art carbon-capture technologies come with major flaws. Many use liquid sorbents, which evaporate or decompose over time and require that...
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