CO2 scrubbers improved
Researchers have developed a new way to remove carbon dioxide from coal-burning power plant emissions.
The process removes CO2 from coal-burning power plant emissions in a similar way to how soda lime works in scuba diving rebreathers.
The research offers an alternative but simpler strategy for carbon capture, and requires 24 per cent less energy than industrial benchmark solutions.
Soda lime is a mixture of calcium and sodium hydroxides used 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 new 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 the Oak Ridge National Laboratory in the US.
Dr 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.
They gained new attention for their ability to selectively bind anions (negatively charged ions). The team realised that the compounds' ability to bind and separate anions could be applied to bicarbonate anions, leading them to develop a CO2-separation cycle by 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℃ 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.
“The main advantage of our 'organic soda lime' is that it can be regenerated at much lower temperatures and with significantly less energy consumption compared to inorganic scrubbers,” says Dr Custelcean.
“The less energy required for regeneration is expected to significantly reduce the cost of carbon capture, which is critical considering that billions of tons of CO2 need to be captured every year to make a measurable impact on the climate.”
The research team believes the process will be scalable, but it has at least one road bump to contend with - its relatively low CO2 capacity and absorption rate, which come from the limited solubility of the BIG sorbent in water.
“We are currently addressing these issues by combining the BIG sorbent with traditional sorbents, such as amino acids, to enhance the capacity and absorption rate,” Dr Custelcean says.
“We are also adjusting the process so it can be applied to CO2 separation directly from the atmosphere in an energy-efficient and cost-effective way.”