Energy efficient carbon capture uses scuba diving tech

A new form of carbon capture that works in a similar way to how soda lime in scuba diving rebreathers could improve the CO2 output of coal burning power plants.

The technique was developed by scientists at the Department of Energy’s Oak Ridge National Laboratory (ORNL), who say it requires 24 per cent less energy than industrial benchmark solutions.

Soda lime is commonly 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. It 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,” said senior author Radu Custelcean.

The team studied a class of organic compounds called bis-iminoguanidines and realised that the compounds’ ability to bind and separate anions could be applied to bicarbonate anions. They used this 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 crystallise into a sort of organic limestone. This solid can then be filtered out of the solution and heated at 120°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.

The researchers believe their method avoid some of the flaws present in current carbon-capture technologies; many use liquid sorbents, which evaporate or decompose over time and require that more than 60 per cent of regeneration energy be spent on heating the sorbent.

Because their approach involves capturing CO2 as a crystallised bicarbonate salt and releasing it from the solid state instead of heating a liquid sorbent, the ORNL team’s technology circumvents these issues. Their take on carbon capture requires 24 per cent less energy than industrial benchmark sorbents. Plus, the team observed almost no sorbent loss after ten consecutive cycles.

“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,” Custelcean said. “The lower 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.”

Although it is still in the early stages, Custelcean and his team believe the process will eventually be scalable. However, the technique does have a 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,” Custelcean said. “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.”

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