Despite the move to renewables gaining pace around the world, fossil fuel-fired power plants will be pumping greenhouse gases into the atmosphere for a long time to come. Now researchers at Oak Ridge National Laboratory (ORNL) have developed a new substance that could effectively soak up carbon from coal-fired power plant emissions, using much less energy than existing methods.
The key to the new technology is a class of organic compounds known as bis-iminoguanidines (BIGs), which bind to specific anions – negatively charged ions – over others. The ORNL researchers realized that included bicarbonate anions, meaning they could be put to work grabbing carbon dioxide.
The team developed a watery BIG solution, then piped flue gas through it. The CO2 molecules bind to the BIG sorbent, which then crystallize into a solid bicarbonate salt. After enough has been collected, these solids can then be filtered out of the mixture, and the CO2 can be extracted by heating them to 120° C (248° F). After that, the solid BIG sorbent can be dissolved back into water and used again indefinitely. Meanwhile the CO2 can be sent off for storage and use, whether that's underground, as concrete or even to add the bubbles to fizzy drinks.
The researchers say their system uses about 24 percent less energy than existing methods, which often use liquid sorbents that require higher temperatures to heat. The team also found that after 10 consecutive cycles, they lost almost none of the solid sorbent – liquid ones tend to evaporate away over time.
"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 Radu Custelcean, senior author of the study. "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."
As well as it works in tests, the team says there are still kinks to iron out before the technology can be scaled up. The BIG sorbents take a while to absorb the CO2, and can't hold too much of it at once, which the researchers blame on the fact that BIG doesn't dissolve all that well 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," says Custelcean. "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."
The research was published in the journal Chem.
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