A simple process for removing carbon dioxide from ambient air may have potential to help with strategies combatting global warming.
A team from the US Department of Energy’s Oak Ridge National Laboratory (ORNL) was studying methods to remove environmental contaminants such as sulfate, chromate or phosphate from water.
One process involved synthesising a simple compound called guanidine designed to bind strongly to the contaminants and form insoluble crystals that are easily separated from water.
In the process, they discovered a method to capture and release carbon dioxide that requires minimal energy and chemical input.
“When we left an aqueous solution of the guanidine open to air, beautiful prism-like crystals started to form,” said ORNL researcher Radu Custelcean.
“After analysing their structure by X-ray diffraction, we were surprised to find the crystals contained carbonate, which forms when carbon dioxide from air reacts with water.”
Current carbon capture and storage strategies involve an integrated system of technologies that collect carbon dioxide from the point of release or directly from the air, then transport it, usually through a pipeline, to designated locations for storage where it is injected deep underground.
Traditional direct air capture materials must be heated up to 900°C to release the gas -- a process that can emit more carbon dioxide than is removed. Custelcean says guanidine offers a less energy-intensive alternative.
“Through our process, we were able to release the bound carbon dioxide by heating the crystals at 80-120°C, which is relatively mild when compared with current methods,” he said.
After heating, the crystals reverted to the original guanidine material. The recovered compound was recycled through three consecutive carbon capture and release cycles.
He warns that, while the direct air capture method is gaining traction, the process needs to be further developed and aggressively implemented to be effective in combatting global warming.
They also need to gain a better understanding of the guanidine material and how it could benefit existing and future carbon capture and storage applications.
The ORNL team is now studying the guanidine’s crystalline structure and properties to better understand the molecular mechanism of carbon dioxide capture and release and help design the next generation of sorbents.
They are also planning to evaluate the use of solar energy as a sustainable heat source to release the bound carbon dioxide from the crystals.
[Radu Custelcean analysing the molecular structure of the guanidine carbonate crystals using X-ray diffraction. Photo: ORNL]