A cost-effective way to capture carbon
The method was developed by collaborating scientists from the École Polytechnique Fédérale de Lausanne (EPFL), University of California Berkeley, and Beijing. It combines elements of the two main methods of capturing carbon that are employed today. One uses powder-like solids, known as metal-organic frameworks (MOFs), that "stick" to CO2, and which pose formidable engineering demands. "Imagine trying to walk with a plateful of baby powder. It's going to go everywhere and it's very difficult to control," explained Berend Smit, director of the EPFL Energy Centre.
The second approach, which is more common, uses liquid amine solutions, which can absorb CO2 from the atmosphere. In large operations, the system uses two columns: one captures CO2, and the other releases it from the liquid, in a process called regeneration. The regeneration is costly because it is necessary to boil the liquid to separate the CO2 from the amine molecules.
The breakthrough method involves a combination of solids and liquids called a slurry. The solid part is an MOF called ZIF-8, suspended in a glycol liquid mixture.
"Pumping slurry is much easier than transporting a pile of baby powder," says Smit. The idea came from one of his former PhD students in Beijing and could be the key to implementing carbon capture more widely in the future. The slurry also doesn't need excessive amounts of energy to regenerate.
The team is now planning to test the ZIF/glycol slurry in the field.