Scientists Investigate the Potential of Organic HQ Clathrates to Capture Key Greenhouse Gases

Finding efficient techniques to separate and remove greenhouse gases from the atmosphere is key to decelerating climate change. In a recent study published online in Chemical Engineering Journal on August 9, 2021 (to be published in Volume 427 of the journal on January 1, 2022), a team of scientists, including Dr. Sol Geo Lim from National Korea Maritime & Ocean University, investigated the potential of a class of compounds called organic hydroquinone (HQ) clathrates to capture two key greenhouse gases, carbon dioxide (CO₂) and nitrous oxide (N₂O).

"In our previous work, we demonstrated the effectiveness of these clathrates for the recovery of CO₂ and N₂O individually. But capturing them simultaneously could be even more environmentally effective," says Dr. Lim.

Organic clathrates, such as HQ clathrates, are substances with a grid-like structure that enable it to trap other molecules (usually gases). The grid structure is termed the 'host' and the gases are 'guests.' But HQ clathrates selectively prefer different guests based on the composition of the gas mixtures they interact with. This makes it important to understand the different guest behaviors in HQ clathrates.

In their work, the research team exposed HQ clathrates to gas mixtures that had varying compositions of CO₂ and N₂O. They then performed experiments to investigate the interactions in the clathrate. They found that, unlike in experiments with other gas mixtures, the final composition of CO₂ and N₂O in the β-HQ was the same as that of the initial gas mixture, i.e., the HQ did not prefer either gas. When two components exist in the same composition in two different phases (here, solid and vapor), the mixture is called an azeotrope. This is the first ever report of an azeotropic HQ clathrate.

The research team further saw that CO₂, N₂O and CO₂–N₂O all had very similar clathrate formation kinetics. "The azeotrope formation can be attributed to the compelling similarity of CO₂ and N₂O guests in HQ clathrates. This valuable knowledge on host–host and guest–guest interactions in clathrates will help us develop new gas capture technologies," says Dr. Lim.

With studies like this to steer the research, perhaps it won't be long before we usher in a new era of climate protection.