Now, that’s some hot carbon capture

Chemists have made a substance that can absorb carbon dioxide at the high temperatures used in industrial processes, like cement or steel-making.

The study, published in Science, could eventually help to lower the emissions of these hard-to-abate industries.

While fossil fuels burned for energy can be readily replaced with low- or zero-emissions technology, it’s trickier to change cement and steel-making to release less CO₂.

The most mature technology for capturing CO₂ emissions at the source is through use of substances called liquid amines, which react with carbon dioxide molecules.

But these chemicals don’t work above about 60°C, and industrial exhausts are usually well above 200°C.

“A costly infrastructure is necessary to take these hot gas streams and cool them to the appropriate temperatures for existing carbon capture technologies to work,” says co-first author Dr Kurtis Carsch, a postdoctoral fellow at the University of California – Berkeley, USA.

Carsch and colleagues investigated a promising category of molecules called metal-organic frameworks, or MOFs.

MOFs are polymers made from carbon-based (organic) molecules and metals with lots of tiny pores, which allow them to act like molecular sponges.

“Our work moves away from the prevalent study of amine-based carbon capture systems and demonstrates a new mechanism for carbon capture in a MOF that enables high temperature operation,” says co-first author Rachel Rohde, a graduate student at UC Berkeley.

Instead of relying on amines, the team’s MOF uses zinc hydride. It can capture carbon efficiently from between roughly 200°C and 400°C.

“This material is highly stable and does something called deep carbon capture, which means it can capture 90% or more of the CO₂ that it comes into contact with, which is really what you need for point-source capture,” says Rohde.

“And it has CO₂ capacities comparable to the amine-appended MOFs, though at much higher temperatures.”

Co-author Professor Jeffrey Long, a chemist at UC Berkeley, says that “it was generally thought to be impossible” to capture molecules like CO₂ in this way at temperatures this high.

This is because matter naturally tends towards gas with increasing temperature – gaseous molecules are more favourable than the solid MOFs.

“This work shows that with the right functionality – here, zinc hydride sites – rapid, reversible, high-capacity capture of CO₂ can indeed be accomplished at high temperatures such as 300°C,” says Long.

The team is now investigating whether they can make variations of this MOF that absorb even more CO₂, or can absorb other gases at high temperatures.

“There’s a tremendous number of ways we can tune the metal ion and linker in MOFs, such that it may be possible to rationally design such adsorbents for other high-temperature gas separation processes relevant to industry and sustainability,” says Carsch.