Polymer proves better at filtering carbon dioxide when wet

"This work demonstrates the polymer's potential for use in industrial gas separation and carbon capture technologies, with benefits for both manufacturing efficiency and efforts to mitigate global climate change."Liyuan Deng, Norwegian University of Science and Technology

An international team of researchers has found that submerging a polymer in liquid water can significantly boost its ability to selectively remove carbon dioxide (CO₂) from gas mixtures.

"Normally, improving the permeability of a gas through a material impairs the material's selectivity," says Rich Spontak, professor of chemical and biomolecular engineering and of materials science and engineering at North Carolina State University, and co-corresponding author of a paper on this work in NPG Asia Materials. "To explain this using CO₂ as an example, the more easily gases can pass through a material, the less able the material usually is to remove CO₂ from a gas mixture. It lets through the CO₂, but it lets through other gases as well. There's a real trade-off when engineering polymers for use as gas-separation membranes.

"What's remarkable about our finding is that we were able to drastically improve the polymer's CO₂ permeability while also slightly improving its CO₂ selectivity. And the process that led to this substantial improvement was related to transforming the microstructure of the membrane in low-cost and nontoxic fashion – we submerged the material in water."

Polymer membranes that can filter out CO₂ are desirable for use in a variety of applications, such as removing CO₂ from natural gas and sequestering CO₂ in order to limit emissions from industrial facilities.

For this work, the researchers utilized a thermoplastic elastomer that is recyclable, relatively tough and shown to have desirable properties for a wide range of contemporary technologies. They set out to see how the morphology of the material – meaning the arrangement of polymer molecules – affects its performance as a CO₂-selective membrane.

The permeability of gases through polymers is frequently measured in Barrer units. When dry, the permeability of CO₂ through the thermoplastic elastomer was less than 30 Barrer. Previous work reported by members of the team had shown that adding water vapor to the CO₂ feed could improve the elastomer’s CO₂ permeability, boosting it to as high as 100–190 Barrer at relative humidity levels above 85%.

"With these new results, we've shown we can reach a permeability of almost 500 Barrer at 90% humidity," says Liyuan Deng, professor of chemical engineering at the Norwegian University of Science and Technology and co-corresponding author of the paper. "At the same time, the selectivity of CO₂ relative to nitrogen (N₂) increases to as high as 60. For comparison, the best commercial polymer membranes that could be used for CO₂ capture possess a permeability up to 200 Barrer and a CO₂/N₂ selectivity up to 50. It's very important that both of these performance metrics are considered simultaneously to achieve competitive membranes.

"This work demonstrates the polymer's potential for use in industrial gas separation and carbon capture technologies, with benefits for both manufacturing efficiency and efforts to mitigate global climate change. It also provides a previously unexplored and facile route by which to transform the morphology of a polymer membrane and achieve tremendous improvement in gas transport properties."

This story is adapted from material from North Carolina State University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.