Polymer-Based Membrane Filter Enhances Efficiency of Capturing CO2

Scientists have created a new membrane technology that facilitates the better elimination of carbon dioxide (CO₂) from mixed gases, for example, emissions from power plants.

To demonstrate the capability of our new membranes, we looked at mixtures of CO₂ and nitrogen, because CO₂/nitrogen dioxide mixtures are particularly relevant in the context of reducing greenhouse gas emissions from power plants. And we’ve demonstrated that we can vastly improve the selectivity of membranes to remove CO₂ while retaining relatively high CO₂ permeability.

Rich Spontak, Study Co-Corresponding Author and Distinguished Professor of Chemical and Biomolecular Engineering, North Carolina State University

“We also looked at mixtures of CO₂ and methane, which is important to the natural gas industry. In addition, these CO₂-filtering membranes can be used in any situation in which one needs to remove CO₂ from mixed gases—whether it’s a biomedical application or scrubbing CO₂ from the air in a submarine,” Spontak added.

Spontak is also a professor of Materials Science and Engineering at North Carolina State University.

Membranes are an appealing technology for eliminating CO₂ from mixed gases as they do not occupy a lot of physical space, they can be manufactured in a wide range of sizes and they can be easily substituted.

The other technology that is frequently used for CO₂ elimination is chemical absorption, which includes bubbling mixed gases via a column that holds a liquid amine — which eliminates CO₂ from the gas. But, absorption technologies have a considerably bigger footprint, and liquid amines are mostly corrosive and toxic.

These membrane filters function by permitting CO₂ to go through the membrane more rapidly than the other elements in the mixed gas. Consequently, the gas coming out the other side of the membrane consists of a greater amount of CO₂ than the gas going into the membrane. By trapping the gas coming out of the membrane, more of the CO₂ is captured compared to the other constituent gases.

An enduring challenge for these membranes has been a compromise between selectivity and permeability. The higher the permeability, the more rapidly gas can be moved via the membrane.

However, when permeability increases, selectivity decreases — meaning that nitrogen, or other elements, also go through the membrane rapidly — decreasing the ratio of CO₂ to other elements in the mixture. Simply put, when selectivity decreases, relatively less CO₂ is captured.

Both the U.S. and Norway research teams aimed to resolve this issue by growing chemically active polymer chains that are both CO₂-philic and hydrophilic on the surface of current membranes. This boosts CO₂ selectivity and causes a comparatively minimal reduction in permeability.

In short, with little change in permeability, we’ve demonstrated that we can increase selectivity by as much as about 150 times. So we’re capturing much more CO2, relative to the other species in gas mixtures.

Marius Sandru, Study Co-Corresponding Author and Senior Research Scientist, SINTEF Industry, Norway

Another hurdle to overcome regarding the membrane CO₂ filters has been the cost. The more functional earlier membrane technologies were, the more costly they were likely to be.

Because we wanted to create a technology that is commercially viable, our technology started with membranes that are already in widespread use. We then engineered the surface of these membranes to improve selectivity. And while this does increase the cost, we think the modified membranes will still be cost-effective.

Rich Spontak, Study Co-Corresponding Author and Distinguished Professor of Chemical and Biomolecular Engineering, North Carolina State University

“Our next steps are to see the extent to which the techniques we developed here could be applied to other polymers to get comparable, or even superior, results; and to upscale the nanofabrication process,” Sandru states. “Honestly, even though the results here have been nothing short of exciting, we haven’t tried to optimize this modification process yet. Our paper reports proof-of-concept results.”

The scientists are also keen to investigate other applications, like whether the new membrane technology could be applied in biomedical filtration devices or ventilator devices in the aquaculture sector.

The scientists are open to partnering with industry players in checking out any of these opportunities or questions to help alleviate global climate change and enhance device function.

An article on the study is reported in the journal Science. It was co-authored by Wade Ingram, a former Ph.D. student at NC State; Eugenia Sandru and Per Stenstad of SINTEF Industry; and Jing Deng and Liyuan Deng of the Norwegian University of Science and Technology.

The study was carried out with support from the Research Council of Norway; UEFSCDI Romania; the National Science Foundation, under grant number ECCS-2025064; and Kraton Corporation.

Journal Reference:

Sandru, M., et al. (2022) An Integrated Materials Approach to Ultrapermeable and Ultraselective CO₂ Polymer Membranes. Science. doi.org/10.1126/science.abj9351.