A team of researchers from North Carolina State University, SINTEF in Norway and the Norwegian University of Science and Technology, has developed a polymer membrane technology that removes carbon dioxide from mixed gases with both high permeability and high selectivity. A paper on their work is published in the journal Science.

We introduce a hybrid-integrated membrane strategy wherein a high-permeability thin film is chemically functionalized with a patchy CO₂-philic grafted chain surface layer. A high-solubility mechanism enriches the concentration of CO₂ in the surface layer hydrated by water vapor naturally present in target gas streams, followed by fast CO₂ transport through a highly permeable (but low-selectivity) polymer substrate. Analytical methods confirm the existence of an amine surface layer. Integrated multilayer membranes prepared in this way are not diffusion limited and retain much of their high CO₂ permeability, and their CO₂ selectivity is concurrently increased in some cases by more than ~150-fold.

—Sandru et al.

Polymer membranes for gas separation face a tradeoff between permeability—i.e., how fast gases can flow through the membrane—and selectivity—i.e., the ability to separate one gas from another. In general, the more selective the membrane, the more slowly gases can flow through it.

The researchers overcame this tradeoff through a layered design. A bottom layer of porous polyacrylonitrile acts as a physical support for the middle layer of either elastomer-like polydimethylsiloxane or glassy-type polytetrafluoroethylene.

The researchers then grafted a patchy layer of polyamine, which selectively attracts carbon dioxide, thus pulling it into the membrane and leading to much higher separation from nitrogen. The technology could play a role in reducing power plant emissions.

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 reducing greenhouse gas emissions from power plants. We've demonstrated that we can vastly improve the selectivity of membranes to remove CO₂ while retaining relatively high CO₂ permeability.

We also looked at mixtures of CO₂ and methane, which is important to the natural gas industry. 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.

—Rich Spontak, co-corresponding author of the study

The selectively permeable membrane works by filtering CO₂ faster than other mixed gases.

The technology started with membranes that are already in widespread use. The researchers then engineered the surfaces of the membranes to improve selectivity.

Our next steps are to see how these techniques could be applied to other polymers to get comparable, or even superior, results, and to upscale the nanofabrication process.

—co-corresponding author Marius Sandru

The researchers plan to investigate potential applications for the polymer, including use in ventilation and filtration devices and climate change mitigation.

Separately, in March, Aker Carbon Capture and SINTEF have entered into a strategic collaboration agreement, with the goal of further developing carbon capture utilization and storage (CCUS) technology to reduce CO2 emissions from industry and energy solutions. This is a vital part of the green transition in Norway.

Resources

• Marius Sandru et al. (2022) “An integrated materials approach to ultrapermeable and ultraselective CO2 polymer membranes” Science doi: 10.1126/science.abj9351