Researchers have developed a new membrane technology that allows for more efficient removal of carbon dioxide (CO2) from mixed gases, such as 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,” says Rich Spontak, co-corresponding author of a paper on the work. “And 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,” says Spontak, who is a Distinguished Professor of Chemical and Biomolecular Engineering and Professor of Materials Science & Engineering at North Carolina State University. “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.”
Membranes are an attractive technology for removing CO2 from mixed gases because they do not take up much physical space, they can be made in a wide variety of sizes, and they can be easily replaced. The other technology that is often used for CO2 removal is chemical absorption, which involves bubbling mixed gases through a column that contains a liquid amine – which removes CO2 from the gas. However, absorption technologies have a significantly larger footprint, and liquid amines tend to be toxic and corrosive.
These membrane filters work by allowing CO2 to pass through the membrane more quickly than the other constituents in the mixed gas. As a result, the gas passing out the other side of the membrane has a higher proportion of CO2 than the gas entering the membrane. By capturing the gas passing out of the membrane, you capture more of the CO2 than you do of the other constituent gases.
A longstanding challenge for such membranes has been a trade-off between permeability and selectivity. The higher the permeability, the more quickly you can move gas