Researchers have developed a new membrane technology for more effective and efficient removal of carbon dioxide (CO2) from mixed gases, such as power plant emissions. "We looked at CO2/nitrogen dioxide mixtures to demonstrate the capability of our new membranes 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.
"We've also shown that we can vastly improve membrane selectivity to remove CO2 while retaining relatively high CO2 permeability."
"We also looked at CO2 and methane mixtures, which is important in the natural gas industry," says Spontak, Distinguished Professor of Chemical and Biomolecular Engineering and Professor of Materials Science and Engineering at North Carolina State University.
"Additionally, these CO2-filtering membranes can be used in any situation where CO2 must be removed from mixed gases, such as a biomedical application or scrubbing CO2 from the air in a submarine."
Membranes- An Appealing Tech
Membranes are an interesting technology for removing CO2 from mixed gases because they take up little physical space, can be manufactured in a variety of sizes, and can be easily replaced. Chemical absorption is another method of CO2 removal that is commonly used. This method involves bubbling mixed gases through a column containing a liquid amine, which removes CO2 from the gas. However, absorption technologies have a much larger environmental footprint, and liquid amines are toxic and corrosive.
These membrane filters function by allowing CO2 to pass through the membrane faster than the other components of the mixed gas. As a result, the gas exiting the membrane contains a higher proportion of CO2 than the gas entering the membrane. By capturing the gas that passes through the membrane, you capture more CO2 than the other constituent gases.
The trade-off between permeability and selectivity has long been a challenge for such membranes. The higher the permeability, the faster gas can pass through the membrane. However, as permeability increases, selectivity decreases, which means that nitrogen or other constituents pass quickly through the membrane, reducing the ratio of CO2 to other gases in the mixture. In other words, as selectivity decreases, you capture less CO2.
"In short, we've demonstrated that with little change in permeability, we can increase selectivity by up to 150 times," says Marius Sandru, co-corresponding author of the paper and senior research scientist at SINTEF Industry, an independent research organization in Norway. "As a result, we're capturing much more CO2 than the other species in gas mixtures."
The researchers are also interested in investigating other applications, such as whether the new membrane technology could be used in biomedical ventilator devices or aquaculture filtration devices. The researchers say they are willing to collaborate with industry partners to investigate any of these questions or opportunities to help mitigate global climate change and improve device functionality.
