“We looked at CO2/nitrogen dioxide mixtures to illustrate the potential of our new membranes since CO2/nitrogen dioxide mixtures are especially relevant in the context of lowering greenhouse gas emissions from power plants,” explains Rich Spontak, co-corresponding author of a publication on the research. “We’ve also shown that we can greatly improve membrane selectivity for CO2 removal while keeping CO2 permeability reasonably high.”
“We also looked at CO2 and methane mixes, which are significant in the natural gas business,” adds Spontak, a Distinguished Professor of Chemical and Biomolecular Engineering and Professor of Materials Science and Engineering “In addition, these CO2-filtering membranes can be employed in any context in which one has to remove CO2 from mixed gases — whether it’s a biomedical application or scrubbing CO2 from the air in a submarine,” says a researcher at North Carolina State University.
Membranes are an appealing method for removing CO2 from mixed gases since they take up little physical area, can be produced in a range of sizes, and are simple to repair. Chemical absorption, which includes bubbling mixed gases through a column containing a liquid amine that removes CO2 from the gas, is another common method for CO2 removal. Absorption technologies, on the other hand, have a far bigger environmental imprint, because liquid amines are poisonous and corrosive.
CO2 passes through the membrane faster than the other constituents in the mixed gas; hence these membrane filters work. As a result, the CO2 content of the gas passing through the membrane is higher than that of the gas entering the membrane. You collect more CO2 than the other constituent gases by capturing the gas traveling through the membrane.
The trade-off between permeability and selectivity has been a long-standing issue for such membranes. The faster you can transfer gas through the membrane, the higher the permeability. However, as permeability increases, selectivity decreases, implying that nitrogen and other elements pass through the membrane more quickly, lowering the CO2-to-other gas ratios in the mixture. To put it another way, when selectivity decreases, CO2 capture decreases.
The researchers from the United States and Norway solved the challenge by developing chemically active polymer chains on the surface of existing membranes that are both hydrophilic and CO2-philic. This boosts CO2 selectivity while causing just a minor decrease in permeability.
“In summary, we’ve proved that we can boost selectivity by as much as 150 times with no change in permeability,” says Marius Sandru, co-corresponding author of the paper and senior research scientist at SINTEF Industry, a Norwegian independent research organization. “As a result, we’re trapping substantially more CO2 in gas mixtures than the other species.”
The cost of membrane CO2 filters has been another issue. Previous membrane technologies tended to be more expensive the more effective they were. “We started with membranes that are already in widespread
use because we wanted to create a commercially viable technology,” says Spontak. “We then improved selectivity by engineering the surface of these membranes.” Even if this raises the price, we believe modified membranes will still be cost-effective.”
“Our next steps are to investigate how well the techniques we discovered here can be applied to different polymers to achieve equivalent, if not better, outcomes,” Sandru says, “as well as to scale up the nanofabrication process.” “To be honest, despite the fact that the outcomes here have been nothing short of spectacular, we haven’t done anything yet.”
The researchers are also looking into other possibilities, such as whether the new membrane technology could be employed in biomedical ventilators or aquaculture filtration systems.
The researchers say they’re willing to collaborate with industry partners to investigate any of these topics or opportunities to assist minimize global climate change while also improving gadget performance.