Saturday, December 9, 2023

Study indicates that carbon-capturing material could help industry reduce emissions and costs

Alberta’s world renown in carbon capture and sequestration is set to receive another lift thanks to the promise of a material invented and tested in the province that offers an efficient way to pull carbon dioxide out of industrial emissions. A team from the University of Alberta’s Faculty of Engineering characterized a CO2-capturing microporous material developed by a group led by George Shimizu at the University of Calgary that attracts gas molecules and sees them stick to its surface. The material, named Calgary framework-20 (CALF-20), belongs to a family of microporous solids called metal-organic frameworks. PhD student Tai Nguyen and Arvind Rajendran, associate professor in the U of A’s Department of Chemical and Materials Engineering, tested the capabilities of CALF-20 to uncover its unique properties that make it an excellent candidate for CO2 capture. Rajendran explained that the idea behind metal-organic frameworks has been around for decades after researchers began proving that a combination of metals and organic molecules, known as linkers, had the potential of concentrating gases from a mixture. In the case of CALF-20, a single gram has a surface area of more than 500 square metres. These materials can be packed in a column, much like a catalytic converter, and essentially fastened to the end of a smokestack. Rajendran likens the process that follows when the emissions are sent through the material to a group of people being sent through a shopping district. “You will start seeing that the people who don’t like to shop move ahead, whereas those who do will move slower,” he said. “Initially, the people who don’t like to shop come out first.” In cases where the emissions are made up of nitrogen and CO2, the nitrogen comes out first while the CO2 is left behind, adhering to the material. To move the CO2 along so the material can be reused, either the pressure in the column is brought down and the concentrated CO2 is vacuumed out, or the system is heated up using waste heat or steam. “When you provide heat, the CO2 is released and we can start collecting it in a more concentrated form than what you sent in,” Rajendran added. The problem with these materials, however, is that while they often work in the controlled confines of a lab, they don’t work in the presence of water or other impurities. That’s where Rajendran’s team stepped in. “The innovation in this material is that it can handle water nicely. This means you don’t have to dry your gas before you filter it through this material, which reduces the need for a whole bunch of energy,” he said. Another challenge for carbon-capturing materials is that even the tiniest quantities of emissions byproducts, such as sulfur dioxide and nitrous oxide, can kill the ability of these materials to capture CO2, Rajendran explained. “The big advantage in CALF-20 is that it works under practical conditions for thousands of hours, where almost all other previous developments did not,” he said. Once concentrated, the CO2 is either compressed and stored in geological formations, pushed back into old wells for enhanced oil recovery or converted back into fuel, such as methanol, to be used in the creation of other products. The research at the U of A was supported by an Alberta Innovates Strategic Research Program award and an NSERC CREATE grant. The study “A scalable metal-organic framework as a durable physisorbent for carbon dioxide capture” was published in Science.

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