Microtubes made of carbon nanotube hybrid materials for CO$_{2}$ separation

Keller, Laura; Wessling, Matthias (Thesis advisor); Lively, Ryan P. (Thesis advisor)

Aachen (2020)
Dissertation / PhD Thesis


Despite political efforts, carbon dioxide emissions continue to increase on a global scale. Among the many discussed measures to combat climate change, carbon capture receives considerable attention as a technological cornerstone to limit anthropogenic warming to 1.5 °C. Adsorption is a promising means for CO2 separation from flue gases or the air. Tubular sorbents aim to overcome drawbacks of conventional packed bed adsorption columns such as high pressure drops or channeling and dead-spacing. So far, they are made of a polymeric matrix that is enhanced with different highly sorbing materials. In this thesis, hollow fibers made of carbon nanotubes (CNT) replace the polymeric matrix. Compared to many polymers, CNTs are thermally and chemically more stable, offer a higher specific surface area, and are thermally more conductive. Different hollow fibers were developed, characterized, and examined with respect to their aptitude as solid sorbents. Pure CNT microtubes and hybrid microtubes with embedded silica particles were impregnated with a polymeric amine. Both fiber types showed similar CO2 uptake capacities. Regeneration through temperature swing was feasible and yielded promising working capacities. The formation of a polymeric, gastight layer on the shell side was successful, which enables isothermal operation with these fibers in the future. Furthermore, hybrid microtubes containing CNTs and zeolites were produced. These exhibited high CO2 uptakes and regenerability through both pressure and temperature swing. Pressure swing adsorption was tested with a prototype module capable of isothermal operation. Since the fibers are conductive, temperature swing can be implemented by using the Joule effect: the fibers are directly heated through an applied electrical current. Thus, the cycle times for a TSA process can be reduced from several hours to several minutes. Experiments with a prototype module revealed the applicability of the CNT-zeolite microtubes for an electrical swing adsorption process. Additional modeling proved promising CO2 purities and recoveries for such a process. CNT microtubes enhanced with CO2 sorbing materials are a favorable possibility to capture CO2 from flue gases or the air. The results obtained with prototype modules emphasize their aptitude for both pressure and temperature / electrical swing adsorption processes. They can be specifically tailored to any sorption task by using new material combinations and adopted for any sorption process with its specific requirements. With this thesis, a platform that can serve a multitude of gas separation challenges was created.