Developing High-Capacity Solid "Molecular Basket" Sorbents for Selective CO 2 Capture and Separation.

ConspectusSince carbon-based energy continues to dominate (over 80%) the global primary energy supply, carbon dioxide capture, utilization, and sequestration (CCUS) is deemed to be a promising and viable option to mitigate greenhouse gas emissions and climate change, for which CO 2 capture is critical to the overall success of CCUS. Although liquid amine scrubbing is a mature technology for carbon capture, it is energy-intensive and costly due to energy consumption in solvent heating and water evaporation apart from the energy needed to break amine-CO 2 bonding. To address this challenge, Song's group developed a new design approach for adsorptive CO 2 capture and separation, namely, "molecular basket" sorbents (MBS), without the need for dealing with solvent heating and water evaporation. The solid MBS consisting of polymeric amines (such as PEI) immobilized into nanoporous materials (such as SBA-15) possesses a high capacity for CO 2 capture with high selectivity, fast kinetics, and good regenerability. Consequently, MBS can greatly reduce energy consumption and carbon capture cost. Conventional adsorbents such as zeolites, activated carbon, alumina, and silica have low adsorption capacities, and their use of CO 2 adsorption requires prior removal of moisture and cooling of flue gas (∼35 °C). On the contrast, the CO 2 sorption capacity of MBS can even be promoted by the presence of moisture/steam and reaches the best performance closer to flue gas temperature (∼75 °C). This Account presents an overview of our research progress in the material development and fundamental understanding of MBS for CO 2 capture and the separation of CO 2 from various gas streams. It begins with an illustration of the MBS concept, followed by efforts to improve the performance and pilot-scale demonstration of MBS for CO 2 capture. With the systematic characterization of MBS by various ex situ and in situ techniques, a better understanding is developed for the CO 2 sorption process mechanistically. Furthermore, this Account demonstrates how the fundamental understanding of the CO 2 sorption mechanism promotes the further development of more robust and advanced sorbent materials with improved CO 2 sorption capacity, kinetics of sorption and desorption, and cyclic stability. Finally, an outlook is provided for the future design and development of novel sorbent materials and the CO 2 sorption process for various gas streams including flue gas, biogas, air, and hydrogen streams.