Mass transfer enhanced CaO pellets for CO₂ sorption: Utilization of CO₂ emitted from CaCO₃ pellets during calcination

In the preparation of CaO-based CO₂ sorbents, particle densification during pelletization significantly limits the mass transfer of CO₂, thereby decreasing the CO₂ sorption performance. In this study, mass transfer enhanced CaO pellets (CaO–PC) were prepared through the formation of channels using CO₂ evacuation from the inside of the pellets. Calcination of CaCO₃ pellets induced CO₂ evacuation and the remaining evacuation pathways provided excellent mass transfer channels for CaO–PC. Conventional CaO pellets (CaO–CP) were also prepared for comparison. Unlike the severely agglomerated (or blocked) morphology of CaO–CP, well-developed channels were observed in CaO–PC. It was experimentally confirmed that these channels directly contributed to the initial stage of CO₂ sorption in CaO–PC, which significantly accelerated the CO₂ sorption kinetics. CaO–PC had increased CO₂ sorption uptakes of 58.9, 65.1, and 67.0 wt% at 500, 600, and 700 °C, respectively, whereas those for CaO–CP were 47.6, 55.4, and 56.8 wt%. In addition to CO₂ sorption, enhanced mass transfer had a positive effect on CO₂ release after capture. Under CO₂ flow, the regeneration of CaO–PC was faster than that of CaO–CP, even at lower temperatures. Both the fast CO₂ sorption and regeneration kinetics of CaO–PC significantly enhance the energy efficiency of continuous CO₂ capture processes. These improvements were accomplished easily without the need of any additional energy-consuming treatments other than the conventional preparation methods.