Understanding the kinetics of CO2 capture and regeneration by CaO sorbents over extended cycles

The practical application of CaO-based sorbents for high-temperature CO2 capture is limited by a lack of understanding of their kinetic evolution over repeated cycles. CaO-based solid adsorbents have emerged as promising candidates for high-temperature CO2 capture due to their high adsorption capacity, reactivity, regenerability, and cost-effectiveness. This study investigates the performance of CaO for CO2 adsorption and subsequent H2 regeneration over 25 calcium looping cycles at 873 K, 923 K, and 973 K. Thermogravimetric analysis was employed to evaluate the reaction conversion of fresh and used CaO/CaCO3 under cyclic conditions. Kinetic parameters were determined using both kinetic model fitting and model-free methods, with strong consistency observed between the two approaches. The Avrami-Erofey'ev second-order model was optimal for both fresh and used CaO, demonstrating mechanistic stability. A key finding is that the activation energy for CO2 adsorption on used CaO was approximately 1.6 times of fresh CaO (1.25 × 108 vs. 7.93 × 107 J/kmol), indicating an enhanced spontaneous nature after cycling. Conversely, regeneration activation energies for fresh and used CaCO3 were similar, underscoring the sorbent's robust regenerability. The strong agreement between different kinetic methods confirms the reliability of our analysis. This work provides crucial kinetic parameters and mechanistic insights into the evolution of sorbent reactivity over cycles, which are essential for designing efficient and durable CaO-based carbon capture systems. This work provides crucial kinetic parameters and mechanistic insights into the evolution of sorbent reactivity over cycles, which are essential for designing efficient and durable CaO-based carbon capture systems.