(225b) CaO-based Sorbents for High-temperature CO2 Capture

To mitigate the global warming issue, worldwide efforts have been made to reduce emission of CO₂ from fossil fuel combustion in power plants and various chemical industries. In recent years, calcium looping (CaL) technology has emerged as an effective way for post-combustion CO₂ capture. The performance of CaO-based high-temperature CO₂ sorbent is well-known to be critical for the process efficiency of CaL technology. For practical application of CaO-based sorbents, this study deals with (i) enhancement of CO₂ sorption performance of CaO and (ii) its long-term operation (cyclic stability), and (iii) reactivation after cyclic usage. CaO-based sorbents with world-best performance was successfully developed via tailoring physicochemical properties using various synthesis methods. Although the high CO₂ uptake was achieved, major drawback of CaO, rapid deactivation of CO₂ sorption performance of CaO with cyclic usage, was unavoidable. Low cyclic stability of CaO is due to low thermal stability of CaCO₃, and for this reason, a small amount of thermally stable ZrO₂ was added to CaO using the citrate sol-gel method. The citrate sol-gel method induced chemically attached Zr on the surface of CaO as tiny grain-like particles, resulting in effective enhancement of cyclic sorption performance. Although deactivation of CaO-based sorbents was noticeably delayed by Zr, perfect prevention from deactivation was impossible. This led to the second issue: to develop reactivation process after cyclic usage of CaO. Particle-size-dependency of CaO on CO₂ sorption uptake was used to physically reactivate the cycled sorbent by reducing the size of CaO particle aggregated after cyclic usage. The lost CO₂ sorption uptake of the used CaO was successfully recovered through ball-milling. The CaO-based sorbents with high CO₂ sorption uptake and good cyclic stability as well as newly suggested reactivation procedure are highly meaningful, considering practical application to CaL process.