Facile reactivation of used CaO-based CO₂ sorbent via physical treatment: Critical relationship between particle size and CO₂ sorption performance

Herein we report a new and facile mechanical approach for maximizing the CO₂ sorption performance of CaO sorbents, and also for recovering the sorption performance of the used (or deactivated) sorbent. We compared the physicochemical properties of CaO-based sorbents, which could change depending on their preparation methods, and determined that the CaO particle size was the most critical factor that affected their CO₂ sorption performance. The CO₂ sorption performance of CaO-based sorbents could be maximized via the simple physical reduction of their particle size, and this was experimentally demonstrated using ball-milling. The CO₂ sorption uptake of CaO prepared using the conventional solid-state method was significantly increased to the highest ever reported level after ball-milling, and it reached 98.0% of the theoretical maximum CO₂ sorption capacity. The most important application of the particle-size-dependency of CaO-based sorbents on their CO₂ sorption uptake is the reactivation of used sorbents via reducing the size of the aggregated or sintered bulky particles that form after cyclic usage. The CO₂ sorption uptake of the used CaO (~32.9 wt% after 10 alternative sorption–regeneration cycles) was successfully recovered (almost doubled) to ~64.7 wt% after ball-milling. This is the first time a facile mechanical-grinding-based reactivation method, which appeared to be highly efficient and directly applicable to the continuous calcium looping technology, has been developed and used.