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

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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.