Sintering of calcium oxide (CaO) during CO2 chemisorption: a reactive molecular dynamics study

Reactive dynamics simulations with the reactive force field (ReaxFF) were performed in NVE ensembles to study the sintering of two solid calcium oxide (CaO) particles with and without CO2 chemisorption. The simulated sintering conditions included starting adsorption temperatures at 1000 K and 1500 K and particle separation distances of 0.3 and 0.5 nm. The results revealed that the expansion of sorbent particles during CO2 chemisorption was attributed to the sintering of two CaO-CaO particles. Increasing the adsorption temperature resulted in more particle expansion and sintering. The shorter the distance between two particles, the faster the rate of sintering during CO2 adsorption. A detailed analysis on atom spatial variations revealed that the sorbent particles with a larger separation distance had a larger CO2 uptake because of less sintering incurred. The chemisorptions of CO2 on CaO particles sintered at high adsorption temperatures were also simulated to mimic the process of sorbent regeneration. It was found that regeneration would be more difficult for sintered particles than for fresh particles. In addition, a possible sintering barrier, magnesium oxide (MgO), was introduced to prevent CaO particles from sintering during CO2 chemisorption. It was found that the MgO particles could reduce the sintering of CaO particles during CO2 chemisorption. Simulation results from this study provided some guidelines on synthesizing or selecting sorbents with less sintering effect for multiple CO2 adsorption-regeneration cycles.