Kinetics of carbon dioxide sorption on potassium-doped lithium zirconate

Potassium-doped lithium zirconate (Li₂ZrO₃) sorbents with similar crystallite but different aggregate sizes were prepared by a solid-state reaction method from mixtures of Li₂CO₃, K₂CO₃, and ZrO₂ of different particle sizes. Carbon dioxide sorption rate on the prepared Li₂ZrO₃ sorbents increases with decreasing sorbent aggregate size. It is the size of the aggregate, not the crystallite, of Li₂ZrO₃ that controls the sorption rate. Temperature effect on CO₂ sorption is complex, depending on both kinetic and thermodynamic factors. A mathematical model based on the double-shell sorption mechanism was established for CO₂ sorption kinetics and it can fit experimental data quite well. Above 500°C, the rate-limiting step of CO₂ sorption is the diffusion of oxygen ions through the ZrO₂ shell formed during the carbonation reaction. Oxygen ion conductivities in the ZrO₂ shell were obtained by regression of the experimental CO₂ uptake curves with the model and are consistent with the literature data.