Promotion of MgO sorbents with eutectic carbonate doping for high-temperature and pressure CO2 capture

MgO-based sorbents are promising candidates for CO2 capture as they are widely available and feasible in thermodynamics, but the development of MgO-based sorbents operating at elevated temperature and pressure is still a challenging task due to sintering. Herein, we selected eutectic carbonates with high melting point as promoters for the application under elevated conditions. Among various eutectic carbonates, MgO with eutectic ternary LiNaK carbonate (ETC) doping exhibited the highest MgO conversion thanks to crystal defects based on the XRD analysis. The highest CO2 capture capacity of 0.73 gCO2/gsorbent was obtained with 20 wt% ETC at 400 degrees C and 2 MPa. With further elevation of operating parameters to 540 degrees C and 5 MPa, the sample still shows a stable MgO conversion of 0.69 after 30 cycles, where the material exhibits a porous structure that inhibits the sintering. The density function theory calculations reveal that the LiNaK doping lowers the formation energy of surface oxygen vacancy, providing possibility for the subsequent oxygen ion migration. The deep K incorporation is most effective to promote the oxygen ion diffusion with decreased oxygen ion migration energy barrier from 3.68 to 2.04 eV. This study can guide the design of high-performance CO2 sorbents at wider application conditions.

Automated summary

This study investigates the use of eutectic carbonates as promoters for MgO-based sorbents operating at elevated temperature and pressure. The results show that MgO doped with eutectic ternary LiNaK carbonate exhibits the highest MgO conversion and CO2 capture capacity. The incorporation of alkali metal ions lowers the energy barrier for oxygen ion migration. This research provides guidance for the design of high-performance CO2 sorbents at wider application conditions.