Reaction Mechanism and Kinetics of the Sulfation of Li₄SiO₄ for High-Temperature CO₂ Adsorption

Abstract

CO2 adsorption is an important approach to control the excessive CO2 emission from energy and industrial plants and mitigating the greenhouse effect. As an acknowledged high-temperature adsorbent, Li4SiO4 shows advantages in capturing a large amount of CO2 with a fast reaction rate and excellent cyclic stability. However, its CO2 adsorption capacity would be significantly affected by the flue gas impurities, such as SO2 and O2. The underlying reaction mechanism of such impurities and Li4SiO4 is still unclear. For this reason, this work studied the reaction path and kinetics between Li4SiO4 and SO2 through experiments, thermodynamic calculations, and characterizations. The results showed that Li4SiO4 reacts with SO2 to produce Li2SiO3 and Li2SO4 in the presence of O2 at 500–700 °C and forms Li2SiO3 and Li2SO3 in the absence of O2 at 500–682 °C. Furthermore, this study revealed a very low activation energy of 7.47 kJ/mol for Li4SiO4 sulfation in the presence of O2 in the kinetic-controlled stage, and the value goes up to 249.7 kJ/mol in the diffusion-controlled stage. These results will provide valuable references for the industrial applications of CO2 adsorption by Li4SiO4.