Absorption Kinetic Behaviors Of K-doped Li₄SiO₄ Under Low CO₂ Concentrations And The Macrostructure Investigations During The Absorption Process

The prepared K-doped Li4SiO4 by solid state reaction were characterized by SEM, XRD and BET. The thermodynamic behaviors and absorption capacity under low CO2 partial pressure of the prepared sample were investigated by thermogravimetric analysis. The results show that the doption of potassium can enhance the absorption equilibrium temperature of Li4SiO4 slightly and decrease its starting absorption temperature which can also broaden the absorption temperature range of the Li4SiO4 sorbents under low CO2 concentrations. It can also enhance the absorption ability of Li4SiO4 largely especially when the absorption temperature is over 575℃. It was because there are plenty of lithium potassium carbonate(KLiCO3) formed by Li2CO3 and Li2SiO3 at and beyond such temperature. Avrami-Erofeev model was applied to study the absorption bahaviors of K-doped Li4SiO4 under 5%-20% CO2 concentration atmosphere.Two different Avrami-Erofeev models were obtained to fit the data at the temperatures below and beyond 600℃ respectively. The Ea of the latter was slightly smaller than that of the former which is attributed to the formation of KLiCO3. Jander model and parabolic model were used to study the macrostructure change during the absorption process. The results show that the Jander model can fit the data of the first 5min of the reaction well while the parabolic model can fit the data of the last 30min of the reaction well. According to the assumption of the models, the reaction structure was sephere at the first 5min and an platform during the last 30min.The period which cannot be fitted by Jander model nor parabolic model was assumed to be the adsorbent’s structure might be a combination of sephere and platform status. The Ea calculated by Jander model was slightly lower than that of the parabolic model which indicate that sinterting of Li2CO3 and made the absorption process more difficult to go through.