Absorption Behaviors And Kinetic Models Analysis Of Li₄SiO₄under Various CO₂Partial Pressures

One key point of sorption-enhanced steam methane reforming (SE-SMR) technology was to choose suitable CO2sorbent. Compared with other sorbents, Li4SiC>4was considered to be a promising CO2sorbent due to its wide operating temperature range, large absorption capacity, low desorption temperature and stable sorption/desorption cycle performance.In the real SE-SMR system, the CO2partial pressure was below20%with a certain amount of steam, however, up to now, most investigations of Li4SiO4sorbent were conducted under pure CO2atmosphere, and the kinetic research of Li4SiO4sorbent under various CO2partial pressure was rarely reported.In this work, the absorption behaviors of Li4SiO4were synthetically investigated under various CO2partial pressures, different temperatures and steam partial pressures. The results showed that the sorption capacity of Li4SiO4increased with CO2partial pressure increasing. The addition of steam was proved to enhances the sorption capacity of Li4SiO4. Meanwhile, after10sorption/desorption cycles, the Li4SiO4sorbent showed a satisfied sorption stability. It was also noted that Li4SiC>4displayed weaker adsorption capacity at higher temperatures (>525℃) under5%CO2partial pressure. For seeking an explanation, the thermodynamics of Li4SiO4under various CO2was calculated by FactSage software, and the results showed that the adsorption equilibrium temperature of Li4SiO4increased with temperature increasing and CO2partial pressure increasing. Furthermore, once the experimental temperature exceeded adsorption equilibrium temperature, Li4SiO4couldn’t adsorb CO2any more in theory, thus, Li4SiO4presented bad adsorption capacity at high temperature with low CO2partial pressure.Based on the thermodynamical analyses, kinetic experiments were conducted under various CO2partial pressures and fitted by Jander model, the results showed that Jander model had a bad agreement with the kinetic data. Assuming that the distribution of CO2concentration was non-linear, the Jander model was analysed and modified based on double-shell mechanism, which was used to describe the CO2sorption mechanism on Li4SiO4. The results showed that the modified Jander model could fit well with the kinetic experimental data under various temperatures, CO2partial pressures and steam pressures. A temperature range of500-650℃and CO2partial pressure range of5%-100%were verified to be the applicative conditions of this modified Jander model, which consisted with the reaction conditions of sorption-enhanced methane steam reforming system. Meanwhile, the conversion function F(a) of this model and the reaction time t showed a straight line relationship, which not only avoided the necessary piecewise calculation of kinetic experimental data, but also be convenient to its application in reactor design.