The properties of Li3NaSiO4as a CO2absorbent were evaluated by thermogravimetry (TG) and X-ray diffraction, which revealed that the CO2absorption and desorption reaction, Li3NaSiO4+ CO2↔ LiNaCO3+ Li2SiO3, is reversible. In scanning-type TG under various CO2partial pressures (P(CO2)), mass gain ascribed to CO2absorption started from approximately 400 °C, irrespective ofP(CO2). CO2desorption was observed at a higher temperature, which was considered the approximate equilibrium temperature of the above-mentioned reaction. A pseudo-Ellingham diagram of the reaction between Li3NaSiO4and CO2, constructed using the obtained approximate equilibrium temperature under eachP(CO2), showed similar behavior to that between Li4SiO4and CO2, especially between 10−2and 10−1bar ofP(CO2). Kinetics analysis by isothermal TG using the Jander model revealed that the reaction rate of CO2absorption of Li3NaSiO4was higher than that of Li4SiO4. The rate-determining step of CO2absorption by Li3NaSiO4was the diffusion process at the examined temperatures andP(CO2), which was different from the rate-determining step of the reaction between Li4SiO4and CO2under lowP(CO2).
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