Thermodynamics and kinetics analyses of high CO2 absorption properties of Li3NaSiO4 under various CO2 partial pressures

The properties of Li3NaSiO4 as a CO2 absorbent were evaluated by thermogravimetry (TG) and X-ray diffraction, which revealed that the CO2 absorption and desorption reaction, Li3NaSiO4 + CO2 <-> LiNaCO3 + Li2SiO3, is reversible. In scanning-type TG under various CO2 partial pressures (P(CO2)), mass gain ascribed to CO2 absorption started from approximately 400 degrees C, irrespective of P(CO2). CO2 desorption 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 Li3NaSiO4 and CO2, constructed using the obtained approximate equilibrium temperature under each P(CO2), showed similar behavior to that between Li4SiO4 and CO2, especially between 10(-2) and 10(-1) bar of P(CO2). Kinetics analysis by isothermal TG using the Jander model revealed that the reaction rate of CO2 absorption of Li3NaSiO4 was higher than that of Li4SiO4. The rate-determining step of CO2 absorption by Li3NaSiO4 was the diffusion process at the examined temperatures and P(CO2), which was different from the rate-determining step of the reaction between Li4SiO4 and CO2 under low P(CO2).