RESUMO
The temperature for realizing the cyclic CO2 absorption/desorption property of Li3NaSiO4 by repetition of switching a CO2/N2 gas mixture and N2 with a partial pressure of CO2, P(CO2), of 0.1 bar was optimized using the pseudo van't Hoff plot of LiNaCO3 + Li2SiO3 â Li3NaSiO4 + CO2 prepared by thermogravimetry at various P(CO2) values.
RESUMO
The starting materials and temperature for the preparation of Li3NaSiO4 powder, which has attracted attention as a CO2 absorbent, were optimized in this study. Mixtures of Li2CO3, Na2CO3, and SiO2 as well as Li4SiO4, Li2SiO3, and Na2CO3 were subjected to thermogravimetry-differential thermal analysis (TG-DTA) to elucidate their reaction mechanisms. The phase, morphology, specific surface area, and CO2 absorption characteristics of the powder specimens that were obtained by heating the two mixtures were examined by X-ray diffraction (XRD), secondary electron microscopy (SEM), N2 adsorption isotherm and isothermal TG-DTA. Melted LiNaCO3 was generated via the heat treatment of the Li2CO3, Na2CO3, and SiO2 powder mixture, yielding a low-purity bulk specimen with inhomogeneous particle size. However, the use of the Li4SiO4, Li2SiO3, and Na2CO3 mixture as a starting material ensured that no liquid phase was generated during heat treatment and successfully yielded Li3NaSiO4 powder which was purer than the product derived from the Li2CO3/Na2CO3/SiO2 mixture, presumably because of the lower volatility of Li and Na in the solid phase than that in the liquid phase of LiNaCO3. The Li3NaSiO4 powder derived from Li4SiO4, Li2SiO3, and Na2CO3 showed a slightly larger surface area with homogeneous particle size and almost identical CO2 absorption kinetics compared to those of the product obtained from Li2CO3, Na2CO3, and SiO2, in addition to absorbing a higher amount of CO2 owing to its higher purity.