2007 Volume 48 Issue 10 Pages 2739-2742
Lithium silicate (Li4SiO4) and lithium zirconate (Li2ZrO3) absorb CO2 in a lower temperature range and the absorbed CO2 is released reversibly in a higher temperature region. In this study, various metal oxides and hydroxides and their complex oxides containing Li were investigated for their CO2 absorption properties at different temperatures in order to get better understanding of the related mechanism.
The inflection points in the TG curves, at which predominant reaction changes from CO2 absorption to CO2 release, are observed at around 973 K for Li4SiO4 and Li2ZrO3. The CO2 absorption is based on the formation of Li2CO3 through the decomposition of Li-containing complex oxides. From the experimental results and thermodynamical calculations, it is noticed that CO2 absorption takes place very slowly in spite of large equilibrium constant in the lower temperature region below 873 K, while the absorption at 973 K happens quickly. When the absorption at 973 K and the release at 1273 K are repeated 5 times for Li4SiO4, the material maintains its crystal structure to give CO2 absorption and release. On the other hand, CaO shows an inflection point at 1173 K in the TG curve. Magnesium oxide and hydroxide do not react with CO2 below 1273 K.