RECOVERY PROCESS OF CARBON DIOXIDE WITH METAL OXIDES AND METAL HYDROXIDES

摘要

Lithium silicate (Li_4SiO_4) and lithium zirconate (Li_2ZrO_3) absorb CO_2 in a lower temperature range andthe absorbed CO_2 is released reversibly in a higher temperature region. In this study, various metaloxides and hydroxides and their complex oxides containing Li were investigated for their CO_2 absorptionproperties 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 CO_2 absorptionto CO_2 release, are observed at around 973 K for Li_4SiO_4 and Li_2ZrO_3. The CO_2 absorption is basedon the formation of Li_2CO_3 through the decomposition of Li-containing complex oxides. From theexperimental results and thermodynamical calculations, it is noticed that CO_2 absorption takes placevery slowly in spite of large equilibrium constant in the lower temperature re gion below 873 K, whilethe absorption at 973 K happens quickly. When the absorption at 973 K and the release at 1273 Kare repeated five times for Li_4SiO_4, the material maintains its crystal structure to give CO_2 absorptionand release. On the other hand, CaO shows an inflection point at 1173 K in the TG curve. Magnesiumoxide and hydroxide do not react with CO_2 below 1273 K.