Effect of Lithium Compound Addition on the Dehydration and Hydration of Calcium Hydroxide as a Chemical Heat Storage Material

Abstract

Many studies on calcium hydroxide [Ca(OH)2] as a chemical heat storage material have been conducted. Generally, calcium hydroxide undergoes a dehydration reaction (heat storage operation) efficiently at about 400 °C or higher. In this study, we aimed to lower the dehydration reaction temperature and increase the dehydration reaction rate to expand the applicability of calcium hydroxide as a chemical heat storage material. For the purpose of improving the dehydration reactivity, calcium hydroxide with added lithium compounds was prepared, and the dehydration/hydration reactivities were evaluated. From the results, it was confirmed that the addition of the lithium compounds lowered the dehydration reaction temperature of calcium hydroxide and enhanced the reaction rate. The dehydration reaction of Ca(OH)2 with Li compounds proceeded efficiently even at 350 °C, and the reversibility of the dehydration/hydration reaction was confirmed. The reason for the improvement of the calcium hydroxide dehydration reactivity upon the addition of a lithium compound was examined from the viewpoint of its crystal structure. It was presumed that when lithium ions enter the calcium hydroxide crystals, the crystals became fragile and the dehydration reaction was accelerated.