Modification of magnesium and calcium hydroxides with salts: An efficient way to advanced materials for storage of middle-temperature heat

• Effect of salt additives on dehydration of Mg(OH)2 and Ca(OH)2 was studied.
• The tested salts were chlorides, nitrates, sulphates and acetates of alkali metals.
• Better dehydration dynamics and variable dehydration temperature were reached.
• LiNO3 was found to decrease the dehydration temperature of Mg(OH)2 by c.a. 80 °C.
• KNO3 was found to decrease the dehydration temperature of Ca(OH)2 by c.a. 40 °C.

Thermochemical heat storage can greatly contribute to higher efficiency of numerous industrial processes and units, especially based on renewable energy sources and/or polygeneration systems. Pure magnesium and calcium hydroxides are convenient materials for storage of middle temperature heat (250–500 °C), however, both suffer from kinetic impediments. In this work, we studied the doping effect of various salts in order to affect the dehydration dynamics of these hydroxides. The screening among the selected classes of salts, namely, chlorides, nitrates, sulphates and acetates of alkaline metals, showed a valuable possibility to a) improve the dehydration dynamics, and b) manage the dehydration temperature. Variation of the dehydration temperature was shown to depend on the salt nature and content. A strong effect of nitrates and acetates on the dehydration rate of both hydroxides was revealed. LiNO3 and XOOCCH3 (X = Li, Na, K) diminished the dehydration temperature of Mg(OH)2 by 50–80 K. Alike, though weaker, effect was found for Ca(OH)2 doped with KNO3 (c.a. 40 K). The modification with salts is proven to be a promising way to get new advanced hydroxide-based materials for middle temperature heat storage with enhanced and controllable dehydration reactivity.