Reaction of Calcium Chloride and Magnesium Chloride and their Mixed Salts with Ethanol for Thermal Energy Storage

The use of thermochemical energy storage systems increasingly gains interest in order to meet the energy targets of the European renewable energy directive. In this study the suitability of calcium chloride, magnesium chloride and mixed salt ethanolates as heat storage materials for practical implementation was determined by investigating specific thermodynamic properties and estimating the materials’ lifetime at various operating conditions. It was proven that the reaction of the before mentioned metal salts with ethanol depends on the applied ethanol vapour pressure. The ethanol sorption increased in the following order: MgCl2 < CaCl2 < 2CaCl2*MgCl2. The enthalpies followed the same sequence. Over-stoichiometric ethanol uptake, in particular for CaCl2 and 2CaCl2*MgCl2 with increasing C2H5OH vapour pressure, was observed. However, the reaction systems CaCl2-C2H5OH and 2CaCl2*MgCl2 -C2H5OH showed the best sorption properties and cycle stability and thus have a great potential for low-grade thermal energy storage as well as cold storage due to their low reaction temperatures in comparison with salt-water-systems. In general, physically mixing of single salts from the same family with different chemical properties leads to superior thermal behaviour with higher heat storage capacities and material stabilities.