Reversible formation of alcohol solvates and their potential use for heat storage

Abstract

In this study, CaCl2- and MgCl2–alcohol solvates of different stoichiometric quantities of ethyl alcohol (EtOH) and methyl alcohol (MeOH) were synthesized and characterized via coupled thermogravimetric–differential scanning calorimetry, thermogravimetric–mass spectrometric evolved gas analysis (TG-MS), spectroscopic analysis (Raman) methods as well as by X-ray diffraction. Correlations between the obtained calorimetric, thermodynamic, kinetic, and crystallographic data were carried out. The CaCl2–alcohol systems seem suitable for heat storage based on the feasible recovery of the salt. However, Raman spectroscopic results revealed that the MgCl2–EtOH solvates were instable compounds. Irreversible transformation of MgCl2–alcohol solvates related to the formation of alkyl chloride appeared upon heating, as proven by TG-MS and Raman spectroscopic measurements. Pure salt–alcohol solvates could not be prepared under technically applicable conditions. The samples contained at least traces of water. Appearance of side reactions resulting in magnesium oxychlorides, oxyhydroxides, and possible release of HCl with cycling may contribute to corrosion of reactor components. Based on these considerations, MgCl2–alcohol solvate systems are not recommended for heat storage.