Understanding CuSO₄·5H₂O conversion behavior relevant to continuously operated three-phase suspension reactor conditions

Abstract

Thermochemical energy storage has a very high potential to significantly decrease greenhouse gases using seasonal heat storage for heating applications. The conversion behavior of the thermochemical energy-carrier system CuSO₄·5H₂O was investigated relevant to continuously operated 3-phase suspension reactor conditions. The temperature in the reactor was measured continuously, and samples were taken periodically and analyzed with XRD, which revealed conversions of up to 95 % from CuSO₄·5H₂O to CuSO₄·H₂O. Investigating single particles in oil under the microscope while heating them up showed that the dehydration reaction is strongly dependent on the heating rate. Reaction temperatures from CuSO₄·5H₂O to CuSO₄·3H₂O started already at 87 °C and from CuSO₄·3H₂O to CuSO₄∙H₂O at 118 °C. In-situ XRD shows the mechanism of the reaction from CuSO₄·5H₂O to CuSO₄∙H₂O, where the intermediate phase CuSO₄·3H₂O is formed, starting at 30 °C. Furthermore, in-line IR spectroscopy, which allows instantaneous live tracking of the conversion, not only confirms the results obtained from in-situ XRD but also proves useful as a tool for process monitoring and control. The CuSO₄ particles have been analyzed with SEM, showing the change of structure and shape of the used CuSO₄ particles in contrast to the original CuSO₄ particles, where the used CuSO₄ particles break into smaller particles but form small agglomerates of an average of 3.5 mm in diameter. The specific surface area measured by BET shows that the specific surface area of the used CuSO₄ particles was reduced by a factor of 3.6, but no loss in performance was observed.