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

Highlights • CuSO 4 ·5H 2 O is investigated in a continuously operated continuously stirred tank as thermochemical material. • Single particles have been investigated under the microscope. • In-situ XRD shows the mechanism of the reaction from CuSO 4 ·5H 2 O to CuSO 4 ·H 2 O. • In-line IR spectroscopy allows instantaneous live tracking of the conversion and can be used for process control and monitoring. • Scanning electron microscopy revealed a change of structure and shape of used CuSO 4 particles, which break into smaller particles but form small agglomerates. 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 CuSO 4 ·5H 2 O 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 CuSO 4 ·5H 2 O to CuSO 4 ·H 2 O. 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 CuSO 4 ·5H 2 O to CuSO 4 ·3H 2 O started already at 87 °C and from CuSO 4 ·3H 2 O to CuSO 4 ∙H 2 O at 118 °C. In-situ XRD shows the mechanism of the reaction from CuSO 4 ·5H 2 O to CuSO 4 ∙H 2 O, where the intermediate phase CuSO 4 ·3H 2 O 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 CuSO 4 particles have been analyzed with SEM, showing the change of structure and shape of the used CuSO 4 particles in contrast to the original CuSO 4 particles, where the used CuSO 4 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 CuSO 4 particles was reduced by a factor of 3.6, but no loss in performance was observed.