Suitability of copper sulphate pentahydrate for thermochemical energy storage in a suspension reactor

Abstract

This study investigates the performance of copper sulphate pentahydrate in the context of thermochemical energy storage in a three-phase suspension reactor using oil as the inert suspension medium. The suspension approach aims to overcome common limitations of the salt hydrate, such as poor heat transfer, slow hydration, and poor cycle stability over several dehydration-hydration cycles by avoiding agglomeration and employing liquid water for hydration. Suspension density measurements show that suspensions with up to 30 wt% oil maintain comparable volumetric energy densities (~1 GJ m⁻³) to bulk salt, despite oil dilution. Dehydration rates reach up to 1.7·10⁻³s⁻¹ at 130 °C, and flash dehydration achieves over 98.66 ± 0.19 % conversion within 5 min, confirming fast reaction kinetics under optimal heat input. Cycle stability is demonstrated over 30 dehydration-hydration cycles in a mineral‑silicone oil mixture and 15 cycles in high-oleic sunflower oil, with minimal performance loss and final hydration levels of 99.25 ± 0.11 % after 30 runs. In contrast, rapeseed oil degraded quickly in only 10 cycles, limiting its suitability and highlighting the importance of a high oleic acid content for thermal stability. Temperature lifts of up to 17.7 ± 0.2 K are recorded during hydration in the batch reactor, while insulated tests at higher salt content achieve up to 66.5 ± 0.3 K (at 60 wt% salt). Overall, CuSO₄·5H₂O in an oil-based suspension shows a promising performance in terms of reaction rate, temperature lift, and cycle stability, making it a viable candidate for thermochemical energy storage in the temperature range of 90–145 °C in the suspension reactor.