Hydrolysis behavior and thermo-physical performance of KCl-MgCl2 salts based on MgCl2·6H2O

Abstract

KCl-MgCl2 eutectic salts prepared using anhydrous MgCl2 have been considered as a candidate heat transfer and storage fluid for the Gen3 concentrated solar power due to the wide service temperature range. However, the preparation of anhydrous MgCl2 from MgCl2·6H2O is complicated and challenging. In order to prepare KCl-MgCl2 eutectic salts using MgCl2·6H2O instead of anhydrous MgCl2, the hydrolysis behaviors of the KCl/MgCl2·6H2O mixtures with different proportions were investigated by differential scanning calorimetry. The pyrolysis behavior changed obviously compared with that for single MgCl2·6H2O due to the interaction between KCl and MgCl2 to form K2MgCl4 at high temperature. The formation of K2MgCl4 prevented the decomposition to MgO. KCl-MgCl2 eutectic salts were firstly obtained using MgCl2·6H2O instead of anhydrous MgCl2 by regulating the temperature and composition. The melting point of the KCl-MgCl2 eutectic salts based the MgCl2·6H2O was 424.9 °C and the fusion enthalpy was up to 170.5 J/g. The specific heat, density and viscosity average value were 1.30 J/(g·K), 1.64 g/cm−3 and 1.78 mPa·s, respectively. The good thermo-physical performances were expected to be the candidate fluid for energy storage. This work explored a simple way to prepare KCl-MgCl2 eutectic salts at lower cost. The promising economical cost would promote the application of KCl-MgCl2 salts in the concentrated solar power plant. It is expected that the findings pave paths for preparing MgCl2-based molten salts based on MgCl2·6H2O.