Heats of water sorption studies on zeolite–MgSO4 composites as potential thermochemical heat storage materials

The use of magnesium sulphate as a means for long term heat storage, offers a compact, clean, and cheap way of storing solar energy during the summer season, and due to its high energy storage density, is a superior candidate for chemical heat storage. The impregnation of MgSO4 in a highly porous host provides a variety of enhancements, particularly offering a large absorption surface area available for MgSO4 and H2O molecules. Four series of wide pore zeolite composite materials containing varying quantities of MgSO4 (from 5 to 15 wt%) have been prepared and characterized. Heats of sorption/desorption cycles were recorded using thermogravimetry coupled to differential scanning calorimetry (TG-DSC). Zeolites Na–X, Mordenite and Y (Na and H) were selected, with the aim of impregnating the highest quantity of MgSO4, whilst achieving the highest heat release/store possible. Zeolites Na–Y and H–Y composites containing 15 wt% MgSO4 achieved the highest heats of hydration (1090 and 867 J g−1 sample, respectively) compared to zeolite Na–X and Mordenite composites containing 15 wt% MgSO4 (731 and 507 J g−1, respectively) and was attributed to the retention of the high surface area and pore volume of the host zeolite.