Water sorption studies on ZnSO4-zeolite composite as potential thermochemical heat storage materials

ZnSO4 center dot 7H(2)O is modified by impregnation method with zeolite matrices (13X-zeolite and LTA-zeolite) to improve its hydration performance. Water sorption ability of composites was carried out in a constant temperature and humidity environment. Composite of ZnSO4/13X-zeolite showed highest water sorption (0.26 g/g) at 75% relative humidity under 45 degrees C air temperature, which is double than pure ZnSO4 center dot 7H(2)O. This is due to larger surface area (491 m(2) g(-1)) and pore volume (0.31 cm(3)). Furthermore, both hydration rate and adsorption mass depends on relative humidity and hydration temperature. However, if the air temperature and the relative humidity are higher than 45 degrees C and 75% RH, the hydration ability of the composite material is significantly reduced. Besides, X-ray measurements of composite (ZnSO4/13X) revealed that sorption/desorption process, crystallinity and phase of partially hydrated ZnSO4 remain the same, which enhance the adsorption mass and enthalpy during the hydration process.