Preparation and thermal properties of zeolite/MgSO4 composite sorption material for heat storage

Thermochemical sorption heat storage based on salt hydrates offers the potential advantages such as high energy density, negligible heat loss, small volume change and flexible working modes. Magnesium sulphate (MgSO4) is a high energy density hydrated salt available for the thermochemical sorption heat storage. In this work, different types of zeolites (including 3A, 5A and 13X zeolites) have been selected as mass-transfer-enhancing and structural stabilizing materials, and a series of zeolite/MgSO4 composites have been fabricated. To investigate the thermal energy storage performance of zeolite/MgSO4 composites, the properties of the composites, such as micro-morphology, pore structure, chemical composition and sorption-desorption behavior, have been characterized and analyzed. Results indicated that the mass transfer performance of the composite materials is significantly better than that of the pure zeolites. As the mass fraction of MgSO4 in the composite sorbents increases, the specific surface area and porosity of the composite sorbent decreases, and the sorption performance has been enhanced. Compared with 3A zeolite-based and 5A zeolite-based composites, 13X zeolite/MgSO4 composite materials show the best heat storage performance. At the condition of 25 °C and 60% RH, the 13XM20 has the highest sorption capacity of 0.21 g/g, which is 24% higher than that of pure zeolite 13X. Accordingly, the maximum heat storage density is 438.4 kJ/kg, which exhibits the superior heat storage performance among of the hydrated salt sorbents. The potential of 13X zeolite/MgSO4 as sorption heat storage material in efficient utilization of solar heat and low-grade industrial waste heat has been revealed.