thermochemical heat storage in zeolitic materials

Thermally driven adsorption processes like heat pumps or cooling applications are important for saving primary energy. The use of porous adsorbents in the field of seasonal heat storage in building is an attractive solution for the reducing of energy consumption as well as improving thermal comfort [1]. In recent years, there have been significant research progresses on microporous adsorbent materials for closed/open systems [2]. Thermochemical heat storage (TCS) is based on the reversible chemical and physical sorption of gases, mostly water vapor, in solid. The water adsorption capacity and heat generated are the most important properties for adsorbents in such TCS system. This study focuses on the determination of sorption capacity and heats of adsorption/desorption of water vapor for different zeolites (MOR, CLP, K-L, 3A, 4A, 5A, Na-X, Na-Y, H-Y, Ca-X and Li-X) and zeolite-type materials like SAPO and AlPO. The measured heats of dehydration (kJ.kg-1) varied in the 360-950 kJ.kg-1 range for the different samples that present also different water vapor sorption capacities (from 0.09 kgH2O. kg-1 to 0.26 kgH2O.kg-1). This behavior can be attributed to the strong interaction of water molecules with the electronegativity of charge-balancing cations of the different zeolites and with the pore size. Relationships between water adsorption in zeolites, the porous structure, the Si/Al ratio, the zeolite framework and the compensating cation have been established. The knowledge of the structural modifications induced by temperature and of the stability of these materials is of prime importance to ensure their durability and effectiveness for seasonal heat storage applications.