Electrical Method for the On-Line Monitoring of Zeolite-Based Thermochemical Storage

Zeolites are used to store sunlight energy in the form of latent heat of adsorption. The energy is stored by dehydration of the substance and released by its rehydration. The availability of an online monitoring technique for this hydration/dehydration process is an extremely useful potentiality for an optimal exploitation of such technology, since it allows establishment of the degree of activation and saturation of the material. Here, an electrical method has been developed and used for monitoring the hydration/dehydration process of a sample of natural clinoptilolite. Clinoptilolite has been selected as a model zeolitic material for testing this monitoring technique since it is a widely spread, very inexpensive, and highly mechanically stable zeolite type, that could be used for such a purpose. The study has been performed in the presence of pure water vapor and wet air (75RH) after having dehydrated the sample by exposition to sunlight for 12 h. The developed monitoring method has also allowed us to have information on the kinetics of the process (Lagergren pseudo-first order), to establish the specific rate of hydration (3.3 × 10 min), and to have an idea of the involved adsorption mechanism. The sample of natural clinoptilolite was also chemically and structurally characterized by EDS, XRD, DSC, and TGA.