Abstract
The objective of this Ph.D. thesis was to test the use of porous solids with enhanced heat release characteristics as adsorbents in long-term low-temperature thermochemical storage of solar energy based on the adsorption of water vapour, while avoiding potentially detrimental conditions of high partial pressures of vapour during the discharging (hydration) stage in combination with elevated temperatures necessary for complete adsorbent regeneration upon precedent charging (dehydration). Cerium-exchanged 13X zeolites and ionosilicas functionalized with different proportions of SO42- species were prepared, their thermal performances being expected to benefit from enhanced energy of hydration of the compensating ions despite the presence of residual water molecules remaining after the regeneration step when performed under mild conditions. A multiscale characterization procedure based on different experimental techniques and modelling tools was systematically applied to understand the hydration mechanisms in the two types of solids, monitor the evolution of their structural and textural properties upon hydration, and quantify the kinetics and rate of heat release as a function of structural specificity of the materials studied. At the final step, the design of a laboratory-scale test-rig was undertaken for evaluating the thermal performance of adsorbents under flow conditions in view of future implementation of an open-sorption storage unit into domestic space heating. By combining the in situ XRD with molecular simulations, the hindered mobility of cerium cations in Ce-13X structures was documented, whereas calorimetry measurements revealed a significant gain in terms of adsorption heat compared to the pristine zeolite sample. In the case of ionosilicas, the heat evolvement was demonstrated to be more regular during a much longer period of time. Some indications for the optimisation of the future storage units were inferred from the laboratory-scale tests, together with an idea of designing a multi-segment reactor containing Ce-exchanged zeolite to obtain an instantaneous temperature lift, in combination with ionosilica to achieve a more steady heating.