Wasseradsorption und ‐diffusion in SAPO‐34 für die adsorptive Wärmetransformation

Abstract

The diffusion of water in SAPO-34 was investigated experimentally in the temperature and loading range relevant for adsorptive heat transformation applications. Corrected diffusivities, which were determined by IR microscopy using adsorptive layers on aluminum supported SAPO-34 during adsorption and desorption and self-diffusion coefficients derived from NMR diffusion studies in thermodynamic equilibrium are found to be consistent to each other. They are both independent of water loading and about two orders of magnitude smaller than the diffusivity of liquid water at the same temperature. The temperature dependence of the water diffusion may be well described by an activation energy of (11 +/- 2)kJmol(-1)

Modeling the Hydration-Induced Structural Transitions of the SAPO-34 Zeolite and Their Impact on the Water’s Sorbed Phase Equilibrium and Dynamics

“…Measured adsorption and desorption (open symbols) isotherms of water in SAPO-34; simulated, individual isotherms within phases A, B, and C, at 313.15 K; colored zones denote phase regions as in Figure .…”

“…The reason is that the apertures of the SAPO-34 windows reduce with the addition of structural waters (see Figure ), thus hindering the passage of guest waters through them. As seen in Figure b, at the loadings of 0.20 g/g and 0.25 g/g, our simulated points for phase B approach the results of PFG NMR with the latter being between the simulated self-diffusivities for phases A and B and rather closer to phase B. Consequently, the observed sorbate-induced phase transition has a large effect on diffusivity, and by controlling the various phases of SAPO-34, one may tune the mobility of sorbate water as well. Activation energies for the self-diffusion coefficients are presented in Tables S6–S8.…”

Phase Transformation of Hydrothermally Stressed Adsorbents

“…Water adsorption and diffusion in SAPO‐34 was already investigated in reference but no hints on similar changes of crystal structure are reported although SAPO‐34 samples were treated from room temperature up to the critical range beginning at a temperature of 85 °C. The adsorbent was synthesized, however, on an aluminum plate carrier which deviate the sorption heat.…”

Insights into the water adsorption mechanism in the chemically stable zirconium-based MOF DUT-67 – a prospective material for adsorption-driven heat transformations

“…Therefore, material scientists are actively searching for alternative materials with desired adsorption properties. [4][5][6][7] Various working uids are considered ranging from ammonia, hydrocarbons, uorinated hydrocarbons, alcohols to water. 8,9 Their coefficient of performance is strongly dependent on their critical temperature and density.…”