Kinetics of the Solid-State Thermal Dehydration of Sodium Acetate Trihydrate: Effects of Water Vapor Pressure and Particle Size

The universal kinetic description of the reversible thermal dehydration of sodium acetate trihydrate (SA-TH) across a range of temperature and water vapor pressure (p(H2O)) was demonstrated toward its application to the thermochemical energy storage system. The thermal dehydration of SA-TH in the solid state can be observed within a limited range of temperatures and atmospheric water vapor pressures (p(H2O)ATM), due to the occurrence of efflorescence at ambient temperature in a dry atmosphere and melting at a temperature 30 K above room temperature. A systematic tracing of the thermal dehydration process at various p(H2O)ATM values was accomplished by employing a humidity-controlled thermogravimetry system. The reactions in flowing wet N2 with various controlled p(H2O)ATM values were subjected to the universal kinetic description across varying temperatures and p(H2O)ATM values by extending kinetic equation and computation method. This extension entailed the incorporation of an accommodation function for the effect of p(H2O)ATM and the consideration of the effect of self-generated water vapor in a stepwise manner. This approach facilitated a comparison of the universal kinetic behaviors of the thermal dehydration of the SA-TH samples with different particle sizes based on a physico-geometrical consecutive reaction model. The demonstrated universal kinetic analysis is proposed as a practically useful method for characterizing the reversible thermal dehydration of inorganic hydrates and a potential tool to obtain further insight into the physicochemical and physico-geometrical kinetic features of the reversible heterogeneous processes in solid–gas systems.