Kinetic analysis of poly-aluminum sulfate hydrate for low-temperature thermochemical heat storage

Abstract

A summary of the research undertaken on poly-aluminum sulfate is performed revealing several disagreements on important thermal properties of the material. Nevertheless, the energy density reported highlights that the material is promising for thermochemical heat storage (THS). A thorough thermal analysis (TA) of (Al2(SO4)3·xH2O) is conducted using TA devices and the ICTAC kinetics committee recommendations, to identify its thermal properties, its most stable form (Al2(SO4)3·18H2O, and the conditions of its use for low-temperature THS (80 °C and 125 °C under atmospheric pressure. The material decomposes in four endothermic stages as shown in the thermal curves and illustrated by possible reaction formulas, three of which are dehydrations followed by a final decomposition. The non-isothermal kinetics of the dehydration for PAS has been determined by the methods of Coats-Redfern (CR) and Achar-Brindley-Sharp (ABS) with 19 different reaction models. It is found that most reaction models exhibit a linear trend. The Janders reaction model is appropriate for the first dehydration with an activation energy of ca. 33.248 kJ/mol by CR and 30.759 kJ/mol by ABS, respectively. Both the power law and the Avrami-Erofeev model can be used for the second stage with an activation energy of ca. 235 kJ/mol. The overall kinetics modeling for aluminum sulfate hydrate is successful for PAS implying the substitution of aluminum sulfate with PAS in applications.