Universal kinetic description for the thermal dehydration of sodium carbonate monohydrate powder across different temperatures and water vapor pressures

Abstract

The thermal dehydration of sodium carbonate monohydrate (SC-MH) exhibits kinetic characteristics that are typical of the thermal decomposition of solids with a reversible nature. One of the characteristics is the physico-geometrical constraints of the reaction due to the heterogeneous reaction feature. Another factor is the considerable impact of the atmospheric and self-generated water vapor on the kinetics. The objective of this study is to develop a universal kinetic description of the dehydration kinetics as a function of temperature, degree of reaction, and partial pressure of water vapor (p(H₂O)), deriving kinetic parameters with physico-chemical significance based on the physico-geometrical kinetic model. The kinetic curves for the thermal dehydration of SC-MH were meticulously documented under isothermal and linear nonisothermal conditions at varying p(H₂O) values using humidity-controlled thermogravimetry. The mass loss curves at a constant temperature exhibited a sigmoidal shape following an induction period, irrespective of the p(H₂O) value. As the p(H₂O) value increased, a systematic decrease in the reaction rate was observed. The challenge of providing a kinetic description for the complex reaction process was addressed by a step-by-step approach, which included the following four steps: (1) the development of a universal kinetic description that could be applied across varying temperatures and p(H₂O) values, (2) the incorporation of the effect of self-generated water vapor into the universal kinetic description, (3) the interpretation of the physico-chemical meanings of the apparent kinetic parameters within the universal kinetic description, and (4) the extension of the universal kinetic description to encompass the physico-geometrical kinetic modeling.