Sorption kinetics of vermiculite-K2CO3 in thermochemical energy storage: Model evaluation and mechanism exploration

Abstract

Thermal energy storage technology is crucial for building heating and domestic hot water supply, playing an essential role in optimizing energy utilization. Hydrated salts have emerged as prominent materials for thermochemical energy storage (TCES), with their sorption kinetics directly impacting thermal energy conversion efficiency. This study experimentally analyzes the microstructure and sorption performance of the EV/K2CO3 composite sorbent. Numerical analysis methods are employed to evaluate the validity of various sorption kinetics models and to elucidate the sorption mechanism and potential limitations of the composite sorbent. The findings indicate that EV can disperse K2CO3 salt particles while preserving a porous structure, thereby improving the sorption kinetics efficiency and stability of the EV/K2CO3 composite sorbent. At low relative pressure, EV/K2CO3 demonstrates a chemical adsorption mechanism, with nucleation models accurately predicting its sorption behavior, primarily limited by the nucleation and growth of hydrated salt crystals. At moderate relative pressure, EV/K2CO3 exhibits a mechanism involving both chemical adsorption and solution absorption, with diffusion models and the first-order model showing higher prediction accuracy, primarily limited by diffusion within or outside the product layer. At high relative pressure, EV/K2CO3 primarily undergoes solution absorption, with geometric contraction models and the first-order model displaying good predictive performance, primarily limited by the reaction phase interface. This study enhances comprehension of the sorption mechanism of the EV/K2CO3 composite, providing a scientific foundation for the development of high-performance TCES materials suitable for building and environmental applications.