Experimental identification and thermodynamic analysis of ammonia sorption equilibrium characteristics on halide salts

Highlights: • A facile method is developed to measure thermodynamic properties of chemisorption. • Thermodynamic characteristics of NH₃ equilibrium sorption on SrCl₂ are clarified. • A stable diamine phase SrCl₂·2NH₃ is experimentally identified. • Equilibrium properties of NH₃ sorption on BaCl₂, SrBr₂, and MnCl₂ are investigated. • A cascaded thermochemical energy storage system is introduced and analyzed. Solid–gas chemisorption based on metal ammine complexes is a kind of promising energy-saving and environment-friendly technology for various thermal engineering applications such as chemical heat pump, thermochemical energy storage, chemisorption refrigeration, etc. The accurate thermodynamic parameters of ammonia sorption on halide salts can allow a significant theoretical and experimental study on a solid–gas chemisorption system using halide salt–ammonia sorption working pairs. In this study, the thermodynamic properties of chemisorption between strontium chloride (SrCl₂) and ammonia is firstly investigated by developing a facile methodology for sorption equilibrium measurement. The facile methodology involves the fabrication of incompact composite sorbent of expanded graphite/SrCl₂ with high porosity and an optimized temperature-controlling method so as to weaken the adverse effect of heat and mass transfer on chemisorption and realize the chemical equilibrium and thermal quasi-equilibrium during the isobaric measurement process. Through the experimental measurement, the stoichiometric equations of chemisorption between SrCl₂ and NH₃ are updated, and thermodynamic parameters including reaction enthalpy, reaction entropy and hysteresis are identified. Similarly, the thermodynamic characteristics of chemisorption between ammonia and halide salts BaCl₂, SrBr₂, and MnCl₂ are also investigated. The facile methodology is proved available for measuring the ammonia sorption equilibrium characteristics on halide salts. At last, the working performance of a cascade thermochemical energy storage system using four halides salts is analyzed based on the obtained thermodynamic parameters.