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

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.