Detailed reaction simulations of ammonium nitrate with gas–liquid mass transfer

Abstract Ammonium nitrate (AN) exhibits different thermal decomposition behavior under open and closed conditions. Although the thermal decomposition reactions and kinetics of AN have been extensively investigated, the origin of this difference remains unclear. In the present study, detailed reaction simulations incorporating gas–liquid mass transfer were performed using the two-film theory. The simulations predicted mass loss, heat flow, and variations in reactants and products under conditions relevant to thermal analysis. For open conditions, the simulated mass loss and heat flow profiles were then compared with the results of thermogravimetry–differential thermal analysis, whereas for closed conditions, the simulated heat flow profiles were compared with differential scanning calorimetry measurements conducted using a sealed pan. The simulated onset temperature and peak temperature were in good agreement with the experimental results. In addition, the simulation results were compared with previously reported pressure differential scanning calorimetry data. The simulated heat flow profiles were consistent with the pressure-dependent shift from endothermic to exothermic decomposition reported in experiments. The thermal characteristics of AN were found to be strongly influenced by the pressure. This pressure dependence reflects the competition between endothermic dissociation accompanied by evaporation (AN → HNO 3 + NH 3 ) and exothermic thermal decomposition (AN → N 2 O + 2H 2 O).