Detailed pyrolysis mechanism for ammonium nitrate and ammonium chloride mixtures

This is the authors' abstract. We don't add key points for this paper.

The contamination of ammonium nitrate (AN) with chlorides is known to significantly decrease the thermal stability of this compound. Although the thermal characteristics and reaction kinetics of AN/chloride mixtures have been thoroughly investigated, the mechanism associated with the condensed phase pyrolysis of such mixtures remains unclear. The present study employed quantum chemistry calculations at the G4//ωB97X-D/SMD level of theory to analyze the condensed phase pyrolysis of AN/ammonium chloride (NH 4 Cl) mixtures. A detailed kinetic model incorporating 72 chemical species and 134 elementary reactions and based on first principles was constructed for this purpose. Using this model, reaction simulations were performed to predict the heat flow profile and variations in reactants and products during AN/NH 4 Cl pyrolysis. The heat flow profile was then compared with experimental data obtained using differential scanning calorimetry. The predicted reaction onset temperature, heat release rate and total heat of pyrolysis were in good agreement with the experimental results. The pyrolysis pathways for this system were determined and HCl was found to act as a catalyst. This process is evidently initiated by the reaction of HCl with HNO 3 to form NO 2 Cl, leading to the formation and subsequent decomposition of NO 2 ClNH 3 to generate HONO and NH 2 Cl. This NH 2 Cl decomposes to produce trans-N 2 H 2 and regenerate HCl, establishing the catalytic cycle AN → 0.5 trans -N 2 H 2 + HONO + H 2 O. The HONO further accelerates AN decomposition as AN + HONO → N 2 + 2H 2 O + HNO 3 .