Investigation of the thermal decomposition mechanism and thermal hazards of hydroxylamine aqueous solution utilizing combined calorimetric methods and DFT calculations

Hydroxylamine, a critical chemical intermediate, predominantly exists in aqueous solutions, posing significant risks of decomposition and thermal hazards. To investigate its thermal decomposition process, DSC tests were conducted to establish a kinetic model. The DSC results indicated that 50 mass%, 30 mass%, and 10 mass% in water decomposed at temperatures of 42–50°C, 72–84 °C, and 87–93 °C, respectively, with corresponding Δ \(\overline{H }\) $\overline{H}$ values of 2037.63 J g ⁻¹, 1033.15 J g ⁻¹, and 390.48 J g ⁻¹. Subsequently, a two-step decomposition kinetic model, referred to as the “N-order + autocatalytic” model, was developed by combining model-free and model-fitting techniques. Furthermore, the stages of “preliminary reaction + autocatalytic interaction” were elucidated using DFT calculations, complemented by TG-FTIR-GCMS testing, aligning with the apparent decomposition model. Intermediate species NH and HNO play crucial roles in the second stage of the reaction, facilitating the autocatalytic process. Specifically, the reaction between HNO and NH₂OH necessitates overcoming an energy threshold of 11.24 kcal mol ⁻¹, underscoring its pivotal role in the reaction mechanism. Ultimately, finite element simulations employing the kinetic model were conducted to predict thermal decomposition patterns, assess thermal explosion scenarios, and evaluate various thermal hazard parameters.