Micro-Calorimetric Study on the Thermal Stability of N, N-Dimethylhydroxylamine in the APOR Process

The thermal stability of N, N-dimethylhydroxylamine (DMHAN) in the HNO₃ solution was studied using microcalorimeter. The influence of concentration of HNO₃, DMHAN, methylhydrazine (MH), atmosphere (air and nitrogen), and metals was investigated. The kinetic parameters and self-accelerating decomposition temperature (SADT) of the feed in process (stripping reagents 1BX, scouring agent 2DS, stripping reagents 2BX, and waste aqueous phase 2DW) were calculated by Advanced Kinetics and Technology Solutions (akts) thermokinetics software. The molar enthalpy of the reaction of NaNO₂ with DMHAN and MH was also determined. The results show that the initial reaction temperature (T₀) of DMHAN/HNO₃ (HNO₃: 1.5–3.0 mol/L, DMHAN: 0.05–0.8 mol/L) is increased as the acidity is reduced or the concentration of DMHAN is increased. Holding reductant MH made the induction period of the autocatalytic reaction longer. The air, nitrogen atmosphere, Fe, and the fission products (Zr, Ru) do not affect the decomposition of DMHAN, but the stainless steel made the T₀ of DMHAN/HNO₃ become lower. The SADT of 1BX/2DS, 2BX, and 2DW is 56 °C, 52 °C and 47 °C, respectively. The molar enthalpies of formation of the reaction of NaNO₂ with DMHAN and MH are −411.3 kJ/mol, −246.0 kJ/mol, respectively.