Kinetic Analysis and Prediction of Thermal Decomposition Behavior of Tertiary Pyridine Resin in the Nitrate Form

The thermal decomposition behavior of the tertiary pyridine resin, which was used during the nuclide-separation process in the Advanced Optimization by Recycling Instructive Elements (Advanced ORIENT) cycle, was investigated in its nitrate form (TPR-NO3), in order to determine ways of preventing its runaway reaction. A thermal analysis of TPR-NO3 and an analysis of the gases produced during decomposition were employed for the purpose. In addition, the kinetics parameters were evaluated via a kinetic analysis of the empirical thermal data. Finally, the validity of the reaction model was assessed by comparing the thermal behavior predicted by the estimated reaction model with that determined by the results of a gram-scale heating test performed in our previous study. We found that, when TPR-NO3 was heated, first, nitric acid was removed. Subsequently, TPR-NO3 was oxidized by the removed nitric acid. Under the assumption that it took place an autocatalytic oxidation and nth order thermal decomposition in parallel, the thermogravimetric analysis data could be fitted very well using a nonlinear regression model. The thermal behavior of TPR-NO3 could be predicted by the reaction model determined in this study under conditions where the cooling effect owing to evaporation was ignored. In addition, the maximum temperature and time to maximum rate of a runaway reaction predicted using the determined reaction model gave the result on the side of prudence.