Investigation of thermal hazard and decomposition pathways of ammonium persulfate by experiments and DFT simulation

Ammonium persulfate (APS) is a very important peroxide that is widely used in many industries. However, if it is subjected to high temperatures during storage and transportation, it may undergo a violent thermal decomposition reaction, leading to accidents. Therefore, studying the thermal effect of its thermal decomposition and the corresponding decomposition mechanism is helpful for predicting and controlling the occurrence of the thermal decomposition reaction, thereby reducing the risk of accidents. In this work, thermal decomposition characteristics of APS were studied using thermogravimetric analysis - differential scanning calorimetry (TG-DSC), differential scanning calorimetry (DSC) and accelerating rate calorimeter (ARC). The solid and gaseous products of APS decomposition were investigated using fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis - fourier transform infrared spectroscopy (TG-FTIR). Finally, thermal decomposition pathways were explored using density functional theory (DFT) method combing with the experimental study. The results indicated that APS decomposition was divided into two stages. The fist step was the rupture of APS peroxide bond (O-O) at about 200$℃$, which was an exothermic self-catalytic reaction, and the products were O₂ and (NH₄)₂S₂O₇. The second step was (NH₄)₂S₂O₇ decomposition at the temperature of 300–400 $℃$, which was an endothermic reaction, and the final decomposition products were NH₃, N₂, SO₂ and H₂O. According to the ARC test results and the risk matrix assessment criteria, APS was classified as level II conditional acceptable hazard. This work provides useful information for safe production, storage and use of APS in the practical chemical process.