Atomistic Insights into the Thermal Decomposition and Runaway Mechanism of Peroxypropionic Acid

Thermal runaway of organic peroxides in chemical production poses a persistent and severe challenge in the field of energy and safety. The ambiguous decomposition mechanism of peroxypropionic acid (PPA), a typical and unstable peroxide, hinders effective risk prevention and control. This study employs a multiscale computational approach integrating reactive molecular dynamics (ReaxFF MD) and density functional theory (DFT) to unravel, for the first time, the complete reaction network and energy evolution pathway of a PPA mixture under thermal runaway conditions at the atomic scale. Simulation results reveal that its decomposition follows a typical free radical chain reaction mechanism, progressing through three self-accelerating stages: initial homolytic initiation, a vigorous exothermic propagation dominated by hydrogen abstraction reactions, and final secondary decomposition of products driven by accumulated heat. DFT calculations precisely quantified the activation energy barriers and reaction enthalpies of key elementary steps, identifying the rate-determining steps that drive thermal runaway. Adiabatic experiments validated the intense exothermic characteristics predicted by the simulations. This work clarifies the microscopic driving forces behind PPA thermal runaway, providing crucial molecular-level insights and thermodynamic data for designing safer operational protocols and developing efficient inhibitors at an industrial scale.