Kinetic Study and Thermal Hazard Assessment of the Clethodim Synthesis Reaction

Thermal runaway in the final condensation step of the clethodim synthesis has caused severe industrial accidents (e.g., the 2020 Liaoning explosion, with 5 deaths). This study focused on the thermodynamics, kinetics, and thermal stability of this step to ensure process safety. Reaction calorimetry was used to determine the reaction heat, with ΔrHm,A = 45,000 J mol–1 and adiabatic temperature rise ΔTad = 35 K. The kinetic parameters were determined, revealing an activation energy Ea of 47,000 J mol–1, a pre-exponential factor k of 17,185 L mol–1 s–1, and the reaction followed second-order kinetics. Differential Scanning Calorimetry and AKTS software revealed that CPHA and clethodim have high thermal decomposition risks, with TD24 values of 65 and 75 °C, respectively, while EPCO was stable below 300 °C. Risk assessment (TP, MTSR, MTT, TD24) showed that the hazard criticality level of normal semibatch feeding was 2, and that of one-time batch feeding was 5, which was of high risk. However, with good mixing, if the time needed to reach TD24 was considered, the risk would also be under control. The 2020 accident was caused by feed errors and local overheating (no mixing/heat transfer). This work provides kinetic data and safety measures for clethodim production.