Thermal Runaway Inhibition of Adipic Acid Green Synthesis Based on a Radical Chain Reaction Mechanism

Adipic acid green synthesis is hazardous due to its highly exothermic nature and thermal instability of the raw material, hydrogen peroxide (H2O2). In this work, an effective chemical method was proposed to inhibit the potential risk of reaction runaway based on a comprehensive study. Reaction species, including reactive intermediates, radicals were identified to establish the radical chain mechanism by various monitoring techniques, such as electron paramagnetic resonance (EPR). Meanwhile, the standard molar reaction enthalpies of each step were determined by theoretical calculations. Combined with the process hazard evaluation and reaction mechanism, the exothermic mechanism was proposed, indicating the heat release was mainly concentrated during the former stage (73 °C stage) of the reaction. Thus, a series of runaway inhibition experiments using radical inhibitor, 2,2,6,6-tetramethylpiperidine oxide (TEMPO) were conducted under different conditions. The results showed that the addition of TEMPO could reduce the maximum temperature, heat release, and maximum exothermic rate of the reaction. The addition of the radical inhibitor could quench all the radicals and terminate the reaction. Thus, the reaction runaway could be inhibited effectively.