Investigation of a violent explosion for nitric acid–n-hexane system using calorimetric method

With the acceleration of the energy transition, new synthetic routes for converting alkanes into high-value products are emerging. However, the thermal safety of these new routes may not have been fully considered, potentially leading to dangers during the optimization of reaction conditions. This study reports, for the first time, a reactor explosion incident during the experiment of a new synthetic route for adipic acid: nitric acid oxidation of n- hexane. Differential Scanning Calorimetry (DSC), Accelerating Rate Calorimetry (ARC), and corrective calculations were used to investigate the cause of the explosion. The results indicate that the polyparaphenol (PPL) liner material, which was used for the first time in the experiment, is unlikely to react with the system and cause the explosion. When the nitric acid concentration is increased from 3.7 mol·L −1 to 5.4 mol·L −1 , the thermal stability of the system decreases, and the heat release surpasses the chemical explosion threshold (1000 J·g −1 ). The maximum self-heat rate ( ) increases by at least 7 times, and the maximum pressure rise rate ( ) increases by at least 11 times. This led to the actual pressure in the reactor increasing from 4.96 MPa to at least 11.09 MPa, which far exceeded the rated pressure (3 MPa) and reached the rupture pressure (3.5 to 4 times their rated pressure), resulting in the explosion. This study aims to provide a warning regarding the safety of new synthetic routes involving the nitric acid-organic systems, particularly the conversion of alkanes, to prevent the recurrence of similar incidents.