Explosion Risk of a Nitration System Triggered by Coolant Leakage

Abstract In nitration processes, continuous-flow and microchannel reactors reduce hazardous inventory and improve heat transfer. However, their short residence times may necessitate the use of highly concentrated fuming nitric acid to achieve rapid conversion. This creates an inherent safety trade off, particularly when coolants circulated close to the process stream are assumed to be chemically inert. Accidental coolant ingress may therefore introduce an additional reactive pathway that is not represented by conventional loss of cooling scenarios. In this study, differential scanning calorimeter (DSC), antiexplosive reaction calorimeter (E-RC), and liquid-nitrogen-assisted accelerating rate calorimeter (ARC) were used to evaluate the incompatibility between fuming nitric acid above 95 wt % and three representative coolants, namely potassium formate solution, ethylene glycol solution, and calcium chloride brine. Potassium formate showed the fastest initial reaction and most intense gas generation, with a combined heat release of approximately −620 to −572 J/g. Ethylene glycol exhibited the greatest overall heat release, reaching −3236.2 to −3123.2 J/g. Under near-adiabatic conditions, the ethylene glycol system exhibited an apparent onset near −10 °C and a maximum self-heating rate of approximately 2400 °C/min. In contrast, calcium chloride brine showed limited reactivity dominated by mixing and dilution effects. These results demonstrate that reactive coolant ingress can rapidly generate localized hot spots and pressure buildup in nitration processes, which is particularly critical for compact continuous-flow reactors with small channels. The obtained calorimetric and kinetic data provide guidance for coolant selection, assessment of the hazard severity of identified leakage scenarios, and inherently safer design of microchannel nitration processes.