Heterogeneous toluene nitration with mixed acid in microreactors: Reaction regime, characteristics and kinetic models

It is critical for reactor design and process safety to determine the reaction kinetics for toluene nitration. Herein, a continuous-flow platform based on capillary microreactors was established. First, reaction regimes for toluene nitration and its consecutive side reaction (MNT (mononitrotoluene) nitration) were identified. On this basis, the influence of process parameters on conversion of toluene, selectivity of MNT and DNT (dinitrotoluene) and their isomer distribution were meticulously examined, including molar ratio of reactants, sulfuric acid strength, reaction temperature, and residence time. Subsequently, reaction kinetic models coupled with mass transfer were developed, allowing the simultaneous kinetic determination for toluene nitration and MNT nitration. It was found that the logarithm of the observed kinetic constant is proportional to the sulfuric acid strength. The kinetic parameters under 72.7 to 80.1 wt% sulfuric acid strengths were obtained. The outcomes provide a basis for process intensification and optimization of toluene nitration as well as other similar aromatics.