Experimental investigation of mononitrotoluene preparation in a continuous-flow microreactor

Mononitrotoluene is an important dye intermediate, which is prepared by nitration of toluene and mixed acid. The nitration of toluene with mixed acid is a fast and highly exothermic process. Due to the poor mass and heat transfer performance of batch or continuous kettle reactors, there are safety risks in the nitration of toluene. In this work, the nitration process of toluene with mixed acid was studied in a continuous-flow microreactor. The conversion of toluene and yield of MNT were investigated by varying reaction temperature, residence time, molar ratio of HNO3 to toluene, and mass fraction of H2SO4 in mixed acid. Variance analysis and significance tests were conducted on the models of toluene conversion and MNT yield. The results showed that the mass fraction of H2SO4 in mixed acid had the greatest influence on toluene conversion and MNT yield, followed by the molar ratio of HNO3 to toluene, reaction temperature and residence time. The experimental values of toluene conversion and MNT yield were in good agreement with the predicted values of the regression equation model. The research results were of great significance for further understanding the nitration characteristics of toluene in a continuous-flow microreactor. This study provides a safe and efficient method for the synthesis of dye intermediates.Graphical abstract