Aromatic nitration by mixed acid was selected as a specific case of heterogeneous liquid-liquid reaction. An extensive experimental programme was followed using adiabatic and heat flow calorimetry and pilot reactor experiments, supported by chemical analysis. A series of nitration experiments was carried out to study the influence of different initial and operating conditions, such as temperature, stirring speed, feed rate and sulphuric acid concentration. In parallel, a mathematical model to predict the overall conversion rate was developed. In this paper, the mathematical modelling, implementation and experimental validation for mononitrations of benzene, toluene and chlorobenzene in the mass transfer controlled regime of fast liquid-liquid reactions are presented and discussed.