No abstract

Aromatic nitrations by mixed acid have been selected as a specific case of a heterogeneous liquid-liquid reaction. An extensive experimental programme has been followed using adiabatic and heat-flow calorimetry and pilot reactor experiments, supported by chemical analysis. A series of nitration experiments has been carried out to study the influences of different initial and operating conditions such as temperature, stirring speed and sulphuric acid concentration. In parallel, a mathematical model to predict the overall conversion rate has been developed. In this paper the mathematical modelling and the implementation and experimental validation for benzene, toluene and chlorobenzene mononitration in the kinetic control regime (slow liquid-liquid reaction) are presented and discussed.

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.

Chemical Engineering and Processing 34 (1995) 529-542 IntroductionDespite aromatic nitrations in mixed acid being one of the oldest and most common industrial reactions. there are still a considerable number of problems in predicting their behaviour in semibatch reactors. The interdependence of reaction and mass-transfer phenomena leads to a complex problem in characterizing and scaling-up these processes. Furthermore, nitrations involve high exothermicity and side reactions. An important phenomenon is phase inversion, which may occur in such systems. When two immiscible liquids are agitated, a dispersion is formed by virtue of the continuous supply of energy by the stirrer. When the external supply of energy is stopped, the dispersion may remain stable or may disengage into two phases. In the first case, the dispersion is called an emulsion, while the term dispersion is normally applied to the second type.After a transition period, a dynamic equilibrium between break-up and coalescence is attained, and a spectrum of drop sizes results. One of the phases becomes dispersed as droplets into the other, continuous phase. The type of dispersion depends on the volume fractions of the two liquids, their physical properties and the dynamic characteristics of the mixing process. AbstractThe eflect of phase inversion during semibatch aromatic nitrations is experimentally characterized and analysed. The influence of various parameters, i.e. interfacial area, effective heat-transfer coefficient and overall mass-transfer coefficient, is studied. The implications for optimizing nitrations are discussed from performance and safety points of view. The accumulation of unreacted nitric acid can be dangerous if accompanied by a phase inversion, owing to the fact that the rate may increase suddenly. Kqwwt~ls:Phase inversion; Liquid-liquid dispersion; Aromatic nitrations.

No abstract