A chemical method has been used to quantify the e ective interfacial area in a ba ed continuous stirred liquid-liquid reactor. Two and four straight paddle impellers were used in the experimental runs, at 34• C, with hold-up fractions of dispersed organic phase between 0.061 and 0.166 and stirring speed ranging from 360 to 1500 rpm. In uence of the residence time on the formation of the interfacial area generated in this system was not registered; however, di erences were reported between continuous and batch mode operations.The interfacial area was correlated to hold-up fraction and Weber number by a new empirical model proposed in this work. This model allows to use only one equation to calculate the interfacial area in this continuous stirred reactor in the wide range of operating conditions tested (490 ¡ We ¡ 9600), which include di erent ow regimes. This is a relevant contribution as previous studies in this ÿeld only contemplate turbulent ow. In the transitional regime the mean drop size diameter decreases abruptly with Weber number, but this pattern changes in the higher range of Weber where the dispersed drops become smaller very smoothly. This pattern does not depend on the agitator used or hold-up fraction. The mean drop size diameter is smaller for the four paddle impeller and increases with hold-up fraction. The model developed may be applicable to dispersions in aromatic nitration reactors, improving its operation and design. ?

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A pilot plant for the continuous adiabatic nitration of benzene was constructed, reproducing the industrial operating conditions, in order to identify the reaction regime prevailing in this industrial process. Important process parameters were tested covering a wide range of operating conditions: reaction temperature (80-135• C), benzene to nitric acid molar feed ratio (0.96-1.15) and stirring speed (390-1700 rpm). The residence time and the sulphuric acid strength were fixed at 2 min and 68%, respectively. The data from a large number of experiments show a good agreement with the results of a mathematical model of the reactor.In the range of operating conditions tested, it was shown that the prevailing reaction regime is the intermediate one (0.3 < Ha < 2). The film model used to predict the mononitrobenzene production according to the intermediate regime achieved a good accuracy. The asymptotic solutions for the fast and slow reaction regimes were compared with the full solution model and it was clearly shown that the last led to improved results. Since the film model is a simple approach to describe the mass transfer with simultaneous chemical reaction, the results achieved confirmed the adequacy of this modelling approach.

The benzene adiabatic nitration process has been carried out in a pilot plant to enable the study of this reaction under relevant industrial operating conditions, aiming to increase the reaction conversion and selectivity by reducing the nitrophenols. The influence of relevant operating parameters such as the reaction temperature, benzene-to-nitric acid molar feed ratio (F B /F N ), and stirring speed was studied. The operation ranges covered were as follows: reaction temperature, 80-135°C; F B /F N , 0.96-1.15; stirring speed, 360-1700 rpm. The residence time and the sulfuric acid concentration were fixed at 2 min and 68 wt %, respectively. The production of cleaner mononitrobenzene (MNB) requires lower nitration temperatures; higher F B /F N ratios than in current industrial practice; and high stirring speeds, allowing the interfacial area in this liquid-liquid mixture to be increased and the decrease in temperature to be compensated. The results reported here highlight the relevance of combining operating parameters to improve the performance of the reactor. In this study, it was possible to accomplish the same MNB production with a significant reduction in nitrophenols concentration. This work presents results that might be useful for conventional industrial benzene adiabatic nitration plants, to improve the prevention of pollution in this process and allow competitiveness with new plants in fulfilment of environmental law requirements.