Continuous adiabatic industrial benzene nitration with mixed acid at a pilot plant scale

Abstract

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.