Nitrophenols Reduction in the Benzene Adiabatic Nitration Process

Abstract

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 (FB/FN), and stirring speed was studied. The operation ranges covered were as follows: reaction temperature, 80-135 °C; FB/FN, 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 FB/FN 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.