Nitration of o-xylene in the microreactor: Reaction kinetics and process intensification

Abstract

Nitration reactions are extensively studied in organic synthesis despite their notorious dangers, high reaction rates, and heterogeneous reaction systems. To date, most industrial nitration reactions rely on conventional batch reactors characterized by low mass transfer rates and limited reaction conditions. In contrast, microreactors represent a valuable technology for intensifying such nitration reactions. In this work, we established a continuous flow system of o-xylene nitration and determined the kinetics and mass transfer. The effects of mixing performance, nitric acid concentration, molar ratio, reaction temperature, and residence time on the process safety were investigated separately. The experimental data is supported by dimensionless number calculations, providing a more comprehensive understanding of the nitration reaction's transport and reaction performance in a heart-shaped microreactor. Remarkably, the residence time of the heart-shaped microreactor was reduced by an order of magnitude, while the volumetric mass transfer coefficient was improved by several orders of magnitude compared to conventional stirred tank reactors. Moreover, the spent nitric acid could be efficiently recovered and reused after concentration, further enhancing the sustainability and cost-effectiveness of the process. Our findings demonstrate the significant potential of microreactors for intensifying nitration reactions and paving the way for the design and optimization of more efficient and safer synthetic processes.