Continuous hydrogenation of 2-(4-nitrophenyl) butanoic acid: Kinetics study in a micropacked-bed reactor

Abstract

Hydrogenation still faces unmet technical challenges in relation to heterogeneous reactions and potential safety issues. In this work, a continuous flow Pd/C-catalyzed hydrogenation of 2-(4-nitrophenyl) butanoic acid (NBA) was developed within a micropacked-bed reactor. Catalytic hydrogenation of NBA involves the interaction of gaseous and liquid reactants on solid catalysts and the mechanism has not been clearly reported. Therefore, the Langmuir-Hinshelwood-Hougen-Watson (LHHW) approach was used to investigate the kinetics and attempted to explain the possible mechanistic path. The effects of internal diffusion, external diffusion, and salt formation were characterized, the intrinsic kinetic model was established and corresponding parameters were obtained. The model showed that the reaction proceeds through the dual site molecular adsorption of reactant specie and NBA can be reduced to 2-(4-aminophenyl) butanoic acid (ABA) either through the generation of hydroxylamine intermediates or directly.