Hydrogenation of nitrobenzene to p-aminophenol in a four-phase reactor: reaction kinetics and mass transfer effects

The kinetics of catalytic hydrogenation of nitrobenzene in acid medium to p-aminophenol was investigated in a batch slurry reactor in a temperature range of 323-353 K. Aniline was formed as a byproduct (upto 20%). The initial rate data were analyzed to assess the mass transfer effects and it was found that gas-liquid mass transfer resistance was important under certain reaction conditions. A Langmuir-Hinshelwood type rate model has been proposed based on the initial rate data in the kinetic regime and considering the reaction taking place in both organic as well as aqueous phase. Since this was a four-phase system, the rate equation was suitably modified to include gas-liquid and liquid-liquid mass transfer steps. The kinetic parameters evaluated from a semibatch reactor model were found to represent the observed experimental data very well indicating the applicability of the proposed rate model