Catalytic hydrogenation of p-nitorcumene in a slurry reactor

The hydrogenation of p-nitrocumene to p-cumidine over supported palladium c atalysts was investigated in a laboratory-scale slurry reactor. The primary objective was to demonstrate the methodology for development of a slurry r eactor model that could predict either isothermal or nonisothermal performa nce using intrinsic kinetic and transport parameters that were determined f rom independent data and engineering correlations; Several catalysts were s creened to identify a suitable one for kinetic and reaction engineering stu dies. Various catalyst supports, such as alumina, calcium carbonate, and ac tivated carbon, as well as reducing agents used during the catalyst prepara tion, including hydrogen, sodium formate, and formaldehyde, were investigat ed. A 1 wt % palladium-on-alumina catalyst was identified as the preferred catalyst because it had both superior activity and selectivity. The effects of hydrogen pressure, catalyst loading, and the initial concentrations of p-nitrocumene, water, and p-cumidine on the initial rate of hydrogenation a nd the concentration-time profiles were also studied in a batch reactor. Th e initial rate data showed that both the kinetic and mass-transfer resistan ces were important for temperatures greater than 353 K, while the kinetic r egime was controlling at lower temperatures. A Langmuir-Hinshelwood (L-H) m odel was proposed based on the rate data in the kinetic regime. The rate mo del was suitably modified to account for combined transport-kinetics resist ances above 353 K. Using a basket reactor, intraparticle diffusion effects were also studied by transforming the catalyst powder used for the kinetic study into catalyst pellets. Equations for an overall catalyst effectivenes s factor were derived for the L-H type rate model. The experimental data fo r different catalyst particles agreed well. with the theoretical prediction s. To verify the applicability of the kinetic model over a wide range of co nditions, a slurry reactor model was also developed for both isothermal and nonisothermal conditions. The predicted concentration versus time profiles were in excellent agreement with the experimental results using model para meters that were independently determined from experiments or correlations.