Kinetics of the Liquid-Phase Hydrogenation of Benzene and Some Monosubstituted Alkylbenzenes over a Nickel Catalyst

The liquid-phase hydrogenation kinetics of benzene and three monosubstituted alkylbenzenes, toluene, ethylbenzene, and cumene, was determined in a semibatch reactor operating at hydrogen pressures of 20−40 atm and at temperatures of 95−125 °C. Commercial preactivated catalyst particles of nickel−alumina were used in all experiments. The hydrogenation activity of the compounds decreased in the order benzene ≫ toluene > ethylbenzene > cumene. The main reaction product was always the completely hydrogenated cycloalkane, whereas only trace amounts of cycloalkenes were detected. The hydrogenation rates had a slow initial period followed by a period of a virtually constant rate, which decreased at the end of the reaction. The analysis of the data with a reaction−diffusion model revealed that the kinetics was influenced by pore diffusion. Rate equations based on a sequential addition mechanism of adsorbed hydrogen to the aromatic nucleus were derived, and the kinetic parameters were estimated from the reaction−diffusion model with nonlinear regression analysis. The rate equations were able to describe all the features of the experimental data.