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.

The liquid phase hydrogenation kinetics of five di- and trisubstituted alkylbenzenes, xylenes, mesitylene, and p-cymene were 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 aromatic compound was affected by both the number of substituents and their relative positions in the benzene ring. The trisubstituted benzene (mesitylene) had a lower reaction rate than the disubstituted compounds (xylenes). The activity of the different substituent positions decreased in the order para > meta > ortho. The main reaction product was always the completely hydrogenated cycloalkane; no cycloalkenes were detected. The hydrogenation rates were virtually constant at low and intermediate conversions of the aromatics, but at high conversions the rates decreased. Rate equations based on the formation of partially hydrogenated surface complexes were derived, and the kinetic parameters were estimated from a heterogeneous reactor model with nonlinear regression analysis. The rate equations were able to describe the features of the experimental data.

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The production of liquid fuels from lignocellulose-derived platform molecules has attracted much interest in recent years. Platform molecules mostly have a shorter carbon chain length, compared to liquid fuels, which have a typical chain length varying between 4 and 25 carbon atoms, whereas aviation and especially diesel fuel have a carbon chain length exceeding 10 carbon atoms. For this reason, some carbon chain length increase reactions are required. In this article, carbon chain length increase reactions are compared for typical lignocellulose-derived platform molecules. The focus is placed on the ability of the molecules to participate in self-condensation reactions in a controlled manner. Hydrogen plays a key role when producing fuels from platform molecules. Hydrotreatment is applied not only when converting the products from a carbon chain length increase reaction into hydrocarbons but also for modifying the functional groups of the model compounds and, thereby, their reactivity.

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The liquid-phase hydrogenation kinetics of one multiaromatic mixture and five binary aromatic mixtures of toluene, ethylbenzene, xylenes, and mesitylene were determined in a semibatch reactor operating at a pressure of 40 bar and a temperature of 125 °C. Commercial preactivated catalyst particles of nickel−alumina were used in the experiments. In mixtures, the aromatic compounds reacted in queues so that the most reactive components started to react immediately while the least reactive components did not react until the most reactive components had been hydrogenated completely. This type of reactivity decreased with the increasing number of substituents, i.e. in the order monosubstituted > disubstituted > trisubstituted. The relative positions of the substituents affected the reaction rate so that the reactivity decreased in the order ortho > para > meta. The queue effect was described with a kinetic model based on the rapid adsorption of aromatic compounds and hydrogen and sequential addition of hydrogen to the aromatic nucleus, the first hydrogen addition step being rate determining. The kinetic parameters were estimated from a heterogeneous reactor model with nonlinear regression analysis. The kinetic model was able to describe hydrogenation kinetics of the binary aromatic mixtures.

A heterogeneous three-phase reactor model is used to simulate an industrial trickle-bed reactor for benzene hydrogenation, and simulated temperature profiles are compared to actual plant data. The agreement of model predictions with measured data is excellent. Analysis of the results shows that the process is limited by gas-liquid mass transfer of hydrogen. The simulation results show high sensitivity toward the liquid film mass transfer coefficient k L a. Some correlations for k L a are tested, and their validity is evaluated. The estimated values of k L a and k G a are comparable to measured values from a bench-scale reactor reported in the literature.

Kinetic studies of catalytic three-phase systems are traditionally performed in autoclaves operating batchwise, and the results are described with rate equations based on the simple Langmuir-Hinshelwood concept. This is not sufficient, as complex organic molecules react on the catalyst surface, and more advanced kinetic models and experimental techniques are needed. Semicompetitive and multicentered adsorption models have been applied to kinetic data, and transient step-response experiments have been carried out for various industrially relevant three-phase systems. The theoretical basis of the advanced kinetic concept is described and successfully applied to several industrially relevant processes, such as hydrogenation of aromatic components and aldehydes on commercial catalysts and enantioselective hydrogenation on modified catalyst surfaces.