Zur Mikro- und Makrokinetik mehrphasiger heterogen-katalysierter Reaktionssysteme : Untersuchungen am Modellsystem der Ni-katalysierten Hydrierung von 1-Octen
Heterogeneous catalysis based upon multiphase reactions is a very important issue in the chemical industry. Various mass transfer resistances (gas-liquid, liquid-solid, pore diffusion) occur in such systems. This results in the fact that the effective rate of reaction is much lower than the reaction rate of the chemical reaction itself. Furthermore the intrinsic kinetic is very difficult to determine experimentally. The present work focuses on the determination of intrinsic kinetic and the derivation of a formal kinetic approach. For this purpose the hydrogenation of 1-octene to n-octane on a commercially Ni-catalyst in a vibrating batch reactor was chosen as the model system. In such a system each mass transfer resistance can be defined stepwise and excluded by the systematical variation of the reaction condition (concentration of catalyst and octene, particle size). The effective rate of reaction is strongly limited by the liquid-solid mass transfer at high concentrations of octene and catalyst. In addition the increase of the particle size of the catalyst leads to decrease of the reaction rate due to the liquid-solid mass transfer and the pore diffusion. In order to determinate the intrinsic kinetic, the concentration of hydrogen and the temperature were varied besides of the variation of the octene concentration. The results show that the rate of chemical reaction is zero order with respect to concentration of hydrogen under higher pressure (up to5 bar). Another aim of this work is the optimization of existing methods for multiphase reactions using the so called pre-saturation technology. The basic idea of this concept is that only the pre-saturated liquid phase is in contact with the catalyst. Hence there are only one (liquid) fluid phase and the solid catalyst within the reactor. Thus the gas-liquid mass transfer resistance is excluded. So the mathematical treatment of the fluid dynamic influence is less complex and a scale-up is easier. The concept offers further advantages compared to the classical three phase technology. Results from experiments performed in the classical trickle-bed reactor are used for a comparison. The data indicate that the effective rate of reaction in the trickle-bed reactor is 20 times lower than the intrinsic rate of the chemical reaction. For the same particle size the effective rate of reaction is higher in the two phase reactor with pre-saturator than in the trickle-bed reactor. In a trickle-bed reactor the rate of reaction is limited by gas-liquid mass transfer. The data of reaction kinetics from continuously operated fixed-bed reactor correspond with the result of a discontinuously vibrating reactor. In addition to kinetic and reaction engineering investigations, considerations and calculations are carried out based on the experimental data in a technical fixed bed reactor. The main objective of this work does not concern of the hydrogenation of octene, which is technical irrelevant, but rather to receive general conclusions for technical multiphase (hydrogenation) processes.
info:eu-repo/classification/ddc/540, Chemie, Octene, Katalytische Hydrierung, Nickelkomplexe, Katalysator, Heterogene Katalyse, Mehrphasensystem, heterogen-katalysierte Mehrphasensysteme
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