Modelling of kinetic and transport effects in aldol hydrogenation over metal catalysts

This work concerned the pathway from intrinsic kinetics to diffusion-affected kinetics in catalytic hydrogenation. Kinetics and mass transfer effects in the liquid-phase hydrogenation process of an aldol (2,2-dimethylol-1-butanal) to the corresponding triol (trimethylol- propane) were studied in a semibatchwise operating autoclave, where finely dispersed and large catalyst particles were used. The intrinsic hydrogenation kinetics was determined with the crushed catalyst particles at 40-80 bar H₂ and 50-90°C in isobaric experiments. A kinetic model based on competitive adsorption and surface reaction between the aldol and hydrogen was successfully fitted to the experimental data. Physical measurements of the density, viscosity as well as hydrogen solubility in the reaction mixture were carried out. The measurements revealed that the governing factor in the physical data is the temperature dependence, while the composition dependence during the hydrogenation is a minor factor under the actual experimental conditions. The models for intrinsic kinetics, physical properties and mass transfer effects were combined to describe the behaviour of large catalyst particles. It turned out that the theoretically developed model agreed well with experimental observations made with large-size catalyst particles. The approach is suitable for the scale-up of catalytic hydrogenation processes.