1,3-Propanediol can be synthesized by the hydrogenation of 3-hydroxypropanal over a nickel catalyst. The aim of the investigation was to obtain information about the mass transfer and degree of wetting in a trickle bed reactor. The model for the concentration and temperature profiles in a pilot reactor employed was based on kinetic measurements in an autoclave. Two different approximations of the overall catalyst effectiveness factor were used : (1) the effectiveness factors of dry, half wetted and totally wetted slabs were weighted as proposed by Beaudry, Mills and Dudukovic; (2) a new cylinder shell model was used, leading to one-dimensional mass balance equations inside the porous catalyst particle for all possible values of the external wetting efficiency on the particle scale.