Concentration-time curves at 45-80 degrees C and 2.60-5.15 MPa were measured, in a spinning basket reactor, to model the hydrogenation of 3-hydroxypropanal (HPA) to 1,3-Propanediol (PD) over Ni/SiO2/Al2O3 catalyst pellets. A mathematical model whose parameters are effective diffusion coefficients and intrinsic kinetic parameters is proposed to describe this process and to avoid the dependence of the model parameters on the catalyst particle size. This model fts the experimental data reasonably and allows a reliable scale up of this process in comparison to other empirical models.