In this work, intrinsic kinetics were decoupled from reactant diffiusivities in the SC sunflower oil hydrogenation reaction on Pd/C using a steady-state diffusion and chemical reaction model under isothermal conditions in order to obtain low trans and stearic final products. A numerical solution combined with nonlinear parameter fitting was employed to solve this model. First, runs with small size of catalyst (0.4 mm) allowed to obtain kinetic constants irrespective of the diffusivity settings. Then, in a second set of runs, reactions were repeated on larger sizes of catalyst (up to 1 mm), that is, in the diffusion-limited regime. The results show that while hydrogen is transported by bulk pore diffusion, the oil seem to diffuse by surface diffusion. Diffusivity of H-2 is about 10 times that of iriglycerides. The overall diffusivity for triglycerides is about 10-8 m(2)/s, and changes 3 times with an increase in pressure, and 20 times with an increase in T Linoleate selectivity (S-LO) and specific isomerization (S-i) also improve with decreasing the diffusion path. (c) 2005 American Institute of Chemical Engineers.