Effective Diffusivity Measurement in Coke-Deactivated Hydrotreating Catalyst

The effective diffusivity of two fresh and two spent catalysts, previously deactivated for 18 months in a commercial unit, were determined. The effective diffusivities were measured using a shallow-bed reactor already developed for this purpose. Nitrogen, isopentane and isooctane effective diffusivity and adsorption coefficients were measured at different temperatures. The catalysts were a NiMo/AlMCM-41 with different pores interconnections. The catalysts were also characterized by chemical analysis, TEM, adsorption desorption of iC5 and iiC8 and chemical reaction with model molecules. The results demonstrated that some areas of the porous networks were blocked by local coke depositions that reduce more the access of iC5 and iiC8 than nitrogen molecules. The catalyst with better pore network interconnections had lower deactivation.