INFLUENCE OF SUPPORT ON CONCENTRATION PROFILES IN ALUMINA PELLETS IMPREGNATED WITH MOLYBDENUM SOLUTIONS

Theoretical models of diffusive impregnation in spherical and cylindri cal pellets were employed to predict concentration profiles of molybde num that would result from the impregnation of two different commercia l alumina supports with molybdenum solutions. The ALC alumina support (cylinder) possesses greater pore volume and less pellet radius than t he ALS alumina (sphere). The effective diffusivity coefficient is grea ter for the impregnation of ALC alumina than in the case of ALS alumin a. Adsorption parameters for both supports are similar. For an initial concentration of impregnating solution of 0.05 MoO3/ml, impregnation time of 1440 min and a ratio of impregnating solution volume to suppor t mass of 5 ml/g, the same flat molybdenum profile was observed in bot h cases. For a shorter time (60 min), initial concentrations of impreg nating solution of 0.05 and 0.15 g MoO3/ml, and ratios of impregnating solution volume to support mass of 0.6, 5 and 50 ml/g, it was observe d that the ALC support allowed more molybdenum penetration than the AL S. Greater molybdenum penetration in the ALC support is favored by a g reater effective diffusivity coefficient and smaller pellet radius wit h respect to the ALS. An increase of molybdenum concentration in the s olution external to the pores and of the ratio of impregnating solutio n volume to support mass make the penetrating molybdenum concentration increasingly different between the supports. The greater the driving force for diffusion the more important the difference of molybdenum co ncentration profiles between both supports.