(349aa) Studies on Hydrocarbon Diffusion and Accessibility in FCC Catalysts

Fluidized Catalytic Cracking (FCC) processes are used in crude oil refining to optimize the conversion of hydrocarbons to higher valuable products, such as gasoline. Feedstocks to FCC units are usually heavy gasoil and/or distillation units residues. Typical desired products from FCC are light gases, LPG, gasoline and diesel, with typical higher yield in gasoline product (ca. 60%). The cracking reactions are favored by the presence of heterogeneous catalysts, normally using as zeolites as active phase. These catalysts must show high selectivity to the desired product showing good material resistance in continuous operation. The catalytic activity of such catalysts may be directly related to the diffusion mechanisms of the components in the feed and in the products of the cracking reactions. In this study, we present diffusion studies of certain probe molecules in commercial FCC catalysts to evaluate the influence of size, volume and chemical nature of such molecules in their accessibility to the pores of the FCC catalyst framework. Diffusion experiments were performed using a column chromatographic method and the Zero Length Column (ZLC) method.