Configurational diffusion of asphaltenes in fresh and aged catalyst extrudates. Quarterly progress report, 20 December 1993--20 March 1994

The objective of this research is to determine the relationship between the size and shape of coal and petroleum macromolecules and their diffusion rates, i.e., effective diffusivities, in catalyst pore structures. That is, how do the effective intrapore diffusivities depend on molecule configuration and pore geometry. This quarter the authors developed a mathematical diffusion model for spent catalyst with a nonuniform pore structure due to nonuniform coke and metals deposition. Diffusion experiments with both spent extrudates and crushed catalysts were performed. Effective diffusivities were obtained by fitting the experimental data with a diffusion model. The results showed that a skin effect due to coke and metals deposition exists in the coal liquefaction catalysts. The uniform particle model did not satisfactorily represent the diffusion behavior in the spent catalyst extrudates, which gave rise to extremely high tortuosity values. On the other hand, the experimental results were well represented by the nonuniform particle model. Due to deposits in catalyst pores during the coal liquefaction process, the effective diffusivity decreased to a very low value.