Effect of nonuniform activity on hydrodemetallation catalyst

Abstract

A model is developed to qualitatively predict the effect of a nonuniform activity distribution on the total quantity of metal deposited in hydrodernetallation catalysts. A fixed catalyst support system is assumed and no restrictions are placed on local or overall catalytic activity in seeking an optimal solution that maximizes the amount of contaminant metal deposition over the useful catalyst life. Results indicate that deposition capacity could be substantially increased by a nonuniform activity profile in which the activity at the catalyst center is higher than that at the outer edge. The shape of the optimum activity profile is presented along with practical design improvements.

Restricted diffusion through granular materials

“…The restricted diffusion of nonspherical molecules in granular materials is less well understood, however, due to the complexities of molecule and pore shape. A better understanding of this type of diffusion would aid in the design of petroleum residue hydrotreating catalysts (Limbach and Wei, 1988).…”

Hydrodemetallation Catalyst Pellets With Nonuniform Radial Pore Size Distribution

“…Thus, the initial pore radius refers to the size after the initial fast coking. The above assumptions have also been used in modelling studies by other investigators (Rajagopalan and Luss, 1979;Limbach and Wei, 1988;Chiang and Fang, 1994).…”

“…The values of the parameters used for the calculations are typical for hydrodemetallation conditions (Rajagopalan and Luss, 1979;Limbach and Wei, 1988;Pereira and Seeckman, 1989) and are given in Table I. Calculations were perrormed for different values of z , and Thiele modulus.…”

“…Hydrodemetallation catalysts are usually replaced when their demetallation rate reaches a limiting value (Limbach and Wei, 1988). Therefore useful catalyst lifetime, r,, is defined as the time on stream required to reach a minimum demetallation rate, Rmi,.…”

“…A few investigators (Limbach and Wei, 1988;Chiang and Fang, 1994) studied the effect of radial nonuniform catalyst activity distribution on catalyst performance, since these catalysts can offer improved performance as compared with uniform catalysts (Gavriilidis et d., 1993). Limbach and Wei (1988) demonstrated that a centerloaded catalyst pellet, which has higher activity near the catalyst interior, could force the pinch point (the point of complete pore plugging) to shift from the pore mouth towards the catalyst interior. In this way the deposition capacity could be improved.…”