Transient Analysis of Deactivation in a Single Pellet with Changing Diffusivity and Voidage

The transient deactivation process is modeled taking into account for the first time pore size reduction due to coke deposition and consequent changes in voidage and Knudsen diffusivity. A coupled set of partial differential equations is set up to describe systems in which the deactivating reaction is too rapid for the pseudo-steady-state analysis to be useful. The model contains three parameters; Ø, the Thiele modulus, γ, the ratio of molal density of coke to the bulk concentration of the fluid reactant, and μ, the reciprocal of the minimum fractional coke loading at which the reaction ceases. The governing equations are solved numerically, and the results are presented in terms of η as a function of time with γ, μ, and Ø as parameters. It is shown that η passes through a minimum value at a time that is characteristic of the system and the operating conditions. This is the time for which it is most beneficial to operate the reactor in question. Copyright © 1986, American Chemical Society. All rights reserved.