Falsification of kinetic parameters by transport limitations and its role in discerning the controlling regime

Abstract

Reactions occurring on the surface of a porous catalyst are accompanied by transport of heat and mass in the pores of the catalyst and across the boundary layer at the external surface. Under the conditions normally encountered in catalytic reactors, heat and mass fluxes can be large enough to cause finite gradients of concentration and temperature in the solid as well as in the film. In such instances the resulting rate of reaction is governed by both the kinetics of the reaction and the transport process (or processes) which gives rise to the gradient. Hence the dependence of the overall or global rate on temperature and the partial pressures of the reacting species can no more be expressed by the intrinsic kinetics of the reaction but is influenced also by the transport parameters of the system. In other words, in the presence of finite transport limitations the catalyst exhibits kinetics falsified by transport processes. This has been referred to as "disguised kinetics" by Wei [l]. Carberry [2] has examined the implications of this disguise in determining the operating regime of a process.