Dispersed porous particles reaction kinetics

It is desirable to list the sequence of space and point steps which together constitute global adsorption. This is not a new concept and such descriptions have frequently been presented (I, 14), particularly for fluid reactions on porous catalyst particles. The first space process, axial dispersion, is not a part of the. sequence, but it does affect the observed kinetics, and is logically considered as a space process. Its significance depends upon the reciprocal of the axial Peclet number, EJ(2R)v. The sequential steps are ... 

In the general case where the active material is dispersed through the pellet and the catalyst is porous, internal diffusion of the species within the pores of the pellet must be included. In fact, for many cases diffusion through catalyst pores represents the main resistance to mass transfer. Therefore, the concentration and temperature profiles inside the catalyst particles are usually not flat and the reaction rates in the solid phase are not constant. As there is a continuous variation in concentration and temperature inside the pellet, differential conservation equations are required to describe the concentration and temperature profiles. These profiles are used with intrinsic rate equations to integrate through the pellet and to obtain the overall rate of reaction for the pellet. The differential equations for the catalyst pellet are two point boundary value differential equations and besides the intrinsic kinetics they require the effective diffusivity and thermal conductivity of the porous pellet. 

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