Internal Mass Transfer Coefficients for Modeling of Diffusion and Reaction in Washcoated Catalytic Monoliths

In the traditional reaction engineering literature, the concept of catalyst effectiveness factor is used to simplify the problem of diffusion and reaction in the washcoated monoliths. But this concept has some major limitations. For example, the effectiveness factor concept does not reduce the local degrees of freedom and requires the solution of the full multi-component diffusion-reaction problem in the washcoat, which can be computationally demanding. Second, it is difficult to generalize for non-uniform or irregular washcoat and channel geometric shapes and multiple reactions with no clearly defined limiting reactant(s). In this work, we extend the recently developed concept of internal mass transfer coefficient to simplify the multi-component diffusion and reaction problem in washcoated catalytic monoliths. Further, we study the dependence of the dimensionless internal mass transfer coefficient (Shi) on washcoat and channel geometric shapes, reaction kinetics, catalyst loading and activity profile. It is also reasoned that the concept of Shi is more useful and fundamental than the classical effectiveness factor concept.