Calculations of gas phase diffusion and reaction in heterogeneous catalysts the importance of viscous flow

The problem of multicomponent gas phase diffusion fora single overall reaction in porous catalysts is analyzed using the dusty-gas theory. Recent authors have shown that neglecting internal pressure gradients results in modeling inconsistencies and errors in computation in small pore catalysts. However, calculations based upon kinetic theory estimates of the transport coefficients reveal that the viscous flow contribution to the component i molar flux can be neglected with excellent justification. The resulting equations are internally consistent and greatly simplified. For illustrative purposes the multicomponent example of P. Schneider⁷ is reformulated to take into account nonuniform pressure (but negligible viscous flux), and as a consequence the inconsistency noted in the original reference is removed. Two methods for computing the effectiveness factor are discussed.