Some observations on the variation of tortuosity with Thiele modulus and pore size distribution

Abstract

Stochastic pore networks have been used to interpret the effects of pore structure on simultaneous diffusion and reaction in a porous catalyst. A stochastic pore network is a square network of pores, each pore segment having a radius assigned at random from any stipulated pore size distribution. The equations for diffusion and reaction within the network are solved rigorously for first order irreversible kinetics. The model is used to predict effectiveness factors and tortuosities for a hypothetical catalyst having one of four pore size distributions. The analysis predicts that tortuosity will vary with the Thiele modulus, the strength of this variation depending on the pore size distribution. It is further observed that the concentrations experienced by pores in a network are markedly different to those predicted by the parallel bundle model. This is relevant to the question of selectivity in complex reaction schemes.