Stochastic Pore Network Research Articles

Diffusion and consecutive reactions in stochastic pore networks

Porous catalyst particles of dimensions greater than a few microns inevitably contain inter-connected pore spaces which are chaotically configured with respect to size, shape and orientation. Within such complex geometry, it is difficult to obtain tractable yet satisfactorily realistic solutions for the equations describing coupled diffusion and catalytic reaction. A general mathematical treatment has been developed for an arbitrarily complex reaction scheme to solve equations describing diffusion coupled with multiple reactions within a stochastic pore network. Representative calculations are presented for the consecutive reaction A → B → C, and are compared with the predictions of parallel bundles having the same pore size distribution. The predictions of the model are compared with experimental results for the dehydrogenation of butene.

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

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.

Deactivation of a supported zeolitic catalyst: Diffusion, reaction and coke deposition in stochastic pore networks

The decline in activity of a commercial, supported catalyst has been interpreted using a model of zeolitic micropores uniformly distributed within a network of macropores representing the silica/alumina support. Using this model, simultaneous deactivation by site coverage and pore plugging can be simulated. Changes in network structure due to fouling are monitored by generation of theoretical adsorption isotherms for both fresh and fouled networks. The observed deactivation for catalytic cumene cracking in a plug flow reactor at 500°C was modelled by a series coking mechanism with the coke reducing the macropore radii by approximately 30 Angstrom.