The use of the dusty-gas model for the description of mass transport with chemical reaction in porous media

Abstract

In the present study, mass transport accompanied by chemical reactions in porous media is studied according to the Fick model and the dusty-gas model. For mass transport accompanied by a chemical reaction in catalyst structures showing a plane, line, or point of symmetry, the approximate analytical concept of an effectiveness factor, accounting for intraparticle diffusion, was also evaluated. For a variety of reaction schemes and kinetic rate equations, a comparison was made between the results of the numerical models (Fick and dusty-gas) and the effectiveness-factor concept. From the results it was concluded that pressure in porous catalyst with a plane, line, or point of symmetry did not affect the fluxes seriously, and, therefore, the pressure-driven flow can be omitted from the flux expression without significant loss of accuracy. Furthermore, both for single and multiple reactions, the Fick model is satisfactorily accurate to estimate the transport rate in all cases, and the results deviate only slightly from the dusty-gas model. It should be noted that this latter model requires substantially more computational time. For catalytic membranes, however, transport of inert components as well as large trans-membrane pressure differences may be present, which affect the transport of the reactants and products. The calculations showed that, in contrast to the above-mentioned structures, in this case the dusty-gas model has to be used to describe the transport.