THE USE OF THE DUSTY-GAS MODEL FOR THE DESCRIPTION OF MASS-TRANSPORT WITH CHEMICAL-REACTION IN POROUS-MEDIA

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 ca talyst structures showing a plane, line, or point of symmetry, the app roximate analytical concept of an effectiveness factor, accounting for intraparticle diffusion, was also evaluated. For a variety of reactio n schemes and kinetic rate equations, a comparison was made between th e results of the numerical models (Fick and dusty-gas) and the effecti veness-factor concept. From the results it was concluded that pressure in porous catalyst with a plane, line, or point of symmetry did not a ffect the fluxes seriously, and, therefore, the pressure-driven flow c an be omitted from the flux expression without significant loss of acc uracy. Furthermore, both for single and multiple reactions, the Fick m odel 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 in ert components as well as large trans-membrane pressure differences ma y be present, which affect the transport of the reactants and products . The calculations showed that, in contrast to the above-mentioned str uctures, in this case the dusty-gas model has to be used to describe t he transport.