PREDICTION OF DIFFUSION RATES IN POROUS MATERIALS AT DIFFERENT PRESSURES

Two current models for diffusion in porous catalysts are applied to diffusion data obtained over the pressure range 1-20 atm, using 12 porous materials with widely different pore-size distributions. The results of this study confirm a previous study of Satterfield and Cadle in two respects-a model of a porous structure by Johnson and Stewart can be used to predict diffusion rates to within a factor of 2 with occasional exceptions, and this model is good for extrapolating data obtained at one pressure to another pressure. In addition, the present investigation found little choice between the absolute predictive capabilities of the Johnson and Stewart model and one of Wakao and Smith, although the latter is inadequate for extrapolation with pressure. Evidence indicates that the infrequent, though serious, exceptions may be the result of severe pore constrictions. A possible converging trend of the value of (observed flux/predicted flux) when using the Wakao and Smith model at higher pressures is also observed and discussed. © 1969.