Mass Transfer with Chemical Reactions in Porous Catalysts: A Discussion on the Criteria for the Internal and External Diffusion Limitations

摘要

In this study, criteria for internal mass transfer given in the literature were investigated by considering tortuosity (t) in the porous catalysts. Uncertainties in τ, which may have values between 2 to 7, have a big impact on the effective diffusivity (D_(eff)) which also affects the Thiele Modulus (Φ). Since effectiveness factor (η) is function of Φ, then the criteria given for limitations are questionable. The value of D_(eff), and in turn the value of Φ calculated for the t=2 to 7. At low Φ the effects are very small, but when the Φ increases the effect becomes more pronounced. As a result, when using internal mass transfer limitations, one has to be very careful not to get trapped by the disguised kinetics, results of which may end up with disaster.