Weisz-Prater Criterion

The Weisz -Prater criterion ( also Weisz module ( Ψ ) ) is a so-called criteria equation of Industrial Chemistry.

Application

The Weisz -Prater criterion is measurable macroscopic properties whose change can affect catalyzed chemical reactions related to each other (see also macrokinetics ).

This equation - in fact it is an inequality - is used in the development of catalysts to thus assess the influence of transport processes, in particular the diffusion of chemical substances on the reaction rate and the catalyst efficiency. The calculation of this correction factor results in a dimensionless parameter, which indicates whether the present reaction is influenced by diffusion effects.

• Ψ: Weisz module
• LC: Characteristic catalyst length in cm
• N: order of reaction
• R: Effective / Observed reaction rate in mol / (g · s )
• ρK Catalyst density in g / cm ³
• Tue, e: Effective diffusion coefficient of component i in cm ² / s
• Ci, 0: concentration of component i at the beginning of the reaction ( t = 0) in mol / l

If the result is less than one, then an influence of the diffusion to the catalyst efficiency probably excluded. It is important to note for the validity of the previous statement that restrictions exist and different catalyst geometries and reaction types not necessarily give comparable values ​​.

The Weisz - module is linked through the catalyst efficiency with the Thiele modulus as above.

• η: Catalyst efficiency
• Φ: Thiele modulus