Weisz-Prater criterion

The Weisz-Prater criterion (also Weisz module ( Ψ )) is a so-called criteria equation in technical chemistry .

application

The Weisz-Prater criterion relates measurable macroscopic properties, the changes of which can affect catalyzed chemical reactions , to one another (see also macrokinetics ).

This equation - strictly speaking, an inequality - is used in the development of catalysts to estimate the effects of transport processes, in particular the diffusion of chemical substances , on the reaction rate and thus on the catalyst efficiency. The calculation of this correction factor results in a dimensionless number that indicates whether the reaction is influenced by diffusion effects.

${\displaystyle \Psi ={L_{C}}^{2}\cdot {\frac {n+1}{2}}\cdot {\frac {r\cdot \rho _{K}}{D_{i,e}\cdot c_{i,0}}}<1}$

• Ψ: Weisz module
• L _C : Characteristic length of the catalyst in cm
• n: reaction order
• r: Effective / observed reaction rate in mol / (g s)
• ρ _K : catalyst density in g / cm³
• D _{i, e} : Effective diffusion coefficient of component i in cm² / s
• c _{i, 0} : concentration of component i at the beginning of the reaction (t = 0) in mol / l

If the result is less than one, an influence of diffusion on the catalyst efficiency is probably excluded. For the validity of the previous statement, it should be noted that restrictions exist and different catalyst - geometries and reaction types may not exactly comparable values.

The Weisz module is linked to the so-called Thiele module via the catalyst efficiency.

${\displaystyle \Psi =\eta \cdot \Phi ^{2}}$

• η: catalyst efficiency
• Φ: Thiele module

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Individual evidence

1. ↑ Technical chemistry: Introduction to chemical reaction technology, by Gerhard Emig, Elias Klemm . books.google.de. Retrieved November 25, 2009.

literature

• Weisz, PB & Prater, CD: Interpretation of measurements in experimental catalysis . Advances in Catalysis, 6 : 143-196 (1954)