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| {{Orphan|date=February 2009}}
| | Alyson is the title people use to contact me and I think it seems fairly good when you say it. To play lacross is the thing I adore most of all. Office supervising is where her main income arrives from. For years he's been living in Alaska and he doesn't plan on changing it.<br><br>Look at my homepage: psychic phone, [http://203.250.78.160/zbxe/?document_srl=1792908 visit here], |
| The '''Weisz-Prater Criterion''' is a method used to estimate the influence of pore diffusion on reaction rates in heterogeneous catalytic reactions.<ref>{{Cite journal|last1=Weisz|first1=P. B.|last2=Prater|first2=C. D.|title=Interpretation of Measurements in Experimental Catalysis|journal=Advances in Catalysis|volume=6|date=1954|pages=143|doi=10.1016/S0360-0564(08)60390-9|postscript=<!--None-->|series=Advances in Catalysis|isbn=978-0-12-007806-6}}</ref> If the criterion is satisfied, pore diffusion limitations are negligible. The criterion is <br />
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| <math>N_{W-P} = \dfrac{\mathfrak{R} R^2_p}{C_s D_{eff}} \le 3\beta</math><br />
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| Where <math>\mathfrak{R}</math> is the [[reaction rate]] per volume of catalyst, <math>R_p</math> is the catalyst particle radius, <math>C_s</math> is the reactant concentration at the particle surface, and <math>D_{eff}</math> is the effective [[mass diffusivity|diffusivity]]. Diffusion is usually in the [[Knudsen number|Knudsen]] regime when average pore radius is less than 100 nm.<br />
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| For a given effectiveness factor,<math>\eta</math>, and [[reaction order]], n, the quantity <math>\beta</math> is defined by the equation:<br /> | |
| <math>\eta = \dfrac{3}{R^3_p} \int_{0}^{R_p} [1-\beta (1-r/R_p)^n] r^2\ dr</math><br />
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| for small values of beta this can be approximated using the [[binomial theorem]]:<br />
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| <math>\eta = 1-\dfrac{n \beta}{4}</math><br />
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| Assuming <math>\eta \ge 0.95</math> with a 1st or zero order reaction gives values of <math>\beta</math>, 0.6 and 6 respectively. Therefore for many conditions, if <math>N_{W-P} \le 0.3</math> then pore diffusion limitations can be excluded.<ref>{{cite book|last=Vannice|first=M. Albert| title=Kinetics of Catalytic Reactions|publisher=Springer Science+Business Media|place=New York|year=2005|pages=63–65}}</ref>
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| == References ==
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| <references />
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| [[Category:Scientific techniques]]
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| [[Category:Laboratory techniques]]
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| [[Category:Transport phenomena]]
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| [[Category:Chemical engineering]]
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Revision as of 11:16, 4 March 2014
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