Day32 - CE 561 Lecture Notes Fall 2009 Day 32 Review of the...

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CE 561 Lecture Notes Fall 2009 p. 1 of 7 Day 32: Review of the second half of the course In this review, I have tried to identify the key points that you should understand from each topic that we have covered in the second part of the course. Since the problem of coupled mass transport and reaction is sort of on the border between chemical kinetics (the first half of the course) and reaction engineering and reactor modeling (the second half of the course), it will also be included in the material for the second exam. Therefore, this review of the 2 nd half of the course will begin with the Days 17 and 18 notes and continue through the day 31 notes. These are the topics that will explicitly be covered on the exam. Of course, there will necessarily be implicit coverage of the 1 st half of the course, other science and engineering knowledge, and your general knowledge of the world around you. So, what have we learned? Transport effects on reactions at solid surfaces (and in catalyst pellets) Conceptual understanding of the consecutive steps that must occur in a reaction at a solid surface inside a porous catalyst and how this impacts reaction rates. Understanding of limiting cases of reaction limited, external mass transfer limited, and pore diffusion limited behavior. External transport limitations and the relationship between the observed or effective reaction rate coefficient, the mass transfer coefficient, and the rate coefficient for surface reaction. g r r g eff k k k k k + = External heat transfer limitations and the relationship between the concentration change and the temperature change across the external boundary layer How external heat transfer limitations can lead to multiple steady states of the catalyst pellet for an exothermic reaction Definitions of the Thiele modulus and effectiveness factor . The relationship between these two. Some idea of how this relationship was derived and the assumptions that go into it. i.e. ( ) φ η tanh = , s A p r D d k l ε τ 4 = for a catalyst slab of thickness 2 l Relationships between catalyst properties: porosity, specific surface area, pellet density, true or material density, effective pore diameter, etc. Generalized Thiele modulus for particles of arbitrary shape: 2 s A r c g D k S S V ρ =
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CE 561 Lecture Notes Fall 2009 p. 2 of 7 Effect of diffusion limitations on the observed reaction order and activation energy Combined internal and external mass transfer – the global effectiveness factor ( ) ( ) φ τ φε η tanh 1 tanh 1 + = g A s G k l D Combined diffusion and heat transfer limitations (non-isothermal catalyst particle). Relationships between the various temperature drops and concentration drops. The possibility of multiple steady states and a qualitative picture of the effectiveness factor as a function of Thiele modulus for a non-isothermal catalyst pellet.
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Day32 - CE 561 Lecture Notes Fall 2009 Day 32 Review of the...

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