lecture 23 - university of michigan
TRANSCRIPT
Chemical Reaction Engineering (CRE) is the field that studies the rates and mechanisms of
chemical reactions and the design of the reactors in which they take place.
Lecture 23
Today’s lecture Interstage Cooling Noble Prize 2007 Catalytic Steps
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Catalysts and Catalysis
A Catalyst is a substance that affects the rate of chemical reaction but emerges from the process unchanged.
Catalysis is the occurrence, study, and use of catalysts and catalytic processes.
Approximately 1/3 of the GNP of materials produced in the U.S. involves a catalytic process.
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Catalysts affect both Selectivity and Yield
Different reaction Paths
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Different shapes and sizes of catalyst.
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Catalytic packed-bed reactor, schematic.
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Steps in a Catalytic Reaction
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Active Site Reactions are not catalyzed over the entire surface but only at
certain active sites or centers that result from unsaturated atoms in the surface.
An active site is a point on the surface that can form strong chemical bonds with an adsorbed atom or molecule.
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The Adsorption Step
Vacant and occupied sites
For the system shown, the total concentration of sites is Ct = Cv + CA.S + CB.S
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Adsorption
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More Catalysis
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Langmuir Adsorption Isotherm
Increasing T
Slope=kA
More Catalysis
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The Surface Reaction Step
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The Surface Reaction Step
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The Surface Reaction Step
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The Surface Reaction Step
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The Surface Reaction Step
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Desorption from surface
Vacant and occupied sites
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Steps in a Catalytic Reaction
Adsorption on Surface
Surface Reaction Single Site
Dual Site
Desorption from Surface
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The Rate Limiting Step: Which Step Has the Largest Resistance?
Electrical analog to heterogeneous reactions
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Collecting information for catalytic reactor design
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Octane Numbers Catalytic Reforming
Normal Pentane Octane Number = 62 Iso-Pentane Octane Number = 95
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Steps in a Catalytic Reaction
Adsorption on Surface
Surface Reaction Single Site
Dual Site
Desorption from Surface
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Steps in a Catalytic Reaction
Adsorption on Surface
Surface Reaction Dual Site
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Steps in a Catalytic Reaction
Surface Reaction Eley-Rideal
Desorption form Surface
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End of Lecture 23
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