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Lecture 23. 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. Today’s lecture. Interstage Cooling Noble Prize 2007 Catalytic Steps. Catalysts and Catalysis. - PowerPoint PPT Presentation
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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 lectureInterstage CoolingNoble Prize 2007Catalytic Steps
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Catalysts and CatalysisA 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 SiteReactions 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 sitesFor the system shown, the total
concentration of sites isCt = Cv + CA.S + CB.S
N
SNVNAAD K
CCPkr
SNSN
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AdsorptionSASA
AASVAAAD k/CCPkr
VAAASAAD
VAAASAD
CPkC 0k/r
CPkC 0r :mequilibriu @
VAAVSAVT CPkCCCC
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AA
AAT
T
AS
AA
AATAS
VAA
TV
Pk1PkC
CC
Pk1PkCC
CPk1CC
More Catalysis
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Langmuir Adsorption Isotherm
AP
T
AS
CC 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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SBSB
Desorption from surface
Vacant and occupied sites
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Steps in a Catalytic ReactionBA
Adsorption on Surface SASA
Surface Reaction Single Site SBSA
Dual Site SSBSSA
Desorption from Surface SBSB
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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 NumbersCatalytic Reforming
Normal Pentane Octane Number = 62Iso-Pentane Octane Number = 95
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Steps in a Catalytic ReactionBA
Adsorption on Surface SASA
Surface Reaction Single Site SBSA
Dual Site SSBSSA
Desorption from Surface SBSB
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Steps in a Catalytic ReactionDCBA
Adsorption on Surface SASA SBSB
Surface Reaction Dual SiteSDSCSBSA
'SDSC'SBSA
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Steps in a Catalytic ReactionSurface Reaction Eley-Rideal
gDSCgBSA
Desorption form Surface SCSC SDSD
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End of Lecture 23
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