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Lecture 24. 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. Normal Pentene Iso -Pentane Langmuir Adsorption Isotherm Catalytic Converters for Automobiles.
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Lecture 24 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’slecture • Normal Pentene Iso-Pentane • Langmuir Adsorption Isotherm • Catalytic Converters for Automobiles
Last Lecture • Catalytic Reforming Reaction (Gasoline) • Normal Pentane Octane Number=62 • Iso-Pentane Octane Number=90 • Normal Pentane Iso-Pentane
Steps in a CatalyticReaction Adsorption on Surface Surface Reaction Single Site Desorption from Surface Dual Site
Al2O3 -H2 0.75 wt% Pt n-pentenei-pentene n-pentanen-pentene NI n-pentanei-pentane Al2O3 Pt +H2 i-pentane Pt Al2O3 i-pentene
Isomerization of n-pentene (N) to i-pentene (I) over alumina N I Surface Reaction: Adsorption on Surface: Desorption: 1. Select a mechanism (Mechanism Dual Site) Al2O3 Treateachreaction step as an elementaryreactionwhenwriting rate laws.
2. Assume a rate-limiting step. Choose the surfacereaction first, sincemorethan 75% of all heterogenousreactions that are not diffusion-limited are surface-reaction-limited. The rate law for the surfacereaction step is
3. Find the expression for concentration of the adsorbed species CI.S. Use the other steps that are not limiting to solve for CI.S (e.g., CN.S and CI.S). For this reaction, From From
4. Write a SiteBalance. 5. Derive the rate law. Combine steps 2, 3 and 4 to arrive at the rate law:
Automotive CatalyticConverters Placed inline with exhaust system (~$500) NOx plays big role in smog formation
Automotive CatalyticConverters 1) Propose a mechanism
Automotive CatalyticConverters (from graph data, we see CO2 is not on the surface and that the surface reaction is irreversible)
Automotive CatalyticConverters Is this consistent with the given data? -No CO2 in rate law -rate law decreases as PN2 increases The contribution of PN2 is very small and can be neglected
Automotive CatalyticConverters optimum