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Lecture 24

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

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  1. 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.

  2. Today’slecture • Normal Pentene Iso-Pentane • Langmuir Adsorption Isotherm • Catalytic Converters for Automobiles

  3. Last Lecture • Catalytic Reforming Reaction (Gasoline) • Normal Pentane Octane Number=62 • Iso-Pentane Octane Number=90 • Normal Pentane  Iso-Pentane

  4. Steps in a CatalyticReaction

  5. Ethylidyne as chemisorbed on platinum (Adapted from G.A.Somorjai, Introduction to Surface Chemistry and Catalysis, Wiley, New York, 1994)

  6. Steps in a CatalyticReaction Adsorption on Surface Surface Reaction Single Site Desorption from Surface Dual Site

  7. Platinum on alumina (Figure from R.I. Masel, Chemical Kinetics and Catalysis, Wiley , New York, 2001, p 700)

  8. -H2 Al2O3 0.75 wt% Pt n-pentenei-pentene n-pentanen-pentene NI n-pentanei-pentane Al2O3 Pt +H2 i-pentane Pt Al2O3 i-pentene

  9. 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.

  10. 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

  11. 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

  12. 4. Write a SiteBalance. 5. Derive the rate law. Combine steps 2, 3 and 4 to arrive at the rate law:

  13. Automotive CatalyticConverters Placed inline with exhaust system (~$500) NOx plays big role in smog formation

  14. Automotive CatalyticConverters 1) Propose a mechanism

  15. Automotive CatalyticConverters (from graph data, we see CO2 is not on the surface and that the surface reaction is irreversible)

  16. Automotive CatalyticConverters

  17. 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

  18. Automotive CatalyticConverters optimum

  19. End of Lecture 24

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