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Lecture 4

Lecture 4. 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. Block 1 Mole Balances Size CSTRs and PFRs given – r A = f(X ) Block 2 Rate Laws

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Lecture 4

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  1. Lecture 4 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 • Block 1 • Mole Balances • Size CSTRs and PFRs given –rA=f(X) • Block 2 • Rate Laws • Reaction Orders • Arrhenius Equation • Block 3 • Stoichiometry • Stoichiometric Table • Definitions of Concentration • Calculate the Equilibrium Conversion, Xe

  3. ReactorMoleBalances in terms of conversion X Batch t X CSTR W PFR PBR

  4. Last LectureRelative Rates of Reaction

  5. Last LectureRate Laws - Power Law Model A reactor follows an elementary rate law if the reaction orders just happens to agree with the stoichiometric coefficients for the reaction as written. e.g. If the above reaction follows an elementary rate law 2nd order in A, 1st order in B, overall third order

  6. Last LectureArrhenius Equation k is the specificreaction rate (constant) and is given by the Arrhenius Equation. Where: k T

  7. ReactionEngineering Mole Balance Rate Laws Stoichiometry These topics build upon one another

  8. How to find Step 1: Rate Law Step 2: Stoichiometry Step 3: Combine to get

  9. We shall set up Stoichiometry Tables using species A as our basis of calculation in the following reaction. Wewilluse the stochiometrictables to express the concentration as a function of conversion. WewillcombineCi = f(X) with the appropriate rate law to obtain-rA = f(X). A is the limitingReactant.

  10. For everymole of A that react, b/a moles of B react. Thereforemoles of B remaining: Let ΘB = NB0/NA0 Then:

  11. Batch System Stoichiometry Table Where: and δ = change in total number of mol per mol A reacted

  12. ConstantVolumeBatch Note: If the reaction occurs in the liquid phase or if a gas phasereactionoccurs in a rigid (e.g. steel) batchreactor Then etc.

  13. Stoichiometry Suppose Batch: Equimolarfeed: Stoichiometricfeed:

  14. ConstantVolumeBatchReactor (BR) if then ConstantVolumeBatch and wehave

  15. BR Example Calculating the equilibrium conversion for gas phase reaction,Xe Consider the following elementary reaction with KC=20 dm3/mol and CA0=0.2 mol/dm3. Xe’ for both a batch reactor and a flow reactor.

  16. BR Example CalculateXe Step 1: Step 2: rate law,

  17. BR Example CalculateXe Totals: NT0=NA0 NT=NA0 -NA0 X/2 @ equilibrium: -rA=0

  18. BR Example Calculating the equilibriumconversion for gas phasereaction At equilibrium Solution: Batch Stoichiometry Constantvolume

  19. BR ExampleXeb

  20. Flow System Stochiometric Table Where:

  21. Flow System Stochiometric Table Where: and Concentration – Flow System

  22. Flow System Stochiometric Table Where: and Concentration – Flow System

  23. Concentration Flow System: LiquidPhase Flow System: Flow LiquidPhase etc. We will consider CA and CB for gas phase reactions in the next lecture

  24. Heat Effects Isothermal Design Stoichiometry Rate Laws Mole Balance

  25. End of Lecture 4

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