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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. Lecture 4 – Tuesday 1/18/2011. 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. Lecture 4 – Tuesday 1/18/2011 • Block 1 • MoleBalances • Size CSTRs and PFRs given –rA=f(X) • Block 2 • RateLaws • Reaction Orders • Arrhenius Equation • Block 3 • Stoichiometry • Stoichiometric Table • Definitions of Concentration • Calculate the Equilibrium Conversion, Xe

  3. Review Lecture 2 Building Block 1: MoleBalancesIn terms of conversion X Batch t X CSTR W PFR PBR

  4. Review Lecture 2 LevenspielPlot

  5. Review Lecture 2 PFR

  6. Review Lecture 2 Reactorsin Series Only valid if there are no side streams

  7. Review Lecture 2 Reactorsin Series

  8. Review Lecture 2 Two steps to get                    Step 1: Rate Law Step 2: Stoichiometry Step 3: Combine to get

  9. Review Lecture 3 Building Block 2: RateLawsPower 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

  10. Review Lecture 3 ArrheniusEquation k E = Activation energy (cal/mol) R = Gas constant (cal/mol*K) T = Temperature (K) A = Frequency factor (same units as rate constant k) (units of A, and k, depend on overall reaction order) T

  11. Review Lecture 3 ReactionEngineering Mole Balance Rate Laws Stoichiometry These topics build upon one another

  12. Review Lecture 3 How to find Step 1: Rate Law Step 2: Stoichiometry Step 3: Combine to get

  13. Building Block 3: Stoichiometry 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 limiting Reactant.

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

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

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

  17. Stoichiometry Suppose Batch: Equimolarfeed: Stoichiometricfeed:

  18. Constant Volume Batch (BR) • Stoichiometry if then ConstantVolumeBatch and wehave

  19. BRExample 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.

  20. BRExample CalculateXe Step 1: Step 2: rate law,

  21. BRExample CalculateXe Totals: NT0=NA0 NT=NA0 -NA0 X/2 @ equilibrium: -rA=0

  22. BRExample Calculating the equilibriumconversion for gas phasereaction At equilibrium Solution: Batch Stoichiometry Constantvolume

  23. BRExample

  24. Building Block 3: StoichiometryFlow System Stochiometric Table Where:

  25. Building Block 3: StoichiometryFlow System Stochiometric Table Where: and Concentration – Flow System

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

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

  28. Heat Effects Isothermal Design Stoichiometry Rate Laws Mole Balance

  29. End of Lecture 4

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