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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 1/22/2013. 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 1/22/2013 • 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. Review Lecture 2 ReactorMole Balances Summary in terms of conversion, X X Batch t CSTR X W PFR PBR

  4. Review Lecture 2 Levenspiel Plots

  5. Review Lecture 2 PFR

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

  7. Review Lecture 2 Reactors in 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: Rate 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

  10. Review Lecture 3 Arrhenius Equation 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 Reaction Engineering Mole Balance Rate Laws Stoichiometry These topics build upon one another

  12. Review Lecture 3 Algorithm 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 Tablesusing species A as our basis of calculation in the following reaction. We will use the stoichiometric tables to express the concentration as a function of conversion. We will combine Ci = f(X) with the appropriate rate law to obtain -rA = f(X). A is the limiting reactant.

  14. Stoichiometry For every mole of A that reacts, 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. Stoichiometry Constant Volume Batch 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 Constant Volume Batch Suppose Batch: Equimolarfeed: Stoichiometricfeed:

  18. Stoichiometry Constant Volume Batch If , then ConstantVolumeBatch and wehave

  19. Batch Reactor - Example Calculate the equilibrium conversion for gas phase reaction, Xe . Consider the following elementary reaction with KC=20 dm3/mol and CA0=0.2 mol/dm3. Find Xe for both a batch reactor and a flow reactor.

  20. Batch Reactor - Example Step 1: Step 2: rate law: CalculateXe

  21. Batch Reactor - Example Totals: NT0=NA0 NT=NA0 -NA0 X/2 @ equilibrium: -rA=0

  22. Batch Reactor - Example Solution: At equilibrium Batch Stoichiometry: Constant Volume:

  23. Batch Reactor - Example

  24. Flow System – Stoichiometry Table Where:

  25. Flow System – Stoichiometry Table Where: and Concentration – Flow System

  26. Flow System – Stoichiometry 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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