HW Help

1. HW Help How do you want to run the reaction? NaOH - Solid, Liquid or Gas T for ΔGrxn = (-) Is this T going to give you S,L or G Can P influence S,L or G? How do you want to run the separation? Safety Issues? Ease of Processing

2. HW Help How do you want to run the reaction? NaOH - Solid, Liquid or Gas T for ΔGrxn = (-), rxn is exo or endo? Is this T going to give you S,L or G? Can P influence S,L or G? How do you want to run the separation? Safety Issues? Ease of Processing

3. Reactor Design for Selective Product Distribution Sieder, et.al. Chapter 15 Terry A. Ring Chemical Engineering University of Utah

4. Onion Model of Process Design

5. Overview • Parallel Reactions • A+BR (desired) • AS • Series Reactions • ABC(desired)D • Independent Reactions • AB (desired) • CD+E • Series-Parallel Reactions • A+BC+D (desired) • A+CE • Mixing, Temperature and Pressure Effects

6. Examples • Ethylene Oxide Synthesis • CH2=CH2 + O22CO2 + 2H2O • CH2=CH2 + O2CH2-CH2(desired) O

7. Examples • Diethanolamine Synthesis

8. Examples • Butadiene Synthesis, C4H6,from Ethanol

9. Examples • Maleic Anhydride Synthesis • C6H6 + 9/2 O2 C4H2O3 + 2 CO2 + 2 H2O • C4H2O3 + 3 O2 4 CO2 + H2O • C6H6 + 15/2 O2 6 CO2 + 3 H2O

10. Rate Selectivity • Parallel Reactions • A+BR (desired) • A+BS • Rate Selectivity • (αD- αU) >1 make CA as large as possible • (βD –βU)>1 make CB as large as possible • (kD/kU)= (koD/koU)exp[-(EA-D-EA-U)/(RT)] • EA-D > EA-U T • EA-D < EA-U T

11. Reactor Design to Maximize Desired Product

12. Maximize Desired Product • Series Reactions • AB(desired)CD • Plug Flow Reactor • Optimum Time in Reactor

13. Fractional Yield (k2/k1)=f(T)

14. Real Reaction Systems • More complicated than either • Series Reactions • Parallel Reactions • Effects of equilibrium must be considered • Confounding heat effects • All have Reactor Design Implications • Use Optimizer in Aspen+to evaluate Reactor Design

15. Reactor Heat Effects Sieder Chapter 15 Terry A. Ring Chemical Engineering University of Utah

16. Problems • Managing Heat effects • Optimization • Make the most product from the least reactant

17. Reaction Heat Heuristics • 21-High exothermic heat of reaction: Consider using excess reactant, inert diluents or cold shots of reactant. Consider them early on in the design • 22-Lower exothermic heat of reaction: Use heat exchanger on/in reactor. Or use intercoolers between adiabatic reaction stages. • 23-High endothermic heat of reaction: Consider use of excess reactant, inert diluents or hot shots. Consider them early on in the design. • 24-Lower endothermic heat of reaction: Use heat exchanger on/in reactor. Or use interheaters between adiabatic reaction stages.

18. Managing Heat Effects • Reaction Run Away • Exothermic • Reaction Dies • Endothermic • Preventing Explosions • Preventing Stalling

19. Equilibrium Reactor-Temperature Effects • Single Equilibrium • aA +bB  rR + sS • ai activity of component I • Gas Phase, ai = φiyiP, • φi== fugacity coefficient of i • Liquid Phase, ai= γi xi exp[Vi (P-Pis)/RT] • γi = activity coefficient of i • Vi =Partial Molar Volume of i Van’t Hoff eq.

20. Kinetic Reactors - CSTR & PFR – Temperature Effects • Used to Size the Reactor • Used to determine the reactor dynamics • Reaction Kinetics

21. Equilibrium and Kinetic Limits • Increasing Temperature Increases the Rate • Equilibrium Limits Conversion

22. PFR – no backmixing • Used to Size the Reactor • Space Time = Vol./Q • Outlet Conversion is used for flow sheet mass and heat balances

23. CSTR – complete backmixing • Used to Size the Reactor • Outlet Conversion is used for flow sheet mass and heat balances

24. Temperature Profiles in a Reactor Exothermic Reaction

25. Reactor with Heating or Cooling Q = UA ΔT Reactor is a Shell and Tube (filled with catalyst) HX

26. Best Temperature Path

27. Optimum Inlet TemperatureExothermic Rxn CSTR PFR

28. Various Reactors, Various Reactions

29. Managing Heat Effects • Reaction Run Away • Exothermic • Reaction Dies • Endothermic • Preventing Explosions • Preventing Stalling

30. Reactor with Heating or Cooling Q = UA ΔT

31. Inerts Addition Effect

32. Managing Heat Effects • Reaction Run Away • Exothermic • Reaction Dies • Endothermic • Preventing Explosions • Preventing Stalling

33. Inter-stage Cooler Lowers Temp. Exothermic Equilibria

34. Inter-stage Cold Feed Lowers Temp Lowers Conversion Exothermic Equilibria

35. Optimization of Desired Product • Reaction Networks • Heuristic 7 • Maximize yield, • moles of product formed per mole of reactant consumed • Maximize Selectivity • Number of moles of desired product formed per mole of undesirable product formed • Maximum Attainable Region – see discussion in Chap’t. 6 SS&L. • Reactors and bypass • Reactor sequences

36. Engineering Tricks • Reactor types • Multiple Reactors • Mixtures of Reactors • Bypass • Recycle after Separation • Split Feed Points/ Multiple Feed Points • Diluents • Temperature Management

37. Reactor Problem on Previous Design I Final Exam

42. Feed Temperature, ΔHrxn Adiabatic Adiabatic Cooling Heat Balance over Reactor Q = UA ΔTlm

43. Aspen KineticsThis is from Aspen Help

44. Aspen Units - Rate=kTn e[-E/RT]πCiαi i Rate Units When Rate Basis is Cat (wt), substitute sec–kg catalyst for sec·m3 in each expression above. For either rate basis, the reactor volume or catalyst weight used is determined by the reactor where the reaction occurs.