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

2. Onion Model of Process Design

3. Overview Parallel Reactions Series Reactions Independent 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
A+CE(desired)
Mixing, Temperature and Pressure Effects

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

5. Examples
Diethanolamine Synthesis
Series-parallel

6. Examples
Butadiene Synthesis, C4H6, from Ethanol
Series-parallel

7. Rate Selectivity Parallel Reactions Rate Selectivity
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

8. Reactor Design to Maximize Desired Product

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

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

11. 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

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

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

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

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

16. 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.

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

18. Equilibrium and Kinetic Limits
Increasing Temperature Increases the Rate
Equilibrium Limits Conversion

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

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

21. Temperature Profiles in a Reactor
Exothermic Reaction

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

23. Best Temperature Path

24. Optimum Inlet Temperature Exothermic Rxn
CSTR
PFR

25. Various Reactors, Various Reactions

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

27. Reactor with Heating or Cooling
Q = UA ΔT

28. Inerts Addition Effect

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

30. Inter-stage Cooler
Lowers Temp.
Exothermic Equilibria

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

32. 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

33. Reactor Problem on Design I Final Exam

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

39. Aspen Kinetics

40. Aspen Units on Rate
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.

41. HW 2 Kinetics Paper’s Rate expression P = atm (assumes 1 atm)
mcat =mass of catalyst
rj = Aj exp(-Ejq)
a = activity of catalyst (dimensionless)
Aj = atm/s/gmcat
Ej=39.9 kJ/mole

42. How to Make Sense of this Mess