1. Lecture 12
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’s lecture Multiple Reactions Selectivety and Yield
Series Reactions
Complex Reactions

3. 4 Types of Multiple Reactions
Series: A → B → C
Parallel: A → D,
A → U
Independent: A → B,
C → D
Complex: A + B →C + D,
A + C → E
With multiple reactors, either molar flow or number of moles must be used (no conversion!)

4. Selectivity and Yield
There are two types of selectivity and yield: Instantaneous and Overall.
Instantaneous
Overall
Selectivity
Yield

5. Selectivity and Yield Example: Desired Product: Undesired Product:
To maximize the selectivity of D with respect to U run at high concentration of A and use PFR.

6. Gas Phase Multiple Reactions

7. Multiple Reactions Chapter 8
A) Mole Balance of Each Species
Flow Batch

8. Multiple Reactions Chapter 8
A) Rates:
a) Rate law for each reaction
b) Net Rates
c) Relative Rates

9. Multiple Reactions Chapter 8
Stoichiometry:
Example: A → B → C
(1) A → B k1
(2) B → C k2

10. Multiple Reactions Chapter 8
1) Mole Balance:
V=V0 (constant batch)

11. Multiple Reactions Chapter 8
Laws
Net rates
2) Rates:
Relative rates

12. Batch Series Reactions
example: A → B → C
(1) A → B
(2) B → C t
topt Ci A B C
1) Mole balances:

13. Batch Series Reactions
2) Rates:
Laws:
Relative:

14. Batch Series Reactions
3) Combine:
Species A:
Species B:

15. Batch Series Reactions
Using the integrating factor,
at t = 0, CB=0

16. Batch Series Reactions
When should you stop the batch series reaction to obtain the maximum amount of B? Let’s see. t
topt Ci A B C

17. Example: CSTR Series Reactions ABC
what is the optimal ?
1) Mole Balance:

18. Example: CSTR Series Reactions ABC
2) Rates:
Laws:
Net:
Relative:

19. Example: CSTR Series Reactions ABC
3) Combine:

20. Example: CSTR Series Reactions ABC
Find maximum concentration of B

22. Net Rate of Reaction for species A
For N reactions, the net rate of formation of species A is:
For a given reaction i:
(i) aiA+biB ciC+diD:

23. Example A: Liquid Phase PFR
Complex Reactions
Example A: Liquid Phase PFR
NOTE: The specific reaction rate k1A is defined with respect to species A.
The complex liquid phase reactions follow elementary rate laws
NOTE: The specific reaction rate k2C is defined with respect to species C.

24. Example A: Liquid Phase PFR
The reaction takes place in a PFR. The feed is equal molar in A and B and FA0=200 mol/min and the volumetric flow rate is 100 dm3/min. The reaction volume is 50 dm3 and the rate constants are:
Plot FA, FB, FC, FD and SC/D as a function of V.

25. Example A: Liquid Phase PFR
Mole Balances:

26. Example A: Liquid Phase PFR
Net Rates:
(5)
(6)
(7)
(8)
Rate Laws:
(9)
(10)

27. Example A: Liquid Phase PFR
Relative Rates:
Reaction 1
(11)
(12)
Reaction 2
(13)
(14)

28. Example A: Liquid Phase PFR
Selectivity
If one were to write SC/D=FC/FD in the Polymath program, Polymath would not execute because at V=0, FC=0 resulting in an undefined volume (infinity) at V=0. To get around this problem we start the calculation 10-4 dm3 from the reactor entrance where FD will not be zero and use the following IF statement.
(15)

29. Example A: Liquid Phase PFR
Stoichiometry:
(16)
(17)
(18)
(19)
Parameters:
(20)
(21)
(22)

30. End of Lecture 12

31. Supplementary Material - Blood Coagulation

33. Notations

34. Notations

35. Mole Balance

36. Mole Balance

37. Mole Balance

38. Result

39. Blood Coagulation
Many metabolic reactions involve a large number of sequential reactions, such as those that occur in the coagulation of blood.
Cut → Blood → Clotting
Figure A. Normal Clot Coagulation of blood
(picture courtesy of: Mebs, Venomous and Poisonous Animals, Medpharm, Stugart 2002, Page 305)

40. Schematic of Blood Coagulation

41. Cut
A + B C D E F
Clot