1. Department of Chemical Engineering – Faculty of Engineering
Modeling and Control of Molecular Weight Distribution in a Liquid-phase Polypropylene Reactor
Dr. Mohammad Al-haj Ali
Department of Chemical Engineering – Faculty of Engineering
King Saud University

2. Motivation
Producing tailor-made polypropylenes, by using a single reactor

3. Motivation
MWD = g (T,H2)
Rp = h (T,H2)

4. Project phases
to develop a predictive kinetic model for propylene polymerization in liquid pool.
to improve the understanding of the relationship between polypropylene molecular weight and MWD and hydrogen concentration in liquid propylene as well as model this dependency.
to study the optimal grade change of polypropylene.
to perform a feasibility study of the optimal broadening of MWD.
to build hollow shaft reactor set-up.

5. Experimental set-up 5.0 L batch reactor. Ziegler-Natta catalyst:
Max. operating Pressure = 60 bar.
Liquid and gas polymerization
reactions.
Ziegler-Natta catalyst:
MgCl2/TiCl4/phthalate – AlEt3/Silane

6. Experimental Results Reproducibility
Experimental conditions: T = 70 °C, mass of catalyst = 3.78 mg, mass of cocatalyst = 1000 mg, hydrogen added = 150 mg

7. Effect of reactor filling on polymerization kinetics
Run
T, °C
Catalyst, mg
Cocatalyst mg
Donor, mg
H2, mg
Yield, kg/gcat. hr
Filling degree 1 70
3.78
500 30
12.6 H 2
1040 50
15.6 T 3
150
59.8 4
82.5

8. Effect of reactor filling on polymerization kinetics
Run
T, °C
Catalyst, mg
Cocatalyst, mg
Donor, mg
H2, mg
Yield, kg/gcat. hr
Filling degree 3 70
3.78
500 30
150
59.8 H 4
1040 50
82.5 T 5 80
1.54
120
52.5 6
119.8

9. Kinetics and Molecular weight distribution
Experimental recipe:
Liquid-pool polymerization in a fully-filled reactor.
Different hydrogen amounts.
0.0 mg mg Hydrogen
Different reaction temperatures.
60 °C - 80 °C

10. Kinetics: hydrogen and temperature effects
T = 70 °C
Run
H2, mg
X*10-3
X=CH2/Cm
tr, min
Rpo, kg/gcat. hr
kd, hr-1 1
0.0 60
16.1
0.34 2 25
0.24
62.5
0.80 3
150
1.44 47
121.6
1.19 4
250
2.47 45
145.1
1.50 5
1000
9.94
139.6
1.93 6
2500
26.7 30
125.9
2.81

11. Kinetics: hydrogen and temperature effects

12. Kinetics: hydrogen and temperature effects

13. Kinetics: modeling

14. Molecular weight distribution

15. Process model

16. Optimal Grade Transition
Objective function:
Solution methods:
Pontryagin’s Minimum Principle
Simultaneous method
Control Parameterization technique

17. Optimal Grade Transition
Control Parameterization technique

18. Optimal Grade Transition
Pontryagin’s Minimum Principle

19. Optimal Grade Transition

20. Optimal Broadening of MWD
Broadened polypropylene produced in the continuous reactor
Objective function:

21. Optimal Broadening of MWD
Broadened polypropylene produced in the continuous reactor

22. Optimal Broadening of MWD
Broadened polypropylene produced in the continuous reactor

23. Hollow Shaft Reactor Minimum dead volume. Can be modeled as CSTR.
2.0 L reactor.
Max. operating Pressure = 250 bar
Max. operating Temperature = 250° C
Minimum dead volume.
Can be modeled as CSTR.

24. Hollow Shaft Reactor
Monomer supply unit

25. Catalyst injection unit
Hollow Shaft Reactor
Catalyst injection unit

26. Hollow Shaft Reactor
The reactor

27. Hollow Shaft Reactor
Experimental results

28. ?

29. Polymerization Mechanism
Initiation
Propagation

30. Polymerization Mechanism
Propagation

31. Dormant site theory

32. Dilatometry
Pressure-drop dilatometry

33. Dilatometry
Pressure-drop dilatometry

34. Pressure-drop dilatometry
Experimental conditions: T = 70 °C, mass of catalyst = 3.78 mg, mass of cocatalyst = 1000 mg, H2 = 150 mg
Experimental conditions: T = 70 °C, mass of catalyst = 3.78 mg, mass of cocatalyst = 1000 mg, H2 = 1000 mg
Extrapolated
H2, mg
0.0 50
250
1000 M1
1.85
1.57
1.62
3.10 M2
2.01
1.99
2.05
4.80
1000
3.2 4

35. Compensation dilatometry

36. Molecular weight distribution

37. Molecular weight distribution

38. Molecular weight distribution

39. Design of Control Scheme

40. Design of Control Scheme
Nonlinear Multivariable Controller:
Generic model control (GMC)-based controller
= 0

41. Design of Control Scheme
Nonlinear Multivariable Controller:
Generic model control (GMC)-based controller

42. Design of Control Scheme
Nonlinear Multivariable Controller:
Generic model control (GMC)-based controller

43. Design of Control Scheme

44. Design of Control Scheme

45. Design of Control Scheme

46. Design of Control Scheme

47. Optimal Broadening of MWD
Batch mixing of two polypropylene samples