Post on 11-Oct-2018
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A great deal of my work is just playing with equations and seeing what they give. Paul Dirac (1902-1984)
ANALYSIS OF ETHYLENE/1-OLEFIN COPOLYMERS MADE WITH ZIEGLER-NATTA CATALYSTS BY DECONVOLUTION
OF GPC-IR DISTRIBUTIONS
João BP Soares, Saeid Mehdiabadi Department of Chemical and Materials Engineering
University of Alberta, Edmonton, AB, Canada
Boping Liu, Keran Chen State Key Laboratory of Chemical Engineering
East China University of Science and Technology, Shanghai, China
International Symposium on GPC/SEC and Related Techniques September 26-29, 2016, Amsterdam, Netherlands
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Acknowledgements
Mr Keran Chen Professor Boping Liu State Key Laboratory of Chemical Engineering East China University of Science and Technology Shanghai, China
Dr Saeid Mehdiabadi Department of Chemical and Materials Engineering University of Alberta Edmonton, AB, Canada
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Deconvolution of GPC-IR distributions identifies the minimum number of active sites on Ziegler-Natta catalysts.
This method also estimates the apparent kinetic constants for activation, propagation, deactivation, and comonomer incorporation of each site type.
Summary
Site Mn (103) SCB/1000C
1 3 29.6
2 12.5 11.3
3 37 6.2
4 112 4.2
5 350 3.4
Introduction Method GPC-IR Kinetics Conclusions
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Ziegler-Natta polyolefins have broad molecular weight and chemical composition distributions.
Problem Formulation
Log MW
W
SCB
Log MW
W
SCB
It should look like this,
but it looks like this,
A reasonable explanation is that there are 2 or more site types, each making polymer with the distribution on the left of the slide.
PDI = 2
PDI > 4
Introduction Method GPC-IR Kinetics Conclusions
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Multiplicity of Active Site Types
1 2 3
0.880.91
0.930.95
0.980
20
40
60
80
100
0.00
1.38
2.75
4.13
FA
w(l
ogr,
FA)
log r
1
2 3
1 2
3
Hypothesis: Different polymer populations are made on each site type
Introduction Method GPC-IR Kinetics Conclusions
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Methodology
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
3 4 5 6 7
SCB/
1000
C
w log
MW
log MW
j 1 2 3 4 5 m 0.0378 0.1800 0.4333 0.2674 0.0815 Mn 7 400 23 900 64 900 164 000 507 000
SCB/1000C 7.05 1.98 1.10 0.99 0.99
BF 0.0143 0.0040 0.0022 0.0020 0.0020
Minimize Σ [(GPC-IR)exp – (GPC-IR)pred]2
Introduction Method GPC-IR Kinetics Conclusions
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Polymerization System
ethylene
MFM
α-olefin
GCA
• 250 mL SS autoclave reactor
• 90 oC polymerization temperature
• 7 bar ethylene
• 2, 4, or 6 g 1-hexene
• 10, 20, 40, 60 min polymerization time
• H2 used a chain transfer agent
Introduction Method GPC-IR Kinetics Conclusions
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Polymerization Kinetics
2.0 g 1-Hexene
10 min
20 min
40 min 60 min
Introduction Method GPC-IR Kinetics Conclusions
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Deconvolution Assumptions
• Sites of different types make polymer populations with the same Mn and SCB/1000 C.
• The changes in Mn and SCB/1000C for the whole polymer result from differences in the polymerization kinetics of the distinct site types. Distinct site types have different
activation/propagation/deactivation rates that affect the properties of the whole polymer.
Introduction Method GPC-IR Kinetics Conclusions
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GPC-IR Deconvolution 2.
0 g
1-He
xene
Introduction Method GPC-IR Kinetics Conclusions
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Deconvolution Results
2.0 g 1-Hexene
Site Mn (103) SCB/ 1000C
1 3 29.6
2 12.5 11.3
3 37 6.2
4 112 4.2
5 350 3.4
The fraction of polymer made in high-Mn sites increases
The fraction of polymer made in low-Mn sites decreases
Introduction Method GPC-IR Kinetics Conclusions
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Results for Other 1-Hexene Concentrations
Site Mn (103) SCB/ 1000C
1 3.5 39.6
2 13 17.5
3 36 13.7
4 101 10.9
5 290 10.4
Site Mn (103) SCB/ 1000C
1 3 35.1
2 12.0 13.8
3 35 9.5
4 107 7.6
5 318 6.2
4.0 g 1-Hexene 6.0 g 1-Hexene
Introduction Method GPC-IR Kinetics Conclusions
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1-Hexene Incorporation per Site Type
Introduction Method GPC-IR Kinetics Conclusions
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Investigating Site Type Kinetics
Description Chemical Equation Rate Constant
Activation ka
Propagation kp
1st Order Deactivation kd
0PAlC →+
1+→+ rr PMP
rdr DCP +→
Introduction Method GPC-IR Kinetics Conclusions
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Effect of kp
0
0.5
1
1.5
2
2.5
3
3.5
0 500 1000 1500 2000 2500 3000 3500 4000
Mon
omer
Upt
ake
(mol
/s)
Polymerization Time (s)
Introduction Method GPC-IR Kinetics Conclusions
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Effect of kd
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
0 500 1000 1500 2000 2500 3000 3500 4000
Mon
omer
Upt
ake
(mol
/s)
Polymerization Time (s)
Low kd
High kd
Introduction Method GPC-IR Kinetics Conclusions
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Effect of KA
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
0 500 1000 1500 2000 2500 3000 3500 4000
Mon
omer
Upt
ake
(mol
/s)
Polymerization Time (s)
Medium KA
High KA
Introduction Method GPC-IR Kinetics Conclusions
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Polymer Yield in a Semi-Batch Reactor
0
1000
2000
3000
4000
5000
6000
7000
0 500 1000 1500 2000 2500 3000 3500 4000
Tota
l Mon
omer
Con
sum
ptio
n (m
oles
)
Polymerization Time (s)
kd = 1.5×10-3 s-1
Ywhole = Σ Yi
High kd
Introduction Method GPC-IR Kinetics Conclusions
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Partitioning the Polymer Among Active Sites
Whole polymer
t = 20 min
Introduction Method GPC-IR Kinetics Conclusions
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Ethylene Homopolymerization Yield per Site Type
0
0.5
1
1.5
2
2.5
3
3.5
4
0 20 40 60 80 100
Mas
s (g
)
Time (min)
Site1 Exp. Site2 Exp. Site3 Exp. Site4 Exp. Site5 Exp.
Introduction Method GPC-IR Kinetics Conclusions
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Ethylene Homopolymerization Site Kinetics
Introduction Method GPC-IR Kinetics Conclusions
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Copolymer Yield per Site Type: 2.0 g 1-Hexene
Introduction Method GPC-IR Kinetics Conclusions
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Copolymerization Site Kinetics: 2.0 g 1-Hexene
Introduction Method GPC-IR Kinetics Conclusions
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Copolymer Yield per Site Type
4.0 g 1-Hexene 6.0 g 1-Hexene
Introduction Method GPC-IR Kinetics Conclusions
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Copolymerization Site Kinetics
4.0 g 1-Hexene 6.0 g 1-Hexene
Introduction Method GPC-IR Kinetics Conclusions
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0
2
4
6
8
Homopolymer6.0g 1-C64.0g 1-C6
Ka
(min
-1)
Site 1 Site 2 Site 3 Site 4 Site 5
2.0g 1-C6
1-Hexene increases Ka
Introduction Method GPC-IR Kinetics Conclusions
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0.00
0.02
0.04
0.06
0.08
0.10kp
(min
-1)
Site 1 Site 2 Site 3 Site 4 Site 5
Homopolymer6.0g 1-C64.0g 1-C62.0g 1-C6
1-Hexene increases kp of low Mn sites but decreases kp of high Mn sites
Introduction Method GPC-IR Kinetics Conclusions
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0.0
0.1
0.2
0.3
0.4
0.5kd
(min
-1)
Site 1 Site 2 Site 3 Site 4 Site 5
Homopolymer6.0g 1-C64.0g 1-C62.0g 1-C6
1-Hexene increases kd
Introduction Method GPC-IR Kinetics Conclusions
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What is this information good for?
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Concluding Remarks
• GPC-IR deconvolution can: • Quantify the MWD x SCB/1000 C evolution of
polyolefins made with multiple-site catalysts (Ziegler-Natta and Phillips).
• Assign Mn and SCB for different site types. • Estimate apparent Ka, kp and kd for each site type.
• We must be aware that our conclusions will depend on
the hypotheses we made during data analysis.
Introduction Method GPC-IR Kinetics Conclusions
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