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Limitations in Thermal Degradation Modelling and Kinetic Parameters Evaluation for Polymeric Blends in Dynamic ThermogravimetryPresented by:Dr. Abdul Rehman Khan – Consultant Environment & Life Sciences Research Center Kuwait Institute for Scientific Research5th Technology Innovations Conference& Exposition.2nd November 2014, Kuwait
1. Introductory Remark.
2. Motivation of Work and Benefits to Clean Fuels.
3. Used Models in Literature.
4. Case Study: Degradation of PET/PMMA & Integral Method
Development.
5. Conclusions & Future Work
Presentation Agenda
Introductory Remark
• Thermal degradation of polymers is arguably one of the
hottest topics in engineering disciplines.
• Typically, results are conflicted especially in micro-scale and
in particular, dynamic thermogravimetric analysis (TGA).
• Such discrepancies result from different factors, such as:
– Experimental setups: Different inert atmospheres (at different scales),
temperature ranges, sample amounts, heating rates (b) and
pressures.
– Adequacy of the kinetic model: Modelling approach and assumptions.
– Thermal lag (T): Heat transfers problems.
• Waste is accumulating in Kuwait with NO GOVRMT
scheme to handle.
• Plastic solid waste (PSW) is estimated at 200 Mtpa.
(2013).
• PSW is typically shipped abroad (exported)/recycled in
private company(ies) for profit.
• THIS IS A WASTE!!!
• Being a crude oil product, plastics encompass energy
that should be taken advantage of.
Introductory Remark
Item CV (MJ kg-1) Item CV (MJ kg-1)PE
PP
PS
Kerosene
43.3-46.5
46.50
41.90
46.50
Gas Oil
Heavy Oil
Petroleum
Household PSW mixture
45.20
42.50
42.30
31.80
Table 1: Calorific Value of Major Polymers in Comparison toCommon Fuels.
Pyrolysis Hydrogenation Gasification
Kiener N
oell
BASF
BP
ABB
VKE
Texaco
Eisenmann W
inkler
Lurgi
SVZ
VEBA -Oel
Oil OilNaphtha &High Boiling Oil
Thermolysis
Main advantages include:
1. Minimal pre-treatment.
2. PCs production & Integration.
3. Waste disposal solution.
4. Sustainable energy source.
Motivation• Today’s refining capacity of Kuwait is around 936 mbpd divided.
• Post CFP, the refining capacity of the country will decrease to a total of
800 mbpd.
• It is anticipated that the NRP will process 615 mbpd of Kuwait Export
Crude (KEC, API≈30). Total refining capacity will be: 1,415 mbpd.
Table 2: Major products specs post CFP (Sulfur ppm).
Product Current Spec. Post CFP
Full Range Naphtha
Gasoline (All Grades)
Gas Oil 1 (Including Domestic Use)
Gas Oil 2
Gas Oil 3 (New Grade)
Fuel Oil (%)
700
500
2000-5000
500
-
4.5
500
10
10-500
10
10
1
• Products from TCT units is the answer. Such include H2, C3, C4, etc. This will intensify production of chemical feedstock from a renewable energy source.
• Polymers, in the form of plastics, are fed to pyrolysis
reactors as a fraction of MSW. They are a mixture of
polymers, not just a single one. Hence, predicting their
degradation behavior and evaluating their kinetic
parameters in a blend is a must.
Problem Statement
Most common kinetic degradation models are isoconversionones:
1. Ozawa-Flynn-Wall:• One of the most used expressions in literature.• This method is considered to be the most exact.• Assumes a first order kinetics (n=1).
2. Friedman’s method:
Established Models
RTE
mmRAE a
oa 05.1)1(33.5)/ln()ln(
RTEmmfAdtdm
m oo
/)(ln)ln()/)(1ln(
• Blends of PET/PMMA (traded under the name of Ropet) are typically used in
electrical applications.
• Hence studying their thermal degradation and stability determines optimal
operating condition of these blends avoiding electrical overshoots in
electronics.
• Thermogravimetric analysis (TGA) was carried out for the blends with pure
dry nitrogen purge of 20 cm3/min.
• Four were used: 5, 10, 15 and 20oC/min.
PET/PMMA Degradation as a blend
Mathematical DerivationThe expression of degradation could be written after rearranging the denominatoras:
dtkxdx
np
P
The results presented in this work reflect first order kinetics. Integrating the resultingexpressions results in the following for each polymer in the blend:
t
B
x
pB
pB
t
A
x
pA
pA
dtkxdx
dtkxdx
pB
pA
01
01
For a given blend of known composition (xA is the PET fraction in the blend), theoverall cumulative weight loss expression will be given as
teAxteAxx RTEA
RTEAp
aa )/(2
)/(1
21 exp)1(exp
N
1i (exp)p
(th)p(exp)P
x
xxmin(O.F.)FunctionObjective
• Several non-isothermal pyrolitic degradation TG curves have been modelled
in this study.
• It was noticed that with the increase of PET fraction in the blends, the TG
curve showed a shift to higher value in the degradation temperature till 75
wt%.
• The 90/10 (wt/wt%) blend of PET/PMMA started decomposing at almost 600
K (beginning of the first shoulder incline).
• Virgin PET and PMMA typically started decomposing at temperatures
around 630 K and 560 K, respectively.
Results & Observations
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
500 550 600 650 700 750 800
PET/PM
MA (50/50
wt/wt%
)
Temperature (K)
Exp.Theor.
Model vs. experimental results for PET/PMMA blend
(25/75 wt/wt%) at 5= oC/min.
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
500 600 700 800 900
PET/PM
MA (50/50
wt/wt%
)
Temperature (K)
Exp.Theor.
Model vs. experimental results for PET/PMMA
blend (50/50 wt/wt%) at 10= oC/min.
• The structural and physical properties of blends of both polymers affect the TG
curves, where the abundance of PET in the 90/10 blend delays the degradation to a
point where the material acts almost like a virgin PET (or pseudo virgin material).
PET/PMMA (25/75) (wt/wt%) PET/PMMA (50/50) (wt/wt%)Ea1 (kJ/mol) Ea2 (kJ/mol) A1 (min-1) A2 (min-1) r2 Ea1 (kJ/mol) Ea2 (kJ/mol) A1 (min-1) A2 (min-1) r2
= 5 oC/min
= 10 oC/min
= 15 oC/min
= 20 oC/min
240
230
220
210
140
130
120
110
1.1x1019
1.03x1017
3.2x1018
5.5x018
1.73x109
2x1011
2.7x108
1.33x104
0.98
0.98
0.98
0.98
250
240
230
220
150
140
130
120
3.9x1015
1.82x1016
2.2x1017
4.2x017
2.7x1010
8.1x1010
2.28x107
2.7x1011
0.99
0.99
0.97
0.99
PET/PMMA (75/25) (wt/wt%) PET/PMMA (90/10) (wt/wt%)
Ea1 (kJ/mole) Ea2 (kJ/mole) A1 (min-1) A2 (min-1) r2 Ea1 (kJ/mol) Ea2 (kJ/mol) A1 (min-1) A2 (min-1) r2
= 5 oC/min
= 10 oC/min
= 15 oC/min
= 20 oC/min
260
250
240
230
160
150
140
130
3.12x1014
2.89x1015
7.6x1016
1.27x017
6.23x108
2.92x109
6.62x107
4.28x106
0.99
0.99
0.98
0.99
270
260
250
240
170
150
150
140
2.32x1016
2.7x1016
6.23x1015
1.4x016
6.4x107
5.9x107
2.1x109
1.07x1010
0.99
0.99
0.98
0.99
Apparent activation energy evaluated for PET (Ea1) and PMMA (Ea2), pre-
exponential factors (A1 and A2) and regression coefficient between experimental
and theoretical fits.
• A general mathematical expression based on the integral solution of
different PET/PMMA blends for non-isothermal (dynamic)
thermogravimtry (TG) has been developed.
• The model results show good agreement with experimental values
depicting the true pyrolitic reaction mechanism.
• The apparent discrepancies are attributable to melt mixing resulting
in the formation of different phases.
• Thermal lag was caused by the evaporation of volatile degraded
products (heat absorption) and also greatly influenced by thermal
characteristics of blend of polymers ensuing in the observable
deviation among experimental and model results.
Conclusions
Thank you
Dr. Abdul R. Khan (Consultant-ELSRC)
Dr. Sultan Al-Salem (PRC)