Limitations in Thermal Degradation Modelling and Kinetic Parameters - - PowerPoint PPT Presentation

Limitations in Thermal Degradation Modelling and Kinetic Parameters Evaluation for Polymeric Blends in Dynamic Thermogravimetry

Presented by:

• Dr. Abdul Rehman Khan – Consultant

Environment & Life Sciences Research Center Kuwait Institute for Scientific Research

5th 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 to Common Fuels.

Pyrolysis

Hydrogenation Gasification

Kiener Noell BASF BP ABB VKE Texaco

Eisenmann Winkler

Lurgi SVZ

VEBA - Oel Oil Oil Naphtha &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 isoconversion

• nes:

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

RT E m m R AE

a

• a

05 . 1 ) 1 ( 33 . 5 ) / ln( ) ln(       RT E m m f A dt dm m

• /

) ( ln ) ln( ) / )( 1 ln(    

• 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
• perating 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 Derivation

The expression of degradation could be written after rearranging the denominator as:

dt k x dx

n p P

 

The results presented in this work reflect first order kinetics. Integrating the resulting expressions results in the following for each polymer in the blend:

   

   

t B x pB pB t A x pA pA

dt k x dx dt k x dx

pB pA

1 1

For a given blend of known composition (xA is the PET fraction in the blend), the

• verall cumulative weight loss expression will be given as

   

t e A x t e A x x

RT E A RT E A p

a a

) / ( 2 ) / ( 1

2 1

exp ) 1 ( exp      



 

N 1 i (exp) p (th) p (exp) P

x x x min (O.F.) Function Objective

• 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

0.1 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/PMMA (50/50 wt/wt%) Temperature (K)

Exp. Theor.

Model vs. experimental results for PET/PMMA blend (25/75 wt/wt%) at  5= oC/min. 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 500 600 700 800 900 PET/PMMA (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)