The influence of the waste ethylene vinyl acetate copolymer on the thermal degradation of the waste polypropylene

F U E L P R O C E S S I N G T E C H N O L O G Y 8 9 ( 2 0 0 8 ) 1 2 0 1 – 1 2 0 6

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The influence of the waste ethylene vinyl acetate copolymer onthe thermal degradation of the waste polypropylene

Suat Uçara, Ahmet R. Ozkanb, Jale Yanikc, Selhan Karagöza,⁎aChemistry Program, Izmir Vocational School, Dokuz Eylül University, 35160, Buca — Izmir, TurkeybPort and Customs Services Management, Petkim Holding Co., 35800, Aliaga — Izmir, TurkeycDepartment of Chemistry, Faculty of Science, Ege University, 35100, Bornova — Izmir, Turkey

A R T I C L E I N F O

⁎ Corresponding author. Tel.: +90 232 420 48 9E-mail addresses: [email protected]

0378-3820/$ – see front matter © 2008 Elsevidoi:10.1016/j.fuproc.2008.05.010

A B S T R A C T

Article history:Received 24 January 2008Received in revised form 8 May 2008Accepted 19 May 2008

The pyrolysis of the waste polypropylene (PP), the waste ethylene vinyl acetate copolymer(EVA) and their blends has been carried out in a fixed bed reactor at 500 °C. The effect ofdifferent ratios of the waste EVA in the waste PP/EVA blends on the thermal degradation ofthe waste PP was investigated in terms of both product distributions and liquid fuelproperties. The compositions of pyrolysis products were characterized in detail. The liquidproducts from the pyrolysis of the waste PP, the waste EVA and their blends were analyzedusing different analytical techniques and fuel properties of pyrolytic liquids wereinvestigated in comparison with commercial diesel. There were no synergistic effectsbetween products from thewaste PP and products from thewaste EVA.While the ratio of thewaste EVA increased in the waste PP/EVA blends, aromatic content of the pyrolytic liquidsincreased and subsequently paraffinic content of the pyrolytic liquids decreased. In addition,the boiling point distributions of pyrolytic liquids derived from thewaste PP/EVAblendswerefound to be similar for all tested ratios of the waste PP/EVA blends.

© 2008 Elsevier B.V. All rights reserved.

Keywords:PyrolysisPolypropylene (PP)Ethylene vinyl acetatecopolymer (EVA)

1. Introduction

Plastic materials are an indispensable part of our daily life asthey provide fundamental contribution to all main dailyactivities. At the same time, it brings about disposal problemswith together. The waste plastics present formidable disposalproblems because they are not biodegradable. Recycling of thewaste plastics is very important from the viewpoint of uti-lization of the waste plastics as an energy source. There aremainly four recycling methods which are namely primary,secondary, tertiary and quaternary. Among them, tertiary(chemical) recycling is one of the most promising methods. Intertiary recycling, polymers are broken down into theircorresponding monomers or basic chemicals or fuels [1]. Oneof the tertiary recycling processes is pyrolysis which is thechemical decomposition of organic material by heating in theabsence of oxygen.

3; fax: +90 232 420 51 81..tr, selhankaragoz@yahoo

er B.V. All rights reserved

There have been many reports on the pyrolysis of poly-olefins such as polyethylene (PE) and polypropylene (PP) sincethey are themain polymers in themunicipal solid waste [2–6].The thermal degradation mechanism of PP and PE has beenstudied in detail. The thermal degradation of PE and PP occursthrough the random-chain scission mechanism and a wholespectrum of hydrocarbon products is obtained [2–3]. Also,the liquefaction of PE and PP in the absence and presence ofcatalyst has been widely investigated under different condi-tions [4–6]. The thermal degradation of PE and PP produces theliquid product having a wide range of carbon numbers (n-C5

to n-C25).Ethylene vinyl acetate (EVA) copolymer, which is member

of the polyolefin family derived from random copolymeriza-tion of vinyl acetate (VA) and ethylene, represents a widerange of applications of any synthetic polymeric material.They have a wide variety of uses such as packaging film,

.com (S. Karagöz).

.

Table 1 – Proximate and ultimate analyses of the waste PPand the waste EVA

Type of waste polymer PP EVA

Proximate analysis (as received, wt.%)Volatile matter 99.27 99.94Fixed carbon 0.04 –Ash 0.69 0.06

Ultimate analysis (dry, wt.%)C 81.91 81.27H 14.50 14.28N – –S 0.83 0.33Oa 2.76 4.12

GCVb, MJ kg−1 46.17 45.15

a By difference.b Gross calorific value.

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adhesives, paper coatings, carpet backings, wire and cableinsulation, foam and health care. EVA copolymer can also beblended with other polyolefins so as to enhance tear strength,low temperature properties, flexibility and heat seal range.There have been many studies on the pyrolysis of EVAcopolymers containing different weight percentages of VA inan inert or oxidative atmosphere [7–10]. All of these studies arerelated to kinetic and degradation mechanism of EVAcopolymer in the absence and presence of catalysts usingThermogravimetry (TG), Thermogravimetry-Fourier Trans-form Infrared Spectroscopy (TG-FTIR). The thermal degrada-tion of EVA copolymer in an inert atmosphere occurs in twosteps. The first step corresponds to the elimination of VA unitfrom the polymer chain and the second step corresponds tothe decomposition of the polyolefin chain resulting from theprevious step.

The pyrolysis of EVA copolymer with different polymerswas also studied [11,12]. The pyrolysis of EVA copolymerwith polystyrene (PS), polyvinylchloride (PVC) and cellulosein various proportions was investigated by TGA [11]. Thekinetic models for the weight loss of the polymer mixtures(EVA/PS, EVA/PVC and EVA/cellulose) were proposed andcompared with the experimental results. In another study,the thermal and catalytic cracking of a low density poly-ethylene (LDPE) with EVA copolymer was investigated [12].Thermal and catalytic cracking of a standard mixture ofLDPE and EVA copolymer (86/14) at 420 °C proceeds withlower conversion than degradation of individual LDPE underidentical conditions.

To the best of our knowledge, there is no work dealing withthe pyrolysis of the mixture of the waste PP and the waste EVAcopolymer. The main objective of the present study is toinvestigate the effect of the waste EVA copolymer on thethermal degradation of the waste polypropylene in terms ofboth product distributions and liquid fuel properties. The wastePP and the waste EVA copolymer and their blends (PP/EVA: 1/1;2/1; 4/1; 9/1) were pyrolyzed at 500 °C under nitrogen atmo-sphere. The liquid products were investigated by means ofgas chromatography with a flame ionization detector (GC-FID),Hydrogen-1 Nuclear Magnetic Resonance (1H NMR) and ele-mental analysis. In addition, the physico-chemical properties ofliquid products from the pyrolysis of the waste polymer blendswere determined in comparison with commercial diesel.

2. Experimental section

2.1. Materials

Thewaste polypropylene (PP) and thewaste ethylene vinyl acetatecopolymer (EVA) with 7 wt.% vinyl acetate content were suppliedfrom ALTERA — Izmir, Turkey. The waste PP and the waste EVAsamples were shredded and sieved to produce an average particlesize of 3.0 mm. The proximate and ultimate analyses of the wastePP and the waste EVA are shown in Table 1.

2.2. Pyrolysis process

The pyrolysis experiments were carried out at 500 °C in the nitrogenatmosphere using a semi-batch operation. Before the experiments,the reactorwaspurgedbynitrogengas flowof 30mlmin−1 for 30min

to remove air inside. Pyrolysis reactor was a fixed bed design ofstainless steel with 6fs diameter and 21 cm height. In a typical run,the waste polymers (PP and EVA) or the waste polymer blends (PP/EVA; 1:1; 2:1; 4:1; 9:1)of 130gwereplaced into the reactor.The systemwas heated at a rate of 5 °C min−1 to the temperature of 500 °C andheld at this temperature for 1 h. The volatile productswere swept bynitrogen gas (30mlmin−1) from reactor to collection traps by coolingwith water-ice bath. The non-condensable volatiles (gases) werecollected in a gas bag. The pyrolysis products were classified intothree groups: gas products, liquid products and solid residues. Thepyrolysis experiments were repeated three times and the reprodu-cibility of the experiments showed excellent precision giving astandard deviation ±0.18 wt.%, ±0.50 wt.%, ±0.01 wt.%, for the gas,liquid and solid residue yields, respectively.

2.3. Characterization of the pyrolysis products

The gas products were totally collected in a gas bag and analyzedby gas chromatography, HP model 5890 series II with a thermalconductivity detector. A stainless steel packed column (6.0 m×1/8 in. Poropack Q, 2.0 m×1/8 in. MS 5A molecular sieve, seriallyconnected to each other by means of a switching valve) was used.The separation of CO2, C1, C2, C3, C4 and C5 hydrocarbons wasmadewith Poropack Q column and the separation of O2, N2 and COwas carried out with MS 5A column.

The liquid products from the pyrolysis of the waste polymersand polymer blends were analyzed by gas chromatography withflame ionization detector (GC-FID) using a Hewlett-Packard model6890 GC. The column was a HP-5 capillary column (30 m length×0.32 mm diameter) coated with cross linked %5 phenylmethyl-siloxane at a thickness of 0.25 μm. GC-FID was temperature-programmed from 40 to 280 °C at 5 °C/min with a final holdingtime of 30 min. The data obtained from GC-FID were used to eval-uate the simulated distillation curves according to ASTM D2887.The determination of the boiling point distribution of petroleumfractions by GC is a rapid analytic tool, which may be used toreplace conventional distillation methods for control of refiningoperations. The sample is introduced into a GC column thatseparates hydrocarbons in the order of increasing boiling point.However, polar compounds such as O-containing compounds exitthe column earlier than the hydrocarbons having similar boilingpoints; therefore, their boiling point distributions would be lowerthan the real value. But, this difference does not affect the relativecomparison of liquid products. Hydrogen-1 Nuclear MagneticResonance (1H NMR) spectra’s of the liquid products were recordedwith Varian AS-400 using CDCl3 as solvent. The hydrocarbon typesof liquid products were calculated according to correlationsdeveloped by Myers et al. [13].

Fig. 1 –TG–DTG curves of the waste PP.

Table 2 – Product distributions from the pyrolysis of thewaste PP, the waste EVA and the waste PP/EVA blends at500 °C

Feed PP EVA PP/EVA(9/1)

PP/EVA(4/1)

PP/EVA(2/1)

PP/EVA(1/1)

Pyrolysis products, wt.%Gasa (G) 10.15 10.95 10.03 11.80 11.97 13.43Liquid (L) 88.92 88.96b 89.11 87.39 87.24 86.10Residue (R) 0.93 0.09 0.86 0.81 0.79 0.46

a G=100− (L+R).b Wax.

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The pyrolytic liquids were identified using the following stand-ard methods; the specific gravity (ASTM D4052-96), the kinematicviscosity (ASTM D445), the flash point (ASTM D93) and the grosscalorific value (ASTM D240). The water content of liquid productswas analyzed by Karl–Fischer titration method according to ASTMD6304-04. The elemental compositions of the waste polymers andliquid products were analyzed with a LECO CHNS 932 elementalanalyzer according to ASTM D5291-96.

Thermogravimetric analyses of the waste polymers wereperformed in a TGA-50 Shimadzu instrument under inert atmo-sphere. The samples were placed in a standard alumina crucible.The experiments were performed under flowing nitrogen atmo-sphere with a flow rate of 100 ml min−1. The temperature wasincreased from ambient temperature to 1000 °C at a heating rate of5 °C min−1.

3. Results and discussion

3.1. Product distributions

The TG and DTG curves of the waste PP and the waste EVAcopolymer are illustrated in Figs. 1 and 2, respectively. Thethermal degradation patterns of these waste plastics showsimilarity with the thermogravimetric analyses of pure PP andEVA copolymer [14]. The thermal degradation of the waste PPshowed distinct weight loss step occurring in the temperaturerange between 310 and 475 °C. At this step, total weight loss ofthe waste PP was found to be 99.30 wt.% which shows that thedecomposition of the waste PP occurred. The inflection point(where the rate of weight loss is maximum) on the TG curve forthewaste PPwas found to be 454 °C. The thermal degradation ofthe waste EVA copolymer showed two weight loss steps. Thefirstweight loss step,which corresponds to release of acetic acid

Fig. 2 –TG–DTG curves of the waste EVA copolymer.

derived from vinyl acetate co-monomers, occurred in the tem-perature range between307 and 410 °C. At this step, totalweightloss of the waste EVA copolymer was 8.70 wt.%. The secondweight loss step, which consists in the cracking of thepolyunsaturated chain obtained after the first step, occurredin the temperature range between 411 and 493 °C and totalweight loss was 91.10 wt.%. The inflection points on the TGcurve for the waste EVA copolymer were found to be 361 and470 °C, respectively.

Based on the TG–DTG results, it is understood that both thewaste PP and the waste EVA copolymer were completelydecomposed at 500 °C. Preliminary pyrolysis experimentswerealso carried out at 400 and 450 °C.With increasing temperaturefrom 400 to 450 °C, a dramatic increase in liquid yield from thepyrolysis of the waste PP was observed. Further increase in thetemperature (from 450 to 500 °C) did not change the yield ofliquid products derived from thewaste PP. However, the wasteEVA derived wax products increased drastically with an in-crease in the temperature from 400 to 450 °C. Further increasein the temperature (from450 to 500) led to increase the amountof wax products derived from EVA. The similar effect was alsoobserved in the case of thewaste PP/EVA blend (1:1) in terms ofthe yields of liquid products. Thus, the pyrolysis of the wastepolymers and their blends was performed at 500 °C. Theproduct distributions from the pyrolysis of the waste PP, thewaste EVA and the waste PP/EVA blends are given in Table 2.The experimental yields of the pyrolysis of the waste PP/EVAblends are close to the theoretical values. The productdistributions from the pyrolysis of the waste PP, the wasteEVA and the waste PP/EVA blends were found to be similar.This suggests that there are no synergistic effects between

Table 3 – Composition of the gas products from thepyrolysis of the waste PP, the waste EVA and the wastePP/EVA blends at 500 °C

Feed PP EVA PP/EVA(9/1)

PP/EVA(4/1)

PP/EVA(2/1)

PP/EVA(1/1)

Gas products, wt.%C1 2.96 3.00 2.44 2.78 3.52 3.24C2 9.12 14.55 8.40 9.64 11.35 12.14C3 39.68 29.23 33.08 32.67 33.11 31.08C4 15.08 28.97 14.90 16.69 17.56 20.51C5 30.65 20.03 38.13 34.21 28.57 28.20CO 0.28 0.44 0.17 0.23 0.48 0.38CO2 2.02 3.51 2.72 3.59 5.14 4.21H2 0.21 0.27 0.17 0.20 0.27 0.24

Table4 – Physico-chemicalproperties of liquidproducts fromthepyrolysisof thewastePP, thewasteEVAand thewastePP/EVAblends

Feed PP EVA PP/EVA (9/1) PP/EVA (4/1) PP/EVA (2/1) PP/EVA (1/1) Commercial diesel

Specific gravity at 25 °C, g cm−3 0.76 0.80 0.76 0.77 0.77 0.78 0.82–0.86Viscosity at 40 °C, cSt 1.62 2.55 1.45 1.46 1.63 1.92 2.0–4.5Flash point, °C b30 b30 b30 b30 b30 b30 N55Water amount (ppm) 46.20 587.40 94.80 119.20 128.60 159.40 b200GCVa, MJ kg−1 46.23 45.33 46.39 46.35 46.34 45.70 45.09

Elemental analysis, wt.%C 85.87 84.64 85.96 85.86 85.50 85.85 86.50H 13.22 13.15 13.00 13.01 12.84 12.58 13.20N – – – – – – b1S b0.01 b0.01 – – b0.01 b0.01 b0.70Ob 0.90 2.20 1.04 1.13 1.65 1.56 –H/C molar ratio 1.84 1.86 1.81 1.81 1.80 1.76 1.83

a Gross calorific value.b By difference.

Fig. 3 –Simulated distillation curves of the liquid productsfrom the pyrolysis of the waste PP and the waste PP/EVAblends.

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products from the waste PP and products from the waste EVA.Wehave also observedno synergistic effects betweenproductsfrom the waste PP and products from the waste EVA at apyrolysis temperature lower than 500 °C. The liquids from thepyrolysis of thewaste PP and thewaste PP/EVAblends (PP/EVA;1:1; 2:1; 4:1; 9:1) were in the form of liquid at the roomtemperature whereas thewaxy productwas obtained from thepyrolysis of the waste EVA alone.

3.2. Composition of gas products

The composition of gas products from the pyrolysis of thewaste PP, thewaste EVA and thewaste PP/EVA blends at 500 °Cis shown in Table 3. The data represented on a nitrogen freebasis the weight percentage of each gas evolved. The majorgaseous products were C3, C4 and C5 hydrocarbons in thewaste PP derived gas products. In a previous study, thepyrolysis of polyethylene and polypropylene in the absenceand presence of catalysts was investigated [15]. Similarly, itwas reported that the thermal degradation of PP producedmainly C3, C4 and C5 hydrocarbons. Interestingly, in thepresent study, the gas products from the pyrolysis of thewaste PP alone contained small amounts of CO and CO2. Thereason is that the elemental composition of the waste PPcontained small amount of oxygen (see Table 1) which mightcome from impurities or additives. The waste EVA derived gasproducts consisted largely of C3, C4 and C5 hydrocarbons andsmall amounts of CH4, CO2 and CO. The gaseous products fromthe pyrolysis of the waste EVA and the waste PP/EVA blendscontained hydrocarbons (C1–C5) together with some gaseousproducts i.e. CO, CO2, and H2. The gas products from thepyrolysis of the waste PP/EVA blends contained mainly C3, C4

and C5 hydrocarbons in a similar way with the waste PPderived gas products. With increasing the ratio of the wasteEVA in the waste PP/EVA blends increased the amounts of C4

hydrocarbons in the waste PP/EVA derived gas products.

3.3. Composition of liquid products

The liquid products obtained from the pyrolysis of the wastePP, the waste EVA and the waste PP/EVA blends were

characterized in terms of both fuel characteristics andchemical composition. The physico-chemical properties ofpyrolytic liquids are shown in Table 4. For comparisonpurpose, the physico-chemical properties of commercialdiesel are also presented in Table 4. The waste EVA derivedcondensed product was in the form of wax at the roomtemperature whereas it was in the form of liquid at atemperature higher than 30 °C. The reason might be due torepolymerization of the waste EVA derived condensed liquidproduct. The specific gravity of the waste EVA derived waxyproduct was found higher than that of the waste PP derivedliquid. The specific gravities of all waste PP/EVA derivedliquids were higher than that of the waste PP derived liquidand lower than that of the waste EVA derived waxy product.The specific gravities of all pyrolytic liquids were not in therange of commercial diesel. Similarly, the viscosities of thewaste PP and the waste PP/EVA blends derived liquids werenot in the range of the commercial diesel. The viscosity of thewaste EVA derived waxy product lies in the range ofcommercial diesel. As expected, flash points of pyrolyticliquids were lower than that of commercial diesel. Thecalorific values of the pyrolytic liquids were close to that ofcommercial diesel. Therefore, the pyrolytic liquids from thepyrolysis of thewaste PP, thewaste PP/EVA blends can be usedas fuels for combustion systems in the industry. Elementalcompositions of all pyrolytic liquids were found to be similar(see Table 4) with the commercial diesel. The pyrolytic liquids

Table 5 – Fractions of liquid products from the pyrolysis ofthe waste PP and the waste PP/EVA blends at 500 °C, vol.%

Feed PP PP/EVA(9/1)

PP/EVA(4/1)

PP/EVA(2/1)

PP/EVA(1/1)

Naphtha 53 51 49 48 45Kerosene 14 16 17 20 20Vacuum gas oil 33 33 34 32 35

Table 7 – The elemental composition of solid residuesfrom the pyrolysis of the waste PP, the EVA and the wastePP/EVA blends

Feed PP EVA PP/EVA(9/1)

PP/EVA(4/1)

PP/EVA(2/1)

PP/EVA(1/1)

Elemental analysis, wt.%C 21.21 53.18 26.23 29.49 42.21 44.99H 1.15 2.37 0.98 1.88 2.69 2.52N – – – – – –S 0.18 0.03 0.14 0.13 0.11 0.09Oa 77.46 44.42 72.65 68.50 54.99 52.40

a By difference.

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contained small amounts of oxygen. In addition, the amountsof sulphur were found to be trace in all pyrolytic liquids.

The boiling point distributions of hydrocarbons in pyrolyticliquids from the pyrolysis of the waste PP and the waste PP/EVA blends at 500 °C are shown in Fig. 3 as simulateddistillation curves. For comparison purpose, the simulateddistillation curve of commercial diesel is also presented inFig. 3. As can be seen from Fig. 3 that there is no significantchange in the boiling point distributions of hydrocarbonswhile the ratio of the waste EVA increases in the waste PP/EVAblends. It should be noted that the initial boiling points ofpyrolytic liquids (61–66 °C for all pyrolytic liquids) were lowerthan that of commercial diesel. All pyrolytic liquids having awide boiling point range contained lighter hydrocarbons thanthat of commercial diesel. For a better understanding, thefractions were classified as naphtha (B.P.b172 °C), kerosene(172 °CbB.P.b232 °C) and vacuum gas oil (B.P.N232 °C) andshown in Table 5. The naphtha content of thewaste PP derivedliquid was the highest and the kerosene content of the wastePP derived liquidwas the lowest among all pyrolytic liquids. Byincreasing the ratio of the waste EVA in the waste PP/EVAblends, the naphtha content of liquid products from thepyrolysis of the waste PP/EVA blends decreased. The contentof vacuum gas oil (VGO) was similar for both the waste PP andPP/EVA derived liquids.

The amounts of hydrocarbon types in the pyrolytic liquidswere determined by 1H NMR analysis [13] and were shown inTable 6. The pyrolytic liquid derived from the waste PPconsisted largely of paraffins and small amount of aromatics.As the ratio of waste EVA increases in the waste PP/EVAblends, the amount of aromatic content in all waste PP/EVAderived liquids increased. This is an expected result asdegradation of EVA produces significant amount of aromaticcompounds. The amounts of olefins in the liquid productsfrom the pyrolysis of the waste PP/EVA blends were higherthan the waste PP derived liquid.

3.4. Composition of solid residues

The elemental compositions of solid residues are shown inTable 7. Although the amounts of residues obtained from the

Table 6 – The amounts of hydrocarbon types in the liquidproducts from the pyrolysis of the waste PP and the wastePP/EVA blends at 500 °C, vol.%

Feed PP PP/EVA(9/1)

PP/EVA(4/1)

PP/EVA(2/1)

PP/EVA(1/1)

Aromatics 9.16 15.66 16.12 16.74 22.44Paraffins 78.80 68.70 67.15 65.49 60.42Olefins 12.04 15.64 16.73 17.77 17.14

pyrolysis of the waste PP, the waste EVA and their blends werevery low, their elemental compositions were determined. Ascan be seen from Table 7, the carbon content of solid residueswas not high due to their high ash content (varying between 60and 82 wt.%, depending on the amount of PP in blends). Byconsidering the sulphur amounts in liquid products and solidresidues, it can be concluded that the most of sulphur presentin the waste plastics was distributed in gas products.

4. Conclusion

The pyrolysis of the waste PP, the waste EVA and their blendswas carried out at 500 °C. The product distributions of thewaste PP, the waste EVA and the waste PP/EVA blends werefound to be similar. The gas products from the pyrolysis of thewaste PP/EVA blends contained mainly C3, C4 and C5 hydro-carbons. As the ratio of the waste EVA increased in the wastePP/EVA blends, the elemental composition of the waste PP/EVA derived liquids did not change significantly. The calorificvalues of the waste PP/EVA derived liquids were close to thatof commercial diesel. There is no significant change in theboiling point distributions of hydrocarbons while the ratio ofthe waste EVA increases in the waste PP/EVAmixtures. As theratio of waste EVA increases in the waste PP/EVA blends,the amount of aromatic content in all waste PP/EVA derivedliquids increased.

Acknowledgment

This work was supported by Dokuz Eylül University.

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