Energy Conversion and Management 75 (2013) 474–481

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Energy Conversion and Management

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Influence of oily wastes on the pyrolysis of scrap tire

0196-8904/$ - see front matter � 2013 Elsevier Ltd. All rights reserved.http://dx.doi.org/10.1016/j.enconman.2013.06.055

⇑ Corresponding author. Tel.: +90 232 301 26 13; fax: +90 232 420 51 81.E-mail address: suat.ucar@deu.edu.tr (S. Uçar).

Mehmet Siva a, Sermin Onenc b, Suat Uçar c,⇑, Jale Yanik b

a Center for Environmental Studies, Ege University, 35100 Bornova, Izmir, Turkeyb Faculty of Science, Department of Chemistry, Ege University, 35100 Bornova, Izmir, Turkeyc Chemistry Technology Program, Izmir Vocational School, Dokuz Eylül University, 35160 Buca, Izmir, Turkey

a r t i c l e i n f o a b s t r a c t

Article history:Received 17 March 2013Accepted 30 June 2013

Keywords:Bilge waterOily sludgeScrap tiresCo-pyrolysisPyrolytic oil

The co-pyrolysis of scrap tires with oily wastes from ships (bilge water oil and oily sludge) was studied toinvestigate the effect of oily wastes on the pyrolysis of scrap tire. Co-pyrolysis experiments were carriedout in a fixed bed reactor in the absence and the presence of catalyst at 500 �C. The catalysts used in thepyrolysis were a commercial refinery catalyst and an industrial by-product containing iron. The fuel char-acteristics and chemical compositions of pyrolysis products were characterized by means of chromato-graphic, spectroscopic and standard ASTM methods. Although, the oily wastes did not affect theproduct yields from the pyrolysis of scrap tire, they improved the fuel characteristics of scrap tire derivedoils. The fuel characteristics of co-pyrolysis oils (except flash point and sulfur content) had similar fuelcharacteristic with the commercial diesel. It was also found that the amounts of metal impurities in allpyrolytic oils were smaller than 0.3 ppm, which was a significantly low amount compared with thosein the original oily wastes. Gross calorific values of pyrolysis gases were found to be in the range of20.4–26.4 MJ Nm�3. It was concluded that co-pyrolysis of scrap tire with oily wastes could be an environ-mentally friendly way for the conversion of disposable and hazardous wastes such as scrap tires, bilgewater oil and oily sludge into fuels.

� 2013 Elsevier Ltd. All rights reserved.

1. Introduction

Evaluation of disposable and hazardous wastes such as oilywastes and scrap tire is an important event in terms of environ-mental and economic reasons. One of the oily wastes is bilge wateroil. It contains seawater, oily fluids, lubricants, cleaning fluids andother similar wastes which cumulate in the lowest part of a ship. Inaddition, it includes volatile organic compounds, semi-volatileorganics, inorganic salts and metals [1]. Besides bilge water oil, an-other waste stream in the ship is oily sludge which is produced bythe constant purification of fuel and lubricating oil by centrifuga-tion. Discharge of untreated oily wastes is prohibited. If wasteshave a hydrocarbon content >15 ppm, they are kept on ship anddischarged to reception facilities in harbor [2]. Because of their var-ied nature and composition, they are difficult wastes to treat. Grav-ity separation is commonly used as a first step to separate the oilyphase from aqueous phase. Then a post treatment technology suchas coagulation, filtration, adsorption and membrane technologies isemployed in order to clean water sufficiently [3–5]. The oily phasederived from all of these treatments creates another problem. Theyare classified as hazardous waste and disposed via incineration,mostly in cement plants [6,7]. However, a strict criteria has to be

met before they can be accepted for incineration. Since they arenot regulated by burner standards, they can only be burned bymixing with conventional solid fuels. Although oily wastes repre-sent a problem for the environment, they can be considered asan energy resource. Recycling of these wastes provides greener,cost effective alternatives to fossil fuels.

Pyrolysis is one of the alternatives to incineration; it is environ-ment friendly way to obtain useful products which may be used asfuels or chemical feedstock. In the case of the wastes containingheavy metals (expect mercury and cadmium), metals could besafely retained in the solid char produced from pyrolysis. Thereare number of studies dealing with conversion of waste lubricantoils [8–11] and oil sludge from oil storage tanks [12–15] into fuelsby pyrolysis. Chang et al. [12] investigated the pyrolysis of oilsludge at 873 K. They obtained the oil, with a yield of 80.68%,which its’ distillation characteristics was close to diesel fuel. Forthe improvement of pyrolysis oil, some catalyst/additives havebeen tested in oil sludge pyrolysis. Shie et al. [13,14] investigatedthe effect of some solid wastes (fly ash, DAY-zeolite and oil sludgeash), sodium and potassium compounds on the pyrolysis of oilsludge. And they have pointed out that the addition of these solidwastes improved the qualities of liquid oils. Moliner et al. [9]investigated the effect of pyrolysis conditions on the product yieldsand composition in the pyrolysis of waste lube oil. Their studyshowed that pyrolysis at high temperatures (650–700 �C) mainly

Table 1The properties of scrap tire and oily wastes.

Feed ST BW OS

Proximate analysis (as received, wt.%)Moisture 1.5 9.6 2.3Volatile matter 66.7 88.4 93.4Fixed carbon 27.4 1.9 3.6Ash 4.4 0.1 0.7

Ultimate analysis (ash free basis, wt.%)C 84.05 80.30 84.53H 7.99 12.05 12.72N 0.23 – –S 1.41 0.84 1.10Oa 6.32 6.81 1.65

HHVb (MJ kg�1) 37.7 44.8 44.1Viscosity at 100 �C (SUS) – 9.8 1900

a Calculated from difference.b High heating value.

M. Siva et al. / Energy Conversion and Management 75 (2013) 474–481 475

produced products (C2–C4 olefins and BTX) as petrochemical feed-stock while pyrolysis at 600 �C mainly yielded liquid product andC1–C3 alkanes. Similarly, Lam et al. [10,11] reported that the pro-duction of light olefins and aromatic compounds enhanced byincreasing the temperature whereas decreased the yield of liquidproduct in a microwave-induced pyrolysis of waste engine oil.

Besides oily wastes, scrap tires can be considered as energysources. The used three main processes for scrap tire valorizationare combustion, gasification and pyrolysis. Among these processes,scrap tire pyrolysis provides valuable fuels such as combustiblegases, liquid and solid fuels. A number of studies have been doneto investigate the pyrolysis of scrap tires. In those studies whichwere carried out in different reactor types such as fluidized bed[16,17], fixed bed [18,19], conical spouted bed [20], plasma [21]and tubular reactor [22], the effect of temperature and/or catalyston the yield and quality of pyrolysis products were investigated. Itwas reported that liquid product produced from pyrolysis of scraptire is a complex mixture of hydrocarbons of 5–20 carbons andcontains a higher proportion of aromatics and sulfur than conven-tional fuel. Co-processing of scrap tire with waste petroleumhydrocarbons may be one of the effective processing method sinceoily wastes can provide good solvency and hydrocarbon sourceespecially aliphatic hydrocarbons. In our previous study [23], westudied the co-pyrolysis of scrap tire with oily sludge in a glassreactor (V = 0.25 L) in the presence of catalyst (in vapor phase con-tact mode). And the synergic effects in co-pyrolysis at differenttemperatures were investigated from the point of pyrolysis yieldsand chemical composition of pyrolysis oil.

The main aim of this study is to investigate the effect of the oilywaste addition on the fuel characteristics of products derived frompyrolysis of scrap tire. For this purpose, co-pyrolysis of scrap tireswith oily wastes was carried out in a fixed-bed reactor (V = 1 L) at500 �C in the presence and absence of catalyst. In the catalyticexperiments, the catalysts were used in contact directly with thefeedstock. Therefore, catalysts effected the degradation of wastesitself. The special interest was placed in the fuel characteristicsof whole pyrolysis products (gases, pyrolytic oil and char). The fuelcharacteristics of pyrolysis products were determined by using ofstandard test methods named as American Society for Testingand Materials (ASTM) and the chemical compositions of pyrolysisproducts were characterized by gas chromatography with a flameionization detector (GC-FID), proton nuclear magnetic resonancespectroscopy (1H NMR) and refinery gas analyzer (RGA).

Table 2Metal contents in bilge water oil and oily sludge.

Feed BW OS

Heavy metals (ppm)Ag <3 <3Al 6.3 44B <3 <3Ba <3 <3Ca 388 1800Cd <3 <3Cr <3 <3Cu <3 <3Fe 62 170Mg <3 29.2Mn <3 <3Mo <3 <3Na 15 33Ni <3 12P 102 215Pb <3 <3Sn 12 39Ti <3 <3V 35 66Zn <3 54.6

2. Experimental section

2.1. Materials

Scrap tire (ST) was provided by a rubber recycling enterprisenamed as Akin Rubber Plant, Samsun, Turkey. Scrap tire sampleswere taken from the sidewall rubber of scrap tires and they wereground to particle size less than 2 mm. The scrap tire includedno steel thread or textile netting. The rubber composition of scraptire was 51 wt.% natural rubber, 39 wt.% styrene butadiene rubberand 10 wt.% butadiene rubber. Oily wastes (bilge water oil and oilysludge) were supplied by one of the companies contracted by thePort Authority of Aliaga-Turkey (Batı Çim Co.). The company isresponsible for the collection, handling, treatment and disposal ofship generated liquid wastes. In the plant, both two oily wastesare treated by an oil/water separator to separate the oil phase fromwater phase and oil phase is sent to a cement fabric for incinera-tion. Oily wastes were centrifuged at 5000 rpm for 30 min in ourlaboratory to separate the water phase from oily wastes. The oilphases obtained by centrifugation were denoted as bilge wateroil (BW) and oily sludge (OS). The main properties of scrap tire

and oily wastes are shown in Table 1. Metal contents of oily wastesare also given in Table 2.

The catalysts used in the pyrolysis were a commercial fluid cata-lytic cracking catalyst (FCC) and a disposable catalyst named as RedMud (RM) which is a by-product from Aluminum Company. The FCCis a faujasite type zeolite catalyst. It contains SiO2 – 58.0 wt.%, Al2O3 –38.0 wt.%, Re2O3 – 1.5 wt.%, Na2O – 0.3 wt.% and Fe – 0.5 wt.%. It hasfollowing properties: density – 0.89 g cm�3; specific surface area –255 m2 g�1; pore volume – 0.25 cm3 g�1. Red mud was supplied bySeydis�ehir Aluminum Company, Turkey. It mainly contains Fe2O3 –37.72 wt.%, Al2O3 – 17.27 wt.%, SiO2 – 17.10 wt.%, TiO2 – 4.81 wt.%,Na2O – 7.13 wt.%, CaO – 4.54 wt.% and has specific surface area of16 m2 g�1. Red mud was calcinated at 600 �C before using as catalystin the pyrolysis process.

2.2. Pyrolysis procedure

The pyrolysis experiments were carried out in a fixed bed de-sign and stainless steel reactor (L; 210 mm; Ø; 60 mm) underatmospheric pressure using a semi-batch operation. The schematicexperimental set-up was given in our previous study [24]. Pyroly-sis was performed at the temperatures of 400, 500 and 600 �C withindividual BW, OS and ST and at 500 �C on binary mixture with a

476 M. Siva et al. / Energy Conversion and Management 75 (2013) 474–481

ST:BW or ST:OS weight ratio of 1:1. In a typical run, a fixed amountof single or mixed type of waste (100 g) and catalyst (5 g) wereloaded into the reactor. After loading, the reactor was heated at aheating rate of 7 �C min�1 up to pyrolysis temperature and holdfor 1 h at the desired temperature. The volatile products producedfrom pyrolysis were swept into the ice-cooled traps by Nitrogengas. The liquid products were condensed in the ice-cooled traps.The non-condensable volatiles named as gas were collected in agas bag. The liquid product contains two phases that are aqueousphase and oil phase. The aqueous phase was separated from oilphase (pyrolytic oil) by a separatory funnel and weighted. Theamounts of liquid product and char were determined by weighting.The amount of gas product was determined by difference. Thepyrolysis and co-pyrolysis experiments were repeated three timesand the reproducibility of the experiments indicated excellent pre-cision giving a standard deviation ±0.6, ±0.8, ±1.0 wt.%, for the gas,liquid (pyrolytic oil + aqueous phase) and solid residue (char)yields, respectively.

2.3. Analysis of the pyrolysis products and wastes

The gas products produced from the pyrolysis of scrap tire, oilywastes and their mixtures were totally collected in a gas bag andanalyzed by using refinery gas analyzer (Agilent 7890A). The sys-tem has five valves and three detectors (FID, TCD1 and TCD2).The amount of hydrogen sulfur in the gas products was determinedas lead sulfur precipitate, which was occurred from the reactionbetween hydrogen sulfur and lead nitrate in traps. The lead sulfurprecipitate was filtered, washed with distillated water, dried at110 �C and weighted.

Some physical properties of co-pyrolysis and pyrolysis oils weredetermined by using the following standard methods: the specificgravity (ASTM D4052-96), the kinematic viscosity (ASTM D445),the flash point (ASTM D93) and the gross calorific value (ASTMD240-02). Water contents of pyrolytic oils were determined byusing Karl–Fischer Coulometric Titrator (Mettler Toledo DL31)according to ASTM D6304-04. The pyrolytic oils were analyzedby gas chromatography with a flame ionization detector (GC-FID)using a Hewlett-Packard 6890 series GC. HP-5 capillary column(30 m length � 0.32 mm diameter coated with cross-linked 5%phenylmethylsiloxane at a thickness of 0.25 mm) was used in theGC system. The GC oven was programmed from 40 to 280 �C at5 �C min�1 with a final holding time of 30 min. The data obtainedfrom GC-FID analysis were used to draw the simulated distillationcurves of pyrolysis and co-pyrolysis oils according to ASTM D2887.

The gas chromatograph equipped with a mass selective detector(GC–MS) analysis of pyrolytic oil was performed by a Thermo Finn-igan Trace GC Ultra GC System coupled to a Thermo Finnigan TraceDSQ series mass selective detector. DB-1701 capillary column(30 m � 0.25 mm i.d. DB-1701 fused silica capillary with0.25 mm film thickness) was used in the GC system. The oven pro-gram was 4 min at 45 �C, then 3 �C min�1 to 130 �C, then to 230 �Cat 2 �C min�1 and finally to 280 �C at 3 �C min�1. The compounds inpyrolytic oil were identified by means of the Xcalibur softwarewith a Wiley 7 N library database.

Proton Nuclear Magnetic Resonance (1H NMR) spectra’s of pyro-lytic oils were recorded on a Varian Mercury Spectrometer at a res-onance frequency of 400 MHz using CDCl3 as solvent. The obtaineddata from 1H NMR spectra’s were used to determine the hydrocar-bon types of the pyrolytic oils [25].

The metal contaminants in oily wastes and pyrolytic oils wereanalyzed by using Inductively Coupled Plasma (ICP-OES)-VarianVista MPX. The elemental analyses of wastes, pyrolytic oils andchars were carried out by a LECO CHNS 932 elemental analyzeraccording to ASTMD 5291-96. The proximate analyses of wastesand chars were done according to ASTM D3174-04 for ash analysis

and ASTM D3175-89 for volatile matter. The viscosities of oilywastes were determined by a Koehler K21590 model Saybolt Vis-cometer according to ASTM D88-07. The gross calorific values ofwastes and chars were also determined using an IKA C-2000 basicmodel calorimeter according to ASTM D240-02.

3. Results and discussion

3.1. Pyrolysis of wastes

In the first part of study, pyrolysis of scrap tire and oily wastesalone was carried out to observe the synergic effects in the co-pyrolysis of wastes. Since temperature played a major role in thepyrolysis, pre-experiments were carried out at the temperaturerange of 400–600 �C in the absence of catalyst. This temperaturerange was chosen based on the TG and DTG curves of scrap tire[23]. Thermogravimetric analysis of scrap tire has indicated twodegradation steps, the first step at 380 �C corresponding to naturalrubber and the second step at 444 �C to butadiene rubber. Almostno weight loss has been observed above 550 �C. Besides, we ob-served that decomposition of oily wastes started as soon as heatingstarted as in the case of distillation of petroleum fractions and fin-ished around 500 �C as in the case of scrap tire [23].

In the pre-experiments with scrap tire, when the temperatureincreased from 400 to 600 �C, oil yield reached a maximum valueat 500 �C and then remain almost constant. Similarly, char andgas yields remained nearly constant above 400 �C. This result isagreement with the previous studies [26,27]. In the case of oilywastes, we observed a faster changing in the product yields be-tween the temperatures 400 and 500 �C and a slower changing be-tween the temperatures of 500 and 600 �C whereas the yield of theoil was nearly constant. From the point of oil yield, the 500 �C wasselected as optimum pyrolysis temperature and the catalyticexperiments were performed at this temperature.

The product yields from the pyrolysis of BW, OS and ST withand without catalyst at 500 �C are presented in Fig. 1. Due to thedifferences in the constituents, ST gives the highest char yieldwhereas BW decomposes in the lowest extent. The thermal pyroly-sis of scrap tires produced an oil yield of 44.1 wt.%, gas yield of11.9 wt.% and char yield of 38.5 wt.%. These results are similar tothose found by other researchers [24,28,29] from pyrolysis of scraptire in a fixed bed reactor. The oil yields from thermal pyrolysis ofoily wastes were around 80 wt.%, which are higher than that ofother studies carried out with oil sludge and waste machine oils[9–11,30,31]. The yields of char resulting tertiary cracking reac-tions were 6–7 wt.%, which are similar to previous reports[9,11,31]. It is important to remark that the yield of aqueous phase(5.5 wt.%) from pyrolysis of ST, which contained about 90 wt.%water, was more than the moisture content of ST (1.6 wt.%). Thesurplus water should be originated from the dehydration of fillingmaterials, such as fatty acids in tire. However, in the pyrolysis ofBW, the yield of the aqueous phase was less than the moisture con-tent of the BW. The reason may be due to the consumption of someof the water in the BW during pyrolysis. The following reactionshave been suggested as a reason for the consumption of the waterduring pyrolysis [32].

Water gas reaction : CþH2O! COþH2 ð1ÞWater gas shift reaction : COþH2O! CO2 þH2 ð2ÞMethane gasification : CH4 þH2O! COþ 3H2 ð3Þ

By considering the absence of carbon monoxide in gas productobtained from pyrolysis of BW, it seems that a water gas shift reac-tion is more favorable. It is difficult to compare the results of thisstudy with previous study [23] since it was carried out in a differ-ent type of reactor providing longer residence time of primary

0

10

20

30

40

50

60

70

80

90

100

Thermal FCC Red mud Thermal FCC Red mud Thermal FCC Red mud

ST BW OS

Yie

ld, w

t%

Char

Water phase

Oil

Gas

Fig. 1. Product distributions from thermal and catalytic pyrolysis of scrap tire and oily wastes at 500 �C.

Table 3Product distributions from the copyrolysis of scrap tire and oily wastes in the absenceand the presence of catalyst at 500 �C.

Catalyst Thermal FCC Red Mud

Exp.a Theo.b Exp. Theo. Exp. Theo.

ST/BW, (wt.%)Gasc 10.5 10.6 11.9 13.1 9.6 9.3Oil 64.8 62.8 59.2 65.2 61.1 65.4Aqueous phase 5.0 4.2 8.5 1.9 5.9 3.2Carbon black 19.7 22.4 20.4 19.8 23.4 22.1

ST/OS (wt.%)Gasc 12.4 12.2 13.4 11.7 13.3 11.2Oil 62.4 61.2 63.5 64.3 61.3 61.4Aqueous phase 2.6 3.8 2.6 1.9 4.3 3.3Carbon black 22.6 22.8 20.5 22.1 21.1 24.1

a Experimental.b Theoretical.c Calculated from mass balance.

M. Siva et al. / Energy Conversion and Management 75 (2013) 474–481 477

degradation products. As known, longer residence time led to anincrease in the tertiary cracking reactions resulting char formation.Because of this, the char yields from pyrolysis of ST, BW and OS inprevious study were found to be 50.4, 15.0 and 20.3 wt.%,respectively [23].

In this study, catalytic pyrolysis experiments were performed at500 �C since high liquid yields were obtained at this temperature.Catalysts were directly in contact with wastes in these experi-ments. As seen from Fig. 1, the catalysts used in the pyrolysishad less effect on the degradation of ST. Only the oil yields ob-tained from catalytic experiments with FCC (47.8 wt.%) wereslightly higher than non-catalytic experiments (44.1 wt.%), whilethe yields of aqueous phases were less than non-catalytic experi-ments. So, we can postulate that FCC provides inherent dehydra-tion reaction during pyrolysis of ST. In the case of BW, utilizationof catalyst has increased gas product yield and decreased charyield, whereas catalysts had no considerable effect on the productsfrom the pyrolysis of OS. However, both FCC and Red Mud in vaporphase contact mode produced more gas products and less oil dur-ing the pyrolysis of BW and OS [23]. It can be concluded that bothtwo catalysts had catalytic activity on volatile products formedfrom thermal degradation of oily wastes. In contrast to our study,the use in situ of an acid catalyst such as ZSM-5, HZSM-5, HY Zeo-lite, SiO2 showed significant effect on both yield and compositionof pyrolysis products [18,33–35]. In addition, the previous studiesreported the effect of the some catalysts on the pyrolysis of oilsludge and waste lubricant oils [13,14,36].

The present work mainly concerns the effect of the oily wasteaddition on the characteristics of scrap tire pyrolysis. Because ofthis, co-pyrolysis experiments were carried out at 500 �C on a mix-ture of a ST:BW or ST:OS at weight ratio of 1:1. The experimentaland theoretical yields obtained from co-pyrolysis of scrap tireand oily wastes are shown in Table 3. There is no synergic effecton the pyrolysis yields as observed by the addition of oily wastesto the scrap tire in the thermal co-pyrolysis experiments. The the-oretical oil yields are close to the experimental yields. One of thereasons may be explained by the different thermal behavior ofthe two components in the blends. Because the weight loss of oilywastes started before the degradation of main materials (rubber)in tire [23], the interaction between the degradation products ofscrap tire and oily wastes was not occurred. Similarly, Conesaet al. [37] who studied thermal decomposition of the scrap tire inan oily environment reported that the decomposition of scrap tire

was similar in the presence of two different oils. However, in cat-alytic co-pyrolysis of ST:BW, theoretical yields of pyrolytic oiland aqueous phase were found to be different than experimentalyields. Although, FCC provided inherent dehydration reaction dur-ing pyrolysis of ST alone and did not affect the dehydration reac-tion in BW pyrolysis, aqueous phase yields from catalytic co-pyrolysis of ST:BW was higher than theoretical yields. It may be as-sumed that the catalysts promote the water formation reaction be-tween primary degradation products of BW and ST.

3.2. Characterization of pyrolysis oils

The main aim of this study was to investigate the effect of theoily waste addition to both quantity and quality of pyrolytic oil ob-tained from the pyrolysis of scrap tire. The idea was to improve thefuel characteristics of oil produced from the pyrolysis of scrap tire.The fuel properties of pyrolytic oils are given in Table 4. For com-parison purpose, fuel characteristics of commercial diesel are alsopresented in the same Table. It can be seen that all pyrolytic oilshave a high calorific value as a commercial diesel. The co-pyrolysisof scrap tire with oily wastes produced the oils having the viscosityin the range of commercial diesel standard whereas viscosities ofpyrolytic oils obtained from pyrolysis of scrap tire alone were quitelow. It should be also noted that pyrolytic oils from oily wasteswere lighter than raw materials.

Table 4Physico-chemical properties of pyrolytic oils obtained from pyrolysis and copyrolysis in the absence and the presence of catalyst at 500 �C.

Feed ST BW OS ST/BW ST/OS Commercialdiesel

Type of catalyst – FCC RM – FCC RM – FCC RM – FCC RM – FCC RM

Specific gravity(kg m�3)

875 884 861 854 867 854 874 846 834 859 873 860 853 863 867 820 – 860

Viscosity at 40 �C(cSt)

1.7 2.2 1.5 3.9 7.6 4.6 4.5 4.1 3.9 2.5 2.8 2.5 2.2 2.6 3.0 2.0 – 4.5

Flash point (�C) < 30 <30 <30 <30 <30 <30 <30 <30 <30 <30 <30 <30 <30 <30 <30 >55HHVa (MJ kg�1) 43.8 43.3 43.6 45.5 45.4 45.9 45.4 45.7 45.8 44.8 44.9 44.2 44.9 44.6 45.0 �45Water amount (ppm) 5100 33061 1868 266 8971 703 521 422 387 7591 551 3161 3530 3923 4658 <200

Elemental analysis (wt.%)C 81.04 80.51 84.16 83.19 83.76 85.33 81.53 82.13 83.80 78.76 77.63 83.08 86.10 80.22 83.22 86.50H 11.11 10.90 10.76 13.09 12.99 13.09 12.87 12.81 13.22 11.77 10.67 12.24 12.55 11.75 12.27 13.20N 0.50 0.43 0.29 Nil Nil Nil Nil Nil Nil 0.11 0.05 Nil Nil 0.06 0.12 < 1S 0.59 0.57 0.97 0.24 0.64 0.21 0.17 0.72 0.46 0.78 0.45 0.75 0.89 1.24 0.96 < 0.70Ob 6.76 7.59 3.82 3.48 2.61 1.37 5.43 4.34 2.52 8.58 11.2 3.93 0.46 6.73 3.43 –

a High heating value.b Calculated from difference.

478 M. Siva et al. / Energy Conversion and Management 75 (2013) 474–481

Although some fuel properties of pyrolytic oils produced fromco-pyrolysis of scrap tire with oily wastes, such as density, viscos-ity and calorific value, are similar to commercial diesel, they havemuch lower flash points than commercial diesel. In addition, thewater, sulfur and oxygen contents of pyrolytic oils were foundhigher than that of commercial diesel. Taking into account theabove results, it has been concluded that pyrolytic oils cannot beused as fuels directly; they should be separated into fractionsand upgraded before using as fuels.

The pyrolytic oils obtained from the pyrolysis of scrap tire, oilywastes and their mixtures were also analyzed by using GC-FIDaccording to the standard test method for boiling range distribu-tion of petroleum fractions (ASTM D2887). The fractions of pyro-lytic oils were classified as light naphtha (< 93 �C), heavynaphtha (93–204 �C), light gas oil (204–343 �C) and heavy gas oil(>343 �C) according to petroleum fractions. The fractions of pyro-lytic oils are shown in Fig. 2. For comparison purpose, the distilla-tion characteristics of commercial diesel are also presented in

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

ST-therm

al

ST-FCCST-R

M

BW-therm

al

BW-FCC

BW-RM

OS-therm

al

OS-FCC

OS-RM

ST/BW-therm

a

ST/B

Cum

ulat

ive

Volu

me,

%

Fig. 2. The fractions of pyrolytic oils obtained from pyrolysis and co

Fig. 2. The pyrolytic oil produced from pyrolysis of ST mostly con-tained heavy naphtha, whereas pyrolytic oils obtained from pyro-lysis of BW and OS mostly contained light gas–oil. Althoughcatalysts used in the pyrolysis and co-pyrolysis had no consider-able effect on the product distribution, the use of catalysts de-creased the naphtha fractions of the pyrolytic oil produced frompyrolysis of scrap tire. In addition, all pyrolytic oils have lightercompounds than commercial diesel.

Analysis of chemical composition of pyrolytic oil derived from STby using gas chromatography–mass spectrometry showed thatpyrolytic oil mainly contained D-limonene, 2-methyl-1,3-butadiene,1,2,3-trimethyl-1H-indene, pentadecane, heptadecane, 2,3,6-trim-ethylnaphthalene and benzene derivatives. Pyrolytic oils derivedfrom BW and OS gave similar chromatograms that show typicalshape of homologues series alkene/alkane from n-C5 up to n-C26

accompanied by branched, cyclic and unsaturated hydrocarbons.The chromatograms of co-pyrolysis oils showed the typical com-pounds coming from components derived from ST and BW or OS.

l

W-FCC

ST/BW-RM

ST/OS-th

ermal

ST/OS-FCC

ST/OS-R

M

Commercial

Diesel

heavy gas-oil

light gas-oilheavy naphtha

light naphtha

pyrolysis in the absence and the presence of catalyst at 500 �C.

M. Siva et al. / Energy Conversion and Management 75 (2013) 474–481 479

The use of catalyst did not show the most remarkable changes in thearomatic compounds with one or more rings in co-pyrolysis oils.

The volume percentages of aromatic, paraffinic, and aliphaticspecies in the pyrolytic oils were determined by using 1H NMRanalysis. The amounts of hydrocarbon types in the pyrolytic oilswere calculated by Myers’s formula [25] which is used for charac-terization of gasoline and middle distillates. The integrated areas of1H NMR spectral regions used in the Myers’s formula are shown inTable 5. A–F indicate the integrated area of the spectral regions de-fined by chemical shifts in ppm from Tetramethylsilane (TMS) inTable 5. To determine volume percents of the hydrocarbon typesincluding aromatics, paraffins and olefins, Myers et al. [25] madecorrections for the varying densities of the different hydrocarbontypes. The following Eqs. (1)–(3) indicating these correlations areshown below.

Aromatics; vol:%¼ ðAþC=3Þ0:97�102

ðAþC=3Þ0:97þðD�2BþE=2þF=3Þ1:02þ3:33B

ð4Þ

Paraffins; vol:%¼ ðD�2BþE=2þF=3Þ1:02�102

ðAþC=3Þ0:97þðD�2BþE=2þF=3Þ1:02þ3:33B

ð5Þ

Olefins; vol:%¼ 3:33B�102

ðAþC=3Þ0:97þðD�2BþE=2þF=3Þ1:02þ3:33B

ð6Þ

As seen from Fig. 3, oils obtained from pyrolysis of OS containedpredominantly paraffinic hydrocarbons (79–80 vol.% of oils). Thismay be expected as mineral oils are degraded by a free-radicalrandom scission mechanism which mainly gives alkane, alkene

Table 5Proton NMR spectral regions.

Proton type Chemical shift region (ppm)

A Ring aromatics 6.6–8.0B Olefin 4.5–6.0C a-Methyl 2.0–3.0D Methine (paraffins) 1.5–2.0E Methylene (paraffins) 1.0–1.5F Methyl (parffins) 0.6–1.0

0

10

20

30

40

50

60

70

80

90

100

ST-therm

al

ST-FCCST-R

M

BW-therm

al

BW-FCC

BW-RM

OS-therm

al

OS-FC

Volu

me,

%

Fig. 3. The amounts of hydrocarbon types in the pyrolytic oils obtained from pyr

and dialkenes. Aromatics are formed by more complex reactionmechanisms and/or through secondary cracking reactions at high-er pyrolysis temperatures [11]. On the other hand, the catalystsused in the pyrolysis and co-pyrolysis had no effect on the typeof hydrocarbons. Although the oil produced from thermal pyrolysisof BW mainly consisted of paraffinic hydrocarbons (�87 vol.% ofoil), the use of red mud catalyst led to a slight increase aromaticand olefin contents of pyrolytic oil.

The pyrolytic oils produced from pyrolysis of scrap tire havehigher aromatic content than oils obtained from pyrolysis of oilywastes. However, their aromatic content (17–18 vol.%) was lowercompared to those of the previous studies [21,38]. This may mainlybe due to the compositional difference of scrap tires between usedin this study and used in the previous studies. In the previous study[23], we observed that polymer types in scrap tire strongly affectedthe hydrocarbon types in pyrolytic oil. The pyrolysis of scrap tirecontaining mostly butadiene rubber (BR) gave the pyrolytic oil richin aromatic hydrocarbons, whereas the pyrolysis of scrap tire con-taining high amount of natural rubber (polyisoprene) produced oilrich in paraffinic hydrocarbons. However, a few studies [39–41]have been published regarding rubber composition factor affectingthe compositions of pyrolytic oil. On the other hand, the amountsof aromatic and olefinic content in co-pyrolysis oils found to be lessthan that of scrap tire derived oils. This shows that the addition ofoily wastes had a positive synergetic effect on quality of oil whichcontained less aromatics and olefins.

It was an important observation that the level of metal impuri-ties in all pyrolytic oils was smaller than 0.3 ppm which was a sig-nificantly low amount compared with those in the original oilywastes. It was suggested that metals occurring in oily wastes couldbe transferred into pyrolytic oil and gas phase by vaporization aschloride compounds and metallic form [11]. Considering the metaltypes in oily wastes (Table 2), it may be suggested that metals re-tained in the char. Similarly, Lam et al. [11] reported that the car-bon residue produced from pyrolysis of used car engine oil acts as asorbent, retains a large amount of Cu, Ni, Pb, Zn, and Fe (P65%) atlower pyrolysis temperatures (6550 �C).

In contrast to the previous study [23], the relatively low effectof catalysts on the pyrolysis might be due to the blocked of the cat-alysts active sites by the metal impurities. The other reason may beascribed to coke formation and consequent active-site deactiva-tion. Catalyst poisoning should be less in vapor phase contact mode[23] compared to catalyst contact directly with the feedstock.

C

OS-RM

ST/BW-therm

al

ST/BW-FCC

ST/BW-RM

ST/OS-th

ermal

ST/OS-FCC

ST/OS-R

M

Aromatics Paraffins Olefins

olysis and copyrolysis in the absence and the presence of catalyst at 500 �C.

Table 7Proximate and ultimate analyses of chars obtained from pyrolysis and copyrolysis at500 �C.

Feed ST ST/BW ST/OS

Proximate analysis (as received, wt.%)Volatile matter 3.7 4.2 3.6Fixed carbon 86.4 85.7 86.3Ash 9.9 10.1 10.1

Ultimate analysis (dry, wt.%)C 70.77 71.15 74.15H 0.76 1.13 1.32N – – –S 3.05 3.12 3.02Oa 25.42 24.60 21.51

HHVb (MJ kg�1) 31.2 31.3 31.3

a Calculated from difference.b High heating value.

480 M. Siva et al. / Energy Conversion and Management 75 (2013) 474–481

3.3. Characterization of gas products

The compositions of the gas products obtained from the ther-mal pyrolysis of scrap tire, oily wastes and their mixtures at500 �C are shown in Table 6. It can be seen that pyrolysis gasesmainly consisted of hydrocarbons and hydrogen together withsome CO and CO2. The carbon oxides (COx) are mostly producedfrom degradation of the oxygenated organic compounds in scraptire and oily wastes. Hydrogen and methane (CH4) were the mostpredominant products; these are formed from secondary aromati-zation reactions [42,43] and/or formed as a primary stable productfrom branched alkenes [44].

Hydrogen content of gas product produced from pyrolysis ofscrap tire was higher than that of from oily wastes whereas hydro-carbon content of gas products obtained from pyrolysis of oilywastes was higher than that of from scrap tire. These results wouldindicate that in scrap tire pyrolysis, aromatization and cyclizationreactions, which increased production of hydrogen and aromatichydrocarbons, were occurred more than in oily waste pyrolysis.In the case of co-pyrolysis, the hydrogen content of gases was morethan the theoretical calculated values. This may be due to thedehydrogenation effect of carbon black on the degradation prod-ucts produced from pyrolysis of oily wastes. More recently, carbo-naceous materials have also been shown to be active in thecatalytic dehydrogenation and oxidative dehydrogenation of lightalkanes [45]. It is important to remark that the catalysts (bothFCC and RM) had no considerable effect on the composition ofgas products from both pyrolysis and co-pyrolysis.

Moreover, pyrolysis and co-pyrolysis gases had high gross calo-rific values in the range of 20.4–26.4 MJ Nm�3. The calorific valuesof pyrolysis gases have been calculated from the concentration ofeach individual gas and its corresponding heating value. Therefore,they can provide some part of the energy required by the pyrolysisprocess or use in the co-generation turbine.

3.4. Characterization of pyrolytic char

Some physico-chemical properties of chars obtained from ther-mal pyrolysis and co-pyrolysis of scrap tire and oily wastes at500 �C are given in Table 7. Adding oily wastes to scrap tire didnot affect the properties of char produced from pyrolysis of scraptire. Although, the calorific value of all chars is less than that ofthe scrap tire itself, it can be compared with high quality coal.The sulfur contents of the chars were found to be high as similarto that obtained by other authors [46,47]. From the elemental anal-ysis results (Table 7 and Table 1), an estimate can be made of sulfurdistribution, bearing in mind the pyrolysis yields. The mostamount of sulfur in scrap tire (�80%) was retained in char. Highamount of sulfur in char shows that sulfur in solid residue is

Table 6Compositions of the gas products obtained from pyrolysis and copyrolysis at 500 �C.

Feed ST BW OS ST/BW ST/OS

Gas products (mol %)C1 27.55 33.48 31.67 28.56 29.54C2 8.87 13.72 12.05 9.82 9.92C2= 4.87 5.01 4.25 4.74 4.54C3 4.76 8.53 7.45 5.30 5.45C4 1.28 3.94 3.76 1.70 1.94C4 derivatives 16.36 17.44 17.54 14.59 14.72CO2 6.08 3.39 5.53 5.40 5.21CO 2.08 0.00 0.00 1.78 1.31H2 27.84 14.33 17.48 27.88 27.06H2S 0.32 0.16 0.27 0.23 0.30

HHVa (MJ Nm�3) 24.6 20.4 26.4 22.1 26.3

a High heating value.

mainly chemically bonded in the form of elemental sulfur, inor-ganic and trace organic sulfides in the chars [48]. The high sulfurcontent is the main drawback of pyrolytic char in its utilizationas fuel. In addition, significant quantity of inorganic impuritiesmay limit its use in other applications, such as carbon black. In or-der to use pyrolytic char as carbon black, a demineralization pro-cess is required, which is well known.

4. Conclusions

In the co-pyrolysis of scrap tires with oily wastes, the oilywastes did not affect the product distribution from the pyrolysisof scrap tires, but they improved the properties of scrap tire de-rived oil as fuel. The amounts of aromatic and olefinic content,which are undesirable compounds for fuels, in the co-pyrolysis oilswere found to be less than that of scrap tire derived oils. The cat-alysts used in the co-pyrolysis had no considerable effect on bothyields and composition of pyrolysis products. The fuel characteris-tics of co-pyrolysis oils (except flash point and sulfur content) werecomparable with commercial diesel. The metal contents of thepyrolytic oils were much lower than the original oily wastes sug-gesting that metals were hold in the pyrolytic char. From these re-sults, it was concluded that co-pyrolysis of scrap tires with oilywastes generated from ships may be an environmental alternativeto direct combustion.

Acknowledgments

The financial support from Ege University under contract 2010-ÇSUM-002 is gratefully acknowledged.

Appendix A. Supplementary material

Supplementary data associated with this article can be found, inthe online version, at http://dx.doi.org/10.1016/j.enconman.2013.06.055.

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