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Copyrolysis of scrap tires with oily wastes
Journal of Analytical and Applied Pyrolysis 94 (2012) 184–189
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Copyrolysis of scrap tires with oily wastes Sermin Önenc¸ a , Mihai Brebu b , Cornelia Vasile b , Jale Yanik a,∗ a b
Ege University, Faculty of Science, Chemistry Department, 35100 Izmir, Turkey “Petru Poni” Institute of Macromolecular Chemistry, Physical Chemistry of Polymers Laboratory, 700487 Iasi, Romania
a r t i c l e
i n f o
Article history: Received 3 October 2011 Accepted 9 December 2011 Available online 17 December 2011 Keywords: Co-pyrolysis Scrap tire Bilge water Oil sludge
a b s t r a c t In this study, the conversion of hazardous wastes into liquid fuels was investigated. The pyrolysis of bilge water oil and oil sludge from ships, scrap tires and their blends was carried out at 400 and 500 ◦ C in absence and presence of catalyst. A commercial fluid catalytic cracking catalyst and Red Mud were used as catalyst. Pyrolysis products were separated as gas, oil and char. The pyrolytic oils were characterized by using gas chromatography-mass selective detector (GC-MSD) and 1 H nuclear magnetic resonance (1 H-NMR). The effect of temperature and catalyst on the product distribution and the composition of oil from pyrolysis were investigated. Co-pyrolysis of scrap tire with oily wastes from ships produced oil that could be used as fuel, while its pyrolysis alone produced oil that could be used as a chemical feedstock. The results obtained in this study showed that co-pyrolysis of oily wastes with scrap tires could be an environmentally friendly way for the transformation of hazardous wastes into valuable products such as chemicals or fuels. © 2011 Elsevier B.V. All rights reserved.
1. Introduction For both economic and environmental reasons, the utilization of waste such as waste lubricant oil, oil sludge, and scrap tires as energy source has become important. Environmental regulatory authorities are increasingly concerned about the potential adverse impacts of scrap tires. Estimates are that 250 millions postconsumer tires are accumulated each year in the European Union (EU) and comparable amounts amassed in North America, Latin America, Asia and the Middle-East, totaling 1 billions new arising per year [1]. Other types of hazardous waste are bilge waste and oil sludge for open oceans and coastal waters. Bilge is located at the vessel’s gravitational low point and collected everything from engine oil, fuel, debris, wash water (containing soap, oil and other organic material), and lake, ocean or river water. Oil sludge is a mud-like residue inside the bottom of a fuel tank or fuel residue that accumulates on the fuel filter before it reaches the main engine. Oil sludge also contains the residual waste oil products such as those resulting from the purification lubricating oil from main or auxiliary machinery or separated waste oil from bilge water separators or oil collected in drip trays, and waste hydraulic and lubricating oils. Annex I of MARPOL 73/78 includes recommendations for oily waste management that limit the discharge of this waste. Typically oily waste can be disposed by incineration. However, it has
∗ Corresponding author. Tel.: +90 232 3112386; fax: +90 232 3888264. E-mail address: [email protected] (J. Yanik). 0165-2370/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jaap.2011.12.006
been found that such method cause secondary pollutants [2]. Some studies such as wet air oxidation [3], ultra filtration [4] and electrochemical methods [5] had been proposed to treat bilge water to meet international standard discharge levels. Also, biodegradation had been performed for conversion of bilge water as a different alternative technology [6–8]. Pyrolysis is an alternative technology for conversion of these kinds of waste materials for energy recovery and environmental protection. Pyrolysis produces more useful products such as gas, oil and solid char which may be used as fuels or as feedstock for petrochemicals and other applications. In addition, heavy metals could be safely enclosed in the solid char. There have been number of studies that concerned conversion of scrap tires [9–11], waste lubricant oil [12–14] and oil sludge from oil storage tanks [15,16] into fuels or chemical feedstock by pyrolysis. Another approach in utilization of carbonaceous waste is coprocessing. Co-processing of scrap tires with coal has been widely studied [17–19]. The idea is to improve coal liquefaction at competitive costs. Co-processing of waste lubricant oil with plastics has also been studied as waste lubricant oil can provide good solvency for the straight chain common thermoplastics [20–22]. Considering the facts stated above, this study concerns the conversion of scrap tires and of oily waste from ships to liquid fuels or chemical feedstock by pyrolysis. In the present investigation, the oily waste was co-pyrolyzed with scrap tires in the absence and the presence of catalysts. For comparison purpose, scrap tires, bilge water and oil sludge were also pyrolyzed individually under the same conditions. The chemical composition of pyrolysis/copyrolysis oils was investigated by GC–MS and 1 H-NMR. The effect
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of temperature and catalysts on the product yield and composition was investigated. To the best of our knowledge there is no study related to pyrolysis of bilge water and oil sludge and their co-pyrolysis with scrap tires. 2. Materials and methods 2.1. Materials Scrap tires (ST) were supplied by Akin Rubber Plant-Samsun, Turkey (a rubber recycling enterprise). Scrap tire samples were shredded, crumbed and sieved from the sidewall rubber of scrap tires to produce a size of 1.5–2.0 mm. The scrap tires contained no steel thread or textile netting. The average rubber composition of the scrap tires was natural rubber 35 wt.% and butadiene rubber 65 wt.%. Oily wastes from ships was supplied by Batı Cim Co., AliagaTurkey, which is the company contracted by the Port Authority of Aliaga. The company provides the collection, handling, treatment and disposal of ship generated liquid (oily) wastes. Both oily bilge water and oil sludge are treated by oil/water separator to separate the oil phase from water phase. Oil recovered from the separation process is sent to cement fabric for incineration. Oily waste provided from company was centrifuged at 5000 rpm for 30 min in our laboratory to separate the water in waste. The oil phases obtained by centrifugation were named as bilge water oil (BW) and oily sludge (OS). The proximate and ultimate analysis of scrap tires and oily waste are shown in Table 1. The catalytic experiments were performed over Red Mud, as a disposable catalyst, and a commercial catalyst. The commercial catalyst is a ReUS-Y faujisite type catalyst, which is being used in fluid catalytic cracking (FCC) unit in the refinery. It has following characteristics: SiO2 - 58.0 wt.%, Al2 O3 - 38.0 wt.%, Re2 O3 - 1.5 wt.%, Na2 O - 0.3 wt.% and Fe - 0.5 wt.%; density - 0.89 g/cm3 ; specific surface area - 255 m2 /g; pore volume - 0.25 cm3 /g. Red Mud (RM) was supplied by Seydisehir Aluminium Company, Turkey. It contains mainly Fe2 O3 - 37.72 wt.%, Al2 O3 - 17.27 wt.%, SiO2 - 17.10 wt.%, TiO2 - 4.81 wt.%, Na2 O - 7.13 wt.%, CaO - 4.54 wt.% and has specific surface area of 16 m2 /g. 2.2. Pyrolysis procedure A glass reactor with an internal diameter of 30 mm and a total length of 350 mm was used in semi-batch operation under selfgenerated pressure. A schematic diagram of experimental set up is given in Fig. 1. Pyrolysis was performed at 400 and 500 ◦ C on individual BW, OS and ST and at 500 ◦ C on ternary mixture with a BW:OS:ST weight ratio of 1:1:2. The catalysts were laid between two layers of quartz wool in a stainless-steel net basket Table 1 Proximate and ultimate analyses of scrap tire and oily waste. Type of waste
Scrap tire
Proximate analysis (as received, wt.%) 1.6 Moisture 58.2 Volatile matter 21.3 Fixed carbon 18.9 Ash Ultimate analysis 74.30 C 7.20 H 0.90 N a 15.89 O 1.71 S Gross calorific value (MJ kg−1 ) Viscosity, at 100 ◦ C (SUS) a
Calculated by difference.
30.5 –
Bilge water oil
Sludge oil
17.8 79.7 2.0 0.5
6.0 89.5 3.5 0.9
79.43 11.98 – 7.74 0.85
76.47 11.18 – 11.00 1.35
29.2 9.80
14.3 1900
Fig. 1. Schematic diagram of the pyrolysis installation.
that was placed in the middle part of the reactor, being in contact with the gaseous products from primary degradation of materials (vapor phase contact mode). A 1:5 catalyst:feedstock mass rate was used and the pyrolysis was conducted at 500 ◦ C. A heating rate of 10 ◦ C/min and a duration time of 1 h were used for all experiments. The degradation products were separately collected as following: liquid products (oils) accumulated in the graduated cylinder, solid residue remained after degradation at the bottom of the reactor and the coke remained on the catalyst. Gaseous products were passed through a flask with water. The graduate cylinder also allowed us to determine the rate of oil accumulation. In each experiment, the solid residue (pyrolytic carbon), oil (pyrolytic oil) and coke (in case of catalytic experiments) yields were determined by weight and the gas yield was calculated by weight difference. 2.3. Analysis methods Thermogravimetric analysis was performed by on a Perkin Elmer Diamond TG/DTA thermogravimetric analyzer under N2 atmosphere. The flow rate of purge gas was kept at 200 mL/min. The sample was heated from the ambient temperature up to 800 ◦ C with a heating rate of 10 ◦ C/min. The composition of rubber from scrap tire was determined in Brisa Co., Izmit-Turkey by serial Curie point pyrolysis–gas chromatography (CuPy–GC) according to ASTM method (ASTM D3452-93, 1998). The degradation oils were characterized by GC-MSD analysis on a 6890N Agilent Technologies chromatograph coupled with an 5975 inert XL Agilent MSD detector, on a HP5-MS column (cross-linked methyl siloxane: 30 m × 0.25 mm × 0.25 m). The following parameters were used during analysis: inlet, 100 ◦ C; split ratio, 100:1; flow rate, 1 mL/min He; temperature program, 35 ◦ C (kept constant for 2 min.) then heated up to 300 ◦ C by 10◦ /min. The composition of the liquid products was characterized using the C–NP gram method (C stands for carbon, and NP stands for normal paraffin) based on chromatographic results [23]. 1 H nuclear magnetic resonance (1 HNMR) spectra of liquid products were recorded with a Varian AS 400 Mercury instrument using CDCl3 as solvent; the obtained data were used to determine the hydrocarbon types of the oils [24]. 3. Results and discussion 3.1. Thermogravimetric investigation Fig. 2 shows the evolution of the weight loss of the scrap tires and oily waste with temperature. In this figure, the derivative plot
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80 60
ST
40 BW:OS:ST
20
OS
OS
0 -20
BW
BW
-40
BW:OS:ST
ST
-60 0
100
200
300
Temperature, °C
400
Derivative mass loss , a.u.
Mass loss , wt%
100
500
Fig. 2. TGA and DTG curves of BW, SO, ST and of BW:SO:ST 1:1:2 mixture.
is also shown. Thermal degradation of scrap tires occurred in a wide temperature range (200–500 ◦ C) that can be explained by the complex composition of this material which beside natural and butadiene rubber also contains plasticizers and other additives [25]. Two degradation stages were present, the first one at 380 ◦ C corresponding to natural rubber and the second one at 444 ◦ C to butadiene rubber. The residue remaining after thermal degradation up to 550 ◦ C was of about 33 wt.% that comes both from the organic residue of the rubbers and from the inorganic additives in the tires. The decomposition of oily waste started as soon as heating starts, due to the loss of water and occurred almost totally, the remaining residue being of less than 5 wt.%. The bilge water degraded in two main degradation steps with maximum rates around 250 and 390 ◦ C and shoulders of the DTG peaks around 165 and 450 ◦ C, respectively. The oil sludge also decomposes in two stages, but contrary to the bilge water the first step occurs slower, with constant increase of degradation rate with increasing temperature up to about 265 ◦ C and no maximum in the DTG curve. The second step is similar to bilge water but is shifted to slightly lower temperatures, the maximum rate being at about 375 ◦ C and the shoulder at about 440 ◦ C. The TG/DTG curves for the ternary BW:OS:ST mixture with weight ratio of 1:1:2 lay between those of the individual components. However the remaining residue was slightly smaller than the calculated value based on additive rule (17.3 compared to 19.6 wt.%), showing that interactions occurred at high temperatures of degradation between the components. 3.2. Pyrolysis The product yields from pyrolysis of BW, OS and ST at different temperatures are presented in Fig. 3. It can be seen that product distribution drastically changed with increasing temperature from 400 to 500 ◦ C that enhances the thermal degradation. The oil yield increased more than 2 times for BW (77.5 vs. 33.8 wt.%) – Fig. 3a, 7 times for OS (71.3 vs. 9.5 wt.%) – Fig. 3b and 3 times for ST (39 vs. 12.3 wt.%) – Fig. 3c. The amount of gases was below 3 wt.% and 10 wt.% at 400 and 500 ◦ C respectively, and was higher for ST compared to OS and BW. The total amount of volatiles (gases and oils) was smaller that that evolved during the TG analysis, leaving more residues, both at 500 and especially at 400 ◦ C. This could be explained by the fact that all volatile products leave the reaction zone in the thermo balance while the cold part of the reactor that was 70 cm out of the furnace (Fig. 1) forced part of degradation products to return into the reaction zone for further degradation. Indeed, a reflux ring of condensed products was observed on the cold walls of reactor. This set-up was deliberately choose in order to shift to the lighter side the range of compounds in pyrolysis
Fig. 3. Product yields for thermal (400 and 500 ◦ C) and catalytic (500 ◦ C) degradation of BW (a), OS (b) and ST (c).
oils in exchange for the decrease of product yield. However the trend of degradation rate (ST < OS < BW) observed in TG analysis was confirmed by the amount of residue remaining after pyrolysis (ST > OS > BW). The liquid yields obtained from oily waste (BW and OS) in this study is comparable to the liquid yields obtained by pyrolysis of oil sludge and waste machinery oil [14,15], which were of about 66–70 wt.%. However we obtained higher amount of pyrolysis residue that could be explained by the presence in BW and OS of contaminants, such as soap and other organic compounds. We did not test temperatures above 500 ◦ C in this study. It has been already reported that for the pyrolysis of scrap tires there was no influence of the temperature on the product distributions over 500 ◦ C [26,27] or on the corresponding oil and gas yields [28,29]. Catalytic pyrolysis experiments were carried out at 500 ◦ C because high liquid yields and reaction rates were observed. It is expected for the contaminants in waste materials to poison the catalysts making their regeneration difficult and less effective. For this reason the vapor phase contact mode use of catalysts looks more reasonable compared to the liquid phase contact mode. In vapor phase contact mode thermal degradation of waste occurs first and the degradation products are catalytically degraded when they pass through the catalyst bed. In the case of BW (Fig. 3a) and of OS (Fig. 3b), the catalytic pyrolysis produced more gaseous products due to the secondary cracking reactions. Thus, the volatile products formed from thermal degradation of waste were further cracked on the catalyst bed leading to formation of gaseous product and coke. The catalysts showed
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Fig. 4. Product yields for thermal and catalytic at 500 ◦ C of ternary BW:OS:ST (1:1:2) mixture.
similar catalytic activity but Red Mud gave slightly more gases and consequently more coke, the effect being stronger for degradation of OS compared to BW. Also Red Mud leaves fewer residues while the amount of residue was slightly increased in the presence of FCC. In contrast to BW and OS, catalysts had less effect on the degradation of ST (Fig. 3c). The gas and oil yields were not significantly changed however the amount of residue was decreased, especially when using Red Mud. We can suppose that FCC acts mainly on the light primary products of thermal degradation while Red Mud also acts on the heavy products that could not normally leave the reactor and refluxed, remaining as residue in the case of thermal degradation. This could also occur on the catalytic degradation of ST compared to BW and OS, explaining the effect of catalysts more on the residue and less on volatiles. The catalytic co-pyrolysis (BW:OS:ST mixture of 1:1:2, w/w/w ratio) share the behavior of both oily waste (BW and OS) and scrap tire. Indeed, the gas yield increased while the total yield of volatiles decreased, that is similar to BW and OS and the amount of residue decreased, which is similar to ST – Fig. 4. Therefore it is difficult to discuss the presence or absence of interactions between components of mixture during pyrolysis. 3.3. Characterization of pyrolysis oils Pyrolysis oils were characterized by GC–MS and the chromatograms from thermal degradation at 500 ◦ C are shown in Fig. 5. BW and OS showed similar chromatograms, with typical shape of homologues series alkene/alkane from n-C5 up to n-C27 ,
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accompanied by their branched, cyclic and unsaturated isomers. The chromatogram of ST looked different, with few main peaks below n-C11 whose identification is given in the legend of Fig. 4 and many other small peaks. ST gave high amounts of d-limonene that is known to be the most important product from pyrolysis of polyisoprene [17]. Isobutene, butene, butane, 1,3-pentadiene and methylbutene (compounds at peaks noted 1 and 2 in Fig. 5) are also structures derived from the isoprene monomer unit of rubbers. ␣,pDimethylstyrene (peak 9) have similar structure with d-limonene but with aromatic ring instead of mono unsaturated cycle. The chromatogram of co-pyrolysis oil shows the typical compounds coming from the components (homologues series of hydrocarbons from BW/OS and peaks from ST). The distribution of compounds in the pyrolysis oils from studied waste is shown in Fig. 6. The NP gram curves (NP stands for normal paraffin) were obtained by plotting the area percent of compounds (as determined from the GC-MSD chromatograms) against the carbon number of normal paraffins having similar boiling points. The pyrolysis oils from BW had similar composition to OS, with a large distribution of compounds from n-C5 up to n-C25 , most of compounds being heavier than n-C10 (Fig. 6a and b). The NP-gram curve is shifted to lighter compounds (lower carbon numbers) for OS compared to BW. ST also gave compounds from n-C5 to n-C25 (Fig. 6c) but most of them are located in the n-C5 to n-C20 range, with two main peaks around n-C11 and n-C15 that correspond to dlimonene and to compounds with complex structure such as two condensed aromatic rings in naphthalene and quinoline (peaks 8 and 11 in Fig. 6). The catalysts shift to the lower side of carbon numbers the distribution of compounds in pyrolysis oils of BW and especially of OS, which is shown by the increased amounts of compounds below n-C15 . However the catalysts had lower effect on the pyrolysis oils of ST (Fig. 6c). FCC had slightly higher effect than Red Mud for the degradation of OS and of ST (more light compounds below n-C10 and less compounds above n-C16 ) but was similar to Red Mud for degradation of BW. Both catalysts had great effect on the distribution of compounds in the pyrolysis oils of tertiary BW:OS:ST mixture where the formation of compounds below nC15 was enhanced while that of heavier compounds above n-C15 was diminished (Fig. 6d). Particularly higher amount of d-limonene was obtained, as shown by the strong peak numbered 8 in the chromatogram (Fig. 5) and by the increase in the peak at n-C11 in the NP gram (Fig. 6d). This was surprising, considering that a similar effect was not observed on the degradation of ST alone.
Fig. 5. GC-MSD chromatograms of oil products from the pyrolysis of individual BW, OS, ST and of ternary BW:OS:ST (1:1:2) mixture at 500 ◦ C. (1) isobutene, butene, butane; (2) 1,3-pentadiene, methylbutene; (3) hexadiene, methylcyclopentene; (4) toluene; (5) ethylbenzene, dimethylbenzene; (6) styrene; (7) ethylmethylbenzene; (8) d-limonene; (9) ␣,p-dimethylstyrene; (10) phenylbutene; (11) dimethylnaphthalene, dimethylquinoline.
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15
BW BW FCC BW RM
GC-MSD area , %
GC-MSD area , %
15
10
5
0
10
5
0
5
10
15 20 Carbon number
15
25
10
5
0 10
15 20 Carbon number
10
15 Carbon number
15
ST ST FCC ST RM
5
5
GC-MSD area , %
GC-MSD area , %
OS OS FCC OS RM
25
20
25
BW:OS:ST BW:OS:ST FCC BW:OS:ST RM
10
5
0 5
10
15 Carbon number
20
25
Fig. 6. NP grams of oil products from the pyrolysis of BW, OS, ST and BW:OS:ST at 500 ◦ C.
The 1 H-NMR analysis was used to determine the percentage of aromatic, paraffinic, and aliphatic species in pyrolytic oils. The amount of hydrocarbon types in the pyrolytic oils, calculated by Myer’s formula [24] is given in Table 2. It should be noted that Myer’s formula is used for characterization of gasoline and middle distillates, which contain low amounts of substituted aromatics. Pyrolysis oils of BW and OS at 500 ◦ C had about 7% olefin content. Although it is seen that ST pyrolysis oil had the highest olefin content (20.5%), most of olefins are not represented by alkenes or alkadienes, which are the common compounds derived from pyrolysis. According to Myer’s formula, d-limonene, which is one of the main degradation compounds of ST, was considered as olefin. It was calculated that 86.5% of olefin contents in pyrolytic oil of ST come from d-limonene. Although aromatics are present among the major peaks seen in GC-MS chromatograph of ST (Fig. 5), the calculated aromatic content was not high. The reason may be due to the long chain groups substituted to aromatic ring, which are calculated as paraffin. The FCC catalyst decreased the paraffin content while increasing the olefin content in pyrolytic oils from BW and OS. In contrast, olefin content decreased and aromatics content increased by using of FCC catalyst in case of ST degradation due to the decreasing of d-limonene and the formation of benzene and naphthalene Table 2 Hydrocarbon content of pyrolsis oils (vol.%).
BW BW FCC BW RM OS OS FCC OS RM ST ST FCC ST RM BW:OS:ST BW:OS:ST FCC BW:OS:ST RM
Aromatics
Paraffins
Olefins
9.2 10.4 8.5 8.1 10.3 8.6 13.9 18.4 18.1 10.0 11.8 12.0
83.6 76.1 84.3 84.6 80.5 80.7 65.6 66.3 51.3 75.3 74.1 69.5
7.2 13.5 7.2 7.4 9.3 10.7 20.5 15.3 30.6 14.7 14.2 18.5
derivatives. RM catalyst had a considerable effect on the hydrocarbon type in pyrolysis oil derived from ST; both olefin and aromatic content was increased while the paraffin content was decreased. In the case of co-pyrolysis of ternary mixture, the amount of hydrocarbons in pyrolysis oil was around average value calculated based on individual components. It can be concluded that co-pyrolysis oil of ST with oily waste such as BW and OS could be used as fuel because of low olefin and aromatic content. 4. Conclusions In this study, conversion of oily waste from ships and of waste scrap tires into liquid fuels by pyrolysis was investigated in absence and presence of catalyst. The increase in temperature from 400 ◦ C to 500 ◦ C led to a considerable increase both of the degradation rate and of the oil yield. The catalysts tested in this study (FCC and Red Mud) showed similar catalytic activity on degradation of waste. Although the use of catalyst yielded low pyrolysis oil, this consisted of lighter hydrocarbons compared to thermal degradation. The pyrolysis oil derived from scrap tires contained considerable amounts of aromatics, while co-pyrolysis of scrap tires with oily waste from ships in absence and in presence of FCC catalyst produced oils with high amounts of paraffin and low amounts of aromatics. Although pyrolysis of scrap tires gives liquid products that could be used as a chemical feedstock, its co-pyrolysis with oily waste from ships produce oils that could be used as fuel after upgrading such as desulphurization and saturation (double bonds) via hydrogenation process. As a conclusion, the results obtained in this study showed that co-pyrolysis of scrap tires with oily waste from ships could be an environmentally friendly way for the transformation of hazardous waste into valuable products such as chemicals or fuels. Acknowledgments The financial support from Ege University under contract 2009FEN-092 is highly appreciated. Support for Dr. Mihai Brebu from
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Journal of Analytical and Applied Pyrolysis journal homepage: www.elsevier.com/locate/jaap
Copyrolysis of scrap tires with oily wastes Sermin Önenc¸ a , Mihai Brebu b , Cornelia Vasile b , Jale Yanik a,∗ a b
Ege University, Faculty of Science, Chemistry Department, 35100 Izmir, Turkey “Petru Poni” Institute of Macromolecular Chemistry, Physical Chemistry of Polymers Laboratory, 700487 Iasi, Romania
a r t i c l e
i n f o
Article history: Received 3 October 2011 Accepted 9 December 2011 Available online 17 December 2011 Keywords: Co-pyrolysis Scrap tire Bilge water Oil sludge
a b s t r a c t In this study, the conversion of hazardous wastes into liquid fuels was investigated. The pyrolysis of bilge water oil and oil sludge from ships, scrap tires and their blends was carried out at 400 and 500 ◦ C in absence and presence of catalyst. A commercial fluid catalytic cracking catalyst and Red Mud were used as catalyst. Pyrolysis products were separated as gas, oil and char. The pyrolytic oils were characterized by using gas chromatography-mass selective detector (GC-MSD) and 1 H nuclear magnetic resonance (1 H-NMR). The effect of temperature and catalyst on the product distribution and the composition of oil from pyrolysis were investigated. Co-pyrolysis of scrap tire with oily wastes from ships produced oil that could be used as fuel, while its pyrolysis alone produced oil that could be used as a chemical feedstock. The results obtained in this study showed that co-pyrolysis of oily wastes with scrap tires could be an environmentally friendly way for the transformation of hazardous wastes into valuable products such as chemicals or fuels. © 2011 Elsevier B.V. All rights reserved.
1. Introduction For both economic and environmental reasons, the utilization of waste such as waste lubricant oil, oil sludge, and scrap tires as energy source has become important. Environmental regulatory authorities are increasingly concerned about the potential adverse impacts of scrap tires. Estimates are that 250 millions postconsumer tires are accumulated each year in the European Union (EU) and comparable amounts amassed in North America, Latin America, Asia and the Middle-East, totaling 1 billions new arising per year [1]. Other types of hazardous waste are bilge waste and oil sludge for open oceans and coastal waters. Bilge is located at the vessel’s gravitational low point and collected everything from engine oil, fuel, debris, wash water (containing soap, oil and other organic material), and lake, ocean or river water. Oil sludge is a mud-like residue inside the bottom of a fuel tank or fuel residue that accumulates on the fuel filter before it reaches the main engine. Oil sludge also contains the residual waste oil products such as those resulting from the purification lubricating oil from main or auxiliary machinery or separated waste oil from bilge water separators or oil collected in drip trays, and waste hydraulic and lubricating oils. Annex I of MARPOL 73/78 includes recommendations for oily waste management that limit the discharge of this waste. Typically oily waste can be disposed by incineration. However, it has
∗ Corresponding author. Tel.: +90 232 3112386; fax: +90 232 3888264. E-mail address: [email protected] (J. Yanik). 0165-2370/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jaap.2011.12.006
been found that such method cause secondary pollutants [2]. Some studies such as wet air oxidation [3], ultra filtration [4] and electrochemical methods [5] had been proposed to treat bilge water to meet international standard discharge levels. Also, biodegradation had been performed for conversion of bilge water as a different alternative technology [6–8]. Pyrolysis is an alternative technology for conversion of these kinds of waste materials for energy recovery and environmental protection. Pyrolysis produces more useful products such as gas, oil and solid char which may be used as fuels or as feedstock for petrochemicals and other applications. In addition, heavy metals could be safely enclosed in the solid char. There have been number of studies that concerned conversion of scrap tires [9–11], waste lubricant oil [12–14] and oil sludge from oil storage tanks [15,16] into fuels or chemical feedstock by pyrolysis. Another approach in utilization of carbonaceous waste is coprocessing. Co-processing of scrap tires with coal has been widely studied [17–19]. The idea is to improve coal liquefaction at competitive costs. Co-processing of waste lubricant oil with plastics has also been studied as waste lubricant oil can provide good solvency for the straight chain common thermoplastics [20–22]. Considering the facts stated above, this study concerns the conversion of scrap tires and of oily waste from ships to liquid fuels or chemical feedstock by pyrolysis. In the present investigation, the oily waste was co-pyrolyzed with scrap tires in the absence and the presence of catalysts. For comparison purpose, scrap tires, bilge water and oil sludge were also pyrolyzed individually under the same conditions. The chemical composition of pyrolysis/copyrolysis oils was investigated by GC–MS and 1 H-NMR. The effect
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of temperature and catalysts on the product yield and composition was investigated. To the best of our knowledge there is no study related to pyrolysis of bilge water and oil sludge and their co-pyrolysis with scrap tires. 2. Materials and methods 2.1. Materials Scrap tires (ST) were supplied by Akin Rubber Plant-Samsun, Turkey (a rubber recycling enterprise). Scrap tire samples were shredded, crumbed and sieved from the sidewall rubber of scrap tires to produce a size of 1.5–2.0 mm. The scrap tires contained no steel thread or textile netting. The average rubber composition of the scrap tires was natural rubber 35 wt.% and butadiene rubber 65 wt.%. Oily wastes from ships was supplied by Batı Cim Co., AliagaTurkey, which is the company contracted by the Port Authority of Aliaga. The company provides the collection, handling, treatment and disposal of ship generated liquid (oily) wastes. Both oily bilge water and oil sludge are treated by oil/water separator to separate the oil phase from water phase. Oil recovered from the separation process is sent to cement fabric for incineration. Oily waste provided from company was centrifuged at 5000 rpm for 30 min in our laboratory to separate the water in waste. The oil phases obtained by centrifugation were named as bilge water oil (BW) and oily sludge (OS). The proximate and ultimate analysis of scrap tires and oily waste are shown in Table 1. The catalytic experiments were performed over Red Mud, as a disposable catalyst, and a commercial catalyst. The commercial catalyst is a ReUS-Y faujisite type catalyst, which is being used in fluid catalytic cracking (FCC) unit in the refinery. It has following characteristics: SiO2 - 58.0 wt.%, Al2 O3 - 38.0 wt.%, Re2 O3 - 1.5 wt.%, Na2 O - 0.3 wt.% and Fe - 0.5 wt.%; density - 0.89 g/cm3 ; specific surface area - 255 m2 /g; pore volume - 0.25 cm3 /g. Red Mud (RM) was supplied by Seydisehir Aluminium Company, Turkey. It contains mainly Fe2 O3 - 37.72 wt.%, Al2 O3 - 17.27 wt.%, SiO2 - 17.10 wt.%, TiO2 - 4.81 wt.%, Na2 O - 7.13 wt.%, CaO - 4.54 wt.% and has specific surface area of 16 m2 /g. 2.2. Pyrolysis procedure A glass reactor with an internal diameter of 30 mm and a total length of 350 mm was used in semi-batch operation under selfgenerated pressure. A schematic diagram of experimental set up is given in Fig. 1. Pyrolysis was performed at 400 and 500 ◦ C on individual BW, OS and ST and at 500 ◦ C on ternary mixture with a BW:OS:ST weight ratio of 1:1:2. The catalysts were laid between two layers of quartz wool in a stainless-steel net basket Table 1 Proximate and ultimate analyses of scrap tire and oily waste. Type of waste
Scrap tire
Proximate analysis (as received, wt.%) 1.6 Moisture 58.2 Volatile matter 21.3 Fixed carbon 18.9 Ash Ultimate analysis 74.30 C 7.20 H 0.90 N a 15.89 O 1.71 S Gross calorific value (MJ kg−1 ) Viscosity, at 100 ◦ C (SUS) a
Calculated by difference.
30.5 –
Bilge water oil
Sludge oil
17.8 79.7 2.0 0.5
6.0 89.5 3.5 0.9
79.43 11.98 – 7.74 0.85
76.47 11.18 – 11.00 1.35
29.2 9.80
14.3 1900
Fig. 1. Schematic diagram of the pyrolysis installation.
that was placed in the middle part of the reactor, being in contact with the gaseous products from primary degradation of materials (vapor phase contact mode). A 1:5 catalyst:feedstock mass rate was used and the pyrolysis was conducted at 500 ◦ C. A heating rate of 10 ◦ C/min and a duration time of 1 h were used for all experiments. The degradation products were separately collected as following: liquid products (oils) accumulated in the graduated cylinder, solid residue remained after degradation at the bottom of the reactor and the coke remained on the catalyst. Gaseous products were passed through a flask with water. The graduate cylinder also allowed us to determine the rate of oil accumulation. In each experiment, the solid residue (pyrolytic carbon), oil (pyrolytic oil) and coke (in case of catalytic experiments) yields were determined by weight and the gas yield was calculated by weight difference. 2.3. Analysis methods Thermogravimetric analysis was performed by on a Perkin Elmer Diamond TG/DTA thermogravimetric analyzer under N2 atmosphere. The flow rate of purge gas was kept at 200 mL/min. The sample was heated from the ambient temperature up to 800 ◦ C with a heating rate of 10 ◦ C/min. The composition of rubber from scrap tire was determined in Brisa Co., Izmit-Turkey by serial Curie point pyrolysis–gas chromatography (CuPy–GC) according to ASTM method (ASTM D3452-93, 1998). The degradation oils were characterized by GC-MSD analysis on a 6890N Agilent Technologies chromatograph coupled with an 5975 inert XL Agilent MSD detector, on a HP5-MS column (cross-linked methyl siloxane: 30 m × 0.25 mm × 0.25 m). The following parameters were used during analysis: inlet, 100 ◦ C; split ratio, 100:1; flow rate, 1 mL/min He; temperature program, 35 ◦ C (kept constant for 2 min.) then heated up to 300 ◦ C by 10◦ /min. The composition of the liquid products was characterized using the C–NP gram method (C stands for carbon, and NP stands for normal paraffin) based on chromatographic results [23]. 1 H nuclear magnetic resonance (1 HNMR) spectra of liquid products were recorded with a Varian AS 400 Mercury instrument using CDCl3 as solvent; the obtained data were used to determine the hydrocarbon types of the oils [24]. 3. Results and discussion 3.1. Thermogravimetric investigation Fig. 2 shows the evolution of the weight loss of the scrap tires and oily waste with temperature. In this figure, the derivative plot
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80 60
ST
40 BW:OS:ST
20
OS
OS
0 -20
BW
BW
-40
BW:OS:ST
ST
-60 0
100
200
300
Temperature, °C
400
Derivative mass loss , a.u.
Mass loss , wt%
100
500
Fig. 2. TGA and DTG curves of BW, SO, ST and of BW:SO:ST 1:1:2 mixture.
is also shown. Thermal degradation of scrap tires occurred in a wide temperature range (200–500 ◦ C) that can be explained by the complex composition of this material which beside natural and butadiene rubber also contains plasticizers and other additives [25]. Two degradation stages were present, the first one at 380 ◦ C corresponding to natural rubber and the second one at 444 ◦ C to butadiene rubber. The residue remaining after thermal degradation up to 550 ◦ C was of about 33 wt.% that comes both from the organic residue of the rubbers and from the inorganic additives in the tires. The decomposition of oily waste started as soon as heating starts, due to the loss of water and occurred almost totally, the remaining residue being of less than 5 wt.%. The bilge water degraded in two main degradation steps with maximum rates around 250 and 390 ◦ C and shoulders of the DTG peaks around 165 and 450 ◦ C, respectively. The oil sludge also decomposes in two stages, but contrary to the bilge water the first step occurs slower, with constant increase of degradation rate with increasing temperature up to about 265 ◦ C and no maximum in the DTG curve. The second step is similar to bilge water but is shifted to slightly lower temperatures, the maximum rate being at about 375 ◦ C and the shoulder at about 440 ◦ C. The TG/DTG curves for the ternary BW:OS:ST mixture with weight ratio of 1:1:2 lay between those of the individual components. However the remaining residue was slightly smaller than the calculated value based on additive rule (17.3 compared to 19.6 wt.%), showing that interactions occurred at high temperatures of degradation between the components. 3.2. Pyrolysis The product yields from pyrolysis of BW, OS and ST at different temperatures are presented in Fig. 3. It can be seen that product distribution drastically changed with increasing temperature from 400 to 500 ◦ C that enhances the thermal degradation. The oil yield increased more than 2 times for BW (77.5 vs. 33.8 wt.%) – Fig. 3a, 7 times for OS (71.3 vs. 9.5 wt.%) – Fig. 3b and 3 times for ST (39 vs. 12.3 wt.%) – Fig. 3c. The amount of gases was below 3 wt.% and 10 wt.% at 400 and 500 ◦ C respectively, and was higher for ST compared to OS and BW. The total amount of volatiles (gases and oils) was smaller that that evolved during the TG analysis, leaving more residues, both at 500 and especially at 400 ◦ C. This could be explained by the fact that all volatile products leave the reaction zone in the thermo balance while the cold part of the reactor that was 70 cm out of the furnace (Fig. 1) forced part of degradation products to return into the reaction zone for further degradation. Indeed, a reflux ring of condensed products was observed on the cold walls of reactor. This set-up was deliberately choose in order to shift to the lighter side the range of compounds in pyrolysis
Fig. 3. Product yields for thermal (400 and 500 ◦ C) and catalytic (500 ◦ C) degradation of BW (a), OS (b) and ST (c).
oils in exchange for the decrease of product yield. However the trend of degradation rate (ST < OS < BW) observed in TG analysis was confirmed by the amount of residue remaining after pyrolysis (ST > OS > BW). The liquid yields obtained from oily waste (BW and OS) in this study is comparable to the liquid yields obtained by pyrolysis of oil sludge and waste machinery oil [14,15], which were of about 66–70 wt.%. However we obtained higher amount of pyrolysis residue that could be explained by the presence in BW and OS of contaminants, such as soap and other organic compounds. We did not test temperatures above 500 ◦ C in this study. It has been already reported that for the pyrolysis of scrap tires there was no influence of the temperature on the product distributions over 500 ◦ C [26,27] or on the corresponding oil and gas yields [28,29]. Catalytic pyrolysis experiments were carried out at 500 ◦ C because high liquid yields and reaction rates were observed. It is expected for the contaminants in waste materials to poison the catalysts making their regeneration difficult and less effective. For this reason the vapor phase contact mode use of catalysts looks more reasonable compared to the liquid phase contact mode. In vapor phase contact mode thermal degradation of waste occurs first and the degradation products are catalytically degraded when they pass through the catalyst bed. In the case of BW (Fig. 3a) and of OS (Fig. 3b), the catalytic pyrolysis produced more gaseous products due to the secondary cracking reactions. Thus, the volatile products formed from thermal degradation of waste were further cracked on the catalyst bed leading to formation of gaseous product and coke. The catalysts showed
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Fig. 4. Product yields for thermal and catalytic at 500 ◦ C of ternary BW:OS:ST (1:1:2) mixture.
similar catalytic activity but Red Mud gave slightly more gases and consequently more coke, the effect being stronger for degradation of OS compared to BW. Also Red Mud leaves fewer residues while the amount of residue was slightly increased in the presence of FCC. In contrast to BW and OS, catalysts had less effect on the degradation of ST (Fig. 3c). The gas and oil yields were not significantly changed however the amount of residue was decreased, especially when using Red Mud. We can suppose that FCC acts mainly on the light primary products of thermal degradation while Red Mud also acts on the heavy products that could not normally leave the reactor and refluxed, remaining as residue in the case of thermal degradation. This could also occur on the catalytic degradation of ST compared to BW and OS, explaining the effect of catalysts more on the residue and less on volatiles. The catalytic co-pyrolysis (BW:OS:ST mixture of 1:1:2, w/w/w ratio) share the behavior of both oily waste (BW and OS) and scrap tire. Indeed, the gas yield increased while the total yield of volatiles decreased, that is similar to BW and OS and the amount of residue decreased, which is similar to ST – Fig. 4. Therefore it is difficult to discuss the presence or absence of interactions between components of mixture during pyrolysis. 3.3. Characterization of pyrolysis oils Pyrolysis oils were characterized by GC–MS and the chromatograms from thermal degradation at 500 ◦ C are shown in Fig. 5. BW and OS showed similar chromatograms, with typical shape of homologues series alkene/alkane from n-C5 up to n-C27 ,
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accompanied by their branched, cyclic and unsaturated isomers. The chromatogram of ST looked different, with few main peaks below n-C11 whose identification is given in the legend of Fig. 4 and many other small peaks. ST gave high amounts of d-limonene that is known to be the most important product from pyrolysis of polyisoprene [17]. Isobutene, butene, butane, 1,3-pentadiene and methylbutene (compounds at peaks noted 1 and 2 in Fig. 5) are also structures derived from the isoprene monomer unit of rubbers. ␣,pDimethylstyrene (peak 9) have similar structure with d-limonene but with aromatic ring instead of mono unsaturated cycle. The chromatogram of co-pyrolysis oil shows the typical compounds coming from the components (homologues series of hydrocarbons from BW/OS and peaks from ST). The distribution of compounds in the pyrolysis oils from studied waste is shown in Fig. 6. The NP gram curves (NP stands for normal paraffin) were obtained by plotting the area percent of compounds (as determined from the GC-MSD chromatograms) against the carbon number of normal paraffins having similar boiling points. The pyrolysis oils from BW had similar composition to OS, with a large distribution of compounds from n-C5 up to n-C25 , most of compounds being heavier than n-C10 (Fig. 6a and b). The NP-gram curve is shifted to lighter compounds (lower carbon numbers) for OS compared to BW. ST also gave compounds from n-C5 to n-C25 (Fig. 6c) but most of them are located in the n-C5 to n-C20 range, with two main peaks around n-C11 and n-C15 that correspond to dlimonene and to compounds with complex structure such as two condensed aromatic rings in naphthalene and quinoline (peaks 8 and 11 in Fig. 6). The catalysts shift to the lower side of carbon numbers the distribution of compounds in pyrolysis oils of BW and especially of OS, which is shown by the increased amounts of compounds below n-C15 . However the catalysts had lower effect on the pyrolysis oils of ST (Fig. 6c). FCC had slightly higher effect than Red Mud for the degradation of OS and of ST (more light compounds below n-C10 and less compounds above n-C16 ) but was similar to Red Mud for degradation of BW. Both catalysts had great effect on the distribution of compounds in the pyrolysis oils of tertiary BW:OS:ST mixture where the formation of compounds below nC15 was enhanced while that of heavier compounds above n-C15 was diminished (Fig. 6d). Particularly higher amount of d-limonene was obtained, as shown by the strong peak numbered 8 in the chromatogram (Fig. 5) and by the increase in the peak at n-C11 in the NP gram (Fig. 6d). This was surprising, considering that a similar effect was not observed on the degradation of ST alone.
Fig. 5. GC-MSD chromatograms of oil products from the pyrolysis of individual BW, OS, ST and of ternary BW:OS:ST (1:1:2) mixture at 500 ◦ C. (1) isobutene, butene, butane; (2) 1,3-pentadiene, methylbutene; (3) hexadiene, methylcyclopentene; (4) toluene; (5) ethylbenzene, dimethylbenzene; (6) styrene; (7) ethylmethylbenzene; (8) d-limonene; (9) ␣,p-dimethylstyrene; (10) phenylbutene; (11) dimethylnaphthalene, dimethylquinoline.
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15
BW BW FCC BW RM
GC-MSD area , %
GC-MSD area , %
15
10
5
0
10
5
0
5
10
15 20 Carbon number
15
25
10
5
0 10
15 20 Carbon number
10
15 Carbon number
15
ST ST FCC ST RM
5
5
GC-MSD area , %
GC-MSD area , %
OS OS FCC OS RM
25
20
25
BW:OS:ST BW:OS:ST FCC BW:OS:ST RM
10
5
0 5
10
15 Carbon number
20
25
Fig. 6. NP grams of oil products from the pyrolysis of BW, OS, ST and BW:OS:ST at 500 ◦ C.
The 1 H-NMR analysis was used to determine the percentage of aromatic, paraffinic, and aliphatic species in pyrolytic oils. The amount of hydrocarbon types in the pyrolytic oils, calculated by Myer’s formula [24] is given in Table 2. It should be noted that Myer’s formula is used for characterization of gasoline and middle distillates, which contain low amounts of substituted aromatics. Pyrolysis oils of BW and OS at 500 ◦ C had about 7% olefin content. Although it is seen that ST pyrolysis oil had the highest olefin content (20.5%), most of olefins are not represented by alkenes or alkadienes, which are the common compounds derived from pyrolysis. According to Myer’s formula, d-limonene, which is one of the main degradation compounds of ST, was considered as olefin. It was calculated that 86.5% of olefin contents in pyrolytic oil of ST come from d-limonene. Although aromatics are present among the major peaks seen in GC-MS chromatograph of ST (Fig. 5), the calculated aromatic content was not high. The reason may be due to the long chain groups substituted to aromatic ring, which are calculated as paraffin. The FCC catalyst decreased the paraffin content while increasing the olefin content in pyrolytic oils from BW and OS. In contrast, olefin content decreased and aromatics content increased by using of FCC catalyst in case of ST degradation due to the decreasing of d-limonene and the formation of benzene and naphthalene Table 2 Hydrocarbon content of pyrolsis oils (vol.%).
BW BW FCC BW RM OS OS FCC OS RM ST ST FCC ST RM BW:OS:ST BW:OS:ST FCC BW:OS:ST RM
Aromatics
Paraffins
Olefins
9.2 10.4 8.5 8.1 10.3 8.6 13.9 18.4 18.1 10.0 11.8 12.0
83.6 76.1 84.3 84.6 80.5 80.7 65.6 66.3 51.3 75.3 74.1 69.5
7.2 13.5 7.2 7.4 9.3 10.7 20.5 15.3 30.6 14.7 14.2 18.5
derivatives. RM catalyst had a considerable effect on the hydrocarbon type in pyrolysis oil derived from ST; both olefin and aromatic content was increased while the paraffin content was decreased. In the case of co-pyrolysis of ternary mixture, the amount of hydrocarbons in pyrolysis oil was around average value calculated based on individual components. It can be concluded that co-pyrolysis oil of ST with oily waste such as BW and OS could be used as fuel because of low olefin and aromatic content. 4. Conclusions In this study, conversion of oily waste from ships and of waste scrap tires into liquid fuels by pyrolysis was investigated in absence and presence of catalyst. The increase in temperature from 400 ◦ C to 500 ◦ C led to a considerable increase both of the degradation rate and of the oil yield. The catalysts tested in this study (FCC and Red Mud) showed similar catalytic activity on degradation of waste. Although the use of catalyst yielded low pyrolysis oil, this consisted of lighter hydrocarbons compared to thermal degradation. The pyrolysis oil derived from scrap tires contained considerable amounts of aromatics, while co-pyrolysis of scrap tires with oily waste from ships in absence and in presence of FCC catalyst produced oils with high amounts of paraffin and low amounts of aromatics. Although pyrolysis of scrap tires gives liquid products that could be used as a chemical feedstock, its co-pyrolysis with oily waste from ships produce oils that could be used as fuel after upgrading such as desulphurization and saturation (double bonds) via hydrogenation process. As a conclusion, the results obtained in this study showed that co-pyrolysis of scrap tires with oily waste from ships could be an environmentally friendly way for the transformation of hazardous waste into valuable products such as chemicals or fuels. Acknowledgments The financial support from Ege University under contract 2009FEN-092 is highly appreciated. Support for Dr. Mihai Brebu from
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