Polycyclic aromatic hydrocarbons (PAHs)

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Thermo-gravimetric analysis (TGA). The initial characterization of the influence of CO2 was con- ducted with a Netzsch STA 449 F1 Jupiter. ®. TGA unit capable ...
Journal of Environmental Management 160 (2015) 306e311

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Research article

Polycyclic aromatic hydrocarbons (PAHs) and volatile organic compounds (VOCs) mitigation in the pyrolysis process of waste tires using CO2 as a reaction medium Eilhann E. Kwon a, *, Jeong-Ik Oh b, **, Ki-Hyun Kim c a b c

Department of Environment and Energy, Sejong University, Seoul, Republic of Korea Environmental Energy Division, Land & Housing Research Institute, Korea National Land & Housing Corporation, Republic of Korea Department of Civil and Environmental Engineering, Hanyang University, Seoul, Republic of Korea

a r t i c l e i n f o

a b s t r a c t

Article history: Received 22 February 2015 Received in revised form 17 June 2015 Accepted 19 June 2015

Our work reported the CO2-assisted mitigation of PAHs and VOCs in the thermo-chemical process (i.e., pyrolysis). To investigate the pyrolysis of used tires to recover energy and chemical products, the experiments were conducted using a laboratory-scale batch-type reactor. In particular, to examine the influence of the CO2 in pyrolysis of a tire, the pyrolytic products including C1-5-hydrocarbons (HCs), volatile organic carbons (VOCs), and polycyclic aromatic hydrocarbons (PAHs) were evaluated qualitatively by gas chromatography (GC) with mass spectroscopy (MS) as well as with a thermal conductivity detector (TCD). The mass balance of the pyrolytic products under various pyrolytic conditions was established on the basis of their weight fractions of the pyrolytic products. Our experimental work experimentally validated that the amount of gaseous pyrolytic products increased when using CO2 as a pyrolysis medium, while substantially altering the production of pyrolytic oil in absolute content (7.3 e17.2%) and in relative composition (including PAHs and VOCs). Thus, the co-feeding of CO2 in the pyrolysis process can be considered an environmentally benign and energy efficient process. © 2015 Elsevier Ltd. All rights reserved.

Keywords: Pyrolysis Used tires Air pollutant control Thermal degradation CO2

1. Introduction Used tires create a challenging disposal issue since they are generated in large quantities (i.e., nearly 300 million used tires per year in the U.S.) and have limited end of life options via current technologies (Collins et al., 1995; Giere et al., 2004, 2006). For instance, they can be treated and reused or coarsely ground and used as filler for artificial turf or civil engineering projects (Gawel and Slusarski, 1999). However, these options account for only ~20% of the generated tire waste (Gawel and Slusarski, 1999; Kwon and Castaldi, 2008). Thus, thermal treatment of used tires (e.g., pyrolysis, gasification, and combustion) for the production of petrochemicals and recovery of energy has been proposed and developed as a feasible alternative technique (Betancur et al., 2009; Conesa et al., 2004; Mastral et al., 2002; Piatkowski and Steinfeld,

* Corresponding author. 209 Neundong-ro, Gwangjin-gu, Seoul 143-747, Republic of Korea. ** Corresponding author. Korea National Land & Housing Corporation, 174, Jeonmin-Dong, Yuseong-Gu, Daejeon, Republic of Korea. E-mail addresses: [email protected] (E.E. Kwon), [email protected] (J.-I. Oh). http://dx.doi.org/10.1016/j.jenvman.2015.06.033 0301-4797/© 2015 Elsevier Ltd. All rights reserved.

2010; Piatkowski et al., 2009; Zabaniotou and Stavropoulos, 2003). Thermal treatment of used tires could be an attractive option because of general compositional properties of tires (e.g., the low levels of moisture, nitrogen, and mineral matter) compared to coal (Giere et al., 2004, 2006). The pyrolytic oil from tire waste can be used directly as a fuel or blended with petrochemical feedstock (Kim et al., 1994). Thus, tire pyrolysis is a promising candidate for tire disposal, while also yielding a versatile, useable product (Xiao et al., 2008). For instance, the products from the pyrolysis of used tires, such as paraffin hydrocarbons, olefins, aromatic hydrocarbons, and syngas, can be potentially used as starting compounds for the synthesis of other chemical compounds (Choi et al., 2014; Undri et al., 2014). Tires are composed of a polymer mixture that is mainly polyisoprene (IR) and styrene butadiene rubber (SBR) (Chen et al., 1997, 2007). In addition to the polymer mixture, black carbon, fiber extender, and vulcanizing agents are added during manufacturing, leading to the observed complex thermal degradation behavior (Mastral et al., 2000, 1999). Thus, the thermal treatment of used tires has been investigated at an overall process level in light of the complex thermal degradation nature of used

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tires (Gupta et al., 2014; Hu et al., 2014). Furthermore, generation of unwanted pyrolytic products that are not suitable for fuel and chemical feedstock can arise due to the heterogeneous composition of used tires (Chien et al., 2009; Hwang et al., 2014). Unfortunately, the operational parameters required to control these unwanted pyrolytic products are very limited without the application of a catalyst (Ji et al., 2012; Stanciulescu and Ikura, 2007; Tang and Curtis, 1996). The objective of this work was to investigate a new method for upgrading and modifying pyrolytic products from used tires without using a catalyst. To achieve this goal, we explored the effect of CO2 as a reaction medium for the pyrolysis of used tires through mechanistic validation and assessments of the pyrolytic products in the overall process level (i.e., between the presence and absence of CO2). 2. Materials, methods, and experiments 2.1. Materials All gases (i.e., N2 and CO2) used for the experiments were ultrahigh purity (UHP) and purchased through Daesung gas (Seoul, Korea). The experimental flow rates were controlled using a thermal mass flow controller (5850 series E) certified by Brooks (USA). The results of both ultimate and proximate analysis of tire samples used for the experiments are summarized in Table 1. The highpurity styrene butadiene rubber (SBR) and polyisoprene (IR) test samples were purchased from SigmaeAldrich Chemicals (St. Louis, USA). The shredded used tires were obtained from the Hyundai cements (Korea). The ultimate analysis was conducted with the FLASH 2000 CHNS/O Analyzers (Thermo Scientific, USA). Prior the experimental work, the samples used for the experimental work were dried for 72 h. 2.2. Thermo-gravimetric analysis (TGA) The initial characterization of the influence of CO2 was conducted with a Netzsch STA 449 F1 Jupiter® TGA unit capable of TGA and differential thermal analysis (DTA). A series of TGA tests were carried out at a heating rate of 10  C min1 over a temperature range, ambient to 700  C. The flow rate of purge and protective gas was maintained as a sum of 200 mL min1, and 50 mg of sample was loaded into the TGA unit. The effluent of the TGA was sent to a GC/MS (Agilent 9890/4973) for identification and quantification of the chemical species from the TGA unit. The lag time of the sample from the TGA unit to the injection block, located on the GC/MS, was calculated to be less than 1 s, considering the size capacity of a 3 mL volume transfer line (Netzsch Unit). The sampling system was maintained at greater than 300  C to mitigate condensation and/or adsorption of chemical species onto the system surface (Marinov et al., 1998). The GC was equipped with a capillary column (0.25 mm  30 m HP-5MS), which was directly interfaced to a quadrupole mass spectrometer. Identification of the species was accomplished by matching their retention times and the mass spectral fragmentation patterns to species found in standard MS libraries. Permanent gases (i.e., H2, N2, O2, and CO2) and C1 and C2 chemical species were

determined using a Carboxen-1010 (Supelco #25467) connected to the TCD. To measure C4 species, a micro-GC (Agilent 3000) was used. The quantitative analysis of gaseous compounds involved in pyrolysis reactions was made by multi-level calibrations using a Restek PAH standard (Lot #A03448), Sigma Aldrich aromatic standard (PIANO Aromatic Lot #2102), and Japanese indoor air standards mixture (Lot# 4M7537-U). 2.3. Tubular reactor for pyrolysis A tubular reactor (TR), made of 1 inch outer diameter (OD) quartz tubing (Chemglass CGQ-0900T-13) and 1 inch Stainless Ultra Torr Vacuum Fitting (Swagelok SS-4-UT-6-400), was used for the investigation of pyrolysis process in this study (TR unit length ¼ 0.8 m). The tire sample (10 g) was packed into the reactor with the residence time of 15 min. The required experimental temperature was achieved using a split-hinged furnace (AsOne, Japan) and controlled via monitoring the temperature of TR with Stype thermocouple. An insulation collar (high temperature Duraboard insulation) at the end of the furnace was used to block heat transfer (i.e., heat loss) during operation and to protect the quartz tubing. To investigate the continuous flow system, a tubular reactor capable of continuous feeding (i.e., 3 g min1 of used tire sample) was used. Fig. SI-1 shows schematic diagrams of the tubular reactor (TR), which was made of 1 in inner diameter (ID) stainless tubing. The rate of sample loading was controlled using two screw feeders. The required experimental temperatures were achieved using a split-hinged furnace. The split-hinged furnace consisted of three individually controlled furnace elements. All gas flow rates were set using a Brooks mass flow controller (5850 series E). A computer-aided control system by LabVIEW (National Instrument, USA) was employed. The condensable pyrolytic products were collected with a condenser, and the temperature of the condenser was maintained at 4  C with a chiller. 3. Results and discussion 3.1. Characterization of the thermal degradation of used tires in CO2 Representative thermograms, obtained from a series of TGA tests using a tire and the main constituents of a tire (i.e., SBR and IR), are shown in Fig. 1. The sample loading of the TGA was made as 50 mg for each run, and the TGA tests were conducted at a heating

Table 1 The results of ultimate and proximate analysis of tire samples used in this study. Ultimate analysis (% w/w) C 84.2

H 6.93

N 0.33

S 1.56

Proximate analysis (% w/w) O 1.54

Volatile 62.8

Fixed Carbon 31.2

Ash 4.24

Metal 1.74

307

Fig. 1. Representative thermograms of tires, SBR, and IR.

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rate of 10  C min1 over a whole temperature range of ambient to 700  C. Subsequent mass changes at temperatures lower than 130  C were not observed because of the negligibly low moisture content. Thus, the thermograms are not shown for temperatures lower than 130  C. The TGA tests were intentionally stopped at 700  C to mechanistically investigate the CO2 co-feed effect on tire pyrolysis because of the possibility of the Boudouard reaction at temperatures above 720  C (i.e., CðsÞ þ CO2 /2CO). Based on the calculation of the Gibbs free energy, such reaction can occur favorably at temperatures above 720  C (Kwon et al., 2013). This is validated in Fig. 1 as no mass change occurred at temperatures above 465  C. Approximately 40% of the residual mass were carbon in line with our previous work (Kwon and Castaldi, 2009). The onset temperature of the tire sample thermal degradation in Fig. 1 is lower than that of the main constituents of a tire (i.e., SBR and IR). However, the end temperatures of thermal degradation for the tire sample, SBR, and IR are the same. Accordingly, the thermal stability of a tire is inferior to that of the main constituents in tires (i.e., SBR and IR). This observation may reflect the effect of the various additives (e.g., reinforced fibers and accelerators) used in tire manufacturing stage. However, the early thermal degradation cannot be fully explained by various additives, as they generally constitute only 2e3% of a tire (in mass) (Antoniou and Zabaniotou, 2013; Williams, 2013; Zhou et al., 2014). This early thermal degradation could be attributed to unknown polymers used in a tire. Fig. 1 shows that the thermal degradation of a tire in both N2 and CO2 has a similar pattern associated with the onset temperature (~280  C) and thermal degradation rate expressed as a slope. This indicates that the interactions and reactions between CO2 and the tire sample surface should be negligible. If there were unknown interactions and reactions between CO2 and the tire sample during the TGA tests, different mass decay curves, with respect to temperature change, should be developed. However, a mass change is not observed in Fig. 1 that suggests any interactions and reactions between CO2 and the tire sample during pyrolysis are negligible. To investigate the CO2 co-feed effect on pyrolysis of tires, the effluent from the TGA unit was analyzed; the concentration profiles of the major chemical species (i.e., n-butane and isoprene) that evolved from the direct bond scission of the tire sample are depicted in Fig. 2. The concentration profiles in this work represent average values. Error bars are not drawn, as they generally ranged ±3.5%. Evolution of n-butane and isoprene from the direct bond cleavage of the SBR and IR backbones was observed, as validated

previously (Castaldi and Kwon, 2007; Castaldi et al., 2007; Kwon and Castaldi, 2008, 2009; Kwon et al., 2012). One interesting observation in Fig. 2 is the concentration of nbutane and isoprene in CO2 compared to N2. As shown in Fig. 2, the concentrations of n-butane and isoprene in CO2 were higher than those in N2. This observation suggests that the thermal degradation of a tire can be enhanced in the presence of CO2. Thus, the CO2 cofeed effect on pyrolysis of a tire would be effective via interactions and reactions with the chemical species that evolve from pyrolysis of a tire. The most interesting observation was that the concentration difference of isoprene in N2 and CO2 was much bigger than that of n-butane in N2 and CO2, as explained in our previous work (Kwon and Castaldi, 2008, 2009). In the work (Kwon and Castaldi, 2009), it was pointed out that a direct bond scission on the monomer followed by hydrogenation or dehydrogenation was observed in the pyrolysis of IR; thus, isoprene (2-methyl-1,3-butadiene), 2-methylbut-2-ene, and 2-methyl-1but-3-yne were observed together as intermediate forms. It was addressed further that the concentration of isoprene was not comparable to that of limonene because the pyrolysis of IR was dominated by the latter (Kwon and Castaldi, 2009). The origin of limonene from the thermal decomposition of IR is explained as follows. Both a-scission and b-scission by thermal cleavage of the IR backbone were considered in our previous work, but the major bond dissociation on the IR backbone was observed by means of bscission. This b-scission initiated two radicals. One of the radicals was converted rapidly into more free radicals, stimulating the generation of limonene. The enhanced generation of isoprene in the presence of CO2 cannot be explained by our previous work (Kwon and Castaldi, 2009). The enhanced generation of isoprene in the presence of CO2 is indicative of unknown reactions (or interactions) between CO2 and chemical species that evolve from the thermal degradation of IR. Thus, the enhanced generation of isoprene suggests that the aforementioned radical reactions are impeded in the presence of CO2 (i.e., blocking the cyclization to form limonene). Furthermore, CO2 seems to expedite the direct bond scission of IR. This thermal cracking behavior induced by CO2 could simultaneously block the gas phase reactions, which would provide favorable conditions for generating more gaseous pyrolytic products. For example, the chemical species formed by the gas phase addition reaction increased the molecular weight, which directly decreased the relative proportion of condensable pyrolytic products (i.e., pyrolytic oil) (Kwon and Castaldi, 2008; Kwon et al., 2012). These atypical effects of co-feeding CO2 could be a key factor in changing the pyrolytic products. 3.2. Pyrolysis of used tires with a tubular reactor (TR)

Fig. 2. Concentration profiles of n-butane and isoprene from pyrolysis of a tire sample with the supply of ultrapure N2 or CO2.

In Sec. 3.1, our discussion was confined to the general aspects regarding the pyrolysis of a tire. To gain a better insight into the pyrolysis of used tire, an in-depth analysis of our experimental results obtained using a tubular reactor (TR) under various temperature conditions is made with the consideration of the mass balance between the pyrolytic products as shown in Fig. 3. The yields of oil and char were measured by weight, and the rest of the products were considered the yield of gaseous pyrolytic products. In practice, the chilling temperature would affect the mass balance of pyrolytic products. Nevertheless, pyrolytic products were chilled at 7  C to measure the yield of gaseous pyrolytic products for the sake of convenience. Fig. 3 depicts the mass balance of the pyrolytic products generated from 10 g of tire sample. A cursory look at the mass balance indicates that the yield of the gaseous pyrolytic products are proportional to the pyrolytic temperature, while reducing the

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Fig. 3. Mass balance of the pyrolytic products of a tire at 450e700  C without cofeeding CO2 (supply of N2 gas only).

yield of pyrolytic oil and char with increasing thermal degradation. Char production (~40 wt.%), shown in Fig. 3, is consistent with the experimental results depicted in Fig. 1. Most of the gaseous products in Fig. 3 are C4-5 hydrocarbons (i.e., n-butane and isoprene) and aromatic compounds such as styrene. These chemical species are expected to evolve from direct bond scissions on the backbones of SBR and IR (Kwon and Castaldi, 2008). As shown in SI-1, the pyrolytic oil can be categorized as aliphatic, aromatic (i.e., BTX, substituted aromatic compounds), heterocompound, and asphalt in line with the mass balance depicted in Fig. 3. The hetero-compounds denoted as hetero-CMPD in Table SI1 represent aromatic compounds with a substitution, i.e., sulfur or nitrogen. The major chemical species was not listed in this work in that our previous work already listed the major chemical species from the thermal degradation of a tire (Kwon and Castaldi, 2009). The H/C molar ratio is inversely proportional to the experimental temperature during the pyrolysis process (Kwon and Castaldi, 2008). The ratio of H/C is indicative of the thermal decomposition of pyrolytic oil (i.e., dehydrogenation) (Castaldi et al., 2007; Kwon and Castaldi, 2008, 2009; Kwon et al., 2012). Thus, the relative proportion of pyrolytic oil in the mass balance is inversely proportional to the experimental temperature in Fig. 3. Furthermore, the observed H/C ratio can also be used to explain the origin of the aromatic compounds, as it generally increases when aromatic compounds form. As such, the enhanced formation of aromatic compounds is observed with the decrease in its ratio (Kwon and Castaldi, 2008, 2009). Thus, the generation of aromatic compounds is indicative of favorable conditions for the creation of PAHs (Castaldi et al., 2007; Kwon and Castaldi, 2008, 2012a, 2009; Kwon et al., 2012). Table SI-1 also shows that the weight percent of aromatic compounds significantly increases with the temperature. For example, 50.5% of aromatic compounds are quantified in pyrolytic oil at 550  C, which is similar to naphtha. Naphtha normally refers to a number of flammable mixtures of hydrocarbons (i.e., volatile aromatic liquid), and the petroleum industry utilizes naphtha as a fuel derived after catalytic processing. In the viewpoint of the fuel processing, it is economically desirable to reduce the proportion of aromatic compounds. Hence, it is critical to identify the formation of these aromatic compounds to modify the composition of pyrolytic oil. In our previous work on TGA unit (Kwon and Castaldi, 2008, 2009), it was confirmed that the main constituents (i.e., SBR and IR) gave off aromatic compounds by means of direct bond

309

Fig. 4. Mass composition of PAHs in pyrolytic oil.

scissions on each monomer. As discussed in Sec. 3.1, limonene evolved from the thermal decomposition of IR via proliferated free radical reactions. It was pointed further that SBR gave off styrene via a direct bond cleavage (Kwon and Castaldi, 2008). These aromatic compounds from the thermal degradation of SBR and IR led to favorable conditions for PAH formation through gas phase reactions (Kwon and Castaldi, 2008, 2009; Kwon et al., 2012). As depicted in Fig. 4, the quantity of PAHs in pyrolytic oil was substantial to considerably degrade the fuel quality. As a result, the modification of pyrolytic oil is highly contingent on impeding the creation of aromatic compounds and blocking the pathways of gas phase addition reactions. Unfortunately, based on the chemical structure of SBR, the formation of aromatic compounds derived from the direct bond scission of SBR, such as styrene, is not controllable (Kwon and Castaldi, 2008, 2012a,b). However, as discussed in Sec. 3.1, for the thermal decomposition of IR, source reduction through the control of aromatic compounds (via the free radical reaction) is possible. Thus, the amount of limonene in pyrolytic oil was carefully quantified as illustrated in Fig. 5. The amount of limonene evolved from the thermal degradation of IR in N2 begins to decrease when the temperature increases; the content of limonene at 700  C is nearly zero. This observation may be explained by two possible scenarios. For example, the generated limonene can be thermally cracked or developed into other chemical forms such as substituted aromatic compounds and PAHs by means of gas-phase addition reactions. However, considering

Fig. 5. Limonene content in pyrolytic oil at varying temperatures.

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Table 2 Comparison of light, medium, and heavy fractions of pyrolytic oil. Pyrolytic temperature ( C) Pyrolytic oil (N2) 650 Pyrolytic oil (CO2) 650

Light fraction (Tb < 200  C) (% w/w) Medium fraction (200  C < Tb < 350  C) (% w/w) Heavy fraction (Tb > 350  C) (% w/w) 23.5 62.5

the results shown in Table SI-1 and Figs. 3e4, the formation of the substituted aromatic compounds and/or PAHs should be more realistic. It is striking to find the insignificant changes in limonene levels with the co-feeding of CO2 in the temperature regime from 550 to 700  C. Furthermore, its concentration was lower with the supply of CO2 than that without supply (co-feeding N2 only) at 450  C, which is consistent with previous discussions (Sec. 3.1). CO2 not only impedes the free radical reaction (i.e., blocks cyclization to form limonene), but it also blocks the gas phase addition reaction. Thus, the co-feed of CO2 on pyrolysis of a tire will lead to modification of the pyrolytic products e increases in gaseous products but decreases in pyrolytic oil (7.3e17.2%). To learn more about this, the composition of pyrolytic oil was fractionated with respect to the boiling point (Tb). The mass balance established using the boiling point could be used as an index for evaluating the CO2 co-feed effect on the pyrolysis of a tire. If CO2 blocks the pathway of the gas-phase addition reaction and impedes the free radical reaction to form aromatic compounds (i.e., PAHs), the boiling point of pyrolytic oil should be lowered significantly. For example, the boiling point of C16-aliphatic compounds like hexadecane (i.e., Tb ¼ 287  C) is lower than that of C16-aromatic compounds like pyrene (i.e., Tb ¼ 404  C). Thus, as shown in Table 2, a significant amount of aliphatic compounds is likely to be produced with the supply of CO2 because of the identified CO2 co-feed effect on pyrolysis in Sec. 3.1 and 3.2. To simulate the actual pyrolysis conditions of a tire, our experiment was conducted using a continuous flow system with the sample loading of 3 g min1 and the CO2 flow rate of 2 L min1 (Fig. SI-1). As shown in Fig. 6, the CO2 effect on tire pyrolysis was represented by the pyrolytic product distribution at 500 and 600  C.

4. Conclusions The use of CO2 as such reaction medium impeded the free

Fig. 6. Mass balance of pyrolytic product formed via a continuous flow system.

36.3 23.2

40.2 14.3

radical reaction leading to cyclization. Moreover, as CO2 blocked the pathway of the gas-phase addition reaction, it contributed greatly to the modification of the pyrolytic products. The effect of cofeeding CO2 on pyrolysis of a tire thus led to the modification of the pyrolytic products so that the production of gaseous compounds increased, while decreasing the formation of pyrolytic oil and PAH. The distinctive effect of the CO2 addition is hence recognized very effectively in various forms of signals in the endproduct of pyrolysis, e.g., H/C ratio, limonene content, and mitigation patterns of VOC and PAH. In the near future, the optimal conditions for utilizing CO2 as the pyrolysis reaction medium should be established as an environmentally benign and energy efficient process. Acknowledgments This work was supported by a National Research Foundation of Korea (NRF) Grant funded by the Korean Government (MSIP) (No. 2914RA1A004893). The third author acknowledges partial support made by a grant from the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (MEST) (No. 2009-0093848). Appendix A. Supplementary data Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.jenvman.2015.06.033. References Antoniou, N., Zabaniotou, A., 2013. Features of an efficient and environmentally attractive used tyres pyrolysis with energy and material recovery. Renew. Sust. Energ. Rev. 539e558. Betancur, M., Martinez, J.D., Murillo, R.N., 2009. Production of activated carbon by waste tire thermochemical degradation with CO2. J. Hazard. Mater. 882e887. Castaldi, M.J., Kwon, E., 2007. An investigation into the mechanisms for styrenebutadiene copolymer (SBR) conversion in combustion and gasification environments. Int. J. Green. Energ. 45e64. Castaldi, M.J., Kwon, E., Weiss, B., 2007. Beneficial use of waste tires: an integrated gasification and combustion process design via thermo-gravimetric analysis (TGA) of styrene-butadiene rubber (SBR) and poly-isoprene (IR). Environ. Eng. Sci. 1160e1178. Chen, K.S., Yeh, R.Z., Chang, Y.R., 1997. Kinetics of thermal decomposition of styrenebutadiene rubber at low heating rates in nitrogen and oxygen. Combust. Flame 408e418. Chen, S.-J., Su, H.-B., Chang, J.-E., Lee, W.-J., Huang, K.-L., Hsieh, L.-T., Huang, Y.-C., Lin, W.-Y., Lin, C.-C., 2007. Emissions of polycyclic aromatic hydrocarbons (PAHs) from the pyrolysis of scrap tires. Atmos. Environ. 1209e1220. Chien, Y.-C., Liang, C.-P., Shih, P.-H., 2009. Emission of polycyclic aromatic hydrocarbons from the pyrolysis of liquid crystal wastes. J. Hazard. Mater. 910e914. Choi, G.-G., Jung, S.-H., Oh, S.-J., Kim, J.-S., 2014. Total utilization of waste tire rubber through pyrolysis to obtain oils and CO2 activation of pyrolysis char. Fuel Proces. Technol. 57e64. Collins, K.J., Jensen, A.C., Albert, S., 1995. A review of waste tire utilization in the marine environment. Chem. Ecol. 205e216. Conesa, J.A., Martin-Gullon, I., Font, R., Jauhiainen, J., 2004. Complete study of the pyrolysis and gasification of scrap tires in a pilot plant reactor. Environ. Sci. Technol. 3189e3194. Gawel, I., Slusarski, L., 1999. Use of recycled tire rubber for modification of asphalt. Progr. Rubber Plast. Recycl. Technol. 235e248. Giere, R., LaFree, S.T., Carleton, L.E., Tishmack, J.K., 2004. Environmental impact of energy recovery from waste tyres. Geol. Soc. Spec. Publ. 475e498. Giere, R., Smith, K., Blackford, M., 2006. Chemical composition of fuels and emissions from a coalþtire combustion experiment in a power station. Fuel 85, 2278e2285.

E.E. Kwon et al. / Journal of Environmental Management 160 (2015) 306e311 Gupta, V.K., Nayak, A., Agarwal, S., Tyagi, I., 2014. Potential of activated carbon from waste rubber tire for the adsorption of phenolics: effect of pre-treatment conditions. J. Colloid Interface Sci. 420e430. Hu, H., Fang, Y., Liu, H., Yu, R., Luo, G., Liu, W., Li, A., Yao, H., 2014. The fate of sulfur during rapid pyrolysis of scrap tires. Chemosphere 97, 102e107. Hwang, I.-H., Kobayashi, J., Kawamoto, K., 2014. Characterization of products obtained from pyrolysis and steam gasification of wood waste, RDF, and RPF. Waste Manage. 402e410. Ji, R., Yu, K., Lou, L.-L., Zhang, C., Han, Y., Pan, S., Liu, S., 2012. Chiral Mn(III) salen complexes immobilized directly on pyrolytic waste tire char for asymmetric epoxidation of unfunctionalized olefins. Inorg. Chem. Commun. 65e69. Kim, J.R., Lee, J.S., Kim, S.D., 1994. Combustion characteristics of shredded waste tires in a fluidized bed combustor. Energy 19, 845e854. Kwon, E., Castaldi, M.J., 2008. Investigation of mechanisms of polycyclic aromatic hydrocarbons (PAHs) initiated from the thermal degradation of styrene butadiene rubber (SBR) in N2 atmosphere. Environ. Sci. Technol. 2175e2180. Kwon, E., Castaldi, M.J., 2009. Fundamental understanding of the thermal degradation mechanisms of waste tires and their air pollutant generation in a N2 atmosphere. Environ. Sci. Technol. 5996e6002. Kwon, E.E., Castaldi, M.J., 2012a. Mechanistic understanding of polycyclic aromatic hydrocarbons (PAHs) from the thermal degradation of tires under various oxygen concentration atmospheres. Environ. Sci. Technol. 12921e12926. Kwon, E.E., Castaldi, M.J., 2012b. Urban energy mining from municipal solid waste (MSW) via the enhanced thermo-chemical process by carbon dioxide (CO2) as a reaction medium. Bioresour. Technol. 23e29. Kwon, E.E., Jeon, E.-C., Castaldi, M.J., Jeon, Y.J., 2013. Effect of carbon dioxide on the thermal degradation of lignocellulosic biomass. Environ. Sci. Technol. 10541e10547. Kwon, E.E., Yi, H., Castaldi, M.J., 2012. Utilizing carbon dioxide as a reaction medium to mitigate production of polycyclic aromatic hydrocarbons from the thermal decomposition of styrene butadiene rubber. Environ. Sci. Technol. 10752e10757.

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Marinov, N.M., Pitz, W.J., Westbrook, C.K., Vincitore, A.M., Castaldi, M.J., Senkan, S.M., Melius, C.F., 1998. Aromatic and polycyclic aromatic hydrocarbon formation in a laminar premixed n-butane flame. Combust. Flame 192e213. Mastral, A.M., Callen, M.S., Garcia, T., 2000. Fluidized bed combustion (FBC) of fossil and nonfossil fuels. Comp. Study. Energy Fuels 275e281. Mastral, A.M., Callen, M.S., Murillo, R., GarcIa, T., 1999. Combustion of high calorific value waste material: organic atmospheric pollution. Environ. Sci. Technol. 4155e4158. Mastral, A.M., Murillo, R., Garcia, T., Navarro, M.V., Callen, M.S., Lopez, J.M., 2002. Study of the viability of the process for hydrogen recovery from old tyre oils. Fuel Process. Technol. 185e199. Piatkowski, N., Steinfeld, A., 2010. Reaction kinetics of the combined pyrolysis and steam-gasification of carbonaceous waste materials. Fuel 1133e1140. Piatkowski, N., Wieckert, C., Steinfeld, A., 2009. Experimental investigation of a packed-bed solar reactor for the steam-gasification of carbonaceous feedstocks. Fuel Process. Technol. 360e366. Stanciulescu, M., Ikura, M., 2007. Limonene ethers from tire pyrolysis oil: part 2: continuous flow experiments. J. Anal. Appl. Pyrolysis 76e84. Tang, Y., Curtis, C.W., 1996. Thermal and catalytic coprocessing of waste tires with coal. Fuel Process. Technol. 195e215. Undri, A., Frediani, M., Rosi, L., Frediani, P., 2014. Reverse polymerization of waste polystyrene through microwave assisted pyrolysis. J. Anal. Appl. Pyrolysis 35e42. Williams, P.T., 2013. Pyrolysis of waste tyres: a review. Waste Manage. 1714e1728. Xiao, G., Ni, M.-J., Chi, Y., Cen, K.-F., 2008. Low-temperature gasification of waste tire in a fluidized bed. Energy Convers. Manage. 2078e2082. Zabaniotou, A.A., Stavropoulos, G., 2003. Pyrolysis of used automobile tires and residual char utilization. J. Anal. Appl. Pyrolysis 711e722. Zhou, H., Meng, A., Long, Y., Li, Q., Zhang, Y., 2014. An overview of characteristics of municipal solid waste fuel in China: physical, chemical composition and heating value. Renew. Sust. Energ. Rev. 107e122.