Characterization of the Liquid Phase Obtained by Copyrolysis of

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Characterization of the Liquid Phase Obtained by Copyrolysis of Mustafa Kemal Pas¸ a (M.K.P.) Lignite (Turkey) with Low Density Polyethylene Ali Sınagˇ,* Melike Sungur, Mustafa Gu¨llu¨, and Muammer Canel Department of Chemistry, Science Faculty, Ankara UniVersity, 06100 Bes¸ eVler-Ankara, Turkey ReceiVed May 10, 2006. ReVised Manuscript ReceiVed July 8, 2006

This study describes the detailed hydrocarbon type characterization of the tar (liquid phase) obtained by copyrolysis of Mustafa Kemal Pas¸ a (M.K.P.) lignite (Turkey) and low density polyethylene (LDPE) and by pyrolysis of coal and LDPE individually. Various spectroscopic techniques [gas chromatography-mass spectroscopy (GC-MS), nuclear magnetic resonance spectroscopy (1H NMR), Fourier transform infrared spectroscopy (FTIR), and gel permeation chromatography (GPC)] are used for characterization, and the effect of the experimental conditions [temperature, lignite:low density polyethylene (LDPE) ratio, and catalyst] on the hydrocarbon distributions is discussed. The results show that the tars obtained by copyrolysis have similar properties with commercial gasoline (especially in the presence of Red mud). Red mud and bentonite used as catalysts make a positive effect on the production of olefins instead aromatics. Polyethylene acts as a hydrogenation medium for the coal product as revealed by FTIR results.

Introduction The disposal of waste plastics is an important environmental problem in developed countries. Most of these materials consist of several polymer types, which cannot be easily converted to hydrocarbons or any useful materials under normal conditions. Copyrolysis of coals with polymers is an attractive method to obtain valuable liquid and gas products. It was found that yields of tar or gas from copyrolysis are dramatically higher than those obtained by pyrolysis of coal alone.1-3 The degradation mechanism of coal and polymer mixtures during the copyrolysis process, such as radicalic, ionic, etc., may be responsible for this variation. The hydrocarbon distributions are also affected by this mechanism. To investigate the effect of the experimental conditions on the amount of generated products in detail, a characterization of the pyrolysis liquid should be performed. In earlier works, characterization of such pyrolysis liquids was performed by using various spectroscopic techniques.4-6 Marin et al.7 characterized the liquid phase obtained by copyrolysis of wood biomass and synthetic polymers mixtures by gas chromatography-mass spectrometry and observed the presence of olefins, paraffins, and some aromatics (benzene, toluene, and * Corresponding author. Tel.: +90 312 212 67 20/1022. Fax: +90 312 223 23 95. E-mail: [email protected]. (1) Straka, P.; Buchtele, J.; Kovarova, J. Co-pyrolysis of waste polymers with coal. Macromol. Symp. 1998, 135, 19-23. (2) Yanik, J.; Uddin, A.; Ikeuchi, K.; Sakata, Y. The catalytic effect of Red Mud on the degradation of poly (vinyl chloride) containing polymer mixture into fuel oil. Polym. Degrad. Stab. 2001, 73, 335-346. (3) Taghiei, M. M.; Feng, Z.; Huggins, F. E.; Huffman, G. P. Coliquefaction of Waste Plastics with Coal. Energy Fuels 1994, 8, 1228-1232. (4) Domınguez, A.; Blanco, C. G.; Barriocanal, C.; Alvarez, R.; Diez, M. A. Gas chromatographic study of the volatile products from co-pyrolysis of coal and polyethylene wastes. J. Chromatogr., A 2001, 918, 135-144. (5) Sharypov, V. I.; Beregovtsova, N. G.; Kuznetsov, B. N.; Membrado, L.; Cebolla, V. L.; Marin, N.; Weber, J. V. Co-pyrolysis of wood biomass and synthetic polymers mixtures. Part III: Characterisation of heavy products. J. Anal. Appl. Pyrolysis 2003, 67, 325-340. (6) Ofosu-Asante, K.; Stock, L. M.; Zabransky, R. F. Pathways for the decomposition of linear paraffinic materials during coal pyrolysis. Fuel 1988, 68, 567.

xylene) in this fraction. They concluded that origin of the polymer plays the most important role in the chemical composition of this fraction and polymer chain scission leads to the production of the light liquids. Songip et al.8 investigated the effects of experimental conditions and the properties of the catalyst on the product yields and the quality of the gasoline fraction. They detected a large amount of gasoline with a high content of isoparaffins obtained by the catalytic cracking of heavy oil over a REY zeolite catalyst. Lazaro et al.9 found that pyrolysis of a lubricating oil waste in the presence or absence of coal yields important quantities of valuable products such as C1-C3 alkanes, C2-C4 olefins, and BTX. They concluded that Samca coal tar constitutes large polynuclear aromatic ring systems as well as heterocyclic structures with alkyl or heteroatom substituents. The tar from the coal/oil mixture is much more similar to the tar from oil than to the tar from coal, reflecting the synergy in the copyrolysis reaction. The aim of the present work is to study the characterization of the liquids obtained by pyrolysis of coal/polyethylene mixtures under different experimental conditions by various spectroscopic techniques (FTIR, GC-MS, GPC and 1H NMR) and to optimize the experimental conditions studied in order to utilize both lignite and polyethylene waste from the valuable chemicals produced of the view. Experimental Section M.K.P. lignite obtained from the Mustafa Kemal Pas¸ a region of Bursa, Turkey, is first analyzed on a LECO 932 CHNS elemental analyzer using coal sample sizes of approximately 1.5 mg for (7) Marin, N.; Collura, S.; Sharypov, V. I.; Beregovtsova, N. G.; Baryshnikov, S. V.; Kutnetzov, B. N.; Cebolla, V.; Weber, J. V. Copyrolysis of wood biomass and synthetic polymers mixtures. Part II: Characterisation of the liquid phases. J. Anal. Appl. Pyrolysis 2002, 65, 41-55. (8) Songip, A. R.; Masuda, T.; Kuwahara, H.; Hashimoto, K. Production of High-Quality Gasoline by Catalytic Cracking over Rare-Earth Metal Exchanged Y-Type Zeolites of Heavy Oil from Waste Plastics. Energy Fuels 1994, 8, 136-140. (9) Lazaro, M. J.; Moliner, R.; Suelves, I.; Herod, A. A.; Kandiyoti, R. Characterisation of tars from the co-pyrolysis of waste lubricating oils with coal. Fuel 2001, 80, 179-194.

10.1021/ef060213v CCC: $33.50 © 2006 American Chemical Society Published on Web 08/05/2006

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Table 1. Ultimate Analysis of the M.K.P. Lignite (d.a.f% wt) C H N O S

69.62 4.87 1.83 19.30 4.38

Table 2. Compositions of Catalysts (wt %)a

Na2O MgO Al2O3 SiO2 P2O6 K2O a

Red mud

bentonite10

7.13 0.40 17.27 17.10 1.15 0.29

0.43 1.69 14.40 72.08 udb 1.05

CaO TiO2 Cr2O3 MnO Fe2O3

Red mud

bentonite10

4.54 4.81 2.17 7.42 37.72

2.15 0.08 ud ud 0.78

The surface area of Red mud is 16 m2‚g-1. b Undetermined.

Figure 1. Experimental setup for pyrolysis.

ultimate analysis. The results are given in Table 1. Low density polyethylene (LDPE) is supplied as a powder from the O ¨ zugˇurAkc¸ im Plastic company (I˙ zmir, Turkey). The catalysts used are Red mud and bentonite. The properties of the catalysts are given in Table 2. The Red mud is supplied by Seydisehir Aluminum Company, Turkey. It is filtered and then dried at 110 °C. It is analyzed by classical chemical analysis. The chemical composition of Red mud is shown in Table 2.2 A white calcium bentonite (CaB) from the Ku¨tahya region, Turkey, is used in the experiments. Bentonite is activated by heating for 6 h at 97 °C in a H2SO4 solution (40 wt %) according to the method proposed by Sarıkaya et al.10 The specific surface area and specific pore volume values of bentonite are 134 m2‚g-1 and 0.295 cm3‚g-1, respectively. Lignite and LDPE are mixed well in 50 % (w/w) (5 g of lignite and 5 g of LDPE) which is equal to the lignite/LDPE ratio of 1:1. Apart from coal/LDPE mixtures, coal (LDPE of 0 % w/w) and LDPE (100 % w/w) were also subjected to pyrolysis at temperatures between 4000 and 7000 °C in the system given in Figure 1. In each catalytic run, 50 % (w/w) (4.9 g of lignite and 4.9 g of LDPE) of LDPE and coal are mixed with 0.2 g of catalyst and, then, charged into the reactor. After the reactor is inserted into the electrically heated furnace, the air of the reactor is purged with a nitrogen flow of 30 mL‚min-1. The reactor is heated from room temperature to a desired temperature, depending on the reaction temperature, at a heating rate of 10 °C‚min-1 and held until no further liquid is produced. The outlet of the reactor is connected to a round-bottomed flask with a reflux condenser where condensation of pyrolysate occurred. The reaction mixture is cooled to about 0 °C with an ice-salt bath. The reaction products are classified into three groups: gases, liquid hydrocarbons (tar), and residual coke. The yield of tar is defined as the amount of liquid collected in the round-bottomed flask, and the yield of residual coke, as the char remaining inside the reactor after the experiment. The gas amount is measured by a gas meter connected to the end of the reflux condenser. Collected tar samples are subjected to the spectroscopic analysis described below. (10) Sarıkaya, Y.; Onal, M.; Baran, B.; Alemdaroglu, T. The effect of acid activation on some physicochemical properties of a bentonite. Turk. J. Chem. 2002, 26, 409-416.

Product Analysis. The instruments used during the analysis of the samples and the conditions are given below. Gas Chromatography to Mass Spectroscopy (GC-MS). GCMS analysis of the samples is conducted by an AGILENT 6890 GC System 5973 MSD. GC-MS conditions are as follows: (column) HP1 (50 m × 0.32 mm × 0.52 µm); (carier gas) He; (flow rate of He) 0.7 mL‚min-1; (temperature program of oven) initial hold at 50 °C for 15 min, ramp to 300 °C at 5 °C‚min-1, and hold for 17 min. The compounds found in tar are identified by comparison of their spectra with that in the NIST library of the GC-MS system as their peak area (%) in the total chromatogram. Fourier Transform Infrared Spectroscopy. IR spectra of the samples as KBR disks of the samples are obtained by a MATTSON 1000 Model FTIR spectrophotometer. 1H NMR Spectroscopy. 1H NMR spectra of the samples are recorded by Bruker Avance DPX-400. 1H NMR is performed to estimate the hydrocarbon types and to provide an indication of product quality. From the NMR spectra, the hydrocarbon types including aromatics, paraffins, and olefins, as well as an isoparaffin index, the H/C ratio, and a research octane number (RON), were estimated using literature correlations developed by Myers et al.16 The hydrocarbon types (aromatics, paraffins, and olefins, as well as an isoparaffin index, H/C atomic ratio, and research octane numbers) are detected according to the method described by Myers et al.16 and Joo and Guin17(see Table 3). Aromatics, vol % ) (A + C/3)0.97 × 102 (1) (A + C/3)0.97 + (D - 2B + E/2 + F/3)1.02 + 3.33B Paraffins, vol % ) (D - 2B + E/2 + F/3)1.02 × 102 (2) (A + C/3)0.97 + (D - 2B + E/2 + F/3)1.02 + 3.33B Olefins, vol % ) 3.33B × 102 (3) (A + C/3)0.97 + (D - 2B + E/2 + F/3)1.02 + 3.33B H/C )

A+B+C+D+E+F (4) (A + C/3)1.28 + (D - 2B + E/2 + F/3)1.02 + 3.42B Isoparaffin index )

CH3 F/3 ) CH2 E/2

(5)

Research octane number (RON) ) 80.2 + 8.9 × isoparaffin index + 0.107 × aromatics (vol %). Gel Permeation Chromatography (GPC). GPC is a high performance liquid chromatography technique for the separation of components based on their molecular size in solution. Also referred to as size-exclusion chromatography (SEC), the center’s capability extends to both organic-soluble and water-soluble systems. GPC separates the sample into its discrete components and determines the molecular weight distribution of the sample. Coupled with a light scattering detector, the GPC provides for the (11) Zhou, Q.; Wang, Y.; Tang, C.; Zhang, Y. Modifications of ZSM-5 zeolites and their applications in catalytic degradation of LDPE. Polym. Degrad. Stab. 2003, 80, 23-30. (12) Ishihara, Y.; Nanbu, H.; Saido, K.; Ikemura, T.; Takesue, T. Mechanism for gas formation in polyethylene catalytic decomposition. Polymer 1992, 33, 3482-3486. (13) Pasadakis, N.; Gaganis, V.; Foteinopoulos, C. Octane number prediction for gasoline blends. Fuel Process. Technol. 2006, 87, 505-509. (14) Nikolaou, N.; Papadopoulos, C. E.; Gaglias, I. A.; Pitarakis, K. G. A new nonlinear calculation method of isomerisation gasoline research octane number based on gas chromatographic data. Fuel 2004, 83, 517523. (15) Meusinger, R.; Moros, R. Determination of octane numbers of gasoline compounds from their chemical structure by 13C NMR spectroscopy and neural networks. Fuel 2001, 80, 613-621.

Characterization of the Copyrolysis Liquid Phase

Figure 2. Temperature influence on the yields at the material ratio of 1:1.

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Figure 3. Effect of material ratio on alkanes at 600 °C.

Table 3. Spectral NMR Regions type of proton A B C D E F

ring armomatics olefin R-methyl methine (paraffins) methylene (paraffins) methyl (paraffins)

chemical shift (ppm) 6.6-8.0 4.5-6.0 2.0-3.0 1.5-2.0 1.0-1.5 0.6-1.0

online determination of absolute molar mass, size, and conformation without the need for calibration standards. The molecular weight distribution of the pyrolytic oil samples is measured by Agilent 1100 GPC/SEC/RID instruments using Zorbax columns (PSM 60 5 × 102-104). The samples are dissolved in tetrahydrofurane (THF). The temperature of the column oven is 30 °C, and a volume rate of 1 mL‚min-1 is injected of each sample. THF is used as eluent with a flow rate of 1 mL‚min-1. A refractive index detector (RID) is used as the detector.

Results and Discussion It is clear from Figure 2 that an increase in temperature leads to a decrease in the residual char yields. It means that the conversion degree of the lignite/polyethylene mixtures into the yields (product mixture) is increased. A distinct increase is observed in the tar yields up to 600 °C, and then, the yield of tar decreases. The reason for this variation is related to the enhanced radical stabilization and the suppression of crosslinking structures occurring until 600 °C. Because the polyethylene acts as a hydrogen donor media during the copyrolysis, free radicals generated under the copyrolysis conditions are stabilized by the hydrogen provided by the polyethylene. As a result of this, tar yields are increased until 600 °C. This is the reason that only the pyrolysis liquids collected at 600 °C are analyzed for the characterization. On the other hand, gas generation reaches its maximum value at a temperature of 700 °C because of the secondary decomposition reactions of the liquid fractions to the gases and the stabilization of radicals by hydrogen released from the polyethylene. GC-MS Analysis Results. Figures 3 and 4 show the effect of the copyrolysis process on the alkane and alkane fraction. (16) Myers, M. E.; Stollstelmer, J.; Wims, A. M. Determination of Hydrocarbon-Type Distribution and Hydrogen/Carbon Ratio of Gasolines by Nuclear Magnetic Resonance Spectrometry. Anal. Chem. 1975, 47, 2010-2015. (17) Joo, H. S.; Guin, J. A. Continuous upgrading of a plastics pyrolysis liquid to an environmentally favorable gasoline range product. Fuel Process. Technol. 1998, 57, 25-40.

Figure 4. Effect of material ratio on alkenes at 600 °C.

According to these figures, it is clear that copyrolysis of coal and LDPE leads to an increase in both alkane and alkene fractions comparing the results obtained from individual coal pyrolysis. As proposed by Dominguez et al.,4 the hydrogen from the coal stabilizes the free radicals produced from the polyalkenes and amount of n-alkanes in the tar is increased. Stabilization of these radicals is enhanced by progressing the pyrolysis, and n-alkenes are generated by β-scission. The peak area (%) of alkenes in the total chromatogram is considerably higher than that of alkanes. It should not be ruled out that the percentage area obtained from GC-MS analysis may not be directly correlated to the actual alkene ratios. A quantification procedure for those products (alkanes, alkenes, and aromatics) is found to be highly difficult due to the absence of standards for every compound. In future work, target products oriented pyrolysis experiments are planned, and then, quantitative analysis will become possible for desired compounds. The H1 NMR results analyzed reveal a more realistic approach to this problem. The copyrolysis procedure affects the formation of toluene, dimethylbenzene, and xylene positively, as seen in Figure 5. Other aromatics generated under the experimental conditions are originated mainly from coal itself. Dehydrogenation, isomerization, dehydrocyclization reactions lead to the formation of aromatic species such as toluene, xylene, styrene, etc. 1H NMR Analysis Results. Aromatics, olefins, and paraffins content of the oils obtained under different conditions and

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Figure 5. Effect of material ratio on aromatics at 600 °C.

Figure 6. Properties of the tars obtained from pyrolysis of the samples at 600 °C according to the 1H NMR results: (1) tar from coal pyrolysis; (2) tar from LDPE pyrolysis; (3) tar from coal:LDPE (1:1) pyrolysis; (4) tar from coal:LDPE:Red mud pyrolysis; (5) tar from coal:LDPE: bentonite pyrolysis.

calculated from eqs 1-3 are given in Figure 6. 1H NMR results indicated that the aromaticity of the oil obtained by copyrolysis of the coal/LDPE mixtures with and without catalyst is very low compared to that of the oil obtained by pyrolysis of the coal alone. The liquid products obtained from the pyrolysis of coal, LDPE, and coal/LDPE mixtures with (Red mud and bentonite) and without catalyst are likely to have a high volumetric energy content because of their relatively high (H/ C) atomic ratio, as seen in Table 4. Table 4 gives the H/C ratio, isoparaffin index number, and research octane number calculated by the equations given above. The extent of saturation as shown by the H/C ratio is a useful indicator of the aromatic character of the product. Saturation of the aromatic components leads to an increase in the paraffin content of the oils, the H/C ratios of which are increased. The oils from copyrolysis of LDPE and coal have mainly aliphatic character, as seen in Figure 6. Further comparison of the H/C ratio with conventional fuels indicates that the H/C ratios of the oil obtained by copyrolysis in this study is around that of commercial petroleum products, as seen in Table 4.

The H/C ratio of oil from copyrolysis of coal and LDPE with Red mud is the highest of the all results. This higher ratio offers lower greenhouse gas emissions and improved fuel properties from the environmental point of view. Clays whose basic clay mineral is montmorillonite or smectite are called bentonites. The chemical and mineralogical structures of the bentonites, which are activated by heating in strong acids, undergo considerable transformations. Acid activated bentonites can also be used as a powder catalyst in the gasification, liquefaction, pyrolysis, and desulfurization processes of solid fuels such as lignites and bituminous coals.10 The isoparaffin index is the proportion of branched to normal paraffins. Noticeably, the isoparaffin index of all the obtained oils except the oil from copyrolysis with Red mud is almost 7 times less than that of the experiments conducted with Red mud. This situation shows the high content of isoparaffins, meaning the improved quality of the liquids.11,12 In the presence of Red mud, a higher isoparaffin index leads to the higher RON. Less isoparaffins are produced during copyrolysis conditions and pyrolysis of polyethylene alone. Thus, the isoparaffin index and RON values are lower compared to those of the oil obtained by copyrolysis of coal and polymer with Red mud. The antiknock property of a gasoline is generally expressed as its octane number.13-15 This number is the percentage by volume of isooctane (assigned 100 octane) in a blend with n-heptane (assigned zero octane) that matches the knock characteristic of a gasoline sample combusted in a standard engine run under controlled conditions as defined by the American Society for Testing and Materials (ASTM). Octane numbers quoted in the literature usually refer to RON, unless stated otherwise. Another interesting property of this oil is the RON number which is in the range of normal gasoline requirements (between 85 and 98). The RON (research octane number) is an indicator of petrol’s antiknock performance at lower engine speeds and under typical acceleration conditions. Petrol is commonly referred to by its RONse.g., 91 regular or 96 premium have RONs of 91 and 96, respectively. The relatively low aromatics content and acceptable RON of the oils obtained in this study show a beneficial liquid from an environmental viewpoint during the copyrolysis of lignite and LDPE. A gasoline range distillate product from the sequential hydrotreating/hydrocracking of the plastics liquid gave an aromatics content of 13.8%, 82.5% of paraffins, 3.7% of olefins, 1.80 of H/C, isoparaffin index of 0.84, 89.2 of RON, and N < 0.3 ppm, also suggesting favorable properties for transportation fuels. FTIR Analysis Results. Fourier transform infrared spectroscopy (FTIR) is a suitable technique to investigate compositional and structural changes of pyrolysis oils. In addition, several structural alterations or the formation of new entities can also be recognized from their corresponding effect on the FTIR spectrum. Because of the chemical complexity of pyrolysis oil samples, it is difficult to obtain quantitative results from FTIR spectra. The FTIR spectras of the tars of various samples during their pyrolysis are given in Figure 7. Characteristic vibrational modes

Table 4. Properties of Tar According to the 1H NMR Results tar from the pyrolysis of the given species H/C isoparaffin index RON

lignite

LDPE

lignite:LDPE (1:1)

lignite: LDPE:red mud

lignite: LDPE: bentonite

commercial gasoline

1.62 1 92.85

1.88 0.1 81.3

1.75 0.1 81

2.15 0.77 88.3

1.8 0.10 81.2

1.85 0.77 87-92

Characterization of the Copyrolysis Liquid Phase

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Figure 7. FTIR results of the tars obtained from pyrolysis of lignite, LDPE, lignite:LDPE (1:1), and lignite:LDPE:Red mud (1:1) at 600 °C.

of aliphatics are observed at 2850-2980 cm-1 (C-H stretching, aliphatic) and at 1350-1470 cm-1 (the C-H and deformation vibrations). The tars obtained by pyrolysis of lignite:LDPE:Red mud and by pyrolysis of LDPE comprise mainly aliphatic fractions as also observed by 1H NMR results which represent the aliphatic (parafinnic) characters of the tars. The broad peak around at 3300 cm-1 in the case of tar from lignite pyrolysis can be attibuted to the O-H stretching vibrations indicating the presence of phenols and alcohols. This peak is diminished in the presence of LDPE. The possible reason for this decrease might be related to the hydrogen content of the polyethylene. This means that polyethylene acts as a hydrogenation medium for the coal product under the experimental conditions studied, yielding products such as cyclohexanol, cyclohexanone, etc. as a result of the ring hydrogenation of phenol as shown in our previous study.18 The peaks at 720-730 cm-1 show -(CH2)n- of group. In the case of liquids from lignite:LDPE:Red mud pyrolysis, the absorption band at 1730 cm-1 (carboxyl or aldehyde groups) is observed. For all liquids from the copyrolysis process, the absorption band at around 1600 cm-1 (aromatic and conjugate olefinic) is observed. The peak at 1642 cm-1 is detected in the case of copyrolysis with and without catalyst. This peak can be attributed to the olefinic CdC stretching vibrations. The intensity of this peak shows the presence of the olefins which are also found in 1H NMR investigations. Gel Permeation Chromatography (GPC) Analysis Results. Figure 8 shows the GPC chromatograms of the oils obtained by pyrolysis of the samples. The peak width of the chromatogram of the oil from M.K.P. lignite’s pyrolysis is lower than the peak widths of the chromatogram of the oils from LDPE and LDPE:lignite pyrolysis. It can also be observed that the curve of oils from lignite is displaced to the right, showing longer elution times than the other two and indicating that oil obtained from lignite pyrolysis is formed by smaller molecules (18) Sınagˇ, A.; Sungur, M.; Canel, M. Effect of experimental conditions on the yields during the copyrolysis of Mustafa Kemal Pas¸ a (M.K.P.) lignite (Turkey) with low-density polyethylene. Energy Fuels 2006, 20 (4), 16091613.

Figure 8. GPC chromatogram of the oils obtained by pyrolysis at 600 °C. Table 5. Various Molecular Weight Numbers of the Samples oil from the pyrolysis of the given species M h w (g‚mol-1) M h n (g‚mol-1) D)M h w/M hn M h v (g‚mol-1)

MKP lignite

LDPE

LDPE:MKP

270 145 1.86 270

277 182 1.52 278

283 165 1.72 283

than the oils from LDPE and lignite:LDPE pyrolysis. This situation is also remarkable in Table 5 which shows the molecular weight numbers of the samples. Figure 9 shows the molecular weight distribution of the oil samples. Oil samples obtained by pyrolysis of LDPE and lignite: LDPE show the similarities regarding the molecular weight distibution, as can also be seen in Table 5. These similarities also comply with the 1H NMR results indicating that both the oils from LDPE and LDPE:lignite pyrolysis have mainly the parafinnic compounds and that these oils have also approximately the same amount of olefinic and aromatic structures. Various molecular weight numbers are calculated from the experimental data. The mass average (Mw) and the number average (Mn) of the molecular weight of oils obtained by

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Figure 9. GPC results of the oils obtained by pyrolysis of lignite, LDPE, and lignite:LDPE (1:1) at 600 °C.

pyrolysis of lignite, LDPE alone, and a mixture of LDPE:lignite are shown in Table 5. In addition, the table presents the ratio of Mw and Mn presented as dispersity (D), which is a measure of the homogeneity of the fragments, and the viscosity average molar mass (Mv) (in grams per mole). The oil obtained by pyrolysis of M.K.P. lignite exhibits the lowest weight average molecular weight distribution (270), while the oil obtained by pyrolysis of M.K.P. lignite:LDPE shows the highest average molecular weight distribution (283). D, the polydispersity index (Mw/Mn), which measures the spread of the molecular weight distribution and accounts for the homogeneity and heterogeneity of the samples, is nearly equal for the oils from M.K.P. lignite and lignite:LDPE pyrolysis, indicating that the nature of the constituting molecules is almost identical, as specified above. The number average molecular weight of the oil from LDPE is the highest (182), while that of the oil from lignite is the lowest (145). The number average molecular weight of the oil from the mixture’s pyrolysis is 165. This term is very sensitive to the total number of molecules in solution. Because the oil from the pyrolysis of lignite has the lowest weight and number molecular mass, it can be said that this oil has more potentially volatile material compared to the others. The viscosity average molar mass is related inversely to the molecular density of the oils. The viscosity average molar masses of the oils are close to each other, representing the finding that the densities of the oils are approximately the same. Conclusions (i) The spectroscopic data of the tars obtained by copyrolysis of lignite:LDPE with catalysts (Red mud and bentonite) such

as the H/C ratios varied between 1.8 and 2.15. The lower aromatic and higher paraffinic contents show that tars are quite similar to currently utilized transport fuel (especially in the presence of Red mud). (ii) Adding LDPE to the lignite leads to an increase in the olefin content of the tars and to a decrease in the aromatic content of the tars. (iii) The alkane and alkene contents of the tar obtained by LDPE pyrolysis are the highest compared to the tars obtained by individual coal pyrolysis and also by coal:LDPE pyrolysis. It can be concluded that copyrolysis of coal with LDPE produces tar comprising more alkane and alkene species than that of tar obtained by the pyrolysis of coal alone. (iv) The maximum tar yield is obtained at 600 °C. Hydrogen released from LDPE leads to this increase, stabilizing the free radicals generated under the copyrolysis conditions. Thus, it can be concluded that polyethylene acts as a hydrogen donor media in view of tar formation during the copyrolysis process. (v) The oils obtained by LDPE and LDPE:lignite pyrolysis have the same structural properties according to the GPC, 1H NMR, and FTIR results. The oil from lignite pyrolysis comprises smaller molecules than the oils from LDPE and lignite:LDPE pyrolysis, and the viscosities of the all three oil samples are close to each other. Acknowledgment. The authors would like to acknowledge the Ankara University B.A.P. for supporting this research under BAP Contract No. 2005 07 05 095. EF060213V