Coliquefaction of Coal with Polyethylene Using Fe(CO) - American

value from the additive values of respective runs. We considered that free radicals produced from YL coal were stabilized by the hydrogen abstraction ...
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Energy & Fuels 2000, 14, 612-617

Coliquefaction of Coal with Polyethylene Using Fe(CO)5-S as Catalyst Toshiyuki Kanno, Masahiro Kimura, Na-oki Ikenaga, and Toshimitsu Suzuki* Department of Chemical Engineering, Kansai University, Suita, Osaka 564-8680, Japan Received September 1, 1999

The coliquefaction of Yallourn coal (YL) with polyethylene (PE) was carried out at 400 or 425 °C under pressurized H2 in 1-methylnaphthalene or tetralin. In the coliquefaction without a catalyst, the conversion and the oil yield increased by 11-12% as compared to that of expected value from the additive values of respective runs. We considered that free radicals produced from YL coal were stabilized by the hydrogen abstraction from PE during the coliquefaction, and as a result β-scission of PE markedly proceeded. The addition of a large amount of Fe(CO)5-S catalyst (Fe ) 1.0 mmol, 2.79 wt %, S/Fe ) 2) increased the conversion and the hexane soluble oil yield in the homoliquefaction of YL coal or PE, except for the conversion of PE in the reaction with TL. However, this catalyst did not promote the conversion and the hexane-soluble oil yield in the coliquefaction of YL coal with PE. When the amount of the iron catalyst was decreased to 0.4 mmol (1.12 wt %) against the same amount of coal and PE, the conversion and the oil yield in the coliquefaction run increased as compared to the reaction without or with the large amount of catalyst (Fe ) 1.0 mmol). Since the excess amount of the catalyst rapidly provided hydrogen from the gas phase to YL coal-derived free radicals, hydrogen transfer from PE to YL coal decreased greatly.

1. Introduction The recovery of waste plastics has recently become of great interest in terms of its relevance to environmental protection and the effective use of resources. Most waste plastics are disposed of in landfills or by combustion, and only few are reused.1 In the reuse of plastics, recycling is most popular, but in this system waste plastics must be separated into their individual components which must be purified by removing contaminants such as paint and additives. The difficulty and complexity of these processes has prevented the commercialization of the reuse of waste plastics. It is possible to reuse waste plastic without the necessity of these complicated processes by recovering it as a fuel using pyrolysis. Considerable research studies have been published.2-4 On the other hand, a petroleum shortage is inevitable in a near future. A large number of efforts to obtain synthetic petroleum, especially transportation fuel by coal liquefaction, have been carried out.5,6 To increase the efficiency of coal liquefaction, various catalysts and solvents have been developed. Although these efforts * Corresponding author. Fax: +81-6-6388-8869. E-mail: tsuzuki@ ipcku.kansai-u.ac.jp. (1) Kaji, M. Nippon Enerugi Gakkaisi 1996, 75, 778. (2) Aguado, J.; Sotelo, J. L.; Serrano, D. P.; Calles, J. A.; Escola, J. M. Energy Fuels 1997, 11, 1225. (3) Ding, W.; Liang, J.; Andeson, L. L. Energy Fuels 1997, 11, 1219. (4) Shabtai, J.; Xiao, X.; Zmierczak, W. Energy Fuels 1997, 11, 76. (5) Huffuman, G. P.; Ganguly, B.; Zhao, J.; Rao, K. R. P. M.; Shah, N.; Feng, Z.; Huggins, F. E.; Taghiei, M. M.; Lu, F. Energy Fuels 1993, 7, 285. (6) Dadyburjor, D. B.; Stewart, W. R.; Stiller, A. H.; Stinespring, C. D.; Wann, J. P.; Zondlo, J. W. Energy Fuels 1994, 8, 19.

have certainly improved the efficiency of coal liquefaction, the cost of synthesized oil from these reactions is still high.7 In light of this, mixtures of coal and wastes such as plastics or used tires have been studied as sources, and in this co-processing a synergistic effect in regard to the conversion and the oil yield has been observed. Studies on the coliquefaction of coal with waste tire have reported that waste tires played a role of hydrogen donor for coal liquefaction8,9 and the favorable capability of tires as a solvent source depended on their various components and a catalytic substance involved as reinforcement.10,11 Ibraham and Seehra investigated the source of synergism using in-situ ESR. They reported that the intensity of the ESR-active free radicals in the 1:1 coal-tire mixture began to increase at around 200 °C and reached a maximum value at 350 oC.12 In the study of the coliquefaction of coal with waste plastics, Taghiei et al. found that synergism appeared on the conversion and the oil yield.13 Luo and Curtis reported the effects of reaction parameters such as plastic type, reaction time, and types of catalysts on the co-processing of waste plastics with coal.14 Joo and (7) Gray, D.; Tomlinson, G. Prepr. Pap.sAm. Chem. Soc., Div. Fuel Chem. 1995, 40, 20. (8) Mastral, A. M.; Murillo, R.; Palacios, J. M.; Mayoral, M. C.; Calle´n, M.; Energy Fuels 1997, 11, 813. (9) Liu, Z.; Zondlo, J. W.; Dadyburjor, D. B. Energy Fuels 1994, 8, 607. (10) Tang, Y.; Curtis, C. W. Fuel Process. Technol. 1996, 46, 195. (11) Orr, E. C.; Burghard, J. A.; Tuntawiroon, W.; Anderson, L. L.; Eyring, E. M. Fuel Process. Technol. 1996, 47, 245. (12) Ibrahim, M. M.; Seehra, M. S. Fuel Process. Technol. 1996, 49, 197. (13) Taghiei, M. M.; Feng, Z.; Huggins, F. E.; Huffman, G. P. Energy Fuels 1994, 8, 1228.

10.1021/ef990188b CCC: $19.00 © 2000 American Chemical Society Published on Web 03/07/2000

Coliquefaction of Coal with Polyethylene

Curtis reported the result of using Maya or Manji residues in the co-processing of coal with waste plastics.15-17 Rothenberger and Cugini reported the result of the coliquefaction of coal with various waste plastics by various ratios of coal to plastics. The two or multicomponent reactions created a synergistic effect wherein the conversion and the oil yield were greater than values that those predicted in the respective runs.18 Ades and Subbaswamy reported the source of synergism using MOPAC calculation.19 They concluded that H2 transport from polyethylene to coal occurred at a closer position than that from polypropylene to coal, and this difference of the distance was the reason for the differences in the behavior of coliquefaction with polyethylene and polypropylene. This study addressed the reaction conditions necessary for the coliquefaction of Yallourn coal with polyethylene, and determined the conditions under which the coliquefaction created synergistic conversions and oil yields. We examined the origin of the synergism by carrying out FT-IR analyses of liquefaction residues. The effect of catalyst on the conversion and the oil yield in the coliquefaction were studied to understand mechanistic aspect of coliquefaction. 2. Experimental Section Dried samples of Australian Yallourn brown coal (C: 67.2, H: 4.8, N: 0.5, S: 0.2, O: 27.3 daf%, ash: 1.1 d%) under 200 mesh was used as a coal source. Low-density polyethylene (specific gravity: 0.88-0.94, melting point: 92-117 °C) was purchased from General Science Co. and was ground to pass 60 mesh screen. A 2.0 g sample of the respective feed or a one-to-one mixture of coal and polyethylene was charged into a 50 mL magnetically stirred autoclave together with 4.0 g of 1-methylnaphthalene or tetralin and a certain amount of catalyst. Hydrogen or nitrogen was charged to 5.0 MPa at room temperature and the autoclave was heated to the required temperature of 400 or 425 oC, where it was maintained for 60 min under stirring at 500 rpm. Fe(CO)5-S was used as a catalyst precursor. Following the reaction, products were separated by solvent extraction with THF, hexane, and toluene under ultrasonic irradiation. We denote the hexane-soluble fraction as oil, the toluene-soluble and hexane-insoluble fraction as asphaltene, the THF-soluble and toluene-insoluble fraction as preasphaltene, and THF-insoluble fraction as residue. The conversion was calculated by the difference between the charged feed and the amount of residue. Experimental error against the liquefaction yield was within (2%. Gaseous products were analyzed by gas chromatography using a Shimadzu GC-14BPF equipped with a FID detector using a Porapak Q column (3 mm × 3m) for the hydrocarbons CH4-C3H8, and a Shimadzu GC-8APT equipped with a TCD detector using an activated carbon column (3 mm × 3m) for CO and CO2. Fourier transform infrared (FT-IR) spectra were obtained by transmission mode using a JEOL JIR 7000. A small amount of liquefaction residues derived from YL coal and/or PE were ground with KBr powder and pelletized, after which FT-IR spectra were taken. Quantitative analyses of residue from YL coal and PE were carried out using the following characteristic (14) Luo, M.; Curtis, C. W. Fuel Process. Technol. 1996, 49, 177. (15) Joo, H. K.; Curtis, C. W. Energy Fuels 1996, 10, 603. (16) Joo, H. K.; Curtis, C. W. Energy Fuels 1997, 11, 801. (17) Joo, H. K.; Curtis, C. W. Fuel Process. Technol. 1998, 53, 197. (18) Rothenberger, K. S.; Cugini, A. V. Energy Fuels 1997, 11, 849. (19) Ades, H. F.; Subbaswamy, K. R. Fuel Process. Technol. 1996, 49, 207.

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Figure 1. Coliquefaction of Yallourn coal with polyethylene. Lower part: product distribution, upper part: hydrogen consumption. Left side: reaction with 1-MN; right side: reaction with TL. PE, YL-PE, YL indicate homoliquefaction of PE, coliquefaction of YL coal with PE, and homoliquefaction of YL coal, respectively. The same abbreviation was used throughout figures. Feeds 2.0 g, solvent (1-MN or TL) 4.0 g, P(H2) 5.0 MPa, 400 °C, 60 min absorptions ascribed to the respective component. C-H vibrations at 2915 and 2850 cm-1 and CH2 rocking vibrations at 720 cm-1 were chosen as a residue from PE. Aromatic CdC vibration at around 1600 cm-1 was selected as a residue characteristic of YL coal residue. Several known amounts of mixtures of YL coal residue and PE residue were prepared, and IR spectra were then measured. Calibration curves were obtained based on absorbances of these peaks. Using the calibration curves, we obtained the relative ratio of YL coal and PE left unreacted in the coliquefaction.

3.Results and Discussion 3.1. Uncatalyzed Reaction. Figure 1 shows the results of coliquefaction of YL coal with polyethylene without catalyst under hydrogen pressure. The numerals in Figure 1 indicate oil yield, and those in parentheses indicate arithmetic mean values of the oil yields calculated from respective runs of the individual components. In the reaction with 1-MN at 400 oC, the oil yield from PE was relatively high (49%), but that from YL coal was very low (13%). In the reaction with TL, the oil yield from YL coal increased to 37%, but that from PE decreased to 28%. To determine differences in the liquefaction behavior of PE and that of YL coal, the amount of hydrogen consumed was calculated from pressure drop, gas composition, and composition of solvent and its hydrogenated or dehydrogenated substances. These results are shown in the upper part of Figure 1. Positive values indicate that feeds consumed hydrogen, and the negative value indicates that feeds released hydrogen. Although experimental errors are inevitable in these data, it is obvious that hydrogen consumption tenden-

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Kanno et al. Table 1. The Amount of Individual Residue in Coliquefactiona g solvent 1-MN TL

YL coal PE total YL coal PE total

estimated valueb

observed valuec

difference

0.57 0.25 0.82 0.07 0.36 0.43

0.45 0.12 0.57 0.13 0.19 0.32

0.12 0.13 0.25 -0.06 0.17 0.11

a YL coal 1.0 g, PE 1.0 g, Solvent 4.0 g, P(H ) 5.0 MPa, 400 °C, 2 60 min. b Calculated from additive values in the respective runs. c Calculated from calibration curves.

Figure 2. FT-IR spectra of liquefaction residues. PE: Residue of homoliquefaction of PE; YL-PE: residue of coliquefaction of YL coal with PE; YL: residue of homoliquefaction of YL coal. Feeds 2.0 g, 1-MN 4.0 g, P(H2) 5.0 MPa, 400 °C, 60 min

cies in the liquefaction of PE differ from those in the liquefaction of YL coal. YL coal consumed a large amount of H2 in TL, and a large amount of naphthalene dehydrogenated from TL was observed after the reaction. In the reaction of PE, H2 consumption was negative in 1-MN and only slightly positive in TL. These results indicate that PE released hydrogen to produce a high conversion and oil yield in 1-MN, and consumed hydrogen in TL with a lower conversion and oil yield. In 1-MN, free radicals generated by the pyrolysis of PE might abstract hydrogen from PE, and β-fission of the PE backbone proceeded to give an oil fraction through radical chain reaction. In the reaction with TL, radicals produced from PE were stabilized by the hydrogen abstraction from TL, whose bond dissociation energy is lower than that of PE. Consequently, the radical chain length in TL is shorter than that in the non-hydrogen donor solvent, the molecular weight of cracked products was high, and the conversion and the oil yield in TL were lower than those of in 1-MN. 3.2. The Origin of the Synergism in the Coliquefaction. In the coliquefaction of YL coal with PE, the conversion and the oil yield were larger than the additive values of respective reactions. To determine the origin of the synergism, we carried out FT-IR analyses of the liquefaction residues. Figure 2 shows FT-IR spectra of liquefaction residues obtained in the reaction with 1-MN. The residue of YL coal exhibited strong hydroxyl group absorption in the region 3000-3500 cm-1, and aromatic CdC in around 1600 cm-1. The

residue of PE showed stretching vibration of aliphatic C-H in 2915 and 2850 cm-1, bending vibration of CH3 and CH2 in 1460 cm-1, and (CH2)n locking vibration in 720 cm-1. The residue from the coliquefaction showed absorptions ascribed to YL coal at 3000-3500 and around 1600 cm-1, and those from PE in 2915, 2850, and 720 cm-1. To calculate the conversion of YL coal and PE in the coliquefaction, the weight ratio of the residue from YL coal to that from PE was calculated from the absorption ratios. Table 1 shows the amount of residues from YL coal and PE in the coliquefaction of YL coal with PE. The estimated values are calculated from the additive values in the respective runs while the observed values are obtained from the absorption ratio using precalibrated results. The result in 1-MN indicates that the coliquefaction reaction proceeded markedly as compared to the homoliquefaction, since the observed values of residues for both YL coal and PE during the coliquefaction were smaller than the estimated values. Free radicals produced from YL coal were stabilized by the hydrogen abstraction from PE during the coliquefaction. PE radicals were produced by the abstraction of hydrogen, and they initiated radical chain reactions involving the β-scission of alkyl radicals. In TL, the hydrogen from TL capped free radicals produced by the decomposition of YL coal in a way similar to YL coal liquefaction, since the difference between the estimated and the observed value is small value. This difference can be ignored since absorbance of the peak ascribed to Yallourn coal was too weak. Therefore, the hydrogenation ability of solvent against PE was weakened, so that the termination of the radical chain reaction of PE by the solvent would be suppressed as compared to the PE homoliquefaction. 3.3. Effect of the Catalyst on the Liquefaction. In previous studies, the Fe(CO)5-S catalyst is known to be the most active catalyst for coal hydroliquefaction.20 Figure 3 shows the results of coliquefaction of YL coal with PE using Fe(CO)5-S (Fe ) 1.0 mmol, S/Fe ) 2) under hydrogen pressure. In the homoliquefaction in 1-MN, the oil yield was 52% for PE and 48% for YL coal, and the conversion was 93 and 97%, respectively. These values were higher as compared to uncatalyzed runs, and similar results were observed in TL, except for the conversion of PE. However, the conversion and the oil yield in the coliquefaction increased only a few percent with the addition of Fe(CO)5-S, being smaller than the arithmetic averages of homoliquefaction. Because the insufficient sulfurization of the iron-based (20) Suzuki, T. Energy Fuels 1994, 8, 341.

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Figure 3. Coliquefaction of Yallourn coal with polyethylene using Fe(CO)5-S. Left side: reaction with 1-MN; right side: reaction with TL. Feeds 2.0 g, solvent (1-MN or TL) 4.0 g, P(H2) 5.0 MPa, 400 °C, 60 min, Fe(CO)5 1.0 mmol, S 2.0 mmol.

Figure 5. FT-IR spectra of coliquefaction residues. Feeds 2.0 g, 1-MN 4.0 g, P(H2) 5.0 MPa, 400 °C, 60 min, Fe(CO)5 1.0 mmol, S 2.0 mmol.

Figure 4. Effect of S/Fe on the product distribution in the coliquefaction of Yallourn coal with polyethylene. Left side: reaction using Fe(CO)5-S at S/Fe ) 2; right side: reaction using Fe(CO)5-S at S/Fe ) 4. Feeds 2.0 g, 1-MN 4.0 g, P(H2) 5.0 MPa, 400 °C, 60 min, Fe(CO)5 1.0 mmol.

catalyst into the active species, Fe1-XS, may occurred this result, coliquefaction with a higher S/Fe ratio of 4 with the same amount of Fe(CO)5 was also performed. Figure 4 shows the effect of the S/Fe ratio on the coliquefaction of YL coal with PE in 1-MN under hydrogen pressure. When the S/Fe ratio was increased to 4, the conversion and the oil yield increased slightly as compared to the reaction at S/Fe ) 2. However, these values were still smaller than the arithmetic averages of the respective runs. To examine that this catalyst hardly promoted the coliquefaction, FT-IR analyses of the coliquefaction residues were carried out. Figure 5 shows the FT-IR spectra of residues from uncatalyzed (a) and catalyzed (b) runs. In the residue from the uncatalyzed run, absorptions ascribed to both YL coal and PE appeared. In the residue from the catalyzed run, absorptions ascribed to YL coal were insignificantly few, and only those of PE were detected. As stated above, the reaction proceeds through abstracting hydrogen from PE by free radicals from YL coal.

Therefore, the residue from the uncatalyzed run contained unreacted portions of both coal and PE. In the reaction with Fe(CO)5-S, however, the residue from YL coal decreased greatly since the free radicals from YL coal were stabilized by hydrogenation ability of the catalyst. As a result, hydrogen activated on the catalyst rapidly transferred to free radicals from YL coal. Consequently, hydrogen abstraction from PE was depleted, and a radical chain reaction involving the β-cleavage of PE proceeded less markedly as compared to the uncatalyzed coliquefaction. In our previous study using model compounds, Fe(CO)5-S catalyst markedly hydrogenated polar radicals containing oxygen functional groups.21 In the present study, a significant amount of radicals from YL coal contained oxygen functional groups, so such an interpretation would be reasonable. Therefore, a large amount of PE residue could be found in the residue from the catalyzed run. If the interaction between YL coal and PE during the coliquefaction did not occur as stated above, the conversion and the oil yield in the coliquefaction ought to have been consistent with the additive value of respective runs. However, these values are lower than expected ones. The reason for this is shown in section 3.5. 3.4. Optimum Amount of Catalyst. The above findings suggest that the amount of Fe(CO)5-S catalyst used in the above run is too large for the coliquefacion. The optimum amount of the catalyst was examined, (21) Ikenaga, N.; Kobayashi, Y.; Saeki, S.; Sakota, T.; Watanabe, Y.; Yamada, H.; Suzuki, T. Energy Fuels 1994, 8, 947.

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Figure 6. Effect of loading level of Fe(CO)5 on the coliquefaction of Yallourn coal with polyethylene. YL coal 1.0 g, PE 1.0 g, 1-MN 4.0 g, P(H2) 5.0 MPa, 400 °C, 60 min, S/Fe ) 2.

with the results shown in Figure 6. Within the range of the experimental conditions, the oil yield did not change. However, the conversion showed the maximum at the amount of Fe of 0.4 mmol. Since with a decrease in the amount of the iron catalyst the hydrogen transfer from the gas phase to coal free radicals decreased, a certain number of free radicals derived from YL coal may abstract hydrogen from the abundant hydrogen of PE to promote coliquefaction. When the amount of the catalyst decreased to Fe ) 0.2 mmol, the conversion decreased as compared to the run at Fe ) 0.4 mmol. The decrease in the amount of catalyst might lead to increase in the amount of free radicals from YL coal that were not provided with hydrogen from either the catalyst or PE. 3.5. Active Species for PE Homoliquefaction. According to the above discussion regarding PE liquefaction proceeding by means of a radical chain reaction, the addition of an iron-based catalyst ought to have decreased the conversion and the oil yield in PE liquefaction because the catalyst provides gas-phase hydrogen which the free radicals from PE use to terminate the radical chain reactions. However, the addition of the Fe(CO)5-S catalyst to the PE liquefaction process improved the conversion and the oil yield. We cannot elucidate the role of this catalyst against PE liquefaction and as an active species for PE liquefaction in the present step. Since the conversion and the oil yield in the PE homoliquefaction at S/Fe ) 4 were significantly higher than those at S/Fe ) 2, we considered that sulfur might have played the role of the initiator of PE radical chain reaction. Sulfur abstracted the hydrogen from polyethylene to convert hydrogen sulfide, giving PE radicals. PE radicals tend to degrade through the radical chain reaction. Such assumption was proved by the generation of hydrogen sulfide during the liquefaction of PE under a nitrogen atmosphere. It was reported that sulfur was used as a dehydrogenation agent to polymerize the anthracene oil.22 Even if radical chain reaction of PE is once started by sulfur, molecular hydrogen activated on the catalyst may terminate the chain reaction by capping the radical derived from PE. (22) Ferna´ndez, A. L.; Grenda, M.; Bermejo, J.; Mene´ndez, R. Energy Fuels 1998, 12, 949.

Kanno et al.

Figure 7. Effect of amount of Yallourn coal on the product distribution in the coliquefaction of Yallourn coal with polyethylene. Feeds 2.0 g, 1-MN 4.0 g, P(H2) 5.0 MPa, 400 °C, 60 min.

Therefore, Fe(CO)5-S (Fe ) 1.0 mmol, S/Fe ) 2) increased the conversion of PE to give larger molecular weight products (AS and PA), without increasing the oil yield (low molecular weight fraction) in the PE homoliquefaction in 1-MN. Differences in the hydrogen abstraction ability of sulfur from YL coal and PE were examined by thermo gravimetric analyses. A mixture of YL coal or PE and molecular sulfur was set in a TGA apparatus, and it was heated under argon atmosphere at a heating rate of 5 °C/min. The weight loss by hydrogen sulfide formation started at a lower temperature for YL coal (190 °C), as compared to that for PE (220 °C). These results seem to indicate that in the coliquefaction of YL coal and PE, sulfur tends to abstract hydrogen from YL coal at the early stage of the coliquefaction. Therefore sulfur did not promote PE degradation. As a result, the conversion and the oil yield of PE decreased in the coliquefaction, as compared to those in the PE homoliquefaction, to give lower conversion and oil yield in the coliquefaction. 3.6. Effect of YL Coal and PE Feed Ratio on the Coliquefaction. Figure 7 shows the effect of the feed ratios of YL coal to PE on the product distribution in the coliquefaction. In all cases, the conversion and the oil yield in the coliquefaction were higher than the arithmetic averages of the respective runs by about 10%. The highest synergistic effect was observed when 0.5 g of YL coal with 1.5 g of PE was coliquefied. The conversion of 77% and the oil yield of 53% were higher than those of the liquefaction of PE alone. These results strongly support the above assumption that coal fragment radicals behaved as an initiator of PE cracking. 3.7. Effect of Reaction Temperature on the Coliquefaction. Figure 8 shows the results of coliquefaction in 1-MN at 425 °C. In the uncatalyzed run, conversions and oil yields in the homoliquefaction and coliquefaction increased as compared to those at 400 °C. In contrast to the runs at 400 °C, the above synergism did not appear. Since the pyrolysis of PE proceeded rapidly at the higher reaction temperature, the initiation of radical chain reactions by the YL coal fragment radicals did not play a significant role in the degradation

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radicals from YL coal were stabilized by hydrogen activated on the catalyst as well as the reaction at 400 °C. However, since free radicals from YL coal were not important for coliquefaction to proceed, as stated above, the conversion of PE in the catalytic coliquefaction did not decrease as compared to that in the uncatalyzed run. Therefore, the addition of the catalyst increased the coliquefaction conversion and oil yield. Conclusion

Figure 8. Effect of reaction temperature on the product distribution in the coliquefaction of Yallourn coal with polyethylene. Left side: reaction with Fe(CO)5-S; right side: reaction without catalyst. Feeds 2.0 g, 1-MN 4.0 g, P(H2) 5.0 MPa, 425 °C, 60 min, Fe(CO)5 1.0 mmol, S 2.0 mmol.

of the PE chain. When Fe(CO)5-S was added, conversions and oil yields in all the reaction increased as compared to those of uncatalyzed runs. Such differences in the behavior of the Fe(CO)5-S catalyst could be interpreted as follows. In the reaction at 425 °C, free

In coliquefaction without a catalyst, the conversion and the oil yield increased by 11∼12% as compared to that of the expected values resulting from the additive values of respective runs. We considered that free radicals produced from YL coal were stabilized by the hydrogen abstraction from PE during the coliquefaction. The addition of an Fe(CO)5-S catalyst in the amount of Fe)0.4 mmol promoted the conversion and the hexane soluble oil yield in the coliquefaction of YL coal with PE, but addition of a larger amount of Fe(CO)5-S catalyst (Fe)1.0 mmol) did not promote the reaction. Free radicals produced from YL coal that could not abstract hydrogen from PE were provided with hydrogen from the gas phase by an appropriate amount of catalyst. EF990188B