Energy & Fuels 2006, 20, 2713-2716
2713
Additive Effect of Waste Tire on the Hydrogenolysis Reaction of Coal Liquefaction Residue Motoyuki Sugano,* Daigorou Onda, and Kiyoshi Mashimo Department of Materials and Applied Chemistry, College of Science and Technology, Nihon UniVersity, 1-8 Kanda surugadai, Chiyoda-ku, Tokyo 101-8308, Japan ReceiVed May 1, 2006. ReVised Manuscript ReceiVed August 31, 2006
A numerous amount of waste tire is landfilled or dumped all over the world, which causes environmental problems, such as destruction of natural places and the risk of fires. On the other hand, the coal liquefaction residue (CLR) is produced in 30% yield through the process supporting unit (PSU) of the NEDOL coal liquefaction process. Therefore, the investigation on an effective method for utilization of waste tire and CLR is required. In this study, the simultaneous hydrogenolysis of CLR and pulverized waste tire was carried out by using tetralin. The yields in the simultaneous hydrogenolysis were compared with algebraic sum of the yields of the individual hydrogenolyses of waste tire alone and coal alone. In the simultaneous hydrogenolysis, the synergistic effects to upgrading, such as an increase in the yield of the oil constituent and a decrease in the yield of the asphaltene constituent, occurred because of the stabilization of asphaltenic radicals from CLR with aliphatic radicals from tire. The decrease in asphaltene yield in the simultaneous hydrogenolysis was pronounced with the increase in the tire:CLR ratio because the solvent effects of liquefied tire, such as stabilization of radicals, hydrogen shuttling, and heat transfer, were enhanced. Accordingly, it is estimated that the simultaneous hydrogenolysis of CLR and waste tire is an effective method for processing both materials.
1. Introduction It is well-known that the amount of waste tire increases every year. In 2003, 2.0 and 1.3 million tons of waste tires were generated in the United States and Japan, respectively. In Japan in 2003, 62% of waste tires were recycled properly as a source of thermal energy, materials for other compounds, and retreaded tires. However, 26% of waste tires were exported, and the fate of 12% of waste tires is not known.1 In the USA in 2003, 78% of waste tires were recycled properly. However, 9% of waste tires were landfilled, and the fate of 10% of waste tires is not known.2 A numerous amount of waste tire is landfilled or dumped all over the world, which causes environmental problems, such as destruction of natural places and the risk of fires. Therefore, investigating an effective method for processing waste tire is a serious problem, and the liquefaction of tire to obtain fuel is one of the processing methods of waste tire.3,4 Tires mainly consist of vulcanized aliphatic and aromatic rubber, zinc and carbon black. It is well-known that coal liquefaction is enhanced by the addition of crude oil,5 which is a source of rubber constituents in tire. Therefore, there are many reports concerning the coprocessing of waste tire and coal. In the coprocessing, the synergistic effect, such as the increase in * Corresponding author. Phone: 81-3-3259-0809. Fax: 81-3-3293-7572. E-mail:
[email protected]. (1) Tire Industry of Japan; The Japan Automobile Tire Manufacturers Association Inc.: Tokyo, 2004; p 17. (2) U.S. Scrap Tire Markets 2003; The Rubber Manufacturers Association: Washington, D.C., 2004; p 1-2. (3) Farcasiu, M.; Smith, C. M. Prepr. Pap.-Am. Chem. Soc., DiV. Fuel Chem. 1992, 37, 472-479. (4) Sato, Y.; Kamo, T.; Yamamoto, Y.; Miki, K.; Kurahashi, S. In Coal Science and Technology 24: Proceedings of the 8th International Conference on Coal Science, Oviedo, Span, Sept 11, 1995; pp 1539-1542. (5) Cugini, A. V.; Lett, R. G.; Wender, I. Energy Fuels 1989, 3, 120126.
conversion6 and yield of the oil7 or asphaltene6,8 constituent, was reported in comparison with the results of the individual hydrogenolyses of waste tire and coal alone. A NEDOL continuous coal liquefaction pilot plant (PP) successfully processed 150 tons of coal per day from 1996 to 1998.9 The process supporting unit (PSU) played a substantial role in the design, construction, and operation of PP, which cumulatively processed 1 ton of coal per day from 1989 to 1998.10 The coal liquefaction residue (CLR) was produced in about 30% yield from PSU.11 The utilization of CLR is considered to be difficult because of the abundance of polycyclic aromatics and minerals in CLR. However, it was reported that CLR was converted into an acetone-soluble constituent in greater than 80% yield in the hydrogenolysis with tetralin.12 Therefore, an investigation about the efficient upgrading of CLR is required. In this study, the simultaneous hydrogenolysis reaction of CLR and pulverized waste tire was carried out by using tetralin to obtain oil constituent effectively. The effects of the ratio of tire/CLR, the amount of tetralin, and the particle size of tire in the simultaneous hydrogenolysis reaction were also discussed. 2. Experimental Section The experimental scheme for hydrogenolysis reactions described below is summarized in Figure 1. (6) Liu, Z.; Zondlo, J. W.; Dadyburjor, D. B. Energy Fuels 1994, 8, 607-612. (7) Mastral, A. M.; Murillo, R.; Perez-Surio, M. J.; Calle´n, M. Energy Fuels 1996, 10, 941-947. (8) Mastral, A. M.; Murillo, R.; Calle´n, M. S.; Garcı´a, T. Fuel Process. Technol. 2001, 69, 127-140. (9) Hirano, K. Fuel Process. Technol. 2000, 62, 109-118. (10) Ikeda, K.; Sakawaki, K.; Nogami, Y.; Inokuchi, K.; Imada, K. Fuel 2000, 79, 373-378. (11) Nogami, Y.; Mochizuki, M. J. Jpn. Inst. Energy 1999, 78, 835844. (12) Sugano, M.; Ikemizu, R.; Mashimo, K. Fuel Process. Technol. 2002, 77-78, 67-73.
10.1021/ef060193x CCC: $33.50 © 2006 American Chemical Society Published on Web 09/26/2006
2714 Energy & Fuels, Vol. 20, No. 6, 2006
Sugano et al. Table 1. Analytical Data of Coal and Tire Samples (wt % daf basis)
CLR tire A tire B a
Figure 1. Experimental Scheme.
2.1. Samples. Two kinds of discarded truck tire particles (tire A and B) were supplied by Bridgestone Corp. These samples were prepared from the same discarded truck tire. The average particle sizes of tires A and B were 1.2 and 0.5 mm, respectively. The tire samples were dried for 1 h under a vacuum at 20 °C before use. A CLR sample was obtained in 29 wt % yield (daf coal basis) from Wyoming subbituminous coal through the PSU process under the conditions as follows: reaction temperature, 435 °C; reaction pressure, 16.7 MPa.11 The CLR sample was pulverized to pass through a 60 mesh screen and dried for 3 h under a vacuum at 110 °C before use. 2.2. Hydrogenolysis Reaction. A mixture (3 g) of CLR and tire (tire A or tire B) with tetralin (7.5 or 30 g) was placed in a 100 cm3 autoclave under an initial H2 pressure of 5.9 MPa. The reactor was heated and maintained at 440 °C for 1 h. After cooling, the gaseous products (gas) were collected and analyzed. The products remaining in the reactor were recovered, filtered, and rinsed with acetone. The acetone-insoluble (residue) material was prepared from the residue by drying for 2 h under a vacuum at 110 °C. On the other hand, after acetone was evaporated from the filtrate, the acetonesoluble material was further extracted with n-hexane under an ultrasonic irradiation. The n-hexane-insoluble but acetone-soluble (asphaltene) material was prepared from the residue by drying under a vacuum at 60 °C. After n-hexane and tetralin were evaporated from the filtrate, a heavy oil material was obtained. Because the range of the boiling point of the heavy oil constituent was higher than 250 °C, the light oil material isolated from the oil constituent was evaporated with the solvent. Therefore, the yield of the acetonesoluble and n-hexane-soluble (oil) constituent was calculated from the difference between the weight of the feed sample and that of the recovered constituents (gas + asphaltene + residue) on a daf basis. The individual hydrogenolyses of CLR and tire samples were carried out in a similar manner. All reactions were carried out in duplicate, and the experimental error was within 3%. 2.3. Analysis. The gas chromatographic analyses of gaseous components (C1-C4, COx) evolved in the hydrogenolyses were performed on a Shimadzu GC-9A instrument equipped with a thermal conductivity detector and dual-column molecular sieve (7 m, Shimadzu) and Porapak N (2 m, Waters). The 1H NMR spectra of the heavy oil constituents obtained from the hydrogenolyses of samples were measured as a CDCl3 solution with a JEOL JNMEX90A (90 MHz, FT mode) spectrometer.
C
H
N
S + Oa
H/C
ashb
85.8 87.4 87.4
5.3 8.2 7.9
1.0 0.3 0.3
7.9 4.1 4.5
0.74 1.12 1.07
27.0 5.1 5.0
By difference. b wt % dry basis.
analytical data of the two kinds of tire samples were almost same, because these samples were prepared from the same discarded truck tire. The contents of ash and heteroatom in CLR were larger than those in the tire samples. The H/C ratio in CLR was smaller than those in the tire samples. Therefore, it was expected that the contents of the polar constituents in CLR were larger than those in tires. The effect of the tetralin:sample ratio on the individual hydrogenolysis of CLR or tire is shown in Figure 2. Compared with the yield of residue in the reaction of tire A without tetralin, the yield decreased with the addition of tetralin. The yields of the residue were almost the same and the asphaltene constituent was not produced in spite of the amount of tetralin; however, the yield of gas decreased with an increase in the tetralin:tire A ratio. The decreased gas constituents were methane, ethane, propane, and butane. These variations in yields for tire B are similar to those for tire A. It is well-known that carbon black, which does not decompose under the hydrogenolysis reaction, is 30% retained in tire. Therefore, most of the radicals derived from rubber constituents in tire were in the oil and gaseous ranges in the hydrogenolysis with tetralin and became oil and gas constituents after the hydrogenolysis. In the hydrogenolysis of CLR alone, the yields of residue and gas decreased and the yields of oil and asphaltene increased with the increase in the tetralin:CLR ratio. The decreased gas constituents were methane and ethane. Therefore, in the hydrogenolysis of CLR alone, dealkylation and the following retrogressive reaction by recombination among the radicals from CLR were considered to be suppressed with the increases in the tetralin:CLR ratio, which resulted in increases in the yields of oil and asphaltene constituents and decreases in the yields of gas and residue constituents. 3.2. Simultaneous Hydrogenolysis of CLR and Tire. The yields in the simultaneous hydrogenolysis of CLR and tire are
3. Results and Discussion 3.1. Hydrogenolysis of CLR or Tire Alone. The analytical data of CLR and tires A and B are given in Table 1. The
Figure 2. Effects of the tetralin:sample ratio on the individual hydrogenolysis of CLR or tire.
Effect of Tire on the Hydrogenolysis of CLR
Energy & Fuels, Vol. 20, No. 6, 2006 2715
Figure 3. Yields in the simultaneous hydrogenolysis of CLR and tire.
Figure 4. Variation in the yield of each constituent in the simultaneous hydrogenolysis of CLR and tire.
shown in Figure 3. As reported previously,13 the increase and decrease in the yields of constituents were calculated by using eqs 1 and 2. The variation in the yield of each constituent is shown in Figure 4.
(
Yield (%) ) FCT - FC
WC WT + FT WCT WCT
WCT ) WC + WT
)
(1) (2)
where WC and WT are the amounts (g) of CLR and tire, respectively. FCT is the yield (%) of each constituent from the simultaneous reaction of CLR and tire. FC and FT are the yields (%) of constituents from each reaction of CLR and tire alone in Figure 3, respectively. From the yields of Figure 4a-c , compared with the result from each reaction of CLR or tire alone, the synergistic effects of upgrading, such as the increase in oil yield and the decrease in asphaltene yield, were observed in the simultaneous reactions of CLR and tire A with 7.5 g of tetralin. In the coprocessing of coal and tire, the synergistic effects, such as the increase in oil7 or asphaltene6,8 yields or the decrease in the yield of the THFinsoluble constituent,6 were reported in comparison with the result of the individual hydrogenolysis of waste tire or coal alone. However, in this study, the synergistic effect appeared as the increase in oil yield and decrease in asphaltene yield in (13) Sugano, M.; Mashimo, K.; Wainai, T. Fuel 1998, 77, 447-451.
the simultaneous reaction of tire and CLR. Because the yield of asphaltene was negligible after the hydrogenolysis of tire alone, it was estimated that the asphaltene constituent derived from CLR decreased with the addition of tire. It was reported that the appearance of the synergistic effect in the coprocessing of coal and tire was explained by the stabilization of radicals from coal with those from tire to prevent the retrogressive reaction.6,8 As mentioned above, most of radicals derived from rubber constituents in tire were considered as being in the oil and gaseous ranges. Accordingly, it was anticipated that the synergistic effect in this study occurred by the stabilization of asphaltenic radicals from CLR with the radicals from tire. As a result, the increase in oil yield in compensation for the decrease in asphaltene yield was observed because of the prevention of the retrogressive reaction among the asphaltenic radicals from CLR. 3.3. Effects of the Tire:CLR Ratio on the Simultaneous Hydrogenolysis of CLR and Tire. As shown in the yields in Figure 4a-c and g-i, the decrease in asphaltene yield was pronounced with the increase in the tire:CLR ratio in the simultaneous reaction with 7.5 g of tetralin. The added catalyst (synthetic iron sulfide) in PSU is concentrated in CLR. However, the ratio of the amount of iron in CLR to the sum of the amount of the organic matter in CLR and tire decreases with the increase in the tire:CLR ratio. Therefore, it was expected that upgrading the asphaltene material was not enhanced by the catalytic effect of iron in CLR. The upgrading occurred because of the enhancement of the solvent effects of liquefied tire, such as stabilization of radicals from CLR with those from tire, hydrogen shuttling, and heat transfer. 3.4. Effects of the Tetralin/Sample Ratio on the Simultaneous Hydrogenolysis of CLR and Tire. Comparing with the yields in Figure 4a-c at each tire:CLR ratio, the residue yield increased in the simultaneous reactions with 30 g of tetralin (Figure 4d-f). The increase in oil yield was not observed except for the reaction of a high tire:CLR ratio. From Figure 2, the hydrogenolysis of CLR was accelerated with the increase in the tetralin:CLR ratio, which resulted in the decreases in the residue and gas yields and the increases in the oil and asphaltene yields. Consequently, the synergistic effects were anticipated to be small because the stabilization among the radicals from CLR and tire was inhibited because of the enhancement of the hydrogenolysis reaction of CLR by the excess amount (30 g) of tetralin on the simultaneous reaction. The ultimate analyses and the average structural parameters in the heavy oil constituents derived from the simultaneous hydrogenolyses of CLR and tire A are given in Table 2. The aromaticity index (fa), the index of condensed aromatic ring (Haus/Caus), and the average length of the aliphatic side chain bonded to aromatic ring (Num) of the unit structure of the heavy oil constituent were calculated from the ultimate analysis and 1H NMR spectrum of the constituent according to the Brown and Ladner method.14 In comparison with the analytical data of the heavy oil constituent from the hydrogenolysis of CLR alone, increases in the H/C ratio and the Num and Haus/Caus values and decreases in the fa value and the content of the heteroatom were observed for the constituent from the hydrogenolysis of tire A alone. Therefore, it was indicated that the unit structure of the heavy oil constituent from the hydrogenolysis of tire A was less aromatic than that of CLR. However, there was no tendency in the analytical data of the heavy oil constituents from the simultaneous hydrogenolyses of CLR and tire A. In comparison with the analytical data of the heavy oil (14) Brown, J. K.; Ladner, W. R. Fuel 1960, 39, 87-96.
2716 Energy & Fuels, Vol. 20, No. 6, 2006
Sugano et al.
Table 2. Ultimate Analyses and Average Structural Parameters in the Heavy Oil Constituents Derived from the Simultaneous Hydrogenolyses of CLR and Tire A ultimate analysesa tetralin (g)
7.5
30.0 a
structural parameters
tire:CLR ratio
C
H
N
Ob
H/C
fa
Num
Haus/Caus
0:3 1:2 1.5:1.5 2:1 3:0 0:3 1:2 1.5:1.5 2:1 3:0
90.1 90.5 91.7 91.4 91.3 90.1 89.1 89.6 89.0 87.5
6.3 6.7 6.1 6.2 7.4 6.7 7.7 7.4 8.0 10.7
1.1 1.1 1.2 1.2 0.3 0.8 1.1 1.1 1.0 0.3
2.5 1.7 1.0 1.2 0.9 2.4 2.1 2.0 1.9 1.5
0.84 0.88 0.80 0.80 0.96 0.88 1.01 0.98 1.08 1.46
0.80 0.77 0.85 0.79 0.77 0.75 0.67 0.68 0.62 0.39
1.59 1.75 1.46 2.07 1.91 1.77 2.46 2.43 3.81 4.70
0.73 0.73 0.71 0.75 0.83 0.72 0.75 0.72 0.70 0.98
wt % daf basis. b By difference.
constituents from the hydrogenolyses with 7.5 g of tetralin, the increases in the H/C ratios and Num values and decreases in the fa values were observed for the constituents from the hydrogenolyses with 30 g of tetralin. Accordingly, it was considered that the hydrogenation and hydrocracking reactions of the heavy oil constituents from the hydrogenolyses of CLR and tire A were accelerated by the hydrogen donatibility in the excess amount (30 g) of tetralin. 3.5. Effects of the Average Particle Size of the Tire on the Simultaneous Hydrogenolysis of CLR and Tire. Comparing the yields in Figure 4a-c at each tire:CLR ratio, the synergistic effects were pronounced on the simultaneous reaction of CLR and tire B (Figure 4g-i). It was reported that coprocessing Blind Canyon coal with pyrolyzed tire oil was more beneficial than that with tire.15 Accordingly, it was considered that particles of smaller size (tire B) liquefied more easily than those of larger size (tire A) during the reaction. Therefore, the solvent effects of liquefied tire appeared in the simultaneous reaction of CLR and tire particles of smaller size, which resulted in the enhancement of the synergistic effects.
in asphaltene yield, occurred because of the stabilization of asphaltenic radicals from CLR with aliphatic radicals from tire. (2) The decrease in asphaltene yield in the simultaneous hydrogenolysis was pronounced with the increase in the tire: CLR ratio because the solvent effects of liquefied tire, such as stabilization of radicals, hydrogen shuttling, and heat transfer, were enhanced. (3) In the simultaneous hydrogenolysis with a large amount of tetralin, the synergistic effects were small because the stabilization among the radicals from CLR and tire was inhibited because of the enhancement of the hydrogenolysis of CLR with the excess amount of tetralin. (4) The synergistic effects were enhanced in the simultaneous hydrogenolysis of CLR and tire particles of smaller size. It was considered that the solvent effects of liquefied tire appeared significantly because tire particles of smaller size liquefied more easily than those of larger size during the reaction. Accordingly, it is estimated that the simultaneous hydrogenolysis of CLR and waste tire is an effective method for processing both materials.
4. Conclusions
Acknowledgment. The authors express their gratitude to Bridgestone Corp. for providing two kinds of tire samples. The authors are also grateful to the New Energy and Industrial Technology Development Organization (NEDO) and the Coal Liquefaction PSU Research Center for providing Wyoming coal liquefaction residue. The authors thank Dr. K. Koyano, Mr. T. Ohba, Mr. N. Uehara, and Miss M. Ishitsuka (Nihon University) for their support of this study.
The simultaneous hydrogenolysis of CLR and tire was compared with the result of the individual hydrogenolysis of CLR or tire alone and concluded as below. (1) In the simultaneous hydrogenolysis, the synergistic effects to upgrading, such as the increase in oil yield and the decrease (15) Orr, E. C.; Burghard, J. A.; Tuntawiroon, W.; Anderson, L. L.; Eyring, E. M. Fuel Process. Technol. 1996, 47, 245-259.
EF060193X
