60
Energy & Fuels 2003, 17, 60-61
Synergic Effect of Sulfur on Activated Carbon-Catalyzed Hydrocracking of Di(1-naphthyl)methane Zhong-Hai Ni, Zhi-Min Zong, Li-Fang Zhang, Lin-Bing Sun, Yi Liu, Xin-Hua Yuan,† and Xian-Yong Wei* Department of Applied Chemistry, School of Chemical Engineering, China University of Mining and Technology, Xuzhou 221008, Jiangsu, China Received May 8, 2002
As a model reaction for coal liquefaction, the hydrocracking of di(1-naphthyl)methane (DNM) was investigated under different reaction conditions. The results show that activated carbon selectively catalyzes DNM hydrocracking and that sulfur has a synergic effect on the activated carbon-catalyzed hydrocracking of DNM. The synergic effect can be ascribed to the catalysis of the activated carbon in H2S dissociation.
Since Farcasiu and Smith reported that a carbon black itself had intrinsic catalytic activity for 4-(1naphthylmethyl)bibenzyl (NMBB) decomposition,1 catalyses of carbon materials such as carbon blacks and activated carbons in coal liquefaction and model reactions have been extensively investigated.2-6 Similar to carbon materials, FeS27,8 and some metal-sulfur systems9 also exhibited extremely high activities for breaking the bond between an aryl unit and methylene linkage. Furthermore, sulfur addition was found to promote FeS2-catalyzed hydrocracking of di(1-naphthyl)methane (DNM)7 and diphenylmethane10 as well as coal liquefaction.11 Schmidt et al.12,13 examined catalytic hydrocracking of NMBB over iron catalysts. They found that sulfur addition to most catalyst precursors led to substantially higher catalyst activity and higher NMBB conversion. However, to our knowledge, no investigations about the additive effect of sulfur on carbon * Corresponding author. Present address: Advanced Chemical Technology Division, Korea Research Institute of Chemical Technology, P.O. Box 107, Yuseong, Daejeon 305-600, Korea. E-mail: weixy@ pado.krict.re.kr. † Present address: School of Material Science and Engineering, Jiangsu University, No. 301 Dantu Road, Zhenjiang 212013, Jiangsu, China. E-mail:
[email protected]. (1) Farcasiu, M.; Smith C. Energy Fuels 1991, 5 (1), 83-87. (2) Farcasiu, M.; Smith, C.; Hunter, E. A. Proc. Int. Conf. Coal Sci. 1991, 166-169. (3) Farcasiu, M.; Petrosius, S. C.; Eldredge, P. A.; Anderson, R. R.; Ladner, E. P. Energy Fuels 1994, 8 (4), 920-924. (4) Farcasiu, M.; Kaufman, P. B.; Ladner, E. P.; Derbyshire, F.; Jagtoyen, M. Proc. Int. Conf. Coal Sci. 1995, 1303-1306. (5) Futamura, S. Proc. Int. Conf. Coal Sci. 1997, 1481-1484. (6) Zhang, Z. G.; Yoshida, T. Energy Fuels 2001, 15 (3), 708-713. (7) Wei, X. Y.; Ogata, E.; Niki, E. Chem. Lett. 1991, (12), 21992202. (8) Wei, X. Y.; Ogata, E.; Niki, E. Sekiyu Gakkaishi 1992, 35 (4), 358-361. (9) Ni, Z. H.; Zhou, S. L.; Zong, Z. M.; Xu, X.; Cai, K. Y.; Jiang, B.; Wei, X. Y.; Ogata, E. Proceedings of the 7th China-Japan Symposium on Coal and C1 Chemistry, Haikou, Hainan, China, 2001; pp 379382. (10) Wei, X. Y.; Ogata, E.; Zong, Z. M.; Niki, E. Energy Fuels 1992, 6 (6), 868-869. (11) Kotanigawa, T.; Yamamoto, M.; Sasaki, M.; Wang, N.; Nagaishi, H.; Yoshida, T. Energy Fuels 1997, 11 (1), 190-193. (12) Schmidt, E.; Song, C.; Schobert, H. H. Prepr. Pap.sAm. Chem. Soc., Div. Fuel Chem. 1995, 40, 580-583. (13) Schmidt, E.; Song, C.; Schobert, H. H. Energy Fuels 1996, 10 (3), 597-602.
materials-catalyzed reactions have been reported. Recently, we investigated activated carbon-catalyzed hydrocracking of DNM under different conditions, finding that sulfur remarkably promoted DNM hydrocracking in the presence of activated carbon. Here, we report our preliminary results about the synergic effect of sulfur on activated carbon-catalyzed hydrocracking of DNM. DNM was synthesized by heating naphthalene and 1-chloromethylnaphthalene in the presence of zinc powder.14 An activated carbon, which was prepared from a bituminous coal by steam activation and purchased from Xinhua Chemical Company, Shanxi, China, was ground to the particle size of < 0.7 µm before use. Its surface area and ash content were measured to be 1350 m2/g and 8.2 wt %, respectively. Sulfur (purity > 99.99%) and solvent n-heptane (purity > 99%, anhydrous) were purchased from Aldrich Chemical Co., Inc. DNM (0.5 mmol), activated carbon (0 or 0.1 g), sulfur (0-0.1 g), and n-heptane (10 mL) were put into a 60 mL stainless, magnetically stirred autoclave. After being pressurized with hydrogen to 0-5 MPa at room temperature (20 °C), the autoclave was heated to 300-375 °C in 15 min and maintained at that temperature for 1 or 3 h. Then the autoclave was immediately cooled to room temperature in an ice-water bath. The products and unreacted DNM taken out of the autoclave were identified by GC/MS (HP 6890/5973) and quantified by GC (HP 6890). Table 1 shows the results from noncatalytic reaction of DNM without sulfur addition. DNM was not converted at all at 350 °C without H2. Under pressurized hydrogen, DNM conversion in 1 h increased from 0.8% at 300 °C to 15.5% at 375 °C, affording naphthalene (NpH) and 1-methylnaphthalene (1-MN) as the main products, i.e., DNM was mainly hydrocracked under the reaction conditions. Comparing the data in Table 1 with those in Table 2 shows that sulfur addition appreciably promoted DNM hydrocracking. Direct cleavage of the Car-Calk bond in DNM is very difficult, because the leaving naphthyl radical is ex(14) Futamura, S.; Koyanagi, S.; Kamiya, Y. Fuel 1988, 67 (10), 1436-1440.
10.1021/ef020105i CCC: $25.00 © 2003 American Chemical Society Published on Web 12/17/2002
Activated Carbon-Catalyzed Hydrocracking of DNM
Energy & Fuels, Vol. 17, No. 1, 2003 61
Table 1. Noncatalytic Reaction of DNM without Sulfur Addition for 1 ha temp., °C
IHP, MPa
conv., %
300 325 350 350 375
5 5 0 5 5
0.8 1.4 0 6.2 15.5
THN 0 0
selectivity, mol % NpH MTs 1-MN H-DNMs 100 100
0.5 0.6
94.5 96.4
0 0
100 100
0.3 0.8
94.7 96.2
0 0 5.0 3.0
a IHP ) initial hydrogen pressure, THN ) tetralin, NpH ) naphthalene, MTs ) methyltetralins, 1-MN ) 1-methylnaphthalene, H-DNMs ) hydrogenated di(1-naphthyl)methanes.
Table 4. Additive Effect of Sulfur on Activated Carbon-Catalyzed Hydrocracking of DNMa selectivity, mol % temp., time, conv. °C S, g h % THN NpH MTs 1-MN H-DNMs 300 300 325 325 350 350 375 a
0.1 0.1 0.1 0.1 0.05 0.1 0.1
1 3 1 3 1 1 1
6.5 15.4 14.6 34.3 42.8 61.4 96.8
0.6 0.5 0.5 0.4 0.8 0.8 0.6
96.4 96.7 94.6 94.4 93.0 94.8 98.6
0.9 0.8 1.0 1.0 1.8 2.5 2.0
96.1 96.4 94.1 93.8 92.0 93.1 97.2
3.0 2.8 4.9 5.2 5.2 4.4 0.8
Activated carbon 0.1 g.
Table 2. Noncatalytic Reaction of DNM with Sulfur Addition for 1 ha temp., °C
IHP, MPa
conv., %
300 325 350 350 375
5 5 0 5 5
1.2 2.5 0 17.5 20.6
a
THN
selectivity, mol % NpH MTs 1-MN H-DNMs
0 0.2
99.0 98.6
0 0.3
99.0 98.5
1.0 1.2
0.6 0.5
93.2 97.5
1.5 1.8
92.3 96.2
6.2 2.0
Sulfur 0.1 g.
Table 3. Activated Carbon-Catalyzed Hydrocracking of DNM without Sulfur Additiona selectivity, mol % temp., IHP, time, conv., °C MPa h % THN NpH MTs 1-MN H-DNMs 300 300 325 325 350 350 350 375 a
5 5 5 5 0 1 5 5
1 3 1 3 1 1 1 1
2.8 7.5 6.0 16.0 0 15.6 24.5 71.5
0 0 0 0 0 0 0.3
100 100 100 97.0
0 0 0 1.0
100 100 100 96.0
0 0 0 3.0
95.4 98.0 98.5
0.5 1.0 2.2
95.0 97.0 96.6
4.6 2.0 1.2
Activated carbon 0.1 g.
tremely labile. Addition of hydrogen atoms to the ipsoposition of DNM should be the crucial step for DNM hydrocracking.7 Under elevated temperatures, sulfur added easily reacts with H2 to afford H2S.15-17 Relatively weaker H-SH bond (389 kJ/mol) than H-H bond (427 kJ/mol)18 makes hydrogen atoms form easier from H2S than from H2. As Table 2 shows, sulfur addition did not lead to DNM hydrocracking without H2. Therefore, the promotional effect of sulfur addition on DNM hydrocracking is closely related to the resulting H2S. Comparison of the data in Tables 1 to 3 shows that activated carbon promoted DNM hydrocracking much more remarkably than sulfur. As shown in Table 3, the addition of activated carbon did not result in DNM hydrocracking either without H2, and DNM conversion increased with increasing H2 pressure and reaction time. Adding sulfur to the activated carbon-catalyzed system further increased DNM conversion (Table 4). It is noteworthy that the increased DNM conversions are larger than DNM conversions in noncatalytic reaction with sulfur addition, suggesting sulfur added to the activated carbon-catalyzed system has a synergic effect on DNM hydrocracking. We call the difference as synergically increased DNM conversion. As shown in Figure 1, the synergically increased DNM conversion (15) Meyer, B. Chem. Rev. 1976, 76 (3), 367-387. (16) Thomas, M. G.; Padrick, T. D.; Stohl, F. V. Fuel 1982, 61 (6), 761-764. (17) Hei, R. D.; Sweeny, P. G.; Stenberg, V. I. Fuel 1986, 65 (4), 577-585. (18) Sondreal, E. A.; Wilson, W. G.; Stenberg, V. I. Fuel 1982, 61 (10), 925-937.
Figure 1. Synergically increased DNM conversions at different reaction temperatures (activated carbon 0.1 g, sulfur 0.1 g, IHP 5 MPa, 1 h).
increased significantly as the reaction temperature was raised from 300 °C to 350 °C but decreased rapidly with further increase in reaction temperature. Zhang et al.6 investigated activated carbon-catalyzed hydrogenation of anthracene. Their results indicate that the activated carbon was catalytically active for H2 dissociation. Keren et al.19 reported that pure carbon could split molecular hydrogen to the atomic form via hydrogen chemisorption. In addition, various carbon-based catalysts were reported by Grunewald and Drago to be both active and selective in the oxidative dehydrogenation of ethylbenzene to styrene20 and in the oxidative dehydrogenation and dehydration of several alcohols and aldehydes,21 suggesting the carbon-based catalysts catalyze hydrogen abstraction. On the basis of their suggestions and our investigation, we consider that the activated carbon catalyzed the dissociation of the resulting H2S, making hydrogen atoms form much more readily and hence facilitating DNM hydrocracking. In other words, the synergic effect of sulfur on activated carboncatalyzed hydrocracking of DNM can be ascribed to the catalysis of the activated carbon in H2S dissociation. Acknowledgment. This work was financially supported by National Natural Science Foundation of China (Projects 29676045). EF020105I (19) Keren, E.; Soffer, A. J. Catal. 1977, 50 (1), 47-53. (20) Grunewald, G. C.; Drago, R. S. J. Mol. Catal. 1990, 58 (2), 227233. (21) Grunewald, G. C.; Drago, R. S. J. Am. Chem. Soc. 1991, 113 (5), 1636-1639.
