Energy & Fuels 2002, 16, 1483-1489
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Elucidation of Hydrogen Mobility in Coal Using a Fixed Bed Flow Reactor -Hydrogen Transfer Reaction between Tritiated Hydrogen, Coal, and TetralinAtsushi Ishihara,* I. Putu Sutrisna, Masahiro Ifuku, Eika Weihua Qian, and Toshiaki Kabe Department of Chemical Engineering, Tokyo University of Agriculture and Technology, Nakacho, Koganei, Tokyo 184-8588, Japan Received March 28, 2002
Hydrogen transfer reactions of coal with tritiated gaseous hydrogen in the presence of tetralin were performed using a flow reactor under the following conditions: pressure 50 kg/cm2, temperature 200-400 °C, and reaction time 120-420 min. When Wandoan coal (WA) was used as a coal sample, functional groups participated in the hydrogen transfer reaction even at 200 °C and then decomposed at 250 °C. At 300 °C, ether bonds were cleaved to generate hydroxy groups which were decomposed at 350 °C. When the higher rank Pocahontas coal (POC) was used, functional groups participated in the hydrogen transfer reaction even at 250 °C and then decomposed at 300 °C. Further, ether bonds were cleaved at 350 °C to generate hydroxy groups which were decomposed at 400 °C. These results showed that in the case of POC coal, a 50 °C higher temperature was needed to obtain functional group behavior similar to the case of WA coal.
1. Introduction Coal liquefaction includes coal conversion through hydrogenolysis and hydrogen addition where hydrogen atoms in gaseous hydrogen and solvent are introduced into coal. In such a reaction, the elucidation of the mobility of hydrogen in coal is quite important. Hydrogen transfer reactions were investigated by many researchers.1-3 Larsen et al. reported interesting results where the diffusion effects of donor solvents on coal conversion was absent.1 They used 2-tert-butyltetralin which is expected to have little effect on the hydrogendonating ability of the tetralin but is expected to significantly reduce its diffusion into coal. Coal conversions to pyridine extractables and the amount of hydrogen transferred from the donor are essentially the same for both tetralin and 2-tert-butyltetralin, demonstrating that diffusion of the hydrogen donor does not play a significant role in conversion of coal. The results showed the possibility that hydrogen atoms can readily move to the radicals generated in coal. Buchanan et al. have also demonstrated the ready mobility of hydrogen atoms in anchored systems.2 In this atom-hopping radical relay mechanism, hydrogen may move from an external donor to a radical site. Further, Malhotra and McMillen reported the implications of the solventmediated hydrogenolysis picture for coal liquefaction.3 They showed that polycyclic aromatic hydrocarbons * Corresponding author. Tel & Fax: 81-42-388-7228. E-mail:
[email protected]. (1) Larsen, J. W.; Amui, J. Energy Fuels 1994, 8, 513. (2) Buchanan, A. C., III; Britt, P. F.; Thomas, K. B.; Biggs, C. A. J. Am. Chem. Soc. 1996, 118, 2182. (3) Malhotra, R.; McMillen, D. F. Energy Fuels 1993, 7, 227.
mediated hydrogen transfer to promote the coal conversion in coal liquefaction. We have already reported that the tritium tracer method is very effective for estimating the reactivity of hydrogen in coal and coal-related compounds during coal liquefaction.4,5 In previous studies, the reactions were performed in a batch-type reactor. To estimate the conversion of coal and the mobility of hydrogen in coal, a flow reactor has some advantages because it can control reaction temperature exactly. However, there are few approaches using the flow reactor to estimate the mobility of hydrogen in coal.6,7 Bockrath et al. performed a similar hydrogen-deuterium exchange reaction using the mixture of a coal and a catalyst packed into a flow reactor.7 Although only hydrogen-deuterium exchange on the catalyst was discussed, the deuteration of coal was not described in this reaction. In the present study, liquefaction of coal with gaseous hydrogen in the presence of tetralin was performed. Gaseous hydrogen was labeled by a radioisotope tritium. Radioactivity in products was traced to determine the hydrogen transfer between gaseous hydrogen, coal, and tetralin. Further the reaction of tritiated coal, which is obtained after the reaction, with water was performed (4) (a) Ishihara, A.; Takaoka, H.; Nakajima, E.; Kabe, T.; et al. Energy Fuels 1993, 7, 362. (b) Qian, W.; Ishihara, A.; Fujimura, H.; Saito, M.; Godo, M.; Kabe, T. Energy Fuels 1997, 11, 1288. (c) Werstiuk, N. K.; Ju, C. Can. J. Chem. 1989, 67, 812. (5) Ishihara, A.; Morita, S.; Kabe, T. Fuel 1995, 74, 63. (6) (a) Ishihara, A.; Nishigori, D.; Saito, M.; Qian, W.; Kabe, T. Energy Fuels 2000, 14, 706; (b) Kabe, T.; Saito, M.; Qian, W.; Ishihara, A. Fuel 2000, 79, 311; (c) Sutrisna, I. P.; Ishihara, A.; Qian, W.; Kabe, T. Energy Fuels 2001, 15, 1129. (7) Bockrath, B. C.; Finseth, D. H.; Hough, M. R. Fuel 1992, 71, 767.
10.1021/ef020078w CCC: $22.00 © 2002 American Chemical Society Published on Web 10/03/2002
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Energy & Fuels, Vol. 16, No. 6, 2002
Figure 1. Schematic diagram of experimental apparatus.
to estimate the behavior of functional groups during the liquefaction. 2. Experimental Section 2.1. Materials. An Argonne Premium Coal Sample Pocahontas No. 3 (POC; C 91.05, H 4.44, N 1.33, S 0.50, O 2.68 (% daf)) was obtained in 5 g ampules (
