Energy & Fuels 1993, 7, 362-366
362
Estimation of Hydrogen Mobility in Coal Using a Tritium Tracer Method. Hydrogen Exchange Reactions of Coals with Tritiated Water and Molecular Hydrogen Atsushi Ishihara, Hisao Takaoka, Eri Nakajima, Yuko Imai, and Toshiaki Kabe* Department of Chemical Engineering, Faculty of Technology, Tokyo University of Agriculture and Technology, Nakamachi, Koganei, Tokyo 184, Japan Received September 18, 1992. Revised Manuscript Received January 29, 1993
The reactions of coals with tritiated water and molecular hydrogen without solvent were investigated under the coal liquefaction conditions to estimate the mobility of hydrogen in coals. In the reactions of Wandoan and Datong coal with tritiated water, the hydrogen exchange ratios (HERS) of coals increased with a rise in temperature and reach 40 and 33%, respectively, even at 300 "C and 120 min. On the contrary, in the reactions of same coals with tritiated molecular hydrogen in the absence of solvent, the HERS of coals were 7.1 and 4.6% (300 OC, 120 min), respectively, much lower than that with water. HER in the reactions of coals with molecular hydrogen remarkably increased with a rise from 300 to 400 "C, while HER in the reactions of coals with water did not change largely. The results suggested that the reaction mechanism with water was quite different from that of molecular hydrogen and that the hydrogens attached to aromatic carbons in coal were able to exchange with water even at 300 "C. The result was confirmed by the model reactions of phenol, 1-naphthol, and 1,5-dihydroxynaphthalenewith water.
Introduction The reactions in coal liquefaction include hydrocracking and hydrogenation by gaseous hydrogen and donor solvents. In order to elucidate mechanisms of coal liquefaction, it is necessary to estimate the hydrogen transfer in the reactions of coals with several hydrogen sources quantitatively. A number of attempts have been made to investigate those reactivities by using deuterium tracer, NMR, and MS methods.14 Deuterium sources in most of these studies were deuterium oxide, molecular deuterium, and deuterated donor solvents. Fu and Blaustein conducted the reaction of coal with deuterium oxide under microwave irradiation.' Schweighardt et al. reported the reaction of coal with deuterium gas and the analysis of coal products by deuterium nuclear magnetic resonance spectroscopy(2HNMR).2 Cronauer et al. used deuterated tetralin (tetralin-d4 and -dlz) in coal liq~efaction.~ Wilson et al. also studied the reaction of coal with deuterium gas.4 Further, Skowronskiet al. performed coal liquefaction by use of both deuterium gas and deuterated tetralin to investigate the hydrogen incorporation into c o d 5 King and Stock studied the exchange of hydrogen and deuterium atoms between coal and tetralin-dl2 and naphthalene-dse6 Because of the poor solubility of a part of coal products and the difficulty of quantification of the deuterium tracer, however, there were few examples which enable the quantitative analysis of the hydrogen mobility in coal. Recently, we have reported that tritium and carbon-14 tracer techniques were effective to trace the hydrogen (1)Fu, Y. C.; Blaustein, B. D. Chem. Ind. 1967, 1257.
(2) Schweighardt, F. K.; Bockrath, B. C.; Friedel, R. A.; Retkofsky, H.
L.Anal. Chem. 1976,48,
1254.
(3) Cronauer, D. C.; Mcneil, R. I.; Young, D. C.; Ruberto, R. G. Fuel 1982, 61, 610. (4) Wilson, M. A.; Vassalo, A. M.; Collin, P. J. Fuel Process. Technol. 1984,8, 213. (5) Skowronski, R. P.; Ratto, J. J.; Goldberg, I. B.; Heredy, L. A. Fuel 1984, 63, 440. (6)King, H. H.; Stock, L. M. Fuel 1982, 61, 257.
quantitatively in the coal liquefa~tion.~-~ In these works, we have performed the reactions of coals with tritiated tetralin7and tritiated molecular hydrogen8and the reaction of tetralin with tritiated molecular hydrogengwhere the hydrogen exchange reactions between coal and gas phase and solvent as well as the hydrogen addition were estimated quantitatively. In our course of study, we investigated the reaction of coal with tritiated water, which can be regarded as a proton donor rather than a hydrogen atom, to estimate the reactivity of hydrogen in coal. We report here the hydrogen exchange reaction of hydrogen attached to aromatics in coal with tritiated water under coal liquefaction conditions. We also investigate the reactions of aromatic compounds having hydroxyl groups such as phenol, 1-naphthol, and 1,5-dihydroxynaphthalenewith tritiated water. Further, the reaction of coal with molecular hydrogen in the absence of solvent is compared with that of water.
Experimental Section Materials. The samples of Wandoan and Datong coals were ground to 100%
