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Energy & Fuels 2001, 15, 128-134
Structural Characterization of High-Softening-Point Pitches By Oxidation with RuO4 A. Me´ndez,† J. Bermejo,† C. Blanco,† R. Santamarı´a,† I. Suelves,‡ and R. Mene´ndez*,† Instituto Nacional del Carbo´ n, CSIC, Ap. 73, 33080 Oviedo, Spain, and Department of Chemical Engineering and Chemical Technology, Imperial College, University of London, London SW7 2BY, U.K. Received June 30, 2000
Selective oxidation with RuO4 is used to detect differences in the molecular structure of two high-softening-point pitches obtained by the thermal treatment and air-blowing of a commercial impregnating pitch. The results of the characterization of the parent pitches and RuO4 oxidation products by chromatographic techniques have revealed differences in the condensation degree of the pitches. These differences are confirmed by the amount of CO2 evolved during the reaction, which also yields information about their reactivities.
Introduction Coal tar pitches are modified to improve their properties as precursors of special carbons, such as fibers,1,2 synthetic graphites,3 carbon-carbon composites,4,5 etc. The aim is to cause the polymerization of pitch components, in this way reducing the release of volatile substances on carbonization and increasing the density of the final carbon material. However, the polymerization of pitch components yields different molecular structures depending on the procedure used. From studies of the X-ray diffraction of pitches, TEM, and the optical structure of the cokes generated on pyrolysis, it is generally agreed that polymerization produced by thermal treatment in an inert atmosphere mainly results in planar macromolecules that are able to stack during pyrolysis, giving cokes with an optical texture of domains (10-60 µm) and flow domains (>60 µm). On the other hand, it is thought that the polymerization of pitches produced as a result of air-blowing not only generates planar macromolecules but also oligomers and other nonplanar structures in amounts which depend on the characteristics of the parent pitch6 and the experimental conditions of the air-blowing, i.e., temperature, time, and air-flow.7 The presence of nonplanar * Author to whom correspondence should be addressed. Fax 34 98 529 76 62. E-mail:
[email protected]. † Instituto Nacional del Carbo ´ n, CSIC. ‡ University of London. (1) Fritz, J. D.; Pennock, G. M.; Taylor, G. H. Carbon 1991, 29, 139164. (2) Zeng, S. M.; Maeda, T.; Mondori, J.; Tokumitsu, K.; Mochida, I. Carbon 1993, 31, 407-412. (3) Schmidt, J.; Moergenthaler, K. D.; Brehler, K.-P.; Arndt, J. Carbon 1998, 36, 1079-1084. (4) Savage, G. Chemistry Industry 1992, 525-529. (5) Mene´ndez, R.; Granda, M.; Ferna´ndez, J. J.; Figueiras, A.; Bermejo, J.; Bonhomme, J.; Belzunce, J. J. Microscopy 1997, 185, 146156. (6) Mene´ndez, R.; Fleurot, O.; Blanco, C.; Santamarı´a, R.; Bermejo, J.; Edie, D. Carbon 1998, 36, 973-979. (7) Ferna´ndez, A. L.; Granda, M.; Bermejo, J.; Mene´ndez, R. Carbon 2000, 38, 1315-1322.
molecules hinders molecular stacking on pyrolysis, leading to cokes with an optical texture of smaller size, such as domains, mosaics (
