Hydrogen-transfer ability of extrographic fractions of coal-tar pitch

Coal-tar pitch was fractionated using extrography into classes of compounds of similar functionality and molecular weight. Hydrogen acceptor and donor abilities of the whole pitch and its extrographic fractions were evaluated by reaction at 360°C with tetralin and anthracene, respectively, and related to structural characteristics by elemental analysis, VPO, 1H NMR and HPLC. Hydrogen acceptor ability (HAA) of the fractions increases markedly with the elution depth. There is a good correlation between HAA and the total oxygen content in the fraction. On the other hand, all extrographic fractions show comparable relatively low hydrogen donor abilities (HDA) in the initial period of reaction with anthracene due to a similar content of hydroaromatic rings and methylene bridges. On further treatment, F2 and F4 are differentiated by a stronger HDA than other fractions. Among the fractions, only in F2 the hydrogen donor ability outweighs over hydrogen acceptor ability. The opposite situation is observed for F5, F6 and F7. In the case of F3 and F4, a comparable amount of hydrogen is transferred from tetralin to fraction and from fraction to anthracene. There is no straight correlation between the observed hydrogen transfer behaviour of fraction and its ability to develop an anisotropic texture in carbonization product. Possible contribution of various fractions to the creation of optical texture of pitch coke is discussed.