Studies on the bond cleavage reactions of coal molecules and coal model compounds

Cleavage reactions of chemical bonds connecting aromatic clusters in coal were investigated. We conducted the heat-treatment of coals and coal model compounds in the presence of a hydrogen donor at 380–420°C for 5–60 min in a sealed tube, respectively. As hydrogen donors, 9,10-dihydroanthracene (DHA) and 9,10-dihydrophenanthrene (DHP) were used. In the reaction of coal with hydrogen donor at 420°C for 5 min, a larger amount of hydrogen was consumed with DHP than with DHA. Bond cleavage reactions using model compounds showed that the yields of homolytically cleaved products were higher than those of ipso position cleaved products, this being reasonable in terms of their bond energies. On the other hand, ipso position cleavage reaction was preferable in the presence of DHP. This indicates that ipso position cleavage reaction makes an important contribution to the reaction of coal with DHP at relatively higher temperature. Since the model compounds having a dimethylene bridge are considered to represent polymethylene bridge bonds, monomethylene linkage connecting two aromatic clusters is concluded to be a significant bridge bond, which governs the coal reactivity.