Liquefaction reaction of coal: 1. Depolymerization of coal by cleavages of ether and methylene bridges

The roles of ether and methylene bridges in the depolymerization of coal have been re-evaluated on the basis of the results of a mild liquefaction reaction (400 °C, 30 min) and the distributions of oxygen and carbon atoms obtained by cross-polarization, magic angle spinning (CP/MAS) ¹³C n.m.r. spectrometry. Coals ranging from 66.2 to 87.4 wt% C (dmmf) were used as sample coals. The content of etheric oxygen was < 3.7 per 100 carbon atoms and the cleavage of ether bridges contributed to the formation of preasphaltene. The conversion to hexane solubles in the mild liquefaction reaction correlated well with CH₂ carbon content of coal, though the conversion to pyridine solubles did not. These results suggest that the formation of oil from preasphaltene is caused by the scission of CH₂ bridges and some naphthenic CH₂ bonds. The phenolic OH oxygen-rich portions in coal tended to remain as a residue formed by the condensation reaction of phenolic OH groups.