Molecular structure, bond cleavage and their relation of four low rank coals

Four demineralized low-rank coals (NMH, ZC, ZD, and DLT, in the order of volatile content on daf basis) were characterized by 13C NMR, with deep analysis on the side chains, bridges between aromatic clusters, and the oxygen form. Bond cleavage of the coals were measured by reaction with an excessive amount of hydrogen donor solvent, and the gas and liquid products were quantified by GC and discussed from the viewpoint of molecular structure. About all the alkyl substituent in NMH, half in ZC and a quarter in ZD and DLT are in side chain. The bridge-substitute degree is 13.0% for NMH and 25.3% for ZC. Almost all the bridges in NMH and half in ZD contain ArO structure. NMH contains the most oxygen (22.18 wt%) and ZC contains the least oxygen (8.44 wt%). The oxygen in ZD (16.93 wt%) is dominated by aryl ester group with some aldehyde/ketone and a little carboxyl group. The amount of bond cleaved follows the order of NMH > DLT ≅ ZD > ZC at 380-420 °C. More aryl-ether bond results in more large-size fragments, and the amount of large-size fragments follows the order of NMH > ZC > DLT > ZD.