Insight into the structural features of macromolecular aromatic species in Huolinguole lignite through ruthenium ion-catalyzed oxidation

Ruthenium ion-catalyzed oxidation (RICO) of Huolinguole lignite (HL) was performed to understand the structural features of macromolecular aromatic species in HL by analyzing the resulting soluble species (SSs) with a gas chromatography/mass spectrometer and atmospheric-pressure solids-analysis probe/time of flight-mass spectrometer. The results show that in the SSs, alkanedioic acids are predominantly abundant and most of them are succinic acid and glutaric acid, indicating that HL is rich in bridged linkages (BLs) and CH2CH2 and CH2CH2CH2 are the main BLs connecting aromatic rings. The total yield of benzenecarboxylic acids with less carboxylic groups (CGs) (the number of CGs <4) is significantly higher than that with more CGs (the number of CGs ⩾4) and small amounts of biphenylpolycarboxylic acids and phenylnaphthalenepolycarboxylic acids were produced from RICO of HL, suggesting that highly condensed aromatics are not predominant and some of them contain biphenyl and phenylnaphthalene skeleton structures.