Oxidative depolymerization of Shenfu subbituminous coal and its thermal dissolution insoluble fraction

The oxidative depolymerizations of Shenfu subbituminous coal (SSBC) and its thermal dissolution insoluble (TDI), which obtained by thermal dissolution (TD) in 1-methylnaphthalene at 320 °C, were investigated with H2O2 aqueous solution as oxidant under different conditions. Their products were characterized by FTIR, ultimate analyses and acidic functional groups determination. Further, the detailed comparison of oxidative depolymerizations of SSBC and its TDI was carried out with 20% H2O2 at 60 °C. The water solubles (WSs) were esterified, and subsequently analyzed by GC/MS in order to understand the macromolecular structural features of SSBC. The results revealed that compared with SSBC, the TDI contained more phenolic hydroxyls and showed higher oxidation reactivity. It suggested that the phenolic hydroxyl should be the active site of oxidative depolymerization, and thermal dissolution generated substantial phenolic hydroxyls in TDI by the rupture of Cal-OAr. The WS from the oxidation of SSBC mainly consists of monocyclic aromatic acids, while the WS from TDI contains much amount of alkanoic acids and α,ω-dicarboxylic acids. Especially the substantial oxalic acid and malonic acid identified in the WS from TDI suggested that significant amount of the aromatic rings in the macromolecules of SSBC could be coupled directly or connected by monomethylene bridge.