Investigation on the macromolecular network structure of Xianfeng lignite by a new two-step depolymerization

Based on thermal extraction (TE) and mild oxidation, a new two-step depolymerization method was presented to investigate the macromolecular structure of Xianfeng lignite (XL). The TE of XL was carried out at 320 °C in 1-methylnaphthalene. The residue was oxidized with 5% H2O2 aqueous solution at 40 °C under normal nitrogen atmosphere for 4 h. Most of organic matter in XL was solubilized by the TE and subsequent oxidation. FTIR analysis reveals that the extract from the TE of XL is rich in aliphatic moieties and carbonyl groups but poor in aromatic rings and hydroxyl groups, whereas the residue is enriched in macromolecular aromatics. The mild oxidation introduced carbonyl groups into the macromolecular matrix of XL. The high yields of malonic acid and succinic acid and without benzene polycarboxlic acids from the residue oxidation suggest that –CH2– and –CH2CH2– are main bridged bonds between aromatic rings and benzene ring should be an important aromatic ring in XL.