H₂O₂ oxidation of Xianfeng lignite and its thermal extraction residue

Thermal extraction of Xianfeng lignite (XL) with 1-methylnaphthalene (1-MN) was carried out at 320 ℃, and the H₂O₂ oxidation of the thermal extraction residue (TR) was compared with that of XL raw coal. The thermal extract (TE), TR and the oxidized residues were characterized by element analysis and FT-IR. The aqueous products from oxidation reaction were esterified and analyzed by GC/MS. The result shows that the yield of TR from XL in 1-MN is 81.01%. It indicates that XL is mainly composed of macromolecular structure cross-linked by covalent bond, with less low molecular compounds associated by non-covalent bond interactions. The TE is mainly composed of aliphatic hydrocarbons, carboxylic acid esters with less aromatic structures and hydroxyl group. GC/MS results suggest that the water-soluble products contained highest content of α, ω-dicarboxylic acids, especially malonic acid and succinic acid, with much amount of benzoic acid and tricarboxylic acids. The low molecular weight compounds associated in the macromolecular structure of raw coal can be easily oxidized under the conditions and more species of oxidation products are obtained. Compared with the structure of raw coal, the structure of TR is more regular. The oxidation of TR mainly occurs on the macromolecular structure cross-linked by covalent bond, resulting in the higher yield of oxidized residue and less species of water-soluble products from TR. The high yields of malonic acid and succinic acid in the water-soluble products suggest that -CH₂-and -CH₂-CH₂-are the main cross-linking bonds in the macromolecular network structure of XL.