Investigation on the structural feature of Shengli lignite

The extraction residue from Shengli lignite was sequentially dissolved in cyclohexane, benzene, methanol, ethanol, and isopropanol in an autoclave at 320 °C to afford soluble portions (SPs) 1–5 (SP₁-SP₅) and the final residue (FR). The total yield of SP₁-SP₅ is ca. 55.1%. The FR was subjected to ruthenium ion-catalyzed oxidation and the resulting products were isolated from the reaction mixture and esterified. Both the esterified products and SP₁-SP₅ were analyzed with a gas chromatograph/mass spectrometer. In total, 342 compounds were identified in SP₁-SP₅. They can be classified into normal alkanes, branched alkanes, alkenes, alkanedienes, arenes, alkanols, methylcycloalkanes, alkenols, alkylbenzenemethanols, arenols, anisol and substituted anisols, polymethyldihydrobenzofurans, arenofurans, dibenzofurans, ethoxymethylbenzenes, aldehydes, ketones, esters, nitrogen-containing organic compounds, sulfur-containing organic compounds, and other compounds. Among the compounds, arenols are predominant in SP₁ and SP₂ and the main compounds in SP₃, while the main compounds in SP₄ and SP₅ are esters and arenes, respectively. According to the esterified products identified, the products from the FR oxidation can be grouped into non-benzene ring carboxylic acids (NBCAs) and benzenepolycarboxylic acids (BPCAs). The total yield of BPCAs is much higher than that of NBCAs, suggesting that the FR is rich in condensed aromatic moieties.