Structural Features of Extraction Residues from Supercritical Methanolysis of Two Chinese Lignites

The methanol-insoluble portions from supercritical methanolysis of Shengli lignite (SL) and Huolinguole lignite (HL) were extracted with an isometric carbon disulfide/acetone mixed solvent under ultrasonic irradiation to afford extracts and extraction residues (ERs). The ERs were subjected to ruthenium-ion-catalyzed oxidation, and soluble portions were separated from the reaction mixture and esterified. The resulting products were analyzed with a gas chromatography/mass spectrometer and atmospheric solids analysis probe/time-of-flight mass spectrometer to reveal structural features of heavy species in the two lignites. The results show that the ER from SL is richer in highly condensed aromatic species than that from HL, while both ERs have the same carbon number range (C₉–C₂₄) of alkyl groups with the highest content at C₁₅ on aromatic rings and the same distribution of alkylene bridges (C₂–C₂₀) connecting aromatic rings with a higher abundance of shorter linkages than that of longer linkages