Molecular characterization of methanolysis products from Xinjiang tar-rich coal by GC–MS and ESI Orbitrap MS

Methanolysis enables high-value chemical extraction from coal, and molecular characterization of tar-rich coal methanolysates supports process optimization and clean coal utilization. In this study, the molecular composition of methanolysates from a Xinjiang tar-rich coal at 260 °C and 340 °C was characterized in detail by gas chromatography-mass spectrometry (GC–MS) and electrospray ionization Orbitrap mass spectrometry (ESI Orbitrap MS). AgNO 3 -modified silica gel column chromatography was used to fractionate the extracts into a saturated hydrocarbon fraction and a DCM-eluted fraction containing esters and aromatic hydrocarbons. Soluble product yield rises from 8.5% at 260 °C to 19.5% at 340 °C, the methanolysates exhibited a high oxygen content (ca. 10 wt%). GC–MS results showed that a broad distribution of n-alkanes in the methanolysates. At 260 °C, fatty acid methyl esters were identified as the primary products, whereas phenolic compounds emerged the major components at 340 °C. The phenolic distribution of 340MP was characterized by relatively high abundances of C3-, C4-, and C5-alkylphenols, showing a shift toward more highly alkyl-substituted homologues compared with representative literature-reported coal-tar phenolic distributions. ESI Orbitrap MS confirms O1-O4 oxygenated species as dominant, with O1 phenols most abundant at 340 °C. The acidic oxygen functionalities included mono- and poly-hydric phenols and carboxylic acids, etc. Basic nitrogen compounds detected in positive-ion mode showed a wide range of double bond equivalent (DBE) and carbon number. This work provides a molecular-level basis for the methanolysis of tar-rich coal to produce high-value phenolic chemicals, and the results offer important molecular information for understanding the chemical composition of tar-rich coals.