A three-step dissociation method for converting Xiaolongtan lignite into soluble organic compounds: Insights into chemicals, geochemical clues, and structural characteristics

摘要

Converting lignite into soluble organic compounds (SOCs) under mild conditions is significant for both evaluating molecular structure and producing clean fuels/chemicals. A three-step dissociation, i.e., sequential extraction, sequential thermal dissolution (TD), and ruthenium-ion-catalyzed oxidation (RICO), was adopted to convert the organic matter (OM) in Xiaolongtan lignite (XL) into SOCs. The perspectives on chemicals, geo-chemical information, and structural characteristics of XL were evaluated based on the molecular compositions of SOCs. Much higher yields of SOCs were obtained from TD than from extraction, which could be attributed to the thermal dissociation of non-covalent interactions in XL. Normal alkanes, alkyl-substituted benzenes, alkyl substituted phenols, ketones, and aliphatic esters are the main group components released from TD. A series of important biomarkers were released and their distributions and evolution pathways during XL-forming process imply that higher terrestrial plants could be the main input of the OM in XL. Benzenecarboxylic acids were produced from TD residue in high selectivity via the RICO. According to the results from the RICO, the insoluble macromolecular structures in XL are rich in peri-condensed aromatics along with some cata-condensed aromatics and polyaryls, and -CH3 is the major alkyl side chain on the aromatic rings. Adjacent aromatic moieties are mainly connected each other directly by C-ar-C-ar bridged bonds.