Mass Spectrometric Evaluation of the Catalytic Deoxygenation of Soluble Organic Matter in Xiaolongtan Lignite

Abstract

The organic matter in Xiaolongtan lignite was thermally dissolved by cyclohexane, methanol and isopropanol (2-propanol) in sequence to obtain thermal dissolution (TD) extracts. Co-Mo/γ-Al2O3 was used as the catalyst for the catalytic hydrogenation of TD extracts to remove oxygen. Both TD extracts and the corresponding catalytic products were analyzed by the combination of gas chromatography/mass spectrometry (GC/MS) and Orbitrap MS to reveal more molecular details. GC/MS analysis shows that cyclohexane can extract low polar organic matter in coal, while methanol and isopropanol as nucleophilic reagents can break C-O bonds in coal, thus removing oxygen. Catalyst can trigger the fracture of alkyl chains and the activation of H2, thus promoting the removal of oxygen atom and the generation of aromatics. Double bond equivalent (DBE) value and carbon number (CN) were obtained through Orbitrap MS data. The decrease of both DBE and CN after catalytic conversion indicates the breaking of bridged bonds. The introduction of various MS systems provides an effective analytical tool for studying the catalytic deoxidation of lignite, thereby guiding the conversion of lignite to clean liquid fuels and high value-added chemicals. Co-Mo/ γ- Al2O3 catalysts activates H2 to H⋯H, which further splits into H+ and H−. H⋯H deoxygenates by hydrogenating C=C bond, attacking C-O bond or directly attacking oxygen atom. H+ will preferentially attack oxygen atom with high electronegativity, and break Cal-O bridge bond to achieve deoxygenation, thus reducing the relative abundance of oxygen containing compounds.