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Characterization of the Oxygenated Chemicals Produced from Supercritical Methanolysis of Modified Lignites

Liu, Fang-Jing, Wei, Xian-Yong, Zong, Zhi-Min, Fan, Maohong
Energy & Fuels 2016 v.30 no.4 pp. 2636-2646
Fourier transform infrared spectroscopy, acids, aromatic compounds, carbon, feedstocks, gas chromatography-mass spectrometry, hydrogen bonding, ionization, lignite, methanolysis, nuclear magnetic resonance spectroscopy, spectrometers, stable isotopes, ultrasonics, value added
Lignites are promising as feedstocks for producing value-added oxygenated chemicals (OCs) due to their high contents of oxygen-containing organic species. Two modified lignites were produced from Xiaolongtan lignite and Shengli lignite via sequential ultrasonic extraction and subsequent supercritical methanolysis to produce OCs. Solid-state ¹³C nuclear magnetic resonance analysis reveals the differences in carbon skeleton structures and oxygen-functional groups between the two modified lignites. The molecular compositions of OCs from the methanolysis were characterized with Fourier transform infrared spectrometer (FTIRS), gas chromatograph/mass spectrometer (GC/MS), and negative-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometer (ESI FTICRMS). Six types of hydrogen bonds and distribution of >CO groups in the OCs were analyzed with FTIRS. Alkylphenols with C₁−C₆ in alkyl group(s) dominate in the GC/MS-detectable organic species and methyl is the major alkyl group. The analysis with high-resolution negative-ion ESI FTICRMS reveals higher-molecular, less volatile, and polar OCs, which are assigned to O₁–O₇ class species, detection of which is difficult with GC/MS. Among the O₁–O₇ class species, O₁–O₃ classes are predominant with double bond equivalent values of 1–17 and carbon numbers of 10–38. They could be acidic OCs, such as arenols, arenediols, alkoxyarenols, and/or arenecarboxylic acids with 1–5 aromatic rings and different alkyl groups, as well as some aliphatic acids. The combination of various advanced analytical techniques should be an ideal approach for characterizing valuable OCs in complex coal-derived liquids.