Comprehensive evaluation of polycyclic aromatic units in three liquefaction-derived heavy fractions from Zhunnan lignite
2022
Liu, Guang-Hui | Gao, Yong | Li, Yan-Jun | Wang, Aimin | Fan, Xiao-Yong | Wei, Xian-Yong | Kang, Yu-Hong | Hao, Hua-Rui | Li, Zhan-Ku | Bai, Hong-Cun
The structural characteristics of polycyclic aromatic units in three liquefaction-derived heavy fractions from Zhunnan lignite, including thermal dissolution (TD) in cyclohexane (HFC), ethanolysis (HFE), and two-step sequential TD in cyclohexane-ethanol (HFCE), were investigated in depth. Combining multiple destructive tools, the intrinsic correlation among dissociated/degraded fragments and organic macromolecular networks, involving the types of alkyl side chain, methylene bridged bond, heteroatom, and aromatic nucleus, was also constructed. The results indicate that HFC with a smaller average molecular weight may be rich in -OH, >C-O-, and >CO units, while HFCE has higher aromaticity. In addition, abundant arenes and arenols were detected in the volatiles released from HFC flash pyrolysis, but macro/ultramolecular groups dominated in HFE and HFCE. Obviously, the differences in thermochemical reactions further confirmed that the component distribution of volatiles is mainly related to the direct gasification of small/medium molecules and the cleavage of weak/moderate strength covalent bonds. The analyses with quadrupole exactive orbitrap mass spectrometer and ruthenium ion-catalyzed oxidation show that HFC also contains abundant oxynitrides, while HFCE may be dominated by cata-condensed aromatics and polyaryl units, followed by few peri-condensed aromatics, long-chain saturated rings, aromatic rings with longer aliphatic side chains, and polymethylene linkage units. Comprehensive evaluation of these difficult-to-detect parts is beneficial to the resource and diversified utilization of such special soluble portions with potential environmental hazards.
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