Variation characteristics of macromolecular structures during biogas production process of Ulan coal
To elucidate the structural characteristics of coal macromolecules and their changes during the biogas production process,lignite from the Ulan Tuhugai mine area in Xilin Gol League,Inner Mongolia,was selected for biogas production experiments.The structural evolution characteristics were studied through 13C-NMR,ultimate analysis,and X-ray photoelectron spectros-copy(XPS).The results show that the aromatic structural units of the original Ulan coal sample con-sist of 3 benzene rings,3 naphthalene rings,1 anthracene ring,and 3 pyrroles,with a total of 129 carbon atoms.After the biogas production action of microorganisms,the total number of carbon atoms decrease by 21,of which the number of aromatic carbons decrease by 4,and the aliphatic car-bons decrease by 17.The original Ulan coal sample's macromolecular structure contains 55 aliphatic carbon atoms.After the biogas production ended,the number of aliphatic carbon decreases by 21.8%,the number of methylene carbon decreases by 25%,the number of methylidene carbon and quaternary carbon decreases by 16.7%,and the number of oxygenated aliphatic carbon and methyl carbon decreases by 14.3%and 33.3%,respectively.Stage analysis of the macromolecular structure of Ulan coal samples indicates that the detachment of the aromatic structural basic units and side chains of coal macromolecules mainly occurs during the hydrolysis stage.In the later methane produc-tion stage,the structural transformation of coal basically stops,relying only on the substances that have already detached into the reaction liquid to participate in biochemical reactions.It is confirmed that during the biogas production process,the transformation of coal macromolecular structure towards a higher degree of aromatization is a significant trend.
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