Macromolecular structure and formation mechanism of raw coal in coal seam 11 of Wumuchang district, Inner Mongolia

Based on the results of proximate analysis, elemental analysis, ¹³C-NMR, FT-IR and XPS results, the structure model of the raw coal in coal seam 11 of Wumuchang district, Yimin Basin of Hulun Buir, Inner Mongolia was built using ACD/lab software. The ¹³C-NMR predicting software ACD/CNMR predictor was used to modify the structure. The macromolecule structure model which coincides with the nuclear magnetic resonance map is achieved. The characteristics of structures of macromolecules are as follows. Benzene, naphthalene, anthracene and phenanthrene are aromatic constitutional units, the quantities are 1, 2, 2, 1 respectively. Ether linkages, hydrogen aromatic rings and ortho methylene are bridges connecting aromatic units. Oxygen atoms exist in forms of phenolic hydroxyl groups, the quantities are 7, 3, 2 respectively. Nitrogen atoms exist in forms of pyridine and pyrrole. Methyl and short fatty chains are distributed in the edges of aromatic rings. The coal structure is compared with lignite in nearby mining area and Shendong long flame coal with similar metamorphic grade. In the environment of high temperature and low pressure, oxygen containing functional groups are lost rapidly in the process of thermal revolution, leading to the formation of short chain aliphatic groups. The environment of low pressure during thermal revolution is benefit with escape of micro molecules, leading to the aggregation of free radicals, so that large aromatic structure units are formed. However, due to the steric effect caused by the linear chain aliphatic groups, the orientation arrangement of aromatic structure units is not favored, leading to the phenomenon that the maturation of chemical components occurs before that of coal structure.