Molecular Representations of Jurassic-Aged Vitrinite-Rich and
Inertinite-Rich Coals in Northern Shannxi Province by
FTIR, XPS and 13C NMR
LI Huan-tong1, 2, ZHU Zhi-rong1, 2, QIAO Jun-wei1, 2, LI Ning3, YAO Zheng3, HAN Wei1, 2
1. College of Geology and Environment, Xi’an University of Science and Technology, Xi’an 710054, China
2. Shaanxi Provincial Key Laboratory of Geological Support for Coal Green Exploitation, Xi’an 710054, China
3. Shaanxi Institute of Geological Survey, Xi’an 710054, China
Abstract Jurassic high-quality coal resources provide the abundant material basis for clean and efficient coal utilization to oil and gas. Microlithotype composition of Jurassic high-quality coal resources is characterized by enrichment of inertinite. The macromolecular structure of vitrinite and inertinite largely determines coal’s physical and chemical properties and process performance, and then determines comprehensive utilization efficiency and added value of coal resources. Thus, raw coal (XR), vitrinite-rich coal (XV, NV) and inertinite-rich coal (XI, NI) samples were collected and prepared from Xiaobaodang and Ningtiaota coal mining area in the Jurassic coalfield of northern Shaanxi Province. Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and solid nuclear magnetic resonance spectroscopy (13C NMR) were used to quantitatively characterize the differences in molecular structures of different maceral enrichments combined with the results of coal quality analysis. The results showed that the aromatic ring substitution degree of aromatic structure in XI and NI coals is low, mainly in the form of three adjacent hydrogen atoms and four to five adjacent hydrogen atoms. Other functional groups less replace hydrogen atoms on benzene ring. At the same time, the vibration of aromaticC═C skeleton in the structure is obvious, and stretching vibration intensity of methylene in aliphatic structure is reduced. Methyl content is slightly higher than that of vitrinite-rich coals, and the relative content of theC═O group is slightly higher, indicating that inertinite-rich coal has more aromatic structures connected by oxygen-containing bridge bonds. Aliphatic chain and aliphatic ring groups fall off, fracture and aromatic enrichment, and branched-chain is relatively small, and the length is short. In addition aromatic carbon rate, aromaticity, aromatic condensation degree and maturity are high. The relative content of “C—C, C—H” and “C—O” in the surface structure of XV and NV coals is higher than that of inertinite-rich coals, which reflects that the structure should contain more aliphatic side chains replaced by aromatic rings. The oxygen species in the surface structure of XI and NI coals are mainly “C—O”, and “C═O” and “COO—” are significantly higher than those of vitrinite-rich coals. The aromatic carbon ratios of XV and XI coals are 57.91 % and 66.02 %, respectively. XV and XI coals’ aliphatic methyl carbon ratios are 10.02 % and 7.84 %, respectively. The protonated aromatic carbon is twice as much as the non-protonated aromatic carbon. The relative content of carbonyl and carboxyl carbon of XV coal is high. The ratios of bridge carbon and per carbon of XV and XI coals are 0.25 and 0.40, respectively. The average number of condensation rings of aromatic nucleus structure is 2.68 and 3.03, and the average sizes are 0.448 nm and 0.676 nm, respectively. The aromatic nucleus in the XI coal structure is mainly naphthalene and anthracene, and the branched-chain degrees are 0.22 and 0.19, respectively. It is indicated that XV has more aliphatic side chains and saturated ring structures than XI coal and has great hydrocarbon generation potential.
LI Huan-tong,ZHU Zhi-rong,QIAO Jun-wei, et al. Molecular Representations of Jurassic-Aged Vitrinite-Rich and
Inertinite-Rich Coals in Northern Shannxi Province by
FTIR, XPS and 13C NMR[J]. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2022, 42(08): 2624-2630.
