Quantitative FTIR Characterization of Chemical Structures of Highly Metamorphic Coals in a Magma Contact Zone
TIAN Ze-qi1, WANG Zhi-yong1, YAO Jian-guo1, GUO Xu1, LI Hong-dou1, GUO Wen-mu1, SHI Zhi-xiang2, ZHAO Cun-liang1, LIU Bang-jun1*
1. School of Earth Science and Engineering, Hebei University of Engineering, Key Laboratory of Resource Exploration Research of Hebei Province, Handan 056038, China
2. School of Resources and Geosciences, China University of Mining and Technology, Xuzhou 221116, China
Abstract:To study the influence of magmatic intrusion on coal chemical structural, the chemical structures of four highly metamorphic coals in the magmatic contact zone in the Yunjialing coal mine in the Hanxing mining area were characterized using Fourier Transform Infrared Spectroscopy. The results showed that the aromatic structures of all samples were dominated by tri-substituted benzene rings, and the highest proportion was 67.4% observed in the parting; the farther away from the intrusive body, the lower the tri-substituted contents of benzene rings, the di-substituted contents of benzene rings gradually increase, whereas the content of the benzene ring tera-substituted and penta-substituted both show a law of increase firstly and then decrease. In terms of oxygen-containing groups, the farther away from the intrusive body, the more active aromatic esters and carboxyl groups, while the C-O content in phenol changes less and the content of alkyl ethers and aryl ethers decreases. The proportion of C C stretching vibration in the aromatic or condensed ring gradually increases. Due to the influence of magmatic intrusion, the content of fatty substances in the sample is very low. The farther away from the intrusive body, the proportion of symmetric and antisymmetric stretching vibrations of methyl groups first increases and then decreases, and the variation rule of methylene symmetry and methylene antisymmetric stretching vibration is opposite to that of the methyl group. In terms of hydroxyl groups, hydroxyl self-association hydrogen bonds are the main type of hydrogen bonds in coal samples, while in the parting, hydrogen bonds formed by hydroxyl and ether oxygen are the main types. With the deepening of magmatic intrusion, the latter gradually decreased in coal samples. The farther away from the intrusive body, the lower the hydrogen bond content formed by hydroxyl-π hydrogen bonds, the rule of the hydroxyl-N hydrogen bond content first increases and then decreases. The results show that magmatic intrusion has a dramatic impact on the chemical structure of organic matter in coal, and has a differential impact on the chemical structure of organic matter in coal and parting. The results will provide theoretical guidance for exploring the evolution mechanism of the macromolecular structure of highly metamorphic coal.
Key words:Highly metamorphic coal; FTIR; Magmatic intrusion; Chemical structure