1. Department of Earth Science & Engineering, Taiyuan University of Technology, Taiyuan 030024, China
2. Shanxi Key Laboratory of Coal and Coal-Measure Gas Geology, Taiyuan 030024, China
3. State Key Laboratory of Coal and CBM Co-Mining，Jincheng 048000, China
4. Shanxi Coalbed Methane Exploration and Development Branch, PetroChina Co., Ltd., Jincheng 048000, China
Abstract：The change of chemical structure of coals with different rank is of great significance to the study of macromolecular structure evolution in coal. The chemical structures of Hequ candle coal, Liulin coking coal and Jincheng anthracite coal are characterized by means of fourier transform infrared spectroscopy. From the four parts of the infrared spectrum, each part has undergone certain changes. In the aromatic structure, the Hequ coal has five peaks, and the Liulin coal is reduced to three peaks, and then the Jincheng coal is increased to five peaks. In the oxygen-containing functional group, as the coal rank increases, the peak area of the wave number between 1 100 and 1 350 cm-1 gradually decreases. And peaks tend to be flatter which indicates that coalification is a process of being carbon-rich and deoxidized. In aliphatic hydrocarbons, in the spectrum, the shoulder number of the wave number near 2 952 cm-1 is widened, which shows an increase in the content of methyl groups. The peak shape near the wave number of 2 895 cm-1 gradually slows down, indicating that the content of methine is decreased. In the range of hydrogen bonding, with the increase of coal rank, the spectrum becomes slower and then steeper, and the wave number is more prominent around 3 400 cm-1, indicating that the content of self-associated hydroxyl groups in coal decreases first and then increases. The peak spectrum of the obtained infrared spectrum is fitted and attributed by origin7.5 software. The results show that the substitution of benzene ring is mainly based on tri-substituted, with the deepening of the coal rank, the content of benzene ring tri- or tetra-substituted decreases, and the content of di- and penta-substituted increases; in which the content of the tri-substituted benzene ring is reduced from 63% to 32%, and the content of the benzene ring tetra-substituted is reduced from 17.21% to 12.86%, however, the percentage of di-substituted is from 12.36% to 24.44%, and the percentage of penta-substituted is increased from 6.55% to 26.58%. The ash content in the infrared attribution is higher, and the ash percentage in the industrial analysis is also higher. As the degree of coalification increases, the proportion of the carbon-oxygen single bond decreases from 37.22% to 27.83%. The carbon-carbon double bond content increases from 31.02% to 36.86%, and then decreases to 25.42%, and the carbon-oxygen double bond content changes slightly, from 13.07% to 13.02%, and then increases to 13.81%. In the aliphatic hydrocarbons, with the deepening of the coal rank, the percentage of the methyl symmetric stretching vibration is 11.67%, 11.81% and 12.92% respectively. The percentage of the methyl anti-symmetric stretching vibration is 18.74%, 18.94%, 24.76%, and the methyl content increases. However, the proportion of stretching vibration of methine decreases from 17.38% to 12.53%, and finally decreases to 11.57%. The content of methine decreases. The proportion of methylene symmetric stretching vibration is 18.09%, 18.14% and 15.43% respectively, the proportion of methylene anti-symmetric stretching vibration is 34.41%, 38.58% and 35.32% respectively, and the content of methylene first increases and then decreases. In addition, the hydroxyl-N hydrogen bond is present in the Hequ coal and the Liulin coal, while there is no such hydrogen bond in Jincheng coal, the lower the coal rank, the higher the percentage content, the ring-associated hydrogen bond is reduced from 19.03% to 12.71%, the hydroxyl-ether hydrogen bond is reduced from 27.20% to 16.89%, which is that the content of oxygen-containing functional groups such as carboxylic acid and hydroxyl group in the lower rank coal is higher. The self-associated hydroxyl content decreases from 39.63% to 34.78% and then increases to 37.88%. The content of hydroxy-π hydrogen bond increases from 9.84% to 27.77%. These changes reveal that coalification is a complex evolutionary process of being carbon-rich, dehydrogenation, deoxygenation, and removal of heteroatoms. The research results have reference significance for exploring the evolution characteristics and control mechanism of coal macromolecular structure.
Key words：Coal; FTIR; Chemical structure; Degree of coalification
郝盼云，孟艳军，曾凡桂，闫涛滔，徐光波. 红外光谱定量研究不同煤阶煤的化学结构[J]. 光谱学与光谱分析, 2020, 40(03): 787-792.
HAO Pan-yun, MENG Yan-jun, ZENG Fan-gui, YAN Tao-tao, XU Guang-bo. Quantitative Study of Chemical Structures of Different Rank Coals Based on Infrared Spectroscopy. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2020, 40(03): 787-792.
