Li Xueping, Zeng Qiang
College of Resource and Environmental Sciences, Xinjiang University, Urumqi, 830046, China.
Institute of Arid Ecology and Environment, Xinjiang University, Urumqi, 830046, China.
Sci Rep. 2022 Mar 23;12(1):4994. doi: 10.1038/s41598-022-09113-z.
Understanding the change in coal structure during heat treatment is the basis of efficient and clean utilization of coal. In this study, high-resolution transmission electron microscopy (HRTEM) was used to analyse the changes in the aggregate structure and ultramicropores of Zhungdong coal samples (Xinjiang, China) that were heated from ambient temperature to 800 °C respectively. Then, the relationship between their HRTEM characteristics and the corresponding reaction activation energy were also analyzed. The results show that the length, curvature, order, layer spacing and stacking height of the aromatic layers of the coal sample vary with an increasing temperature, and are related to the activation energy of the reaction. As the temperature reaches 300 °C, the HRTEM characteristics of the heated coal samples are obviously different from those of the raw coal sample. It is shown that the length of lattice fringes is in the range of 0.3-1.15 nm which accounts for approximately 95% of the total number of fringes. The overall orientation of lattice fringes is not good, but there are two main directions. After heating, the number of naphthalenes in the coal samples decreased, while the number of larger aromatic layers increased. The distance between the aromatic layers of the coal sample decreased with an increasing stacking height, the order of the aromatic layers was enhanced, and the number of aromatic sheets with a larger curvature increased. The coal ultramicropores are mainly concentrated from 0.4 to 0.7 nm. Heat treatment reduces the total number of ultramicropores, but the maximum number of pores is increased. The non-six-membered ring and lattice defects lead to the bending of the fringes, the distribution of fatty structures affects the orientation of the fringes, and the relationship between the pore and molecular structure does not exist independently. After heat treatment, the aggregate structure and ultramicropore size of coal have a high correlation with the activation energy. The activation energy is closely related to the 0.6 nmultramicropores. However, the current experiment could not explain the underlying causes of these relationships. The aggregated state in coal is the macromolecular group formed between different aromatic structures, fat structures and other molecules, which is formed by the interaction of internal defects and pores in the molecular group. The structural differences at different temperatures therefore reflect the interaction of different macromolecules in coal.
了解煤在热处理过程中的结构变化是煤炭高效清洁利用的基础。在本研究中，利用高分辨率透射电子显微镜（HRTEM）分析了准东煤样（中国新疆）从室温加热到800℃时团聚结构和超微孔的变化。然后，还分析了它们的HRTEM特征与相应反应活化能之间的关系。结果表明，煤样芳香层的长度、曲率、有序度、层间距和堆积高度随温度升高而变化，且与反应活化能有关。当温度达到300℃时，加热后煤样的HRTEM特征与原煤样明显不同。结果表明，晶格条纹长度在0.3 - 1.15nm范围内，约占条纹总数的95%。晶格条纹的整体取向不好，但有两个主要方向。加热后，煤样中萘的数量减少，而较大芳香层的数量增加。煤样芳香层之间的距离随堆积高度增加而减小，芳香层的有序度增强，曲率较大的芳香片数量增加。煤超微孔主要集中在0.4至0.7nm之间。热处理减少了超微孔的总数，但最大孔隙数量增加。非六元环和晶格缺陷导致条纹弯曲，脂肪结构的分布影响条纹的取向，孔隙与分子结构之间的关系并非独立存在。热处理后，煤的团聚结构和超微孔尺寸与活化能具有高度相关性。活化能与0.6nm超微孔密切相关。然而，目前的实验无法解释这些关系的潜在原因。煤中的聚集态是不同芳香结构、脂肪结构等分子之间形成的大分子基团，是分子基团内部缺陷和孔隙相互作用形成的。因此，不同温度下的结构差异反映了煤中不同大分子之间的相互作用。
