Zhang Xiaobing, Jia Tianrang, Zhang Hang, Ju Yiwen, Zhang Yugui
Safety and Emergency Management Research Center of HPU (Henan Polytechnic University), Jiaozuo Henan 454003, China.
Collaborative Innovation Center of Coalbed Methane and Shale Gas for Central Plains Economic Region, Henan Province, Jiaozuo 454003, China.
J Nanosci Nanotechnol. 2021 Jan 1;21(1):636-645. doi: 10.1166/jnn.2021.18452.
Coal is a pressure-sensitive organic rock. The effect of tectonism on the structural evolution of medium-rank coal has been confirmed by the change in the crystal state of tectonic coal, but the organic molecular level response has not been reported. In this paper, three sets of medium-rank tectonic coals and symbiotic nontectonic coals were selected. The distributions of their functional groups and their molecular structure evolution were assessed using Fourier Transform Infrared Spectroscopy (FTIR), and their structural parameters were determined from the curve-fitting analysis. The nanoscale structural jump characteristics and mechanisms of medium-rank tectonic coal were revealed. Compared with symbiotic nontectonic coal, tectonism accelerated the exfoliation of side chains (groups) in the macromolecular structure, enlarged the aromatic system, and removed the unstable groups such as associative hydrogen bonds at first, which indicated that the molecular structure of tectonic coal was affected by nanoscale deformation, showing obvious advanced evolution characteristics. For the fat coal, the removal of side chains (groups) during the formation of tectonic coal makes the aromatic ring condensation obvious. For the coking coal, the formation of tectonic coal is dominated by cycloaliphatic dehydrogenation and aromatization, accompanied by the condensation of the aromatic rings. The tectonic coal formed from lean coal shows obvious aromatization characteristics. The molecular depolymerization and chemical tailoring caused by tectonism promotes the removal of hydrophobic side chains (groups) and activates some polar structure sites in coal. It is considered that the nanoscale structural jump of medium-rank tectonic coal is the result of the competition between the aromatic system and aliphatic structures.
煤是一种对压力敏感的有机岩石。构造作用对中阶煤结构演化的影响已通过构造煤晶体状态的变化得到证实，但有机分子水平的响应尚未见报道。本文选取了三组中阶构造煤及其共生的非构造煤。利用傅里叶变换红外光谱（FTIR）对其官能团分布及其分子结构演化进行了评估，并通过曲线拟合分析确定了其结构参数。揭示了中阶构造煤的纳米级结构跳跃特征及机制。与共生的非构造煤相比，构造作用加速了大分子结构中侧链（基团）的脱落，扩大了芳香体系，并首先去除了诸如缔合氢键等不稳定基团，这表明构造煤的分子结构受到纳米级变形的影响，呈现出明显的超前演化特征。对于肥煤，构造煤形成过程中侧链（基团）的去除使芳环缩合明显。对于焦煤，构造煤的形成以脂环族脱氢和芳构化为主，伴有芳环的缩合。由瘦煤形成的构造煤呈现出明显的芳构化特征。构造作用引起的分子解聚和化学剪裁促进了疏水侧链（基团）的去除，并激活了煤中的一些极性结构位点。认为中阶构造煤的纳米级结构跳跃是芳香体系与脂肪族结构之间竞争的结果。
