Dang Han, Wang Guangwei, Yu Chunmei, Ning Xiaojun, Zhang Jianliang, Zhang Nan, Gao Yi, Xu Runsheng, Wang Chuan
School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing, No. 30 Xueyuan Road, Haidian, Beijing 100083, China.
Laboratory for Thermal Science and Power Engineering of MOE, Tsinghua University, Beijing 100084, China.
ACS Omega. 2021 Sep 21;6(39):25772-25781. doi: 10.1021/acsomega.1c03866. eCollection 2021 Oct 5.
The molecular structure model of lignite was constructed, and the dissociation and removal mechanism of different C-O bonds and oxygen-containing functional groups was investigated using density functional theory (DFT) calculations. First, the bond order and bond dissociation enthalpy (BDE) were analyzed to predict the strength of different chemical bonds, and differences in the BDE and bond order were related to the difference in the fragment structure and electronic effects. The first group to break during hydrothermal carbonization (HTC) is the methyl of Ph(CO)O-CH, followed by the C-O of CH-OC(O)OH; the hydroxyl in Ph-OH is the most thermally stable group, followed by the hydroxyl in CHOC(O)-OH. In addition, the orbital localization analysis has also been carried out. All three chemical bonds of Ph(CO)OCH show the characteristics of σ bond, while Ph(C=O)OCH and Ph(CO)-OCH with the Mayer bond order (MBO) greater than 1 also contains certain π bond characteristics. The lignite van der Waals (vdW) surface electrostatic potential (ESP) was constructed and visualized, and the results showed that the oxygen-containing functional groups mainly contributed to the area with a large absolute ESP. Finally, weak interactions between water molecules and lignite at different sites were described by independent gradient model (IGM) analysis. Models A, B, and E formed weak interactions with the hydrogen bond as the main force; model E showed the weakest hydrogen bond, while model C showed van der Waals interaction as the dominant force. In addition, some steric effect was also observed in model D.
构建了褐煤的分子结构模型，并利用密度泛函理论（DFT）计算研究了不同C-O键和含氧官能团的解离和去除机理。首先，分析键级和键解离焓（BDE）以预测不同化学键的强度，BDE和键级的差异与片段结构和电子效应的差异相关。水热碳化（HTC）过程中首先断裂的基团是Ph(CO)O-CH的甲基，其次是CH-OC(O)OH的C-O键；Ph-OH中的羟基是最稳定的基团，其次是CHOC(O)-OH中的羟基。此外，还进行了轨道定域分析。Ph(CO)OCH的所有三个化学键都表现出σ键的特征，而Mayer键级（MBO）大于1的Ph(C=O)OCH和Ph(CO)-OCH也含有一定的π键特征。构建并可视化了褐煤范德华（vdW）表面静电势（ESP），结果表明含氧官能团主要对ESP绝对值较大的区域有贡献。最后，通过独立梯度模型（IGM）分析描述了水分子与褐煤不同位点之间的弱相互作用。模型A、B和E以氢键为主要作用力形成弱相互作用；模型E的氢键最弱，而模型C以范德华相互作用为主导作用力。此外，在模型D中还观察到了一些空间效应。
