典型宁东煤热解阶段硫迁移路径的分子动力学模拟

以典型宁东煤为研究对象,采用工业分析、元素分析、X射线光电子能谱(XPS)分析和¹³C固体核磁共振(¹³C-NMR)等手段研究了煤样的元素组成、原子比、官能团类型及含量等分子结构特征,构建了含硫原子的宁东煤有机化学结构。通过反应力场分子动力学(ReaxFF MD)模拟,考察了热解温度和升温速率对典型宁东煤热解产物的影响,结果表明:热解温度低于1500 K时,热解产物中气体组分较少,重质焦油较多;随着热解温度升高(1500 K~2500 K),大分子化合物和活性自由基均会发生二次反应产生小分子碎片,气体产物快速增加;增大升温速率会减少C1~C4有机气体的生成,促进重质焦油的产生;16 K/ps和2500 K分别是合适的模拟升温速率和热解温度。污染性元素S的迁移路径分析结果表明:宁东煤热解过程中S原子容易迁移到相对分子质量小的有机碎片中,最终将以硫氢根的形式与H自由基结合生成H₂S参与后续燃烧反应。

Molecular Dynamics Simulation of Sulfur Migration Path in the Pyrolysis Process of Typical Ningdong Coal

By means of the proximate analysis,ultimate analysis,X-ray photoelectron spectroscopy(XPS)and ¹³C nuclear magnetic resonance(¹³C-NMR),its molecular structure characteristics of the typical Ningdong coal was tested and analyzed with respect to the element composition,atomic ratio,type and distribution of functional groups,and then the organic chemical structure of Ningdong coal containing sulfur atom was constructed.The effects of the pyrolysis temperature and the heating rate on the pyrolysis products of Ningdong coal were investigated by reaction force field molecular dynamics(ReaxFF MD)simulation.The results show that there are less gas components in the pyrolysis products and more heavy tar is produced when the pyrolysis temperature is below 1500 K.With the increasing simulated temperature(1500 K-2500 K),the secondary reaction from the macromolecular compounds and radicals produces small fragments,and the gas products increase rapidly.Besides,the heating rate increasing reduces the formation of the organic gas but promotes the formation of the heavy tar.Comparably,16 K/ps is the appropriated heating rate and 2500 K is the appropriate pyrolysis temperature.The migration path analysis of the pollutant sulfur shows that sulfur is easy to migrate into the organic fragments of small molecular weights,which will eventually become SH radical and combine with H radical to form H₂S,and then participate in the subsequent combustion reaction.