基于瞬态中间体识别的多尺度超细煤粉大分子网络模型构建及其热转化分子机理研究

With the increasing concern on the exhausted energy resources and serious environmental problems, more thorough knowledge on the essence of combustion becomes the key of increasing the combustion efficiency and eliminating the pollutants. Due to the limitation of the experimental devices, studies were always focused on the macroscopic results in the past. There were few reports about the research on the influence of inherent fuel characteristics. A comprehensive research on the microstructure and surface chemistry of superfine pulverized coal applying the advanced test platforms like synchrotron radiation facility is proposed in this application. Firstly, the multi-scale structural characteristics will be investigated for coals with different ranks and particle sizes, including lattice structure, heteroatomic species, carbon skeleton, functional group, ash property and pore configuration etc., which can be clarified from the microcosmic, mesoscopic and macroscopical points of view. The relationship between the mechanical comminution and multi-scale structural characteristics is summarized. On the basis of the above mentioned studies, the inherent nature of mechanochemistry will be proposed. Secondly, using the technology of molecular simulation, we will establish a macromolecular network model. This model, with reasonable coupling of the selected superfine parameters, combines the microcosmic, mesoscopic and macroscopical characteristics of superfine coal. Thirdly, the thermo-chemical conversion of coal will be investigated on the molecular level with the help of computational quantum chemistry. Herein, much attention will be focused on the free-radical type and ionic type reactions. The electronic structures of transition states and intermediates presented during the thermo-chemical conversion processes will be characterized, which can give more inspiration for understanding the detailed reaction mechanisms. Meanwhile, experiments will be performed at the national synchrotron radiation laboratory. The technique of synchrotron radiation vacuum ultraviolet photon ionization combining supersonic molecular beam sampling is applied for identification of the transient intermediates. The detailed information of the transient intermediates such as aliphatic, aromatic and heteratomic molecular fragments will be beneficial for the validation of the macromolecular network model, and improving the interpretation of thermo-chemical conversion processes. The findings from this project will be of great importance for developing the new combustion technology with high efficiency and clean emissions.

随着全球化石燃料的枯竭及环境污染问题的加剧，更为深入、细致地探索燃烧本质已成为提高燃烧效率及控制污染物排放的关键。由于研究设备与分析手段所限，前人对于煤粉燃烧的研究往往集中在宏观结果和外部因素的调控上，关于燃料自身理化特性对其热化学转化机理的研究甚少。本项目提出从内因着手，采用上海同步辐射光源等先进的实验平台表征煤粉的微观原子/分子级化学形貌、介观纳米级晶格与孔隙结构以及宏观粒度与密度等多尺度特性；在此基础上借助量子化学理论构建完善的具有超细特征的多尺度煤大分子网络模型；进而开展基于自由基反应（均裂）和离子型反应（异裂）的煤热化学转化机理研究，获得关键转化路径上的过渡态及中间体电子结构信息。此外，应用同步辐射真空紫外光电离质谱结合超声分子束取样技术，以瞬态中间体识别为核心，验证和完善多尺度超细煤粉大分子网络模型及热化学转化分子机理，为新型一体化煤粉高效洁净燃烧技术的开发与应用奠定理论基础。

超细煤粉的提出为人们重新认识颗粒粒度对煤粉燃烧机理及污染物生成机制的影响提供了崭新的视角。但是由于研究设备及分析手段所限，前人的研究往往集中在宏观结果与外部因素的调控，而对于其内在的煤粉微观结构与表面化学特性对燃烧过程影响的研究尚属空白。对煤粉热化学转化分子机理的认识不足已成为研发新型煤粉清洁高效燃烧技术的关键瓶颈问题。. 本项目从内因着手，通过同步辐射光源等先进的实验装置完成了自由基、孔隙结构、微晶乱层结构、杂原子形态、近邻原子环境等多尺度物化特性的定量表征，揭示了其与机械力化学效应的关联耦合。其中，项目基于SAXS首次构建了超细煤粉全尺度孔隙结构模型，并通过XANES阐明了煤中有机硫与无机硫之间的相互转化机制，促进了含硫煤大分子结构的精确构建；在此基础上，选择具有超细特征的官能团、碳骨架、游离小分子等关键结构，进而耦合表面形貌、孔隙结构、微晶组成、密度等多尺度特征，成功构建了多组分多尺度超细煤粉大分子网络模型，并进行了验证；通过均相异相解耦实验研究，阐明了超细煤粉热解过程含氮前驱体释放机制，进而结合ReaxFF反应分子动力学研究，获得了热化学转化关键分子片段信息。其中，项目创新性地引入指前因子与分布活化能二维概念，实现了2D-DAEM的开发、求解与应用，显著提高了DAEM的精度与燃料适应性，解决了DAEM延拓带来的高维度、强补偿等求解难题；此外，项目结合量子化学研究，精确捕捉了热化学转化基元反应的过渡态、中间体以及自由基结构，获得了基于自由基竞争/选择/协同作用的NOx迁移转化多通道反应网络与定向调控机制，阐明了超细特征结构诱导微区定位活化与局部钝化的煤氮电子环境变异机制，填补了国内外关于特征结构作用下煤氮转化分子机理的研究空白；依托以上机理研究，本项目与工程实践相结合，成功开发了改进型煤粉高效洁净燃烧工艺，并有几十套工业锅炉装置已成功运行，创造了巨大的社会经济效益。