褐煤中含氧桥键定向加氢裂解的基础研究

The organic matter of lignite is rich in oxygen-containing bridged bonds, especially for aryl ethers C-O band, which is not readily cleaved by coal conversion technology, such as catalytic hydrogenation, because of the relatively strong bond dissociation energies and thermal stability of these linkages. It is of great importance for the selective cleavage of aryl ethers C-O band under milder conditions to understand the macromolecular structure of lignite and to achieve the selective depolymerization of lignite and the subsequent value-added utilization. In this project, we mainly use four typical chinese lignites. Main investigations include: (1) sequential extraction and thermal dissolution of lignite to dissociate the weak bonds with diffenet solvents and charaterization of the oxygen-containing species in the resulting soluble reaction mixtures with multiple advanced analytical instruments, and reveal the structures and compositions of the aryl ethers in molecular level in the species which is joined by a weak bond in lignite. (2) preparation of supported nickel based catalyst to catalytic seletive hydrogenolysis aryl ethers C-O band in the macromolecular network structure in lignite extracton residue and the related aryl ethers model compounds, optimization of the catalyst preparation and the catalysis process to improve the selectivity and conversion of the hydrogenolysis. (3) understanding of the structures and compositions of the macromolecular in lignite, especially for the insoluble aryl ethers C-O band species and the aromatic rings connected, through meticulous separation and characterization of cracking products and the comparison of results of hydrogenolysis of aryl ethers model compounds, and subsequently reveal the mechanisms for the seletive hydrogenolysis cracking of aryl ethers C-O band in lignite. These investigations will provide important scientific basis for the improvement of organic structure composition of lignite and the development of lignite selective depolymerization process to aromatic chemicals.

褐煤有机质中富含氧桥键，其中芳醚桥键离解能大且热稳定性强，难以通过加氢等定向断裂。在较温和的条件下选择性切断褐煤有机质大分子的芳醚桥键不仅有利于了解褐煤大分子结构组成，而且可望实现褐煤的定向解聚和后续的高附加值利用。本项目通过分级萃取和变温热熔逐级解离褐煤弱键合有机质小分子，并利用多种先进的分析手段了解产物中含氧化合物的组成结构，进而从分子水平上揭示褐煤有机质中弱键合小分子芳醚的组成结构；制备高活性负载型镍基催化剂用以在温和条件下催化选择性加氢断裂褐煤萃取残渣及芳醚模型化合物中有机质大分子的芳醚键，以提高选择性和转化率为目标优化催化剂制备和催化过程，通过对所得裂解产物的细致分离和分析并借助芳醚模型化合物的反应反演褐煤中有机质大分子的组成结构特征，特别是难解离的芳醚桥键及所连接芳环的类型，推测褐煤芳醚桥键选择性加氢裂解的机理；以期为完善褐煤有机结构组成和定向解聚制备芳香族化学品提供理论依据。

褐煤有机质富含芳醚桥键，通过催化加氢选择性切断褐煤有机质大分子的芳醚桥键不仅有利于了解褐煤大分子结构组成，而且可望实现褐煤的定向解聚和后续的高附加值利用。设计合成了Ni、Ru、Pd负载活性炭、ZSM-5和Al2O3催化剂，以褐煤模型化合物为探针研究了C-O键催化氢解，深入考察了不同氢源、温度、压力和反应时间等条件下模型化合物的催化氢解性能，进一步揭示C-O键氢解反应机理。然后对木质素和胜利褐煤（SL）及其热溶物进行催化转化，深入分析反应前后油品中轻质组分的组成和含量，为褐煤加氢裂解定向制备化学品提供理论依据和技术支持。.通过初始转换频率（TOF）和表观活化能（Ea）等理论计算并进一步结合实验证明Ni/AC相比Ni/HZSM-5和Ni/γ-Al2O3对苄基苯基醚（BPE）氢解具有更高活性，甲苯和苯酚是BPE氢解的主要产物，提出了Ni/AC断裂BPE的C-O键的反应机理。进一步掺杂Ru制备了Ni-Ru/AC，通过深入表征证明了Ni和Ru形成了“协同效应”，这种“协同效应”可产生额外的表面活性位点，小尺寸的金属颗粒和高度分散的金属颗粒，进而改善总转化率和产物分布。Ni-Ru/AC催化氢解木质素和SL发现其不仅可有效断裂木质素C-O键形成芳香单体，还可选择性脱除酚类化合物的羟基。Ni-Ru/AC催化剂可以高效裂解煤大分子结构中的C-O键形成芳香族化合物。.Pd/AC在常温常压下即可断裂BPE中的C-O键，H2吸附在Pd位点上形成活性氢自由基（H•），然后H•与BPE中的氧原子反应定向断裂C-O键生成甲苯和苯酚，温和条件显著抑制苯环加氢。合成了一系列高度分散Ru纳米催化剂，H2吸附在Ru位点上形成高活性H•，其与BPE中的氧原子反应导致C-O键断裂，且进一步导致苯环加氢；异丙醇在Ru上主要形成H+，H+倾向于与电负性更大的氧原子反应断裂C-O键，使反应路径最终趋向于氢解而非加氢。将Pd/AC和Ru/AC应用于褐煤催化解聚，发现在H2作用下，苯环加氢的副产物产率高于Ar条件下的产率，说明H2与异丙醇存在协同供氢作用。由于催化剂可定向断裂C-O键，显著提高了油品中酚类及其加氢产物的相对含量，实现了褐煤定向加氢裂解。