褐煤温和催化加氢裂解和氧化解聚制备高值含氧有机化学品

High oxygen content in organic matter is an important characteristic of lignites. The oxygen-containing moieties in organic matter of lignites are promising precursors for many high-value oxygenated organic chemicals. Selectively cleaving some bridged bonds in organic matter of lignites via appropriate chemical reactions under mild conditions to depolymerize the organic matter into high-value small-molecular oxygenated organic compounds is of great importance for realizing lignite directional conversion and value-added utilization. In this project, a highly active and recoverable Ni/TiN@Fe3O4 was used for catalytic hydrocracking of weak oxygen-containing bridged bonds in the organic matter of lignites under mild conditions to produce oxygenated organic compounds like phenols. Then, the residue from the above lignite hydrocracking was oxidized in H2O2 aqueous solution at low temperature with g-C3N4 as a catalyst to produce value-added small-molecular fatty acids and benzene polycarboxylic acids. The Ni/TiN@Fe3O4 and g-C3N4 catatlyzed reactions of lignite-related model compounds are performed to reveal the mechanisms for the catalytic hydrocracking and oxidative depolymerization. In combination with detailed analyses of the soluble portions from the catalytic hydrocracking and oxidative depolymerization of lignites, the characteristics of bridged linkages (oxygen-containing and methlylene bridged linkages) and aromatic structures connected by bridged linkages are understand. These investigations will provide important scientific basis for lignite directional conversion to high-value oxygenated organic chemicals.

有机质中氧含量较高是褐煤的重要特征。褐煤有机质中的含氧结构是诸多高值含氧有机化学品的前驱体。通过合适的化学反应在温和条件下选择性地断裂褐煤有机质中的一些共价键，使有机质解聚为高值的小分子含氧有机化合物对实现褐煤定向转化和高附加值利用至关重要。本项目拟通过温和条件下高活性且易回收的Ni/TiN@Fe3O4催化的加氢裂解切断褐煤有机质中较弱的含氧桥键，生成酚类等含氧有机化合物。进而以g-C3N4为催化剂，用H2O2水溶液在低温下氧化解聚褐煤加氢裂解所得残渣生成高附加值的小分子脂肪酸和苯羧酸。通过褐煤相关模型化合物的催化反应，揭示催化加氢裂解和氧化解聚的机理，结合褐煤催化加氢裂解和氧化解聚所得可溶物的详细分析，明晰褐煤有机质中桥链（含氧桥链和亚甲基桥链）的类型和被桥链连接的芳环结构的特征。上述研究可望为褐煤的定向转化制备高值含氧有机化学品提供科学依据。

褐煤有机质中的含氧结构是诸多高值含氧有机化学品的前驱体。通过合适的化学反应在温和条件下选择性地断裂褐煤有机质中的一些共价键，使有机质解聚为高值的小分子含氧有机化合物对实现褐煤定向转化和高附加值利用至关重要。本项目利用浸渍法制备了在温和条件下对褐煤及其相关模型化合物中C-O桥键加氢裂解具有高活性、高选择性和高稳定性的Ni/TiN催化剂。褐煤相关模型化物的催化加氢裂解产物以芳香族化合物为主，芳环几乎不发生加氢反应。褐煤在乙醇中的催化加氢裂解效果最佳，所得可溶物显著高于在其他溶剂中加氢裂解所得可溶物收率且显著高于非催化加氢裂解所得可溶物的收率。通过正庚烷萃取可有效地将褐煤加氢裂解的可溶物分离为轻质组分和重质组分。催化加氢裂解能够显著提高轻质组分中芳香族化合物特别是酚类的收率。重质组分的组成分析结果表明非催化加氢裂解所得重质组分含有较多的缩合芳环结构且含氧量高于催化加氢裂解所得重质组分，而催化加氢裂解所得重质组分的饱和程度高于非催化所得重质组分，且芳环上含有较多高碳数的烷基侧链。利用绿色的氧化剂H2O2水溶液，通过温和条件下的氧化解聚将褐煤催化加氢裂解的残渣中的缩合芳环结构转化为高附加值的芳酸。氧化产物中苯羧酸的收率在所有族组分中占绝对的优势，约占总收率的78.3%，其中苯五甲酸和苯六甲酸的收率最高，通过后续的精细分离有望从褐煤残渣的氧化产物中分离出高附加值的苯五甲酸和苯六甲酸。本项目通过催化加氢裂解和氧化解聚两步法在尽可能温和的条件下最大程度地将褐煤中的有机质转化为高附加值化学品特别是芳香族含氧化学品，为褐煤的高效清洁利用和定向转化制高附加值化学品提供了重要的科学依据和理论基础。