基于含氧桥键温和逐级选择性催化降解的褐煤分子结构研究

The efficient and clean utilization of lignite has very important practical significance. The selective degradation of relatively weak oxygen-containing bridged bonds in lignite is vitally important for the oriented conversion and subsequent value-added utilization of lignite. In consideration of several bottlenecks involved in traditional degradation technologies, such as high energy consumption, poor selectivity, complex components in products and complicated subsequent treatments, etc, this project presents a theory and methodology for the oriented catalytic decomposition of lignite under mild conditions, namely, iridium pincer complexes, (tris(pentafluorophenyl)borane and Ni ligand complexes are used as catalysts successively for the setpwise and selective degradation of oxygen-containing bridged bonds in lignite to produce deoxygenated species, such as alkanes and benzene-containing compounds. Our main investigations are: 1), to optimize reaction conditions for the stepwise and selective degradation of lignite; 2), to analyze the components in the reaction products with combination of several separation methods and advanced analytical instruments; 3), using alkyl aryl ethers as model compounds, to understand the distribution of oxygen-containing bridged bonds and the rule as well as mechanisms of their cleavage in corresponding reactions; 4), to reveal the structure model of lignite basing on the compositional analysis of the degradation products and the cleavaging mechanisms of oxygen-containing bridged bonds, and; 5) to present methods for separation and production of value-added chemicals from the degradation products. This project provides scientific basis for the oriented conversion of lignite.

褐煤的高效和洁净利用具有重要的现实意义。在温和条件下选择性地将褐煤分子结构中较弱的含氧桥键断裂对于实现褐煤的定向解聚和后续利用至关重要。针对传统的降解技术存在能耗高、选择性差和产品成分复杂等问题，本项目提出温和条件下实现褐煤定向催化解聚的理论和方法，即分别以含铱螯合物、三(五氟苯基)硼和含镍配合物为催化剂在优化的反应条件下将褐煤中不同类型含氧桥键逐级选择性地断裂，降解产物实现脱氧且组成简单，主要为烷烃和芳香族化合物；借助组合多种高效的组分分离与分析手段对反应降解产物进行详细地成分分析；以烷芳基醚为模型化合物，考察模型化合物在相应催化反应中含氧桥键的断裂规律，了解反应机理和各类型含氧桥键的强弱及其分布规律；以降解产物成分分析和含氧桥键降解机理为依据，推测褐煤分子结构模型，提出褐煤降解产物中分离制备燃料和高附加值化学品的方法，为实现褐煤的定向转化提供科学依据。

针对传统的褐煤降解技术，如热解和生物降解等，存在能耗高、选择性差、速度慢和产品成分复杂等问题，在温和条件下选择性地将褐煤分子结构中较弱的含氧桥键断裂对于实现褐煤的定向解聚和后续利用提供有效途径。本研究分别以含铱螯合物、三(五氟苯基)硼和含镍配合物为催化剂在优化的反应条件下将褐煤中不同类型含氧桥键逐级选择性地断裂，降解产物实现脱氧且组成简单，主要为烷烃、芳烃和酚类化合物；考察模型化合物在相应催化反应中含氧桥键的断裂规律，了解反应机理和各类型含氧桥键的强弱以及其在褐煤中的分布规律；以降解产物成分分析和含氧桥键机理为依据，推测褐煤分子结构模型，提出褐煤降解产物中分离制备燃料和高附加值化学品的方法，为实现褐煤的定向解聚提供了科学依据。. 以锡林浩特褐煤XL和霍林郭勒褐煤HL为煤种，存在于芳环内、芳环的侧链上和连接芳环的含氧桥键，所占比例分别为2-5%、60-80%和5-15%。褐煤在含铱螯合物的催化体系中，烷基醚键经历硅烷化后发生断裂，主要降解生成烷烃；以三(五氟苯基)硼为催化剂，将降解剩余物用氢化硅烷试剂将芳环间的含氧桥键（除Ar-OAr外）随反应活性强弱依次断裂，生成烷烃、芳烃和酚；再采用镍基配合物催化剂，叔丁醇钠为强碱性试剂，使Ar-OAr键发生选择性断裂，进一步降解褐煤中芳环间的含氧桥键，生成芳烃和酚。在B(C6F5)3催化体系中，含氢硅烷可将芳基醚转化为硅醚和烷烃，各模型化合物的反应活性顺序为酚>伯醇>甲氧基苯>烷基硅基醚。若反应体系中存在足量的含氢硅烷，则还原反应进行得更为彻底。采用0.5%（mol%）的Ni(CH2TMS)2(TEMEDA)为催化剂，SIPr•HCl作为配合物前驱体与催化剂相结合，强碱性试剂为叔丁醇钠，间二甲苯为反应溶剂，反应温度为80-120 oC，压力为1 bar H2，即在异相催化条件下，具有很好的选择性。各级降解混合物，经蒸馏-高速逆流色谱-中压制备色谱进行分级提取制备，可获得高附加值的芳烃和酚，产率（相比于褐煤原样）分别为7.4 g/100 g和19.2 g/100 g。. 本研究的科学意义在于温和条件下结合不同的催化体系以逐级选择性地断裂较弱的含氧桥键实现褐煤的定向解聚，保留芳环和C-C结构，可作为从褐煤中获取高附加值化学品（如芳烃和酚）的科学依据。