煤直接液化过程中催化剂和溶剂的协同供氢机制研究

The direct coal liquefaction (DCL) is an important direction for the clean and efficient utilization of coal, which can transform solid coal resources into clean, high-calorific liquid fuels and high value-added chemicals. However, it has not been fully understood about the hydrogen transfer mechanism in DCL, which hampered the design of high efficient catalysts and the performance improvement of hydrogen-donor solvents. In this proposal, the method of computational chemistry will be utilized to clarify the active site and the action mechanism of catalysts in DCL. The hydrocracking reaction mechanism of coal model compounds will be elucidated. High efficiency catalysts will be designed by theoretical calculations and verified by experiments. The hydrogen transfer pathway between hydrogen-donor solvents and coal model compounds and the hydrogenation reaction of nondonor solvents on the active catalysis surface will be clarified. The relationship between the molecular characteristics of hydrogen-donor solvents and their hydrogen-donating abilities and hydrogenated activities will be established. The aim of this proposal is to explore the synergistic hydrogen-donating mechanism of catalysts and solvents in DCL, develop the chemistry theory of DCL, grasp effective ways to improve the hydrogen-donating ability of catalysts, and build a simple and effective evaluation method of DCL solvents.

煤直接液化是煤炭清洁高效利用的重要研究方向，可以将固体的煤炭资源转化为清洁、高热值的液体燃料以及高附加值的化工原料。然而，对于煤直接液化反应过程中的氢转移机制至今仍尚无定论，从而限制了高效催化剂的开发以及供氢溶剂性能的提升。本项目拟运用理论计算方法从原子和电子层面上阐明催化剂的活性单元结构及其在反应过程中的作用机制，计算研究煤模型化合物在催化剂表面氢化裂解的反应机理，从理论上设计更加高效的煤直接液化催化剂，并通过实验手段进行验证。通过理论计算研究供氢溶剂与煤模型化合物之间氢传递的机制，考察溶剂分子在催化剂表面上的再加氢反应活性，建立溶剂分子结构特性与其供氢能力和再加氢反应活性之间的有效关联。本项目旨在探索煤直接液化过程中催化剂和溶剂的协同供氢机制，丰富和发展煤直接液化化学理论，掌握提高催化剂供氢能力的有效途径，构建简便、有效的评价煤直接液化溶剂优劣的理论模型。

本项目采用实验分析结合理论计算的方法，对煤直接液化溶剂和催化剂的协同供氢机制进行了系统研究。项目首先对煤直接液化溶剂的组成和结构进行分析，接着研究了煤直接液化溶剂转移氢原子的机制，以及煤直接液化溶剂向煤热解自由基转移氢的反应速率常数，并揭示煤直接液化溶剂分子结构与供氢能力的关系。结果显示，煤直接液化溶剂均具有明显的缩合芳环结构，芳香环数集中在二、三环。液化溶剂以氢化芳烃为主，氢化芳烃中主要含有四氢萘、甲基四氢萘、对称八氢蒽、对称八氢菲、二氢芘、六氢芘等。环数的增加，体系的π键有利于未成对电子的离域，增加自由基的稳定性，进而有利于C1–H键的断裂。在煤直接液化过程中，从四氢萘同时转移β-H和α-H二苯甲烷DPM的ipso-C和meta-C是一种可能的途径，即协同双氢-转移机制。供氢溶剂向自由基转移氢原子的反应速率常数与溶剂分子的环数、取代基、环张力密切相关，环数越多分子中电子的离域能力越强，形成的自由基越稳定，进而供氢的速率常数越大。通过褐煤直接液化实验，总结了供氢溶剂参与下氧元素的迁移规律，解耦了含氧官能团阶段反应特征，探讨了缩合作用加剧的本质，明确了自由基诱导对供氢及煤中化学键解离的促进机理。