基于密度泛函理论的β-O-4型木质素模型物亚临界水热解聚机理研究

In view of the complexity of lignin depolymerization under subcritical water conditions and the difficulty of exploring its microscopic reaction mechanism by laboratory experimental work, a creative idea that combined with quantum chemical and experiment method to illustrate lignin hydrothermal depolymerization mechanism is presented. Density functional theory methods will be used to build structural models of lignin model compounds, find its thermochemical active sites and calculate the thermodynamic parameters etc. Experimental methods will be mainly used to study the depolymerization pathway of lignin and the product distribution. A typical β-O-4 type lignin dimer model compound, guaiacyl glycerol-β-guaiacyl ether, will be synthesized by bromine replace with copper bromide, catalytic polymerization under alkaline conditions, and then reduction with sodium borohydride. Density functional theory (DFT) calculations were performed at B3LYP level 6-31++G(d,p) basis set for the title compounds in order to construction of the structure model, geometry optimization, equilibrium geometries, and calculation of bond energy and thermodynamic parameters. The transition states will be located by transition state theory method and were confirmed by visual inspection of the imaginary frequency. The possible reaction pathways will be designed according to hydrothermal conversion results of the model compound. The thermodynamics and kinetics of these reactions will be thoroughly investigated based on the optimization and quantum chemistry calculation results of reactants, intermediates, transition states and products. By these means, we can explore the elementary reactions and the speed control step of lignin converted to phenolic compounds in subcritical water, such as homolytic cleavage, β-O bond cleavage, free radical rearrangement. Finally, combining of the theoretical analysis and experimental results, we will explain the depolymerization mechanism of lignin model compound in subcritical water conditions, and reveal formation process of the main phenolic products. The present research will provide theoretical and technical support to molecular modeling of lignin structure, key regulatory of subcritical hydrothermal conversion, and development and utilization of value-added chemicals.

针对木质素亚临界水热反应的复杂特性和实验室试验难以探索其微观反应历程的技术瓶颈问题，提出利用分子模拟和量子化学计算方法构建其模型物结构模型及分析热化学性能，并与实验结合揭示其水热解聚机理的构思。通过4-羟基-3-甲氧基苯乙酮溴代后碱催化聚合、还原等步骤合成具有β-O-4型连接的木质素模型物愈创木基丙三醇-β-愈创木基醚，运用密度泛函理论B3LYP/6-31++G(d,p)方法，进行几何构型优化，寻找最低能量稳定构型和热化学活性位；基于模型物水热反应产物分析设计可能的反应路径，采用过渡态理论寻找过渡态，计算反应路径的热力学、动力学变量，探索模型物水热解聚为酚类化合物的均裂、β键断裂、自由基重排等基元反应网络、速控步骤；结合水热转化实验结果，揭示模型物亚临界水热解聚机理、主要产物形成的微观演化过程。本项目的实施将为木质素结构构建、亚临界水热反应调控及高附加值化学品开发利用提供理论和技术支持。

项目针对木质素水热反应的复杂特性和实验手段难以探索其微观反应历程的技术瓶颈问题，建立了基于密度泛函理论量化计算结合水热转化实验研究木质素模型物亚临界水热解聚机理的思路与方法。以愈创木酚为原料经过五步有机化学合成反应，制备了木质素β-O-4型二聚体模型物愈创木基丙三醇-β-愈创木基醚；利用分析热解技术，研究了愈创木基丙三醇-β-愈创木基醚的热解特性，明晰了其在不同热解条件下的化学键断裂及产物分布规律；运用分子模拟和量子化学计算方法，对二聚体模型物进行量化模拟，揭示了模型物最低能量稳定构型、热化学活性位，计算出了β-O-4型二聚体模型物关键化学键的键长、键离解能（BDE）等参数；通过愈创木基丙三醇-β-愈创木基醚的亚临界水热转化研究及产物分析，阐明了二聚体模型物在水热环境下化学键的断裂、迁移规律；基于实验结果并结合量子化学理论计算，探讨了木质素及其二聚体模型物的亚临界水热解聚途径，揭示了主要产物的形成演化机理，为木质素结构构建和亚临界水热反应调控奠定了理论基础，进一步完善了生物质炼制过程中木质素高值转化相关理论体系。项目研究成果获山东省高等学校优秀科研成果奖二等奖1项、三等奖1项；申请国家发明专利3项；参编英文学术专著1部；发表学术论文10篇、会议论文3篇，其中SCI收录9篇，EI收录1篇；培养硕士研究生3名；组织6人次参加国内外学术会议。