Lignin hydrolyzes during alkali-heat pretreatment of lignocellulose, due to the cleavage of covalent linkages between lignin and lignin-carbohydrate complex. Various structure of lignin monomers are responsible of the complicated hydrolysis mechanism of lignin and lignin-carbohydrate complex. This study used density functional theory to reveal the hydrolysis mechanism of lignin with various substituents and lignin-carbohydrates complex with different linkages. The results indicated that the S2 reaction was observed to take place in the lignin. Methoxy groups and methyl group had an insignificant influence on hydrolysis reaction pathway of lignin, whereas the presence of a methyl group on the α-carbon atom had a hindering effect on the nucleophilic attack during alkaline pretreatment. The lignin-carbohydrate complex with different linkage showed a significant difference in hydrolysis reaction pathway. Additionally, the reaction energy barrier of ester bond hydrolysis was lowest among the hydrolysis of ester bond, phenyl glycosidic bond, benzyl ether bond, γ-ester bond, coumarin ester bond and acetal bond under alkaline condition. This study provides valuable insights into the process control, reactor design, and performance enhancement for lignocellulose pretreatment.

中文翻译：

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密度泛函理论研究碱性条件下木质素及木质素-碳水化合物复合物水解机理


由于木质素和木质素-碳水化合物复合物之间的共价键断裂，木质纤维素在碱热预处理过程中发生水解。木质素单体的各种结构决定了木质素和木质素-碳水化合物复合物的复杂水解机制。本研究利用密度泛函理论揭示了不同取代基的木质素和不同键合的木质素-碳水化合物复合物的水解机理。结果表明，观察到木质素中发生了S2反应。甲氧基和甲基对木质素的水解反应途径影响不大，而α-碳原子上甲基的存在对碱预处理过程中的亲核攻击有阻碍作用。不同键合的木质素-碳水化合物复合物的水解反应途径存在显着差异。另外，在碱性条件下，酯键、苯基糖苷键、苄基醚键、γ-酯键、香豆素酯键和缩醛键的水解中酯键水解的反应能垒最低。这项研究为木质纤维素预处理的过程控制、反应器设计和性能增强提供了宝贵的见解。