基于γ-戊内酯/水体系制备再生纤维素级纤维过程中糖甙键的断裂与调控机制

The efficient separation and ultilization of biomass-based natural polymers is an important approach to realize the sustainable development of economy and society. Recently, the solvent consisted of gamma-valerolactone (GVL) and water was found to be a bio-based green solvent being capable of simultaneously separation and conversion of three major components from biomass, which is with advantages to separate lignin with high activity, to convert carbohydrate with high efficiency, to separate products and recycle GVL with low cost. However, there existed insufficiency using this solvent system to prepare regenerated cellulosic grade fibers. Therefore, this project will adopt exogenous organic acids as hydrogen ion sources, and research on the cleavage and controllable mechanisms of two types of glycoside bonds in carbohydrates with the GVL/water system. The main research contents are as follows: solvation effect of solvent molecule clusters on organic acids and glycoside bonds; effect of solvent molecule clusters on the ionization of organic acids and catalytic cleavage of glycoside bonds by organic acids; mechanisms of hydrogen bond in carbohydrates and lignin-carbohydrate complex from biomass on differential cleavage of two types of glycoside bonds. Finally, according to the micro environment and molecular structure peculiarity of recalcitrant hemicelluloses, this project will provide the regulation approaches for preparation of regenerated cellulosic grade fibers with high degree of polymerization. This project aims at providing theoretical basis for realizing the green efficient preparation of regenerated cellulose grade fibers and increasing the fine ultilization efficiency of lignin and hemicelluloses.

生物质天然高分子的高效分离利用是实现经济社会可持续发展的重要途径。最近研究发现，由γ-戊内酯（GVL）与水组成的溶剂是一种可实现生物质三大组分同步分离转化的生物质基绿色溶剂，具有分离的木质素活性高、碳水化合物转化率高、溶剂回用和产物分离成本低等优势。然而，该体系目前在制备高聚合度再生纤维素级纤维方面还存在不足。对此，本项目拟采用外源有机酸作为GVL/水体系的氢离子源，研究该体系下两类碳水化合物糖甙键的断裂与调控机制，主要内容包括：溶剂分子簇对有机酸和糖甙键的溶剂化效应；溶剂分子簇对有机酸电离及其催化断裂糖甙键的影响；碳水化合物氢键、木质素-碳水化合物复合体对两类糖甙键差异化断裂的作用机制；针对顽抗性半纤维素的微区环境和分子结构特点，提出制备高聚合度再生纤维素级纤维的调控途径。本项目旨在为基于GVL/水体系实现再生纤维素级纤维的绿色高效制备、提升木质素和半纤维素的精细化利用水平提供理论依据。

通过研究生物质炼制溶液有机酸组成及GVL/H2O分子簇对有机酸的溶剂化机制，确定甲酸作为一种质子电离性很强的弱酸，十分适合用作GVL/H2O溶剂体系的质子源，并建立了甲酸电离平衡常数与溶剂比例的数学模型。研究了GVL/H2O分子簇对有机酸催化断裂两种糖甙键与木质素β-O-4化学键的作用机制，建立了纤维二糖与木质素二聚体愈创木酚基甘油-β-愈创木基丙醚的降解动力学模型，阐明了反应活化能与反应速率常数随温度与溶剂比例的变化规律。在此基础之上，通过研究纤维二糖与GBG降解速率比值随反应温度与溶剂组成的变化规律，确定了溶剂体系的最佳GVL含量为60-80%。最后，在该溶剂比例范围内，研究了甲酸浓度、制浆时间、溶剂组成对制备高聚合度再生纤维素级竹纤维的影响；在优化的高选择性反应条件下，成功制备出高品级竹溶解浆，其纤维素聚合度高达1193、得率达到49.0%、半纤维素含量仅为4.54%，超过项目计划书制订的各项指标要求。本项目的部分研究成果已在Advanced Functional Materials、Journal of Material Chemistry A、Renewable Energy等SCI收录期刊发表论文10篇，授权的发明专利4项，并获得梁希林业科技进步奖1项。

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