农作物秸秆分子结构的化学解聚机制研究

With the global climate warm and the depletion of fossil fuels, many countries pay much attention to the research on the development and utilization of biomass energy, especially highlighting straw energy. However, the pace of research on the efficient depolymerization of straw, which is a crucial prerequisite for achieving the high added-value conversion of straw polymer, is severely limited because of lack of deep understanding for scientific problem about depolymerization mechanism of straw structure. In this work, three typical crop straws, i.e. wheat straw, rice straw, and corn stalk, are used to study the chemical depolymerization mechanism of crop straw by investigating chemical structure and bonding styles of constituent units in straw in the molecular level, researching the changing mode, characteristic, and mechanism of straw structure under various conditions of chemical depolymerization, analyzing the structural characteristics of products and the formation mechanism of by-products in the depolymerization, ascertaining the breakage mode of bond existing in straw in the process of depolymerization, and calculating and simulating the interactional character between straw molecule and chemical depolymerization reagent under the complicated and interfacial conditions using the method of calculational chemistry. Then, the structure-activity relationship between the upstream structure depolymerization and the downstream conversion for fuel ethanol of straw is investigated and further clarified by feedback evaluation of the results from the enzymolysis and fermentation of straw after chemical depolymerization. These studies mentioned above may provide the scientifically theoretical and practical foundation for the design and selection of economical, environmentally friendly, and highly operable straw depolymerization strategy.

随着全球变暖及化石燃料的枯竭,许多国家都非常重视生物质能源尤其秸秆能源的开发与应用研究。然而，由于缺乏对秸秆结构解聚机制科学问题的深层次认识，极大地限制了高效解聚秸秆方法的研究步伐，而后者是实现秸秆高附加值转化的先决条件。本课题在前期研究基础上，以麦秸、稻秸和玉米秸三种典型农作物秸秆为研究对象，在分子水平上探讨秸秆化学结构及其构筑单元的键合方式，研究不同化学解聚条件下秸秆分子结构演变规律、特征及机制，解析解聚产物的结构特性及副产物的形成机制，推断秸秆在化学解聚过程中的断链模式，并引入计算化学研究手段，从微观上计算和模拟复杂环境与界面条件下秸秆与化学解聚剂相互作用的本质，从而提出农作物秸秆的化学解聚机制。然后通过对解聚后秸秆下游酶解和发酵效果的评价，反馈性探讨和阐明秸秆上游结构解聚与下游转化燃料乙醇的构效关系，为经济、环保、可操作性强的秸秆大分子解聚方案的设计与选择提供科学的理论和应用依据。

随着全球变暖及化石燃料的枯竭,许多国家都非常重视生物质能源尤其秸秆能源的开发与应用研究。然而，由于缺乏对秸秆结构解聚机制科学问题的深层次认识，极大地限制了高效解聚秸秆方法的研究步伐，而后者是实现秸秆高附加值转化的先决条件。本课题在前期研究基础上，开展农作物秸秆分子结构的化学解聚机制研究，旨为经济、环保、可操作性强的秸秆大分子解聚方案的设计与选择提供科学的理论和应用依据。结果表明：（1）秸秆经酸解聚，主要脱除的是半纤维素。获得了酸解聚过程葡萄糖、木糖和阿拉伯糖以及副产物乙酸和糠醛生成的动力学行为；（2）发现相比于时间和浓度对CSP的影响，温度更加敏感。当CSP0=1.80时，可以获得44.31%的总还原糖，在此条件下，葡聚糖回收率达到88.02%，聚戊糖脱除率达到97.21%；（3）酸解聚秸秆的机理是：氢质子首先使半纤维素和木质素的连接键断裂，半纤维素支链断裂形成阿拉伯糖、葡萄糖和乙酸，随后主链水解形成木糖。降解产物葡萄糖和木糖在酸催化下进一步产生5-HMF和糠醛，5-HMF会继续降解生成甲酸和乙酰丙酸，糠醛降解成甲酸；（4）碱解聚主要脱除秸秆中木质素，最佳解聚条件为NaOH浓度2.24%、温度81 ℃、解聚时间4.30 h，木质素脱除率达85%。（5）用复合酶酶解评价秸秆解聚效果，发现先酸后碱预处理，可获得67.83%的葡萄糖得率和较高的乙醇产率；（6）3%硫酸+50%NMMO耦合处理秸秆，可有效降低纤维素的结晶度，使后续酶解得率达到65.05%，乙醇得率48.43%。1%碱+50%NMMO处理秸秆，后续酶解得率达到98.03%，乙醇得率64.64%；（7）制备了负载型金属催化剂，用于解聚后秸秆的催化加氢研究。发现碱处理的效果要优于酸处理的，其中Ni–W2C/CSAC催化加氢可获得72.74%的乙二醇和丙三醇；5%Ni-15%W/MCM-41可得60.72~71.37%的乙二醇和1.2-丙二醇，并提出了秸秆催化加氢转化多元醇的机理。