常压甘油相有机溶剂预处理解构木质纤维素类生物质及促进其高效酶解的机理分析

The key to current enzyme-based biorefinery industrialization is to find an efficient pretreatment strategy that is supposed to deconstruct the recalcitrant cell wall of lignocellulosic biomass, and thus to enhance the enzymatic hydrolysis of it efficiently. Numerous studies made by us and other researchers on the pretreatment have demonstrated glycerol organosolv pretreatment (GOP) is extremely effective and competitive in improving the hydrolyzability of lignocellulosic biomass, but the mechanism behind that is yet to elucidate with the overall analysis. To shed light on the process mechanism of the GOP improving the substrate susceptibility effectively, accordingly, some plans have been made in this research proposal as follows: First, such aspects as disintegration point of the fiber and split-off place / way of the lignin-carbohydrates, involving the lignin dissolution, will be taken into consideration during the various GOP condition. Then, the chemical compositional and physical structural changes, including supermolecular structure, of substrates during the GOP and enzymatic hydrolysis will be characterized and compared at multi-dimensional scales with various modern analytic equipment. Meantime, the main / side chain sugar units of hemi-cellulosic polysaccharides and constitutional units of lignin polymers will be characterized with quantitative analysis, to gain insights into why the pretreatment has presented such a good selectivity at component removal, thereafter resulting in the superior hydrolyzability of substrates. Finally, our efforts will be made to understand the reason that the atmospheric GOP process initiated by us has resulted hardly in producing furan inhibitors to the downstream saccharification / fermentation from lignocellulosic feedstock. To make it clear, the chemical distribution and state of the glycerol bound in dissolved polysaccharides and pretreated substrates will be studied, together with some model experiments. The research proposal is purposed to supply a solid support to further development and scale-up of the GOP process.

找到有效的预处理方法来疏解木质纤维素类生物质顽抗性以促使其高效酶解，是当前酶基生物质炼制工业化瓶颈的破解之道。常压甘油相有机溶剂预处理已初步显示出独特优势，但缺乏系统性分析和机理性认识。因此，本课题围绕“阐明甘油有机溶剂处理提高基质可酶解性的机制”提出如下研究思路：首先，课题拟分析比较各种甘油有机溶剂预处理过程，研究纤维素分离点、木质素-碳水化合物的断裂位点/方式和木质素溶出规律；接着，本课题拟利用现代分析技术手段多尺度表征基质在预处理和酶解时组成结构变化，定量分析甘油半纤维素多糖的主/侧链糖单元和甘油木质素组成结构单元的特征，以便解析该预处理选择性脱除组分和有效促进基质水解的原因；最后，课题拟研究甘油在预处理后基质和溶液里化学分布和存在方式，结合模拟实验阐明常压甘油相有机溶剂预处理不产生糠醛类抑制物的真正原因。本课题的实施将为该技术的工艺应用型研究，提供理论依据和技术支撑。

关于木质纤维素的生物炼制已经成为近年来的研究热点，但由木质纤维类生物质实现生物能源和生物基产品仍旧面临着许多瓶颈问题，其中找到有效的预处理方法来疏解木质纤维素类生物质顽抗性以促使其高效酶解，是当前酶基生物质炼制工业化瓶颈的破解之道。常压甘油相有机溶剂预处理已初步显示出独特优势，但缺乏系统性分析和机理性认识。基于此，本项目开展如下内容：1）木质纤维素原料甘油有机溶剂预处理工艺的系统优化。本项目建立了常压碱/酸催化甘油有机溶剂预处理方法，其预处理后基质都展示了较好的酶解效果，2%（w/v）基质在5 FPU/g酶解48 h后，酶解率都达到90%以上。2）甘油有机溶剂预处理木质纤维素基质的组成结构特征的解析。甘油有机溶剂预处理的基质其粗糙度和比表面积增加，基质结构疏松，增加了纤维素酶的吸附作用。3）探讨了甘油有机溶剂预处理环境中木质素-碳水化合物的断裂规律，发现甘油接枝性修饰木质素形成甘油木素现象。另外，甘油作为亲核试剂淬灭共振稳定的苄基碳阳离子并形成具有羟基尾部的α-醚化木质素，使得木质素脂肪族羟基含量增加，增强其在甘油中的溶解，在一定程度上保留了木质素中的β-O-4´键；同时甘油有机溶剂木质素具有高纯度、窄多分散性、低分子量和高化学反应性的特点，有利于后续木质素的高值化利用。4）分析了常压甘油相有机溶剂预处理不产生呋喃类发酵抑制物的根本原因。纤维质原料中纤维素和半纤维素多糖大分子结构、常压预处理以及高甘油浓度可能是导致预处理几乎不产呋喃类发酵抑制物的原因。项目通过从理论与技术上探讨木质纤维素原料的甘油有机溶剂预处理过程，利用现代分析技术全方位地剖析甘油有机溶剂预处理木质纤维素基质的组成结构变化，初步阐明该预处理对纤维基质的作用机制；明晰了该预处理在酸/碱催化条件下断裂木质素-碳水化合物组成结构的差异性；阐明了常压甘油相有机溶剂预处理不产糠醛类发酵抑制物的原因；清楚了该预处理促进木质纤维素基质高效酶解的重要原因。