高温液态水中木质素迁移行为及其对多糖水解的联动反应机制

How to break the recalcitrance of lignocellulosic biomass with a lower energy-consumption, non-pollution and higher sugars recovery process is one of the practical problems occurring in course of biomass energy conversion. Compared with the dilute acid, lime and ammonia fiber expansion pretreatment, liquid hot water pretreatment using pressure to maintain the water in the liquid state at elevated temperatures is a green and attractive approach because of its no chemicals addition, and high recovery of most of the pentosan. But problems caused by the low xylose monomer yields and low lignin removal have become the bottlenecks in the industrial applications of liquid hot water pretreatment. A deeper understanding of mechanisms of how lignin influences the saccharification of hemicellulose and cellulose in the process of pretreatment and enzymatic hydrolysis is now required to optimize the overall conversion process. Multi-scale (micro- to nanometer scale)characterization of lignin in the cell wall ultrastructure regions, droplets on the cell wall or on the surface of model compounds and decomposition products in the liquid fraction were carried out by electron microscopy, spectral and chromatographic analysis to elucidate the fate of lignin in the liquid hot water. Moreover, the influences of lignin migration on the saccharification of hemicellulose and cellulose in the process of pretreatment and on the accessibility of cellulose to enzymes were determined by detecting the distributions and penetration of xylan, glucan and cellulase with the help of immuno electron microscopy using polymer and enzyme-specific antibodies. Overall, the research on the mechanism of biomass decomposition in the liquid hot water would provide insight into the industrial applications of liquid hot water pretreatment.

寻找低能耗、无污染、高糖收率的预处理方法是生物质能生化转化迫切需要解决的问题之一。与酸碱法、氨纤维爆破等传统预处理法相比，高温液态水预处理具有无化学试剂添加和高半纤维素糖收率等优点，但低木糖得率和低木质素去除率等诱发的问题阻碍了其工业化进程。本项目拟以木质素在预处理和酶解过程中对半纤维素和纤维素糖化作用机制为切入点，结合微观和宏观分析，借助免疫电镜、光谱和色谱等多尺度表征手段，研究不同高温液态水预处理过程中木质纤维素类生物质及其模型物的木质素在细胞微区迁移、细胞壁上沉积和水解液中分解的规律，来阐明木质素的迁移和强化机制；通过追踪预处理过程中多糖和酶解时纤维素酶在细胞微区的穿透行为，及多糖超分子结构变化，揭示预处理过程中木质素对半纤维素和纤维素水解的联动反应机制，及木质素形态或分布变化对纤维素酶解的影响机制。本项目的完成，将为解决限制高温液态水技术大规模应用的瓶颈问题提供理论依据和科学导向。

寻找低能耗、无污染、高糖收率的预处理方法是生物质能生化转化迫切需要解决的问题之一。与酸碱法、氨纤维爆破等传统预处理法相比，高温液态水预处理具有无化学试剂添加和高半纤维素糖收率等优点，但低木糖得率和低木质素去除率等诱发的问题阻碍了其工业化进程。本项目以木质素在预处理和酶解过程中对半纤维素和纤维素糖化作用机制为切入点展开相关机理研究。未处理原料细胞壁分层现象明显，由外至内分别为胞间层、初生壁及次生壁，高温液态水预处理后各层界线变得模糊。SEM-EDXA分析表明细胞壁各层木质素分布发生了迁移，水解液中的木聚糖和木质素衍生物在细胞壁表面凝集生成类木质素滴状沉淀物，部分木质素发生降解生成愈创木基丙烷、紫丁香基丙烷和对-羟基苯基丙烷的小分子衍生物。增加反应过程的剪切力如流速加大、加强半纤维素的脱除如氯化铜的添加，都会促进细胞壁木质素的固体溶出。过氧乙酸可以特异性脱除木质素，而原料中半纤维素和纤维素损失较少，经高温液态水处理后半纤维素单糖得率为100%。相比而言，木质素对纤维素具有一定“保护作用”。物料表面类木质素滴状物对纤维素酶的吸附作用不显著，主要通过空间位阻作用抑制纤维素酶水解。