竹材预提取过程糖组分降解机制及完善APMP竹浆性能的机理研究

Hemicellulose accounts for nearly one third of lignocellulosic biomass on earth. A problem to be solved in the process of biomass refining is how to increase the yield of fermented sugars from hemicellulose, while at the same time decrease the formation of inhibitors during the hemicellulose pre-extraction. It was found out in our previous investigation that the abundant bamboo raw material we studied contained excellent fibers. After extraction of hemicellulose by pre-extraction, APMP pulp of high quality could be made. In this proposal, we would like to firstly establish a theoretical kinetics models which could be used to predict the dissolution of some major polysaccharides and monosaccharides during the pre-extraction. We are going to study the degradation of each polysaccharide alone, as well as the degradation of multiple polysaccharides together by simulating the pre-extraction process, respectively. The structural and morphological changes of polysaccharide in different degradation conditions will be investigated in order to understand the interference effect of the different polysaccharides on each other. Compared with the method of single polysaccharide degradation system, the multiple polysaccharide degradation system can illustrate more adequately the degradation mechanism of polysaccharide during pre-extraction. Moreover, the method of molecular simulation technology will be employed to analyze the intermediate transition state of monosaccharides (hexoses and pentoses) during degradation process. Compared with the method of experimental detection, this simulation method can be used to study the degradation mechanism of monosaccharides and the formation mechanism of inhibitors in more detail. Through the above research, the mechanism of hemicellulose hydrolysis during the pre-extraction process can be revealed, which will provide the theoretical foundation for obtaining fermentable sugar with high yield. In addition, the mechanism of pre-extraction improving the pulping performance of bamboo APMP will also be elaborated by examining the influence of pre-extraction on the physical and chemical properties of bamboo. Results from this research will be valuable for the development of biomass refining technology based on pulping.

如何高效利用占生物质组成近1/3的半纤维素、在半纤维素预提取过程如何提高发酵糖产率和降低抑制物产生，是制约生物质精炼发展亟待解决的关键问题。前期研究结果表明，纤维质量高、储量丰富的竹材经预提取后，具有优异的APMP制浆性能。本项目首先建立预测提取液中各主要聚糖和单糖的溶出动力学模型；然后模拟预提取过程，分别研究半纤维素、单种聚糖及多种聚糖模型物降解的形态和结构变化，探索半纤维素中多种聚糖降解的相互影响机制，相比单种聚糖降解体系，更能充分说明半纤维素聚糖的水解机制；以及采用Materials Studio分子模拟软件分析己糖和戊糖降解过程的中间过渡态形式，比采用检测方法更能深入透析单糖降解及抑制物形成途径，揭示预提取过程抑制物产生机制，为如何调控预提取过程获得高得率发酵糖提供理论支持。同时，从竹片理化性质变化阐述预提取完善APMP竹浆性能的机理，对基于制浆平台的生物质精炼发展具有较大意义。

本项目首先研究单因素对水热提取（水热及碱性水热）竹子半纤维素影响，明确了影响水热预提取过程的主要影响因素，建立了碱性水热条件下预测提取液中阿拉伯糖、半乳糖、葡萄糖和木糖的溶出动力学模型。模拟预提取过程，研究半纤维素模拟物木聚糖和单糖水热过程降解及抑制物形成规律，进而优化水热过程提高发酵糖产率和降低抑制物产生，并获得不同水热条件下木糖的降解路径。采用量子化学模拟软件分析聚糖在水热降解过程过渡态结构、能垒以及反应路径的焓变、吉布斯自由能等热力学参数变化，结合客观基础实验数据，深入阐明水热过程抑制物形成途径、产生机制。这些结果为如何调控水热过程获得高得率发酵糖提供有利的技术支持。同时，阐述了不同水热预提取方式对竹片理化性质、漂后有机卤素生成、纤维制浆性能以及成纸物理性能等方面的影响，系统研究了预提取对APMP竹浆性能的影响机理。此外，在对液态产物分离时发现了荧光性能优异的碳量子点（CQDs），对预处理后的纤维底物进行机械研磨时发现非常有利于微纳米纤丝的制备。因此，该项目的实施及完成，拓展了本课题组今后的研究方向，同时为梯度定向高值化利用木质纤维原料提供了强有力的支持。