浓H3PO4联合H2O2预处理木质纤维素的机理及其对高基质浓度酶水解的调控

In order to give better soulutions to the key isssues of high-efficient pretreatment and high-solids enzymatic hydrolysis in the conversion process of lignocellulose to bioethanol, a pretreament method for lignocellulose is being proposed using the concentrated H3PO4 with H2O2 according to the solubilitity of concentrated H3PO4 to lignocellulose,and regenerated cellulose with relatively low DP (degree of polymerization) and CS (crystallinity). In this wrok, the in-deepth investigations will be performed on the key chemical reaction paths of lignin, hemicellulose and cellulose during the dissolution process in concentrated H3PO4.The depolymerization kinetics of lignin, hemicellulose and cellulose will be deeply investigated as well. Moreover, the machensims of H2O2 in the concentrated H3PO4 pretreatment will also give a considerable investigation. Based on the machensims of concentrated H3PO4/H2O2 pretreatment, the adaptability of the pretreatment to different lignocellulosice materials will be evaluated. Meanwhile, the potential enhancement of substrate consistency for enzymatic hydrolysis will be seriously evaluated. The regulative mechanisms between the pretreatment conditions and high-solids enzymatic hydrolysis will also be investigated. Besides, the optimization of pretreatment for improving high-solids enzymatic hydrolysis and fermentable sugar recovery will be carried out as well. Based on the results of this work, a green, modest and high-efficient pretreatment method can be offered for lignocelluloses. They also can offer some references to potentially improve the efficiency of lignocellulose to ethanol and reduce the cost of lignocellulosic ethanol in practice.

以木质纤维素乙醇转化技术中高效预处理和高基质浓度酶水解两个关键环节为研究切入点，基于木质纤维素组分在浓磷酸中具有可溶性和再生性，且获得的再生纤维素具有低聚合度和结晶度等技术特征为基础依据，本研究提出浓磷酸联合H2O2预处理实际木质纤维素。深入探讨浓磷酸在预处理中与木质纤维素各组分的主要反应途径及解聚动力学；并探讨H2O2 在浓磷酸条件下的对木质纤维素的作用机理；以预处理机理研究结果为基础，评价该预处理方法对原料的适应性；结合高基质浓度酶水解，明确预处理对酶水解基质浓度提高的潜力和内在调控机制，并优化浓磷酸联合H2O2预处理工艺，改善高基质浓度酶水解效率和可发糖回收率。通过本项目的研究，可为木质纤维素原料提供一种绿色、条件温和、高效的预处理方式，并为纤维素乙醇生产提高生产效率，降低生产成本提供理论依据和技术参考。

为了提升木质纤维素-乙醇转化的效率，降低生产成本，本研究以木质纤维素乙醇转化技术中新型预处理技术开发及配套的高基质浓度酶水解和发酵3个关键问题为研究切入点，系统开展了浓磷酸联合过氧化氢（PHP）预处理技术的研究。PHP实现了对多类典型生物质原料（软木、硬木、农作物秸秆、竹木以及园林废弃物）的高效预处理，纤维素酶水解率达90%以上，表现出良好的原料通适性和较低的粒径依赖性；在PHP预处理过程中，提升预处理温度可以有效的改善酶水解速率，但过高的温度(>50℃)降低了葡萄糖的转化率。延长预处理时间有利于酶水解性能的提高。此外，增加磷酸浓度可以提高水解速率，但也会导致葡萄糖转化率的微小降低。通过优化获得，40.2℃，2.9h， 79.6%磷酸为较优的预处理条件。在此条件下，水解率可以实现100%，100g小麦秸秆可以产出28.2 g的葡萄糖。相比于现有的主流预处理技术，提升优势明显。采用PHP预处理木质纤维素，可以提升酶水解基质浓度潜力至20%，Ctec2酶的添加量可以降低至17.5 mg/g，葡萄糖产量可以到达155.35 g/L。PHP预处理未对后续的乙醇发酵产生抑制，通过优化获得，在16.4%基质浓度下，维持13.24mg/g酶用量，酵母添加1.0g/L，可以实现最大78.43%的理论乙醇转化率，乙醇产量为66.08 g/L。在预处理机理方面，基本明确了高效的半纤维素脱出和木质素去除是提升纤维素酶水解率提升的关键。浓磷酸的溶解功能是半纤维素去除的主要机制，在浓磷酸体系中，由半纤维素中的乙酰基团和过氧化氢形成的过氧酸是木质素去除的主控机制。通过本研究为该技术在木质纤维乙醇转化体系中应用提供有力且全面的理论支撑，同时为PHP预处理机理的厘清奠定了良好的研究基础。