基于甲酸分级预处理的蔗渣全组分资源化利用新路线及过程机理

Economical and efficient deconstruction or fractionation of lignocellulose into cellulose, hemicellulose and lignin is key to realize the high value utilization of lignocellulose. Formic acid pretreatment is economic, effective and clean for the component separation of sugarcane bagasse. In order to further analyze the mechanism of formic acid pretreatment, expand the application range of formic acid pretreatment and achieve the resource utilization of the main components of sugarcane bagasse, the project intends to proceed from the mesoscopic and microscopic scale and the changes in physical properties and chemical structure were studied by mean of multi-scale analysis. A new kinetic model of lignin removal and glycan hydrolysis based on the hierarchical structure of sugarcane bagasse cell wall was to be established, which can more accurately describe the kinetic behavior of the pretreatment process. The variation of multi-structure of sugarcane bagasse and general rule of lignin and hemicellulose dissolution during the formic acid pretreatment can be obtained by studying the changes of the microstructure and nanostructure of sugarcane bagasse through multiple analysis methods. Controllable crystallinity of cellulose and molecular weight controllable lignin can be obtained by controlling formic acid pretreatment conditions. Formic acid pretreatment fractionated sugarcane bagasse into two fractions: (i) a primarily cellulose-rich water-insoluble solid fraction that can transformed into lignocellulosic nanomaterials and then be used to prepare the composite membrane based on polylactic acid/nanocellulose; (ii) a spent acid liquor stream containing mainly dissolved lignin and degraded hemicellulose. Dissolved lignin can be easily separated as lignin by diluting the spent acid liquor to below the minimal hydrotrope and then be used for preparation of lignin phenol formaldehyde resins. The degraded hemicellulose can be converted into sugars through subsequent enzymatic hydrolysis. The whole process of fractionation and resource utilization of sugarcane bagasse will be established.

纤维素、半纤维素和木质素的经济高效分离是木质纤维素原料高值化利用的关键。甲酸分级预过程已实现蔗渣三大组分经济、高效、清洁的分离。为进一步解析甲酸预处理机制、扩大甲酸预处理的应用体系和实现三大主要组分的资源化利用，本项目拟从介观和微观尺度出发，对预处理过程中蔗渣物理性能和化学结构进行多尺度分析，建立基于蔗渣细胞壁的层次结构的木质素脱除和聚糖水解的新动力学模型，以更为准确地描述预处理过程的动力学行为；同时结合多种分析手段，研究甲酸预处理过程对纤维素结晶度、甲酰基取代度、木质素分子量的影响，获得蔗渣的多重结构在预处理过程中的变化规律，明晰纤维素、木质素结构组成控制的机理；并通过调控甲酸预处理条件获得甲酰化程度可控的纤维素及分子量可控的木质素原料，为其进一步资源化利用提供合适原料；最终建立了以聚乳酸/纳米纤维素复合膜、木质素基酚醛树脂和木糖醇为最终产品的蔗渣全组分分级分离及资源化利用的工艺路线。

本项目针对现有木质素脱除和木聚糖水解的动力学模型不能准确的描述和模拟木质纤维素在化学试剂中的实际反应过程，未能明晰化学试剂对木质纤维素中各组分连接键的作用力大小和顺序以控制木质纤维素中聚糖和木质素的水解过程，使得目前木质纤维素难以实现全组分综合利用的问题，引入可反应度参数，采用同步检测液相和固体中残留木质素的方法，建立了与实验数据拟合良好的新动力学模型，同时获得了甲酸预处理中质子对木质纤维素细胞壁中三种成分间连接键的作用次序和影响大小，进一步了解了木质纤维素的降解机制，为通过控制木质纤维素预处理过程获得符合后续资源化利用要求的纤维素、木质素原料提供了有效的技术手段；通过控制预处理条件获得了结构、组成可控的纤维素、木质素，以此为原料制备得到了性能良好的纤维素/聚乳酸复合膜和酚醛树脂，在食品包装材料和木材粘结剂领域有良好的应用前景。