木质纤维素选择性水解制备糖类小分子化合物方法及机理研究

Lignocellulose is the most abundant resource of biomass. Cellulose and hemicellulose are the main components of lignocellulose. Depolymerization of these polysaccharides to monosaccharides using lignocellulose as raw material is a key step in the conversion of biomass to fuel and chemicals. This project will apply the high-pressure CO2-H2O and oxidation-depolymerization strategy, to realize the depolymerization of polysaccharide components of lignocellulose in the absence of catalyst. In the first step, selective depolymerization of hemicellulose is fulfilled by the weak acidity of high pressure CO2-H2O as solvent and low concentration of acetic acid as co-catalyst. For the depolymerization of cellulose, partial -CH2OH on glucose units of the cellulose component is converted to –COOH by oxidation; and then the oxidized cellulose is depolymerized via the catalysis of carboxyl groups with water as solvent. The project will focus on the method and mechanism of CO2-H2O for the removal and depolymerization of hemicellulose from lignocellulose, the selective oxidation method for lignocelluloses, and the mechanism of polysaccharide hydrolysis in presence of the generated acid sites. Through this project, it is expected to realize the depolymerization of cellulose and hemicellulose from lignocelluloses by an environmental-friendly new route and clarify the mechanism of this method. The research of this project will supply a new technical support and theoretical basis for the utilization of polysaccharide components of biomass.

木质纤维素是生物质的最主要存在形式，纤维素和半纤维素是其主要组分。以木质纤维素为原料，解聚其多聚糖组分至单糖，是生物质转化为燃料和化学品的关键步骤。本项目拟采用高压CO2-水体系处理结合氧化-解聚策略，逐次解聚木质纤维素的半纤维素和纤维素组分。首先以高压CO2-水为溶剂，低浓度乙酸为助催化剂，利用体系的弱酸性选择性催化木质纤维素的半纤维素组分水解。然后氧化预处理，将纤维素组分部分葡萄糖单元上的-CH2OH转化为-COOH；在羧基的催化作用下，实现水溶剂中纤维素组分的解聚。项目重点研究CO2-水体系催化木质纤维素中半纤维素组分去除和解聚的方法和原理，木质纤维素的选择性氧化方法，以及氧化处理产生的酸性催化多糖组分水解的机理。通过本项目的研究，预期开辟木质纤维素多聚糖组分解聚的环境友好新路线，阐明该线路解聚多聚糖的原理，为生物质资源的利用提供新的技术支持与理论依据。

木质纤维素是生物质的最主要存在形式，纤维素和半纤维素是其主要组分。以木质纤维素为原料，解聚其多聚糖组分至单糖，是生物质转化为燃料和化学品的关键步骤。农作物秸秆是木质纤维素最主要的来源之一。本项目采用高压CO2-水-低浓度乙酸体系处理结合氧化-解聚策略，逐次解聚秸秆生物质的半纤维素和纤维素组分。首先以高压CO2-水为溶剂，低浓度乙酸为助催化剂，利用体系的弱酸性选择性催化秸秆生物质的半纤维素组分水解，半纤维素的去除率大于80%，主要产物为低聚木糖及木糖。然后以分子氧为氧化剂对去除半纤维素的生物质氧化预处理，将纤维素组分部分葡萄糖单元上的-CH2OH转化为-COOH；以水为溶剂，在羧基的催化作用下水解纤维素组分，生成葡萄糖。小麦秸秆和玉米秸秆葡萄糖的最高收率分别为41.6%和32.6%(以秸秆中纤维素含量计算)。该路线应用玉米芯及糠醛渣的纤维素组分解聚制备葡萄糖，也表现出了良好的葡萄糖收率。开发的方法有望在秸秆生物质解聚制备低聚木糖、葡萄糖及高附加值的生物质平台化合物中得到应用。