温和条件下物理化学预处理木质纤维超微结构变化及促进酶解的机理研究

Pretreatment and enzymatic saccharification are the key steps of biomass conversions. With the development of biotechnology, the cost of cellulase has been reduced remarkably, while the high cost of pretreatment is still the bottleneck of high-value utilization of lignocellulose, due to some problems, such as high energy consumption, environmental protection, and low efficiency. Our previous studies showed that, after the BIVIS pretreatment of corn stover under mild conditions, 70% of the dissolution rate of hemicellulose and 92% of the enzymatic hydrolysis yield of cellulose could be obtained. In the mean time, the energy consumption was lowered significantly. In this research, the changes of chemical components and ultrastructure of biomass materials during the physical and chemical pretreatment will be studied, to elucidate the mechanism of the dissolution of hemicellulose and lignin under mild pretreatment conditions, and the effective promotion of enzymatic hydrolysis of cellulose. Subsequently, a new approach of simultaneous saccharification and co-fermentation of acid-soluble hemicellulose together with alkaline pretreated cellulose will be established, through the selection or combination of hemicellulase, and cellulase, as well as thermoanaerobic bacteria, which can simultaneously ferment pentose and hexose. The goal of the co-fermentation is to realize the needed reaction environment in the system and resolve the issues of chemical recycling and environmental protection. At last, based on the understanding of the mechanism, the system parameters will be further optimized, to set up a method of mild pretreatment and saccharification, which are economically efficient and environment-friendly. These studies will lay the foundation for the industrialization of the conversion of lignocelluloses into bioenergy, biomaterials or biochemicals.

预处理酶水解糖化是木质纤维原料生物转化的关键步骤，而随着生物技术的发展，纤维素酶的成本已经取得了突破性进展，但是预处理因为能耗、环保及效率等问题成为木质纤维高值化利用的瓶颈。申请者前期研究表明BIVIS双螺旋挤压机协同酸碱温和条件下预处理玉米秸秆，可在大幅度降低预处理过程能耗的同时，使半纤维素的溶出率达到70%，纤维素酶解得率达到92%。本项目旨在通过对物理化学预处理木质纤维原料化学组分和超微结构变化的研究，阐明这种新型预处理方法温和条件下溶出半纤维素、木质素及高效促进纤维素酶解的机理。然后，筛选或复配适合的半纤维素酶、纤维素酶，建立酸溶半纤维素和碱处理纤维素耦合酶水解糖化的新路线，以在系统内实现所需要的反应环境，解决化学品回收及环保问题。最后，根据机理性认识，进一步优化系统参数，建立一套经济高效环保温和的预处理糖化方法,为木质纤维原料转化为能源、材料或化学品的产业化奠定基础。

阻碍木质纤维原料生物质转化为能源、材料或高附加值化学品的关键瓶颈问题是缺乏经济高效的生物质预处理技术及各组分的分别高效转化。项目发明了一种BIVIS机双螺旋挤压预处理技术，在高浓（约35%）低温（小于100℃）低用碱量（NaOH用量6%）的条件下处理玉米秸秆，木质素脱除率为71%，预处理后秸秆在纤维素酶用量20PFU/g、木糖酶用量5IU/g、水解时间48h的条件下进行酶水解，水解后葡聚糖水解效率高达87.5%，总糖得率约78%，水解液使用丙酮丁醇梭菌ATCC824发酵，总糖转化率92.7%，ABE总产率为112kg/t玉米秸秆；利用BIVIS机分离的半纤维素转化为功能性低聚木糖，具有成本低、有效成分含量高、过程绿色环保的优点，低聚木糖的转化率达到了80%，可代替市场上从玉米芯或甘蔗渣中提取的低聚木糖；分离的半纤维素可以使用固体酸脱水一步法制备糠醛，糠醛产率达到80.5%，且固体酸可循环利用，有效解决了液体酸的腐蚀和环境污染问题；以分离的半纤维素为原料，利用自由基聚合反应，将丙烯酸单体接枝到半纤维素骨架上，制备的具有较高力学性能的水凝胶，其压缩强度105.1kPa±12.9 kPa、应变34.8%、最大吸水率192，该水凝胶对pH，盐以及乙醇迅速响应，可以广泛应用在药物释放、污水处理以及细胞固定等领域；分离出的木质素氧化磺化反应后可以作为混凝土减水剂，此减水剂添加量为0.3%时，水泥净浆流动度185mm。基于双螺旋挤压预处理的玉米秸秆实现了全组分的高效综合利用，具有较好的产业化前景。