低共熔溶剂/水体系中半纤维素的选择性解离机制及其对酶解影响的机理研究

Deep eutectic solvents (DES), emerged as a new generation of green solvents with low cost, straightforward preparation, biodegradable and adjusted performances by choosing different composition and ratio, have attracted much attention in lignocellulose treatment and conversion. The current barriers on lignocellulose treatment is to synthesize and optimize the DES media for fractionation the major components as well as to interpret the influence and the mechanism on the cell wall after the treatment. The project focuses on the exploitation of ideal DES aqueous media which could realize the efficient dissociation and isolation of hemicelluloses from lignocellulose and interpret the mechanism of the hemicellulose dissociation and the influence on the enzymatic hydrolysis efficiency of cellulose. Various DES will be explored and different DES aqueous solutions will be prepared by diluting the neat DES in deionized water. The solubility of hemicellulose will be investigated to evaluate and optimize the ideal media. Hollocelluose and lignocellulose will be chosen as the raw materials to interpret the mechanism of the hemicellulose dissociation in DES aqueous media. The exact structure features of hemicelluloses obtained from the media will be characterized and the influence of lignin on hemicellulose dissociation will be investigated. Combined with the recovery and structure features of hemicelluloses from recycled DES aqueous and the hemicellulose dissolution characteristics, the mechanism of hemicellulose dissociation from lignocellulose will be interpreted. Besides, the structure, surface morphology, thermal property, and spatial distribution changes of the cell wall before and after DES aqueous treatment will be investigated; thus the influence and mechanism of DES treatment on enzymatic digestibility will be clarified. The project will provide theoretical idea for the DES preparation and the efficient utilization of lignocellulosic biomass.

低共熔溶剂廉价易得、制备简单、生物可降解，可通过改变组成及配比调节其性能，近年来在生物质转化领域备受瞩目。利用低共熔溶剂实现木质纤维素的全组分分离是该领域的研究难点，选择理想的溶剂体系溶解及解离半纤维素是制约全组分分离的瓶颈。本项目拟在优选的低共熔溶剂中引入一定量的水分子，通过考察其对半纤维素的溶解度，筛选和构建可溶解半纤维素的低共熔溶剂/水体系，实现综纤维素及木质纤维素原料中半纤维素的选择性解离，揭示木质素对半纤维素解离的影响规律，研究低共熔溶剂的回收和循环利用率，解译解离产物的结构及性质，结合体系对半纤维素单一组分的溶解机理，阐明低共熔溶剂/水体系木质纤维素中半纤维素的解离机理。探讨低共熔溶剂/水体系处理前后木质纤维素组成、结构、热稳定性及主要组分微区分布的变化，揭示低共熔溶剂/水体系提高木质纤维素酶解效率的作用机理，为木质纤维素新型绿色溶剂的设计及全组分分离利用奠定理论基础。

以低共熔溶剂（DES）进行木质纤维素的全组分分离是目前生物质转化领域的研究热点，其中理想溶剂体系的选择及半纤维素的完整解离是该研究中的难点。本项目根据氢键供受体的结构和设计理论，构建了新型碱性DES、胆碱氨基酸基DES及多元醇基Brønsted酸DES及其水体系，通过考察溶剂体系对半纤维素单一组分的溶解性能，筛选了三类具有强氢键网络、适宜氢键酸碱度及较高循环稳定性的DES体系，这些体系均可在较低温度下实现半纤维素的选择性解离。系统研究了半纤维素在不同DES体系中的解离规律及DES体系含水量及反应条件对半纤维素结构的影响，结果表明DES解离所得半纤维素具有高分子量及线性结构，而高含水量的DES/水体系可获得高分支度、低分子量的半纤维素。结合DES预处理前后木质纤维素的结构变化，揭示了DES及其水体系增效木质纤维素酶解的作用机理。无定形组分的溶出使得纤维素残渣结晶度增大，晶型均保持纤维素Ⅰ结构。在多元醇基Brønsted酸DES预处理中，多元醇可捕获木质素在此过程中产生的碳正离子中间体，从而抑制木质素的缩合反应，使处理残渣具有高可及性，极大地提高了木质纤维素的酶解效率。本项目为选择性解离半纤维素DES体系的高效设计提供了理论依据，为木质纤维素的全组分分离及DES预处理增效木质纤维素酶解研究奠定了基础。基于以上研究，本项目共培养硕士研究生3名，发表SCI收录论文7篇（均为中科院一、二区论文），授权国家发明专利2项。