助溶剂型低共熔体系对木质素分离的弱相互作用诱导机制

The lack of efficient lignin fractionation strategies which gives the consideration to both yield and reactivity is the bottleneck of lignin valorization. The ideal lignin fractionation strategy should have strong lignin solubility, mild reaction conditions and effective prevention of lignin degradation. In this study, a hydrotropic deep eutectic solvent system (HDES) with strong lignin solubility is predicted and constructed by computer simulation based on Hansen solubility parameters and weak intermolecular interaction. Under mild conditions, the lignin fractionated by HDES is studied, and the combined delignification factor (CDF) is fitted, β−O−4 structure is quantified and lignin depolymerization performance is evaluated, the equilibrium relationship between lignin yield and reactivity is analyzed, and the β−O−4 degradation regulation of lignin is established. Based on the above studies and computational chemistry, the inducement mechanism of increased weak intermolecular interaction between solvent and lignin on the increased lignin phase transfer after the introduction of quaternary ammonium salts to cosolvent is discussed. Therefore, the mechanism of lignin micro-dissolution is improved. The study is expected to solve the key technical challenges in the process of lignin fractionation, which are difficult to give consideration to both yield and reactivity. It also provided the theories foundation for the directional development of lignin fractionation strategy.

缺乏可兼顾得率和反应活性的木质素高效分离策略，是当前木质素资源高效转化的瓶颈问题。理想的木质素分离策略应具备较强的木质素溶解性、温和的反应条件及有效的降解调控手段。本课题利用计算机模拟，以汉森溶解度参数和分子间弱相互作用为筛选依据，预测并构建有较强木质素溶解性的助溶剂型低共熔体系（HDES）。通过HDES体系木质素分离过程中脱木质素因子（CDF）拟合、β−O−4结构定量分析及木质素解聚性能评价等手段，探讨木质素得率与反应活性的平衡关系，建立木质素β−O−4降解调控机制。结合理论化学计算，研究助溶剂体系引入季铵盐后，溶剂分子间弱相互作用渠道的增加对木质素相转移增效的诱导作用规律，从而完善木质素微观溶解机理。本项目有望解决木质素分离过程中得率与反应活性难以兼顾的关键技术难题，为木质素高效分离策略的研发奠定理论基础。

基于对甲苯磺酸/水（p-TsOH/H2O）助溶剂体系以及对甲苯磺酸/氯化胆碱（p-TsOH/ChCl）低共熔溶剂（DES）体系，对松木、麦草等原料中的木质素在低温（80℃）短时间（20-40分钟）的条件下进行了分离。并通过对木质素脱离过程中原料化学成分以及木质素结构变化的研究，发现H+浓度在木质素溶解过程中起到了重要的作用。相比p-TsOH/H2O，p-TsOH/ChCl系统能够有效控制H+的释放，从而获得更高的β-O-4含量及更低缩合度的木质素，且p-TsOH/ChCl木质素与p-TsOH/H2O具有不同的理化性质，如粒径、极性、表面电荷和官能团等。相较于麦草，甲苯磺酸/氯化胆碱体系对松木木质素的提取并不理想。因此，本文利用水热接p-TsOH/ BTMAC(苄基三甲基氯化铵)两步法来提高松木木质素的分离效率。利用该法松木的木质素溶出率达到了71.6%，该结果与p-TsOH/ ChCl法相比，木质素溶出率提高了58%。分离出来的木质素中β-O-4含量，直接关系到后续木质素催化解聚中的反应活性。木质素中β-O-4含量越高，木质素氢解的产率就越高，含有35%芳醚的P70T80t60C样品中，单体产物得率能达到27.6%。以上研究成果将为低共熔溶剂用于木质纤维资源组分的高效分离提供理论基础, 为实现生物质资源全组分高品位利用提供可行之径。