SGER - Fundamental Understanding of Catalytic Cleavage of Lignin in Ionic Liquids

木质素是木质纤维素生物质的主要成分之一。木质素对微生物分解的抵抗性是保护天然林免受自然本身快速降解的一个非常有益的特征。尽管自然界已经进化出许多酶，这些酶可以有效地将纤维素和半纤维素水解成它们的建筑单元，但木质素的存在已经被认为严重抑制了这些活动。本研究解决了生物质转化中最紧迫的问题，并寻求发展木质素解聚的关键步骤，这是有效生物质转化的第一步。这项研究建立在先前的研究和文献的基础上，这些研究和文献表明木质素可以溶解在离子液体中，并且木质素会受到碱的攻击。木质素具有复杂但特征不明确的组成和结构，这也取决于生产木质纤维素生物质的植物种类和条件。为了避免分析上的复杂性，以理解碱催化木质素氧键水解的机制，本研究将研究木质素中含有氧键的模型化合物。该研究调查了中性离子液体和碱性离子液体，每种液体都有最佳的水量，使用和不使用催化剂。测试介质的pH值和温度将被控制和遵循。考察了反应时间、工艺压力、碱催化剂类型和浓度的影响。本研究将采用芳香碱，其碱度可由金属离子的碱度、芳香基团的类型和大小以及多碱度来调节。碱性芳香羧酸盐将被纳入研究，以利用它们在合适的载体溶剂（如离子液体）中对木质素结构的强亲和力。通过选择不同碱度的催化剂和不同的操作条件，我们建议在不同的键网络中选择性地靶向不同键强度的氧键。通过使用一些模拟木质素中氧键的模型化合物，本研究试图对木质素水解裂解的机制有一个基本的了解。将溶解木质素的离子液体溶剂作为介质进行反应。不同碱度的碱催化剂将用于研究碱强度对离子液体溶剂中氧键水解裂解活性的影响。模型木质素化合物中的氧键类型将根据它们在离子液体中碱存在时的裂解难易程度进行排序。通过这项研究获得的知识将有助于设计离子液体中木质素的快速破碎性质的过程。此外，基于对木质素中氧键水解裂解的理解，模型木质素化合物将在离子液体中进一步研究，以选择性裂解产生芳香分子作为潜在的燃料和化学品。

0849342EkerdtIntellectual Merit Lignin is one of the major components in lignocellulosic biomass. The recalcitrant nature of lignin toward microbial breakdown is a highly beneficial feature in guarding natural forestry from rapid degradation by nature itself. Even though nature has evolved a number of enzymes that collectively are efficient in hydrolytically cleaving cellulose and hemicelluloses into their building units, the presence of lignin has been known to severely inhibit such activities. This research addresses this most pressing of issues in biomass conversion and seeks to develop processes and insight into key steps in lignin depolymerization, which are first steps in efficient biomass conversion. The research builds on previous studies and literature that demonstrate lignin can be dissolved in ionic liquids and that lignin is attacked by bases. Lignin has a complicated but poorly characterized composition and architecture, which also depend on the plant species and conditions in which the lignocellulosic biomass are produced. To avoid analytical complication for the purposes of understanding the mechanisms involved in base catalyzed hydrolysis of lignin oxygen linkages, this research will study model compounds that contain oxygen linkages found in lignin. The research investigates neutral ionic liquids and basic ionic liquids, each with an optimized amount of water, and with and without using a catalyst. The pH and the temperature of the test media will be controlled and followed. The effects of reaction time, process pressure, base catalyst type and concentration will all be examined. The research will employ aromatic alkali, of which the basicity can be tuned by the alkalinity of the metal ion, the type and the size of aromatic moiety, and polybasicity. Basic aromatic carboxylates will be included in the study to leverage their strong affinity toward lignin structure in a suitable carrier solvent, such as ionic liquids. By selecting catalysts of varying basicity and by varying operating conditions, we propose to target selectively oxygen linkages of different bond strength in different bonding networks. Broader Impacts By working with a number of model compounds that simulate the oxygen linkages in lignin, this research seeks to achieve a fundamental understanding of the mechanisms involved in lignin hydrolytic cleavage. Ionic liquid solvents that dissolve lignin will be used as media to carry out the reactions. Base catalysts with varying basicity will be used to study the effect of base strength in their activity toward the hydrolytic cleavage of oxygen linkages in ionic liquid solvents. The types of oxygen linkages in the model lignin compounds will be ranked according to their ease of cleavage in the presence of a base in ionic liquids. The knowledge to be gained through this research will help design processes for the rapid fragmentation nature of lignin in ionic liquids. Further, building upon an understanding in the hydrolytic cleavage of oxygen linkages in lignin, the model lignin compounds will be further studied in ionic liquids for selective cracking to produce aromatic molecules as potential fuels and chemicals.