On the Meaning and Origins of Lignin Recalcitrance: A Critical Analysis of the Catalytic Upgrading of Lignins Obtained from Mechanocatalytic Biorefining and Organosolv Pulping
On the Meaning and Origins of Lignin Recalcitrance: A Critical Analysis of the Catalytic Upgrading of Lignins Obtained from Mechanocatalytic Biorefining and Organosolv Pulping
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DOI：
10.1002/cctc.201700473
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发表时间：
2017-07
期刊：
影响因子：
4.5
通讯作者：
G. Calvaruso;Matthew T Clough;M. D. K. Rechulski;R. Rinaldi
中科院分区：
文献类型：
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作者：
G. Calvaruso;Matthew T Clough;M. D. K. Rechulski;R. Rinaldi
在催化木质素增殖的广泛背景下，“顽固性”一词通常用于描述木质素进行化学转化（通常是还原过程）的抵抗力，使小分子可溶于反应介质。不幸的是，目前“顽固性”一词的用法往往在意义上仍然模糊，阻碍了寻找更好的木质素增值催化剂。在探索解决研究问题的过程中-什么是木质素顽固性？-我们从不同的角度展示了我们对木质素抵抗还原性催化过程的因素的研究。在本研究中，研究了从水溶性木质纤维素（由山毛榉木、松木或甘蔗渣的无溶剂机械催化解聚产生）糖化过程中分离出的沉淀物木质素，以及通过溶剂萃取（有机溶剂制浆）分离出的同类木质素。对结构和键合的批判性分析，以及对轻度和极端条件下Raney Ni和H2压力存在下木质素流催化升级结果的深入了解，表明简单评价液体产品的总产率并不能定量衡量木质素的顽固性。我们的研究结果揭示了“木质素顽抗”的真正意义、起源和催化研究的意义。结果表明，木质素的顽固性不仅与其内在性质（如分子量、天然键的发生及其键解离焓）有关，而且与其外在性质（如残余多糖和溶解度）有关。总体而言，本研究通过对产品混合物性质（例如H/C和O/C比率，分子量分布，关键单个产品的产率等）的批判性分析，对木质素的顽固性进行了详细的评估。
In the broad context of catalysis for lignin valorization, the term “recalcitrance” is often used to describe the resistance of lignin to undergo chemical transformations (generally, reductive processes) rendering small molecules soluble in the reaction medium. Unfortunately, the current usage of the term “recalcitrance” often remains vague in meaning, hindering the search for better catalysts for lignin valorization. In the quest to address the research question—What is lignin recalcitrance?—we present our search for the factors responsible for the resistance of lignin to reductive catalytic processes, from various perspectives. In this study, lignins isolated as a precipitate obtained from the saccharification of water‐soluble lignocelluloses (produced by solvent‐free mechanocatalytic depolymerization of beechwood, pinewood, or sugarcane bagasse) and their counterparts isolated by solvent extraction (organosolv pulping) are investigated. The critical analysis of structure and bonding, in addition to the in‐depth understanding of results from the catalytic upgrading of lignin streams, in the presence of Raney Ni and H2 pressure under mild and extreme conditions, reveals that the simple evaluation of the total yield of liquid products provides no quantitative measure of the lignin recalcitrance. Our results shed light on the real meaning, origins and implications of “lignin recalcitrance” for catalysis research. The results demonstrate that lignin recalcitrance is associated not only with its intrinsic properties (i.e. molecular weight, the occurrence of native linkages, and their bond dissociation enthalpies) but also with its extrinsic properties (e.g. residual polysaccharides and solubility). Overall, this study presents a detailed evaluation of recalcitrance of lignin through the critical analysis of the product mixture properties (e.g. H/C and O/C ratios, molecular weight distribution, yield of key individual products, and several others).