Understanding the chemical transformations of lignin during ionic liquid pretreatment
Understanding the chemical transformations of lignin during ionic liquid pretreatment
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DOI：
10.1039/c3gc41752b
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发表时间：
2014-01-01
期刊：
影响因子：
9.8
通讯作者：
Sun, Run-Cang
中科院分区：
文献类型：
--
作者：
Wen, Jia-Long;Yuan, Tong-Qi;Sun, Run-Cang
揭示木质素在离子液体（IL）预处理下的基本化学性质将有助于理解预处理过程中涉及的生物质降解。为了更详细地检查木质素在不同IL预处理条件下的化学转化而不与植物多糖竞争反应，分离的白杨碱木质素（硬木木质素）在不同IL预处理条件下的IL预处理（即，110-170 ℃，1-16小时）。通过元素分析、2D-HSQC谱、定量C-13-NMR谱、P-31 NMR谱和GPC分析研究了木质素的结构转变。结果表明，随着预处理的进行，木质素中的脂肪族羟基减少，酚羟基增加。酚羟基的增加主要是由于β-O-4'键的断裂，而脂肪羟基的减少可能归因于脱水反应。在高温下，β-O-4'键断裂，β-β'和β-5'键降解明显，导致分子量下降。此外，IL预处理选择性降解G型木质素组分和缩合反应更容易发生在S单元比G单元。此外，脱甲氧基优先发生在G单元中，特别是在较高温度下。研究木质素在离子液体预处理过程中的基本化学过程，将有助于优化和控制预处理过程。
Unveiling the fundamental chemistry of lignin under ionic liquid (IL) pretreatment will facilitate the understanding of biomass recalcitrance involved in pretreatment processes. To examine in greater detail the chemical transformations of lignin under different IL pretreatment conditions without competing reactions from plant polysaccharides, the IL pretreatment of the isolated poplar alkaline lignin (hardwood lignin) under varying IL pretreatment conditions (i.e., 110-170 degrees C, 1-16 hours) was performed in an appropriate manner. The structural transformations of the lignin have been investigated by elemental analysis, 2D-HSQC spectra, quantitative C-13-NMR spectra, P-31 NMR, and GPC analysis. Results revealed that a decrease of aliphatic OH and an increase in phenolic hydroxyl groups occurred in lignin as the pretreatment proceeded. The increased phenolic OH was mainly as a result of cleavage of beta-O-4' linkages, while the reduced aliphatic OH is probably attributed to the dehydration reaction. The cleavage of beta-O-4' linkages, degradation of beta-beta' and beta-5' linkages obviously happened at high temperatures and resulted in the decrease of molecular weights. In addition, IL pretreatment selectively degraded the G-type lignin fractions and the condensation reaction took place more easily at S units than G units. Moreover, the demethoxylation preferentially occurred in G units, especially at higher temperatures. It is believed that investigating the fundamental chemistry of lignin during IL pretreatments would be beneficial to optimize and control the pretreatment process.