作者:Alireza Rahimi、Arne Ulbrich、Joshua J. Coon、Shannon S. Stahl
DOI:10.1038/nature13867
日期:2014.11
A method for the depolymerization of oxidized lignin under mild conditions in aqueous formic acid is described that results in more than 60 wt% yield of low-molecular-mass aromatics. The aromatic biopolymer lignin, a major component of plant cell walls and generally obtained from wood, is a valuable and renewable source of aromatic chemicals. Considerable progress has been made in the conversion of cellulose and hemicellulose to fuels and chemicals, but lignin has proved more recalcitrant. In this manuscript, the authors report a high-yield method for conversion of lignin to low molecular mass aromatics. The CâO cleavage reaction proceeds under mild conditions in aqueous formic acid. It produces small number of well-defined aromatic products, providing raw materials well suited for targeted conversion to a variety of valuable chemicals. Lignin is a heterogeneous aromatic biopolymer that accounts for nearly 30% of the organic carbon on Earth1 and is one of the few renewable sources of aromatic chemicals2. As the most recalcitrant of the three components of lignocellulosic biomass (cellulose, hemicellulose and lignin)3, lignin has been treated as a waste product in the pulp and paper industry, where it is burned to supply energy and recover pulping chemicals in the operation of paper mills4. Extraction of higher value from lignin is increasingly recognized as being crucial to the economic viability of integrated biorefineries5,6. Depolymerization is an important starting point for many lignin valorization strategies, because it could generate valuable aromatic chemicals and/or provide a source of low-molecular-mass feedstocks suitable for downstream processing7. Commercial precedents show that certain types of lignin (lignosulphonates) may be converted into vanillin and other marketable products8,9, but new technologies are needed to enhance the lignin value chain. The complex, irregular structure of lignin complicates chemical conversion efforts, and known depolymerization methods typically afford ill-defined products in low yields (that is, less than 10â20wt%)2,10,11. Here we describe a method for the depolymerization of oxidized lignin under mild conditions in aqueous formic acid that results in more than 60wt% yield of low-molecular-mass aromatics. We present the discovery of this facile CâO cleavage method, its application to aspen lignin depolymerization, and mechanistic insights into the reaction. The broader implications of these results for lignin conversion and biomass refining are also considered.
一种在温和条件下使用水合甲酸对氧化木质素进行解聚的方法被描述,该方法的产物中低分子量芳烃的收率超过60wt%。木质素是植物细胞壁的主要成分,通常来自木材,是一种宝贵且可再生的芳烃化学品来源。在将纤维素和半纤维素转化为燃料和化学品方面已经取得了显著进展,但木质素的转化则证明更为困难。在本文中,作者报告了一种将木质素转化为低分子量芳烃的高产率方法。C–O断裂反应在水合甲酸的温和条件下进行,生成少量界定良好的芳香产物,为针对性转化为多种有价值化学品提供了合适的原材料。木质素是一种异质芳香生物聚合物,约占地球有机碳的30%1,也是少数可再生的芳香化学品来源之一2。由于木质素是木质纤维素生物质(纤维素、半纤维素和木质素)3中最难处理的成分,木质素在纸浆和造纸工业中被视为废弃物,通常燃烧以提供能量和回收造纸化学品4。从木质素中提取更高价值的产品越来越被认为对综合生物精炼厂的经济可行性至关重要5,6。解聚是许多木质素增值策略的重要起点,因为它能够产生有价值的芳香化学品和/或提供适合下游处理的低分子量原料7。商业先例表明,某些类型的木质素(木素磺酸盐)可以转化为香草醛和其他可销售产品8,9,但需要新技术来增强木质素的价值链。木质素复杂、不规律的结构使得化学转化工作变得复杂,已知的解聚方法通常导致低产率(即低于10–20wt%)的定义不清的产物2,10,11。在这里,我们描述了一种在温和条件下使用水合甲酸对氧化木质素进行解聚的方法,其低分子量芳烃的产率超过60wt%。我们展示了这种简便的C–O断裂方法的发现,及其在白杨木质素解聚中的应用,以及对反应机制的深入理解。这些结果对木质素转化和生物质精炼的更广泛影响也进行了探讨。