Alabama Center for Paper and Bioresource Engineering, Department of Chemical Engineering, Auburn University, Auburn, AL 36849, United States.
United States Department of Agriculture - Forest Service, Southern Research Station, Auburn, AL 36849, United States.
Int J Biol Macromol. 2021 Jul 31;183:1505-1513. doi: 10.1016/j.ijbiomac.2021.05.100. Epub 2021 May 21.
The retro-aldol reaction is one of the key steps involved in the oxidative conversion of lignin to aromatic aldehydes and acids. In principle, the retro-aldol reaction can proceed in the absence of oxygen. In this work, a new approach based on the influence of oxygen on the oxidation of lignin was investigated. In this approach, the duration of oxygen charged during the reaction was optimized to, for the first time, improve the yield of aromatic aldehydes and acids. The effect of reaction chemistry, time, temperature, and lignin feedstock plays a key role on the yield of aromatic aldehydes and acids. At 140 °C, oxidation of softwood Lignoboost kraft lignin for 40 min results in combined maximum yield of 5.17% w/w of vanillin and vanillic acid. In comparison, using the new approach in which oxygen was charged for only 20 min during the 40 min reaction improved this yield considerably to 6.95%. Further, yield improvement was obtained when applying this approach to different lignin feedstocks. Oxidation also increased the carboxyl content in lignin from 0.49 mmol/g to 1.41 mmol/g which represents a marked improvement. The current study provides new evidence showing that the oxidation reaction is a crucial pathway for lignin valorization.
反醛醇缩合反应是木质素氧化转化为芳香醛和酸的关键步骤之一。原则上，反醛醇缩合反应可以在无氧的情况下进行。在这项工作中，我们研究了一种基于氧气对木质素氧化影响的新方法。在该方法中，优化了反应过程中充氧的持续时间，首次提高了芳香醛和酸的产率。反应化学、时间、温度和木质素原料的影响对芳香醛和酸的产率起着关键作用。在 140°C 下，对软木木质素 Lignoboost 硫酸盐木质素进行 40 分钟的氧化反应，可得到 5.17%w/w 的香草醛和香草酸的总最大产率。相比之下，在 40 分钟的反应中仅充氧 20 分钟的新方法可将产率大大提高到 6.95%。此外，当将该方法应用于不同的木质素原料时，产率也得到了提高。氧化还将木质素中的羧基含量从 0.49mmol/g 提高到 1.41mmol/g，这是一个显著的提高。本研究提供了新的证据，表明氧化反应是木质素增值的关键途径。
