2023-07-31 ワシントン州立大学(WSU)
◆リグニンは再生可能な炭素源であり、植物の細胞壁を形成して剛性を提供します。しかし、従来の抽出方法では均一なリグニンを得ることが難しく、多くは低価値な用途に利用されてきました。
◆今回の研究では、溶媒を用いた抽出法により、リグニンの性質が保持され、より均一な材料が得られることが確認されました。これにより、リグニンの高付加価値な産業利用や石油由来のプラスチックやポリマーの代替材料の開発が可能になると期待されています。
＜関連情報＞
- https://news.wsu.edu/press-release/2023/07/31/lignin-separation-method-could-make-renewable-material-profitable/
- https://www.pnas.org/doi/10.1073/pnas.2307323120
N-ヘテロ環ベースの深部共晶溶媒抽出により構造特性を制御したリグニン Lignin with controlled structural properties by N-heterocycle-based deep eutectic solvent extraction
Kuan-Ting Lin, Chenxi Wang, Mond F. Guo, Edoardo Aprà, Ruoshui Ma, Arthur J. Ragauskas, and Xiao Zhang
Proceedings of the National Academy of Sciences Published:July 31, 2023
DOI:https://doi.org/10.1073/pnas.2307323120
Significance
Lignin is the most abundant renewable aromatic carbon on earth. It has been a formidable challenge to separate lignin from plant biomass without causing significant structural changes to the macromolecule. Despite a decades-long effort, there is no method capable of generating lignin from any biomass with consistent structural properties. This study demonstrates a lignin extraction method using lactic acid and pyrazole-based deep eutectic solvents (La–Py DES). By adjusting the treatment conditions as well as La–Py DES composition, lignin with targeted levels of ether linkages, phenolic hydroxyl group content, and average molecular weight can be obtained. La–Py DES extraction provides a breakthrough in generating lignin from plant biomass in large quantities with high purity and controlled structural properties.
Abstract
The complex and heterogeneous nature of the lignin macromolecule has presented a lasting barrier to its utilization. To achieve high lignin yield, the technical lignin extraction process usually severely modifies and condenses the native structure of lignin, which is a critical drawback for its utilization in conversion processes. In addition, there is no method capable of separating lignin from plant biomass with controlled structural properties. Here, we developed an N-heterocycle-based deep eutectic solvent formed between lactic acid and pyrazole (La–Py DES) with a binary hydrogen bonding functionality resulting in a high affinity toward lignin. Up to 93.7% of lignin was extracted from wheat straw biomass at varying conditions from 90 °C to 145 °C. Through careful selection of treatment conditions as well as lactic acid to pyrazole ratios, lignin with controlled levels of ether linkage content, hydroxyl group content, and average molecular weight can be generated. Under mild extraction conditions (90 °C to 120 °C), light-colored native-like lignin can be produced with up to 80% yield, whereas ether linkage–free lignin with low polydispersity can be obtained at 145 °C. Overall, this study offers a new strategy for native lignin extraction and generating lignin with controlled structural properties.
