In-depth interpretation of the structural changes of lignin and formation of diketones during acidic deep eutectic solvent pretreatment,Green Chemistry

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In-depth interpretation of the structural changes of lignin and formation of diketones during acidic deep eutectic solvent pretreatment
Green Chemistry ( IF 9.3 ) Pub Date : 2020/02/14 , DOI: 10.1039/d0gc00006j
Si Hong _{1,

2,

3,

4,

5} , Xiao-Jun Shen _{6,

7,

8,

9,

10} , Bo Pang _{2,

3,

4,

5} , Zhimin Xue _{2,

3,

4,

5} , Xue-Fei Cao _{2,

3,

4,

5} , Jia-Long Wen _{2,

3,

4,

5} , Zhuo-Hua Sun _{11,

12,

13,

14} , Su Shiung Lam _{15,

16,

17,

18,

19} , Tong-Qi Yuan _{1,

2,

3,

4,

5} , Run-Cang Sun _{4,

20,

21,

22}

Affiliation

Beijing Advanced Innovation Center for Tree Breeding by Molecular Design
Beijing Forestry University
Beijing
P. R. China
Beijing Key Laboratory of Lignocellulosic Chemistry
Beijing National Laboratory for Molecular Sciences
CAS Key Laboratory of Colloid and Interface and Thermodynamics
CAS Research/Education Center for Excellence in Molecular Sciences
Institute of Chemistry
Chinese Academy of Sciences
Instituto de Tecnología Química (UPV-CSIC)
Universitat Politècnica de València–Consejo Superior de Investigaciones Científicas
46022 Valencia
Spain
Pyrolysis Technology Research Group
Institute of Tropical Aquaculture and Fisheries Research (Akuatrop) & Institute of Tropical Biodiversity and Sustainable Development (Bio-D Tropika)
Universiti Malaysia Terengganu
21030 Kuala Terengganu
Malaysia
Center for Lignocellulose Chemistry and Materials
Dalian Polytechnic University
Dalian

Deep eutectic solvents (DESs) as novel and green solvents can extract high-purity lignin from lignocellulose in a high yield; however, further utilization of the extracted lignin in the DES is a severe challenge in biorefinery processes. Nevertheless, the potential of lignin valorization can be precisely reflected by unveiling the chemical transformations of lignin during DES pretreatment. In this study, we aimed to understand the possible transformation pathway via thorough characterization of the regenerated lignin and lignin oil and transformation of lignin into value-added products. During this process, alkali lignin (AL) isolated from poplar was pretreated with choline chloride-lactic acid (ChCl-LA) and choline chloride-oxalic acid (ChCl-OA) at 80–120 °C for 6 hours to produce the regenerated lignin and lignin oil. The yield of the regenerated lignin ranged from 44 to 75% after DES pretreatment. During ChCl-LA pretreatment, γ-acetylated groups in the regenerated lignin were observed at low temperatures and then deacylation occurred at high temperatures, which was beneficial for oxidizing lignin and producing phenolic diketones. Additionally, the depolymerization of lignin fractions was the dominant reaction during DES pretreatment, accompanied by partial condensation reactions. More importantly, this is the first report of obtaining S- and G-derived diketones from lignin oil after DES pretreatment. The degradation mechanism of lignin in the DES system has been proposed. This work opens a way to produce value-added chemicals from lignin in DESs, which needs to be researched in the future.

中文翻译：

深入解释酸性深共熔溶剂预处理过程中木质素的结构变化和二酮的形成

深度共晶溶剂（DESs）作为新型绿色溶剂可以以高收率从木质纤维素中提取高纯度木质素。然而，在生物精炼过程中，在DES中进一步利用提取的木质素是一个严峻的挑战。尽管如此，通过揭示DES预处理过程中木质素的化学转化，可以准确反映木质素增值的潜力。在这项研究中，我们旨在了解通过全面表征再生木质素和木质素油，并将木质素转化为增值产品。在此过程中，将从杨树中分离出的碱性木质素（AL）在80-120°C下用氯化胆碱-乳酸（ChCl-LA）和氯化胆碱-草酸（ChCl-OA）预处理6小时，以产生再生的木质素和木质素油。DES预处理后，再生木质素的产率为44％至75％。在ChCl-LA预处理过程中，在低温下观察到再生木质素中的γ-乙酰基，然后在高温下发生脱酰作用，这对于氧化木质素和生产酚二酮是有利的。另外，木质素部分的解聚是DES预处理期间的主要反应，伴随着部分缩合反应。更重要的是，这是DES预处理后从木质素油中获得S和G衍生的二酮的首次报道。提出了DES系统中木质素的降解机理。这项工作为在DES中用木质素生产增值化学品开辟了道路，这需要在未来进行研究。

更新日期：2020-03-24

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