Deep eutectic solvent (DES) is intrinsically cheaper than many ionic liquids (ILs) due to low precursor cost, simple synthesis, and improved recyclability. Meanwhile, DES can be as effective as ILs toward dissolving lignin from plant materials. However, the lignin depolymerization mechanism in DES, the structural and chemical properties of DES-extracted lignin (DES-EL), and the possible valorization pathways of DES-EL toward value-added products were not well understood. This study aims to characterize the lignin streams from DES (1:2 choline chloride:lactic acid) treated sorghum and further upgrade the extracted lignin to phenolic compounds. As revealed by HSQC, 13C, and 31P NMR analysis, DES cleaved nearly all ether linkages in native lignin, resulting in significant size reduction. We further catalytically upgraded DES-EL to phenolic compounds via catalytic transfer hydrogenolysis in the presence of isopropyl alcohol. Among the three tested catalysts (Ru/C, Pd/C, and Pt/C), Ru/C proved the most effective in deconstructing DES-EL, with oil, char, and gas yields of 36.3, 46.4, 17.3 wt %, respectively. Major lignin monomeric products in the oil were phenol, 4-ethylphenol, 4-ethyl-2-methoxyphenol, 2-methoxy-4-propylphenol, and 4-hydroxy-benzenepropanoic acid. This study provides a mechanistic understanding of lignin depolymerization in DES and demonstrates a possible way to catalytic upgrading of DES-EL to low molecular weight phenolic compounds.
|Number of pages||13|
|Journal||ACS Sustainable Chemistry and Engineering|
|State||Published - Aug 6 2018|
Bibliographical noteFunding Information:
We acknowledge the National Science Foundation under Cooperative Agreements 1355438 and 1632854 for partially supporting this research. The information reported in this paper (No. 18-05-062) is part of a project of the Kentucky Agricultural Experiment Station and is published with the approval of the Director. Oak Ridge National Laboratory is managed by UT-Battelle, LLC under Contract DE-AC05-00OR22725 with the U.S. Department of Energy (DOE). This work was partially supported by the BioEnergy Science Center (BESC) and the Center for Bioenergy Innovation (CBI). The BESC and CBI are U.S. DOE Bioenergy Research Centers supported by the Office of Biological and Environmental Research in the DOE Office of Science. The views and opinions of the authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, expressed or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. We acknowledge Idaho National Laboratory for providing sorghum samples and Dr. Muthu Gnanamani for assistance with gas composition analysis.
Copyright © 2018 American Chemical Society.
- Deep eutectic solvents
ASJC Scopus subject areas
- Chemistry (all)
- Environmental Chemistry
- Chemical Engineering (all)
- Renewable Energy, Sustainability and the Environment