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. 2024 Nov 27;16(23):3325.
doi: 10.3390/polym16233325.

Silver-Catalyzed Aqueous Electrochemical Valorization of Soda Lignin into Aliphatics and Phenolics

Affiliations

Silver-Catalyzed Aqueous Electrochemical Valorization of Soda Lignin into Aliphatics and Phenolics

Lucie Lindenbeck et al. Polymers (Basel). .

Abstract

Transitioning from crude oil to renewable sources of carbon-based chemicals is critical for advancing sustainable development. Lignin, a wood-derived biomacromolecule, holds great potential as a renewable feedstock, but efficient depolymerization and dearomatization methods are required to fully unlock its potential. In this investigation, we present a silver-catalyzed aqueous electrocatalytic method for the selective depolymerization and partial dearomatization of soda lignin under mild, ambient conditions. Utilizing a water/sodium carbonate solvent system and a silver electrode to mediate the electrochemical reduction, we achieved significant lignin depolymerization over reaction times ranging from 5 to 20 h. Analysis by nuclear magnetic resonance (NMR) and high-resolution mass spectrometry (HRMS) revealed sodium levulinate, sodium acetate, and sodium formate as the main aliphatic products, alongside various aromatic species in the depolymerized lignin products (DL). This selective conversion of lignin into both valuable aromatic compounds and reactive aliphatic intermediates offers promising opportunities for further synthesis of a wide range of organic chemicals, contributing to the development of a more sustainable and circular economy.

Keywords: dearomatization; depolymerization; electrocatalysis; lignin; silver.

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Conflict of interest statement

Author Marcella Frauscher was employed by AC2T Research GmbH. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The authors declare the study received fundings from COMET InTribology project (FFG No. 872176,347 project coordinator: AC2T research GmbH). The funder was not involved in the study design, collection, analysis, interpretation of data, the writing of this article or the decision to submit it.

Figures

Scheme 1
Scheme 1
Schematic representation of the silver-catalyzed electrocatalytic depolymerization and partial dearomatization of soda lignin in an aqueous sodium carbonate medium. The process involves the application of a constant current (−175 mA), driving the electrochemical reduction of lignin at ambient temperature and pressure. The selective cleavage of lignin results in the formation of both aliphatic compounds (e.g., sodium levulinate, sodium formate, and sodium acetate) and aromatic species, which are extracted using ethanol as a solvent. The mechanism highlights the role of silver as an electrocatalyst in enhancing product distribution and selectivity compared to previous systems.
Figure 1
Figure 1
The color of the solution changes during the depolymerization process in a time-dependent manner, becoming clearer as the reaction progresses. This observation serves as an indirect indicator of the extent of depolymerization.
Figure 2
Figure 2
1H NMR spectra (D2O, 600.13 MHz) of DL for different reaction times: 0 h, 5 h, 15 h, and 20 h. Levulinate (yellow), formate (green), and acetate (purple) could be identified as main aliphatic products.
Figure 3
Figure 3
FTIR spectra of DL for different reaction durations (0 h, 5 h, 10 h, 15 h, and 20 h).
Figure 4
Figure 4
FTIR spectra of DL for different reaction durations zoomed in in the region between 1800 and 400 cm−1 (0 h, 5 h, 10 h, 15 h, and 20 h).
Figure 5
Figure 5
Comparison of DL products obtained in the current study with those from previous experiments, where soda lignin and kraft lignin were subjected to electrochemical reductive depolymerization under varying conditions [4,5]. This figure highlights the impact of using different electrocatalysts (silver, carbon, copper) and reaction parameters (current, time, and electrolyte composition) on the product distribution. The comparison illustrates how the choice of electrocatalyst significantly influences the selectivity toward aliphatic and aromatic compounds, with silver showing a broader range of products compared to previous studies using carbon and copper.

References

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