Electrochemical Depolymerization of Lignin in a Biomass-based Solvent

The successive breakdown of the lignin macromolecule into smaller units is the key to generate high value-added products from this complex plant polyphenol. Obtaining well-defined aromatic compounds is, therefore, an important step towards the production of biobased chemicals for the fuel, coating and lubricant industries. Nevertheless, processes requiring lignin dissolution are always challenging. Dissolving this macromolecule in an environment-friendly way takes this challenge to a whole new level. Levulinic acid, an organic compound formed during the hydrothermal processing of lignocellulosic biomass, has been shown to efficiently dissolve lignin. Herein, we describe a system consisting of levulinic acid as a biobased solvent for the reductive electrochemical depolymerization of lignin. Copper was used as an electrocatalyst due to the economic feasibility and low activity towards the hydrogen evolution reaction. After depolymerization, high-resolution mass spectrometry and NMR structural characterization revealed lignin-derived monomers and dimers. A predominance of aryl ether and phenolic groups was observed. The effect of the depolymerized lignin as an anti-corrosion coating was assessed, revealing enhancements on the electrochemical stability of the metal. Via a simple depolymerization process of biomass waste in a biomass-based solvent, these results demonstrate a straightforward approach to produce high value-added compounds or tailored biobased materials.