Electrochemical depolymerisation of lignin in a deep eutectic solvent

Abstract

Lignocellulosic biomass is an important renewable resource that could substitute fossil feedstocks as a raw material for high value chemicals production. While the cellulosic fraction of biomass gives access to saccharides only, lignin could possibly give access to low molecular weight aromatic compounds. Strong alkalinity of the reaction medium is necessary in order to dissolve lignin and to obtain an electrically conducting solution. However, strong alkalinity is supposed to be one of the reasons for consecutive oxidations to undesired organic acids and carbon dioxide. The high pH also limits the use of only a few metals as electrode materials. We report the use of pure deep eutectic solvents (DES) in order to dissolve lignin in combination with electrochemical oxidative depolymerisation. We also present successful extraction of the products through liquid–liquid extraction and their characterization by size exclusion chromatography and GC-MS, proving that a successful depolymerisation of lignin was achieved. Guaiacol and vanillin were the two most abundant detected products.