Lignin depolymerization via an integrated approach of anode oxidation and electro-generated H2O2 oxidation

Abstract

Lignin is a natural aromatic macromolecule in huge quantity and might serve as sustainable resources for the chemical industry after being depolymerized. An electrochemical approach combining anode oxidation and electro-generated H₂O₂ oxidation has been developed for converting lignin into value-added aromatic chemicals in this study. Lignin in alkali solution was electrolyzed in an undivided electrolytic cell with a cylindrical graphite felt cathode and a RuO₂–IrO₂/Ti mesh anode, in which the by-product O₂ on the anode could be efficiently reduced to H₂O₂ on the cathode in situ. Results display that the depolymerization productivity via the integrated approach obviously surpassed the sum of that by separate H₂O₂ oxidation and anode oxidation. Moreover, the analysis results of GC-MS, GPC, and C9 expanded formula confirmed that C–C bonds and C–O–C bonds in lignin were cleaved synergistically by direct anodic oxidation and indirect H₂O₂ oxidation, and the macromolecules are gradually depolymerized into final products of monomers and dimers.