Electrochemical depolymerization of lignin for production of renewable aromatic compounds is presented. In the designed non-diaphragm electrolytic cell, lignin in alkaline electrolyte was directly electro-oxidized on the anode and chemically oxidized by the electro-generated H₂O₂ formed on the cathode simultaneously. The linkages among C9 units in lignin were broken down and more than 20 kinds of low-molecular-weight (LMW) aromatic compounds containing hydroxyl, aldehyde, carbonyl and carboxyl groups were generated and identified by GC-MS and ESI-MS/MS measurements. The effects of electrolysis conditions on the concentration of H₂O₂, the decomposition rate of H₂O₂ into reactive oxygen species (ROS) and the yields of LMW products were investigated in detail. Results show that H₂O₂ and ROS play very important roles in lignin depolymerization. The electrolysis conditions for producing higher concentrations of H₂O₂ and ROS are in favor of giving higher yields of LMW products. 59.2% of lignin was depolymerized into LMW products after 1 hour-electrolysis at 80 °C under a current density of 8 mA cm⁻² with extra O₂ supplement.

Lignin, a natural macromolecule containing substantial aromatic rings and abundant hydroxyl groups, was firstly chemically grafted with phosphorus–nitrogen-containing groups via a liquefaction–esterification–salification process to prepare lignin-based phosphate melamine compound (LPMC). And then the LPMC which has remaining hydroxyl groups was used to substitute parts of polyols and copolymerize with isocyanate to produce lignin-modified-PU foam (PU-LPMC) with excellent flame retardancy. Owing to the rigid aromatic structure of lignin and the covalent linkages between LPMC and the polymer–matrix, PU-LPMC showed a nearly 2-fold increase in compression strength and excellent performance of thermal stability, char residue formation, self-extinguishment and inhibition from melt-dripping and smoke generation. Moreover, a large amount of non-flammable gases were released during thermal degradation and a compact and dense intumescent (C–P–N–O)_x char layer formed on the surface of the foams after combustion, resulting in the improvement of anti-flaming properties of the polymer by the flame retardancy of both gas phase and condensed phase.

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.