Electrochemical depolymerization of lignin into renewable aromatic compounds in a non-diaphragm electrolytic cell

Abstract

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.