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