Magnesium Oxide‐catalyzed Oxidative Depolymerization of EFB Lignin

Empty fruit bunch ( EFB ) lignin, which had been isolated by the previous sulfuric acid treatment of EFB , was oxidized in the presence of a base and air to depolymerize the solvent‐insoluble lignin into smaller solvent‐soluble molecules. Depending on the types of base and solvent, the yield of solvent‐soluble lignin ( SSL ) varied, and the highest yield of 54% was obtained when MgO and ethanol were used at 150 °C with an air pressure of 500 psig for 3 h. Gel permeation chromatography analysis of the oxidized lignin showed that SSL had decreased molecular weight compared to native EFB lignin. 31 P NMR experiments revealed that concentrations of hydroxy group and acid group were increased by the oxidation. 2D 1 H‐ 13 C HSQC NMR was performed, and it was found that the area intensities related to methoxy group and β‐O‐4′ unit as well as guaiacyl, oxidized syringyl, and p ‐hydroxybenzoate group were decreased by the oxidation.