Magnesium Oxide-catalyzed Oxidative Depolymerization of EFB Lignin

Abstract

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 degrees 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. P-31 NMR experiments revealed that concentrations of hydroxy group and acid group were increased by the oxidation. 2D H-1-C-13 HSQC NMR was performed, and it was found that the area intensities related to methoxy group and -O-4 unit as well as guaiacyl, oxidized syringyl, and p-hydroxybenzoate group were decreased by the oxidation.