Extraction and Assessment of Lignin from Lignocellulosic Oil Palm Biomass

There are abundant lignocellulosic components of the oil palm biomass (OPB) which are renewable and appealing for diverse applications. The fractionated individual components of OPB, i.e. cellulose, hemicelluloses and lignin with attractive and unique chemical properties, are actively being pursued. Lignin, in particular, is the least exploited due to its rigidity in the presence of heterogeneous cross-linkages. Its enriched aromatic compounds attract attention for biochemical and biofuel production. Hence, lignin extraction was performed on different sources of OPB, i.e. oil palm empty fruit bunch (OPEFB), oil palm frond (OPF), oil palm mesocarp fibre (OPMF) and oil palm trunk (OPT), using 72% concentrated sulfuric acid in accordance to the TAPPI standard method. The morphology, crystallinity, thermal stability and functionality of the lignin extracted components were assessed via scanning electron microscope-energy-dispersive X-ray spectroscopy (SEM–EDX), thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR). The highest lignin recovery (49.7%) was attained from OPMF and the lowest from OPT (26.3%). SEM images of all the lignin extracts depicted a smooth surface, suggesting complete isolation of the lignin from silica and other impurities. This was further supported by EDX findings, where cellulose and hemicellulose components were undetectable. The FTIR spectra indicated high purity of lignin with the presence of O–H, C–H, N–O, C=O and C–O stretching vibrations and N–H bending. The TGA thermogram confirmed that OPF-lignin possessed the highest thermal stability (633.5 °C). These results provided an overview of lignin characteristics from various OPB sources, which are beneficial in guiding future OPB valorization for potential commercialization.