Optimized glycerol-based organosolv pretreatment for lignin removal: Enhancing sawdust pyrolysis efficiency and bio-oil properties

Efficient lignin removal from raw sawdust (RS) is essential for increasing bio-oil yield, which can be further converted into value-added products through biomass valorization. The separation of hemicellulose, cellulose, and lignin is quite challenging. Among pretreatment methods employed, the organosolv pretreatment method appeared to be a promising way to isolate the lignin from the biomass. In this research, the optimum conditions for lignin removal were identified before performing the organosolv pretreatment using glycerol. Then, the pretreated sawdust (PS) was subjected to pyrolysis at 4 different temperatures (400 degrees C, 450 degrees C, 500 degrees C, and 550 degrees C). The raw and pretreated biomass, together with the pyrolytic products, were characterized using Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and gas chromatography (GC). The optimum conditions of glycerol-based pretreatment using sodium hydroxide (NaOH) catalyst (3 w/w%) were found to be at 112.10 degrees C for 45 min with a glycerol concentration of 51.14 %. Glycerol-based organosolv pretreatment (GOP) under optimum conditions removed 78 % of lignin from raw sawdust (RS). The bio-oil from PS exhibited a 20.7 % reduction in phenol content compared to RS, resulting in a more stable bio-oil with fewer oxygenated compounds, highlighting the effectiveness of lignin removal. Furthermore, the biochar produced from PS gives a lower yield than RS at a temperature range of 450-550 degrees C. The successful removal of lignin compound had minimized the biochar formation, and subsequently, biochar fractional composition in the final product. Consequently, the bio-oil and biogas fractional compositions in the final product can be further enhanced and increased during the pyrolysis process. Besides, the levoglucosan yield from glycerol-pretreated sawdust was enhanced to 11.1 % from 1.1 %.