Integrated approach for co-production of bioethanol and light aromatics from lignocellulose through polyethylene glycol-aided acidic glycerol pretreatment

Abstract

Acid-catalyzed glycerol organosolv (GO) pretreatment is a promising method for lignocellulosic biomass (LCB) fractionation. However, this method often leads to lignin repolymerization, intensifying lignin's inhibitory effects on subsequent enzymatic hydrolysis and limiting the production of highly active lignin, thereby hindering its valorization. This study explored incorporating polyethylene glycol (PEG) into acidic-catalyzed GO to improve bioethanol and bio-oil yields, with a focus on improving the yield of light aromatics, from LCB. Optimized PEG-aided GO pretreatment achieved a significantly higher bioethanol yield (23.7 g/L) compared to GO (17 g/L) and dilute acid (DA: 11.3 g/L) pretreatments. This improvement is attributed to the ability of PEG to mitigate lignin inhibition and modify the physicochemical properties of the pretreated substrate. Furthermore, thermal pyrolysis of PEG-aided GO lignin, obtained after the fermentation process, resulted in a substantially increased bio-oil yield (45.5 %) compared to GO (19 %) and DA (12 %). The enhanced bio-oil yield from PEG-aided GO lignin is ascribed to the promotion of β-O-4 linkages and the formation of β-O-4′ linkages. Characterization of the pyrolysis bio-oil revealed that light aromatic compounds were the dominant fraction, with their relative abundance significantly increasing from DA (5.9 %) to GO (9.7 %) and PEG-aided GO lignin (24.9 %). The PEG-aided GO method achieved an energy output of 8.85 MJ/kg, exceeding that of the GO and DA methods by 31 % and 57 %, respectively. The energy conversion efficiency of the PEG-aided GO method was 70 %, demonstrating a significant improvement compared to GO (57 %) and DA (51 %). This approach promotes the circular economy by upcycling LCB for bioethanol and valuable light aromatic compound production.