Alkaline sulfite thermomechanical pretreatment of sugarcane bagasse

Abstract

Chemithermomechanical (CTMP) processing of lignocellulosic materials can be used as an efficient pretreatment of lignocellulosic materials. This type of process has been largely used in the mechanical pulping industry with currently available equipment and robust technology. The use of alkaline sulfite in this process provides selective lignin removal up to 50% delignification, which has been proved efficient to decrease recalcitrance of the pretreated materials. The current work evaluates sugarcane bagasse pretreatment by alkaline sulfite CTMP processing. Solids yield after processing with increasingly chemical loads (from 1.25% to 10% sulfite) were in the range of 87% to 82%, respectively. The most severe pretreated sample was completely hydrolyzed by 10 FPU cellulases (Cellic CtecII)/g of substrate within 24 h hydrolysis. Lower chemical doses in the pretreatment provided substrates with higher recalcitrance. Mass balance of sugarcane bagasse components at the most severe condition indicated 49% and 28% of lignin and xylan removal, respectively. Under this condition, the glucan loss was limited to 4%. Besides delignification, the residual lignins appeared sulfonated after CTMP pretreatment. Both delignification and sulfonation of residual lignins resulted in significant increases in the water retention values of the pretreated material (from 134% to 244% in the untreated and severely pretreated material, respectively). 2D-NMR evaluation of the pretreated materials corroborated intense delignification with increasingly sulfite loads. Xylan side groups were progressively removed, whereas part of the original p-coumaric acid (PCA), acylating gama-OH of the lignin side chain, resisted to the most severe pretreatment condition. Direct correlations were observed for lignin removal, WRV, sulfonation of residual lignins and digestibility of the polysaccharides fraction.FAPESP 2014/06923-6Peer Reviewe