Co-production of soluble sugars and lignin from short rotation white poplar and black locust crops

Co-production of sugars and lignin from short rotation white poplar and black locust crops is evaluated. Acid-catalyzed ethanol/water organosolv and dilute acid pretreatments are analyzed. Resulting pretreated materials are hydrolyzed enzymatically for sugar production, whereas solubilized lignins from pretreatment liquors are precipitated, analyzed by analytical standard, and characterized by FTIR spectroscopy, SEC chromatography, and solid-state 13C NMR. Organosolv produces in both materials a high delignification degree (46–50%) and a considerable hemicelluloses removal (62–67%), while acid hydrolysis is more efficient at removing hemicelluloses (86–90%), showing a delignification of 43% (white poplar) and 31% (black locust). Organosolv followed by enzymatic hydrolysis results in 37.8% (white poplar) and 38.2% (black locust) total sugars yields, whereas acid pretreatment and subsequent saccharification show higher sugars yields for white poplar (43.3%) and lower for black locust (29.1%). Regarding lignin samples, higher concentrations are recovered from organosolv liquors of both materials (67.8% and 44.9% yields for white poplar and black locust, respectively) compared to the quantities extracted from acid liquors of white poplar (4.6%) and black locust (6.8%). Organosolv lignins display a lower content of S units and phenols, and higher molecular weights. Contrary, acid lignins consist mainly of phenolic fragments with a higher content of S units and lower molecular weights.