Understanding the influences of poplar recalcitrance during combinatorial pretreatment on ethanol production

A combinatorial pretreatment process with liquid hot water (LHW) and sodium hydroxide were explored to compare the potential impact of each pretreatment on ethanol production from poplar. The physicochemical properties and ultrastructure of substrates before and after pretreatment were characterized to highlight their impacts on subsequent simultaneous saccharification and fermentation (SSF). The results revealed that 200 degrees C LHW combinatorial 1% NaOH pretreatment achieved the highest ethanol yield of 50.90% with 22.71 g/L of ethanol concentration, which was strongly correlated with the removal of hemicellulose and delignification. Then, the key factors related to biomass recalcitrance, such as cellulose crystallinity index (CrI), accessibility and degree of polymerization (DP) were analyzed by X-ray diffraction (XRD), Simons' staining and Gel Permeation Chromatography (GPC) method, respectively. After pretreatment, an increased cellulose CrI/accessibility and decreased cellulose DP were obtained in pretreated poplar, which could effectively improve the subsequent fermentation yield, and in this study, hemicellulose/lignin removal and cellulose accessibility exhibited positive correlation with the adsorption capability of cellulase, whereas, cellulose DP were negatively potential associated with SSF. This work will provide important guidance for better understanding the influences of biomass recal-citrance on ethanol production during the pretreatment process.