(452b) Hydrothermal Pretreatment of Switchgrass for Ethanol Production

Switchgrass is emerging as a potential lignocellulosic biomass for ethanol production. Unfortunately, switchgrass has a very low enzymatic reactivity. Therefore, pretreatment of switchgrass is viewed as a critical step to make the cellulose accessible to enzymes and for an adequate yield of fermentable sugars during enzymatic hydrolysis. Hydrothermal pretreatment of biomass has attracted much attention as a non-toxic, environmentally benign, and inexpensive method. The process mainly removes lignin and resulting structural changes improve the accessibility and hydrolysis of cellulose. The increase of ionization constant of water with temperature and formation of organic acids during pretreatment process causes the reaction medium to become more acidic (pH <4) and enhances the hydrolysis of majority of hemicelluloses. The hydrothermal pretreatments of switchgrass and corn stover were conducted in a semi-continuous reactor to enhance and optimize the enzymatic reactivity. The study was aimed to maximize the retention of hemicelluloses in solid fraction and increase the removal of lignin during such treatments. The effects of pretreatment temperature (150-200°C), pressure 34-138 bar, and addition of K2CO3 (0-0.90 wt.%) were examined. The enzymatic reactivity of the pretreated substrate was investigated with cellulase and β-glucosidase enzymes. In addition, the changes in crystallinity, surface area, and surface morphology were examined by X-ray diffraction, BET surface area measurement, and electron microcopy, respectively.