Sodium Hydroxide Pretreatment of Switchgrass for Ethanol Production

Lignocellulose-to-ethanol conversion is a promising technology to supplement corn-based ethanol production. However, the recalcitrant structure of lignocellulosic material is a major obstacle to the efficient conversion. To improve the enzymatic digestibility of switchgrass for the fermentable sugar production in hydrolysis, sodium hydroxide pretreatment of the biomass feedstock was investigated. At 121, 50, and 21 degrees C, raw switchgrass biomass at a solid/liquid ratio of 0.1 g/mL was pretreated, respectively, for 0.25-1, 1-48, and 1-96 h at different NaOH concentrations (0.5, 1.0, and 2.0%, w/v). Pretreatments were evaluated based on the yields of lignocellulose-derived sugars in the subsequent enzymatic hydrolysis. At the best pretreatment conditions (50 degrees C, 12 h, and 1.0% NaOH), the yield of' total reducing sugars was 453.4 mg/g raw biomass, which was 3.78 times that of untreated biomass, and the glucan and xylan conversions reached 74.4 and 62.8%, respectively. Lignin reduction was closely related to the degree of pretreatment. The maximum lignin reductions were 85.8% at 121 degrees C, 77.8% at 50 degrees C, and 62.9% at 21 degrees C, all of which were obtained at the combinations of the longest residence times and the greatest NaOH concentration. Cellulase and cellobiase loadings of 15 FPU/g dry biomass and 20 CBU/g dry biomass were sufficient to maximize sugar production.