Effects of Temperature and Moisture on Dilute-Acid Steam Explosion Pretreatment of Corn Stover and Cellulase Enzyme Digestibility

摘要

Corn stover is emerging as a viable feedstock for producing bioethanol from renewable resources. Dilute-acid pretreatment of corn stover can solubilize a significant portion of the hemicellulosic component and enhance the enzymatic digestibility of the remaining cellulose for fermentation into ethanol. In this study, dilute H_2SO_4 pretreatment of corn stover was performed in a steam explosion reactor at 160 deg C, 180 deg C, and 190 deg C, approx 1 wt% H_2SO_4, and 70-s to 840-s residence times. The combined severity (Log_(10)[R_0]-pH), an expression relating pH, temperature, and residence time of pretreatment, ranged from 1.8 to 2.4. Soluble xylose yields varied from 63 to 77% of theoretical from pretreatments of corn stover at 160 and 180 deg C. However, yields >90% of theoretical were found with dilute-acid pretreatments at 190 deg C. A narrower range of higher combined severities was required for pretreatment to obtain high soluble xylose yields when the moisture content of the acid-impregnated feedstock was increased from 55 to 63 wt%. Simultaneous saccharification and fermentation (SSF) of washed solids from corn stover pretreated at 190 deg C, using an enzyme loading of 15 filter paper units (FPU)/g of cellulose, gave ethanol yields in excess of 85%. Similar SSF ethanol yields were found using washed solid residues from 160 and 180 deg C pretreatments at similar combined severities but required a higher enzyme loading of approx 25 FPU/g of cellulose.