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Poster Presentation 1-24
Effects of Temperature and Moisture on Dilute-Acid Steam-Explosion Pretreatment of Corn Stover and Cellulase Enzyme Digestibility
Melvin P. Tucker, Kyoung H. Kim, Mildred M. Newman, and Quang A. Nguyen
National Renewable Energy Laboratory Biotechnology Division for Fuels and Chemicals National Bioenergy Center 1617 Cole Boulevard Golden, CO 80401
E-mail: Melvin_tucker@nrel.gov
Corn stover is emerging as a viable feedstock for production of bioethanol from renewable resources. Solubilization of hemicellulosic sugars and enhancement in cellulose digestibility occurs during pretreatment of corn stover feedstock. In this study, dilute sulfuric acid pretreatment of corn stover was performed in a steam explosion reactor at 160°C, 180°C and 190°C, approximately 1 wt-% H2SO4, and 70 s to 150 s residence times. The combined severity (Log Ro-pH), an expression relating pH, temperature and residence time of pretreatment, ranged from 1.85 to 2.2. Soluble xylose yields varied from 63% to 77% of theoretical from pretreatments of corn stover at 160°C and 180°C. However, yields greater than 90% of theoretical were found with dilute-acid pretreatments at 190° C. A marked increase in xylose yields was found by increasing pretreatment temperatures from 180°C to 190°C at similar combined severities. Increasing moisture content from 55 wt-% to 63 wt-% resulted in a narrower range of higher combined severities required for high xylose solubilization. Simultaneous saccharification and fermentation (SSF) of washed solids from corn stover pretreated at 190oC, using an enzyme loading of 15 FPU/g cellulose, gave ethanol yields in excess of 85%. Similar SSF ethanol yields were found using washed solid residues from 160°C and 180°C pretreatments at similar combined severities using an enzyme loading of 26.5 FPU/g cellulose.
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