2-20: Effect of reactor operation on dilute acid pretreatment of corn stover

Conversion of lignocellulosic biomass to sugars and ethanol requires an effective pretreatment to increase the accessibility of cellulose to hydrolytic enzymes.  This work has investigated the impact of reactor operation on the dilute acid pretreatment of corn stover. Corn stover was pretreated in zipperclave, steam gun and continuous horizontal screw reactors under the same nominal conditions (160°C, 5 min residence time, 2.0 wt% sulfuric acid). The steam gun and horizontal reactor pretreated corn stover achieved much higher cellulose digestibilities (88% and 95%, respectively after 96 hours) than the zipperclave treated sample (68%). Chemical, physical,, spectroscopic and imaging characterizations were conducted to gain an understanding of the reasons for the differences in digestibility between the pretreated corn stover samples. Particle size was one property that showed a high degree of variability between the samples, which could be related to the differences in cellulose conversion. The chemical compositions, and cellulose degrees of polymerization for these three pretreated samples had smaller differences. Scanning electron microscopy and transmission electron microscopy images showed more porous and defibriliated structures in the steam gun and horizontal reactor treated samples because of the explosive depressurization that occurs during the operation of these two reactors.  This highly porous structure and more exposed surface area elevated the accessibility of the cellulose to cellulase enzymes causing the enhanced cellulose conversion obtained for the corn stover pretreated in the horizontal and steam gun reactors.