Monday, April 30, 2012
Napoleon Ballroom C-D, 3rd fl (Sheraton New Orleans)
Dilute acid as well as water-only (hydrothermal) pretreatments often lead to a significant hemicellulose loss to soluble furans and insoluble products collectively termed as humins, chars, or pseudo-lignin. In order to understand the factors contributing to low sugar yields from pretreated biomass and the possible role of hemicellulose derived humins on cellulose conversion at the low to moderate enzyme loadings necessary for economical processing, dilute acid pretreatments of Avicel cellulose alone and Avicel mixed with beechwood xylan or xylose were performed at various severities. Following pretreatment, the solids were subjected to enzymatic hydrolysis and physical and chemical characterizations such as compositional analysis, NMR, FT-IR, and SEM. It was found that hemicellulose derived humins form even at moderate severities, and these insoluble degradation products may significantly retard cellulose hydrolysis. Furthermore, although pretreatment of Avicel cellulose mixed with xylan at low severity (CSF~1.94) formed negligible amounts of humins, enzymatic digestion of the resulting solids experienced a significant drop in conversion compared to cellulose pretreated alone. Plausible mechanisms to explain the drop in cellulose conversions will be discussed.