(516a) Comparative Data for Enzymatic Digestion of Corn Stover and Poplar Wood after Pretreatment by Leading Technologies

Cellulosic biomass must be pretreated to realize high yields of glucose in enzymatic digestion and achieve low enough sugar costs to be economically viable as substrates for production of fuels and commodity chemicals that would open up major new agricultural markets with powerful societal benefits. A Biomass Refining Consortium for Applied Fundamentals and Innovation (CAFI) among researchers experienced with cellulosic biomass hydrolysis is applying most of the promising pretreatment options on a comparative basis for the first time. Ammonia explosion, aqueous ammonia recycle, controlled pH, dilute acid, flowthrough, lime, and sulfur dioxide steam explosion are being applied to single sources of corn stover and poplar wood, and comparative data are being developed on the digestibility of cellulose in the pretreated solids using a controlled source of enzyme. Application of identical material balance approaches show that all of the pretreatments gave similar high yields of xylose and glucose sugars for corn stover, with xylanase activity being particularly important to releasing residual xylan in the pretreated solids for pretreatments at higher pH. However, consistently high digestion yields are proving to be more difficult to attain with poplar, with yields from some pretreatments being higher than for others. In addition, results are found to differ between two sources of poplar due to higher lignin content or other variables. This study is also examining how addition of hemicellulase enzymes improves recovery of hemicellulose sugars from the pretreated solids and examining tradeoffs in glucose yields over a wide range of cellulase loadings. Mechanistic models are being developed to relate the observed cellulose digestibility to key substrate features including degree of polymerization, crystallinity, and accessible surface area.