Tuesday, April 20, 2010
8-47

Surface and ultrastructural characterization of raw and pretreated switchgrass from various leading pretreatment technologies

Bryon S. Donohoe1, Todd B. Vinzant1, Richard T. Elander2, Venkata Ramesh Pallapolu3, Y.Y. Lee3, Rebecca Garlock4, Venkatesh Balan4, Bruce E. Dale4, Youngmi Kim5, Nathan S. Mosier5, Michael R. Ladisch5, Matthew Falls6, Rocio Sierra6, Mark T. Holtzapple6, Jian Shi7, Mirvat A. Ebrik7, Tim Redmond7, Bin Yang7, Charles E. Wyman7, Bonnie R. Hames8, Steven R. Thomas8, and Ryan E. Warner9. (1) Biosciences Center, National Renewable Energy Laboratory, 1617 Cole Blvd., Golden, CO 80401, (2) National Bioenergy Center, National Renewable Energy Laboratory, 1617 Cole Blvd., Golden, CO 80401, (3) Chemical Engineering, Auburn University, 212 Ross Hall, Auburn, AL 36849, (4) Department of Chemical Engineering and Material Science, Michigan State University, 2527 Engineering building, East Lansing, MI 48824, (5) LORRE/Ag. and Bio. Engineering, Purdue University, 500 Central Dr., West Lafayette, IN 47907, (6) Chemical Engineering, Texas A&M University, 3122 TAMU, College Station, TX 77843-3122, (7) Center for Environmental Research and Technology Department of Chemical and Environmental Engineering Bourns College of Engineer, University of California at Riverside, 1084 Columbia Avenue, Riverside, CA 92507, (8) Ceres, Inc., 1535 Rancho Conejo Blvd, Thousand Oaks, CA 91320, (9) Genencor, A Danisco Division, 925 Page Mill Road, Palo Alto, CA 94304

The U.S. Department of Energy, Office of Biomass Program-funded CAFI 3 project is developing leading pretreatment technologies for application to switchgrass and is evaluating their effectiveness in recovering sugars from the coupled operations of pretreatment and enzymatic hydrolysis. Key chemical and physical characteristics have been determined for selected pretreated switchgrass samples. At NREL, several analytical microscopy approaches utilizing instruments in the Biomass Surface Characterization Laboratory (BSCL) have been applied to CAFI pretreated switchgrass samples. The results of this work has shown that each of the CAFI pretreatment approaches on switchgrass result in different structural impacts at the tissue, cellular, and cell wall scales. Some of these structural changes can be correlated to changes in chemical composition upon pretreatment, as there is evidence of lignin removal and re-arrangement by the lime and soaking in aqueous ammonia (SAA) pretreatment methods and evidence of hemicellulose removal in the liquid hot water (LHW) and dilute acid pretreatments. The ammonia fiber expansion (AFEX) pretreatment shows no gross change in composition upon pretreatment, but does show significant structural changes at the cellular and cell wall level. When comparing the pretreated solids enzymatic digestibility data to the images generated for each of the pretreated samples, it becomes apparent that different structural mechanisms are responsible for achieving the highest enzymatic hydrolysis sugar yields. This is most evident when comparing the lime pretreatment to the LHW and dilute acid pretreatments, as similar enzymatic hydrolysis yields are reported, although substantial differences in pretreated solids composition and structural changes at the cellular and cell wall levels are evident.

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