Tuesday, April 20, 2010
LL Conference Facility (Hilton Clearwater Beach)
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.