Sunday, May 3, 2009
3-75
Measurement of total lignin mass balance closure after dilute sulfuric acid pretreatment from herbaceous feedstocks
Rui Katahira, David W. Templeton, Daniel J. Schell, and Mark F. Davis. National Bioenergy Center, National Renewable Energy Laboratory, 1617 Cole Blvd., Golden, CO 80401
Determining the lignin mass balance closure in biomass materials after dilute sulfuric acid pretreatment is an important element to optimize pretreatment conditions for bioethanol production. Previous research at NREL has found the lignin mass balance closure determined in pretreated corn stover appears to be greater than the original lignin in the unpretreated material. We investigated the factors affecting lignin measurement in dilute acid pretreated feedstock using combinations of nitrogen analysis, 13C cross polarization/magic-angle spinning (CP/MAS) solid-state nuclear magnetic resonance (NMR) spectroscopy, removal of lignin using acid chlorite bleaching, and pretreatment with 13C-labeled sugars. It was found that remaining protein in acid insoluble residue is 0.5-1.0 wt% of original corn stover and only minimal contamination due to carbohydrate was observed. However, degradation products were present in acid insoluble residue suggesting that low molecular weight compounds can be condensed on to the biomass substrate after pretreatment. The acid-soluble lignin released during the pretreatment was determined by UV-Vis spectrometry to be an unrealistic 22-30% of unpretreated feedstock lignin. However, no substantial intensity assigned to lignin peaks could be detected in the pretreatment hydrolysate by quantitative 13C liquid-state NMR. This indicates interference from low molecular weight compounds or sugar degradation products may be affecting the UV-Vis method. We are attempting to improve the determination of soluble lignin content after pretreatment using isolated lignin from native corn stover.
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