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Title: Saccharification and Fermentation of Dilute-Acid-Pretreated Freeze-Dried Switchgrass

item YANG, YING - North Carolina State University
item SHARMA-SHIVAPPA, RATNA - North Carolina State University
item Burns, Joseph
item CHENG, JAY - North Carolina State University

Submitted to: Energy and Fuels
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/19/2010
Publication Date: 2/27/2010
Citation: Yang, Y., Sharma-Shivappa, R., Burns, J.C., Cheng, J.J. 2010. Saccharification and Fermentation of Dilute-Acid-Pretreated Freeze-Dried Switchgrass. Energy and Fuels. 23:5626-5635

Interpretive Summary: Three Switchgrass germplasm, recently released as ‘BoMaster’, ‘Performer’, and ‘Colony’, were evaluated for potential ethanol production. Acid pretreatment did not result in appreciable delignification due to an acid-lignin interaction. This resulted from simultaneous lignin degradation and accumulation. However, more than 80% of the hemicellulose was solubilized, especially in the leaf fraction. This has importance as hemicellulose contributes about as much to the dry matter as dose cellulose. Further, pretreatment also improved cellulose conversion. The glucose produced was converted efficiently into ethanol. The greatest ethanol yield obtained was 0.083 g of ethanol per g of raw performer switchgrass which is 60 % of the theoretical yield. Consequently, the switchgrass cultivars evaluated in this study show appreciable potential as energy crops for the production of ethanol when using dilute sulfuric acid pretreatment. Scale-up studies are warranted to assess the economics of the process.

Technical Abstract: Bioethanol production potential of three oven-dried switchgrass germplasms (St6-1, St6-3 3E and St6-3F) containing 26.65 to 29.28% glucan, 17.92 to 19.37% xylan, and 17.74 to 19.23% lignin (dry matter basis) was investigated. Evaluation of the effect of three acid concentrations (0.5, 1.0 and 1.5% w/v) and residence times (30, 45 and 60 min) on composition of all germplasms indicated significant hemicellulose solubilization relying greatly on pretreatment intensity. No apparent delignification was observed during pretreatment. Pretreated samples with least lignin content or greatest hemicellulose solubilization within each germplasm were selected for hydrolysis and fermentation. Enzymatic hydrolysis at cellulase activities of 0, 15 and 30 FPU/g dry biomass indicated that addition of cellulase significantly improved glucan hydrolysis (P < 0.05) but supplementation with xylanase did not statistically improve hydrolysis (P > 0.05). Glucan-to- glucose conversion was enhanced by acid pretreatments especially those resulting in greater hemicellulose solubilization. The greatest glucan conversion of 91.8% was obtained from 60 min/1.5% acid pretreated St6-3E switchgrass hydrolyzed at 30 FPU cellulase/g dry biomass supplemented with xylanase. Fermentation of hydrolyzates by Saccharomyces cerevisiae (ATCC 24859) resulted in nearly complete utilization of glucose. The highest ethanol yield of 0.082 g ethanol/g raw St6-3E switchgrass corresponded with 53.5% of theoretical yield based on glucose fermentation. These results demonstrate that the new switchgrass germplasms are potential energy crops for bioethanol production through appropriate processing.