P141a: Dilute Acid Hydrolysis Pretreatment of Switchgrass: Quantifying the Effect of Sugar to Furfural Selectivity on Ethanol Yields

Second generation biofuel research emphasizes the use of sustainable plant materials as feedstock for the carbon fixation of biomass. However, these plant products cannot be converted to biofuels easily, resulting in an increased emphasis on optimizing treatment methods to convert feedstock into monomeric sugars prior to their fermentation to biofuels. Our objectives were to analyze dilute acid hydrolysis pretreatment of switchgrass at varying temperatures and to quantify the effect of selectivity between glucose and the inhibitory material furfural on ethanol yields.

The pretreatment reactor design allowed for improved milling, continuous sampling of hydrolysate, and controlled delivery of acid to the feedstock. Tube fermentation was used on both pretreatment hydrolysates and prepared stock solutions of varying glucose and furfural concentrations.

Hydrolysate samples with furfural to glucose selectivities of 0.56 or greater were expected to produce little to no ethanol, demonstrating threshold-like inhibitory effect of furfural on the fermentation process. Further, although increasing pretreatment operating temperatures yielded higher amounts of glucose in the hydrolysate, significant ethanol production was expected to occur only at our lowest temperature (125˚C), indicating that a higher glucose content was not the sole indicator of higher ethanol production. Expected ethanol yields in our experiments were calculated based on extrapolations made using data from stock solution fermentation and literature.