Tuesday, April 20, 2010
8-67

Simultaneous saccharification and fermentation of steam-pretreated sugarcane bagasse using SO2 and CO2 as acid catalysts

Stefano Macrelli, Mats Galbe, and Guido Zacchi. Department of Chemical Engineering, Lund University, Getingevägen 60, Lund, 22100, Sweden

Sugarcane bagasse is a promising lignocellulosic feedstock for second generation ethanol production mainly for its availability and high yield achievable after fermentation. The enzymatic process approach used in this work involves a pretreatment step to open up the lignocellulosic structure followed by enzymatic hydrolysis of cellulose. Steam explosion with the addition of SO2 and CO2 as acid catalysts was used for pretreatment and its efficacy assessed by SSF, which can be also seen as a combined hydrolysis and fermentability test. Pretreatment conditions are the bottleneck in the enzymatic process since they affect the most important parameter as the solubilization of hemicellulose (yielding a higher porosity and wider surface for enzymatic attack) and the release of degradation byproducts (which determines the toxicity level for yeast). Therefore ethanol production price is directly influenced by the pretreatment which contribute to determine the overall ethanol conversion and the enzymes amount needed. Several studies have proven SO2 to be an efficient catalyst, but considering the process cost, SO2 might have drawbacks such as the need of corrosion-proof equipment, a recovery stage, and its cost. CO2 instead might have the potential to be a valuable alternative to SO2 since it does not present any of those issues; it is readily available in the plant as an abundant and almost pure stream flow in the fermentation off-gas and might improve the biogas production from the stillage. A comparison of SO2 and CO2 as pretreatment catalyst is presented, focusing on the ethanol yield and biogas production.

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