ARS | Publication request: Comparative Study of SPORL and Dilute Acid Pretreatments of Spruce for Cellulosic Ethanol Production

Submitted to: Bioresource Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 9, 2009
Publication Date: January 10, 2010
Citation: Shuai, L., Yang, Q., Zhu, J.Y., Lu, F.C., Weimer, P.J., Ralph, J., Pan, X.J. 2010. Comparative Study of SPORL and Dilute Acid Pretreatments of Spruce for Cellulosic Ethanol Production. Bioresource Technology. 101:3106-3114.

Interpretive Summary: Plant cell wall biomass is an abundant biofuels resource, but is very difficult to economically convert to ethanol. Better conversion of this plant biomass can be obtained by treating the biomass with certain chemicals before treatment with enzymes and yeast. A new pretreatment process, combining dilute sulfuric acid and a salt of sulfite, was tested and found to permit more complete conversion of the biomass than a pretreatment process employing the acid alone. In addition, the known chemical inhibitors of fermentation were produced to a smaller extent with this pretreatment, although some other types of inhibitors may have been produced instead. Overall, the new acid sulfite pretreatment process represents an improvement over the standard dilute sulfuric acid pretreatment process.

Technical Abstract: The performance of two pretreatment methods, Sulfite Pretreatment to Overcome Recalcitrance of Lignocellulose (SPORL) and Dilute Acid (DA), was compared in pretreating softwood (spruce) for fuel ethanol production under the same conditions of temperature (180°C), time (30 min), sulfuric acid loading (5% on oven-dry wood) and liquor-to-wood ratio (5). SPORL was supplemented with 9% sodium sulfite on wood. The recoveries of total saccharides (hexoses and pentoses) were 86.1% (SPORL) and 55.6% (DA), while those of cellulose were 92.3% (SPORL) and 77.7% (DA). The total of known inhibitors (soluble lignin, furfural, 5-hydroxymethylfurfural, and formic, acetic and levulinic acids) formed in SPORL were only 35% of those formed in DA. SPORL pretreatment dissolved approximately 28% of the lignin as lignosulfonate, which is a potentially high-value co-product. With an enzyme loading of 15 FPU (filter paper units) per gram of cellulose, the cellulose-to-glucose conversion yields were 91% at 24 hours for the SPORL substrate and 55% at 48 hours for the DA substrate, respectively.