ARS | Publication request: Ethanol Production from SPORL-pretreated Lodgepole Pine: Preliminary Evaluation of Mass Balance and Process Energy Efficiency

Submitted to: Applied Microbiology and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 12, 2009
Publication Date: January 14, 2010
Citation: Zhu, J.Y., Zhu, W., O Bryan, P.J., Dien, B.S., Tian, S., Gleisner, R., Pan, X.J. 2010. Ethanol Production from SPORL-Pretreated Lodgepole Pine: Preliminary Evaluation of Mass Balance and Process Energy Efficiency. Applied Microbiology and Biotechnology. 86(5):1355-1365.

Interpretive Summary: Lodgepole pine, which is used as a feedstock in this study, is a major wood species from forest thinning of the unmanaged forests in the United States. As such, it is available in large volumes and ethanol is a potential value-added product that would mitigate expensive thinning costs for sustainable healthy forest and ecosystem management. In this study, lodgepole pine wood was converted into ethanol using a novel procedure based upon the sulfite pulping process. For the sulfite pretreatment to overcome recalcitrance of lignocellulose (SPORL) process, the wood chips are treated in a pulp digester with a combination of sulfite and sulfuric acid, drained, and disk-milled prior to enzymatic hydrolysis and fermentation. The liquor off the digester also contains sugars and is fermented separately. This study showed that 276 liters of ethanol could be recovered per ton of wood, which is 72% of the maximum realizable yield. This work should be of interest to pulp and paper companies, related forestry industries, and potential manufacturers of advance biofuels.

Technical Abstract: Lodgepole pine from forest thinnings is a potential feedstock for ethanol production. In this study, lodgepole pine was converted to ethanol with a yield of 276 liters (73 gallons) per ton of wood or 72% of theoretical. The lodgepole pine chips were directly subject to the sulfite pretreatment to overcome recalcitrance of lignocellulose (SPORL) process and then disk-milled; the recovered cellulose substrate was simultaneously saccharified enzymatically and fermented (SSF) to ethanol using commercial cellulases and Saccharomyces cerevisiae D5A. The liquor stream from the pretreatment that contained hydrolyzed hemicellulose sugars was fermented by the same yeast strain after detoxification using an XAD resin column. The SPORL pretreatment was conducted at 180 deg C for a period of 25 min with a liquor-to-wood ratio of 3:1 in a laboratory digester. Three levels of sulfuric acid charge (0.0, 1.4, 2.2%, on an oven dried wood basis) and three levels of sodium bisulfite charge (0.0, 4.0, 8.0%) were applied. Mechanical and thermal energy consumption for milling and pretreatment were determined. These data were used to determine the efficiency of sugar recoveries, net ethanol energy production values, and to formulate a preliminary mass and energy balance.