Xuejun Pan1, Li Shuai2, Qiang Yang2, and J. Y. Zhu3. (1) Department of Biological Systems Engineering, University of Wisconsin, 460 Henry Mall, Madison, WI 53706, (2) Biological Systems Engineering, University of Wisconsin, 460 Henry Mall, Madison, WI 53706, (3) USDA Forest Service, Forest Products Laboratory, One Gifford Pinchot Dr, Madison, WI 53726
SPORL (Sulfite Pretreatment to Overcome Recalcitrance of Lignocellulose) is a newly developed pretreatment for cellulose ethanol production. Feedstocks react first with acidic sulfite solution, and then defiberized to fibrous substrate using a disk refiner. The removal of the recalcitrance to enzymatic hydrolysis is achieved by combined effects of dissolution of hemicelluloses, slight depolymerization of cellulose, partial delignification, sulfonation of lignin, and increased surface area by the defiberization. During SPORL pretreatment, most hemicellulose sugars and partial lignin (as lignosulfonate) were dissolved. The former can be further fermented to ethanol, and the later is a high-value co-product that can be directly sold. The resulting substrates are readily digestible. The SPORL is effective to all species of feedstocks, in particular woody biomass, and easy to commercialize by using existing infrastructure and capital equipment in paper industry.
In this report, we update the optimization and fundamental understanding of the SPORL technology. Pretreatment parameters (chemical charge, temperature, catalyst, reaction time) were optimized to maximize sugar recovery and enzymatic hydrolysis. Mass balance of the major components (cellulose, hemicellulose and lignin) during the pretreatment was conducted. Lignin behavior during the pretreatment was investigated using 2-D NMR techniques. Fermentability of hemicellulose sugars from the pretreatment was evaluated using an in vitro gas production method. In addition, comparison study between the SPORL and dilute acid pretreatments indicated that at the same acid charge and temperature, the former gives higher overall sugar recovery, produces more readily digestible substrate, and forms fewer inhibitors to fermentation than the later.
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