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Biomass pretreatment constitutes an important part in the whole process of bioethanol production. The main goals of pretreatment include improving cellulose accessibility to enzyme, enhancing sugar yields from hemicellulose, achieving low capital and energy costs, as well as low sugar degradation and low chemical requirements. Extrusion, as a continuous and high throughput pretreatment method, requires much less chemical compared to traditional alkali pretreatment. In this research, twin-screw extrusion was evaluated for its effect with regard to promoting sugar yields from corn stover. Also, the underlying factors contributing to this improvement were examined. It was found that extrusion with no chemicals and post-pretreatment steps achieved significantly higher sugar yields than the untreated corn stover. It was shown that crystallinity indices were not different among the extruded and untreated samples. However, for pretreated samples, the specific surface areas estimated from the Langmuir adsorption model, were significantly different than the untreated corn stover. Extrusion using sodium hydroxide was shown to transform the structure of lignin. The sugar yields were greatly increased over the extrusion only and untreated corn stover. Crystallinity index and pore quantity were both examined. Crystallinity index was not significantly different from the untreated corn stover, however, pore quantities, measured by Congo red adsorption, were significantly amplified due to alkali combined extrusion.
Advisor: Milford A. Hanna