Sandeep Kumar, Urvi D. Kothari, Y. Y. Lee, and Ram B. Gupta. Chemical Engineering, Auburn University, 212 Ross Hall, Auburn, AL 36849-5127
Switchgrass is emerging as a potential lignocellulosic biomass for ethanol production. Unfortunately, switchgrass has very low enzymatic reactivity; hence, pretreatment is required to enhance the reactivity for an efficient conversion to fermentable sugars. Hydrothermal pretreatment of biomass has attracted much attention as a non-toxic, environmentally benign and inexpensive media for chemical reactions. Increase in ionization constant of water with temperature causes hydrolysis of hemicelluloses, degradation of lignin and cleavage of acetyl group during hydrothermal treatment. The process mainly removes hemicelluloses and resulting structural change after the pretreatment improves the accessibility and hydrolysis of cellulose. Hydrothermal pretreatment of switchgrass was carried out in a flow-through reactor in at 150-180 °C and 35-136 bar. The process removed nearly 50 wt% of lignin and 55-80 wt% of hemicelluloses. The hydrolysate (liquid fraction) is acidic (pH ~3), which can be reduced by an small (0.45-0.9 wt%) addition K2CO3 which in turn retains the majority of hemicelluloses in the solid fraction. Enzymatic reactivity of after pretreatment was tested with cellulase enzyme at 15 FPU/g glucan. In addition , the changes in crystallinity and surface morphology were examined by X-ray diffraction and electron microcopy, respectively. The pretreated substrates at 150 °C (with or without K2CO3) were further studied for ethanol yield by fermentation using E. Coli KO11. The effect of temperature, pressure, and use of K2CO3 in hydrothermal pretreatment of switchgrass is discussed with respect to its enzymatic digestibility.
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