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Pretreatment of Switch Grass by Aqueous Ammonia

Y. Y. Lee1, V. Ramesh Pallapolu2, and Urvi D. Kothari2. (1) Department of Chemical Engineering, Auburn University, 207 Ross Hall, Auburn University, AL 36849, (2) Chemical Engineering Department, Auburn University, 207 Ross Hall, Auburn University, AL 36849

Switch grass is one of the most promising energy crops for production of cellulosic ethanol. In this study, pretreatment of switch grass by aqueous ammonia was investigated applying two different modes of operation: ammonia recycle percolation (ARP), and soaking in aqueous ammonia (SAA). ARP is operated at high temperature (150C-180C) and short residence time (10-20 minutes) in a flow-through reactor, whereas SAA is carried out at low temperature (below 70oC) and long reaction time (6-24hrs) in batch reactor. The pretreated samples were analyzed for composition and subjected to enzymatic digestibility test using commercial cellulases with and without supplementation of xylanase. The results were analyzed to assess the overall effectiveness of the pretreatment and to determine the optimum conditions. Selected samples were further investigated for crystallinity, surface area, and surface composition by XRD, FTIR, and TGA in an attempt to verify the effects of these physical properties on the enzymatic reaction. Most of hemicellulose content is retained after pretreatment by aqueous ammonia due to high selectivity in ammonia reaction with lignin over carbohydrates. Simultaneous saccharification and co-fermentation (SSCF) was applied for optimally treated switch grass samples using recombinant E. coli (ATCC-55124) and aforementioned cellulase preparations. When it is properly operated, SSCF converts both glucan and xylan contents simultaneously in one stage. The simplicity of this process offers a significant economic benefit. The results of the SSCF test obtained from this work reaffirmed these claims.