Doctor of Philosophy / Department of Biological & Agricultural Engineering / Donghai Wang / Sweet sorghum accumulates high concentrations of fermentable sugars in the stem, produces significant amount of starch in the grain (panicle) and has shown to be a promising energy feedstock. Sweet sorghum has a short growing season so adding it to the sugar cane system would be good. The overall goal of this dissertation is to enhance the attractiveness of biofuel production from sweet sorghum to fully utilize fermentable sugars in the juice, starch in the panicle and structural carbohydrates in the stalk for high efficiency and low-cost ethanol production. Sweet sorghum juice was incorporated into the dry-grind process which increased ethanol yield by 28% increase of ethanol yield compared to the conventional ethanol method and decreased enzymatic hydrolysis time by 30 minutes. A very high gravity fermentation technique was applied using sweet sorghum juice and sorghum grain yielded 20.25% (v/v) of ethanol and 96% fermentation efficiency. Response surface methodology was applied in order to optimize diffusion conditions and to explore effects of diffusion time, diffusion temperature, and ratio of sweet sorghum biomass to grain on starch-to-sugar efficiency and total sugar recovery from sweet sorghum. Starch hydrolysis efficiency and sugar recovery efficiency of 96 and 98.5% were achieved, respectively, at an optimized diffusion condition of 115 minutes, 95 °C, and 22% grain loading. Extraction kinetics based on the optimized diffusion parameters were developed to describe the mass transfer of sugars in sweet sorghum biomass during the diffusion process. Ethanol obtained from fermented extracted sugars treated with granular starch hydrolyzing enzyme and those with traditional enzymes were comparable (14.5 – 14.6% v/v). Ethanol efficiencies also ranged from 88.92 –92.02%.

Doctor of Philosophy / Department of Biological & Agricultural Engineering / Donghai Wang / Sweet sorghum accumulates high concentrations of fermentable sugars in the stem, produces significant amount of starch in the grain (panicle) and has shown to be a promising energy feedstock. Sweet sorghum has a short growing season so adding it to the sugar cane system would be good. The overall goal of this dissertation is to enhance the attractiveness of biofuel production from sweet sorghum to fully utilize fermentable sugars in the juice, starch in the panicle and structural carbohydrates in the stalk for high efficiency and low-cost ethanol production. Sweet sorghum juice was incorporated into the dry-grind process which achieved 28% increase of ethanol yield compared to the conventional ethanol method and decreased enzymatic hydrolysis time by 30 minutes. A very high gravity fermentation technique was applied using sweet sorghum juice and sorghum grain yielded 20.25% (v/v) of ethanol and 96% fermentation efficiency. Response surface methodology was applied in order to optimize diffusion conditions and to explore effects of diffusion time, diffusion temperature, and ratio of sweet sorghum biomass to grain on starch-to-sugar efficiency and total sugar recovery from sweet sorghum. Starch hydrolysis efficiency and sugar recovery efficiency of 96 and 98.5% were achieved, respectively, at an optimized diffusion condition of 115 minutes, 95 °C, and 22% grain loading. Extraction kinetics based on the optimized diffusion parameters were developed to describe the mass transfer of sugars in sweet sorghum biomass during the diffusion process. Ethanol obtained from fermented extracted sugars treated with granular starch hydrolyzing enzyme and those with traditional enzymes were comparable (14.5 – 14.6% v/v). Ethanol efficiencies also ranged from 88.92 –92.02%.

The Fe(II) regeneration process is an important aspect of Alternate Anode Reaction Technology (AART) using Fe(II)/Fe(III)-SO2 reactions for copper hydrometallurgy; however little has been done to study it specifically. The process regenerates Fe(II) via Fe(III) reduction by SO2(aq), catalyzed by activated carbon particles. To better understand and improve the process, two studies have been conducted with respect to variable factors and their affects on the regeneration. A study of fundamental kinetics confirms that the regeneration reaction is mass transfer-controlled, requiring adsorption of reactants onto the catalyst surface for reaction. The reaction rate is limited by the diffusivity of Fe(III). Initial Fe(III) concentration and carbon particle size are determined to be the most influential factors on the rate under the condition studied. Furthermore, it is observed that flow rate may inhibit the reaction by reducing ion diffusivity. A rate expression for the regeneration is derived and experimentally validated, and the Fe(III) diffusivity is determined to be 1.1x10-7 cm2/s. An optimization problem is also developed and solved for the process, constrained by the requirement that negligible SO2 could be present in the process effluent. Before optimization, a relationship is developed between regeneration rate and variable factors. Again, carbon size and initial Fe(III) are the most influential factors on the regeneration rate, related to it linearly; temperature is significant with a squared relationship to the rate; initial SO2 is insignificant. Optimal conditions are found with minimum carbon particle size, maximum initial Fe(III) concentration, and moderate temperature. / Master of Science