Experimental and Computational Analysis of Bioethanol Production from Sweet Sorghum

Abstract

Environmental, economic and energy security aspects of relying on fossil fuels motivate research on alternative fuel sources such as biofuel. Sweet sorghum, with high productivity and low production cost, has enormous potential as a bioenergy crop. The use of energy, water, land, equipment, labor and other resources are factors affecting final cost of bioethanol production from sweet sorghum. Fermentation, distillation and dewatering are main chemical processes involved in production of 99.8 wt% dehydrated ethanol from sweet sorghum juice. Distillation and dehydration are final stages of the production and demand high amount of cost and energy. One of the goals of this research is optimization and comparison of two main commonly used dehydration technologies of extractive distillation and pressure swing adsorption (PSA) alongside with distillation step. ASPEN PLUS software version 11.1 and MATLAB programming language were used to find the optimized cost and energy usage for both dehydration methods. Our results show applying extractive distillation using ethylene glycol as entrainer leads to a total annualized cost that is 12% less than that of PSA with molecular sieve. The other goal of this project is evaluation and optimization of the fermentation process that yields bioethanol from sweet sorghum juice. The effect of three main factors of temperature, pH and dissolved oxygen (DO) on ethanol yield efficacy was studied. Fermentation experiments were done on sweet sorghum juice from M81E cultivar, grown in the University of Arizona West Campus Agricultural Center in Tucson, Arizona. A full factorial design with center points were applied to study the influence of the main factors and their binary and ternary interactions on ethanol yield produced from sweet sorghum juice fermented by Saccharomyces cerevisiae (Ethanol Red). Maximum ethanol yield efficiency of 0.74 was obtained at pH (5.5), temperature 6 (28 °C) and a zero dissolved oxygen conditions. This value has good agreement with maximum experimental yield efficiency of 0.75 for bioethanol produced from the M81E variety.