(251e) Process Design and Economic Analysis of Ethanol and Diesel Production from Genetically Modified Lipid-Accumulating Sorghum

Recent metabolic engineering strategies have been successful to genetically modify different plant species to accumulate triacylglycerides in their tissues. Sorghum is a drought resistant crop and less recalcitrant to genetic modifications that has already shown high oil accumulation yields in laboratory studies. The aim of this study is to design and evaluate the economics of biodiesel and ethanol coproduction from genetically modified lipid-accumulating sorghum. In the coproduction process, carbohydrates are utilized for ethanol production through acid thermal pretreatment, enzymatic hydrolysis, and fermentation, while the solid residues of fermentation are used for making biodiesel by lipid extraction, purification, and upgrading through the transesterification. Process models are simulated in Aspen Plus v.10 for coproduction from GM-sorghum and an ethanol-only process from regular sorghum. Technoeconomic models are developed to calculate the minimum ethanol selling price (MESP) for a 10% internal rate of return and 30 years of service life. Results show that coproduction has better economics with an MESP value of $2.46/gal compared to $3.08/gal for the ethanol-only process. Lipid extraction and solvent recovery units are the two main cost contributors in the coproduction process, mainly because of large solvent (hexane)-to-solids ratio (5:1) required to reach 95% lipid extraction efficiency and high capital costs of extraction and solvent distillation columns. Sensitivity analyses indicate that a lipid content above 13 wt% (dry basis) or a biomass price less than $65/Mg (dry basis) is required to reach an MESP value lower than 2014 ethanol wholesale price of $2.25/gal for the coproduction process. Insights offered in this study could help researchers identify the main challenges in ethanol and diesel coproduction from lignocellulosic biomass and guide future research and development to improve the economics of such biorefineries.