Scale-up and optimization of a bioethanol plant utilizing biochemical production pathways for economic viability

Our research focuses on the optimization of bioethanol production utilizing biochemical pathways and sugar intermediates. Our current interest includes the effects of various pretreatment methods, used in the enzymatic saccharification and fermentation of cellulosic biomass, and biomass feed composition on the economic viability of a large-scale bioethanol production plant. Pretreatment of the biomass involves the breakdown of the rigid cell wall, leading to greater accessibility of enzymes to the cellulosic material in further downstream processing. Our research focuses on four pretreatment technologies, ammonia fiber expansion (AFEX™), liquid hot water, sulfur dioxide and dilute acid, as investigated within the Biomass Refining Consortium for Applied Fundamentals and Innovation (CAFI). The effectiveness of the pretreatment process varies based on biomass type, so three different biomass alternatives, corn stover, switchgrass and hybrid poplar, are investigated as possible feed components.

To find the optimal pretreatment method and biomass feed composition, a mixed integer nonlinear program for the whole plant was developed. This model consisted of mass and energy balances around all of the unit operations in the plant along with cost correlations to determine the resulting capital and operating costs. The biomass feed consisted of any or all of the three different biomass options. The total cost of the plant was then minimized to find the break-even selling price per gallon of the ethanol produced. Results indicate the production of ethanol from a predominantly corn stover feed via liquid hot water pretreatment is a strong option when considering the replacement of petroleum derived fuels.