Techno-economic analysis of integrating first-generation (1G) with second-generation (2G) bioethanol production with onsite enzyme production from wet DDGS

There has always been a wide gap between research and industrial practice for lignocellulosic-based biofuels. One of the numerous prominent uncertainties that drive industry's behavior toward low adaptation of lignocellulosic biofuel production facilities is the high cost of lignocellulolytic enzymes needed for conversion of complex biomass into simple sugars prior to fermentation into the respective biofuels. Enzymes such as cellulases and hemicellulases should not only be inexpensive but should also be of high quality so that lower enzyme loading rates will yield high conversion rates. In this research, techno-economic analysis (TEA) is presented where first-generation (1G) ethanol production is linked to the second-generation (2G) ethanol production by onsite enzyme production using wet distillers' dried grains with solubles (DDGS), which is a byproduct of 1G bioethanol plant. The TEA model was built using SuperPro Designer software. The model shows that 582 million l/year of ethanol can be produced at the rate of 128 ton/h corn grains and 110 ton/h of corn stover. This integrated scenario would result in an average cost of $0.96/kg ($0.75/l or 2.84/gal) of ethanol. The price of lignocellulosic ethanol was lower ($1.05/kg; $0.82/l or $3.11/gal) than the price ($1.5/kg; $1.17/l or $4.44/gal) estimated by NREL's onsite enzyme production from hydrolyzed corn stover. The cost of the enzyme mixture produced was majorly affected by the total capital cost including the equipment cost of the production plant. The sensitivity analysis also shows that enzyme cost is one of the most prominent factors contributing to the unit production cost of lignocellulosic ethanol. Therefore, this study clearly offers a solution to onsite production of lignocellulolytic enzymes by using wet DDGS or WDGS. Future studies should focus on life cycle assessment of the suggested process and further evaluation of techno-economical aspects.