Monday, April 30, 2012
Napoleon Ballroom C-D, 3rd fl (Sheraton New Orleans)
Many recent techno-economic models of enzyme-based, lignocellulosic biomass-to-ethanol processes have focused on co-product development and unit operations such as anaerobic digestion and on-site cellulase enzyme production as ways in which to reduce the cost of ethanol production. In simulations of the softwood-to-ethanol process, the acid catalyzed steam pretreatment step has generally received less attention, despite its enormous impact on all aspects of the process. In fact, use of so-called ‘static conversion factors’ means that changes to the reaction conditions of this unit operation do not result in realistic changes to the process as a whole. To overcome this limitation, a more dynamic model of SO2 catalyzed steam pretreatment was employed in an existing Aspen Plus simulation of the entire softwood-to-ethanol process. The statistical model, developed according to response surface methodology, also encompassed the subsequent step of enzymatic hydrolysis. As a result, it was possible to evaluate the effects of the operating conditions of steam pretreatment on the combined sugar yield from this step and enzymatic hydrolysis, as well as total ethanol product cost. Previous work has established the influence of feedstock size and moisture content on the performance of steam pretreatment. However, the effects of these two variables on combined sugar yield have not yet been established. For this reason, feedstock size and moisture content were investigated over industrially relevant ranges during the development of the statistical model, which made an evaluation of their effects on combined sugar yield and ethanol product cost possible.