Tuesday, May 3, 2011
Reducing enzyme loadings while maintaining high ethanol yields is a key to low cost cellulosic ethanol production. Although many economic studies assume continuous Simultaneous Saccharification and Fermentation (cSSF) will be the preferred configuration for commercial applications to achieve higher productivity and eliminate the need for seed fermentors, little information is available to guide process design or optimization. Rate limitations by enzymatic hydrolysis especially at low enzyme loadings and high solids concentrations and challenges in formulating enzymes and selecting fermentative organisms must be addressed to make cSSF economically viable. Therefore, in this paper, we focus on developing optimal operating strategies for cSSF based on new experiments and kinetic models. Enzyme loadings, fermentor residence times, fermentative organism features, and organism washout are considered for this continuous process, and the effects of features of steam exploded corn stover are also studied. Comparisons are made between batch and continuous processing to understand how end-product inhibition and other characteristics differ and their effects on performance under different operating conditions and solids loadings. Enzyme loadings and residence times are then selected and applied to establish performance data.