18-14: Commercially relevant fermentation advances for biomass-to-ethanol processes

Tuesday, May 1, 2012
Napoleon Ballroom C-D, 3rd fl (Sheraton New Orleans)
Kate Brandon Sutton, Brandon Emme, Sarah McHatton, Lindsay Jones and Mads Torry Smith, Novozymes North America, Inc., Franklinton, NC
In efforts to enable commercial biomass-to-ethanol processes, Novozymes has taken a holistic approach in designing enzymes solutions for the evolving industry. Novozymes’ Advance Biofuel cost model, which has been developed to direct research and evaluate processes, has identified the fermentation-step cost as a significant driver for the minimum ethanol selling price (MESP). Compared to their starch-to-ethanol counterparts, pentose-utilizing organisms for biomass-to-ethanol processes are less robust while having to ferment mixed sugars in a much more inhibitory environment. Fermentation inhibition can be overcome with a high yeast pitch which also maximizes xylose uptake rates in fermentation. The high yeast pitch requirement drives the necessity of dedicated onsite propagation for the majority of cells needed. Thus the variable cost of the propagation step, specifically the carbohydrate source, is the most significant contributor to the step cost. Maximization of the cost performance of C5 yeast propagation is necessary to ensure an economically feasible biomass-to-ethanol fermentation step. 

Two complementary approaches are suggested to reduce the fermentation cost: first, increase propagation cell yields from sugars to reduce the realized organism cost, or second, produce a more robust organism from propagation with a higher realized xylose uptake rate in fermentation which would enable fermentation at a lower yeast pitch in a reasonable processing time. We will discuss cost model results, including sensitivities on cost from propagation and fermentation process variables, in conjunction with reactor data to break down fermentation step costs and pinpoint potential savings opportunities to lower overall fermentation cost for second generation ethanol.

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