Submitted to: American Institute of Chemical Engineers
Publication Type: Abstract Only
Publication Acceptance Date: September 23, 2008
Publication Date: N/A
Technical Abstract: To expand the biomass to fuel ethanol industry, process strategies are needed to foster the production and utilization of microorganisms which can survive and ferment hexose and pentose sugars while exposed to inhibitors (such as ethanol, furfural, and hydroxymethylfurfural (HMF)). Furfural and HMF are key byproducts of what is currently the most economical dilute acid pretreatment of biomass to allow efficient enzymatic release of fermentable sugars. The conversion of xylose to ethanol and the inhibitor tolerance of the natural pentose-fermenting yeast Pichia stipitis were optimized using a culture medium that supplied sufficient minerals and nitrogen as a mixture of urea and amino acids. Priming inocula with a high xylose concentration was observed to induce faster fermentation rates in ethanol production fermentors and to eliminate diauxic lag during mixed sugar conversion by P. stipitis NRRL Y-7124. Using both nutrition and culture priming technologies, P. stipitis Y-7124 yields an economically recoverable 66 g/L ethanol in 48 h at a conversion efficiency of 88% (0.44 g ethanol/g sugar) from 95 g/L of glucose and 55 g/L xylose. This performance is a vast improvement in efficiency over “stuck” fermentations commonly observed during the switch from glucose to xylose utilization by yeasts. Use of these process strategies in industrial plant designs has the potential to lower the cost of ethanol from biomass.