Conversion of hemicellulose hydrolyzates to ethanol
1994
McMillan, J.D.
This chapter provides an overview of research directed at conversion of biomass-derived hemicellulose hydrolyzates generated by dilute acid pretreatment. The composition of hemicellulose hydrolyzates differs markedly from synthetic laboratory media formulations commonly used to assess pentose fermentation performance. In addition to containing sugars other than xylose, hemicellulose hydrolyzates contain a variety of components that are potent inhibitors when present at typical levels. As a result, hydrolyzates must be substantially detoxified prior to fermentation to achieve performance objectives. Following a brief review of the subject of pentose fermentation, performance data for conversion of highly detoxified hydrolyzates are tabulated for two organisms currently being evaluated for use in large scale pentose fermentation processes, P. stipitis, a wildtype xylose-fermenting yeast, and recombinant E. coli, an ethanologenic bacterium. Suspected inhibitory components present in biomass hydrolyzates are then identified, and their relative toxicity is qualitatively compared. Finally, methods commonly used to detoxify hydrolyzates prior to fermentation are summarized. Discussion focuses on relevant process considerations for selecting a biocatalyst for the pentose fermentation step of an integrated ethanol-from-biomass process.
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