HEMICELLULOSE HYDROLYSIS AND FERMENTATION OF RESULTING PENTOSES TO ETHANOL

Abstract

Hemicellulose can be hydrolyzed from lignocellulosics under mild acidic conditions resulting in the release of pentoses and other sugars. The ease with which hemicellulose can be hydrolyzed makes it possible to selectively recover the hemicellulose portion of lignocellulose biomass. Hydrolysis of hemicellulose occurs in sequential reactions involving random depolymerization, hydrolysis of oligomers to monomers, and degradation of monomers. Under mild acidic conditions the hydrolytic reactions are much more rapid than the decomposition reaction, making it possible to achieve relatively high yields of sugar. A variety of microorganisms produce ethanol from hexoses, but relatively few produce ethanol from pentoses. The yeast Pachysolen tannophilus NRRL Y-2460 produces higher yields of ethanol from D-xylose than other yeasts reported to date. However, the yield of ethanol from acid hydrolyzate of wood hemicellulose is low because of the presence of microbial inhibitors. Further advances in the bioconversion of biomass-derived sugars to ethanol and other chemicals would require that more attention be given to this effect. (Refs. 34).