Sunday, April 29, 2007

Biological conversion of hemicelluloses extracted from hardwood: Enabling co-production of ethanol and pulp in an integrated forest bio-refinery

Sara L. Walton and Adriaan R. van Heiningen. Chemical Engineering, University of Maine, 5737 Jenness Hall Rm. 117, Orono, ME 04469

As part of an integrated forest products bio-refinery concept, the hemicellulosic component of woody biomass can be pre-extracted, preserving the cellulosic component for pulp production while creating an additional value added product stream.  Hemicelluloses, once extracted, may be hydrolyzed to give a mixture of five and six carbon monosugars, of which xylose is the principal component in hardwoods.  This mixture of monosugars can be fermented to generate new fuel and chemical products within the pulp and paper industry.  It is critical in fermenting hemicellulose extracts that the fermentation organism used be able to utilize pentose sugars effectively in the presence of hexoses and inhibitors generated during hydrolysis such as acetic acid and furfural. 

Hemicelluloses are removed from woodchips in a modified Dionex ASE100 extractor by treatment with hot water at high pressure.  The hemicellulosic components are more soluble due to their lower degree of polymerization and their branched structure.  Fermentation experiments have been carried out in a 3L BioFlo110 fermentor from New Brunswick Scientific.  The biological conversion of hardwood hemicellulose extracts to ethanol is being evaluated using E. coli K011.  A comparison of fermentation results for simulated hemicellulose extracts consisting of pure monosugars and for actual hemicellulose extracts will be presented, focusing on ethanol yields and carbon mass balance.