Submitted to: Industrial and Engineering Chemistry Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/1/2002
Publication Date: 12/1/2002
Citation: WEIL, J.R., DIEN, B.S., BOTHAST, R.J., HENDRICKSON, R., MOSIER, N.S., LADISCH, M.R. REMOVAL OF FERMENTATION INHIBITORS FORMED DURING PRETREATMENT OF BIOMASS BY POLYMERIC ADSORBENTS. INDUSTRIAL AND ENGINEERING CHEMISTRY RESEARCH. 2002. V. 41. P. 6132-6138.
Interpretive Summary: Fuel ethanol production in the U.S. is over 1.7 billion gal/yr, 95% of which is produced from corn. Converting fibrous biomass to ethanol could increase production 10 fold. A major impediment to producing ethanol from biomass is converting the biomass to fermentable sugars. Extracting the sugars usually involves treating the biomass with a combination of heat and ddilute acid. In addition to freeing sugars, these pretreatments also produce aromatic side-products that are highly toxic to microorganisms. We have discovered that an adsorbent, used in wastewater treatment, effectively removes aromatics from pretreated biomass, while not affecting the fermentable sugars. When pretreated biomass was exposed to the adsorbent, sugar was readily fermented to ethanol with a yield that was 90% of the maximum possible. In contrast, because of the toxicity, no ethanol was formed when pretreated biomass was fermented without adsorption.
Technical Abstract: The production of aldehydes that are microbial inhibitors may occur when hexoses and pentoses are exposed to temperatures above 150 deg C and acidic pH in water. Conditions encountered when biomass is pretreated by acid catalyzed hydrolysis. Concentrations of about 0.1% or higher of the degradation product, furfural, strongly inhibit fermentation as was confirmed for hydrolysate that contained 0.5% (w/o) furfural. Methods of furfural removal that have been tested include sulfite addition to achieve chemical reduction, ion exchange, non-polar solvent extraction and irreversible adsorption on activated carbon. This paper reports contacting of a polymeric adsorbent, XAD-4, with biomass hydrolysate that contains furfural. Liquid chromatographic analysis of the remaining effluent showed that furfural concentrations were less than 0.01 g/L compared to the initial concentrations which were in the range of 1 to 5 g/L. Fermentation nof the resulting sugars with recombinant E. coli ethanologenic strain K011 confirmed that the concentration of furfural in the hydrolysate was at a low enough level that the inhibition effect was negligible. Fermentation of XAD-4 treated hydrolysate with E. coli K011 was nearly as rapid as the control medium which was formulated with reagent grade sugars of the same concentration. Ethanol yields for both fermentations were 90% of theoretical. Modeling of the adsorptive properties of this styrene based adsorbent indicates that it is suitable for on-off chromatography and could be useful for removing small amounts of aldehydes that might otherwise inhibit fermentation.