Fractionation of Processed Spruce Wood Obtained in the Production of Ethanol

Fuel ethanol can be produced from pretreated spruce wood through enzymatic hydrolysis and fermentation. Processed spruce wood samples (acid-catalyzed steam hydrolysis followed by enzymatic hydrolysis and fermentation) were fractionated into water-soluble products and residual solids. The dioxane/water soluble portions of the solids were fractionated by liquid-liquid extraction. A substantial portion of the processed wood (20-70 %) was insoluble in both water and dioxane/water. An almost pure lignin fraction, corresponding to about 20 % of the total lignin of the wood, was isolated. Examinations by H NMR spectroscopy showed that the processes led to extensive cleavage of arylglycerol β-aryl ethers in the lignin. The lignin content of other fractions could be estimated very roughly by IR spectroscopy. Purified lignin from SO2-catalyzed steam hydrolysis contained approx. 0.2 % sulphur.