PEER-REVIEWED ARTICLE bioresources.com Johansson et al. (2009). “Wood fractionation after ethanol,” BioResources 4(1), 15-25. 15 FRACTIONATION OF PROCESSED SPRUCE WOOD OBTAINED IN THE PRODUCTION OF ETHANOL Christian Johansson, †* Knut Lundquist, and Hans Theliander 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 1 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 SO 2 -catalyzed steam hydrolysis contained approx. 0.2 % sulphur. Keywords: Lignin; Fractionation; Ethanol; Enzymic hydrolysis; Lignin content; Sulphur content Contact information: Forest Products and Chemical Engineering, Department of Chemical and Biological Engineering, Chalmers University of technology, SE-412 96 Göteborg, Sweden; †: Present address: Epsilon Utvecklingscentrum Väst AB, Lindholmspiren 9, SE-417 56 Göteborg, Sweden; *Corresponding author: christian.johansson@epsilon.nu INTRODUCTION Softwood is an abundant raw material in the northern hemisphere, and therefore it has the potential of being a renewable feedstock in the production of fuel ethanol. The hemicelluloses and cellulose in the wood can be hydrolyzed to monosaccharides using enzymes and or an acid catalyst. The monosaccharides, in turn, can be fermented with yeast. No full scale plant for ethanol production from wood is in operation as yet. The complexity of the processes has so far thwarted the development of full scale production of ethanol from wood. Lignin is the structural wood constituent that has the highest specific energy value; the mass and energy balances of the ethanol production are therefore affected by the solubility of lignin in the hydrolysis liquor. Processes involving dilute or concentrated acid hydrolysis of wood give only low yields of monosaccharides. Processes in which a preliminary mild acidic treatment of the wood, such as SO 2 -catalyzed steam hydrolysis is followed by enzymatic hydrolysis, are favourable in that the yields of monosaccharides obtained are comparatively high (Galbe and Zacchi 2002; Taherdazeh and Karimi 2007a,b). The conditions prevailing during SO 2 -catalyzed steam hydrolysis have similarities to those applied in sulphite pulping, even though the reaction times are shorter and temperatures are higher (Glennie 1971). It is therefore probable that lignin structures are sulphonated to some extent during SO 2 -