Fractionation of wheat and barley straw to access high-molecular-mass hemicelluloses prior to ethanol production Tobias Persson a , Jun Li Ren b , Elisabeth Joelsson a , Ann-Sofi Jönsson a, * a Department of Chemical Engineering, Lund University, P.O. Box 124, SE-221 00 Lund, Sweden b State Key Laboratory of Pulp and Paper Engineering, South China University of Technology, 510640 Guangzhou, China article info Article history: Received 14 January 2009 Received in revised form 26 February 2009 Accepted 28 February 2009 Available online 5 April 2009 Keywords: Steam pretreatment Arabinoxylan Enzymatic hydrolysis Biorefinery abstract The cost efficiency of the biorefining process can be improved by extracting high-molecular-mass hemi- celluloses from lignocellulosic biomass prior to ethanol production. These hemicelluloses can be used in several high-value-added applications and are likely to be important raw materials in the future. In this study, steam pretreatment in an alkaline environment was used to pretreat the lignocellulosic biomass for ethanol production and, at the same time, extract arabinoxylan with a high-molecular-mass. It was shown that 30% of the arabinoxylan in barley straw could be extracted with high-molecular-mass, with- out dissolving the cellulose. The cellulose in the solid fraction could then be hydrolysed with cellulase enzymes giving a cellulose conversion of about 80–90% after 72 h. For wheat straw, more than 40% of the arabinoxylan could be extracted with high-molecular-mass and the cellulose conversion of the solid residue after 72 h was about 70–85%. The high cellulose conversion of the pretreated wheat and barley straw shows that they can be used for ethanol production without further treatment. It is therefore con- cluded that it is possible to extract high-molecular-mass arabinoxylan simultaneously with the pretreat- ment of biomass for ethanol production in a single steam pretreatment step. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Interest in utilizing cereal straw and wood for high-value-added applications has increased during recent years and the term biore- finery is now frequently used. In order to meet future demands, biorefineries have to produce both biofuels and chemical products from lignocellulosic biomass (Ragauskas et al., 2006). Bioethanol is a liquid transportation fuel that is likely to be an important product in the future, in reducing greenhouse gas emis- sions (Huang et al., 2008). The second generation of bioethanol, produced from lignocellulosic plant materials such as softwood (Söderström et al., 2003), hardwood (Sassner et al., 2006), cereal straw (Ballesteros et al., 2004; Chen et al., 2008; Linde et al., 2007, 2008) and corn stover (Öhgren et al., 2006), has, however, not yet been commercialised. These materials contain both hexose and pentose sugars, but the industrial fermentation of pentoses has not yet been achieved in a cost-efficient way (Ragauskas et al., 2006). This is a drawback, especially for the cost efficiency of the process when using lignocellulosic biomass containing a large amount of arabinoxylan, such as cereal straw and hardwood. When producing bioethanol from a lignocellulosic feedstock, the biomass must be pretreated prior to enzymatic hydrolysis to improve the accessibility of the enzymes (Mosier et al., 2005). During pretreatment it is important to limit the formation of deg- radation products such as furfural and hydroxymethylfurfural (HMF), which inhibit the fermentation process (Palmqvist and Hahn-Hägerdal, 2000). Pretreatment can be carried out by a phys- ical or a chemical method, or a combination of both. Steam pretreatment can be performed on its own, or in an acidic or alkaline environment. Sulphuric acid and sulphur dioxide have been used as catalysts in several studies on the production of bioethanol (Linde et al., 2007, 2008; Sassner et al., 2006; Söderström et al., 2003), since acid hydrolyses both cellulose and hemicelluloses. Sodium hydroxide has been used as a catalyst when extracting hemicelluloses from softwood (Palm and Zacchi, 2004) and barley husks (Krawczyk et al., 2008; Persson et al., in press; Roos et al., 2009). Another common method of extracting hemicelluloses from biomass is alkaline extraction (Glasser et al., 2000; De Lopez et al., 1996; Ren et al., 2006, 2007; Sun et al., 1995; Sun and Sun, 2002). Alkaline conditions at elevated temper- atures can also be used to pretreat biomass for bioethanol produc- tion, for example, ammonia recycled percolation (ARP) (Mosier et al., 2005) and wet oxidation (Klinke et al., 2002). Alkalis hydro- lyse the ester linkages between plant polysaccharides and lignin, which increases the solubility of the hemicelluloses, without reducing their molecular mass, provided the conditions are not too severe. The aim of the present study was to investigate the possibility of extracting hemicelluloses with high-molecular-mass and 0960-8524/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2009.02.063 * Corresponding author. Tel.: +46 46 222 82 91; fax: +46 46 222 45 26. E-mail address: Ann-Sofi.Jonsson@chemeng.lth.se (A.-S. Jönsson). Bioresource Technology 100 (2009) 3906–3913 Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech