Separation of hemicellulosic oligomers from steam-treated spruce wood using gel filtration
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Interest in the use of renewable raw materials for the production of various compounds that can replace fossil-based products is steadily increasing. In this study, the extraction and separation of hemicellulosic oligomers from spruce, to be used for the production of polymers such as hydrogels, was investigated. The focus of the study was on gel filtration of the solution from steam treatment of water impregnated spruce wood at 200degreesC for 2 min to separate oligomers from low-molecular-weight compounds. The total amount of oligomers extracted was approximately 6 g oligomers per 100 g dry wood, which corresponded to mannan and xylan yields of 30 and 17% of the theoretical amounts, respectively. The gel filtration yielded oligomer fractions completely free from low-molecular-weight compounds. The oligomer fractions collected for further processing had molecular weights of 600-12,000 g/mol, with the mean molecular weights of 5800 and 2900 g/mol, respectively. The composition of the O-acetyl-galactoglucomannan oligomers obtained, expressed as the ratio between mannan, glucan and galactan, was approximately 100:24:10. After gel filtration, the carbohydrate content of the dry matter in the oligomer fractions collected was 87-100%. The results of this Study indicate that gel filtration can be used to reduce the lignin content in the oligomer fractions, but not to remove it completely. (C) 2003 Elsevier B.V. All rights reserved.