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Kinetics and Mechanism of Autohydrolysis of Mixed Hardwoods

Abstract: Autohydrolysis using water is a promising method to extract hemicelluloses from wood prior to pulping in order to make co-products such as ethanol and acetic acid besides pulp. Many studies …

Abstract: Autohydrolysis using water is a promising method to extract hemicelluloses from wood prior to pulping in order to make co-products such as ethanol and acetic acid besides pulp. Many studies have been carried out on the kinetics and mechanism of autohydrolysis. However, most studies were performed in batch reactors which are not best suited to determine intrinsic kinetics of hemicellulose dissolution due to further reaction of the hemicelluloses in solution. Therefore a continuous mixed batch reactor was used in the present study to obtain the intrinsic kinetics of dissolution of hemicelluloses from a mixture of hardwoods. The xylan removal rate follows an S-shaped behavior. GPC analysis of the continuously removed extract shows that the dissolved xylan oligomers have a DP smaller than about 20. Lignin free xylan and cellulose oligomers are the major components dissolved in the initial stage of autohydrolysis, while xylan covalently bound to lignin (i. e. an LCC) is the major hemicellulose component removed from wood in the second stage. The molecular weight of the dissolved components decreases with time in the second stage. The kinetics of xylan removal are explained in terms of a mechanism based on recent knowledge of the ultrastructure of hardwood fibre walls.

Paper presented at the PAPTAC Annual Meeting 2010 in Montreal, Que., February 2-3, 2010.

Keywords: KINETICS, DISSOLUTION MECHANISM, AUTOHYDROLYSIS, HARDWOODS, ULTRASTRUCTURE, HEMICELLULOSES, LIGNIN-CARBOHYDRATE COMPLEXES

Full manuscript available at www.paptac.ca.