Generation of xylose solutions from Eucalyptus globulus wood by autohydrolysis±posthydrolysis processes: posthydrolysis kinetics Gil Garrote, Herminia Dom  õnguez, Juan Carlos Paraj  o * Chemical Engineering Department, University of Vigo Campus Ourense), Edi®cio Polit ecnico, As Lagoas s/n, 32004 Ourense, Spain Received 11 September 2000; received in revised form 5 February 2001; accepted 25 February 2001 Abstract Eucalyptus wood samples were treated with water under selected operational conditions autohydrolysis reaction) to obtain a liquid phase containing hemicellulose-decomposition products mainly acetylated xylooligosaccharides, xylose and acetic acid). In a further acid-catalysed step posthydrolysis reaction), xylooligosaccharides were converted into xylose, a carbon source for further fermentation. The kinetic pattern governing the posthydrolysis step was established by reacting xylooligosaccharide-containing liquorsat100:5°C,115°C,125°Cor135°Cinmediacontaining0.5,1.0,1.5or2wt%ofcatalystsulphuricacid).Thetimecourseof the concentrations of xylooligosaccharides, xylose, furfural and acetic acid were determined, and the results were interpreted by means of a kinetic model which allowed a close reproduction of the experimental data. Almost quantitative conversion of xy- looligosaccharides into xylose was achieved under a variety of experimental conditions. The ®rst-order, kinetic coecient for xy- looligosaccharide hydrolysis k 1 ,h 1 ) varied with both temperature T, K) and molar sulphuric acid concentration C) according to the equation ln k 1  36:66  1:00ln C  108:0=8:314T . The hydrolysis of acetyl groups followed a ®rst-order kinetics. The cor- responding kinetic coecient k a ,h 1  was correlated with the operational conditions by the equation ln k a  26:80 1:18ln C  73:37=8:314T . Ó 2001 Elsevier Science Ltd. All rights reserved. Keywords: Autohydrolysis; Eucalyptus globulus; Furfural; Posthydrolysis; Wood; Xylooligosaccharides; Xylose 1. Introduction The ``biomass re®nery'' approach for biomass utili- sation Myerly et al., 1981) is based on the ``fractiona- tion'' of lignocellulosics to obtain a variety of marketable chemicals from the polymeric fractions of the raw materials cellulose, hemicelluloses and lignin). In this ®eld, autohydrolysis can be conceived as a pos- sible ®rst processing step for an integral bene®t of bio- mass. In this kind of treatment, hemicelluloses can be almost completely solubilised Conner and Lorenz, 1986), whereas little alteration is caused in both lignin and cellulose, which are recovered in the solid phase. Incomparisonwithprehydrolysisinwhichamineral acid is added to the reaction media, see Springer, 1966; du Toit et al., 1984; Maloney et al., 1985; Ranganathan et al., 1985; Wayman and Yu, 1985; Paraj  o et al., 1993, 1994, 1995), in autohydrolysis reactions the catalytic species hydronium ions) come from water autoioniza- tion and from the acetic acid generated from acetyl groupsBarnetetal.,1989;OverendandChornet,1989; Heitz et al., 1991; Aoyama et al., 1995; Saska and Ozer, 1996; Weil et al., 1997; Garrote et al., 1999a). Owing to this, autohydrolysis causes low environmental impact no neutralisation sludges are generated) with limited equipment corrosion Lamptey et al., 1985). Under mild operational conditions, the reaction is very selective towards cellulose decomposition and lignin repolymer- ization is avoided. In most cases, autohydrolysis has been applied to lignocellulosics such as hardwoods or agricultural wastes, in which xylan was the main hemicellulose component Garrote et al., 1999b). The liquors from typical autohydrolysis assays contain a mixture of sugar oligomers mainly xylooligomers), monosaccharides mainly xylose), sugar-decomposition products such as furfural or hydroxymethylfurfural) and acetic acid from acetyl groups). Under harsh operational condi- tions, condensation reactions between furfural, lignin and/or reaction intermediates may occur Lora and Wayman, 1978; Dekker and Wallis, 1983; Muzzy et al., 1983). Bioresource Technology 79 2001) 155±164 * Corresponding author. Tel.: +34-9-8838-7047; fax: +34-9-8838- 7001. E-mail address: jcparajo@uvigo.es J.C. Paraj o). 0960-8524/01/$ - see front matter Ó 2001 Elsevier Science Ltd. All rights reserved. PII:S0960-852401)00044-X