Vol. 46 (1992) No. 2 Steam Prctreatment and Enzymatic Hydrolysis of Ccllulosic Substrates 149 Holzforschung 46(1992)149-154 Steam Pretreatment Conditions for Effective Enzymatic Hydrolysis and Recovery Yields of Eucalyptus viminalis Wood Chips By L.P. Ramos 1 , C. Breuil 1 , D.J. Kushner 2 and J.N. Saddler 1 1 Forest Products Biotechnology, Faculty of Forestry, University of British Columbia, Vancouver, CanadaV6TlW5 2 Department of Microbiology, Faculty of Medicine, University of Toronto, Toronto, Canada M5S 1A8 Keywords Steam pretreatmcnt Lignoccllulose Enzymatic hydrolysis Eucalyptus viminalis Summary Wood chips from Eucalyptus viminalis were steam treated over a ränge of tempcratures and rcsidence times in the abscnce or presence of SO 2 . When the Substrate was steam treated without explosion, the initial moisture content of the chips had a significant influence on the recovery yield and the degrce of enzymatic hydrolysis. Prctreatment by steam explosion showed no Variation resulting from differences in the initial moisture content of the chips. SO 2 catalysis was shown to be particulary beneficial for the steam treatment of green chips. More than 95% of the original cellulose could be hydrolyscd to glucose with more than 80% of the original pentosan recovered äs xylose in the water soluble fraction.This indi- cated a need for chips with a high enough moisture content necessary to generate enough sulphurous acid from SO 2 to act äs an effective catalyst. Introduction It is recognized that lignocellulosic Substrates require some form of pretreatment if efficient enzymatic hy- drolysis is to be achieved. A variety of physical and chemical methods have been advocated, with the rela- tive success of each method usually dependant on how much of the starting materials is recovered after the pretreatment step and the extent to which enzymatic hydrolysis of cellulose is improved. It has been demon- strated by various groups that steam pretreatment of both wood and agricultural residues can be an effec- tive method of fractionating lignocellulosic Substrates into their major components äs well äs enhancing the enzymatic hydrolysis of cellulose (Foody 1980; Sadd- ler et al. 1982; Mammers and Menz 1984; Mackie et al. 1985;Dekkerefö/. 1987; Eklund et al 1988). The pre-impregnation of wood chips with low levels of SO 2 prior to steam treatment has been shown to im- prove the enzymatic hydrolysis of the cellulosic com- ponent of the Substrate äs well äs increasing the recov- ery of sugars in the water soluble fraction (Mackie et al. 1985; Clark and Mackie 1987; Schwald et al. 1989a, b).There are several other advantages associated with SO 2 impregnation. These include, the even and ef- fective distribution of the catalyst throughout the Substrate, enhanced survival and recovery of the hemicellulose derived sugars and reduced tempera- ture and residence time requirements for Optimum steam treatment. Holzforschung /Vol. 46 /1992 / No, 2 © Copyright 1992 by Walter de Gruyter · Berlin · New York Although a considerable amount of work has looked at the influence of factors such äs chip size, concentra- tion of catalyst, need for explosion, etc., much of this research has utilised relatively few wood species such äs aspen (Brownell and Saddler 1984; Brownell et al. 1986) and willow (Eklund etal. 1988). When softwood species such äs spruce (Schwald et al. 1989b) or radiata pine (Clark and Mackie 1987) were examined it was apparent that different pretreatment conditions were required and that a catalyst was essential if high cellulose hydrolysis yields were to be obtained. During the last ten years, Brazil has established exten- sive plantations of fast growing Eucalyptus sp. Al- though these trees will be primarily used for pulp and paper production, it has been proposed that wood re- sidues from the harvesting and processing stages could be used äs a feedstock for producing ethanol. There has been some past work on the steam pretreat- ment of Eucalyptus sp., however, pretreatment condi- tions were not optimised for maximum recovery of the hemicellulose sugars while enzymatic hydrolysis was generally assessed after relatively high concentrations of enzyme were added to the pretreated Substrate (Dekker et al. 1987). In the work described in this paper we have looked at the influence of SO 2 impre- gnation on the recovery yield, äs a percentage of the original Substrate, and the enzymatic hydrolysis of the cellulosic fraction from wood chips with varying mois- ture contents. We have identified how parameters such äs the temperature, residence time and initial Brought to you by | University of Arizona Authenticated Download Date | 7/19/15 4:28 AM