Comparison of the susceptibility of two hardwood species, Mimosa scabrellaBenth and Eucalyptus viminalis Labill, to steam explosion and enzymatic hydrolysis

Steam explosion of two hardwood species was carried out with and without ad dition of sulfuric acid (H2SO4 0.5%, p/v) as a pretreatment catalyst In gen eral, wood chips of Eucalyptus viminalis Labill were shown to be more amena ble to pretreatment than chips derived from bolds of Mimosa scabrella Benth (bracatinga). This was apparent from all pretreatment parameters tested in cluding the overall recovery yields of pretreated fractions, carbohydrates (pentoses and hexoses) recovered as water-solubles, yield of dehydration by -products and lignin susceptibility to acid hydrolysis. There was no eviden ce for complete deacetylation of both wood species during pretreatment and lignin appeared to undergo extensive acid hydrolysis at higher pretreatment severities. Steam treatment at 205 degrees C for 5 min without addition of an acid catalyst was shown to be uncapable of removing the hemicellulose c omponent from bracatinga chips, as determined by chemical analysis of the s team-treated water-insoluble fractions. Nearly 30% of the hemicellulose (xy lan)found in bracatinga remained unhydrolysed after pretreatment, whereas m ore than 90% of this component could be removed from eucalypt chips under t he same pretreatment conditions. Likewise, pretreatment of eucalypt chips r esulted in a more extensive solubilization of glucans (cellulose) by acid h ydrolysis. Addition of dilute H2SO4 as a pretreatment catalyst generally in creased the recovery yield of fermentable sugars in the water-soluble fract ions and this effect was more pronounced for the pretreatment of bracatinga chips. Steam-treated substrates produced from bracatinga were also less ac cessible to enzymatic hydrolysis than those produced from eucalypt chips, r egardless of the use of an acid catalyst.