Enzymatic cellulose hydrolysis of Eucalyptus grandis wood pretreated by autohydrolysis for fuel ethanol production

Bioethanol production from lignocellulosic materials is very attractive because of its low cost and abundance, and non-competition with foodstuffs. Due to its structural characteristics, an appropriate pretreatment method is required to overcome its recalcitrant complex structure and makes sugars easily available for enzyme digestion. In this work, the effect of autohydrolysis pretreatment of Eucalyptus grandis wood on enzymatic hydrolysis of cellulose was evaluated. Autohydrolysis was performed under mild operational conditions (140-160ºC, liquid to solid ratio 6-10 g/g, reaction times up to 150 min). Solid residues were then subjected to enzymatic hydrolysis (50 mM citrate buffer pH 4.8, 16% w/v solids loadings and enzyme dosage of 25 FPU/g cellulose at 48ºC for 96 h). Also, a further alkaline step (4% w/v NaOH, 10% w/v solids, 60°C during 24 h) and the addition of surfactant (PEG₆₀₀₀) were evaluated to enhance enzymatic hydrolysis. Autohydrolysis at 160ºC for 150 min was the best condition showing high glucan content in the solid residue compared to the original raw material, and good hemicellulose (as xylans) recovery as xylose. The liquid extract (hydrolyzate) contained 8.5 g/L of xylose and low level of fermentation inhibitors as acetic acid, furfural and hydroxymethylfurfural. The cellulose conversion into glucose improved from 22% to 39% in presence of surfactant. The alkaline pretreatment and the addition of surfactant increased the cellulose conversion to 43%.