Combined autohydrolysis and alkali pretreatments for cellulose enzymatic hydrolysis of Eucalyptus grandis wood

Abstract

Lignocellulosic materials represent a promising low-cost and abundant raw material which does not compete with foodstuffs, but an appropriate pretreatment is required to make sugars easily available. In this work, Eucalyptus grandis wood was subjected to autohydrolysis pretreatment under mild operational conditions (6–10 g/g liquid to solid ratio, 140–160 °C, reaction times up to 150 min) in order to recover and preserve hemicelluloses, while enhancing enzyme accessibility to cellulose. The severity of the pretreatment should be chosen depending on the subsequent use of the separated products. Pretreatment at 160 °C for 150 min using a liquid to solid ratio of 6 g/g was the best condition for hemicellulose recovery (mostly as xylose) in the liquid fraction. Under these autohydrolysis pretreatment conditions, an additional alkaline pretreatment applied to the autohydrolyzed solids was evaluated in order to improve the enzymatic hydrolysis of pretreated wood. Also, the addition of surfactant was assessed in order to enhance the enzymatic hydrolysis. The highest cellulose hydrolysis was obtained in the presence of PEG 6000. For the autohydrolysis-pretreated solids, a cellulose conversion of 39% was obtained, corresponding to an overall glucose yield of 18.7 kg per 100 kg of dry raw material. Additionally, for the autohydrolysis-alkaline-pretreated solids, a cellulose conversion of 43% was achieved, which corresponds to an overall glucose yield of 15.4 kg per 100 kg of dry raw material.