Energy & Fuels
Straw is one of the main lignocellulosic waste produced during cereal crop cultivation. The abundance of barley straw makes it a good candidate for bioethanol production. This work deals with barley straw pretreatment by means of autohydrolysis in order to get xylooligosaccharides in the liquid phase, followed by an organosolv treatment using ethanol to increase the solid phase enzymatic susceptibility. Up to 17.4 g oligomers/L were obtained in the hydrothermal stage, in which practically all the cellulose and lignin remained in the solid phase. The solid phase from the hydrothermal-delignification was subjected to an experimental design in order to study the effect of pretreatment conditions in the bioethanol production, with values of solids concentrations in the range 7.7 to 20 weight % and values of enzyme loading in the range 14 FPU/g to 6 FPU/g. In the experiments carried out at a liquid to solid ratio = 4 g/g it is possible to obtain 31.6 g ethanol/L in just 9 h (corresponding to 100% ethanol conversion), with optimum results of 44.5 g ethanol/L in 46 h (90-93% glucose to ethanol conversion) and with a maximum concentration of 48.7 g ethanol/L in 89 h (79% conversion). The combination of a hydrothermal pretreatment (under conditions that lead to the recovery of high amounts of hemicellulosic by-products), followed by an organosolv treatment under mild conditions turns out to be suitable for second generation bioethanol production, applying a high solids loading, by means of fed-batch simultaneous saccharification and fermentation.