A biorefinery scheme for residual biomass using autohydrolysis and organosolv stages for oligomers and bioethanol production

Energy & Fuels

DOI: 10.1021/acs.energyfuels.6b00277

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.

Barley straw (Hordeum vulgare) as a supplementary raw material for Eucalyptus camaldulensis and Pinus sylvestris kraft pulp in the paper industry

BioResources, 10 (2) 3682-3693 (2015)

DOI: 10.15376/biores.10.2.3682-3693

The present study shows that barley straw (Hordeum vulgare) can be a supplementary raw material of softwoods and hardwoods such as Pinus sylvestris and Eucalyptus camaldulensis, respectively, for the production of cellulose and paper, reducing an agricultural residue that has no added value. Barley straw has a lower content of cellulose at 36.4% than P. sylvestris and E. camaldulensis, but it contains a lower quantity of lignin, 15.9%. After pulping with soda anthraquinone (AQ), high contents of cellulose (56.5 to 67.5%) and holocellulose (>80%) were attained. Paper sheet properties were able to reach, and even improve upon, those of wood species (Pinus and Eucalyptus) pulped with kraft. Better values of total yield (56.5%), Kappa number (8.9), and ISO brightness (36.4%), were attained for paper sheets from barley straw pulp versus E. camaldulensis and P. sylvestris, respectively, and comparable values for viscosity, tensile, and burst index were obtained.