Evaluation of strategies for second generation bioethanol production from fast growing biomass Paulownia within a biorefinery scheme

Applied Energy

http://dx.doi.org/10.1016/j.apenergy.2016.11.114

Fast-growing and short-rotation biomass is identified as glucan-rich feedstock to be used for bioenergy purposes. For the first time to our knowledge, fast growing biomass (Paulownia tomentosa) was evaluated for bioethanol production in a biorefinery scheme. For that, Paulownia wood was subjected to autohydrolysis pretreatment under severity (S0) conditions in the range of 3.31–5.16. The effect of this treatment on its fractionation was evaluated by means of hemicelluloses solubilization as hemicellulose-derived compounds in liquid phase and enzymatic hydrolysis of glucan (remained in the solid phase) into glucose. A xylose and xylooligosaccharides concentration of 17.5 g/L was obtained at S0 = 3.99 which corresponds to complete xylan solubilization. On the other hand, glucose yield of enzymatic hydrolysis increased up to reach 99% at S0 = 4.82. In addition, separate and simultaneous saccharification and fermentation assays (SHF and SSF) of autohydrolyzed Paulownia were compared for ethanol production. An increase of 47% in ethanol concentration was obtained by SHF in comparison with results achieved by SSF for Paulownia treated at S0 = 4.19. In SSF, Paulownia was successfully converted into ethanol (52.7 g/L which corresponded to 80% of ethanol yield) operating at 20% solid loadings and S0 = 4.72. Energy analysis of results obtained in this work showed that 83% of energy respect to raw material can be recovered considering the ethanol and the combustion of residual lignin. This work provides a feasible process for bioethanol production using fast growing specie which could enrich the feedstock needs for biofuels sector.

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.

Combined alkali and hydrothermal pretreatments for oat straw valorization within a biorefinery concept

Bioresource Technology

http://dx.doi.org/10.1016/j.biortech.2016.08.077

The aim of this work was the evaluation of lime pretreatment combined or not with previous step of autohydrolysis for oat straw valorization. Under selected conditions of lime pretreatment, 96% of glucan and 77% of xylan were recovered and 42% of delignification was achieved. Xylose fermentation to ethanol by metabolic engineered Saccharomyces cerevisiae (MEC1133) strain improved the ethanol production by 22% achieving 41 g/L. Alternatively, first step of autohydrolysis (S0=4.22) allowed a high oligosaccharides recovery (68%) and subsequent lime pretreatment attained a 57% of delignification and 99% of glucan to glucose conversion. Oat straw processed by autohydrolysis and lime pretreatment reached the maximal ethanol concentration (50 g/L). Both strategies led to oat straw valorization into bioethanol, oligosaccharides and lignin indicating that these pretreatments are adequate as a first stage within an oat straw biorefinery.

Second-generation bioethanol of hydrothermally pretreated stover biomass from maize genotypes

Biomass and Bioenergy, 90 (2016) 42–49

http://dx.doi.org/10.1016/j.biombioe.2016.03.029

Twelve maize genotypes, were agronomically evaluated and their stover hydrothermally pretreated in a temperature range of 210–225 °C to assess the effects of genotype and pretreatment severity on stover recalcitrance toward bioethanol conversion. Maize genotypes exhibited significant variation for biomass yield and all agronomic evaluated, while among all cell wall constituents measured in the unpretreated stover, only ash content showed differences among genotypes. The pretreatment severities assayed impacted most stover compositional traits, and the glucose recovered after enzymatic hydrolysis displayed a similar profile among genotypes with similar genetic background. Harsher pretreatment conditions maximized the potential cellulosic bioethanol production (208–239 L/t), while the mildest maximized the bioethanol from the hemicellulosic hydrolysates (137–175 L/t). Consequently, when both pentose and hexose sugars were considered, the total potential bioethanol produced at the lowest and highest pretreatment temperatures was similar in all genotypes (292–358 L/t), indicating that the lowest temperature (210 °C) was the optimal among all assayed. Importantly, the ranking of genotypes for bioethanol yield (L/ha) closely resembled the ranking for stover yield (t/ha), indicating that breeding for biomass yield would increase the bioethanol production per hectare regardless of the manufacturing process. Similarly, the genetic regulation of corn stover moisture is possible and relevant for efficient energy production as biomass moisture has a potential impact on stover transportation, storage and processing requirements. Overall, these results indicate that local landrace populations are important genetic resources to improve cultivated crops, and that simultaneous breeding for production of grain and stover bioethanol is possible in corn.

Phenolics production from alkaline hydrolysis of autohydrolysis liquors

CyTA - Journal of Food, 14 (2016) 255-265

http://dx.doi.org/10.1080/19476337.2015.1094516

The objective of this work was to study the release, identification and characterization of phenolic compounds by saponification of non-isothermal autohydrolysis liquors of corn (Zea mays) cobs and Eucalyptus globulus. Corn cobs and E. globulus are lignocellulosic materials with high contents in cellulose and hemicelluloses. Efficient use of these materials can be achieved using autohydrolysis as the first stage of a biorefinery, resulting in a solid phase rich in cellulose and lignin, and a liquid phase containing essentially hemicelluloses-derived compounds and phenolic compounds from the partial solubilization of lignin. This work studied the combination of alkaline hydrolysis and extraction with organic solvents to maximize the amounts of released phenolic compounds since these compounds are interesting for their properties and food applications.