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  • Artículo
    Acceso Abierto
    Comparing cell viability and ethanol fermentation of the thermotolerant yeast Kluyveromyces marxianus and Saccharomyces cerevisiae on steam-exploded biomass treated with laccase
    (2013-12-12) Moreno, David; Ibarra, David; Ballesteros, Mercedes; Ballesteros, Ignacio; González, Alberto
    In this study, the thermotolerant yeast Kluyveromyces marxianus CECT 10875 was compared to Saccharomyces cerevisae Ethanol Red for lignocellulosic ethanol production. For it, whole slurry from steam-exploded wheat straw was used as raw material, and two process configurations, simultaneous saccharification and fermentation (SSF) and presaccharification and simultaneous saccharification and fermentation (PSSF), were evaluated. Compared to S. cerevisiae, which was able to produce ethanol in both process configurations, K. marxianus was practically inhibited, and neither growth nor ethanol production occurred during the processes. However, the prior laccase treatment of the whole slurry, which removed specifically the lignin phenols content from the overall inhibitory compounds present in slurry, triggered the fermentation by k. marxianus, attaining ethanol concentrations and yields comparable to those obtained by S. cerevisiae.
  • Artículo
    Acceso Abierto
    Enzymatic hydrolysis from carbohydrates of barley straw pretreated by ionic liquids
    (2013-12-12) Ballesteros, Mercedes; Saez, Felicia; Ballesteros, Ignacio; Manzanares, Paloma; Oliva, Jose Miguel; Negro, Maria José
    Lignocellulosic biomass offers many potential advantages in comparison with the traditionally used sugars or starchy biomass since it’s vastly available and it does not compete with food and feed production. The abundance and high carbohydrates content of barley straw make it a good candidate for bioethanol production in Europe. Since biomass must be pretreated before enzymatic hydrolysis to improve the digestibility of both the cellulose and the hemicellulose biomass, the use of ionic liquids (IL) has been proposed as an environmental friendly pretreatment of biomass.Different pretreatment conditions were investigated to determine the effects of the experimental conditions (temperature and time) on the enzymatic digestibility of pretreated material. The pretreatment of barley straw with 1-ethyl-3-methyl imidazolium acetate treatment resulted in up to a 9-fold increase in the cellulose conversion and a 13- 22 fold increase in the xylan conversion when compared with the untreated barley straw.Ionic liquid pretreatment of barley straw at 110 ºC for 30 minutes, 24 followed by enzymatic hydrolysis, leads to a sugar yield of 53.5 g/100 g raw material. 25 It’s then ready available for conversion into ethanol and is equivalent to more than 86%from potential sugars. The increase in saccharification was possible due to the rupture in lignin-hemicellulose linkages with treatment of 1-ethyl-3-methyl imidazolium acetate
  • Artículo
    Acceso Abierto
    Hierarchical TiO2 nanofibres as photocatalyst for CO2 reduction: Influence of morphology and phase composition on catalytic activity
    (Journal of CO2 Utilization (ELSEVIER), 2016-04-18) Reñones, Patricia; Moya, Alicia; Fresno, Fernando; Collado, Laura; Vilatela, Juan J.; de la Peña O’Shea, Víctor A.
    In this research work, the gas phase CO2 photocatalytic reduction using water as electron donor has been performed using hierarchical assemblies of mesoporous TiO2 1-D nanofibres synthesised by a combination of electrospinning and sol–gel methods. In order to compare the effect of the crystallisation step on oxygen vacancies and conductivity, two different annealing conditions have been undertaken: under a high Ar flow (“TiO2 Fibres-A” sample) and under static Ar (“TiO2 Fibres B” sample). Moreover, these materials have been compared with individualised TiO2 nanoparticles prepared by a sol-gel procedure. CO and H2 are detected as major products with all photocatalysts, with lower amounts of CH4 and CH3OH. The TiO2 nanofibres exhibit better results than the sol-gel photocatalyst, behaviour that may be ascribed to an improved nanocrystals connection, which favours a fast charge transport along the grain boundaries, as measured by electrochemical impedance spectroscopy (EIS). The highest CO2 reduction activity is achieved with the TiO2 Fibres B catalyst, which gives rise to ca. 4 and 2.5 times higher H2 and CO production, respectively, than the TiO2 Fibres-A one. This sample is composed of a mixture of anatase and rutile crystalline phases (80:20), leading to a decrease in the electron-hole recombination rate observed by photoluminescence (PL) measurements.
  • Artículo
    Acceso Abierto
    Improving the fermentation performance of Saccharomyces cerevisiae by laccase during ethanol production from steamexploded wheat straw at high substrate loadings
    (2013-12-12) Alvira, Pablo; Moreno, David; Ibarra, David; Saez, Felicia; Ballesteros, Mercedes
    Operating the saccharification and fermentation processes at high substrate loadings is a key factor for making ethanol production from lignocellulosic biomass economically profitable. However, increasing the substrate loading presents some disadvantages, among them larger generation of inhibitors, which negatively affect fermentation performance. In this study, laccase enzymatic treatment was evaluated as a method to reduce these inhibitory effects. The laccase efficiency was analyzed in a presaccharification and simultaneous saccharification and fermentation process (PSSF) at different high substrate loadings. Water insoluble fraction (WIS) from steam-exploded wheat straw was used as substrate and Saccharomyces cerevisiae as fermenting organism. Laccase supplementation reduced strongly the phenolics content in the media, without affecting weak acids and furan derivates. It resulted in an improved yeast performance during simultaneous saccharification and fermentation process, increasing significantly ethanol productivity.
  • Artículo
    Acceso Abierto
    OPTIMIZATION OF INTEGRATED ALKALINE-EXTRUSION PRETREATMENT OF BARLEY STRAW FOR SUGAR PRODUCTION BY ENZYMATIC HYDROLYSIS
    (2013-12-12) Duque, Aleta; Manzanares, Paloma; Ballesteros, Ignacio; Negro, Maria José; Oliva, Jose Miguel; Saez, Felicia; Ballesteros, Mercedes
    In this work, an integrated one-step alkaline-extrusion process was tested as pretreatment for sugar production from barley straw (BS) biomass. The influence of extrusion 10 temperature (T) and the ratio NaOH/BS dry matter (w/w) into the extruder on pretreatment effectiveness was investigated in a twin-screw extruder at bench scale . A 23 factorial response surface design of experiments was used to analyze the effect of process conditions [T: 50- 100ºC; NaOH/BS ratio: 2.5-7.5% (w/w)] on composition and enzymatic digestibility of pretreated substrate. The optimization of these process variables for a maximum glucan to 15 glucose conversion was determined to be at 6% NaOH/DM and 68ºC. At these conditions, glucan yield reached close to 90% of theoretical, while xylan conversion was 71 % of theoretical. These values are 5 and 9 times higher than that of the untreated material, which supports the great potential of this one-step combined pre-treatment technology for sugar production from lignocellulosic substrates