María E. Eugenio

Kraft pulp biobleaching using an extracellular enzymatic fluid produced by Pycnoporus sanguineus.

The aim of this work was to obtain a LMS pre-treatment applicable to industrial TCF bleaching. Kraft pulp from Eucalyptus globulus was treated at 40 degrees C/pH 3 and 60 degrees C/pH 5 for 1h using an extracellular fluid enriched in laccase produced by Pycnoporus sanguineus and acetosyringone as mediator (HBT was used as a control mediator) (L). Alkaline extraction (E) and hydrogen peroxide (P) stages were then assayed. The LEP alternative was an efficient sequence to bleach kraft pulp since the enzymatic pre-treatment boosted the subsequent chemical bleaching. The best L pre-treatment was obtained with laccase-acetosyringone at 40 degrees C/pH 3. It reduces kappa number and hexenuronic acids, increases pulp viscosity, lowers hydrogen peroxide consumption down to an 87.4% (94.0% without L) and enhances brightness up to a 59% ISO (51% ISO without L).

Integration of a kraft pulping mill into a forest biorefinery: Pre-extraction of hemicellulose by steam explosion versus steam treatment

Growing interest in alternative and renewable energy sources has brought increasing attention to the integration of a pulp mill into a forest biorefinery, where other products could be produced in addition to pulp. To achieve this goal, hemicelluloses were extracted, either by steam explosion or by steam treatment, from Eucalyptus globulus wood prior to pulping. The effects of both pre-treatments in the subsequent kraft pulping and paper strength were evaluated. Results showed a similar degree of hemicelluloses extraction with both options (32-67% of pentosans), which increased with the severity of the conditions applied. Although both pre-treatments increased delignification during pulping, steam explosion was significantly better: 12.9 kappa number vs 22.6 for similar steam unexploded pulps and 40.7 for control pulp. Finally, similar reductions in paper strength were found regardless of the type of treatment and conditions assayed, which is attributed to the increase of curled and kinked fibers.

Laccase production by Pycnoporus sanguineus under different culture conditions.

Pycnoporus sanguineus is a white‐rot fungus that produces ligninolytic enzymes such as laccases. These enzymes can endure temperatures as high as 60 °C and are useful for pulp bleaching, dye decolorization and phenolic degradation.

Enhancement of enzymatic saccharification of Eucalyptus globulus: Steam explosion versus steam treatment

Steam explosion and steam pre-treatment have proved capable of enhancing enzymatic saccharification of lignocellulosic materials. However, until now, these methods had not been compared under the same operational conditions and using the same raw material. Both pre-treatments lead to increased yields in the saccharification of Eucalyptus globulus; but results have been better with steam pre-treatments, despite the more accessible surface of exploded samples. The reason for this finding could be enzymatic inhibition: steam explosion causes a more extensive extraction of hemicelluloses and releases a greater amount of degradation products which can inhibit enzymatic action. Enzymatic inhibition is also dependent on the amount and chemical structure of lignin, which was also a contributing factor to the lower enzymatic yields obtained with the most severe pre-treatment. Thus, the highest yields (46.7% glucose and 73.4% xylose yields) were obtained after two cycle of steam treatment, of 5 and 3 min, at 183°C.

Combination of steam explosion and laccase-mediator treatments prior to Eucalyptus globulus kraft pulping.

The effect of a pretreatment consisting of steam explosion (SE) followed by a laccase mediator system (LMS) stage on Eucalyptus globulus kraft pulping has been evaluated and compared with fungal pretreatments. Pretreatment with SE and LMS was more efficient than pretreatments using Pycnoporus sanguineus and Trametes sp. I-62. Steam explosion not only improved the enzyme penetration into the wood chips and shortened the pulping process by 60%, but also extracted around 50% of the hemicelluloses which could be converted into value-added products. The optimal conditions for the LMS treatment were 3h, 3UA/g and 40°C. Compared to SE, the SE/LMS treatment yielded an increase in delignification of 13.9% without affecting pulp properties, provided a similar screened kraft yield, and reduced consumption of chemical reagents Na(2)S and NaOH by 11.5% and 6.3%, respectively. Therefore, SE/LMS is a promising pretreatment for converting the pulp mill into a forest bio-refinery.

Biobleaching of pulp from oil palm empty fruit bunches with laccase and xylanase.

Laccase and xylanase were tested for their suitability for biobleaching of soda-anthraquinone pulp from oil palm empty fruit bunches (EFB). An enzymatic stage with xylanase (X) and/or laccase (L) was incorporated before the alkaline extraction stage (E) and the hydrogen peroxide bleaching stage (P). Compared with controls, the LEP sequence resulted in an improvement of optical properties (brightness and colorimetric properties) and a reduction of the kappa number. When xylanase and laccase were used jointly, no improvement was detected, however, when the xylanase application preceded the laccase stage, the beneficial effects of laccase were boosted. Thus, the final XLEP bleached pulp showed a kappa number of 5.4 and a brightness of 60.5% ISO, although the hydrogen peroxide consumption increased (77.0% vs. 64.5% and 73.8% for EP and LEP respectively). Finally, after subjecting the bleached pulps to accelerated ageing, the best optical properties were observed in the XLEP pulp.

Use of new endophytic fungi as pretreatment to enhance enzymatic saccharification of Eucalyptus globulus

New endophytic fungi are assessed for the first time as pretreatment to enhance saccharification of Eucalyptus globulus wood. The fungi are all laccase-producing ascomycetes and were isolated from eucalyptus trees in Spain. After five endophytes had been assayed alone or in combination with white-rot fungus Trametes sp. I-62, three were pre-selected. To improve sugar production, an autohydrolysis pretreatment was performed before or after fungal treatment. Pretreatment increased sugar production 2.7 times compared to non-pretreated wood. When fungal and autohydrolysis pretreatments were combined, a synergistic increase in saccharification was observed in all cases. Endophytic fungi Ulocladium sp. and Hormonema sp. produced greater enhancements in saccharification than Trametes sp. I-62 (increase in sugar yields of 8.5, 8.0 and 6.0 times, respectively), demonstrating the high potential of these new endophytic fungi for saccharification enhancement.

Evaluating Lignin-Rich Residues from Biochemical Ethanol Production of Wheat Straw and Olive Tree Pruning by FTIR and 2D-NMR

Lignin-rich residues from the cellulose-based industry are traditionally incinerated for internal energy use. The future biorefineries that convert cellulosic biomass into biofuels will generate more lignin than necessary for internal energy use, and therefore value-added products from lignin could be produced. In this context, a good understanding of lignin is necessary prior to its valorization. The present study focused on the characterization of lignin-rich residues from biochemical ethanol production, including steam explosion, saccharification, and fermentation, of wheat straw and olive tree pruning. In addition to the composition and purity, the lignin structures (S/G ratio, interunit linkages) were investigated by spectroscopy techniques such as FTIR and 2D-NMR. Together with the high lignin content, both residues contained significant amounts of carbohydrates, mainly glucose and protein. Wheat straw lignin showed a very low S/G ratio associated with p-hydroxycinnamates (p-coumarate and ferulate), whereas a strong predominance of S over G units was observed for olive tree pruning lignin. The main interunit linkages present in both lignins were β-O- ethers followed by resinols and phenylcoumarans. These structural characteristics determine the use of these lignins in respect to their valorization.

Biobleaching of Eucalyptus globulus kraft pulps: Comparison between pulps obtained from exploded and non-exploded chips

The aim of this work was to evaluate the response to biobleaching of steam exploded kraft pulps and to compare the results with the controls. For this end, a laccase-mediator treatment using commercial laccase (Novozyme 51003) and a natural mediator (acetosyringone) were assayed, followed by alkaline extraction and hydrogen peroxide stages. Our approach resulted in exploded biobleached pulps with lower kappa number and improved optical properties compared to controls, even after subjecting pulps to accelerated ageing. Additionally, use of hydrogen peroxide was reduced. The LMS (laccase-mediator system) had a smaller impact on the properties of the bleached pulps and on hydrogen peroxide consumption than the steam explosion process did.

Effect of steam explosion and enzymatic pre-treatments on pulping and bleaching of Hesperaloe funifera.

A non-wood raw material with high potential for pulp and paper applications (Hesperaloe funifera) was subjected to a steam explosion pre-treatment, and the subsequent effect of this pretreatment on biopulping and biobleaching was studied. An increase in the delignification rate, bigger than that reported for autohydrolysis and acid hydrolysis pre-treatments, and a reduction in chemical consumption were found during kraft pulping of the exploded samples. However, biopulping with the laccase-mediator system (LMS) did not lead to a reduction in the kappa number in either non-exploded or exploded unbleached pulps. On the other hand, the steam explosion pretreatment boosted the advantages of the LMS pre-treatment (decrease in kappa number and increase in brightness) favored biobleaching, with a 53.1% delignification rate and a final brightness of 67% ISO. Finally, the steam explosion pre-treatment also improved the color properties of the bleached pulp and reduced the hydrogen peroxide consumption by 24.6%.