Maria Cristina Area

Low liquid–solid ratio (LSR) hot water pretreatment of sugarcane bagasse

Low liquid–solid ratio (LSR) can be used to obtain high-content xylo-oligosaccharide (XOS) spend liquor by hot water pretreatment. Developing a technology based on low LSR results in more efficient water usage in the system and thus in lower capital and operating costs. Xylans from xylan rich agro-industrial waste are abundant hemicellulosic polymers with enormous potential for industrial applications. Currently, freeze-dried xylo-oligosaccharides are used as bio-based polymers and hydrolysates containing high xylose contents are converted to several chemical products. In this study, sugarcane bagasse was treated with water at low LSRs and mild temperatures in order to assess the effects of varying the pretreatment conditions on the xylo-oligosaccharide and xylose concentrations, and use a central composite experimental design to optimize the process parameters. The pretreatments were performed in the ranges temperature: 143.3–176.7 °C, time: 20–70 min and LSR: 1u2006:u20061 to 11u2006:u20061 (g g−1). The maximum concentrations of xylose and xylan were 13.76 and 36.18 g L−1 (equivalent to 48.29 g L−1 of xylan), respectively, which were achieved by treating bagasse at 170 °C for 60 min, with LSR of 3 g g−1. The amount of xylan removed under these conditions was almost 57%. The soluble xylan consisted mainly of xylo-oligosaccharides (74 wt% of the identified compound in the spent liquor).

Nanofibrillated cellulose (CNF) from eucalyptus sawdust as a dry strength agent of unrefined eucalyptus handsheets

Nanofibrillated cellulose has been obtained from the cellulosic fraction of eucalyptus sawdust. The fractionation process involved the partial removal of hemicelluloses and lignin. CNF was obtained using TEMPO oxidation with NaOCl in basic medium followed by mechanical homogenization. The obtained CNF was subsequently used as a dry strength agent on unbleached unrefined eucalyptus pulp. The addition of 3, 6 and 9 wt.% of CNF increased lineally the tensile index of handsheets to about 55 N mg(-1) at 35°SR, compatible with papermachine runnability. The other mechanical properties also increased substantially, and porosity decreased moderately. The estimated specific surface and average diameter of these CNF were 60 m(2)g(-1), and of 41.0 nm, respectively. The addition of 9 wt.% of CNF produced an increase in mechanical strength, equivalent to that produced by PFI refining at 1600 revolutions.

Lignocellulosic nanofibers from triticale straw: The influence of hemicelluloses and lignin in their production and properties

The present work aims to determine the influence of hemicellulose and lignin content in the production of lignocellulosic nanofibers (LCNF) from triticale straws. Triticale straws were digested and then gradually delignified, preserving as much hemicelluloses as possible. The obtained LCNF was characterized and used as paper strength additive, observing that hemicellulose and lignin have a key role on the final properties thereof, as well as on their reinforcing potential as paper additive, obtaining LCNF with the same paper reinforcing potential than CNF obtained by TEMPO ((2,2,6,6-Tetramethyl-piperidin-1-yl)oxyl) mediated oxidation.

Oxidation of hazardous compounds by heterogeneous catalysis based on Cu/Al2O3 system in Fenton-type reactions

ABSTRACT This review examines in detail all components involved in heterogeneous Fenton-type reactions, with special focus on copper species supported on alumina for H2O2 decomposition, their redox chemistry, and their practical advantages over traditional Fenton for the degradation of recalcitrant organic compounds. Several aspects for a deeper comprehension of the properties of γ-Al2O3 as support for catalytic applications are discussed. Iron-free systems stability after calcination and catalyst performance during the oxidation reaction are evaluated to solve the disadvantages of iron-based system. Copper species supported on alumina for H2O2 decomposition in Fenton-like reactions are examined, with special focus on their redox chemistry and practical advantages over traditional Fenton system for recalcitrant compounds degradation. Characterization techniques for the elucidation of the structures, compositions, and chemical properties of both the solids used in heterogeneous catalysis, and the adsorbates and intermediates present on the surfaces of the catalysts during reaction are explained. Global indicators for chemical characterization of wastewaters and measurement of catalytic efficiency are described.

Xylitol as Bioproduct From the Agro and Forest Biorefinery

Abstract Xylans from hemicelluloses can be depolymerized into xylose for the bioproduction of xylitol. Xylitol is used as a sweetening agent, and it can be an important platform for sustainable bioproducts. A key point in xylitol production is the availability of xylose solutions at low cost, which would facilitate the emergence of new markets and applications. Xylitol can be industrially produced by the fermentation of xylose extracted from hemicelluloses as an alternative to the expensive chemical process. Improvements in biomass treatment, detoxification, and fermentation processes are needed to make xylitol production cost-effective, opening new markets and creating new applications for it. The aim of this chapter is to discuss several strategies for the extraction of the xylose from biomass, the detoxification of the hydrolyzed result to obtain xylose syrup at a relatively low cost, the critical factors for the fermentation of xylose to xylitol, and the recovery of xylitol from fermentation broths.

Kinetic modeling of a heterogeneous Fenton-type oxidative treatment of complex industrial effluent

This work proposes a kinetic model for the reactions involved in the heterogeneous copper-based Fenton-type oxidation of mixed recalcitrant compounds in a real industrial effluent from the alkaline sulfite treatment of wood. This kind of treatment is unusual in this industry due to the complexity of the effluents and the high costs involved in total mineralization of the organic matter. Nevertheless, conversion of recalcitrant to degradable compounds and catalyst recovery can make the difference. The complexity of the effluent and the great number of compounds formed as intermediates, make extremely difficult the identification and quantification of the individual reactions that occur during oxidation. To solve this drawback TOC parameter was used as a representative measurement. To verify the level of TOC degradation produced by the heterogeneous catalysis reaction, experiences of homogeneous catalysis and adsorption were accomplished. The studied temperature range was 45–80xa0°C. A “two-step” kinetic model was applied to TOC reduction in heterogeneous and homogeneous oxidations, admitting two sequential steps of oxidation: a first fast stage (“seconds stage”) followed by a slow one (“minutes stages”). Kinetic constants were obtained for both processes and activation energies were also determined for the “minutes stage” step (33.17xa0kJ/mol and 15.13xa0kJ/mol, respectively). Homogeneous catalysis studies confirm mass transfer limitations in heterogeneous oxidations. Experiences of adsorption of organic matter on CuO/γ-Al2O3 catalyst demonstrated that this phenomenon is exothermic and cannot be neglected. The activation energy of adsorption was determined as 7.32xa0kJ/mol. Catalysts were characterized through SEM, EDS, XRD, FTIR, and TGA.Graphical Abstract