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Miscanthus x giganteus Extractives: A Source of Valuable Phenolic Compounds and Sterols

The chemical composition of the lipophilic extracts of bark and core, of the Miscanthus x giganteus stalk, was studied by gas chromatography-mass spectrometry (GC-MS). Aromatic compounds, sterols, and fatty acids, followed by long-chain fatty alcohols, were the major families of components present in the M. x giganteus stalk. Aromatic compounds are more abundant in the M. x giganteus bark (521 mg/kg of bark), with vanillic acid, vanillin, and p-hydroxybenzaldehyde as the major compounds of this family. In the M. x giganteus core, sterols represent about 949 mg/kg of dry core with beta-sitosterol, 7-oxo-beta-sitosterol, stigmasterol, and campesterol as the major components. The detection of small amounts of esters in the GC-MS analysis with short columns explains the small increase in the abundance of the identified families after alkaline hydrolysis. The high content of valuable sterols and aromatic compounds in M. x giganteus and, particularly, in the core, which is considered a residue in most applications, can open new perspectives for the integrated upgrading of this grass within the biorefinery perspective.

Delignification of Miscanthus×Giganteus by the Milox process

Miscanthus x giganteus stalks were subjected to delignification with formic acid-hydrogen peroxide-water in two stages. A face-centered experimental design was used to study the effects of different variables (formic acid and hydrogen peroxide concentrations, time and temperature) on yield, lignin content and viscosity of pulps on the first stage. Fitting equations described satisfactorily the system behaviour and showed that hydrogen peroxide concentration and temperature were the most influencing variables. A set of independent variables (90% formic acid, 1.5% hydrogen peroxide, 60 min, and 67 degrees Celsius) produced a pulp with low lignin content (kappa 17.2) and high viscosity (899 cm(3)/g), in the first stage. For the second stage a treatment time of 30 min was the more suitable, producing good quality pulps (kappa number 4.6, viscosity 788 cm(3)/g). Phenolic hydroxyl and carboxyl group contents were higher lignins from the first stage.

Miscanthus x giganteus as a Source Of Biobased Products Through Organosolv Fractionation: A Mini Review

This paper deals with the chemical treatments with selected organic compounds that have been applied to Mis- canthus to upgrade it, for pulp production or fractionation purposes. Organosolv processes have demonstrated their effec- tiveness as fractionation treatments; therefore special emphasis is placed on these systems and, in particular, those making use of carboxylic acids. That is, Acetosolv process that uses acetic acid-water-hydrochloric acid mixtures as delignifying agents, the process with formic acid-water-hydrochloric acid and the Milox process, which replaces the hydrochloric acid in the medium by hydrogen peroxide, thus forming peroxyacetic acid. Furthermore, we present the results of the charac- terizations that have been made in relation to extractives and lignin of Miscanthus. It also is analyzed the major changes undergone by lignin during organosolv treatments. Finally, some progresses in the field of TCF bleaching of the cellulose pulps obtained are summarized.

Bleaching Miscanthus x giganteus Acetosolv pulps with hydrogen peroxide/acetic acid. Part 1: Behaviour in aqueous alkaline media

Miscanthus x giganteus bark samples subjected to fractionation by the Acetosolv process under optimal conditions were bleached using hydrogen peroxide and acetic acid in aqueous media under alkaline conditions. The influence of the main operational variables in the bleaching of Acetosolv pulps of M. x giganteus (i.e. hydrogen peroxide concentration, 3-7%; temperature, 55-75 degrees C; pH 9-11), obtained after treatments, have been assessed on pulp yield, kappa number, viscosity and brightness of bleached pulps. For this purpose, a rotatable and orthogonal second-order factorial design of experiments was used, in order to identify the optimum operating conditions. The obtained empirical mathematical models demonstrate that, in general, the bleaching was efficient, achieving pulps with kappa numbers below 10. The chemical composition and physicochemical properties of the bleached pulps fulfilled the requirements for forthcoming bleaching stages. Moreover, an alkaline extraction stage to eliminate saponifiable groups of Acetosolv pulps was studied, as well as the necessity of use chelating agents in the stage with hydrogen peroxide.

Miscanthus x giganteus Bark Organosolv Fractionation: Fate of Lipophilic Components and Formation of Valuable Phenolic Byproducts

The behavior of Miscanthus x giganteus bark lipophilic extractives during three acid organosolv pulping processes (Acetosolv, formic acid fractionation, and Milox) was investigated. It was demonstrated that nearly 90% of the lipophilic extractives were removed from pulps by either dissolution in the organosolv liquors (fatty acids and alcohols) or extensive degradation (sterols). The organosolv liquors were found to be rich in vanillin, syringaldehyde, and ferulic, vanillic, and p-coumaric acids. The Acetosolv fractionation process was found to be the most efficient in the removal of lipophilic components from pulps, and it was also the process that generated higher amounts of valuable monomeric phenolic compounds that could be exploited within the biorefinery context.

Sludge Granulation in UASB Digesters Treating Low Strength Wastewaters at Mesophilic and Psychrophilic Temperatures

This work reports a comparative study of the granulation process during the start-up of UASB digesters treating a diluted wastewater (500 mg COD l−1 as sucrose) at mesophilic (30°C) and psychrophilic (20°C) temperatures. The results show that the granulation process follows a similar pattern at both temperatures, complete granulation being achieved between 1 and 2 months from the start-up, at upflow superficial liquid velocities of 0.05 to 0.15 m h−1 and hydraulic retention times (HRT) of 6 to 3h. The UASB systems showed excellent stability and high treatment efficiency at HRT of 2h and organic loading rate (OLR) of 6 kg COD m−3 d−1, the percent COD removals being 95% (30°C) and 92% (20°C), while the percent COD converted to methane reached 67% (30°C) and 48% (20°C). The digester operated at 20°C maintained similar efficiencies when the OLR was increased up to 9 kg COD m−3 d−1, at an HRT of only 1.3h. The developed granules were similar in shape and size (2 to 3mm diameter), although different microbial m...

Milox fractionation of empty fruit bunches from Elaeis guineensis

Milox pulping of EFB was used to obtain pulps. In the first Milox stage, the influences of operating variables on pulp properties were studied and polynomial and neural fuzzy models that reproduced the experimental results with errors less than 10% were developed. Operating variables were found (93 wt.% of formic acid, 3 wt.% of hydrogen peroxide, and 165 min) that yielded acceptable pulp properties (40.5% yield, 50.3% brightness and 608 mL/g viscosity) at reasonable chemical and energy costs. The second stage was studied by subjecting the liquors of the previously optimized first stage to different treatment times. This time should be 30 min or less, to avoid a negative effect on viscosity. The residual liquor from the first Milox stage contained virtually no precipitable lignin and only low amounts of sugar (wt.%): glucose 0.71, xylose 4.22, galactose 1.19, mannose 0.22, all on original raw material dry.

Evaluation of agave fiber delignification by means of microscopy techniques and image analysis.

Recently, the use of different types of natural fibers to produce paper and textiles from agave plants has been proposed. Agave atrovirens can be a good source of cellulose and lignin; nevertheless, the microstructural changes that happen during delignification have scarcely been studied. The aim of this work was to study the microstructural changes that occur during the delignification of agave fibers by means of microscopy techniques and image analysis. The fibers of A. atrovirens were obtained from leaves using convective drying, milling, and sieving. Fibers were processed using the Acetosolv pulping method at different concentrations of acetic acid; increasing acid concentration promoted higher levels of delignification, structural damage, and the breakdown of fiber clumps. Delignification followed by spectrometric analysis and microstructural studies were carried out by light, confocal laser scanning and scanning electron microscopy and showed that the delignification process follows three stages: initial, bulk, and residual. Microscopy techniques and image analysis were efficient tools for microstructural characterization during delignification of agave fibers, allowing quantitative evaluation of the process and the development of linear prediction models. The data obtained integrated numerical and microstructural information that could be valuable for the study of pulping of lignocellulosic materials.

Spectroscopic and Microscopic Study of Peroxyformic Pulping of Agave Waste.

The peroxyformic process is based on the action of a carboxylic acid (mainly formic acid) and the corresponding peroxyacid. The influences of processing time (60-180 min), formic acid concentration (80-95%), temperature (60-80°C), and hydrogen peroxide concentration (2-4%) on peroxyformic pulping of agave leaves were studied by surface response methodology using a face-centered factorial design. Empirical models were obtained for the prediction of yield, κ number (KN) and pulp viscosity as functions of the aforementioned variables. Mathematical optimization enabled us to select a set of operational variables that produced the best fractionation of the material with the following results: pulp yield (26.9%), KN (3.6), and pulp viscosity (777 mL/g). Furthermore, this work allowed the description and evaluation of changes to the agave fibers during the fractionation process using different microscopic and spectroscopic techniques, and provided a comprehensive and qualitative view of the phenomena occurring in the delignification of agave fibers. The use of confocal and scanning electron microscopy provided a detailed understanding of the microstructural changes to the lignin and cellulose in the fibers throughout the process, whereas Raman spectroscopy and X-ray diffraction analysis indicated that cellulose in the pulp after treatment was mainly of type I.

Fotonic and Electron Microscopy Images for Quality Evaluation of Delignification of Agave Fibers

The present work is aimed to study the microstructural changes that occurred during the delignification process of agave fibers using microscopy techniques and image analysis AI. Acetosolv kinetic was followed by chemical analysis and by light LM, confocal laser scanning CLSM, and scanning electron SEM microscopies, evaluating the micrographs by image analysis IA. Kinetic studies showed that delignification process followed three stages: initial, bulk and residual; these stages kept a relation with the microstructural changes occurring in the fibers. The data obtained integrate numerical information that could be valuable for study of pulping of lignocellulosic materials and these techniques can be used as useful non-destructive methods for the evaluation of the delignification process.