Dmitry V. Evtuguin

Characterization of an acetylated heteroxylan from Eucalyptus globulus Labill

A heteroxylan was isolated from Eucalyptus globulus wood by extraction of peracetic acid delignified holocellulose with dimethyl sulfoxide. Besides (1-->4)-linked beta-D-xylopyranosyl units of the backbone and short side chains of terminal (1-->2)-linked 4-O-methyl-alpha-D-glucuronosyl residues (MeGlcA) in a 1:10 molar ratio, this hemicellulose contained galactosyl and glucosyl units attached at O-2 of MeGlcA originating from rhamnoarabinogalactan and glucan backbones, respectively. About 30% of MeGlcA units were branched at O-2. The O-acetyl-(4-O-methylglucurono)xylan showed an acetylation degree of 0.61, as determined by 1H NMR spectroscopy, and a weight-average molecular weight (M(w)) of about 36 kDa (P=1.05) as revealed from size-exclusion chromatography (SEC) analysis. About half of the beta-D-xylopyranosyl units of the backbone were found as acetylated moieties at O-3 (34 mol%), O-2 (15 mol%) or O-2,3 (6 mol%). Practically, all beta-D-xylopyranosyl units linked at O-2 with MeGlcA residues were 3-O-acetylated (10 mol%).

Enzymatic saccharification of biologically pre-treated wheat straw with white-rot fungi

Wheat straw was submitted to a pre-treatment by the basidiomycetous fungi Euc-1 and Irpex lacteus, aiming to improve the accessibility of cellulose towards enzymatic hydrolysis via previous selective bio-delignification. This allowed the increase of substrate saccharification nearly four and three times while applying the basidiomycetes Euc-1 and I. lacteus, respectively. The cellulose/lignin ratio increased from 2.7 in the untreated wheat straw to 5.9 and 4.6 after the bio-treatment by the basidiomycetes Euc-1 and I. lacteus, respectively, thus evidencing the highly selective lignin biodegradation. The enzymatic profile of both fungi upon bio-treatment of wheat straw have been assessed including laccase, manganese-dependent peroxidase, lignin peroxidase, carboxymethylcellulase, xylanase, avicelase and feruloyl esterase activities. The difference in efficiency and selectivity of delignification within the two fungi treatments was interpreted in terms of specific lignolytic enzyme profiles and moderate xylanase and cellulolytic activities.

(2-O-α-d-Galactopyranosyl-4-O-methyl-α-d-glucurono)-d-xylan from Eucalyptus globulus Labill

Abstract An unusual heteroxylan composed of galactosyl, 4- O -methyl-glucuronosyl and xylosyl residues with molar ratio 1:3:30 was isolated from the wood of Eucalyptus globulus Labill. The results of linkage analysis, supported by data of 1 H, 2D 1 H– 1 H COSY and 13 C NMR spectroscopy, revealed that the polysaccharide is a (2- O -α- d -galactopyranosyl-4- O -methyl-α- d -glucurono)- d -xylan with a (1→4)-linked β- d -xylopyranosyl backbone branched at O-2 by short side chains composed of terminal 4- O -methyl-α- d -glucuronic acid and of 4- O -methyl-α- d -glucuronic acid substituted at O-2 with α- d -galactose.

Chemical characterisation of bark and of alkaline bark extracts from maritime pine grown in Portugal

Abstract The chemical composition of maritime pine (Pinus pinaster) bark and of alkaline bark extracts has been investigated with bark from trees grown in Portugal. Bark is composed of lignin and polyphenolics (ca. 44%), polysaccharides (ca. 39%), dichoromethane, ethanol and water extractives (ca. 17%) and ashes (ca. 1%). The lignin content determined by the Klason method, after the extraction of polyphenolics (tannin-rich fraction) from the bark by alkali solution, is 33.2%. Cellulose content is about 24%. Hemicelluloses (about 15% of bark dry weight) are suggested to be predominantly composed of arabinoglucuronoxylans and minor amounts of galactoglucomanans. The bark lignin is composed by p-hydrophenylpropane and guaiacylpropane units in proportions of 20:80. The condensed tannins are constituted mainly by catechin-type structural units. The direct extraction of bark with aqueous alkaline solutions yields extracts which contain sugars, lignin and condensed tannins. The number average molecular weights (Mn) of alkaline extracts are in the range 1000–1500. The composition and Mn of extracted substances depends on the alkaline extraction conditions.

Alternatives for lignocellulosic pulp delignification using polyoxometalates and oxygen: a review

A review on the use of polyoxometalates (POMs) and oxygen, for the delignification of lignocellulosic pulps is presented. Two main processes using POMs for the delignification of pulp have been investigated: an anaerobic process in which the POMs have been used, in aqueous solutions, as stoichiometric reagents for the oxidative degradation of residual lignin, with their re-oxidation by oxygen occurring in a subsequently separate stage; and an aerobic process in which the POMs were designed to perform as catalysts in the oxygen delignification. In the aerobic approach, the lignin oxidation and the reactivation of the POM take place in the same stage of the process. The feasibility of the catalytic system was shown by pilot plant experiments. Following the green chemistry goals, these processes are environmentally friendly approaches and may allow a significant decrease of chlorine-based chemical consumption by the pulp-and-paper industry. The use of the POMs together with laccase for the oxygen delignification of lignocellulosic pulps will also be considered. Final comments regarding the practical application of the POMs are pointed out.

Chemical composition and structural features of the macromolecular components of Hibiscus cannabinus grown in Portugal

Different morphological regions of Hibiscus cannabinus plants grown in Portugal were submitted to chemical composition studies. General chemical composition was determined by established methods. The polysaccharides were fractionated by successive extractions of holocellulose with aqueous KOH solutions. The sugar composition was determined by hydrolysis of polysaccharides followed by gas chromatography (GC) analysis of neutral sugars and spectrophotometric determination of uronic acids. In situ lignins and milled wood lignins (MWL) were characterised by permanganate oxidation followed by GC and GC-MS (mass spectrometry) analysis of the methylated oxidation products. The results of general chemical analysis have evidenced the different relative abundance of holocellulose, lignin, proteins, extractives and ashes in bark, core and foliage, at different stages of maturity. About 70–80% of the core hemicelluloses (about 20% o.d. material) was easily extracted with 5% KOH aqueous solutions against 60–70% (about 15% o.d. material) for the hemicelluloses of the bark. This hemicellulose fraction was composed mainly by glucuronoxylans with high content of uronic acids (xylose: uronic acid: 3–5: 1 for bark and 5–10: 1 for core). The hemicellulose fraction extracted with 24% KOH aqueous solutions was composed mainly by glucuronoxylans (80–90%) and glucomannans (10–15%). The results obtained by the permanganate oxidation method indicated that kenaf lignins are H-G-S type with approximate H: G: S molar proportions of (9–13): (55–60): (27–34) in bark and (14–20): (57)-(74): (12–23) in core, which evidences a high content of H and G units and a relatively low content of S units when compared with traditional dicotyledons. The relative proportion of H, G and S units as well as the structural features of lignins depends on the stage of maturity and on the morphological region of the plant. Kenaf lignins present a lower degree of condensation when compared with traditional wood lignins.

Polyurethanes based on oxygen-organosolv lignin

Abstract Oxygen-organosolv lignins, isolated from spent liquors after delignification of wood in different acidic organic solvent–water media, were used as unmodified macromonomers in conjuction with an oligoethyleneoxide di-isocyanate. This led to crosslinked elastomeric polyurethanes which were thoroughly characterized. It was found that the nature of the organic solvent used for the organosolv pulping had an influence on the reactivity of the isolated lignins towards the di-isocyanate because of the variation in the amount of alcoholic groups caused by reactions with solvent molecules during the delignification.

Second-generation bioethanol from eucalypt sulphite spent liquor

The spent liquor from acidic sulphite pulping of Eucalyptus globulus (HSSL) is the side product from sulphite pulp production and besides sulphonated lignin contains sugars from degraded hemicelluloses, mainly pentoses. Pichia stipitis fermentation of these sugars for bioethanol production was the primary goal of this work. The increasing of HSSL proportion in fermentation media affected negatively the ethanol yield. Thus with 20% of HSSL (v/v) attained maximum ethanol yield was 0.15 g of ethanol by g of sugar consumed (g(e) g(s)(-1)) and with 60% (v/v) only 0.08 g(e) g(s)(-1). Biological removal of acetic acid from HSSL improved fermentation though the complete removal of acetic acid and polyphenolics (including sulphonated species) by treatment with ion-exchange resins was required for highly successful bioethanol production. Accordingly, the fermentative metabolic pathway of P. stipitis has been promoted allowing fair ethanol productivity and yield (Yp/s = 0.49 g(e) g(s)(-1)) at relatively low maximum of cell growth rate (micro(max) = 0.21 h(-1)).

Chemical Composition of Spent Liquors from Acidic Magnesium-Based Sulphite Pulping of Eucalyptus globulus

Abstract The major components of industrial thin (SSL) and thick (THSL) liquors from acidic magnesium–based sulphite pulping of Eucalyptus globulus wood have been characterized. The analysis of sugars in SSL revealed the predominance of xylose, which was present in the form of sugar monomer (ca. 70%) and as xylo-oligosaccharides (ca. 30%). Lignosulphonates (LS) were the most abundant organic fraction of spent liquor (ca. 50% of liquor dry matter) consisting of sulphonated oligomers (SO3H ≈ 20% w/w) of low molecular weight (Mw ≈ 1000–1300 Da) and constituted mainly by syringyl units (syringyl:guaiacyl ratio = 81:19). The major phenolic extractives of THSL were pyrogallol (93 g/ton) and gallic acid (1020 g/ton), and the most abundant fatty acid and sterol were tetracosanoic acid (6 g/ton) and β -sitosterol (45 g/ton), respectively. The structural changes of macromolecular components during the liquor evaporation were discussed.

Sulfonated Graphene Oxide as Effective Catalyst for Conversion of 5‐(Hydroxymethyl)‐2‐furfural into Biofuels

The acid-catalyzed reaction of 5-(hydroxymethyl)-2-furfural with ethanol is a promising route to produce biofuels or fuel additives within the carbohydrate platform; specifically, this reaction may give 5-ethoxymethylfurfural, 5-(ethoxymethyl)furfural diethylacetal, and/or ethyl levulinate (bioEs). It is shown that sulfonated, partially reduced graphene oxide (S-RGO) exhibits a more superior catalytic performance for the production of bioEs than several other acid catalysts, which include sulfonated carbons and the commercial acid resin Amberlyst-15, which has a much higher sulfonic acid content and stronger acidity. This was attributed to the cooperative effects of the sulfonic acid groups and other types of acid sites (e.g., carboxylic acids), and to the enhanced accessibility to the active sites as a result of the 2D structure. Moreover, the acidic functionalities bonded to the S-RGO surface were more stable under the catalytic reaction conditions than those of the other solids tested, which allowed its efficient reuse.