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Pressurized hot water pretreatment was performed on softwood (SW) and hardwood (HW) chips following the same conditions (1 h at 170 °C) in order to partly hydrolyse hemicelluloses. The complete characterization of these sugar enriched autohydrolysates (AH) being rather complex, two different purification methods were conducted. Nanofiltration (NF) 1kDa membrane and ultrafiltration (UF) 3 and 5kDa membranes were used to separate oligosaccharides (OS) from undesired compounds and for their molar mass fractionation. Granulated activated charcoal (GAC) adsorption was also used for hydrolysates detoxification. The chemical nature of OS and side charge groups vary significantly depending of the fractions obtained, e. g. xylans' chain length is positively correlated with the degree of acetylation. UF at 5kDa allows for the total separation of galactoglucomannans (GGMs) from xylans, in SW AH, however, this result was not achieved with HW. From the acid soluble lignin (ASL) removal point of view, membrane filtration from 1kDa is more efficient than activated carbon treatment concerning HW AH, on the contrary to SW AH. Regarding the lignin to OS ratio, for both species, GAC leads to a better sugar purity. [ABSTRACT FROM AUTHOR]

Birch samples were subjected to non-isothermal autohydrolysis to obtain a solution of hemicellulosic saccharides and a solid phase mainly made up of cellulose and lignin. Based on kinetic modeling, operational conditions were identified which give rise to soluble saccharides and furfural derived from xylan in a yield of 80.5%. The soluble mixture was supplemented with 1% sulfuric acid and heated (directly or in the presence of methyl isobutyl ketone, MIBK) for furfural production. MIBK is used as an extraction agent to limit furfural consumption by side reactions. Operating in single phase at 170°C, up to 44.8% of the potential substrates were converted into furfural. In experiments performed in biphasic media, the effects of MIBK were assessed by empirical modeling and about 75% of the potential substrates were converted under selected conditions. [ABSTRACT FROM AUTHOR]

The chemical composition of black liquors obtained from the soda-AQ pulping of birch ( Betula pendula) sawdust was studied as a function of cooking time, effective alkali content, and hot-water pretreatment of the sawdust prior to delignification. Special attention was paid on the formation of lignin-derived materials and low-molecular-mass carbohydrate-derived degradation products containing aliphatic carboxylic acids. In the case of the hot-water-pretreated feedstock, less acetic acid and formic acid and more nonvolatile hydroxy acids (especially monocarboxylic acids) were obtained. The observations can be interpreted as a result of the extensive removal of hemicelluloses during the hot-water pretreatment. [ABSTRACT FROM AUTHOR]

Furans (furfural and hydroxymethylfurfural) are the results of dehydration of monosaccharides, which can be obtained by acid hydrolysis of wood or other lignocellulosic materials. In this work, Pinus pinaster wood was subjected to aqueous autohydrolysis processing to obtain dissolved hemicellulose-derived polymeric or oligomeric saccharides made up of mannosyl, glucosyl, galactosyl, xylosyl, and arabinosyl structural units. The aqueous liquors were then heated in the presence of sulfuric acid and methyl isobutyl ketone to obtain furans. The effects of selected operational variables, such as the ratio of organic to aqueous phase, temperature, and reaction time, were assessed by empirical modeling in terms of the conversion into furans and levulinic acid. The maximum furfural conversion (71.4%) was predicted to occur operating at 165°C and a ratio of organic to aqueous phase of 2 for 68.5 min. In additional experiments, dimethyl sulfoxide and/or 1-butanol were added to the aqueous phase and the change in furan conversion rates was observed. [ABSTRACT FROM AUTHOR]

Industrial Eucalyptus globulus wood chips were submitted to different autohydrolysis conditions followed by kraft cooking and soda-anthraquinone cooking. The autohydrolyzed wood chips were much easier to delignify than the control wood chips. Soda-anthraquinone cooking could be performed at a cooking temperature that was 20 ° C lower than that for the kraft cooking on control wood chips. Furthermore, the active alkali could be reduced. The resulting unbleached pulps reacted as well to oxygen delignification as the control pulps and could be further bleached to 90 % ISO brightness with a D(EP)D sequence. The autohydrolysis liquors were investigated for their suitability as a source for the synthesis of alkylpolyxylosides (APX). These surface-active agents are synthesized through the reaction between the saccharides of the autohydrolysates and a fatty alcohol, with the former being the hydrophilic and the latter being the hydrophobic part of the molecule. The impact of the substances detected in autohydrolysates on the APX synthesis was studied. It was demonstrated that lignin dissolved during autohydrolysis should at least partially be removed before the production of APX. [ABSTRACT FROM AUTHOR]

The effects of hydrothermal treatments of Eucalyptus globulus wood have been evaluated in terms of the solid yield and the composition of the treated wood. The contents of cellulose, xylan, and Klason lignin in treated solids were determined and interpreted by means of kinetic models. Particular attention was paid to the degree of polymerization (DP) lowering of cellulose caused by hydrothermal treatments, which was assessed by measurements of intrinsic viscosity. [ABSTRACT FROM AUTHOR]

To improve enzymatic hydrolysis, hydrothermal treatment was carried out on the shrub Tamarix ramosissima. Milled wood lignin (MWL) was isolated from T. ramosissima stems before and after hydrothermal treatment, and its chemical structure was characterized by carbohydrate analysis, elemental analysis, methoxy group determination, FT-IR spectroscopy, quantitative 13C NMR spectroscopy, 2D heteronuclear single quantum coherence spectroscopy, and gel permeation chromatography. The analyses confirmed that T. ramosissima MWL is very rich in syringyl units. It was found that the main reaction responsible for the lignin degradation is the homolytic cleavage of aryl-ether bonds resulting in a reduced amount of β-O-4′ interlinkages and, as a consequence, in elevated amounts of β-β′ and β-5′ linkages. The MWL isolated from the pretreated solid residue was more condensed and had a lower molecular weight than the MWL isolated from untreated material. [ABSTRACT FROM AUTHOR]

Autohydrolysis of wood as a pretreatment stage before alkaline pulping is seen as an opportunity to approach the ideals of a forest biorefinery. In autohydrolysis the degradation products of primarily hemicelluloses and some other wood components are mainly dissolved (liquid phase) and they also escape partly as gas. In the present paper, birch was autohydrolysed at two intensity levels (characterised by P-factors of 200 and 1000) and the mass balances of autohydrolysis including solid, liquid, and gaseous phases were established. Approximately 10% and 25% of the total wood substance was transferred to the liquid phase at the two autohydrolysis intensities, respectively. In both cases about 50% of the degraded wood substance consisted of xylose-based material. The share of monomeric xylose was about 6% and 50% in the two samples, respectively. From the residual oligosaccharide fractions, 13% and 90% accounted for the DP2 to DP4 components in the P200 and P1000 samples, respectively. As expected, the weight-average molar mass of the components in the P1000 hydrolysate was substantially lower (0.4 kDa) than those in the corresponding P200 hydrolysate (2.1 kDa). Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) measurements revealed that relative to xylotriose the P1000 sample contained significantly fewer acidic pentosan fractions than the P200 sample. Xylooligosaccharides dissolved at both intensity levels remained highly acetylated, and some of these also carried 4-O-methylglucopyranosyluronic acid substituents. [ABSTRACT FROM AUTHOR]

The implementation of biorefinery concepts into existing pulp and paper mills is a key step for a sustainable utilization of the natural resource wood. Water prehydrolysis of wood is an interesting process for the recovery of xylo-oligosaccharides and derivatives thereof, while at the same time cellulose is preserved to a large extent for subsequent dissolving pulp production. The recovery of value-added products out of autohydrolyzates is frequently hindered by extensive lignin precipitation, especially at high temperatures. In this study, a new high-temperature adsorption process (HiTAC process) was developed, where lignin is removed directly after the autohydrolysis, which enables further processing of the autohydrolyzates. The suitability of activated charcoals as a selective adsorbent for lignin under process-relevant conditions (150 and 170°C) has not been considered up to now, because former experiments showed decreasing efficiency of charcoal adsorption of lignin with increasing temperature in the range 20-80°C. In contrast to these results, we demonstrated that the adsorption of lignin at 170°C directly after autohydrolysis is even more efficient than after cooling the hydrolyzate to room temperature. The formation of lignin precipitation and incrustations can thus be efficiently prevented by the HiTAC process. The carbohydrates in the autohydrolysis liquor remain unaffected over a wide charcoal concentration range and can be further processed to yield valuable products. [ABSTRACT FROM AUTHOR]

The objective of this work was to study the kinetics of hemicelluloses extraction during hydrothermal pretreatment of sugar maple wood meal. Pretreatment was conducted in a batch reactor at 145–185°C with reaction times up to 8 h and with liquor to solid ratio of 20:1. Under these conditions, hemicelluloses were selectively solubilized and little degradation (approximately 6–9% of the initial amount) of cellulose and lignin was observed. A kinetic model was developed. It was supposed that there are no diffusion limitations and that the reaction rate constants have first-order kinetics with Arrhenius-type temperature dependence. The model proposes the formation of xylose directly from wood xylan as well as from xylooligomers formed in the liquid phase by the hydrolysis of xylan. The model is able to correlate satisfactorily experimentally measured yields of residual xylan, xylooligomers, xylose, and furfural obtained during the pretreatment. [ABSTRACT FROM AUTHOR]