Search

The fermented corn stover residues are abundant renewable lignin-rich bioresources that show great potential to produce aromatic phenols. However, selective catalytic hydrogenolysis of this residual material still remains challenge to obtain high yields. Herein, a novel strategy to produce monophenolic compounds from the fermented stover over a commercial Pd/C catalyst was proposed. Taking the reaction temperature as the key variable, the highest monomer yield was 28.5 wt% at 220 °C in compaction with that of the pristine corn stover (22.8 wt%). The enhanced monophenol yield was due to the higher contents of lignin and less recalcitrance in the fermented stover. Moreover, the van Krevelen diagram revealed a slight selective CO bond scission of lignin macromolecular during fermentation as well as the dehydration and deoxygenation in hydrogenolysis reaction. Overall, this work opens a new avenue for the valorization of lignin through reductive catalytic fractionation of agricultural wastes., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Hydrothermal processes are an attractive clean technology and cost-effective engineering platform for biorefineries based in the conversion of biomass to biofuels and high-value bioproducts under the basis of sustainability and circular bioeconomy. The deep and detailed knowledge of the structural changes by the severity of biomasses hydrothermal fractionation is scientifically and technological needed in order to improve processes effectiveness, reactors designs, and industrial application of the multi-scale target compounds obtained by steam explosion and liquid hot water systems. The concept of the severity factor [log 10 (R o )] established>30 years ago, continues to be a useful index that can provide a simple descriptor of the relationship between the operational conditions for biomass fractionation in second generation of biorefineries. This review develops a deep explanation of the hydrothermal severity factor based in lignocellulosic biomass fractionation with emphasis in research advances, pretreatment operations and the applications of severity factor kinetic model., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Different pretreatments strategies have been developed over the years mainly to enhance enzymatic cellulose degradation. In the new biorefinery era, a more holistic view on pretreatment is required to secure optimal use of the whole biomass. Hydrothermal pretreatment technology is regarded as very promising for lignocellulose biomass fractionation biorefinery and to be implemented at the industrial scale for biorefineries of second generation and circular bioeconomy, since it does not require no chemical inputs other than liquid water or steam and heat. This review focuses on the fundamentals of hydrothermal pretreatment, structure changes of biomass during this pretreatment, multiproduct strategies in terms of biorefinery, reactor technology and engineering aspects from batch to continuous operation. The treatise includes a case study of hydrothermal biomass pretreatment at pilot plant scale and integrated process design., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Hereon, tobacco stalk was deconstructed by lyophilization, ball-milling, ultrasound-assisted alkali extraction, hydrothermal pretreatment (HTP), and alkali presoaking, respectively, followed by dilute alkali cooking to both improve its enzymatic digestibility and isolate the hemicellulosic streams. It was found that a maximum cellulose saccharification rate of 93.5% was achieved from the integrated substrate by ball-milling and dilute alkali cooking, which was 4.4-fold higher than that from the raw material. Interestingly, in this case, 76.9% of hemicelluloses were simultaneously recovered during the integrated treatment. Structural determination indicated that the hemicelluloses released from tobacco stalk by dilute alkali cooking were mixed polysaccharides, and the (1 → 4)-linked β-D-Xylp backbone branched with L-Araf units at O-2/O-3 and 4-O-Me-α-D-GlcpA units at O-2 of the xylose residues was the main structure. In comparison, ultrasound-assisted alkali extraction, ball-milling, and HTP favored the extraction of hemicelluloses with less branched structure and lower molecular weights in the following alkali cooking., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Reductive catalytic fractionation (RCF) has emerged as a new biorefinery paradigm for the fractionation and sequential utilization of entire components of biomass. Herein, we investigated the RCF of bamboo, a highly abundant herbaceous feedstock, in the presence of Pd/C catalyst. The lignin fraction in bamboo was preferentially depolymerized into well-defined low-molecular-weight phenols, with leaving carbohydrates pulp as a solid residue. In the soluble fraction, four major phenolic compounds, e.g., methyl coumarate/ferulate derived from hydroxycinnamic units and propanol guaiacol/syringol derived from β-O-4 units, were generated up to 41.7 wt% yield based on original lignin content. In the insoluble fraction, the carbohydrates of bamboo were recovered with high retentions of cellulose (68%) and hemicellulose (49%), which upon treatment with enzyme gave glucose (90%) and xylose (85%). Overall, the three major components of bamboo could efficient to be fractionated and converted into useful platform chemicals on the basis of this study., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

In this study, bamboo (Phyllostachys pubescens) was successfully deconstructed using an integrated process (autohydrolysis and subsequent delignification). Xylooligosaccharides, high-purity lignin, and digestible substrates for producing glucose can be consecutively collected during the integrated process. The structural change and fate of lignin during autohydrolysis process was deeply investigated. Additionally, the structural characteristics and active functional groups of the lignin fractions obtained by these delignification processes were thoroughly investigated by NMR (2D-HSQC and 31 P NMR) and GPC techniques. The chemical compositions (S, G, and H) and major linkages (β-O-4, β-β, β-5, etc.) were thoroughly assigned and the frequencies of the major lignin linkages were quantitatively compared. Considering the structural characteristics and molecular weights of the lignin as well as enzymatic saccharification ratio of the substrate, the combination of autohydrolysis and organic base-catalyzed ethanol pretreatment was deemed as a promising biorefinery mode in the future based on bamboo feedstock., (Copyright © 2017. Published by Elsevier Ltd.)

Eucommia ulmoides Oliver (EU) wood was consecutively treated by autohydrolysis pretreatment and chemical carbonization post-treatment based on a biorefinery process. Results showed that the optimal condition of the autohydrolysis pretreatment and carbonization process yielded 10.37kg xylooligosaccharides (XOS), 1.39kg degraded hemicellulosic products, 17.29kg other degraded products from hemicelluloses and 40.72kg activated carbon (S BET of 1534.06m 2 /g) from the 100kg raw materials. Simultaneously, 29.14kg gas products generated from the optimum integrated process was significantly lower than that from the direct carbonization process (68.84kg). Besides, the optimal activated carbon (AC 170-1.0 ) also showed a moderate catalytic activity and high stability for hydrogen production by catalytic methane decomposition. Overall, the data presented indicated that the integrated process is an eco-friendly and efficient process to produce XOS and activated carbon, which is beneficial for value-added and industrial application of EU wood., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

A novel pretreatment process was developed to achieve valorization of bamboo components into digestible cellulose, degraded sugars and lignin. In this case, bamboo was pretreated with 60% γ-valerolactone (GVL)/40% water containing 0.05mol/L H 2 SO 4 , yielding solid fraction rich in cellulose. The resulting liquor was further treated with the addition of NaCl and ultrasound, resulting in water phase rich in degraded sugars and GVL phase containing lignin, which was easy to recover. Results showed that the enzymatic hydrolysis was enhanced by 6.7-fold after treatment as compared to the control. The degraded sugars released in water phase contained monosaccharides (70.72-160.47g/kg) together with oligo- and polysaccharides (46.4-181.85g/kg). The lignin obtained had high purity, low molecular weight (1820-2970gmol -1 ) and low polydispersity (1.93-1.98). The present study creates a novel pretreatment process for the conversion of Gramineae biomass into useful feedstocks with potential applications in the fields of fuels, chemicals and polymers., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

The aim of the research was to evaluate the effect of combined treatments on fermentable sugar production from rapeseed straw. An optimum condition was found to be the combination of hydrothermal pretreatment at 180°C for 45min and post-treatment by 2% NaOH at 100°C for 2h, which was based on the quantity of monosaccharides released during enzymatic hydrolysis. As compared with the raw material without treatment, the combination of hydrothermal pretreatment and alkali post-treatment resulted in a significant increase of the saccharification rate by 5.9times. This process potentially turned rapeseed straw into value added products in accordance with the biorefinery concept., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

An integrated process based on ionic liquids ([Bmim]Cl and [Bmim]OAc) pretreatment and successive alkali post-treatments (0.5, 2.0, and 4.0% NaOH at 90°C for 2h) was performed to isolate lignins from Eucalyptus. The structural features and spatial distribution of lignin in the Eucalyptus cell wall were investigated thoroughly. Results revealed that the ionic liquids pretreatment promoted the isolation of alkaline lignin from the pretreated samples without obvious structural changes. Additionally, the integrated process resulted in syringyl-rich lignin macromolecules with more β-O-4' linkages and less phenolic hydroxyl groups. Confocal Raman microscopy analysis showed that the dissolution behavior of lignin was varied in the morphologically distinct regions during the successive alkali treatments, and lignin dissolved was mainly stemmed from the secondary wall regions. These results provided some useful information for understanding the mechanisms of delignification during the integrated process and enhancing the potential utilizations of lignin in future biorefineries., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Bio-oil derived from fast pyrolysis of rice husk was gasified for producing gas. The effectiveness of equivalence ratio and gasifying agents on the gas composition, ratio of H2/CO, tar amount, low heating value, degree of oxidation and cold gas efficiency of the gas were comprehensively investigated. Under different equivalence ratios and gasifying agents, the gases can be used as synthesis gas for Fischer-Tropsch synthesis, fuel gas for gas turbines in a power plant and reducing gas for ore reduction, respectively. The H2 concentration, CO level and cold gas efficiency of the resulted gas derived from gasification of bio-oil were significantly higher, while tar content was remarkably lower than those derived from gasification of solid biomass using the same equivalent ratio value and gasifying agent. In short, bio-oil gasification is economically feasible for large scale production of fuels and chemicals., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

In this study, Eucalyptus camaldulensis was pretreated with 0.02 M aluminum chloride (AlCl3) at 140-180 °C to obtain digestible substrates for glucose and lignin. The effects of AlCl3-catalyzed hydrothermal pretreatment on the degradation of carbohydrates, structural changes of lignin, crystallinity, morphologic changes, and cellulose conversion of the pretreated biomass have been investigated by HAPEC, HPLC, FT-IR, XRD, CP/MAS NMR, SEM, and 2D-HSQC NMR. Results showed that the pretreatment significantly removed hemicelluloses and cleaved β-O-4 linkages of lignin at high temperatures. Under an optimum condition (at 170 °C for 1 h), almost all of hemicelluloses were removed and most of β-O-4 linkages in lignin were cleaved, and 77.8% cellulose conversion of the pretreated biomass was achieved, which was 7.3-fold higher than that of the original biomass. In short, this process was regarded as a promising approach to achieve an efficient conversion of lignocellulosic biomass to fermentable glucose and residual lignin., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

In this study, mild acid hydrolysis using γ-valerolactone (GVL)/water system integrated with enzymatic hydrolysis was carried out for the enhancement of enzymatic saccharification efficiency. The quantitative analysis of soluble carbohydrates and structural characterizations of solid residues were conducted. Results showed that the soluble carbohydrates in the water-phase were mainly composed of monomers and oligomers from xylose and glucose, while the contents of which were depended on the ratio of GVL to water. Moreover, the inhibitors were hardly detected due to the moderate pretreatment severity. Compared with the untreated feedstock, the yields of enzymatic hydrolysis from pretreated samples increased by two-fold with the mixture of 80/20 GVL/H2O. Combined with the amount of glucose (14.6%) dissolved in the water-phase, over 92.6% of glucose in cotton stalk was released and recovered. Based on the comprehensive analysis, treatment with GVL/H2O system provided us a more effective approach for sugar production from biomass., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Organosolv fractionation is a promising process to separate lignocellulosic biomass for the preparation of multiply products including biofuels, chemicals, and materials. This review presents the state of art of different processes applying alcohols and organic acids to treat lignocellulosic biomass for the production of ethanol, lignin, xylose, etc. The major organosolv technologies using ethanol, formic acid, and acetic acid, are intensively introduced and discussed in depth. In addition, the structural modifications of the major components of lignocelluloses, the technical processes, and the applications of the products were also summarized. The object of the review is to provide recent information in the field of organosolv process for the integrated biorefinery. The perspectives of the challenge and opportunity related to this topic are also presented., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

The application of the acidic ionic liquid (IL), 1-butyl-3-methylimidazolium hydrogensulfate ([bmim]HSO4), as a catalyst in the hydrothermal microwave treatment (HMT) and green upgradation of eucalyptus biomass has been investigated. The process was carried out in a microwave reactor system at different temperatures (140-200°C) and evaluated for severities. The xylooligosaccharides (XOS, refers to a DP of 2-6) yield up to 5.04% (w/w) of the initial biomass and 26.72% (w/w) of xylan were achieved. Higher temperature resulted in lower molecular weight product, and enhanced the concentration of monosaccharides and byproducts. The morphology and structure of the solid residues were performed using an array of techniques, such as SEM, XRD, FTIR, BET surface area, and CP/MAS (13)C NMR, by which the increase of crystallinity, the destruction of surface structure, and the changes in functional groups and compositions were studied after the pretreatment, thus significantly enhancing the enzymatic hydrolysis., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

A simple and effective route for the production of levulinic acid (LA) from cellulose has been developed in SO3H-functionalized ionic liquids. The effects of ionic liquid structures, reaction conditions and combination of metal chlorides with ILs on the yield of LA were investigated, where the highest yield of 39.4% was obtained for 120 min in the presence of 1-(4-sulfonic acid) butyl-3-methylimidazolium hydrogen sulphate ([BSMim]HSO4) with addition of H2O. The catalytic activities of ionic liquids depended on the anions and decreased in the order: CF3SO3(-)>HSO4(-) > OAc(-), which was in good agreement with their acidity order. The ILs play a dual solvent-acid role for the cellulose conversion into LA and exhibited favorable catalytic activity over four repeated runs., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Eucommia ulmoides Oliver (EU) wood was successively treated by autohydrolysis and organosolv pretreatment integrated process. Autohydrolysis pretreatment facilitated xylooligosaccharides production, subsequent organosolv pretreatment to obtain high-purity lignin and digestible cellulose-rich residue. Results showed that the lignin fractions obtained exhibited smaller molecular weights, narrow polydispersity, more phenolic OH groups and higher syringyl/guaiacyl ratios (S/G) than the milled wood lignin. NMR characterization of the lignin revealed that the β-O-4 linkages significantly cleaved and the structure of stilbene formed, but its resinol (β-β) was resistant to be degraded by organosolv delignification. Moreover, the glucose yield of the integrated residue achieved a maximum value of 89.3% after enzyme hydrolysis, separately about 1.0, 1.3, 3.8 times as compared to that of the ethanol organosolv residue, the hydrothermally treated residue and the EU wood, respectively, which indicated that the integrated process was a promising approach to value-added utilization of the EU wood., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

In this work, the structural features of the lignin isolated with 2% NaOH at 90°C for 2.5h from the hydrothermally pretreated eucalyptus fibers at different temperatures (100-200°C) for different times (15-60min) were thoroughly investigated. Results showed that the hydrothermal pretreatment facilitated the separation of alkali lignin from the pretreated fibers. It was found that the linkages of β-O-4, β-β, and β-5 decreased gradually with the increase of hydrothermal severity. Furthermore, decreased molecular weights (1630-510g/mol), associated carbohydrates contents (1.99-0.05%) and aliphatic OH contents (3.37-0.65mmol/g), and increased phenolic OH contents (0.71-2.98mmol/g) and thermal stability of the alkali lignins were observed with the increase of the hydrothermal severity., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

In this study, sweet sorghum stem was subjected to hydrothermal pretreatment (HTP) and alkaline post-treatment to enhance its saccharification ratio by reducing its recalcitrance. The results showed that the HTP (110-210°C, 0.5-2.0h) significantly degraded hemicelluloses, and the pretreatment at the temperature higher than 190°C led to the partial degradation of the cellulose. As compared to the sole HTP, the integrated process removed most of lignin and hemicelluloses, which incurred a higher cellulose saccharification ratio. Under an optimum condition evaluated (HTP at 170°C for 0.5h and subsequent 2% NaOH treatment), 77.5% saccharification ratio was achieved, which was 1.8, 2.0 and 5.5 times as compared to the only HTP pretreated substrates, alkaline treated substrates alone and the raw material without pretreatment, respectively. Clearly, the integrated process can be considered as a promising approach to achieve an efficient conversion of lignocellulose to fermentable glucose., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

In this study, cellulose-rich fractions from bamboo were prepared with steam explosion pretreatment (SEP) followed by a successive alkaline delignification to improve the enzymatic digestibility for an efficient bioethanol production. The cellulose-rich fractions obtained were characterized by FT-IR, XRD, CP/MAS (13)C NMR, SEM, and BET surface area. It was found that the SEP alone significantly removed partial hemicelluloses, while the synergistic treatment by SEP and alkaline delignification removed most hemicelluloses and lignin. Results from enzymatic hydrolysis showed that SEP alone improved the enzymatic hydrolysis rate by 7.9-33.1%, while the synergistic treatment by SEP and alkaline delignification enhanced the rate by 45.7-63.9%. The synergistic treatment by SEP at 2.0 MPa for 5 min with water impregnation followed by a successive alkaline delignification with 0.5% NaOH and 70% ethanol containing 1.5% NaOH resulted in a maximum enzymatic hydrolysis rate of 70.6%., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Bamboo was non-isothermally pretreated with hot water at 140-200°C for different times (10-120 min). The effects of pretreatment conditions on the degradation of carbohydrates, cellulose crystallinity, partial removal/relocation of lignin, morphologic change of the feedstock, and glucose yield during the enzymatic hydrolysis were investigated. The effective removal of amorphous cellulose and hemicelluloses led to the increase of crystalline index of the residues. In comparison with the raw material, the surface of the pretreated samples was irregular and numerous lignin droplets appeared on the cellulose bundle surface under the intense pretreatment conditions. The glucose conversion increased with the raise of pretreatment temperature and the prolongation of time, and the maximum conversion of 75.7% was achieved for the sample pretreated at 200°C for 120 min, whereas the untreated sample was only 15.7%. The result illustrated that hydrothermal pretreatment affected the composition of bamboo, and remarkably enhanced the enzymatic hydrolysis efficiency., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Bamboo (Phyllostachys pubescens) was successfully fractionated using a three-step integrated process: (1) autohydrolysis pretreatment facilitating xylooligosaccharide (XOS) production (2) organosolv delignification with organic acids to obtain high-purity lignin, and (3) extended delignification with alkaline hydrogen peroxide (AHP) to produce purified pulp. The integrated process was comprehensively evaluated by component analysis, SEM, XRD, and CP-MAS NMR techniques. Emphatically, the fundamental chemistry of the lignin fragments obtained from the integrated process was thoroughly investigated by gel permeation chromatography and solution-state NMR techniques (quantitative (13)C, 2D-HSQC, and (31)P-NMR spectroscopies). It is believed that the integrated process facilitate the production of XOS, high-purity lignin, and purified pulp. Moreover, the enhanced understanding of structural features and chemical reactivity of lignin polymers will maximize their utilizations in a future biorefinery industry., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

In order to establish the correlation between hemicelluloses removal and bioconversion efficiency of cellulose, fractionation process with increasing NaOH concentration selectively released the hemicellulosic polymers with increasing molecular weight and decreasing degree of substitution. Not only the initial hydrolysis rates also the concentrations of glucose and ethanol were significantly enhanced from 5.93 and 8.39 g/L to the range of 8.67-9.60 g/L and 11.53-13.71 g/L after alkaline treatment, respectively. However, the maximum conversions of cellulose to glucose (61.9%) and ethanol (64.6%) were achieved as 33.0% hemicelluloses was still remained. Excluding the negligible effect on the crystal transformation of cellulose, the improvement of bioconversion efficiency was resulted from the synergetical effects of surface exposure, multi-layers collapse and the hydrophilic property of the cellulosic substrate. It is critical task to balance these factors by the partial removal of hemicellulosic component, not complete., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Furfural residues (FR), the abundant lignocellulosic residues from commercial furfural production, were delignified with alkaline peroxide process and then taken as substrates for ethanol production by simultaneous saccharification and fermentation (SSF). It was apparent that the delignification efficiency was increased with higher chemical addition and temperature, reaching the maximum removal (73.5%) of lignin. The widespread accessible-cellulose in FR favored the enzymatic hydrolysis and achieved the considerable bioconversion (75.7% with 5 FPU+10 IU/g substrate). The delignification process increased the relative glucose content and then the bioconversion efficiency, closely relating to the increased specific surface area. As the cellulose contents were higher than 60%, the final conversions conversely fell to around 75%, probably due to the insufficient utilization of all active cellulose with low enzyme cocktails addition. Although the SSF bioconversion slightly decreased as the elevated amount of fermentable cellulose, the maximum of ethanol concentration (16.9 g/L) was expectedly obtained., (Crown Copyright © 2013. Published by Elsevier Ltd. All rights reserved.)

An environmentally friendly pretreatment process was developed to fractionate hemicelluloses and lignin from poplar wood by ionic liquid (IL) pretreatment coupled with mild alkaline extraction. Hemicellulosic and lignin fractions were obtained in high yields, amounting to 59.3% and 74.4%, respectively, which can served as raw materials for production of value-added products. The yield of glucose for the integrated pretreated poplar wood was 99.2%, while it was just 19.2% for the untreated material. The synergistic benefits of the removal of lignin and hemicelluloses, the increase of the cellulose surface area, and the conversion of cellulose fibers from the cellulose I to the cellulose II crystal phase resulted in the high glucose yield for the integrated pretreated substrate. Therefore, the IL based biorefining strategy proposed can integrate biofuels production into a biorefinery scheme in which the major components of poplar wood can be converted into value-added products., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Bamboo culm (Dendrocalamus giganteus Munro) was treated with hot water in non-isothermal conditions (140, 160, 180 and 200°C) for various reaction times (10, 30, 60 and 120 min) to generate xylo-oligosaccharides in a batch reactor at a solid to liquor ratio of 1:10 g/g. The influence of reaction conditions on yields, compositions and characteristics of the products were evaluated. The maximum yield of xylo-oligosaccharides of 47.49% was achieved at 180°C for 30 min with a relatively low level of xylose (4.73%) and other products (arabinose 0.20 g/L, galactose 0.19 g/L, HMF 0.15 g/L, furfural 0.36 g/L, acetic acid 0.64 g/L and formic acid 0.26 g/L). Higher temperature and/or longer reaction time reduced the yield of oligosaccharides, and enhanced concentrations of monosaccharides and byproducts. The result demonstrated that the yield of xylo-oligosaccharides obtained by autohydrolysis depends on the reaction temperature and time., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

The present work investigated the effects of hydrothermal treatment (HTT) of Tamarix ramosissima by determination of sugar and inhibitor formation in the liquid fraction, and chemical and morphological changes of the pretreated solid material coupled with an evaluation of enzymatic hydrolysis. HTT was carried out in a batch reactor system at a maximal temperature (TMAX 180-240 °C) and evaluated for severities logRo ranging from 2.40 to 4.17. The liquid fractions were analyzed by HPLC, GPC, and GC-MS. The morphology and composition of the solid residues were characterized using an array of techniques, such as SEM, XRD, BET surface area, and CP/MAS (13)C NMR. Using a variety of tools, we have developed a better understanding of how HTT process affects biomass structure and cellulose properties that impact on its digestibility. These results provided new insights into the factors limiting enzymatic digestibility and mechanism of biomass deconstruction during hydrothermal process., (Crown Copyright © 2012. Published by Elsevier Ltd. All rights reserved.)

The effect of proposed integrated pretreatment on enzymatic hydrolysis of poplar wood has been reported in Part 1. Part 2 of this work investigated the detailed structural features of the isolated lignin and hemicellulosic fractions, which were obtained in high yields. The chemical structures of these polymer fractions obtained were compared with the corresponding alkaline lignin and hemicelluloses extracted from the raw material without ionic liquid (IL) pretreatment. The yields of alkaline lignin and hemicelluloses obviously increased after the IL pretreatment. No apparent degradation occurred for both lignin and hemicellulosic fractions during this integrated pretreatment process. The lignin fraction (RCEL), which obtained after the enzymatic hydrolysis, exhibited high percentages of β-O-4' aryl ether linkages and S/G ratio. It is believed that the high molecular weight and high purity hemicellulosic and lignin fractions obtained can serve as raw materials for the production of value-added products., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Successive treatments with fungus and alkali were proposed to reduce the recalcitrance and improved the enzymatic digestibility of triploid poplar. Biopretreatment with Trametes velutina D10149 for 0, 4, 8, 12 and 16weeks gradually degraded hemicelluloses and lignin, and improved the digestibility of cellulose from 4.0% to 19.5% with the increasing dry mass loss of lignocelluloses from 15.5% to 53.4%. Combining with alkaline fractionation, biopretreatment for 4weeks significantly enhanced the availability of cellulose and achieved a maximum glucose yield (38.8% of the original cellulose) with a dry mass loss of 24.4%. The BET surface area of lignocelluloses increased from 1.7 to 10.6m(2)/g after combination of 8weeks biopretreatment and alkaline fractionation. Moreover, alkaline fractionation removed amorphous and low molecular components, which incurred a higher crystalline index and narrower molecular weight distribution of residual carbohydrates in synergistically treated samples as compared to biopretreated samples., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Hydrothermal liquefaction of cornstalk at 180-300 °C at ratios of water to cornstalk of 6-14 was conducted, and the reaction products were lumped into gas, water-soluble organics (ethanol-insoluble and ethanol-soluble organics), heavy oil, volatile organic compounds, and acid-soluble and acid-insoluble solid residues. Low temperature, high ratio of water to cornstalk, and short reaction time favored the formation of bio-oil (ethanol-insoluble organics, ethanol-soluble organics, and heavy oil) but inhibited the formation of acid-insoluble solid residue. Increasing temperature and reaction time increased the yields of gas and volatile organic compounds, whereas decreased the yield of acid-soluble solid residue. Bio-oil yields increased first and then decreased at a ratio of water to cornstalk higher than 10. Overall, the studied reaction parameters influenced the conversion among the lumps and product properties. This study suggests that lump analysis provides a promising approach to describe the product distributions in biomass liquefaction., (Crown Copyright © 2012. Published by Elsevier Ltd. All rights reserved.)

Xylooligosaccharides (XOS) were prepared from xylan-rich hemicelluloses isolated by potassium hydroxide from sugarcane bagasse by hydrolysis with crude xylanase secreted by Pichia stipitis. Hydrolysis for 12h produced XOS with a maximum yield of 31.8%, equivalent to 5.29 mg mL(-1) in the hydrolyzate. XOS with degrees of polymerization (DP) from 2 to 4 (xylobiose, xylotriose, and xylotetraose) were the major components in the hydrolysates, whereas the oligosaccharides with higher DP of 5-6 (xylopentaose and xylohexose) showed a constant low level. FT-IR and NMR ((1)H, (13)C, HSQC) demonstrated that XOS contained Araf and 4-O-Me-α-D-GlcpA residues. The 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay showed that the XOS exhibited concentration-dependent antioxidant activity. The results obtained indicate that the XOS produced from sugarcane bagasse can be employed in food-related applications., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Succinoylation and benzoylation of ball-milled eucalyptus wood using succinic anhydride and benzoyl chloride as acylating reagent, respectively, were investigated at room temperature using dimethyl sulfoxide/N-methylimidazole (DMSO/NMI) as reaction medium without additional catalysts. The effects of the corresponding acylating reagent dosage (1-5:1 for succinoylation and 0.5-5:1 for benzoylation) and reaction time (0.35-5h for succinoylation and 0.5-3h for benzoylation) on the extent of acylation, measured by weight percent gain (WPG), were studied. WPG of succinoylation and benzoylation was in the range of 70.8-144.7% and 17.3-43.1%, respectively. The efficiency of acylation at room temperature significantly increased in DMSO/NMI compared with ionic liquid 1-butyl-3-methylimidazolium chloride because of the role of NMI as solvent, base and catalyst. Fourier transform infrared (FT-IR), and solid-state cross-polarization/magic-angle spinning (CP/MAS) (13)C nuclear magnetic resonance (NMR) spectroscopy studies provided evidence for the occurrence of succinoylation and benzoylation reactions and the attachment of functional groups via ester bonds., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Hydrothermal carbonization (HTC) is a novel thermochemical conversion process to convert lignocellulosic biomass into value-added products. HTC processes were studied using two different biomass feedstocks: corn stalk and Tamarix ramosissima. The treatment brought an increase of the higher heating values up to 29.2 and 28.4 MJ/kg for corn stalk and T. ramosissima, respectively, corresponding to an increase of 66.8% and 58.3% as compared to those for the raw materials. The resulting lignite-like solid products contained mainly lignin with a high degree of aromatization and a large amount of oxygen-containing groups. Liquid products extracted with ethyl acetate were analyzed by gas chromatography-mass spectrometry. The identified degradation products were phenolic compounds and furan derivatives, which may be desirable feedstocks for biodiesel and chemical production. Based on these results, HTC is considered to be a potential treatment in a lignocellulosic biomass refinery., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

In order to understand the behaviors of hemicelluloses and lignin under the given acidic conditions with increasing severity, the structural characteristics were elucidated in detail by both wet chemistry methods and spectroscopic analyses in this study. Although acidic pretreatment significantly hydrolyzed the glycosidic linkages in xylan backbone and then reduced the molecular weight of xylan from 89,600 to 19,630 g/mol, a slightly increased amount of glucuronic acid was observed, probably attributing to the maintenance of ester bonds. The serious structural variation occurred in lignin macromolecule was evidenced by the extensive degradation of β-O-4 ether linkages and resinol substructure, together with the changes in the ratios of the three monolignols in ester-bond, ether-bond and non-condensed phenolic compounds. At the most severity, obvious condensation reactions introduced the clear shift of C(2) and C(5) correlations and the absence of C(6) correlation in guaiacyl units by 2D HSQC analysis., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

The dewaxed sample from Triploid of Populus tomentosa Carr. was extracted by using organic alkaline solvent (Dimethylformamide, DMF) via hydrothermal pretreatment. Neutral sugar compositions and molecular weight analysis demonstrated that the hemicellulosic fractions with a higher Uro/Xyl ratio, namely the more branched hemicelluloses, had higher molecular weights. Interestingly, these results were different from the previous report, in which the ratio of Uro/Xyl in the water-soluble hemicellulosic fraction was more than that of the alkali-soluble hemicellulosic fraction. Spectroscopy (FTIR, (1)H NMR, (13)C NMR, and HSQC) analysis indicated that the hemicellulosic fractions were mainly composed of (1→4)-linked α-D-glucan from starch and (1→4)-linked β-D-xylan attached with minor amounts of branched sugars from hemicelluloses. In addition, thermal analysis implied that linear hemicelluloses showed more thermal stability than the branched ones during pyrolysis., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

The efficient production of fermentable sugars is a prerequisite for economic ethanol production from lignocellulosic biomass. A cellulose-enriched fraction was obtained by complete dissolution of ball-milled hybrid poplar wood in dimethyl sulfoxide and lithium chloride (DMSO/LiCl). The cellulose-enriched fraction was mainly composed of glucose and xylose. Spectral fitting analysis of CP/MAS (13)C NMR revealed that the cellulose-enriched fraction had para-crystalline structures with somewhat larger contents of crystalline cellulose І(β) than І(α). The cellulose-enriched fraction was much easier to be converted into mono sugars by cellulases than the untreated sample. Scanning electron microscopy (SEM) indicated that the cellulose-enriched fraction was porous, which could likely explain the high enzymatic hydrolysis efficiency. This study provides a novel pretreatment method based on fractional separation of the three biopolymers via complete dissolution system for enhancement of conversion from ignocellulose to biofuels., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Three organosolv and three alkaline hemicellulosic fractions were prepared from lignocellulosic biomass of the fast-growing shrub Tamarix austromongolica (Tamarix Linn.). Sugar analysis revealed that the organosolv-soluble fractions contained a higher content of glucose (33.7-6.5%) and arabinose (14.8-5.6%), and a lower content of xylose (62.2-54.8%) than the hemicellulosic fractions isolated with aqueous alkali solutions. A relatively high concentration of alkali resulted in a decreasing trend of the xylose/4-O-methyl-D-glucuronic acid ratio in the alkali-soluble fractions. The results of NMR analysis supported a major substituted structure based on a linear polymer of β-(1→4)-linked d-xylopyranosyl residues, having ramifications of α-L-arabinofuranose and 4-O-methyl-D-glucuronic acid residues monosubstituted at O-3 and O-2, respectively. Thermogravimetric analysis revealed that one step of major mass loss occurred between 200-400°C, as hemicelluloses devolatilized with total volatile yield of about 55%. It was found that organosolv-soluble fractions are more highly ramified, and showed a higher thermal stability than the alkali-soluble fractions., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

This study aims to establish an efficient pretreatment process using cellulose-dissolution solvents to enhance the enzymatic saccharification. LiOH/urea, LiCl/DMAc, concentrated phosphoric acid, ionic liquid (1-butyl-3-methylimidazolium chloride; [BMIM]Cl) and N-methyl-morpholine-N-oxide (NMMO) were selected as the cellulose dissolution agents. Except the cellulosic sample regenerated from LiCl/DMAc system, all the other treated samples exhibited lower cellulose crystallinity and degree of polymerization (DP), and consequently, exhibited a significant enhancement on enzymatic hydrolysis kinetic. Ionic liquid pretreatment offered unique advantages in the hydrolysis rate in the first 10h, probably due to the extensively structural transformation of cellulose from the crystalline to the amorphous region. Meanwhile, the regenerated cellulose from concentrated phosphoric acid almost completely consisted of cellulose II, and achieved the highest saccharification yield., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Wood meal was dissolved under identical conditions in the ionic liquid 1-butyl-3-methylimidazolium chloride ([C(4)mim]Cl) and homogeneously esterified with butyryl chloride and lauroyl chloride in the presence of triethylamine as a neutralizer. The effect of the molar ratio of reagent to the hydroxyl groups in wood on the properties of the esterified wood and the possible mechanism of the homogeneous esterification of wood in this reaction medium were studied. Furthermore, the physicochemical properties of the esterified wood were characterized by FTIR, solid-state CP/MAS (13)C NMR, TGA/DTG and SEM. The results confirmed that the homogeneous modifications were successfully processed and highly substituted wood esters could be obtained by reacting the dissolved wood in this homogeneous system., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

The synergistic effect of steam explosion pretreatment and sodium hydroxide post-treatment of Lespedeza stalks (Lespedeza crytobotrya) has been investigated in this study. In this case, Lespedeza stalks were firstly exploded at a fixed steam pressure (22.5 kg/m(2)) for 2-10 min. Then the steam-exploded Lespedeza stalks was extracted with 1 M NaOH at 50 degrees C for 3 h with a shrub to water ratio of 1:20 (g/ml), which yielded 57.3%, 53.1%, 55.4%, 52.8%, 53.2%, and 56.4% (% dry weight) cellulose rich fractions, comparing to 68.0% from non-steam-exploded material. The content of glucose in cellulose rich residues increased with increment of the steaming time and reached to 94.10% at the most severity. The similar increasing trend occurred during the dissolution of hemicelluloses. It is evident that at shorter steam explosion time, autohydrolysis mainly occurred on the hemicelluloses and the amorphous area of cellulose. The crystalline region of cellulose was depolymerized under a prolonged incubation time. The characteristics of the cellulose rich fractions in terms of FT-IR and CP/MAS (13)C NMR spectroscopy and thermal analysis were discussed, and the surface structure was also investigated by SEM.

The chemical modification of sugarcane bagasse with succinic anhydride using pyridine as solvent after ultrasound irradiation was studied. The optimized parameters included ultrasound irradiating time 0-50 min, reaction time 30-120 min, succinic anhydride concentration by the ratio of dried sugarcane bagasse to succinic anhydride from 1:0.25 to 1:1.50, and reaction temperature 75-115 degrees C are required in the process. The extent of succinoylation was measured by the weight percent gain (WPG), which increased with increments of reaction time, succinic anhydride concentration, and reaction temperature. The ultrasound irradiation has a positive effect on bagasse succinoylation process. On the other hand, the ultrasonic pre-treatment application broke down the cell wall polymers, resulting in, therefore, a negative effect on the WPG. Evidences of succinoylation were also provided by FT-IR and CP MAS (13)C NMR and the results showed that the succinoylation at C-2 and C-3 occurred. The thermal stability of the succinylated bagasse decreased upon chemical modification.

Seven residual hemicellulosic preparations (19.6-45.0% of the original hemicelluloses) were extracted from wheat straw pre-treated with various organic solvents using 1.8% H2O2-0.18% cyanamide at 50 degrees C and pH 10.0 for 4 h. Their chemical compositions and physicochemical properties were determined using GC, HPLC, GPC, FT-IR and 13NMR spectroscopy. The results indicated that all the residual hemicellulosic preparations were heteropolysaccharides containing xylose, glucose, arabinose, galactose, mannose, rhamnose and 4-O-methyl-alpha-D-glucopyranosyluronic acid. The predominant monosaccharide was xylose, ranging between 67.7% and 81.9% of the total neutral sugars, composed mainly of L-arabino-(4-O-methyl-D-glucurono)-D-xylan. The content of contaminant lignin in the isolated residual hemicelluloses was 2.89-5.31%. The Mw values of the two residual hemicellulosic preparations H6 and H7 (42,710 and 44,080 g mol-1, respectively) obtained from the aqueous-alcohol pre-treated straw were much higher than those of H1-H5 (12,980-15,950 g mol-1) extracted from the organic acid pre-treated straw.

Sugarcane bagasse was esterified with acetic anhydride using N-bromosuccinimide as a catalyst under mild conditions in a solvent free system. The extent of acetylation was measured by weight percent gain, which varied from 2.1% to 24.7% by changing the reaction temperature (25-130 degrees C) and duration (0.5-6.0 h). N-Bromosuccinimide was found to be a novel and highly effective catalyst for acetylation of hydroxyl groups in bagasse. At a concentration of 1% of the catalyst in acetic anhydride, a weight percent gain of 24.7% was achieved at 120 degrees C for 1 h, compared with 5.1% for the un-catalyst reaction under the same reaction condition. FT-IR and CP-MAS 13C-NMR studies produced evidence for acetylation. The thermal stability of the products decreased slightly upon chemical modification, but no significant decrease in thermal stability was observed for WPG > or = 24.7%. More importantly, the acetylation significantly increased hydrophobic properties of the bagasse. The oil sorption capacity of the acetylated bagasse obtained at 80 degrees C for 6 h, was 1.9 times higher than the commercial synthetic oil sorbents such as polypropylene fibres. Therefore, these oil sorption-active materials can be used to substitute non-biodegradable materials in oil spill cleanup.

Treatment of wheat straw with hot water at 80-95 degrees C for 0.5 h at pH 6.0-8.0 released 41.0-53.0% of the original lipophilic extractives. The chemical compositions of six lipophilic extractives were determined by GC on a medium-length high-temperature capillary column without derivatization, thus giving a method for direct determination of individual components of free fatty and resin acids, sterols, waxes, sterol esters, and triglycerides. The extracts contained 68.7-75.8% lipophilic substances, comprising mainly free fatty acids (25.8-48.4%), waxes (9.4-27.0%), sterols (4.1-8.0%), triglycerides (3.3-11.0%), and sterol esters (2.6-5.1%). Minor amounts of diglycerides (0.3-0.5%), resin acid (0.5-3.1%), and phenolic compounds (0.9-3.6%) were also quantitatively determined in the extractives.