Xylan Conversion Research Articles

An endoxylanase rapidly hydrolyzes xylan into major product xylobiose via transglycosylation of xylose to xylotriose or xylotetraose

Here, we proposed an effective strategy to enhance a novel endoxylanase (Taxy11) activity and elucidated an efficient catalysis mechanism to produce xylooligosaccharides (XOSs). Codon optimization and recruitment of natural propeptide in Pichia pastoris resulted in achievement of Taxy11 activity to 1405.65 ± 51.24 U/mL. Analysis of action mode reveals that Taxy11 requires at least three xylose (xylotriose) residues for hydrolysis to yield xylobiose. Results of site-directed mutagenesis indicate that residues Glu119, Glu210, and Asp53 of Taxy11 are key catalytic sites, while Asp203 plays an auxiliary role. The novel mechanism whereby Taxy11 catalyzes conversion of xylan or XOSs into major product xylobiose involves transglycosylation of xylose to xylotriose or xylotetraose as substrate, to form xylotetraose or xylopentaose intermediate, respectively. Taxy11 displayed highly hydrolytic activity toward corncob xylan, producing 50.44 % of xylobiose within 0.5 h. This work provides a cost-effective and sustainable way to produce value-added biomolecules XOSs (xylobiose-enriched) from agricultural waste.

Selective conversion of hemicellulose into furfural over low-cost metal salts in a γ-valerolactone/water solution

Thermochemical conversion of biomass into platform chemicals and fuels is recognized as the most promising process for the partial substitution of fossil resources. Notably, selective liquefaction is a critical step for the integrated utilization of waste lignocellulosic biomass resources. Herein, we demonstrated an efficient and environmentally benign liquefied process for converting hemicellulose and waste lignocellulosic residues into furfural in a γ-valerolactone/water solution using inexpensive Al2(SO4)3 as the catalyst. Due to the synergistic effect between the γ-valeroctone (GVL) and active acid center which was derived from the metal salt, more than 50.2 mol% yield of furfural could be obtained from xylan, accompanying with 95.5 wt% of xylan conversion in GVL/H2O (m/m = 9:1, 40.0 g in total) at 140 °C for 3 h. A combination of 27Al NMR spectroscopy and electrospray ionization tandem mass spectrometry (ESI-Q-TOF-MS/MS) revealed that the [Al(OH)2(aq)]+ species contributed to the isomerization and dehydration processes. In addition, the existence of an appropriate amount of water was believed to be responsible for promoting the destruction of hemicellulose and restrain the formation of humins. The liquefied system sheds light on its considerable potential for the industrial utilization of agriculture and forestry lignocellulosic residues.

Towards furfural from the reaction of cellulosic biomass in zinc chloride hydrate solvents

Cellulosic biomass is abundant and is readily accessible for the renewable production of industrially useful chemicals. In the present study, we develop a method for the selective synthesis of furfural directly from native lignocellulose and algal biomass employing acidic zinc chloride hydrate solvents. To do this, we first optimise the conversion of xylans (hemicellulose) and separately of cellulose, to find an optimum compromise between the reaction conditions. The acidic inorganic media, along with the solvent-extractant anisole, enable simultaneous transformation of xylans and glucans into significantly value added furfural under mild processing conditions. This unique process affords substantial progress towards the valorisation of native carbohydrates into furfural, compared to existing methods based on the reactions of simple pentoses or pentosans. It enables the direct processing or raw, unrefined bulk biomass.

Fed-batch enzymatic hydrolysis of alkaline organosolv-pretreated corn stover facilitating high concentrations and yields of fermentable sugars for microbial lipid production

BackgroundLignocellulosic biomass has been commonly regarded as a potential feedstock for the production of biofuels and biochemicals. High sugar yields and the complete bioconversion of all the lignocellulosic sugars into valuable products are attractive for the utilization of lignocelluloses. It is essential to pretreat and hydrolyze lignocelluloses at high solids loadings during industrial processes, which is more economical and environmentally friendly as capital cost, energy consumption, and water usage can be reduced. However, oligosaccharides are inevitably released during the high solids loading enzymatic hydrolysis and they are more recalcitrant than monosaccharides for microorganisms.ResultsA fed-batch enzymatic hydrolysis of corn stover pretreated by the sodium hydroxide–methanol solution (SMs) at high solids loading was demonstrated to reach the high concentrations and yields of fermentable sugars. Glucose, xylose, cello-oligosaccharides, and xylo-oligosaccharides achieved 146.7 g/L, 58.7 g/L, 15.6 g/L, and 24.7 g/L, respectively, when the fed-batch hydrolysis was started at 12% (w/v) solids loading, and 7% fresh substrate and a standardized blend of cellulase, β-glucosidase, and hemicellulase were fed consecutively at 3, 6, 24, and 48 h to achieve a final solids loading of 40% (w/v). The total conversion of glucan and xylan reached 89.5% and 88.5%, respectively, when the oligosaccharides were taken into account. Then, a fed-batch culture on the hydrolysates was investigated for lipid production by Cutaneotrichosporon oleaginosum. Biomass, lipid content, and lipid yield were 50.7 g/L, 61.7%, and 0.18 g/g, respectively. The overall consumptions of cello-oligosaccharides and xylo-oligosaccharides reached 74.1% and 68.2%, respectively.ConclusionsHigh sugars concentrations and yields were achieved when the enzyme blend was supplemented simultaneously with the substrate at each time point of feeding during the fed-batch enzymatic hydrolysis. Oligosaccharides were co-utilized with monosaccharides during the fed-batch culture of C. oleaginosum. These results provide a promising strategy to hydrolyze alkaline organosolv-pretreated corn stover into fermentable sugars with high concentrations and yields for microbial lipid production.

Enhanced Conversion of Xylan into Furfural using Acidic Deep Eutectic Solvents with Dual Solvent and Catalyst Behavior.

An efficient process for the production of furfural from xylan by using acidic deep eutectic solvents (DESs), which act both as solvents and catalysts, is developed. DESs composed of cholinium chloride ([Ch]Cl) and malic acid or glycolic acid at different molar ratios, and the effects of water and γ-valerolactone (GVL) contents, solid/liquid (S/L) ratio, and microwave heating are investigated. The best furfural yields are obtained with the DES [Ch]Cl:malic acid (1:3 molar ratio)+5 wt % water, under microwave heating for 2.5 min at 150 °C, a S/L ratio of 0.050, and GVL at a weight ratio of 2:1. Under these conditions, a remarkable furfural yield (75 %) is obtained. Direct distillation of furfural from the DES/GVL solvent and distillation from 2-methyltetrahydrofuran (2-MeTHF) after a back-extraction step enable 89 % furfural recovery from 2-MeTHF. This strategy allows recycling of the DES/GVL for at least three times with only small losses in furfural yield (>69 %). This is the fastest and highest-yielding process reported for furfural production using bio-based DESs as solvents and catalysts, paving the way for scale-up of the process.

Pyrolysis behavior of xylan-based hemicellulose in a fixed bed reactor

Investigation on the biomass components pyrolysis behaviors in a lab-scale reactor is a necessary step before its industrialization due to the poor transportability of the findings obtained from the micro-scale pyrolyzer which often neglects the heat and mass transfer effect. In present study, the pyrolysis behavior of xylan-based hemicellulose in a fixed bed reactor was investigated. The residue evolution and bio-oil composition of xylan, xylose, arabinose and glucose show the close relationship of pyrolysis characteristics between xylan and its components. It is noteworthy that the xylan and those mono-sugar units melted during pyrolysis, and many bubbles formed. Investigation of the effect of temperature, material thickness and carrier gas flow rate on the products distribution and bio-oil composition indicates that high temperature promotes the xylan conversion and increases the yield of bio-oil, however, if the temperature is too high (>500°C), violent decomposition of xylan occurs and leads to the formation of low molecular weight compounds (such as hydroxyl acetaldehyde, acetic acid and 1-hydroxyl-2-propaone etc.). And interestingly, the bio-oil yield increases monotonically with the material thickness, and thick material layer can increase the content of furfural in bio-oil. Carrier gas flow rate has a little influence on the xylan char yield, and relative high carrier gas flow rate (>2.55L/min) could decrease the secondary decomposition of primary didehydrated pentose but reduce the bio-oil yield.

An Effective and Stable HfP/SiO2 Catalyst for the Production of Furfural from Xylan

Silica-supported hafinum phosphide (HfP/SiO2) was prepared and applied as an effective solid acid catalyst to drive furfural production from xylan. Various characterizations were employed to analyze the intrinsic properties of the HfP/SiO2 catalyst, and the effects of process parameters on its performance were investigated in detail. The results showed that the performance of the HfP/SiO2 catalyst was excellent, which allowed up to 85% of the furfural yield to be achieved at 180 °C for 60 min in the water(NaCl)/THF biphasic system. There was no significant decrease in the performance of the HfP/SiO2 catalyst after seven consecutive cycles. Characterization analysis of the recovered catalyst revealed that its elemental composition and total acidity were maintained, indicating the desired hydrothermal stability of the HfP/SiO2 catalyst. In addition, by-products produced during xylan conversion were identified as humins and soluble molecular fragments or polymers.

Xylo-oligosaccharides preparation through acid hydrolysis of hemicelluloses isolated from press-lye

The preparation of xylo-oligosaccharides (XOSs) through hydrolysis of hemicelluloses was studied. The hemicelluloses were isolated from the press lye discharged in the production of viscose, which contained about 30% xylan. Then, a factorial experimental design was applied to compare the influences of several factors including the concentrations of sulphuric acid and hemicelluloses, the duration and temperature of the hydrolysis, on the conversion of xylan, and the selectivity for the product–XOSs. The results showed that the hydrolysis duration affects the yield of XOSs to the greatest extent. It is difficult to obtain a high yield of XOSs with sulphuric acid as the hydrolysis catalyst.

Ru/H-beta as an efficient catalyst for the conversion of furfural into 3-acetyl-1-propanol (3-AP) toward one-pot transformation of xylan to 3-AP

A highly active and robust catalyst composed of Ru nanoparticles highly dispersed on zeolite H-beta was developed for transforming furfural into 3-acetyl-1-propanol (3-AP) in good yield (81%)under mild conditions (80 °C, 1 MPa H2). Both the support nature and the preparation methods had significant impacts on the dispersion of Ru, eventually on the yield of 3-AP. Ion-exchange method proved best for obtaining the highly active and selective catalyst for this reaction. Moreover, the catalyst can be regenerated easily by calcination and reduction. This catalyst was further explored for the one-pot conversion of xylose and xylan to 3-AP with a yield of 46% and 31%, respectively, thus opening a new feasible pathway from biomass to valuable fine chemicals.

Effect of microwave-assisted ionic liquid/acidic ionic liquid pretreatment on the morphology, structure, and enhanced delignification of rice straw

In the present study, was investigated an environmentally friendly method for pretreating lignocellulosic rice straw (RS) by using 1-butyl-3-methylimidazolium chloride ([Bmim]Cl) as an ionic liquid (IL) and 1-butyl-3-methylimidazolium hydrogen sulfate ([Bmim]HSO4) as an acidic-IL (Acidic-IL) under microwave irradiation (microwave-[Bmim]Cl and microwave-[Bmim]HSO4). The conversion of lignocellulosic biomass into simple sugars requires both efficient pretreatment and hydrolysis enzymes to produce biofuels and specialty chemicals. Therefore, the applied [Bmim]Cl, [Bmim]HSO4, microwave-[Bmim]Cl, and microwave-[Bmim]HSO4 to improve hydrolysis yields. Structural analyses of the pretreated solids were performed to understand the synergistic effects of [Bmim]Cl, and [Bmim]HSO4 pretreatment under microwave irradiation (microwave-[Bmim]Cl and microwave-[Bmim]HSO4) on the efficiencies of enzymatic hydrolyses. The results of a chemical composition analysis of untreated and all pretreated RS samples by using the difference pretreatment methods showed that significant lignin removal was achieved using microwave-[Bmim]Cl (57.02 ± 1.24%), followed by [Bmim]Cl only (41.01 ± 2.67%), microwave-[Bmim]HSO4 (20.77 ± 1.79%), and [Bmim]HSO4-only (16.88 ± 1.14%). The highest glucan yield and xylan conversion achieved through the enzymatic saccharification of microwave-[Bmim]Cl-regenerated cellulose was consistent with the observations obtained from a structural analysis, which indicated a more disrupted, amorphous structure, with lowered crystallinity index (CrI) and lateral order index (LOI) of cellulose polymers. Thus results demonstrated that the pretreatment of lignocellulosic biomass with [Bmim]Cl under microwave irradiation has potential as an alternative method for pretreating lignocellulosic materials.

Extraction and Characterization of Hemicellulose from Eucalyptus By-product: Assessment of Enzymatic Hydrolysis to Produce Xylooligosaccharides.

Eucalyptus wood is the primary source of fibers to produce paper and cellulose in South American countries. The major by-product generated in the cellulose industry is sawdust derived from chip wood production, which is designated as Eucalyptus by-product (EB). The xylooligosaccharides (XOS) are xylose-based oligomers with proven effects over maintenance and stimulation of beneficial human gut bacteria. This study reported the EB extraction and characterization along with an assessment of hemicellulose hydrolysis using commercial xylanases to produce XOS. Hemicellulose derived from extracted and NaClO2 pretreated (HEEBPT) presented xylan content of 55%, which was similar to 58.5% found in commercial Birchwood hemicellulose (CBH). The enzymatic hydrolysis of HEEBPT and CBH presented 30% as maximum conversion of xylan into XOS without significant difference among the enzymatic extracts evaluated. The XOS production from EB was proven as a technically feasible alternative to recover a value-added product from hemicellulosic fraction generated in the cellulose industry. However, lignin removal with NaClO2 from EB affects the feasibility of an industrial process because they generate toxic compounds in the pretreatment step. Thus, further studies with alternative reagents, such as ionic liquids, are required to asses selectively lignin removal from EB. Graphical Abstract.

Catalytic Conversion of Xylose and Xylan into Furfural Over Cr3+/P-SBA-15 Catalyst Derived from Spent Adsorbent

The mesoporous SBA-15 has long been used as an adsorbent for the removal of toxic metal ions. Achieving secondary utilize of spent adsorbent is undoubtedly an advisible option for environmental protection and recycling economy. In the present study, phosphoric acid-modified SBA-15 (P-SBA-15) was found to be an available adsorbent, and the composites (Cr3+/P-SBA-15) formed after adsorption of Cr3+ ions have the ability to efficiently catalyze the conversion of xylose and xylan into furfural. The physicochemical properties of the Cr3+/P-SBA-15 composites were characterized, and the effects of various reaction parameters on their catalytic performance were also investigated. Among the Cr3+/P-SBA-15 composites with different Cr3+ contents, the (0.25)Cr3+/P-SBA-15 composite not only achieved excellent 91% and 58% furfural yields from xylose and xylan, but also had almost constant catalytic performance after five cycles. The findings herein provided a reference for achieving high yields of furfural and reuse of spent adsorbents.

Enzymatic hydrolysis of hemicellulose from pretreated Finger millet (Eleusine coracana) straw by recombinant endo-1,4-β-xylanase and exo-1,4-β-xylosidase

This study focuses on enzymatic saccharification of hemicellulose part of the pretreated Finger millet straw (FMS) for production of xylose. The variation in the carbohydrate composition of FMS was analysed when subjected to different pretreatments. The recombinant endo-1,4-β-xylanase (CtXyn11A) was most active on the FMS pretreated with 1% (w/v) NaOH combined with oven heating at 120 °C for 20 min, resulting in a total reducing sugar yield (TRS) of 32 mg/g pretreated biomass. The pretreatment aided in concentrating the holocellulose content from 69.3% of raw powdered FMS to 76.4%. The post-treatment solid biomass yield was 0.36 g/g raw biomass. The two-step optimization of hemicellulose saccharification from the above pretreated FMS with i) endo-1,4-β-xylanase (CtXyn11A) at 55 °C and ii) exo-1,4-β-xylosidase (BoGH43A) at 37 °C, both at pH 7.5 by Box-Behnken design yielded the TRS of 70 mg/g pretreated biomass. The percentage conversion of xylan to xylose by CtXyn11A and BoGH43A was 24.7%.

High Titer Ethanol Production from Combined Alkaline/Alkaline Hydrogen Peroxide Pretreated Bamboo at High Solid Loading

Enzymatic hydrolysis and fermentation at high solid loading is generally required for the production of high titer ethanol from lignocellulosic biomass at a relatively low cost. In this paper, bamboo pretreated by alkaline and alkaline hydrogen peroxide was subjected to downstream enzymatic hydrolysis and ethanol fermentation at high solid loading for the production of high titer ethanol. The effects of solid loading (5–25% w/v) and enzyme dosage (10–50 mg protein/g glucan) on sugar conversion and ethanol production during separate enzymatic hydrolysis and fermentation (SHF) and simultaneous enzymatic saccharification and co-fermentation (SSCF) processes were investigated. During the fermentation process, the pentose-hexose fermenting Saccharomyces cerevisiae LF1 strain was used. The results showed that the increase of solid loading decreased sugar conversion during enzymatic hydrolysis. At relatively high solid loadings (≥ 20% w/v), SSCF resulted in higher sugar conversion and final ethanol titer compared to SHF. With this proposed process, an ethanol concentration of 68.2 g/L, along with approximately 83.5% of glucan and 73.8% of xylan conversions, could be reached through SSCF at 20% solid loading with an enzyme dosage of only 20 mg protein/g glucan.

RETRACTED: High-solids hydrolysis of corn stover to achieve high sugar yield and concentration through high xylan recovery from magnesium oxide-ethanol pretreatment

MgO-ethanol pretreatment was studied to boost sugar conversions and concentrations during enzymatic hydrolysis. Although corn stover pretreated by MgO and 50% ethanol had the highest glucan and xylan recoveries (89 and 71%), excessive xylan/glucan ratio (54.8%) hinders the access of enzyme to internal cellulose and hemicellulose and only 57% glucan and 46% xylan conversions and 43 g/L sugars were obtained after hydrolysis (10%-solids loading and 2 mL enzyme/g treated biomass). Corn stover pretreated by MgO and 30% ethanol had a moderate xylan/glucan ratio (39.1%), achieving higher glucan and xylan conversions (58 and 48%) and sugar concentrations (70 g/L) after hydrolysis (16%-solids loading and 1 mL enzyme/g treated biomass). A 16%-solids loading largely avoids the poor mixing issue caused by excessive high-solids loading. The addition of Tween 80 effectively eased the binding of lignin with enzyme, boosting glucan and xylan conversions to 67 and 68% and sugar concentrations to 89 g/L.

Enhanced bioconversion of hemicellulosic biomass by microbial consortium for biobutanol production with bioaugmentation strategy

As a renewable and sustainable source for next-generation biofuel production, lignocellulosic biomass can be effectively utilized in environmentally friendly manner. In this study, a stable, xylan-utilizing, anaerobic microbial consortium MC1 enriched from mangrove sediments was established, and it was taxonomically identified that the genera Ruminococcus and Clostridium from this community played a crucial role in the substrate utilization. In addition, a butanol-producing Clostridium sp. strain WST was introduced via the bioaugmentation process, which resulted in the conversion of xylan to biobutanol up to 10.8 g/L, significantly improving the butanol yield up to 0.54 g/g by 98-fold. When this system was further applied to other xylan-rich biomass, 1.09 g/L of butanol could be achieved from 20 g/L of corn cob. These results provide another new method to efficiently convert xylan, the main hemicellulose from lignocellulosic biomass into biofuels through a low-cost and eco-friendly manner.

Mild reaction conditions induce high sugar yields during the pretreatment of Agave tequilana bagasse with 1-ethyl-3-methylimidazolium acetate

Sequential 2k factorial and central composite designs were used to optimize Agave tequilana bagasse (ATB) pretreatment by using 1-ethyl-3-methylimidazolium acetate ([Emim][OAc]). Reaction time, temperature and solids loading were the studied factors while sugar yield was the response variable. Results indicated that optimal conditions (119 °C, 142 min) using high solids loading (30%) were achieved at lower temperatures and reaction times than those previously reported in the literature. It was also revealed that solid recovery after pretreatment with [Emim][OAc] is a key factor. The increase in enzymatic digestibility of pretreated ATB was correlated to a decrease in crystallinity and lower lignin content as observed using microscopy techniques and weaken chemical bonds by Fourier transform infrared spectroscopy. Yields of glucose and xylose in the hydrolysate were 41.3, and 13.0 kg per 100 kg of untreated ATB, which are equivalent to glucan and xylan conversions of 75.9% and 82.9%, respectively.

Study of the Application of Alkaline Extrusion to the Pretreatment of Eucalyptus Biomass as First Step in a Bioethanol Production Process

Eucalyptus biomass was studied as a feedstock for sugars release using an alkaline extrusion plus a neutralization-based pretreatment. This approach would be a first step in a bioconversion process aimed at obtaining fuel bioethanol from eucalyptus biomass. The best operation conditions of extrusion (screw speed, temperature, liquid to solid ratio and NaOH amount) that lead to an effective destructuration of lignocellulose and enhanced sugar release were investigated. Two process configurations, with and without filtration inside the extruder, were tested. In the case without filtration, washed and not washed extrudates were compared. It was demonstrated that filtration step was convenient to remove inorganic salts resulting from neutralization and to promote the mechanical effect of extrusion, but limitations in the machine used in the work prevented testing of temperatures above 100 °C using this configuration. In the no filtration strategy, a temperature of 150 °C allowed attaining the highest glucan and xylan conversion rates by enzymatic hydrolysis of extruded biomass, almost 40% and 75%, respectively, of the maximum yield that could be attained if all carbohydrates contained in raw eucalyptus were converted to sugars. Some of the mechanisms and individual effects underlying alkaline extrusion of eucalyptus were figured out in this work, providing guidelines for a successful pretreatment design that needs to be further studied.

Combining Chemical and Biological Catalysis for the Conversion of Hemicelluloses: Hydrolytic Hydrogenation of Xylan to Xylitol

The conversion of xylan to xylitol is commonly realized via the two separate process steps hydrolysis and hydrogenation (or fermentation). Recent research activities aim at developing one-pot processes to facilitate this conversion to save resources and operation time. To avoid hazardous chemicals like liquid acids for the initial xylan hydrolysis, enzymes are a suitable green alternative. A series of experiments are discussed wherein process conditions for chemical conversion were adjusted to more enzyme-friendly reaction conditions to overcome xylose-induced product inhibition by direct hydrogenation of sugar to xylitol. A novel combination of enzymes and precious metal catalyst (Ru/C) in an one-pot process is demonstrated. Based on these results, limiting factors and potentially advantageous process parameters as well as catalyst combinations are discussed.Graphical

Xylo-Oligosaccharide Preparation through Enzyme Hydrolysis of Hemicelluloses Isolated from Press Lye

Abstract The emerging food additive, xylo-oligosaccharide (XOSs), was prepared through enzymatic hydrolysis of hemicelluloses isolated from press lye. Two of the three experimental enzyme preparations presented favourable effects, while the other one consisting of the nominal enzyme preparations with high enzyme activity was found to have poor catalytic effects. The conversion of xylan exceeded 40% and the selectivity for XOSs reached 90% when the temperature, hemicellulose concentration, dosage of enzymes, and hydrolysis time were 40 °C, 100 g/L, 1 ku/g, and 4 h, respectively. Xylo-oligosaccharide preparation through enzymatic hydrolysis of hemicelluloses isolated from press lye was proved to be a feasible process to utilize the by-product of the lye regeneration, which will substantially improve the economy of the lye regeneration and recycling. Supported by Science and Education Integration Program of Henan University of Technology.