Xylose Decomposition Research Articles

Mechanism of solvothermal conversion of xylose to furfural in rich-methanol solution: A study based on density functional theory

The hydrothermal conversion of biomass is an important method for furfural (FF) production. The development of methods for converting five-carbon sugars to FF can improve the utilization rate of biomass polysaccharides, which has important research value. FF is a valuable furan organic compound in the decomposition of xylose and can be produced in large quantities under hydrothermal conditions. In this study, density functional theory (DFT) method was used to study the mechanism of xylose forming FF and the effect of methanol-water mixed solution on FF formation. In this paper, through quantitative calculations, the best way to convert xylose to FF is explored, in order to understand the basic conversion way of biomass hydrothermal conversion to high-value molecular FF. It shows that water molecules participate in the catalytic reaction, and the Gibbs free energy is significantly reduced. This is consistent with the experimental results. In the gas phase, the catalytic reaction shows excellent effects. The Gibbs free energy in the solution is significantly lower than the Gibbs free energy in the gas phase. Combining experimental results and theoretical calculations, it is confirmed that the yield of FF produced by hydrothermal liquefaction of xylose is significantly higher than that of gas-phase pyrolysis. It was also confirmed that methanol played a role in protecting active functional groups, while water played a role as a catalyst. At the same time, methanol and water have a synergistic effect on the solvent.

Xylan and xylose decomposition during hot water pre-extraction: A pH-regulated hydrolysis

One of the key issues in the development of biofuels using lignocellulosic feedstocks is to increase the yield of fermented sugar, and simultaneously decrease the generation of fermentation inhibitors. Therefore, it is essential to understand the degradation mechanism of xylan during hot-water pretreatment. We analyzed the hydrothermal degradation products of xylan and xylose under different conditions. Results showed that furfural and formic acid formed from xylose reached a maximum value of 32.56 % and 35.14 %, respectively. By increasing the initial pH of the xylan solution, the furfural concentration can be reduced effectively to 2% and the formation of formic acid was preferred under alkaline conditions. On this basis, we proposed a new hydrothermal degradation pathway of xylan in alkaline solution. The in-depth understanding of xlyan degradation during hot water pre-treatment will be beneficial for improving the efficiency of biofuel production.

Degradation Techniques of Hemicellulose Fraction from Biomass Feedstock for Optimum Xylose Production: A Review

The utilization of xylose, one of the C-5 sugars released from hemicellulose deconstruction of biomass feedstock, is intensively studied, in particular for producing valuable fermentation products. More xylose in the initial fermentation broth is highly expected to induce more final products formed. The techniques for lignocellulose fractionation to obtain the expected xylose amount are widely developed. Nevertheless, these are slightly different from the methods for glucose production. The production of glucose is initiated by delignification to facilitate enzyme accessibility in degrading cellulose to glucose. The delignification process, however, requires harsh conditions causing further decomposition of xylose corresponded to the formation of inhibitors detected in the spent liquor of pretreatment. Hence, xylose recovery needs particular treatments and the corresponding condition. Several strategies offered attributed to xylose production involved in conventional treatment using dilute acid and other promising methods such as an autohydrolysis, solid acids, steam explosion, inorganic salt, and ionic liquid. Post-treatments by enzymatic or acid hydrolysis of xylooligosaccharides dissolved in the liquid fraction are also considered to enhance xylose recovery. This review provides such techniques and the challenges frequently arising during xylose yield optimization performed. Each method has specific benefits and drawbacks that are also addressed in this paper.

Sugars production from corn stover after pretreated by nitric acid for biogas fermentation process

In the present work, corn stover samples were hydrolysed with 0.6% nitric acid at 135–165 °C. The concentrations of hydrolysate—sugars (xylose, glucose, and arabinose), acetic acid and furfural were determined. The kinetic parameters of the Saeman model for predicting hydrolysis products were obtained. The optimal reaction condition (150 °C and 5 min) were determined by comparing the values of E (the efficiency of factors that affected hydrolysis). Under optimal conditions, the yield of glucose, xylose, and arabinose were 8.02 g/L, 16.59 g/L, and 3.28 g/L, respectively. At 150 °C with a nitric acid concentration of 0.6%, the reaction kinetic coefficient of xylose release (k1) and the reaction kinetic coefficient of xylose decomposition (k2) were 0.488 and 0.007 when the Saeman model was applied to the experimental data. The results showed that it was suitable to hydrolyze corn stover under the relatively low temperature with extremely low concentration of nitric acid as a catalyst. The hydrolyzate obtained by dilute acid pretreatment favors later acidic fermentation processes and biogas production. © 2019 American Institute of Chemical Engineers Environ Prog, 38:e13146, 2019

Effect of Acetic Acid Addition on Decomposition of Xylose in Supercritical Water

The supercritical water gasification of xylose, a model substrate for hemicellulose, was carried out at 400 and 450 °C and at a constant pressure of 25 MPa in the presence of acetic acid using a continuous flow reactor. More specifically, we aimed to compare the reaction rate constants of xylose decomposition in both the presence and absence of acetic acid. Upon the application of a residence time of 0.5–5 s, a xylose concentration of 1.5 wt %, and an acetic acid concentration of 1.5 wt %, we successfully elucidated the effect of acetic acid on each reaction within the reaction network for the first time. In the presence of acetic acid, the retro-aldol reactions and carbon gasification production (i.e., the radical reactions) were suppressed, while the acetic-acid-catalyzed dehydration of xylulose to furfural (i.e., an ionic reaction) was enhanced by 2 orders of magnitude. As such, reaction control through the addition of chemical species to either stabilize ions or react with radicals appears possible.

Development of dilute sulfuric acid pretreatment method for the enhancement of xylose fermentability

Abstract Dilute acid pretreatment of sorghum stalks was performed for the characteristic xylulosic ethanol production using Pichia stipitis . In this regard, various pretreatment parameters were studied for the maximum xylose production with minimized xylose decomposition. As a result, 89% of xylan conversion was attained along with 22 mg of xylose decomposition at 121 °C with 0.2 M sulfuric acid for 120 min. In addition to this, prehydrolyzate liquors were detoxified with calcium hydroxide [Ca(OH) 2 ] at different pH levels (i.e., 8.5–11.5) to investigate the fermentative inhibitors removal and their impact on xylulosic ethanol production. Consequently, the highest theoretical ethanol yield (91%) was achieved during the fermentation of prehydrolyzate detoxified at pH 11.5. Moreover, 0.46 g p /g s ethanol yield and 0.48 g/L/h ethanol productivity was achieved within 24 h incubation time of Pichia stipits NCIM 3498.

The Role of Various Chlorides on Xylose Conversion to Furfural: Experiments and Kinetic Modeling

AbstractIn this paper, the catalytic activity of thirteen different metal chlorides in aqueous solution for the conversion of xylose into furfural was studied in comparison with both the auto‐ and HCl‐catalyzed reactions. A maximum furfural yield of 60.3 mol % was reached with the addition of FeCl3 to the aqueous xylose solution. However, the catalytic efficiency of FeCl3 decreased on use of birch hydrolysate as a raw material, resulting in 43.5 mol % furfural yield. The obtained experimental results were incorporated in a kinetic modeling study. The assessed reaction rates for xylose dehydration to furfural and xylose decomposition to byproducts, in the presence of AlCl3 and CrCl3 are significantly higher than during acid‐catalyzed conversion. The logarithms of the reaction rates show a linear correlation with the ionization energy as well as with the acidity of the metal ions.

P-64 Intermediate products of xylose decomposition in sub- and supercritical water

P-64 Intermediate products of xylose decomposition in sub- and supercritical water

Efficient Hydrolysis of Polysaccharides in Bagasse by in Situ Synthesis of an Acidic Ionic Liquid after Pretreatment

A highly efficient hydrolytic method using an acidic ionic liquid is proposed: pretreatment of biomass with H2SO4; simple in situ synthesis of an acidic ionic liquid, 1-(1-butylsulfonic)-3-methylimidazolium hydrosulfate ([(HSO3)4C4C1im]HSO4), through addition of a zwitterion to the pretreated solution; and subsequent hydrolysis in the [(HSO3)4C4C1im]HSO4 solution at 100 °C under microwave heating. The high yields of glucose and xylose (around 80 and 100%, respectively) were attributed to the pretreatment by H2SO4 and the efficient catalytic activity of the [(HSO3)4C4C1im]HSO4. The high yields were comparable to the highest yields of acid hydrolysis at around 100 °C among previous literature, and the present method achieved more rapid hydrolysis. Decomposition of glucose and xylose was negligible because the reaction temperature was relatively mild. We also identified an electrodialysis method to separate [(HSO3)4C4C1im]HSO4 into H2SO4 and the zwitterion for reuse. Almost all of the H2SO4 (97%) was transfe...

Detailed Mechanism of Xylose Decomposition in Near-Critical and Supercritical Water

The aim of this study was to determine the complete reaction network of xylose decomposition in sub- and supercritical water, including small-molecule intermediates, such as organic acids, which are thought to be the final intermediates in the formation of gaseous products. Solutions of xylose in water were heated under sub- and supercritical conditions in the temperature range of 350–450 °C in a continuous reactor at a controlled pressure of 25 MPa. The intermediates found in the liquid phase were xylulose, furfural, retro-aldol products (glyceraldehyde, glycolaldehyde, dihydroxyacetone, and formaldehyde), and organic acids (acetic and formic acids). The reaction types involved were classified according to Arrhenius behavior: the ionic reaction (not showing Arrhenius behavior in the supercritical region) and the free-radical reaction (showing Arrhenius behavior in the supercritical region). Formic acid was the final intermediate before gasification, while acetic acid and formaldehyde were not gasified in...

Characterization of products evolved from supercritical water gasification of xylose (principal sugar in hemicellulose)

ABSTRACTThe catalyst decomposition of xylose (the principal sugar in hemicellulose) was examined in supercritical water for temperature from 400 to 600°C. Experiments were performed in the absence and presence of three main types of catalysts [alkali catalysts (K2CO3 and KOH) and metal impregnated activated carbons (Ni/AC) and (Ru/AC)] with a reaction time of 1h. Gasification yield reaches maximum values by using K2CO3 and KOH at the highest temperature of 600°C. The highest H2 yield and the highest CH4 yield were obtained by using Ru/AC and Ni/AC, respectively. Acetic acid and 5-methyl furfural were determined as the main aqueous products and reached maximum value by using Ru/AC.

Reaction Kinetics of Concentrated-Acid Hydrolysis for Cellulose and Hemicellulose and Effect of Crystallinity

Batch experiments for the hydrolysis of xylan and pure cellulose (Avicel) hydrolysis and the decomposition of xylose and glucose were performed at varying sulfuric acid concentrations in the range of 10 to 50 wt.% and varying temperatures in the range of 80 to 100 °C. Increasing the temperature and acid concentration hastened the hydrolysis and the sugar decomposition rates. The hydrolysis rate of Avicel was much slower than that of xylan because of its crystallinity. The kinetic parameters for the concentrated acid hydrolysis reaction were estimated for both glucose and xylose reaction paths. The effect of initial cellulose crystallinity on the acid hydrolysis rate was also investigated, such that the cellulose was treated with various concentrations of phosphoric acid. A dramatic reduction in the cellulose crystalline index was observed when the phosphoric acid concentration was in a narrow range around 80 wt.%. It was found that the hydrolysis rate significantly increased with the decrease in initial cellulose crystalline index.

Theoretical insight into the conversion of xylose to furfural in the gas phase and water.

Furfural (FF) is a valuable ring-containing organic compound in the decomposition of xylose and can be produced massively in hydrothermal condition. In this study, density functional theory (DFT) methods are employed to investigate the formation mechanism of FF from xylose and the solvent effects on FF formation. Kinetic and thermodynamic analyses indicate that xylulose could be the intermediate that leads to the formation of FF in the gas phase and water. The formation of xylulose is initiated by a six-membered transition state with energy barriers of 163.6 and 150.8 kJ mol(-1) in the gas phase and water, respectively. It is found that the strong stabilization of the reactants and transition states and the overall energy barriers of formation pathways of FF are reduced in water. The formation of FF is more thermodynamically favored in water compared with that in the gas phase. In addition, the inclusion of an explicit water molecule transforms four-membered transition states of ring-opening reaction, hydrogenation-cyclization, and dehydrations into less distorted six-membered transition states, which leads to the significant reduction of reaction barriers of FF formation.

Decomposition of Xylose in Sub- and Supercritical Water

The purpose of this study was to elucidate the decomposition characteristics of xylose, a model compound for hemicellulose, in subcritical and supercritical water. The experiment was carried out at temperatures of 300–450 °C, a pressure of 25 MPa, and a residence time of less than 7 s; xylose decomposed rapidly, but it was still detected at a temperature of 300 °C. Furfural and retro-aldol condensation products were found to be the major liquid intermediates. A reaction network was proposed and the kinetics parameters of all reactions were calculated on the basis of data fitting, assuming that all reactions are first-order. Finally, the temperature effect was used to classify the reactions as radical reactions (showing Arrhenius behavior in the supercritical region) or as ionic reactions (not showing Arrhenius behavior in the supercritical region).

3-4-2 Determination of kinetic rate of xylose decomposition in sub- and supercritical water

3-4-2 Determination of kinetic rate of xylose decomposition in sub- and supercritical water

Tandem mass spectrometric characterization of the conversion of xylose to furfural

Thermal decomposition of xylose into furfural under acidic conditions has been studied using tandem mass spectrometry. Two different Brønsted acids, maleic and sulfuric acids, were used to demonstrate that varying the Brønsted acid does not affect the mechanism of the reaction. Two selectively labeled xylose molecules, 1-13C and 5-13C-xyloses, were examined to determine which carbon atom is converted to the aldehyde carbon in furfural. This can be done by using tandem mass spectrometry since collision-activated dissociation (CAD) of protonated unlabeled furfural results in the loss of CO from the aldehyde moiety. The loss of a neutral molecule with MW of 29 Da (13CO) was observed for protonated furfural derived from 1-13C-labeled xylose while the loss of a neutral molecule with MW of 28 Da (CO) was observed for protonated furfural derived from 5-13C labeled xylose. These results support the hypothesis that the mechanism of formation of furfural under mildly hot acidic conditions involves an intramolecular rearrangement of protonated xylose into the pyranose form rather than into an open-chain form.

Deoxy-liquefaction of switchgrass in supercritical water with calcium formate as an in-situ hydrogen donor

Switchgrass was liquefied in supercritical water (SCW) using Ca(HCOO)2 as an in-situ source of hydrogen to enhance deoxygenation and the quality of the biocrude obtained. In SCW, Ca(HCOO)2 produces hydrogen via decomposition and hydrolysis reactions, and simultaneously switchgrass hydrolyzes to form oxygenated hydrocarbon compounds. Because of the close proximity of the newly-formed hydrogen and active hydrocarbons, hydrodeoxygenation occurred whereby some of the oxygenated compounds were upgraded by the removal of oxygen in the form of water. The analysis of the so-formed biocrude revealed the presence of benzene, polyaromatic hydrocarbons, and alkyl phenolics. The benzene formation is attributed to the hydrogenation of phenols but also due to the Diels-Alder alkene addition, followed by dehydrogenation. The addition of Ca(HCOO)2 doubled the yield of biocrude (10 wt%) and increased the heating value from 28 to 34 kJ/g. Formic acid amount increased in the aqueous biocrude due to the enhanced decomposition of xylose and glucose.

A novel mechanism and kinetic model to explain enhanced xylose yields from dilute sulfuric acid compared to hydrothermal pretreatment of corn stover

Pretreatment of corn stover in 0.5% sulfuric acid at 160°C for 40min realized a maximum monomeric plus oligomeric xylose yield of 93.1% compared to a maximum of only 71.5% for hydrothermal (no added mineral acid) pretreatment at 180°C for 30min. To explain differences in dilute acid and hydrothermal yields, a fast reacting xylan fraction (0.0889) was assumed to be able to directly form monomeric xylose while a slow reacting portion (0.9111) must first form oligomers during hydrothermal pretreatment. Two reactions to oligomers were proposed: reversible from fast reacting xylan and irreversible from slow reacting xylan. A kinetic model and its analytical solution simulated xylan removal data well for dilute acid and hydrothermal pretreatment of corn stover. These results suggested that autocatalytic reactions from xylan to furfural in hydrothermal pretreatment were controlled by oligomeric xylose decomposition, while acid–catalytic reactions in dilute acid pretreatment were controlled by monomeric xylose decomposition.

Reaction rates for supercritical water gasification of xylose in a micro-tubular reactor

Two kinetic models describing supercritical water gasification of xylose at reaction temperatures from 450 °C to 650 °C and 250 bar were developed. Reaction rate constants were non-linearly estimated from product yield vs. residence time data by sum of the least squares method. The xylose decomposition kinetic model uses a detailed reaction mechanism to predict liquid intermediate production and gasification rates, whereas the xylose gasification kinetic model uses a simplified reaction mechanism to better predict gas yield and gas composition at conditions where gasification is dominant. Both models assume the gas phase reactions are in thermodynamic equilibrium, however, the gasification kinetic model accounts for non-ideal interactions in the reacting fluid by incorporating the fugacity of the gas phase species into the model using the Peng–Robinson equation of state. Major gas products were CO 2, H 2, CH 4, CO, and C 2H 6. The highest measured concentration of liquid intermediate products were acetic and propanoic acid. Finally, an analysis of gas composition and gas yields for concentrated feed stocks is discussed based on the gasification kinetic model.

Multiscale Modeling of Hydrothermal Pretreatment: From Hemicellulose Hydrolysis to Biomass Size Optimization

In the general process for lignocellulosic bioconversion to ethanol, pretreatment has been viewed as the main cause of low process yield. Consequently, it is believed that obtaining a better understanding of the hydrothermal pretreatment method would pave the way for overall process optimization. This work focuses on developing a model for a pretreatment process that considers both the chemical and physical natures of the process. The chemical aspect of the process mainly involves the hydrolysis of hemicellulose to monomeric sugars. This paper considers all xylooligomers, with a degree of polymerization up to 30 as soluble, and that the bond breakage is a function of the position in the hemicellulose chain. Also, all of the bonds with the same position undergo breakage at the same time. The physical aspect of the process involves reducing the size of the feedstock as well as heating the feedstock to a desired temperature. For this aspect, we have developed a model to estimate the energy requirements for size reduction and proposed a method to find the optimum chip size for pretreatment. Finally, we performed two sets of sensitivity analysis: first, to compare the dynamic importance of xylooligomer size evolution versus xylose decomposition and, second, to compare the relative importance of kinetic parameters versus the length of particle on the overall process yield. Sensitivity analysis revealed that, at the beginning of the process, the chemical reaction is more important than diffusion; however, as the reaction proceeds, diffusion becomes the determinant factor. It was also shown that the solid-phase reaction rate, xylooligomer size evolution, and xylose decomposition are all determinant factors; therefore, any model for hemicellulose hydrolysis should take all three of these factors into account. © 2010 American Chemical Society.