Insights into the Kinetics and Reaction Network of Aluminum Chloride-Catalyzed Conversion of Glucose in NaCl–H2O/THF Biphasic System

Theoretical comparison of fructose with methylglucoside for the production of formate and levulinate catalyzed by Brønsted acids in a methanol solution

For the conversion of fructose/methylglucoside (MG) into both methyl formate (MF) and methyl levulinate (MLev), the C-source of formate [HCOO]- remains unclear at the molecular level. Herein, reaction mechanisms catalyzed by [CH3OH2]+ in a methanol solution were theoretically investigated at the PBE0/6-311++G(d,p) level. For the conversion of fructose into MF and MLev, the formate [HCOO]- comes from the C1-atom of fructose, in which the rate-determining step lies in the reaction of 5-hydroxymethylfurfural (HMF) with CH3OH to yield MF and MLev. The reaction of fructose with CH3OH kinetically tends to generate HMF intermediates rather than yield (MF + MLev). When MG is dissolved in a methanol solution, its O2, O3, and O4 atoms are closer to the first layer of the solvent than O1, O5, and O6 atoms. For the dehydration of MG with methanol into MF and MLev, the formate [HCOO]- stems from the dominant C1- and secondary C3-atoms of MG. Kinetically, MG is ready to yield (MF + MLev), whereas fructose can induce the reaction to remain at the HMF intermediate, inhibiting the further conversion of HMF with CH3OH into MF and MLev. If MG isomerizes into fructose, the reaction will be more preferable for yielding HMF rather than (MF + MLev).

Aluminum ion intercalation in mesoporous multilayer carbocatalysts promotes the conversion of glucose to 5-hydroxymethylfurfural

In this study, an efficient modification strategy was proposed by facile loading of trace aluminum ions and p-toluene sulfonic acid (p-TSA) in carbon materials to improve their catalytic activity. p-TSA is then proven to regulate the carbonization process and promote the formation of mesoporous and multilayer structures. The hexa-coordinated aluminum structure is characterized by 1H-27Al solid-state nuclear magnetic resonance (SSNMR) and X-ray photoelectron spectroscopy, which serves as the Lewis-Brønsted acid site in carbocatalysts. Accordingly, the resulting catalyst facilitates a yield of ∼70% for converting glucose to 5-hydroxymethylfurfural (HMF) with a maximum carbon balance of around 91.4% at 150 °C in 6 h. In situ NMR, electrospray ionization mass spectrometry and isotope labeling analysis reveal that the hexa-coordinated aluminum sites promote the isomerization of glucose, and the sulfonic groups facilitate the subsequent dehydration and rehydration of fructose and levoglucosan intermediates. Kinetic models further indicate the decreased energy barrier for glucose conversion over the Al3+/p-TSA intercalated carbocatalyst. This work provides a promising strategy for engineering waste-derived carbocatalysts toward effectively converting carbohydrates to precursors of biofuels and bioplastics.

Photocatalytic conversion of sugars to 5-hydroxymethylfurfural using aluminium(III) and fulvic acid

5-hydroxymethylfurfural (HMF) is a valuable and essential platform chemical for establishing a sustainable, eco-friendly fine-chemical and pharmaceutical industry based on biomass. The cost-effective production of HMF from abundant C6 sugars requires mild reaction temperatures and efficient catalysts from naturally abundant materials. Herein, we report how fulvic acid forms complexes with Al³⁺ ions that exhibit solar absorption and photocatalytic activity for glucose conversion to HMF in one-pot reaction, in good yield (~60%) and at moderate temperatures (80 °C). When using representative components of fulvic acid, catechol and pyrogallol as ligands, 70 and 67% HMF yields are achieved, respectively, at 70 °C. Al³⁺ ions are not recognised as effective photocatalysts; however, complexing them with fulvic acid components as light antennas can create new functionality. This mechanism offers prospects for new green photocatalytic systems to synthesise a range of substances that have not previously been considered.

Fabrication of lignin-derived mesoporous carbon/magnesium oxide composites for microwave-assisted isomerization of glucose in water

A series of mesoporous carbon/magnesium oxide composites (LDMC@MgO-x) with different Mg doping ratios were synthesized by using alkali lignin as the carbon source, potassium chloride as the salt template and magnesium nitrate as the catalytic site precursor, respectively. The BET, FTIR, SEM, and TEM analyses indicated that the as-prepared LDMC@MgO-x possessed a unique hierarchical porous structure with high specific surface area, rich functional groups, and uniformly distributed MgO nanoparticles. Among them, LDMC@MgO-20%, as an optimized base catalyst, could realize effective isomerization of glucose with a maximum fructose yield of 34.4 % in water at 130 °C for only 5 min under microwave assistance. In addition, the activation energy of glucose isomerization catalyzed by LDMC@MgO-20% was estimated to be about 43.6 kJ·mol^-1, which was lower than that of most Lewis acid-catalyzed systems.

Transformation of bread waste into 2,5-furandimethanol via an efficient chemoenzymatic approach in a benign reaction system

Via combination catalysis with deep eutectic solvent lactic acid:betaine (chemocatalyst) and HMFOMUT cell (biocatalyst: E. coli HMFOMUT whole-cell), one-pot manufacture of 2,5-furandimethanol from waste bioresource was constructed in a chemoenzymatic approach. With bread waste (50 g/L) as substrate, the 5-hydroxymethylfuran yield reached 44.2 Cmol% (based on bread waste) by lactic acid:betaine (15 wt%) at 180 °C for 15 min. With glucose as co-substrate, HMFOMUT could transform 5-hydroxymethylfurfural (150 mM) to 2,5-furandimethanol (84.5 % yield) after 1 day at 37 °C and pH 7.0. In lactic acid:betaine-H₂O, HMFOMUT effectively converted bread-derived 5-hydroxymethylfurfural into 2,5-furandimethanol in a productivity of 700 kg 2,5-furandimethanol per kg 5-hydroxymethylfurfural (230 kg 2,5-furandimethanol per kg bread). In an eco-friendly lactic acid:betaine system, an effective one-pot chemoenzymatic strategy was firstly developed to convert bread waste into 2,5-furandimethanol, which would reduce the operation cost and has potential application value for valorizing waste food bioresource into value-added furan.

Preparation of 5-(Acyloxymethyl)furfurals from Carbohydrates Using Zinc Chloride/Acetic Acid Catalyst System and Their Synthetic Value Addition

5-(Acyloxymethyl)furfurals (AMFs) have received considerable attention as hydrophobic, stable, and halogen-free congeners of 5-(hydroxymethyl)furfural (HMF) for synthesizing biofuels and biochemicals. In this work, AMFs have been prepared directly from carbohydrates in satisfactory yields using the combination of ZnCl₂ as the Lewis acid catalyst and carboxylic acid as the Brønsted acid catalyst. The process was initially optimized for 5-(acetoxymethyl)furfural (AcMF) and then extended to producing other AMFs. The effects of reaction temperature, duration, loading of the substrate, and dosage of ZnCl₂ on AcMF yield were explored. Fructose and glucose provided AcMF in 80% and 60% isolated yield, respectively, under optimized parameters (5 wt % substrate, AcOH, 4 equiv ZnCl₂, 100 °C, 6 h). Finally, AcMF was converted into high-value chemicals, such as 5-(hydroxymethyl)furfural, 2,5-bis(hydroxymethyl)furan, 2,5-diformylfuran, levulinic acid, and 2,5-furandicarboxylic acid in satisfactory yields to demonstrate the synthetic versatility of AMFs as carbohydrate-derived renewable chemical platforms.

Numerical Studies on Cellulose Hydrolysis in Organic-Liquid-Solid Phase Systems with a Liquid Membrane Catalysis Model

The catalytic hydrolysis of cellulose to produce 5-hydroxymethylfurfural (HMF) is a powerful means of biomass resources. The current efficient hydrolysis of cellulose to obtain HMF is dominated by multiphase reaction systems. However, there is still a lack of studies on the synergistic mechanisms and component transport between the various processes of cellulose hydrolysis in a complex multiphase system. In this paper, a liquid membrane catalytic model was developed to simulate the hydrolysis of cellulose and its further reactions, including the adsorption of the liquid membrane on cellulose particles, the consumption of cellulose solid particles, the complex chemical reactions in the liquid membrane, and the transfer of HMF at the phase interface. The simulations show the synergistic effect between cellulose hydrolysis and multiphase mass transfer. We defined an indicator () to characterize the sensitivity of HMF yield to the initial liquid membrane thickness at different reaction stages. decreased gradually when the glucose conversion increased from 0 to 80%, and increased with the thickening of the initial liquid membrane thickness. It was shown that the thickening of the initial liquid membrane thickness promoted the HMF yield under the same glucose conversion. In summary, our results reveal the mechanism of the interaction between multiple physicochemical processes of the cellulose liquid membrane reaction system.

Soluble and reusable polymer-based catalysts with Brønsted and Lewis acidity for the one-pot synthesis of hydroxymethylfurfural from glucose

One-pot synthesis of hydroxymethylfurfural from glucose using polymer-based catalysts with Brønsted and Lewis acidity.

Probing the effects of fructose concentration on the evolution of humins during fructose dehydration

A universal understanding on the concentration-aggravated evolution of humins during fructose dehydration has been demonstrated, wherein difructose anhydrides act as the key intermediates for both 5-hydroxymethylfurfural and humin formations.

Evolution of catalytically active species in paired PdCl2-CuCl2/[BMim]Cl for hydrolysis of β-1,4-glycosidic bonds

In this work, we identified the prevailing catalytically active species evolved from paired PdCl2-CuCl2 in 1-butyl-3-methylimidazolium chloride ([BMim]Cl) that displayed dramatic synergism between the two metal chlorides in catalyzing the...

Continuous hydrothermal furfural production from xylose in a microreactor with dual-acid catalysts

An effective continuous furfural production from xylose in a microreactor over dual-acid catalysts was proposed. In this work, furfural was synthesized in an organic solvent-free system using formic acid and aluminum chloride as catalyst. The role of these catalysts in the consecutive reactions was examined and verified. The influence of operating conditions including xylose concentration, reaction temperature, residence time, total catalyst concentration, and catalyst ratio on the yield of furfural was investigated and optimized. The furfural yield of 92.2% was achieved at the reaction temperature of 180 °C, residence time of 15 min, catalyst molar ratio of 1 : 1, xylose concentration of 1 g L⁻¹, and total catalyst concentration of 16 mM. The superior production performance of our process was highlighted in terms of the low catalyst concentration and short residence time compared to those of other systems based on the literature. In addition, a continuous in situ catalyst removal (purification) was demonstrated, providing further insights into the practical development of continuous furfural production.

An effective continuous furfural production from xylose in a microreactor over dual-acid catalysts was proposed. In this work, furfural was synthesized in an organic solvent-free system using formic acid and aluminum chloride as catalyst.

Humins with Efficient Electromagnetic Wave Absorption: A By-Product of Furfural Conversion to Isopropyl Levulinate via a Tandem Catalytic Reaction in One-Pot

Both one-pot catalytic conversion of furfural (FAL) to isopropyl levulinate (PL) and carbonization of by-product (humins) for electromagnetic wave absorption are discussed, which provides inspiration that humins can be applied to electromagnetic wave absorption. In the former, phosphotungstic acid (PW) is employed as a homogeneous catalyst to convert FAL to PL via a tandem reaction in one pot, with the formation of a vast amount of humins. With FAL and various intermediates as substrates, it was found that humins was a polymerization product of FAL, furfuryl alcohol (FOL) and furfuryl ester (FE) with furan rings. In addition, the in situ attenuated total reflection infrared (ATR-IR) spectra also provided a basis for the proposed reaction route. In the latter, with the humins as raw material, P species and WO₃ doped nano-porous carbon (Humins-700) platform formed after high-temperature annealing is used for electromagnetic wave absorption and manifests desirable absorption performance. The minimum reflection loss (RL_min ) value is -47.3 dB at 13.0 GHz with a thickness of 2.0 mm and the effective absorption bandwidth reaches 4.5 GHz (11.2-5.7 GHz).

Catalytic mechanism for the isomerization of glucose into fructose over an aluminium-MCM-41 framework

Al-Containing MCM-41 catalysts exhibit good catalytic activity toward glucose-to-fructose isomerization.

Controlling the Reaction Networks for Efficient Conversion of Glucose into 5-Hydroxymethylfurfural

Biomass-derived hexose constitutes the main component of lignocellulosic biomass for producing value-added chemicals and biofuels. However, the reaction network of hexose is complicated, which makes the highly selective synthesis of one particular product challenging in biorefinery. This Review focuses on the selective production of 5-hydroxymethylfurfural (HMF) from glucose on account of its potential significance as an important platform molecule. The complex reaction network involved in glucose-to-HMF transformations is briefly summarized. Special emphasis is placed on analyzing the complexities of feedstocks, intermediates, (side-) products, catalysts, solvents, and their impacts on the reaction network. The strategies and representative examples for adjusting the reaction pathway toward HMF by developing multifunctional catalysts and promoters, taking advantage of solvent effects and process intensification, and synergizing all measures are comprehensively discussed. An outlook is provided to highlight the challenges and opportunities faced in this promising field. It is expected to provide guidance to design practical catalytic processes for advancing HMF biorefinery.

An integrated effluent free process for the production of 5-hydroxymethyl furfural (HMF), levulinic acid (LA) and KNS-ML from aqueous seaweed extract

This paper demonstrates an integrated zero liquid discharge (ZLD) process for time-dependent recovery of 5-hydroxymethyl furfural (HMF), levulinic acid (LA) and potassium, nitrogen and sulphur rich mother liquor (KNS-ML) - manure from agar/agarose containing seaweed aqueous solution using transition metal-free KHSO₄ as an eco-friendly and reusable catalyst. The selectivity of HMF is higher at 115 °C in 3 h and favorable to LA in 6 h in autoclave conditions. The proposed concept could be fine-tuned for the selective production of 5-HMF (up to 91% yield) or levulinic acid (56% yield) in the presence of the KHSO₄ catalyst. We have also achieved recyclability of KHSO₄ up to nine (09) cycles and the gram-scale reaction has been demonstrated. The (KNS-ML) obtained after nine cycles followed by neutralization with ammonia solution utilized for manure makes the process zero-liquid discharge and more cost-effective. The efficacy of the KNS-ML after nine cycles has been tested on groundnut plants.

The effect of sodium chloride concentration on the mutarotation and structure of d-xylose in water: Experimental and theoretical investigation

The effect of NaCl concentration on the structure of d-xylose in H₂O was studied. It was found that NaCl could prolong the equilibrium time between the two main configurations, α-xylopyranose and β-xylopyranose. The proportion of α-xylopyranose was slightly increased in NaCl-H₂O solution than that in H₂O, and the alteration of NaCl on α-xylopyranose and β-xylopyranose was different. Theoretical calculations demonstrated that NaCl was more favorable to stabilize the structure of α-xylopyranose. Na⁺ had attraction with O atoms (α: O₆; β: O₆ and O₁), with the outflow of electron from C atom to O atom on the C₁-O₆ bond, which was beneficial to the transformation between chain form and pyran forms. Cl^- had interaction with the hydroxyl groups of xylose. The interaction between xylose and NaCl, was also evidenced by the variation of ³⁵Cl and ²³Na NMR spectra. The findings could provide guidance for understanding the conformational change and design of xylose conversion ways. It also provided valuable information for making efficient use of hemicellulose.

The Roles of H2O/Tetrahydrofuran System in Lignocellulose Valorization

Lignocellulosic biomass as a potential alternative to fossil resource for the production of valuable chemicals and fuels has attracted substantial attention, while reducing the recalcitrance of lignocellulosic biomass is still challenging due to the complex and cross-linking structure of biomass. Solvent system plays important roles in the pretreatment of lignocellulose, enabling the transformation of solid biomass to liquid fluid with better mass and heat transfer, as well as in the selective formation of target products. In particular, H2O/tetrahydrofuran (H2O/THF) system has recently been widely applied in lignocellulose valorization, which has been proved to exhibit outstanding efficiency for the conversion of lignocellulose, solubilization of the intermediates and products, and shifting reaction equilibrium, thereby significantly improving the yield and selectivity of target products, as well as the full utilization of lignocellulose. In addition, THF shows low toxicity, and is known as a renewable solvent which can be produced from bio-derived chemicals. Herein, this review concentrates on the advances of H2O/THF system in lignocellulose valorization in recent years. Several aspects relative to the roles of H2O/THF system are discussed as follows: the pretreatment of lignin, conversion of hemicellulose and cellulose components in lignocelluloses, and the promoting formation of valuable chemicals like furfural, 5-hydroxymethyl furfural (HMF), levulinic acid, and so on, as well as the inhibiting role in humins formation. This review might provide useful information for the design of effective solvent system in full utilization of lignocellulosic biomass.

Solvent Effects on Degradative Condensation Side Reactions of Fructose in Its Initial Conversion to 5-Hydroxymethylfurfural

The degradative condensation of hexose, which originates from the C-C cleavage of hexose and condensation of degraded hexose fragment, is one of the possible reaction pathways for the formation of humins in hexose dehydration to 5-hydroxymethylfurfural (HMF). Herein, the impacts of several polar aprotic solvents on the degradative condensation of fructose to small-molecule carboxylic acids and oligomers (possible precursors of humins) are reported. In particular, a close relationship between the tautomeric distribution of fructose in solvents and the mechanism of degradative condensation is demonstrated. Typically, α-fructofuranose in 1,4-dioxane and acyclic open-chain fructose in THF favor the conversion of fructose to formic acid and oligomers; α-fructopyranose in γ-valerolactone or N-methylpyrrolidone favors levulinic acid and oligomers, whereas β-fructopyranose in 4-methyl-2-pentanone favors acetic acid and corresponding oligomers. This close correlation highlights a general understanding of the solvent-controlled formation of oligomers, which represents an important step toward the rational design of effective solvent systems for HMF production.

Catalytic mechanisms of oxygen-containing groups over vanadium active sites in an Al-MCM-41 framework for production of 2,5-diformylfuran from 5-hydroxymethylfurfural

In the V-doped Al-MCM-41 framework, the [V-1] active site with a hydroxyl group displays better catalytic activity than the [V-0] active site without a hydroxyl group toward the oxidation of 5-hydroxymethylfurfural to 2,5-diformylfuran.

A Simple and Efficient Device and Method for Measuring the Kinetics of Gas-Producing Reactions

We present a new device for quantifying gases or gas mixtures based on the simple principle of bubble counting. With this device, we can follow reaction kinetics down to volume step sizes of 8–12 μL. This enables the accurate determination of both time and size of these gas quanta, giving a very detailed kinetic analysis. We demonstrate this method and device using ammonia borane hydrolysis as a model reaction, obtaining Arrhenius plots with over 300 data points from a single experiment. Our device not only saves time and avoids frustration, but also offers more insight into reaction kinetics and mechanistic studies. Moreover, its simplicity and low cost open opportunities for many lab applications.

Hydrothermal Dehydration of Monosaccharides Promoted by Seawater: Fundamentals on the Catalytic Role of Inorganic Salts

In biorefining, the conversion of carbohydrates under subcritical water conditions is a field of extensive studies. In particular, the hydrothermal decomposition of benchmark C6- and C5-monosaccharides, i.e., D-glucose and D-xylose, into furanics and/or organic acids is fully considered. Herein, we propose to establish the fundamentals of the decomposition of D-glucose and D-xylose under subcritical water conditions in the presence of specific salts (i.e., NaCl and KI) and in seawater. Our results demonstrated that the introduction of inorganic salts was found to modify sugars dehydration yields. Different NaCl concentrations from 0.21 to 1.63 mol L-1 promoted the conversion of D-xylose to 2-furfural (2-F) from 28 to 44% (molar yield). NaCl also improved 5-hydroxymethylfurfural (5-HMF) generation from D-glucose as well as rehydration of 5-HMF to levulinic and formic acid. KI favored other pathways toward formic acid production from D-glucose, reaching 20% in the upper concentration. Compared to a solution of equivalent NaCl concentration, seawater enhanced selectivity toward lactic acid which was raised by 10% for both monosaccharides, and sugars conversion, especially for D-glucose whose conversion was increased by 20%. 5-HMF molar yield around 30% were achieved from D-glucose in seawater at 211°C and 20 bars after 15 min.

Effect of metal chlorides on glucose mutarotation and possible implications on humin formation

An in situ Raman spectroscopic kinetic study of the glucose mutarotation reaction in the presence of Lewis acids is presented herein. The effect of Lewis acids on humin formation reactions is also discussed.

Adjusting the acidity of sulfonated organocatalyst for the one-pot production of 5-ethoxymethylfurfural from fructose

A novel sulfonated organocatalyst bearing stable double H-bonds shows high catalytic performance and good reusability for the tandem production of 5-ethoxymethylfurfural (EMF), a biofuel candidate, from biomass-derived fructose.

Liquid membrane catalytic model of hydrolyzing cellulose into 5-hydroxymethylfurfural based on the lattice Boltzmann method

Conversion of cellulose to 5-hydroxymethylfurfural (HMF) is an important means of biomass utilization.

New Understandings of the Relationship and Initial Formation Mechanism for Pseudo-lignin, Humins, and Acid-Induced Hydrothermal Carbon

The generation of pseudo-lignin as byproduct during the lignocellulose acidic pretreatment has been proposed for many years. However, the detailed formation mechanism is still unclear. Moreover, there is a lack of understanding in the initial reaction during the formation of humins (byproducts in furfural production) and acid-induced hydrothermal carbon (carbon material). In this work, the initial formation of these three substances were investigated. We first found the common feature of their formation process was that carbohydrate-hydrolyzed compounds could form black polymers by condensing in acidic media, but the difference was dependent on the reaction degree. Furthermore, the results revealed that oxidation was an accelerator for condensations during producing black polymers because oxidized compounds could enhance the acidity of the reaction system. However, condensations of oxidized compounds were more difficult to proceed. Meanwhile, during the initial stage, the dominating pathway was that furfural condensed with itself and isomerized xylose via aldol-condensation.