5-Hydroxymethylfurfural production from sugars and cellulose in acid- and base-catalyzed conditions under hot compressed water

Efficient Conversion of Glucose to Hydroxymethylfurfural: One-pot Brønsted Base and Acid Promoted Selective Isomerization and Dehydration

Development of elegant, selective, and efficient strategies for the production of value-added platform chemicals from renewable feedstocks are in high demand to achieve the future needs and sustainable goals. In this context, an efficient acid-promoted synthesis of highly valuable hydroxymethylfurfural (HMF) has been demonstrated from glucose, a major constituent of lignocellulosic biomass. The major challenge in the conversion of glucose to HMF is the selective isomerization of glucose to ketose, which in the present work has been successfully addressed through the amine-mediated rearrangement of glucose to aminofructose under Amadori rearrangement. Importantly, subsequent dehydration step affords HMF and regenerates the amine employed in the first step, which could be readily recovered. In addition, scale-up and successful integration into one-pot synthesis of HMF proves the efficiency and applicability of the present transformation in large scale application. In addition, the method was also successfully extended to other monosaccharides and disaccharides to produce HMF.

Reaction Kinetics of Levulinic Acid Synthesis from Glucose Using Bronsted Acid Catalyst

Glucose is one of the primary derivative products from lignocellulosic biomass, which is abundantly available. Glucose has excellent potential to be converted into valuable compounds such as ethanol, sorbitol, gluconic acid, and levulinic acid (LA). Levulinic acid is an exceptionally promising green platform chemical. It comprises two functional groups, ketone and carboxylate, acting as highly reactive electrophiles for a nucleophilic attack. Therefore, it has extensive applications, including fuel additives, raw materials for the pharmaceutical industry, and cosmetics. This study reports the reaction kinetics of LA synthesis from glucose catalyzed by hydrochloric acid (HCl), a Bronsted acid, that was carried out under a wide range of operating conditions; i.e. the temperature of 140–180 °C, catalyst concentration of 0.5–1.5 M, and initial glucose concentration of 0.1–0.5 M. The highest LA yield of 48.34 % was able to be obtained from an initial glucose concentration of 0.1 M and by using 1 M HCl at 180 °C. The experimental results show that the Bronsted acid-catalyzed reaction pathway consists of glucose decomposition to levoglucosan (LG), conversion of LG to 5-hydroxymethylfurfural (HMF), and rehydration of HMF to LA. The experimental data yields a good fitting by assuming a first-order reaction model. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0). 

Development of a continuous-flow tubular reactor for synthesis of 5-hydroxymethylfurfural from fructose using heterogeneous solid acid catalysts in biphasic reaction medium

5-Hydroxymethylfurfural (5-HMF) is an important biomass-derived platform chemical used to produce polymers, biofuels, and other valuable industrial chemicals.

Effect of substituents and promoters on the Diels-Alder cycloaddition reaction in the biorenewable synthesis of trimellitic acid

An efficient route to produce oxanorbornene, a precursor for the production of bio-based trimellitic acid (TMLA) via the Diels-Alder (DA) reaction of biomass-derived dienes and dienophiles has been proposed by utilizing density functional theory (DFT) simulations. It has been suggested that DA reaction of dienes such as 5-hydroxymethyl furfural (HMF), 2,5-dimethylfuran (DMF), furan dicarboxylic acid (FDCA) and biomass-derived dienophiles (ethylene derivatives e.g., acrolein, acrylic acid, etc.) leads to the formation of an intermediate product oxanorbornene, a precursor for the production of TMLA. The activation barriers for the DA reaction were correlated to the type of substituent present on the dienes and dienophiles. Among the dienophiles, acrolein was found to be the best candidate showing a low activation energy (<40 kJ mol^-1) for the cycloaddition reaction with dienes DMF, HMF and hydroxy methyl furoic acid (HMFA). The FMO gap and (IP_diene + EA_dienophile)/2 were both suggested to be suitable descriptors for the DA reaction of electron-rich diene and electron-deficient dienophile. Further solvents did not have a significant effect on the activation barrier for DA reaction. In contrast, the presence of a Lewis acid was seen to lower the activation barrier due to the reduction in the FMO gap.

Mechanistic aspects of saccharide dehydration to furan derivatives for reaction media design

The conversion of abundant hexoses (e.g. glucose, mannose and galactose) and pentoses (e.g. xylose and arabinose) to 5-hydroxymethylfurfural (5-HMF) and 2-furfural (2-F) is subject to intensive research in the hope of achieving competitive production of diverse materials from renewable resources. However, the abundance of literature on this topic as well as the limited number of studies systematically comparing numerous monosaccharides hinder progress tracking. Herein, we compare and rationalize reactivities of different ketoses and aldoses. Dehydration mechanisms of both monosaccharide types are reviewed regarding the existing experimental evidence. Ketose transformation to furan derivatives likely proceeds through cyclic intermediates and is hindered by side-reactions such as isomerization, retro-aldol reactions and polymerization. Different strategies can improve furan derivative synthesis from ketoses: limiting the presence of water, improving the dehydration rate, protecting 5-HMF and 2-F reactive moieties with derivatization or solvent interactions and extracting 5-HMF and 2-F from the reaction medium. In contrast to ketoses, aldose conversion to furan derivatives is not favored compared to polymerization reactions because it involves their isomerization or a ring contraction. Enhancing aldose isomerization is possible with metal catalysts (e.g. CrCl3) promoting a hydride shift mechanism or with boric/boronic acids promoting an enediol mechanism. This catalysis is however far more challenging than ketose dehydration because catalyst activity depends on numerous factors: Brønsted acidity of the medium, catalyst ligands, catalyst affinity for monosaccharides and their accessibility to several chemical species simultaneously. Those aspects are methodically addressed to support the design of new monosaccharide dehydration systems.

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.

Selective Microwave-Assisted Pyrolysis of Cellulose towards Levoglucosenone with Clay Catalysts

Levoglucosenone (anhydrosugar) is one of the most promising chemical platforms derived from the pyrolysis of biomass. It is a chiral building block for pharmaceuticals as well as an intermediate in the production of solvents and polymers. Therefore, the development of cost-efficient, low-energy production methods is vital for a future sustainable biorefinery. Here, a novel, green approach to the production of levoglucosenone was developed by using a microwave (MW)-assisted pyrolysis of cellulose in the presence of readily available clays. It was shown that natural and pillared clays in the presence of MW irradiation significantly increase the yield of levoglucosenone from cellulose. Both the water content and the presence of acid centres are critical characteristics that influence the yield and distribution of catalysed products. A unique experiment was designed by using a synergetic effect between different types of catalysts, which enhanced the levoglucosenone yield to 12.3 wt % with 63 % purity.

Dilute acid hydrolysis of spoiled wheat grains: Analysis of chemical, rheological and spectral characteristics

In this work, hydrolysis of spoiled wheat grains using dilute acid (5, 10%; 1 N HCl) was investigated and the effect of hydrolysis conditions on reducing sugars, soluble proteins, rheology and infrared spectra of the hydrolysates was determined. Hydrolysis with 10% acid concentration released more quantities of reducing sugar (16.47 mg/mL) at shorter hydrolysis times whereas 5% acid concentration produced higher protein content (28.74 mg/mL) for similar durations. Flow characteristics demonstrated an increased apparent viscosity of the hydrolysates retrieved after 4.5 h of hydrolysis possibly due to breakdown of hemicelluloses and lignin into sugars. Infrared spectroscopy showed release of carbonates after 1.5 h and 5.5 h of hydrolysis perhaps due to oxidation of lignin or a reaction between acid and sugars. The study highlights that acid hydrolysis would be a rapid and cost effective approach to produce fermentable hydrolysates for bio-processing industry applications while generating an avenue for waste grain utilization.

Synthesis of 5-hydroxymethyl furfural from cellulose via a two-step process in polar aprotic solvent

The synthesis of 5-hydroxymethyl furfural (HMF) from cellulose via a two-step process was investigated. To optimize reaction conditions, the separate conversion of cellulose and glucose was first performed in tetrahydrofuran (THF) and N, N-dimethylformamide (DMF) via a one-step process using hosphotungstic acid (PHA) as catalyst. The direct conversion of cellulose to HMF was then performed via the two-step process. The first step and the second step were carried out in THF and the mixture solvent composed of THF/DMF, respectively. Cellulose was converted to HMF and glucose in the first step in THF. Both of cellulose and the as-formed glucose were then converted to HMF in the second step. The conversion of cellulose to HMF and glucose were significantly improved by the two-step process, and the total yield of HMF and glucose was elevated from 52.1 to 97.0%. A possible mechanism for the formation of HMF from cellulose via the two-step process was also proposed.

The Influence of Different Strategies for the Saccharification of the Banana Plant Pseudostem and the Detoxification of Concentrated Broth on Bioethanol Production

Pseudostem of the Musa cavendishii banana plant was submitted to chemical pretreatments with acid (H₂SO₄ 2%, 120 °C, 15 min) and with alkali (NaOH 3%, 120 °C, 15 min), saccharified by commercial enzymes Novozymes® (Cellic CTec2 and HTec2). The influences of the pretreatments on the degradation of the lignin, cellulose and hemicellulose, porosity of the surface, particle crystallinity, and yield in reducing sugars after saccharification (Y _RS), were established. Different concentrations of biomass (70 and 100 g/L in dry matter (dm)), with different physical differences (dry granulated, crushed wet bagasse, and whole pseudostem), were used. The broth with the highest Y _RS among the different strategies tested was evaporated until the concentration of reducing sugars (RS) was to the order of 100 g/L and fermented, with and without prior detoxification with active carbon. Fermentation was carried out in Erlenmeyer flasks, at 30 °C, initial pH 5.0, and 120 rpm. In comparison to the biomass without chemical pretreatment and to the biomass pretreated with NaOH, the acid pretreatment of 70 g/L of dry granulated biomass enabled greater digestion of hemicellulose, lower index of cellulose crystallinity, and higher Y _RS (45.8 ± 0.7%). The RS increase in fermentation broth to 100 g/L, with posterior detoxification, presented higher productivity ethanol (Q _P = 1.44 ± 0.02 g/L/h) with ethanol yield (Y _P/RS) of 0.41 ± 0.02 g/g. The value of Q _P was to the order of 75% higher than Q _P obtained with the same broth without prior detoxification.

Multicolor Functional Carbon Dots via One-Step Refluxing Synthesis

Carbon dots are admirable fluorescent nanomaterials due to their low cost, high photostability, excellent biocompatibility, and environmental friendliness. Most conventional carbon dot fabrication approaches produce single-colored fluorescent material in the preparation process; different methods are therefore required to synthesize distinct carbon dots for specific optical applications. In this study, carbon dots carrying different emission colors are prepared through a one-step refluxing process. The emission of these materials can be well-tuned by sodium hydroxide content in the precursor solution. The carbon dots produced are used as sensing probes based on the spectrofluorometric inner filter effect for target molecule detection. Three sensing categories that combine carbon dots and inner filter effect are demonstrated, including direct, metal nanoparticle-assisted, and enzymatic reaction-supported detection. Caffeine, melamine, and fenitrothion are selected as targets to demonstrate the strategies, respectively. These multifunctional carbon dot-based sensors achieve comparable sensitivity toward analytes with a much more convenient preparation route.

Heterogeneous Catalytic Conversion of Biobased Chemicals into Liquid Fuels in the Aqueous Phase

Different biobased chemicals are produced during the conversion of biomass into fuels through various feasible technologies (e.g., hydrolysis, hydrothermal liquefaction, and pyrolysis). The challenge of transforming these biobased chemicals with high hydrophilicity is ascribed to the high water content of the feedstock and the inevitable formation of water. Therefore, aqueous-phase processing is an interesting technology for the heterogeneous catalytic conversion of biobased chemicals. Different reactions, such as dehydration, isomerization, aldol condensation, ketonization, and hydrogenation, are applied for the conversion of sugars, furfural/hydroxymethylfurfural, acids, phenolics, and so on over heterogeneous catalysts. The activity, stability, and reusability of the heterogeneous catalysts in water are summarized, and deactivation processes and several strategies are introduced to improve the stability of heterogeneous catalysts in the aqueous phase.

Pretreatment and conversion of lignocellulose biomass into valuable chemicals

Lignocellulose biomass can be utilized in many sectors of industry such as energy, chemical, and transportation. However, pretreatment is needed to break down the intricate bonding before converting it into wanted product.

Glucose transformation to 5-hydroxymethylfurfural in acidic ionic liquid: A quantum mechanical study

Isomerization and transformation of glucose and fructose to 5-hydroxymethylfurfural (HMF) in both ionic liquids (ILs) and water has been studied by the reference interaction site model self-consistent field spatial electron density distribution (RISM-SCF-SEDD) method coupled with ab initio electronic structure theory, namely coupled cluster single, double, and perturbative triple excitation (CCSD(T)). Glucose isomerization to fructose has been investigated via cyclic and open chain mechanisms. In water, the calculations support the cyclic mechanism of glucose isomerization; with the predicted activation free energy is 23.8 kcal mol(-1) at experimental condition. Conversely, open ring mechanism is more favorable in ILs with the energy barrier is 32.4 kcal mol(-1) . Moreover, the transformation of fructose into HMF via cyclic mechanism is reasonable; the calculated activation barriers are 16.0 and 21.5 kcal mol(-1) in aqueous and ILs solutions, respectively. The solvent effects of ILs could be explained by the decomposition of free energies and radial distribution functions of solute-solvent that are produced by RISM-SCF-SEDD.

Reaction Mechanism for m-Xylene Oxidation in the Claus Process by Sulfur Dioxide

In the Claus process, the presence of aromatic contaminants such benzene, toluene, and xylenes (BTX), in the H2S feed stream has a detrimental effect on catalytic reactors, where BTX form soot particles and clog and deactivate the catalysts. Among BTX, xylenes are proven to be most damaging contaminant for catalysts. BTX oxidation in the Claus furnace, before they enter catalyst beds, provides a solution to this problem. A reaction kinetics study on m-xylene oxidation by SO2, an oxidant present in Claus furnace, is presented. The density functional theory is used to study the formation of m-xylene radicals (3-methylbenzyl, 2,6-dimethylphenyl, 2,4-dimethylphenyl, and 3,5-dimethylphenyl) through H-abstraction and their oxidation by SO2. The mechanism begins with SO2 addition on the radicals through an O-atom rather than the S-atom with the release of 180.0-183.1 kJ/mol of reaction energies. This exothermic reaction involves energy barriers in the range 3.9-5.2 kJ/mol for several m-xylene radicals. Thereafter, O-S bond scission takes place to release SO, and the O-atom remaining on aromatics leads to CO formation. Among four m-xylene radicals, the resonantly stabilized 3-methylbenzyl exhibited the lowest SO2 addition and SO elimination rates. The reaction rate constants are provided to facilitate Claus process simulations to find conditions suitable for BTX oxidation.