Reaction media dominated product selectivity in the isomerization of glucose by chromium trichloride: From aqueous to non-aqueous systems

Industrial Routes from Sugars and Biomass to CMF and Other 5-(Halomethyl)furfurals

The synthesis of 5-(halomethyl)furfurals (XMFs, X=F, Cl, Br, I), including 5-(chloromethyl)furfural (CMF), 5-(bromomethyl)furfural (BMF), 5-(iodomethyl)furfural (IMF), and 5-(fluoromethyl)furfural (FMF), from biomass represents a pivotal advancement in renewable chemistry and engineering. Harnessing waste biomass as a raw material offers a sustainable alternative to fossil-based resources, mitigating environmental degradation and addressing pressing energy needs. CMF and BMF, characterized by their enhanced stability over the hydroxyl analog, 5-(hydroxymethyl)furfural (HMF), exhibit promise as renewable building blocks for scale-up and commercialization. The surge in research interest, particularly from 2010 to 2024, reflects a growing recognition of XMFs' potential as novel platform chemicals. This review highlights the evolution of XMF synthesis methods, focusing on their transformation from saccharides and lignocellulosic biomass. Mechanistic insights and experimental setups are scrutinized for industrial feasibility and scalability, shedding light on technical challenges and avenues for further research. The analysis underscores the burgeoning significance of XMFs in the transition towards sustainable chemical production, emphasizing the importance of process optimization and mechanistic understanding for commercial deployment.

Biobased Chemicals from d-Galactose: An Efficient Route to 5-Hydroxymethylfurfural Using a Water/MIBK System in Combination with an HCl/AlCl3 Catalyst

5-Hydroxymethylfurfural (HMF) is an attractive building block for biobased chemicals. Typically, ketoses like d-fructose (FRC) are suitable starting materials and give good yields of HMF in a simple aqueous phase process with a Bro̷nsted acid catalyst. With aldoses, such as d-glucose (GLU), much lower yields were reported in the literature. Here, we report an experimental and modeling study on the use of d-galactose (GAL) for HMF synthesis, using a liquid-liquid system (water/MIBK) in combination with an HCl/AlCl3 catalyst. Experiments were conducted in a batch system with temperatures between 112 and 153 °C, HCl and AlCl3 concentrations ranging from 0.02 to 0.04 M, and initial GAL concentrations between 0.1 and 1.0 M. The highest HMF yield was 49 mol % obtained for a batch time of 90 min at 135 °C. This value is much higher than in experiments with GAL in a monophasic aqueous system with HCl as the catalyst (2 mol % HMF yield) under similar reaction conditions. Based on detailed product analyses, a reaction scheme is proposed in which the isomerization of GAL to tagatose (TAG), catalyzed by the Lewis acid AlCl3, is the first and key step. TAG is then converted to HMF by Bro̷nsted acid HCl. The experimental data were modeled using a statistical approach as well as a kinetic approach. The kinetic model demonstrates a good agreement between the experimental and modeled data. Our findings reveal that temperature is the reaction variable with the most significant influence on the HMF yield. The use of a biphasic system appears to be a promising method for HMF production from GAL.

Interfacial Thermoconvection and Atomic Relay Catalysis Enable Equilibrium Shifting and Rapid Glucose-to-Fructose Isomerization

The aqueous glucose-to-fructose isomerization is controlled by thermodynamics to an equilibrium limit of ~50 % fructose yield. However, here we report an in situ fructose removal strategy enabled by an interfacial local photothermal effect in combination with relay catalysis of geminal and isolated potassium single atoms (K SAs) on graphene-type carbon (Ksg/GT) to effectively bypass the equilibrium limit and markedly speed up glucose-to-fructose isomerization. At 25 °C, an unprecedented fructose yield of 68.2 % was obtained over Ksg/GT in an aqueous solution without any additives under 30-min solar-like irradiation. Mechanistic studies expounded that the interfacial thermoconvection caused by the local photothermal effect of the graphene-type carbon and preferable glucose adsorption on single-atom K could facilitate the release of in situ formed fructose. The geminal K SAs were prone to form a stable metal-glucose complex via bidentate coordination, and could significantly reduce the C-H bond electron density by light-driven electron transfer toward K. This facilitated the hydride shift rate-determining step and expedited glucose isomerization. In addition, isolated K SAs favored the subsequent protonation and ring-closure process to furnish fructose. The integration of the interfacial thermoconvection-enhanced in situ removal protocol and tailored atomic catalysis opens a prospective avenue for boosting equilibrium-limited reactions under mild conditions.

High Conversion of Concentrated Sugars to 5-Hydroxymethylfurfural over a Metal-free Carbon Catalyst: Role of Glucose-Fructose Dimers

To reduce the production cost of chemicals from renewable resources, the feedstock loading must be high and the catalyst must be of low cost and efficient. In this study, at a very short reaction time of 10 min at 125 °C, concentrated sugar solutions (20 wt %, 101 wt % on solvent) were converted to 5-hydroxymethylfurfural (HMF) over a cotton gin trash (CGT)-derived sulfonated carbon catalyst in a 1-butyl-3-methyl-imidazolium chloride ([BMIM]Cl) and 2-methyltetrahydrofuran (MeTHF) biphasic system. We report, for the first time, that the presence of glucose either as a covalently bonded monomer in sucrose or in a mixture with fructose achieved yields of HMF up to 62 mol % compared to a value of only 39 mol % obtained with fructose on its own. In the concentrated reaction medium, glucose, fructose, and sucrose molecules produce difructose anhydrides, dimers/reversion products, and sucrose isomers. The glucose-fructose dimers formed in sucrose and glucose/fructose reaction systems play a critical role in the transformation of the sugars to a higher-than-expected HMF yield. Thus, a strategy of using cellulosic glucose, where it is partially converted to fructose content and the high sugar concentration sugar mixture is then converted to HMF, should be exploited for future biorefineries.

Solvent Effects Enable Efficient Tandem Conversion of Cellulose and Its Monosaccharides Towards 5-Hydroxymethylfurfural

The biomass-derived platform compound 5-hydroxymethylfurfural (HMF) has been hailed as the "Sleeping Giant" due to its promising applications, and it occupies a critical spot in the biomass upgrading roadmap. HMF is typically produced from cellulose and its monosaccharides via a complex tandem conversion with multiple steps (i. e., cellulose depolymerization, glucose isomerization, fructose dehydration, etc.). Previous investigations have confirmed the irreplaceable contribution of solvents in regulating the tandem conversion of cellulose and its monosaccharides to HMF. However, the potential effects of solvents in contributing to this multi-step tandem process have not yet been clearly elucidated. In this context, this Review aims to provide in-depth insights into the intrinsic interactions between solvent system and substrate conversion (cellulose and its monosaccharides conversion), reaction regulation (reaction activity and selectivity regulation), as well as product acquisition (humins formation inhibition and product purification). It attempts to elucidate specific solvent effects to promote a more efficient tandem conversion of cellulose and its monosaccharides towards HMF. The insights provided in this Review may contribute to a more sustainable HMF production from biomass feedstocks and a further development of greener solvent systems.

High Selective Isomerization of Glucose to Fructose Catalyzed by Amidoximed Polyacrylonitrile

The isomerization of glucose to fructose provides an important way to expand the utilization of biomass. Herein, an amidoximated polyacrylonitrile (PAO) with an amidoxime functional group was prepared and used as an active heterogeneous catalyst for the isomerization of glucose to fructose. The PAO was characterized by SEM, XPS, and FTIR. The yield of fructose reached 48.9% with a selectivity of 98.6% for a 5 h reaction in aqueous solution at an initial pH of 6.5 and 85 °C. The pH caused a great influence on the conversion of glucose and selectivity of fructose while a little effect on the yield of fructose in the range of pH 5-10. The activation energy of isomerization reaction was evaluated as 79.7 kJ·mol^-1. The catalysis mechanism was proposed, and the synergistic effect of oxime and amino groups played an important role in the isomerization of glucose. PAO maintained good catalytic activity after four cycles.

Fast microflow kinetics and acid catalyst deactivation in glucose conversion to 5-hydroxymethylfurfural

Continuous flow microreactors operating at short residence times and high temperatures can give high HMF productivity and contribute to process intensification of biorefineries.

Valorization of an underused sugar derived from hemicellulose: efficient synthesis of 5-hydroxymethylfurfural from mannose with aluminum salt catalyst in dimethyl sulfoxide/water mixed solvent

Mannose, an underused sugar derived from hemicellulose, can be effectively converted into 5-hydroxymethylfurfural (5-HMF) with aluminum chloride catalyst under mild conditions, offering useful reference for the refinery of biomass in the future.

Glucose dehydration to 5-hydroxymethylfurfural in ionic liquid over Cr3+-modified ion exchange resin

Cr³⁺-D001-cc resin shows excellent catalytic performance for the dehydration of glucose to 5-hydromethylfurfural, which is prepared by a simple ion-exchange method.

Speciation and kinetic study of iron promoted sugar conversion to 5-hydroxymethylfurfural (HMF) and levulinic acid (LA)

Identification of catalytic species and their contributions in iron catalyzed sugar conversion to hydroxymethylfurfural and levulinic acid.