Rapid, High-Yield Fructose Dehydration to 5-Hydroxymethylfurfural in Mixtures of Water and the Noncoordinating Ionic Liquid [bmim][OTf]

The key role of pretreatment for the one-step and multi-step conversions of European lignocellulosic materials into furan compounds

Nowadays, an increased interest from the chemical industry towards the furanic compounds production, renewable molecules alternatives to fossil molecules, which can be transformed into a wide range of chemicals and biopolymers. These molecules are produced following hexose and pentose dehydration. In this context, lignocellulosic biomass, owing to its richness in carbohydrates, notably cellulose and hemicellulose, can be the starting material for monosaccharide supply to be converted into bio-based products. Nevertheless, processing biomass is essential to overcome the recalcitrance of biomass, cellulose crystallinity, and lignin crosslinked structure. The previous reports describe only the furanic compound production from monosaccharides, without considering the starting raw material from which they would be extracted, and without paying attention to raw material pretreatment for the furan production pathway, nor the mass balance of the whole process. Taking account of these shortcomings, this review focuses, firstly, on the conversion potential of different European abundant lignocellulosic matrices into 5-hydroxymethyl furfural and 2-furfural based on their chemical composition. The second line of discussion is focused on the many technological approaches reported so far for the conversion of feedstocks into furan intermediates for polymer technology but highlighting those adopting the minimum possible steps and with the lowest possible environmental impact. The focus of this review is to providing an updated discussion of the important issues relevant to bringing chemically furan derivatives into a market context within a green European context.

Influence of Pretreatment Severity Factor and Hammett Acidity on Softwood Fractionation by an Acidic Protic Ionic Liquid

The impact of pretreatment severity in the acidic protic ionic liquid (IL) N,N-dimethylbutylammonium hydrogen sulfate, [DMBA][HSO₄] using pine softwood was investigated using a modified severity factor that considers the IL solution acidity based on Hammett acidity. A Box-Behnken experimental design was employed to evaluate pretreatment severity with temperature, pretreatment time, and IL concentration as factors and degree of delignification as the response variable. The optimal pretreatment conditions were found to be at 170 °C, 30 min, and 80 wt % IL, which yielded nearly 90% of delignification and 95% of glucose yield in enzymatic saccharification. The modified severity factor showed an improved correlation with the fractionation indicators relative to the classical pretreatment severity factor, indicating that it can better predict the pretreatment outcomes, particularly for delignification and hemicellulose removal. The fate of hemicellulose, its conversion to humins, and its impact on the precipitated lignin properties were also investigated and correlated to the modified pretreatment severity factor. It was found that such parameters alone cannot be used to predict the fate of dissolved hemicellulose sugars in the IL medium. Furthermore, IL acidity greatly impacts the degradation of the dissolved hemicellulose sugars and the formation of humins.

New Biobased Sulfonated Anionic Surfactants Based on the Esterification of Furoic Acid and Fatty Alcohols: A Green Solution for the Replacement of Oil Derivative Surfactants with Superior Proprieties

The surfactant market represents a key sector of the chemical industry and encompasses many diverse applications. Their sustainability in terms of feedstock used, synthetic procedure, biodegradability, and formulation are crucial parameters to assessing the environmental impact of the surfactant. The anionic surfactant linear alkyl benzene sulfonates have proven successful to date because of their high performance, low cost, and extensive studies within formulations to optimize performance, allowing usage in a large variety of applications, especially in cleaning. Due to their advantageous properties and extensive research and development, their substitution with a biobased surfactant such as sodium dodecyl sulfate has struggled to succeed. Furan surfactants have been reported as valuable candidates for the implementation of green alternatives to traditional anionic sulfonated surfactants with a perfect trade-off between performances and green credentials. However, their implementation suffers of scalability and high cost in producing the final product due to feedstock availability and low yields of the final product. Herein, we report a new class of furan surfactants, sulfonated alkyl furoates, which are derived from the esterification of furoic acid and fatty alcohols, followed by a sulfonation step. Compared to traditional surfactants, they showed more favorable behavior in basic proprieties (such as critical micelle concentration, ecotoxicity, hard water resistance, surface tension water/oil), which gives a good prospective for the introduction of a new biobased chemical with superior performances.

Recent Approaches in the Catalytic Transformation of Biomass-Derived 5-Hydroxymethylfurfural into 2,5-Diformylfuran

The conversion of biomass into a great variety of valuable chemicals, polymers, and fuels gives a sustainable alternative for the insufficiency of non-renewable fossil fuel resources and reduces environmental pollution. 5-Hydroxymethylfurfural (HMF), converted from sustainable carbohydrates, is a significant building block chemical, and the selective oxidation of HMF into 2,5-diformylfuran (DFF) presents an ongoing challenge. DFF is a versatile platform molecule derived from biomass and has promising application in pharmaceuticals and polymers. This Review provides an overview of the latest developments of efficient catalytic systems for the sustainable conversion of HMF to DFF.

Advances of Ionic Liquids and Deep Eutectic Solvents in Green Processes of Biomass-Derived 5-Hydroxymethylfurfural

5-Hydroxymethylfurfural (HMF) is identified as an important bio-based platform chemical to bridge petroleum-based and biomass-based resources. It can be obtained through dehydration of various carbohydrates as well as converted to value-added fuels and chemicals. As designer solvents, ionic liquids (ILs) and deep eutectic solvents (DESs) have been widely used in catalytic transformation of biomass derivatives to various chemicals. This Review summarizes recent progress in experimental and theoretical studies on dehydration of carbohydrates such as fructose, glucose, sucrose, cellobiose, chitosan, cellulose, inulin, and even raw biomass to generate HMF using ILs and DESs as catalysts/cocatalysts and/or solvents/cosolvents. It also gives an overview of IL and DES-involved catalytic transformation of HMF to downstream products via oxidation, reduction, esterification, decarboxylation, and so forth. Challenges and prospects of ILs and DESs are also proposed for further production of HMF and HMF derivatives from biomass in green and sustainable processes.

Fabrication of Brønsted acidic ionic liquids functionalized organosilica nanospheres for microwave-assisted fructose valorization

A series of Brønsted acidic ionic liquids (BAILs) functionalized hollow organosilica nanospheres ([C_3/4Im][OTs/OTf]-Si(Et)Si, C_3/4 = Pr/BuSO₃H) were synthesized by two steps. The process involved the preparation of hollow nanosphere supports via a toluene-swollen sol-gel co-condensation of 1,2-bis(trimethoxysilyl)ethane and 3-chloropropyltriethoxysilane in the presence of F127, and followed by a successive quaternary ammonization and protonation with imidazole, 1,3-propane/1,4-butane sultone and trifluoromethane sulfonic acid/p-toluenesulfonic acid. The adjustable acid property, hollow inner diameter (5-15 nm) and shell thickness (5-9 nm) of [C_3/4Im][OTs/OTf]-Si(Et)Si are achieved by introducing different organic acids and controlling toluene concentration, respectively. The [C_3/4Im][OTs/OTf]-Si(Et)Si were applied in selective conversion of fructose to 5-hydroxymethylfurfural (HMF) and 5-ethoxymethylfurfural (EMF) under microwave heating. Under the optimized conditions, the [C₄Im][OTs]-Si(Et)Si3.0 nanospheres with the largest inner diameter and the smallest shell thickness exhibit the highest HMF yield (79.4%, 15 min) in fructose dehydration. And the [C₃Im][OTf]-Si(Et)Si0.5 nanospheres with the highest acid strength possess the highest EMF yield (70.4%, 30 min) in fructose ethanolysis. The high Brønsted acid-site density and acid strength of [C_3/4Im][OTs/OTf]-Si(Et)Si catalysts accompanied by high microwave heating energy lead to excellent dehydration/ethanolysis activity. The product selectivity strongly depended on the BAILs structures and morphological characteristics of the catalyst. More importantly, the [C_3/4Im][OTs/OTf]-Si(Et)Si can be reused three times without changes in leaching of BAILs, due to strong covalent bond between BAILs and silicon/carbon framework. This work will provide a simple strategy of chemically bonded BAILs on suitable supports as efficient solid acids, and an approach of combining morphology-controlled solid acids with microwave-heating for catalytic conversion of biomass/derivatives to fuels and value-added chemicals.

The Role Played by Ionic Liquids in Carbohydrates Conversion into 5-Hydroxymethylfurfural: A Recent Overview

Obtaining industrially relevant products from abundant, cheap, renewable, and low-impacting sources such as lignocellulosic biomass, is a key step in reducing consumption of raw fossil materials and, consequently, the environmental footprint of such processes. In this regard, a molecule that is similar to 5-hydroxymethylfurfural (5-HMF) plays a pivotal role, since it can be produced from lignocellulosic biomass and gives synthetic access to a broad range of industrially important products and polymers. Recently, ionic liquids (ILs) have emerged as suitable solvents for the conversion of biomass and carbohydrates into 5-HMF. Herein, we provide a bird's-eye view on recent achievements about the use of ILs for the obtainment of 5-HMF, covering works that were published over the last five years. In particular, we first examine reactions involving homogeneous catalysis as well as task-specific ionic liquids. Then, an overview of the literature addressing the use of heterogeneous catalysts, including enzymes, is presented. Whenever possible, the role of ILs and catalysts driving the formation of 5-HMF is discussed, also comparing with the same reactions that are performed in conventional solvents.

Production of 5-hydroxymethylfurfural from Japanese cedar (Cryptomeria japonica) in an ionic liquid, 1-methylimidazolium hydrogen sulfate

Production of 5-hydroxymethylfurfural (5-HMF) from Japanese cedar (Cryptomeria japonica) using an ionic liquid, 1-methylimidazolium hydrogen sulfate ([MIM]HSO₄), was investigated. 5-HMF can be produced from C. japonica at temperatures above 120 °C. The maximum yield of 5-HMF was about 9 wt% after 15 min of treatment at 160 °C. However, 5-HMF produced in this process tended to decompose as the treatment continued. To avoid decomposition and to provide a means of recovering 5-HMF from [MIM]HSO₄, three reaction systems based on [MIM]HSO₄ were investigated: biphasic [MIM]HSO₄/organic solvent system, [MIM]HSO₄ with vacuum distillation, and [MIM]HSO₄ with vacuum steam distillation. The [MIM]HSO₄ reaction system combined with vacuum steam distillation was most effective. The maximum yield of 5-HMF was 17.5 wt% after treatment for 45 min at 160 °C. The combination of [MIM]HSO₄ treatment with vacuum steam distillation is suitable for 5-HMF production because it is a one-pot process without the need for catalysts or pretreatment.

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.

Sugar dehydration to 5-hydroxymethylfurfural in mixtures of water/[Bmim]Cl catalyzed by iron sulfate

Stabilization effect of [Bmim]Cl on HMF is demonstrated, which can suppress the rehydration and polymerization side-reactions and enhance HMF yield.