Synthesis of 5-hydroxymethylfurfural from highly concentrated aqueous fructose solutions using activated carbon

Mechanochemical Hydrolysis of Polysaccharide Biomass: Scope and Mechanistic Insights

Mechanical forces can affect chemical reactions in a way that thermal reactions cannot do, which may have a variety of applications. In biomass conversion, the selective conversion of cellulose and chitin is a grand challenge because they are the top two most abundant resources and recalcitrant materials that are insoluble in common solvents. However, recent works have clarified that mechanical forces enable the depolymerization of these polysaccharides, leading to the selective production of corresponding monomers and oligomers. This article reviews the mechanochemical hydrolysis of cellulose and chitin, particularly focusing on the scope and mechanisms to show a landscape of this research field and future subjects. We introduce the background of mechanochemistry and biomass conversion, followed by recent progress on the mechanochemical hydrolysis of the polysaccharides. Afterwards, a considerable space is devoted to the mechanistic consideration on the mechanochemical reactions.

Synthesis of Sulfonated Carbon from Discarded Masks for Effective Production of 5-Hydroxymethylfurfural

5-hydroxymethylfurfural (HMF), as one of the top ten important platform chemicals, can be used to produce 2,5-furandicarboxylic acid (FDCA), 2,5-dimethyl furan (DMF), levulinic acid, and other chemicals. An environmentally friendly system for the synthesis of sulfonated carbon materials from discarded masks has been proposed. A series of mask-based solid acid catalysts (bMC-SO3H) were prepared by a simple two-step process. Mechanochemical pretreatment (ball milling) of waste mask and sulfonated group precursor, followed by thermal carbonization under nitrogen gas, were used to synthesize sulfonated porous carbon. The total acid amount of the prepared bMC-SO3H was measured by the Boehm method, which exhibited 1.2–5.3 mmol/g. The addition of the sulfonated group precursor in the mechanochemical treatment (ball milling) process caused intense structure fragmentation of the discarded masks. These sulfonated porous carbons (bMC(600)-SO3H) as solid acid catalysts achieved fructose conversion of 100% and HMF yield of 82.1% after 120 min at 95 °C in 1-butyl-3-methylimidazolium chloride. The bMC-SO3H could be reused five times, during which both the HMF yield and fructose conversion were stable. This work provides a strategy for the synthesis of sulfonated carbon from discarded masks and efficient catalyzed fructose upgrading to HMF.

Supported Poly(Ionic Liquid)-Heteropolyacid Based Materials for Heterogeneous Catalytic Fructose Dehydration in Aqueous Medium

Two sets of four different supported catalyst materials were prepared. One set was obtained by polymerization of a bis-vinylimidazolium salt, which formed a poly(ionic liquid) coating on SiO2, TiO2, boron nitride BN, and carbon nitride C3N4. The other set was, instead, obtained by immobilizing Keggin heteropolyacid H3PW12O40 onto poly-imidazolium functionalized materials. All the catalysts, including the bare supports, were subjected to physical and chemical characterization by XRD, SEM, Specific Surface Area and pore size measurements, TGA, FTIR, and acidity-basicity measurements. The catalytic activity of the materials was tested versus the fructose dehydration in water solution at two different sugar initial concentrations (0.3 and 1 M). Tests lasted 3 h with an amount of catalyst of 2 g∙L−1. The presence of the poly-imidazolium on the surface of the supports increased the catalytic conversion of fructose to 5-hydroxymethylfurfural (the most abundant compound obtained) and was further improved by the contemporary presence of the heteropolyacid, at least for the highest initial fructose concentration. In the latter conditions, the highest yield of 5-hydroxymethylfurfural (>40%) was also obtained.

Toward Economical and Sustainable Production of Renewable Plastic: Integrative System-Level Analyses

2,5-Furandicarboxylic acid (FDCA) is one of the promising renewable plastic monomers enabling to address several environmental issues, instead of petroleum-based terephthalic acid (TPA). In this study, an integrative process for the co-production of FDCA and furfural as well as activated carbon was developed, and the economic feasibility and environmental sustainability for the proposed process were evaluated. In the proposed process, there were major four catalytic conversion reactions: (1) hydrolysis of biomass to its derivatives (cellulose, hemicellulose, and lignin), (2) dehydration of hemicellulose to furfural, (3) dehydration of cellulose to 5-hydroxymethylfurfural (HMF), and (4) successive oxidation of HMF to FDCA. Particularly, a heat exchanger network coupled with a heat pump was established to minimize the utility consumption, thereby reducing 72 % of the heating requirement. Techno-economic analysis revealed that the minimum selling price of FDCA was $1380 ton^-1 , which is comparable to that of petroleum-based TPA ($1445 ton^-1 ). Uncertainty analysis using the Monte Carlo simulation method was employed to quantify the risk associated with the unforeseen market condition. From the life-cycle assessment, we observed that the proposed process is more environmentally sustainable than conventional TPA production in terms of climate change and fossil depletion metrics.

Insight into the dehydration of high-concentration fructose to 5-hydroxymethylfurfural in oxygen-containing polar aprotic solvents

A high 5-HMF yield of 85.4% was achieved in polar aprotic oxygen-containing solvent with strong electrophilic maleic acid by quenching DHH.

Adsorption-Enhanced Glucan Oligomer Production from Cellulose Hydrolysis over Hyper-Cross-Linked Polymer in Molten Salt Hydrate

Selective saccharification of cellulose into glucose is a critical step for utilization of lignocellulosic biomass. Molten salt hydrates (MSHs) have shown promising performance in selectively converting cellulose into glucose because of the high solubility of cellulose in the solvent. However, the separation of formed glucose from the MSHs is still a grand challenge. To address this issue, we developed a two-step process, where crystalline cellulose is hydrolyzed into short-chain glucan oligomers in MSHs followed by separation and subsequent hydrolysis of the formed oligomers into glucose under mild conditions. The two-step method provides an easy separation for glucan oligomers from the MSHs without sacrificing the selectivity to glucose. Application of the method for crystalline cellulose is, however, limited to a relatively low concentration, 26.2 mg/mL, because of the formation of byproducts in the MSH that facilitate oligomers degradation. In this work, reactive adsorption was employed to in situ remove the byproducts formed during cellulose hydrolysis in the MSH. It was found that hyper-cross-linked polymer (HCP) made from the polymerization of 4-vinylbenzyl chloride and divinylbenzene can selectively adsorb 5-hydroxymethylfurfural (5-HMF) and levulinic acid (LA) while showing negligible sugar adsorption in both water and the MSH. With the reactive adsorption approach, byproducts including 5-HMF and LA were removed from the reaction media under reaction conditions, and their negative effects on oligomer degradation were inhibited. In the presence of the HCP, the obtained glucan oligomer concentration was enhanced from less than 54.2 to 247.1 mg mL-1 when the weight ratio of cellulose was increased to MSH from 1:60 to 1:4, exhibiting an oligomer yield of 69.5%. The HCP can be effectively separated from the reaction media by filtration and regenerated by oxidation with hydrogen peroxide. Application of reactive adsorption with HCP for cellulose hydrolysis in the MSH provides a promising method to produce glucan oligomers and glucose with an improved yield and efficiency.

Catalytic Dehydration of Fructose to 5-Hydroxymethylfurfural in Aqueous Medium over Nb2O5-Based Catalysts

The catalytic dehydration of fructose to 5-hydroxymethylfurfural (HMF) in water was performed in the presence of pristine Nb2O5 and composites containing Nb and Ti, Ce or Zr oxides. In all experiments, fructose was converted to HMF using water as the solvent. The catalysts were characterized by powder X-ray diffraction, scanning electron microscopy, N2 physical adsorption, infrared and Raman spectroscopy and temperature-programmed desorption of NH3. Experimental parameters such as fructose initial concentration, volume of the reacting suspension, operation temperature, reaction time and amount of catalyst were tuned in order to optimize the catalytic reaction process. The highest selectivity to HMF was ca. 80% in the presence of 0.5 g·L-1 of bare Nb2O5, Nb2O5-TiO2 or Nb2O5-CeO2 with a maximum fructose conversion of ca. 70%. However, the best compromise between high conversion and high selectivity was reached by using 1 g·L-1 of pristine Nb2O5. Indeed, the best result was obtained in the presence of Nb2O5, with a fructose conversion of 76% and a selectivity to HMF of 75%, corresponding to the highest HMF yield (57%). This result was obtained at a temperature of 165° in an autoclave after three hours of reaction by using 6 mL of 1 M fructose suspension with a catalyst amount equal to 1 g·L-1.

The formation of 5-hydroxymethylfurfural and hydrochar during the valorization of biomass using a microwave hydrothermal method

5-Hydroxymethylfurfural (HMF) and levulinic acid (LA) are regarded as value-added platform chemicals that can be derived from biomass waste. However, humins are inevitably produced during valorization processes, reducing the product yields. Previous studies indicated that microwave heating combined with acidic seawater as a reaction medium promotes HMF formation. The present work therefore investigated the relationship between the production of HMF and LA in the liquid phase and that of insoluble humins (that is, hydrochar) under microwave heating in acidic seawater. The selectivities for HMF and LA were found to decrease as the reaction time was increased, as a result of hydrochar formation, and both dehydration and decarboxylation evidently dominated the production of hydrochar in succession. HMF evidently played the most important role in hydrochar formation, and was consumed approximately seven times more rapidly than either fructose or LA. The hydrochar formation mechanism reported herein may be applicable to other similar hydrothermal processes.

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.

Preparation of activated carbon from Dipterocarpus alatus fruit and its application for methylene blue adsorption

Activated carbons were prepared from three parts of Dipterocarpus alatus fruit (wing, endocarp and pericarp), an abundant and renewable waste in Southeast Asia, by chemical activation using ZnCl₂, FeCl₃, H₃PO₄ and KOH and physical activation using CO₂ and steam. This study indicated that activated carbon prepared from Dipterocarpus alatus fruit could be employed as a promising adsorbent for the removal of methylene blue from aqueous solution. ZnCl₂ activation led to an activated carbon with a surface area of 843 m² g⁻¹ and was able to remove methylene blue from aqueous solution. Adsorption studies were performed and analysed using Langmuir and Freundlich isotherm equations. Adsorption data demonstrated an excellent fit with the Langmuir isotherm model, with the maximum adsorption capacity of 269.3 mg g⁻¹ at equilibrium. Pseudo-first order and pseudo-second order kinetic models were used in this study to describe the adsorption mechanism. The results show that methylene blue adsorption is pseudo-second order, indicating that liquid film diffusion, intra-particle diffusion and surface adsorption coexisted during methylene blue adsorption on the activated carbon. The activated carbon prepared from Dipterocarpus alatus fruit is a low cost and effective adsorbent with a fast rate for the removal of methylene blue from aqueous solutions when compared with a number of activated carbons studied in the literature.

Activated carbons were prepared from Dipterocarpus alatus fruit by chemical and physical activation and used for the removal of methylene blue from aqueous solution.