HMF Production Research Articles

Determination of Sugar Concentrations in Aqueous Solution Using Multivariate Predictions Based on 1H‐NMR Spectroscopy

AbstractRenewable chemicals from carbohydrate‐rich wastes, like furfural and 5‐hydroxymethylfurfural (HMF), are gaining prominence as alternatives to petroleum‐based resources. Assessing the suitability of biomass as feedstock for furfural and HMF production requires knowledge of its composition. This study focuses on developing and validating predictive models for individual sugar concentrations in hydrolysates using quantitative 1H NMR data. Utilizing partial least square (PLS) regression, the dataset includes 137 NMR spectra of multi‐component sugar standards (arabinose, fructose, galactose, glucose, mannose, maltose, sucrose, and xylose). The best‐performing model achieved an R2 of 0.987–0.999 and RMSECV of 0.37–1.56 mM and is based on the non‐overlapping area of the NMR spectrum. Real‐world samples were used for validation, resulting in predicted sugar concentrations with a mean standard deviation of 0.5 mM. This high accuracy and streamlined analysis process make these models practical for quantifying large sample sets, showcasing the reliability and accessibility of extracting statistical information from H‐NMR data.

Valorization of White Lupin Straw Through Mild Dilute Acid Hydrothermal Treatment: A Sustainable Route for Monosaccharide and 5-Hydroxymethylfurfural Production

This study investigates the potential use of white lupine straw (WLS), an underutilized agricultural by-product, as a raw material to produce valuable biochemicals such as monosaccharides and 5-hydroxymethylfurfural (5-HMF) through hydrothermal pretreatment. The aim was to optimize mild reaction conditions to maximize the recovery of these products while minimizing degradation. The hydrothermal treatment of WLS in subcritical water with trace amounts of sulfuric acid was performed, followed by a two-step approach to evaluate the yields of hemicellulose and 5-HMF. The highest monosaccharide yield (163 g/kg) was achieved at temperatures between 174 and 181 °C and a holding time of 7–14 min, while the 5-HMF production was 139.9 g/kg at 199–203 °C and after 0.5–4.5 min. These results suggest that optimal 5-HMF production also increases the remaining solid residue. This study highlights the feasibility of WLS as a sustainable, low-cost biomass resource. It highlights the balance between temperature and time to maximize valuable product yields. The results contribute to advancing biorefinery processes by demonstrating that WLS can be effectively converted into bioethanol precursors and industrial chemicals, supporting circular bioeconomy principles and providing an environmentally friendly alternative to burning crop residues.

Unlocking the Anion Effect on Steerable Production of 5‐Hydroxymethylfurfural

AbstractHomogeneous metal salt catalysts play a pivotal role in industrial production of 5‐hydroxymethylfurfural (HMF). Herein, we first proposed the anion effect on steerable production of HMF using metal salts with different anions as catalyst in a biphasic system of tetrahydrofuran (THF)/NaCl aqueous solution (NaCl aq). Notably, the anions affected the catalytic activity of the metal salts, leading to an order of magnitude difference in the HMF yields, i.e., AlBr3 (74.0 mol %)>AlCl3 (60.8 mol %)>Al2(SO4)3 (35.2 mol %)>Al(NO3)3 (14.9 mol %). The anion effect on steerable production of HMF could be attributed to the proximity effect and electron tension. Anions form close‐range interactions with glucose molecules by proximity effect to promote electron transfer, facilitating the isomerization of glucose to fructose. Besides, anions induce a reduction of the electron cloud density of glucose carbon atoms, generating electron tension that rapidly transforms glucose from the ground state to the transition state, thereby increasing the HMF yield. Based on the revelation of anions effect and evaluation of techno‐economic process, we expect to provides theoretical guidance for high‐throughput screening of metal salt catalysts in industrial biorefinery.

Unlocking the Anion Effect on Steerable Production of 5-Hydroxymethylfurfural.

Homogeneous metal salt catalysts play a pivotal role in industrial production of 5-hydroxymethylfurfural (HMF). Herein, we first proposed the anion effect on steerable production of HMF using metal salts with different anions as catalyst in a biphasic system of tetrahydrofuran (THF)/NaCl aqueous solution (NaCl aq). Notably, the anions affected the catalytic activity of the metal salts, leading to an order of magnitude difference in the HMF yields, i.e., AlBr3 (74.0 mol %)>AlCl3 (60.8 mol %)>Al2(SO4)3 (35.2 mol %)>Al(NO3)3 (14.9 mol %). The anion effect on steerable production of HMF could be attributed to the proximity effect and electron tension. Anions form close-range interactions with glucose molecules by proximity effect to promote electron transfer, facilitating the isomerization of glucose to fructose. Besides, anions induce a reduction of the electron cloud density of glucose carbon atoms, generating electron tension that rapidly transforms glucose from the ground state to the transition state, thereby increasing the HMF yield. Based on the revelation of anions effect and evaluation of techno-economic process, we expect to provides theoretical guidance for high-throughput screening of metal salt catalysts in industrial biorefinery.

Selectivity control in catalytic glucose dehydration using iron- and tungsten-modified ZSM-5 catalysts

The conversion of lignocellulosic biomass into valuable chemicals and fuels has received considerable attention owing to the issues related to global warming. 5-Hydroxymethylfurfural (HMF) is a versatile lignocellulose-derived platform chemical used in a wide range of high-value bioproducts. However, the HMF production is completed with polymerization by which humins are inevitably formed as a by-product. Recently, the potential of humins for various applications has been explored. In this study, a series of ZSM-5 zeolite catalysts modified with iron (Fe) and tungsten (W) were used to selectively control glucose dehydration to HMF and humins. The zeolite catalysts possessing tunable bifunctional Brønsted–Lewis acid characteristics were prepared through pretreatment using a diluted nitric acid solution, followed by metal impregnation. The impregnation of Fe into ZSM-5 induced the formation of highly dispersed extraframework isolated Fe3+ ions and Fe2O3 species, which increased the content of Lewis acid sites. The W species added to ZSM-5 existed in the form of Si–OH–W linkages and polytungstates with moderate-to-strong Brønsted acidity. The selective synthesis of HMF was efficiently performed over the Fe-modified ZSM-5 catalysts. Furthermore, the W-modified catalysts exhibited potential application as novel catalysts for the selective production of humins. The controlled selectivity to each product depended on the acidic properties and Lewis/Brønsted acidity ratio of the catalysts as well as the transition metal-dependent characteristics of the Brønsted and Lewis acid sites.

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.

Biphasic Production of 5-hydroxymethylfurfural (HMF) in a Recyclable Deep Eutectic Solvent-based System Catalyzed by H4SiW12O40.

The reaction with in situ extraction to yield 5-hydroxymethylfurfural (HMF) from Fru was investigated using a biphasic system based on a self-consuming deep eutectic solvent (DES) as reaction phase. The significance of choline chloride (ChCl), a cost-effective and safe quaternary ammonium salt, was evident in enhancing 5-HMF yield through fructose dehydration and concurrently suppressing side reactions. The DES system demonstrated fast reactions with high selecivities and recyclability across five cycles. The observed decline in H4SiW12O40 activity, primarily due to proton leaching, was successfully restored with the addition of HCl. Furthermore, ChCl exhibited ease of recrystallization in the presence of acetonitrile. This research proposes an environmentally friendly approach for 5-HMF production through a reusable-biphasic process. The presented reaction system suppresses completely the formation of levulinic and formic acid leading to HMF yields of up to 84% of selectivities of up to 88% after 30 minutes at 80 °C. The system was recycled over 16 runs and after an initial slight loss of activity the system in the run 0-5, run 6-15 has shown a constant HMF output as in the first recycling run.

Pt nanoparticles in cooperation with Mn-P composite drive base-free selective oxidation of 5-hydroxymethylfurfural

Selective oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) is a key approach to sustainable upgrading of furfural based biomass resources. In this work, small Pt nanoparticles (about 2.1 nm) loaded on MnPnOx composite were shown to effectively drive the base-free aerobic oxidation of HMF to FDCA in water. Regulating the P content in carrier enabled to tune HMF conversion and product distribution. The optimal Pt/MnP0.5Ox catalyst can reach 98% yield of FDCA at 110 °C under 10 bar of O2 after 24 h. It also showed the highest initial conversion rate of HMF (13 mmol molPt−1 s−1) and productivity of FDCA (4.1 mmol molPt−1 h−1) among all the Pt/MnPnOx catalysts. The carrier effect of P addition on promoting Pt oxidation catalysis was elucidated by using rigorous kinetic investigations and comprehensive characterizations. The initial conversion rate, rate constant and apparent activation energy were independently measured on oxidation of HMF and its derived intermediates. ICP-MS, XRD, TEM, H2-TPR, O2-TPD and XPS were used to acquire catalytic properties. It was demonstrated that P addition led to changes in carrier structure and metal-support interaction, which eventually promoted the formation of highly active electron-rich Pt0 sites and mobile reactive defect oxygen species. These features allowed improving the selective oxidation catalysis of supported-Pt nanoparticles for the base-free conversion of HMF to FDCA.

Structural engineering of metal-organic framework catalysts for efficient conversion of glucose into 5-HydroxyMethylFurfural

The research on sustainable and efficient routes to produce valuable chemicals from renewable biomass has garnered considerable attention in recent years. Among these chemicals, 5-hydroxymethylfurfural (5-HMF) holds significant promise as a versatile platform molecule for various applications in the chemical industry. This study investigates the production of 5-HMF from glucose using zirconium-based metal-organic frameworks (Zr-MOFs) as environmentally friendly catalysts, an alternative to the traditional homogeneous catalysts. UiO-66 and its functionalized derivatives (e.g. UiO-66(NH2),UiO-66(COOH)2, and UiO-66(OH)2) were synthesized to study the effect of the functional groups on the dehydration reaction. The synthesized MOFs were fully characterized using powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), N2 adsorption-desorption, Infrared spectroscopy (IR), Pyridine-Fourier Transform Infrared spectroscopy (Py-FTIR), and scanning electron microscopy (SEM). The catalytic performance of the synthesized MOFswas evaluated for the dehydration of glucose to 5-HMF in DMSO and further optimized in other monophasic and biphasic systems. Results indicated that UiO-66(COOH)2 exhibited exceptional catalytic activity for the conversion of glucose to HMF, with a significantly higher HMF yield of 44 % compared to other reported MOF catalysts and to that of H2SO4, which yielded 35 % at a temperature of 140 °C and a 6 h reaction time. This is mainly attributed to the effect of the bifunctional active acid sites of the metal nodes and the functional group of the organic linker (free carboxylic groups), which acted as the main source of Lewis and Brønsted acid sites respectively, compared to UiO-66. Additionally, the results suggested that the catalyst with higher acid density, higher relative mesopority, and a moderate B/L ratio could enhance glucose dehydration regardless of the surface area. Furthermore, the catalyst demonstrated excellent reusability and stability, with a decrease of only 10 % after four reaction cycles. The recycled catalyst revealed no structural alterations in its framework. This study contributes to the growing body of research on Zr-based MOF as a stable and efficient catalyst for glucose valorization to produce 5-HMF under mild reaction conditions.

Ultra-Dilute SnCl4-Catalyzed Conversion of Concentrated Glucose to 5-Hydroxymethylfurfural in Aqueous Deep Eutectic Solvent.

5-Hydroxymethylfurfural(HMF) is a versatile chemical synthesized from glucose dehydration catalyzed by metal chloride (MClx) in deep eutectic solvents (DESs). However, the low glucose concentration and high catalyst dosage hinder large-scale HMF production. Herein, we report an aqueous DES of tetraethylammonium bromide(TEAB)-glucose for converting concentrated glucose (40 wt%, relative to TEAB) using ultra-dilute SnCl4 (0.25 mol%), achieving a 62% yield of HMF. Ultra-dilute MClx-catalyzed selective conversion of glucose is feasible only when combining SnCl4 with Br-based DES, which is elucidated by density functional theory and molecular dynamic calculations. Using SnCl4 is essential due to its higher glucose isomerization activity than AlCl3 and CrCl3, which can be attributed to its low-barrier coordination with glucose and its barrier-free separation from fructose. Halide anions in DESs strongly interact with glucose, hindering the MClx-glucose coordination and thereby reducing MClx's activity for glucose isomerization. Consequently, Br-based DESs facilitate higher activity of MClx than Cl-based DESs, due to the weaker interaction between halide anion and glucose. In addition, we elucidated the side reactions including condensation, polymerization, and isomerization, and proposed a reaction network. Our findings clarify the differential activity of MClx and the impact of halide anions in DESs on MClx's activity.

Sulfonated graphitic carbon catalyst derived from coffee waste: A sustainable valorization approach for highly efficient production of 5-hydroxymethylfurfural (5-HMF) from fructose

According to recent research, a sulfonated 2D graphitic carbon catalyst for the dehydration of fructose to the platform chemical 5-Hydroxymethylfurfural (5-HMF) can be made from used ground coffee. By carbonizing and activating at different temperatures, sulfonated graphitic carbon (SC) catalysts with varied chemical compositions and textural characteristics were obtained. The physical and chemical characteristics of the SC catalysts were assessed using XRD, Raman, SEM-EDX, HR-TEM, BET analysis, and XPS. Due to its microporous structure, SC-900 exhibited a high specific area and demonstrated selective and efficient production of 5-HMF from fructose. All in all, the surface acidity of catalysts was measured by NH3-TPD, and acid-base titration methods. The SC-900 catalyst, designed through carbonization at 900 ℃, achieved a fructose conversion rate of 100 % and a 5-HMF yield of 97.91 % without generating any by-products. This indicates the catalyst essentially produces 5-HMF under the specified optimal conditions (140 ℃, 90 min) observed in this study. To determine the origins of the highly efficient and highly selective conversion of fructose to 5-HMF, the performance of the SC catalysts was systematically investigated vi-a-vis their physical and chemical properties. The development of microporous SC catalysts and their application as catalysts not only enhances the value of waste coffee but also provides an environmentally friendly approach for converting carbohydrates into 5-HMF.

A binary catalytic system of sulfonated metal–organic frameworks and deep eutectic solvents towards highly efficient synthesis of 5-hydroxymethylfurfural from fructose

The green synthesis of 5-hydroxymethylfurfural (HMF) from biomass feedstocks is a crucial step for the development of sustainable fuels, resins and plastics. Here, a novel binary catalytic system was developed with metal–organic frameworks (MOFs) and deep eutectic solvents (DESs), which synergically exhibited a superior fructose dehydration efficiency with a HMF yield of 98.5% within 40 min. The replacement from terephthalic acid to 2,5-furandicarboxylic acid as the organic ligand in MOFs catalysts altered the coordination microenvironment of metal nodes, resulting in remarkably enhanced fructose conversion rates. The formation of hierarchical porous structures and moderated Brønsted acid sites in sulfonated MOFs further promoted the HMF production. Notably, HMF could be readily separated from the MOFs-DESs system and the MOF catalyst maintained stable performance after six recycles. Theoretical calculations clarified a positive correlation between the hydrogen bond interaction (between fructose and DESs components) energy and reaction efficiency. This study provided a new strategy to couple hierarchical solid acid catalysts with functional solvents binary towards effective and sustainable upgrading of biomass-derived molecules.

Evaluation of OxiOrganosolv pretreated hardwood and softwood lignocelluloses as substrates for the chemoenzymatic production of 5-hydroxymethylfurfural (HMF)

Furans, such as 5-hydroxymethylfurfural (HMF), are compounds of great importance that can serve as starting materials for the synthesis of polymers. Their production from lignocellulose-derived sugar streams offers a promising alternative to fossil fuels, while enabling biomass transformation to chemicals with higher value. In the present work, the production of HMF from OxiOrganosolv pretreated beechwood and pine was assessed by integrating a three-step process of enzymatic saccharification and isomerization followed by catalytic dehydration. The use of isobutanol in the pretreatment solvent and the addition of polyoxometallates (POMs) as oxidative catalysts were evaluated. The results showed that isobutanol leads to high delignification rates for both beechwood and pine, yielding cellulose-rich pulps with high susceptibility to enzymatic hydrolysis and isomerization. A fructose production up to 51.2 and 53.4 g/g of pretreated material was achieved for beechwood and pine, respectively, corresponding to 14 and 11.3 g of HMF/g of pretreated material. Regarding the use of POMs, the commercially available phosphomolybdic acid (HPMO) and POMs modified with oxidation metals (Fe-PMO, Cu-PMO) were tested, verifying their beneficial effect to lignin depolymerization and the composition of the final pulp. Hydrolysates produced from HPMo and Cu-PMo-assisted OxiOrganosolv pretreatment were efficiently used for the production of HMF, while severe inhibition of the dehydration reaction was observed with the hydrolysates from Fe-PMo pretreated biomass due to the presence of residual metals. This is the first systematic report comparing two lignocellulosic materials subjected to different pretreatment conditions for their potential to produce fructose and, subsequently, HMF.

Unveiling kinetics post rate-determining step in Brønsted acid-catalyzed reactions of fructose: A strategy for 5-hydroxymethylfurfural production from concentrated feedstock

The development of high-yielding catalytic systems is pivotal in biomass upgrading. However, the investigation of kinetics in these complex reaction systems is often highly challenging, especially when reactions leading to byproduct formation are obscured by a preceding, slow rate-determining step. In this work, we introduce a unique approach to kinetic analysis that enables the investigation of reactions occurring post rate-determining step. The technique was applied to the conversion of sugars to 5-hydroxymethylfurfural (HMF), an important platform molecule for sustainable chemical production. First, screening experiments were carried out to identify a catalytic solvent system that achieves a balance between solvent stability, HMF yield, and cost-effectiveness. Our kinetic analysis on the identified system reveals that the fructose reactant undergoes a rate-determining dehydration step to form an unstable reactive intermediate. This intermediate further reacts competitively with other reactive species, such as the hexose reactants or the HMF product, ultimately lowering the HMF selectivity. The calculated relative activation energies of these reactions post rate-determining step provide intuitive insights into the effects of temperature, co-existing reactive species, as well as the previously unexplained effect of feed concentration on HMF selectivity. Additionally, we propose a novel reaction strategy that significantly enhances HMF yield when compared to a traditional batch synthesis. Notably, a high HMF yield of 74 % was achieved with an extreme 55 wt% fructose loading on an aqueous basis (20 wt% loading on a total weight basis) in a low-boiling 80 wt% dioxane/water mixture using an HCl catalyst at 393 K.

H-Beta Zeolite as Catalyst for the Conversion of Carbohydrates into 5-Hydroxymethylfurfural: The Role of Calcination Temperature

H-Beta zeolite is a solid acid catalyst commonly utilized in the catalytic conversion of biomass resources. In this study, H-Beta zeolite was calcined at different temperatures (350, 550, 750, and 1000 °C) to explore the effects of high temperature-induced dealumination on its physicochemical properties and its catalytic ability to convert glucose into 5-hydroxymethylfurfural (HMF). It was shown that as the calcination temperature increased, the Si-O-Al bond of H-Beta zeolite was broken and its dealumination effect was enhanced. Dealumination led to the collapse of the framework of H-Beta zeolite and a reduction in the number of acid sites, which in turn reduced its catalytic performance and the efficiency of HMF formation from glucose. Furthermore, H-Beta zeolite exhibited an extraordinary catalytic ability for the production of HMF from carbohydrates. Using glucose and cellulose as substrates, superior HMF yields of 91% and 46%, respectively, were achieved under optimal reaction conditions. Further, calcination removes carbon deposits in the recovered H-Beta zeolite, but it affects the cycling stability of the catalyst. Meanwhile, the by-products formed during the synthesis of HMF from glucose catalyzed by H-Beta zeolite catalyst were also clearly detected.

Sn-modified SBA-15 with tailored acid properties for efficient 5-hydroxymethylfurfural production from glucose

Interest in production and utilization of 5-hydroxymethylfurfural (5-HMF) has risen greatly as 5-HMF is considered as an extremely important platform compound. It remains a huge challenge to develop efficient and low-cost solid catalysts with suitable acid properties for sustainable production of 5-HMF from glucose. Herein, a bifunctional Sn-modified SBA-15 (Sn–OH/SBA-15) catalyst containing both Lewis and Brønsted acid sites was fabricated. Dimethyldichlorostannane was grafted onto mesoporous SBA-15, and the methyl groups were then converted to hydroxyl groups by calcination. The synergistic effects of Lewis and Brønsted acid significantly boosted the synthesis of 5-HMF from glucose adopting the one-pot method. By optimizing the reaction conditions, the Sn–OH/SBA-15 sample was able to achieve a glucose conversion of 96.9% with a 5-HMF yield of 70.6% (180 °C, 5 h). Moreover, the catalyst demonstrated superior recyclability and reusability. This work would enlighten the exploitation and preparation of highly efficient catalysts for the transformation of carbohydrates into value-added chemicals.

Conversion of biomass-derived carbohydrates into 5-hydroxymethylfurfural over sulfonated zirconium/tin mixed-metal metal–organic frameworks in deep eutectic solvents-water based biphasic system

5-hydroxymethylfurfural (5-HMF) is a key platform chemical that can be applied to generate varied value-added products. Herein, the sulfonated zirconium/tin Mixed-Metal metal–organic frameworks (MOFs), Sn/UiO-66-SO3H catalysts were employed for catalytic conversion of biomass-derived carbohydrates (glucose, sucrose, maltose, starch, and cellulose) to 5-HMF in green deep eutectic solvents (DESs)-water based biphasic system. The Sn/UiO-66-SO3H catalysts were prepared by infiltrating Sn4+ into the UiO-66-SO3H via post-synthesis modification. The synthesized catalysts were characterized by PXRD, SEM, FTIR, N2 adsorption–desorption analysis, XPS, ICP-OES, NH3-TPD and Py-FTIR. The synergistic effect of Zr4+ and Sn4+ increased the total acidity and pore size of MOFs, thus promoting the catalytic performance of MOFs towards carbohydrates conversion to 5-HMF. The 24-Sn/UiO-66-SO3H with impregnation of Sn4+ for 24 h presented desired catalytic ability, which resulted in 81.5 % and 41.7 % 5-HMF yields from glucose and cellulose in DES betaine-malic acid–water/MIBK biphasic system, respectively. Moreover, the five-recycling test for 24-Sn/UiO-66-SO3H demonstrated excellent reusability of the prepared catalyst. This study offered a novel sulfonated Mixed-Metal strategy on MOFs in DES betaine-malic acid–water based biphasic system for the production of 5-HMF from biomass-derived carbohydrates.

Efficient catalytic conversion of cellulose into 5-hydroxymethylfurfural by modified cerium zirconium phosphates in a biphasic system

Numerous metal phosphates have shown activity in the conversion of cellulose into 5-hydroxymethylfurfural (HMF). However, challenges persist due to low HMF yields and unclear structure-reactivity relationships. Herein, a series of zirconium-cerium phosphate-based catalysts were prepared by the co-precipitation method. These catalysts were sulfonated and loaded with tungsten to introduce Brønsted acidity. The effects of catalyst types and operating conditions on the production of HMF from cellulose using a biphasic system of tetrahydrofuran (THF) and water were systematically investigated in an autoclave reactor. The structure-reactivity relationship of these catalysts was subsequently elucidated using various catalyst characterization techniques. For an understanding of the reaction mechanism, in-situ attenuated total reflectance infrared spectroscopy (ATR-FTIR) was employed to monitor the reaction process. Experimental results revealed that the optimal HMF yield of 41.5% could be obtained using the 2W/CeZr2P + AC–SO3H–2 catalyst at 180 °C with a reaction time of 4 h. Compared to monometallic phosphate pairs of zirconium and cerium, this represents an enhancement in HMF yield by approximately 8%–20%. The enhancement could be attributed to the adequate acid amount and the balanced Brønsted/Lewis acid site ratio of this catalyst. These findings provide valuable guidance for future design and optimization of bimetallic phosphate catalysts.

Hydrothermal Valorization via Liquid Hot Water and Hydrothermal Carbonization of Pea Pod Waste: Characterization of the Biochar and Quantification of Platform Molecules

Pea pod cultivation spans various regions and climates, with a global production of around 20 million tons. The pea peel wastes, which make up 30–40% of the total weight of the peas, are freely available in large quantities. The biomass used was characterized via ultimate, proximate, and structural analysis, obtaining 20.2%w of cellulose and 17.4%w of hemicellulose, which, via valorization processes, can be transformed into platform chemicals. Hydrothermal valorization presents itself as a clean form of treatment for these wastes, ranging from 120 to 180 °C (LHW) and from 180 to 260 °C (HTC). The use of LHW can lead to the production of sugars (up to 70%w yield) and levulinic acid (4%w yield), while the use of HTC leads to formic acid (40%w yield) and levulinic acid (4%w yield). The use of LHW for longer periods favors the production of HMF and furfural. The use of homogeneous catalysts (H2SO4, CH3COOH, KOH, and NaHCO3) was implemented, and their selectivity was described. Solid fractions of LHW and HTC were characterized via FTIR and elemental analysis, and the change in their structure was described as they shifted from biomass to biochar. Optimal conditions for each platform chemical were reported to best utilize the pea pod waste.

A Closed-Loop Biorefinery Approach for the Valorization of Winery Waste: The Production of Iron-Sulfonated Magnetic Biochar Catalysts and 5-Hydroxymethyl Furfural from Grape Pomace and Stalks

In this work, a closed-loop strategy for the management and valorization of winery waste was proposed. The exhausted pomace and grape stalks that are typically obtained from white wine industries were used as a source of simple sugars, namely, glucose and fructose, and of lignocellulosic feedstock for the preparation of selective catalysts for the 5-hydroxymethylfurfural (5-HMF) production from fructose. A novel synthetic procedure was developed for the synthesis of iron-sulfonated magnetic biochar catalysts (Fe-SMBCs). Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), BET surface area, porous structure analysis and determination of total amount of acid sites were performed in order to characterize the physico-chemical properties of the synthesized systems. Then, these heterogeneous catalysts were successfully tested via the dehydration of simple sugars into 5-HMF by using methyl isobutyl ketone (MIBK) and gamma valerolactone (GVL) as co-solvents. The optimum 5-HMF yield of 40.9 ± 1.1%mol with a selectivity of 59.8 ± 2.6%mol was achieved by adopting the following optimized conditions: 0.1 g of catalyst, volume ratio of GVL to H2O = 2 to 1, 403 K, 6 h. In addition, the catalyst was easily recycled using an external magnetic field and used for at least five reaction cycles without significant loss of catalytic activity.