Experimental and Kinetic Modeling Studies on the Conversion of Sucrose to Levulinic Acid and 5-Hydroxymethylfurfural Using Sulfuric Acid in Water

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.

Precursor-Driven Catalytic Performances of Al2O3-Supported Earth-Abundant Ni Catalysts in the Hydrogenation of Levulinic Acid and Hydroxymethylfurfural into Added-Value Chemicals

It has been shown that the nature of the metal precursor and the thermal effects during calcination determine the physicochemical properties of the catalysts and their catalytic activity in the levulinic acid (LA) and 5-hydroxymethylfurfural (HMF) hydrogenation reactions. The endothermic effect during calcination of the inorganic nickel precursor promoted higher metal dispersion and stronger interaction with the alumina surface. In contrast, the exothermic effects during the calcination of organic nickel precursors resulted in smaller metal dispersion and lower interaction with the support surface. A clear relationship was found between the size of the metal crystallites and the yield of LA hydrogenation reaction. The smaller crystallites were more active in the LA hydrogenation reaction. In turn, the size of the metal particles and their nature of interaction with the surface of the alumina influence the hydrogenation pathways of the HMF.

Integrated Humin Formation and Separation Studied In Situ by Centrifugation

We present a novel method for studying the integrated formation and separation of humins formed during the Brønsted acid-catalyzed conversion of fructose (here, at 90 °C with 20 wt % fructose and 5 wt % sulfuric acid). For the first time, we report the reaction carried out in situ during systematic centrifugation experiments, which allows combining humin formation and separation along with investigation of the phase behavior of humins. Analysis of the formed humin deposits employing scanning electron microscopy reveals deposits that are formed from a layer of monodisperse microspheres with a narrow diameter range of 0.9-1.9 μm. In the centrifugal force field, the microspheres partially coalesce, which increases with time and relative centrifugal force up to the formation of a thin and uniform layer of microspheres covering a continuous humin bulk phase with 80-90 μm thickness. These findings give evidence that humin spheres are highly viscous droplets rather than solid particles during formation. Our result is in line with the often-reported spherical and planar deposits formed during acidic carbohydrate conversion in technical systems and supports the development of strategies for deposit prevention, on the one hand, and humin preparation for material utilization, on the other hand.

Recent Advances in Zeolites-Catalyzed Biomass Conversion to Hydroxymethylfurfural: The Role of Porosity and Acidity

Biomass is an attractive raw material for the production of fuel oil and chemical intermediates due to its abundant reserves, low price, easy biodegradability, and renewable use. Hydroxymethylfurfural (5-HMF) is a valuable platform chemically derived from biomass that has gained significant research interest owing to its economic and environmental benefits. In this review, recent advances in biomass catalytic conversion systems for 5-HMF production were examined with a focus on the catalysts selection and feedstocks' impact on the 5-HMF selectivity and yield. Specifically, the potential of zeolite-based catalysts for efficient biomass catalysis was evaluated given their unique pore structure and tunable (Lewis and Brønsted) acidity. The benefits of hierarchical modifications and the interactions between porosity and acidity in zeolites, which are critical factors for the development of green catalytic systems to convert biomass to 5-HMF efficiently, were summarized and assessed. This Review suggests that zeolite-based catalysts hold significant promise in facilitating the sustainable utilization of biomass resources.

Formic acid as a sacrificial agent for byproduct suppression in glucose dehydration to 5-hydroxymethylfurfural using NaY zeolite catalyst

Biomass-derived 5-hydroxymethylfurfural (HMF) holds potential for applications in green materials, but its conventional synthesis is hindered by undesired side reactions. This study presents a catalytic system that effectively suppresses the formation of byproducts, thus enhancing HMF yield. The system demonstrated synergistic effects between Lewis acid NaY zeolite and formic acid sacrificial agent for the production of HMF from glucose. The results indicate that formic acid reacts with reactive intermediates from glucose decomposition, preventing their interactions with other sugar-derived species in the dehydration path to HMF. Such effect originates from the neutral formic acid species rather than the dissociated acidic proton normally observed in Brønsted acid-catalyzed reactions. The NaY/formic acid catalysts in isopropanol/water achieved a 57% HMF yield, a significant improvement over 31% and 27% yields with NaY or formic acid alone, respectively. Moreover, performance of the spent catalysts was easily restored to the original state via a simple NaCl wash.

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.

Scaling-up of carbon dots hydrothermal synthesis from sugars in a continuous flow microreactor system for biomedical application as in vitro antimicrobial drug nanocarrier

Carbon dots (CDs) are a new class of nanomaterials exhibiting high biocompatibility, water solubility, functionality, and tunable fluorescence (FL) property. Due to the limitations of batch hydrothermal synthesis in terms of low CDs yield and long synthesis duration, this work aimed to increase its production capacity through a continuous flow reactor system. The influence of temperature and time was first studied in a batch reactor for glucose, xylose, sucrose and table sugar precursors. CDs synthesized from sucrose precursor exhibited the highest quantum yield (QY) (175.48%) and the average diameter less than 10 nm (~6.8 ± 1.1 nm) when synthesized at 220°C for 9 h. For a flow reactor system, the best condition for CDs production from sucrose was 1 mL min-1 flow rate at 280°C, and 0.2 MPa pressure yielding 53.03% QY and ~ 6.5 ± 0.6 nm average diameter (6.6 mg min-1 of CDs productivity). CDs were successfully used as ciprofloxacin (CP) nanocarrier for antimicrobial activity study. The cytotoxicity study showed that no effect of CDs on viability of L-929 fibroblast cells was detected until 1000 µg mL-1 CDs concentration. This finding demonstrates that CDs synthesized via a flow reactor system have a high zeta potential and suitable surface properties for nano-theranostic applications.

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.

Reaction Mechanism of the Microwave-Assisted Synthesis of 5-Hydroxymethylfurfural from Sucrose in Sugar Beet Molasses

5-hydroxymethylfurfural (HMF) stands out among the chemical products derived from biomass as a building block in the chemical industry. The conventional production of HMF is usually carried out from fructose, glucose, or other monosaccharides as feedstock, but sugar beet molasses, a by-product of the sugar industry containing sucrose (45–55%), is promising. This exploratory study used three aqueous stock solutions and one biphasic system as the sources of sucrose. The dehydration of sucrose to 5-hydroxymethylfurfural was assisted by microwave heating and subcritical water conditions. The maximum yield of HMF was 27.8 mol % for the aqueous solution of synthetic sucrose at 80 min of treatment. Although HMF yield was 7.1 mol % in the aqueous sugar beet molasses solution, it increased 2-fold after clarification (15.1 mol %) and 1.6-fold in the biphasic system (11.4 mol %). These are favorable outcomes since this is an exploratory investigation. The pseudo-first-order model fitted experimental data from the conversion of the sucrose from the stock solutions, and kinetic parameters were estimated and compared. The estimated reaction rate constant showed that inversion of sucrose is faster than fructose dehydration to HMF, but the latter reaction was the rate-determining step only for the biphasic system. The maximum partition coefficient value was four between 40 min and 60 min of reaction, calculated at room temperature. These predictions help investigators to estimate conversions and selectivity when pilot plants need to be simulated.

Kinetic studies of 5-(hydroxymethyl)-furfural formation and change of the absorption at 420 nm in fruit juices for the improvement of pasteurization plants

Preservation of juices is essential to obtain microbial safe products. There are various established methods as pasteurization. Heretofore, only the kinetic figures of microbial inactivation were considered but not those of reaction impairing the chemical quality. For a gentler processing, knowledge of the kinetics of relevant chemical conversion reactions is necessary. 5-(Hydroxymethyl)-furfural (HMF) formation and the color change of juices are important attributes. The non-isothermal Rhim method was used to determine the activation energy and pre-exponential factor for HMF formation in different juices and an isothermal method for the reaction order. Values for the activation energy from 133 to 303 kJ/mol were obtained with a zeroth reaction order. A correlation between HMF and the color change could be found. Based on the kinetic figures, lines with equal effects for the chemical changes and for the lethal effect on microorganisms were calculated. Time-temperature settings for the gentlest treatment could be found.

Simultaneous quantification of total carbohydrate and protein amounts from aqueous solutions by the sulfuric acid ultraviolet absorption method (SA-UV method)

Based on the sulfuric acid-ultraviolet assay (SA-UV, developed by Albalasmeh et al., 2013), we have further expanded this method for the simultaneous quantification of saccharides (carbohydrates) and proteins by ultraviolet spectrophotometry. The absorbance of saccharides depends on the formation of furfurals by dehydration in the presence of concentrated sulfuric acid, whereas proteins are unaffected and can be quantified by UV active peptide bonds and aromatic amino acid residues. In saccharide/protein mixtures the SA-UV assay offers a good alternative and substitutes the need for two different methods, like the phenol-sulfuric acid (PSA, developed by DuBois et al., 1951) and bicinchoninic acid (BCA, developed by Smith et al., 1985) assays. For the development of this method, we used glucose and BSA as model substrates and performed a method validation in terms of linearity, LOD, LOQ, accuracy, and precision. Simultaneous quantification in glucose/BSA mixtures is possible down to 20 mg/L from 30 μL sample volumes, and even low content mixtures with concentrations down to 2 mg/L can appropriately be quantified from higher volumes by an evaporation technique.

A Novel Kinetic Modeling Framework for the Polycondensation of Sugars Using Monte Carlo and the Method of Moments

The kinetics of the hydrolysis and polycondensation reactions of saccharides have made the subject of numerous studies, due to their importance in several industrial sectors. The present work, presents a novel kinetic modeling framework that is specifically well-suited to reacting systems under strict moisture control that favor the polycondensation reactions towards the formation of high-degree polysaccharides. The proposed model is based on an extended and generalized kinetic scheme, including also the presence of polyols, and is formulated using two different numerical approaches, namely a deterministic one in terms of the method of moments and a stochastic kinetic Monte Carlo approach. Accordingly, the most significant advantages and drawbacks of each technique are clearly demonstrated and the most fitted one (i.e., the Monte Carlo method) is implemented for the modeling of the system under different conditions, for which experimental data were available. Through these comparisons it is shown that the model can successfully follow the evolution of the reactions up to the formation of polysaccharides of very high degrees of polymerization.

Seagrass-based platform strategies for sustainable hydroxymethylfurfural (HMF) production: toward bio-based chemical products

Today, sustainable chemistry is a key trend in the chemical manufacturing industry due mainly to concerns over the global environment and resource security. In sustainable chemical manufacture, the choice of a bio-based feedstock plays a pivotal pillar. In terms of feedstock utilization for producing HMF, which is a multivalent platform intermediate easily convertible to valuable chemical products; biopolymers, biofuels, and other important chemicals, seagrass biomasses can be more favorable feedstocks compared with land plant resources due primarily to easy availability and no systematic farming. Moreover, seagrass feedstocks could contribute cost-effectively and sustainably producing HMF by exploiting the beach-cast seagrasses on seagrass-prairies with no feedstock cost, indicating that seagrass biomasses could be a most promising biofeedstock source for sustainable HMF production. We afford a platform bioprocessing technology that has not been attempted before for sustainable HMF production using raw seagrass biomass. This bioprocess can be operated by simple reaction conditions using inorganic Brønsted acids (mainly HCl) and ionic liquid solvents at relatively low temperatures (120-130 °C). In addition, some bioengineering strategies for improving the growth of seagrass biomass and the quantity/quality of nonstructural carbohydrates (starch, sucrose) that can be used as the feeding substrates for HMF production are also discussed. The main aim of this review is to provide some important information about breakthrough bio/technologies conducive to cost-effective and sustainable HMF production.

Current Situation of the Challenging Scale-Up Development of Hydroxymethylfurfural Production

Hydroxymethylfurfural (HMF) is a high-value platform chemical derived from renewable resources. In recent years, considerable efforts have been made to produce HMF also at industrial scale, which still faces some challenges regarding yield as well as sustainable and economic process designs. This critical Review evaluates the industrial process development of sustainable biomass conversion to HMF. Qualitative and quantitative guidelines are defined for the technological assessment of the processes described in patent literature. The formation of side products, difficulties in the separation and purification of HMF as well as catalyst regeneration were identified as major challenges in the HMF production. A first small-scale, commercial HMF production plant with a capacity of 300 tHMF per year has been operating in Switzerland since 2014.

Stabilization strategies in biomass depolymerization using chemical functionalization

A central feature of most lignocellulosic-biomass-valorization strategies is the depolymerization of all its three major constituents: cellulose and hemicellulose to simple sugars, and lignin to phenolic monomers. However, reactive intermediates, generally resulting from dehydration reactions, can participate in undesirable condensation pathways during biomass deconstruction, which have posed fundamental challenges to commercial biomass valorization. Thus, new strategies specifically aim to suppress condensations of reactive intermediates, either avoiding their formation by functionalizing the native structure or intermediates or selectively transforming these intermediates into stable derivatives. These strategies have provided unforeseen upgrading pathways, products and process solutions. In this Review, we outline the molecular driving forces that shape the deconstruction landscape and describe the strategies for chemical functionalization. We then offer an outlook on further developments and the potential of these strategies to sustainably produce renewable-platform chemicals.

The Effect of Mechanocatalytic Pretreatment on the Structure and Depolymerization of Willow

In this study, the effect of a mechanocatalytic pretreatment on the structure of willow and sugar release from pretreated willow was explored. In the mechanocatalytic approach, the pretreatment consists of solvent-free impregnation with sulfuric acid and a mechanical treatment with ball milling. Willow sawdust and pretreated samples were analyzed with field emission scanning electron microscope and X-ray diffraction. The products in the sugar solution were determined as the total reducing sugars with the 3,5-dinitrosalicylic acid method and monosaccharides with capillary electrophoresis. According to the results, milling increased the sugar production, depending on the sulfuric acid load. The milling parameters, such as the rotation speed of the mill, the catalyst-to-willow ratio, and the milling time influenced the amount of sugars in the hydrolysate and the composition of the sugar solution produced. Changes were observed in the surface of the willow particles as well as changes in the crystalline structure. Glucose and xylose yields increased after 15 min of milling and reached their maximum level after 45 min of milling with the 0.5 mmol/g sulfuric acid load.

High-Yield 5-Hydroxymethylfurfural Synthesis from Crude Sugar Beet Juice in a Biphasic Microreactor

5-Hydroxymethylfurfural (HMF) is an important biobased platform chemical obtainable in high selectivity by the hydrolysis of fructose (FRC). However, FRC is expensive, making the production of HMF at a competitive market price highly challenging. Here, it is shown that sugar beet thick juice, a crude, sucrose-rich intermediate in sugar refining, is an excellent feedstock for HMF synthesis. Unprecedented high selectivities and yields of >90 % for HMF were achieved in a biphasic reactor setup at 150 °C using salted diluted thick juice with H2 SO4 as catalyst and 2-methyltetrahydrofuran as a bioderived extraction solvent. The conversion of glucose, obtained by sucrose inversion, could be limited to <10 mol %, allowing its recovery for further use. Interestingly, purified sucrose led to significantly lower HMF selectivity and yields, showing advantages from both an economic and chemical selectivity perspective. This opens new avenues for more cost-effective HMF production.

Influence of the pH Value on the Hydrothermal Degradation of Fructose

The hydrothermal treatment of sugars features a promising technology for the production of fine and platform chemicals from renewable resources. In this work the hydrothermal decomposition of fructose was studied in a buffered medium at a pH range between 2.2 and 8.0. It is demonstrated that at lower pH values mainly 5-hydroxymethylfurfural (HMF), levulinic acid and humin are generated, while lactic acid and acetic acid are produced at higher pH values. The work shows that the use of moderate acidic conditions may have advantages for the hydrothermal HMF production over the use of strongly acidic conditions, as especially the degradation into levulinic acid is suppressed. Besides, this study deals with a rather complex reaction network, hence limitations and need for adaption of the kinetic model are discussed.

Improvement of hydrogen production from Chlorella sp. biomass by acid-thermal pretreatment

BACKGROUND

Owing to the high growth rate, high protein and carbohydrate contents, and an ability to grow autotrophically, microalgal biomass is regarded as a promising feedstock for fermentative hydrogen production. However, the rigid cell wall of microalgae impedes efficient hydrolysis of the biomass, resulting in low availability of assimilable nutrients and, consequently, low hydrogen production. Therefore, pretreatment of the biomass is necessary in order to achieve higher hydrogen yield (HY). In the present study, acid-thermal pretreatment of Chlorella sp. biomass was investigated. Conditions for the pretreatment, as well as those for hydrogen production from the pretreated biomass, were optimized. Acid pretreatment was also conducted for comparison.

RESULTS

Under optimum conditions (0.75% (v/v) H2SO4, 160 °C, 30 min, and 40 g-biomass/L), acid-thermal pretreatment yielded 151.8 mg-reducing-sugar/g-biomass. This was around 15 times that obtained from the acid pretreatment under optimum conditions (4% (v/v) H2SO4, 150 min, and 40 g-biomass/L). Fermentation of the acid-thermal pretreated biomass gave 1,079 mL-H2/L, with a HY of 54.0 mL-H2/g-volatile-solids (VS), while only 394 mL/L and 26.3 mL-H2/g-VS were obtained from the acid-pretreated biomass.

CONCLUSIONS

Acid-thermal pretreatment was effective in solubilizing the biomass of Chlorella sp. Heat exerted synergistic effect with acid to release nutrients from the biomass. Satisfactory HY obtained with the acid-thermal pretreated biomass demonstrates that this pretreatment method was effective, and that it should be implemented to achieve high HY.

Effects of Sulfuric Acid on the Curing Behavior and Bonding Performance of Tannin⁻Sucrose Adhesive

The development of biomaterials-based adhesives is one of the main research directions for the wood-based material industry. In previous research, tannin and sucrose were used as adhesive to manufacture particleboard. However, the reaction conditions need to be optimized. In this study, sulfuric acid was added to the tannin⁻sucrose adhesive as a catalyst to improve the curing process. Thermal analysis, insoluble mass proportion, FT-IR, and solid state 13C NMR were used to investigate the effects of sulfuric acid on the curing behavior of tannin and sucrose. Thermal analysis showed weight loss and endotherm temperature reduced from 205 and 215 to 136 and 138 °C, respectively, by adding sulfuric acid. In case of the adhesive with pH = 1.0, the insoluble mass proportion achieved 81% at 160 °C, which was higher than the reference at 220 °C. FT-IR analysis of the uncured adhesives showed that adding sulfuric acid leads to hydrolysis of sucrose; then, glucose and fructose converted to 5-hydroxymehthylfurfural (HMF) and levulinic acid. Dimethylene ether bridges were observed by FT-IR analysis of the cured adhesives. The results of solid state 13C NMR spectrum indicated that 5-HMF participated in the curing process and formed methylene bridges with the C8 position of the resorcinol A-rings of tannin, whereas dimethylene ether bridges were detected as a major chemical chain of the polymer. Lab particleboards were produced using 20 wt % resin content at 180 °C and 10 min press time; the tannin⁻sucrose adhesive modified with sulfuric acid to pH = 1.0 exhibited better performance than the unmodified tannin⁻sucrose adhesive; the properties of the boards fulfilled the requirement of Japanese Industrial Standard (JIS) A5908 type 15.