Valorization of humin-based byproducts from biomass processing-a route to sustainable hydrogen

Valorization of Humins by Cyclic Levulinic Acid Production Using Polyoxometalates and Formic Acid

At a time when increasing attention is paid to sustainability in chemistry, levulinic acid (LA) is one of the most important platform chemicals for the goal of overcoming our dependence on fossil raw materials. However, a so far limiting obstacle on the way to efficient LA production from biomass is the formation of undesirable humin byproducts. In this work, a new catalytic route for the effective utilization of these humin byproducts, enabling a cyclic synthesis of LA using formic acid (FA) as organocatalyst is proposed. Selective catalytic oxidation (SCO) of humins using the H5PV2Mo10O40 (HPA-2) polyoxometalate (POM) catalyst produces FA that can be isolated from the aqueous reaction mixture by using nanofiltration membranes accompanied by a complete catalyst recycling (>99 %). After concentration of FA by distillation, the latter can be used as organocatalyst for LA production from sugars, whereby the formed humins can in turn be separated and used as substrates for further FA production via SCO to close the catalytic cycle. By using FA as a green and sustainable acidic organocatalyst, relatively high yields of LA (up to 42 mol %) could be achieved. In the future this can potentially lead to the creation of a closed cycle for an environmentally friendly and efficient production of green LA without undesired humin formation.

Valorization of Soybean Peel-Derived Humins for Carbon Dot (CD) Production

Over the past few decades, awareness has risen substantially about the limitations of non-renewable resources and the environmental challenges facing the chemical industry. This has necessitated a transition toward renewable resources, such as lignocellulosic biomass, which is among the most abundant renewable carbon sources on the planet. Lignocellulosic biomass represents a significant yet often underutilized source of fermentable sugars and lignin, with potential applications across multiple sectors of the chemical industry. The formation of humins (polymeric byproducts with a complex conjugated network, comprising furanic rings and various functional groups, including ketones) occurs inevitably during the hydrothermal processing of lignocellulosic biomass. This study presents the use of humin byproducts derived from soybean peels for the production of fluorescent carbon dots (CDs). A comparison between sonochemical and thermochemical methods was conducted for the synthesis of this nanomaterial. The obtained nanoparticles were characterized in terms of size, morphology (TEM, DLS), and Z-potential. Subsequently, the spectroscopic properties of the prepared CDs were studied using absorption and emission spectroscopy. In particular, the CDs displayed a blue/cyan fluorescence under UV irradiation. The emission properties were found to be dependent on the excitation wavelength, shifting to longer wavelengths as the excitation wavelength increased. The carbon dots that exhibited the most favorable photochemical properties (QY = 2.5%) were those produced through a sonochemical method applied to humins obtained from the dehydration of soybean husks with phosphoric acid and prior treatment.

Molecular structure and composition elucidation of an industrial humin and its fractions

Humins, (side-)products of the acid-catalysed dehydration of carbohydrates, will be produced in substantial quantities with the development of industrial biorefining processes. Most structural knowledge about such humins is based on synthetic model humins prepared at lab-scale from typical carbohydrate(-derived) compounds. Here, we report the first extensive characterisation study of an industrial humin. The soluble humin was generated from pilot plant-scale methanolic cyclodehydration of D-fructose to 5-methoxymethyl-2-furfural (MMF), as part of the Avantium YXY® process to produce FDCA. Purification of the industrial humin followed by fractionation allowed isolation of a water-insoluble, high molecular weight fraction (WIPIH) and a water-soluble, low-to-middle molecular weight soluble fraction (WES). Characterisation by elemental analysis, thermogravimetry, IR and NMR spectroscopy and size exclusion chromatography provided a detailed picture of the humin structure in both fractions. Aided by a comprehensive NMR spectral library of furanic model compounds, we identified the main furanic building blocks and inter-unit linkages and propose a structure for this industrial humin sample. The WIPIH and WES fractions were found to be composed of furanic rings interconnected by short aliphatic chains containing a wide range of functionalities including alcohols, ethers, carboxylic acids, esters, aldehydes and ketones. The low level of crosslinking and high functional group content of the industrial humin differ from the more extensively studied, (highly over-)condensed synthetic model humins, towards which they can be considered intermediates. The structural and compositional insights into the nature of an actual industrial humin open up a broad spectrum of valorisation opportunities.

Valorization of Glucose-Derived Humin as a Low-Cost, Green, Reusable Adsorbent for Dye Removal, and Modeling the Process

Glucose can be isomerized into fructose and dehydrated into key platform biochemicals, following the "bio-refinery concept". However, this process generates black and intractable substances called humin, which possess a polymeric furanic-type structure. In this study, glucose-derived humin (GDH) was obtained by reacting D-glucose with an allylamine catalyst in a deep eutectic solvent medium, followed by a carbonization step. GDH was used as a low-cost, green, and reusable adsorbent for removing cationic methylene blue (MB) dye from water. The morphology of carbonized GDH differs from pristine GDH. The removal efficiencies of MB dye using pristine GDH and carbonized GDH were 52% and 97%, respectively. Temperature measurements indicated an exothermic process following pseudo-first-order kinetics, with adsorption behavior described by the Langmuir isotherm. The optimum parameters were predicted using the response surface methodology and found to be a reaction time of 600 min, an initial dye concentration of 50 ppm, and a GDH weight of 0.11 g with 98.7% desirability. The MB dye removal rate optimized through this model was 96.85%, which was in good agreement with the experimentally obtained value (92.49%). After 10 cycles, the MB removal rate remained above 80%, showcasing the potential for GDH reuse and cost-effective wastewater treatment.

Investigation of the Formation, Characterization, and Oxidative Catalytic Valorization of Humins

The industrial use of biomass, e.g., for the production of platform chemicals such as levulinic acid, became increasingly important in recent years. However, the efficiency of these processes was reduced by the formation of insoluble solid waste products called humins. Herein, the formation of humins from various carbohydrates was investigated under different process conditions, in order to obtain information about the structure and the formation mechanism. During this process, new potential structural fragments of humins were identified. Subsequently, the produced humins were oxidatively converted to low-molecular-weight carboxylic acids with the use of polyoxometalate catalysts. The experiments showed that the use of sugars in acetic acid and ethanol only lead to the formation of a small amount of humins, which were also structurally most suitable for conversion to carboxylic acids. The main products of the oxidative valorisation of these humins were acetic acid, formic acid, and CO₂, respectively, and our results indicate that certain functional groups were converted preferentially. These findings will help to improve processes for the valorisation of biomass by enabling an overall more efficient use of thermo-sensitive feedstock such as carbohydrates.

Mechanistic Investigation into the Formation of Humins in Acid-Catalyzed Biomass Reactions

Humins are carbonaceous, polymeric byproducts formed during the acid-catalyzed condensed phase transformation of biomass-derived moieties and are responsible for significant carbon loss and catalyst deactivation. There exists very limited knowledge about their formation chemistry and composition. Infrared spectra of humins formed during the dehydration of glucose/fructose to 5-HMF show that the furan ring and the hydroxy methyl group of 5-HMF are present in humins, but the carbonyl group is not. Based on this, aldol addition and condensation between 5-HMF and other derived species are proposed as the main reactions that initiate humin formation. Hence, in this work, density functional theory (DFT)-based calculations are performed to compute the reaction pathways, activation barriers, and reaction free energies associated with all elementary reaction steps in the 5HMF-initiated, acid-catalyzed reactions leading to humin formation. The humin formation is initiated with the rehydration of HMF to form 2,5-dioxo-6-hydroxy-hexanal or DHH (key promoter of humin formation), followed by its keto-enol tautomerization and aldol addition and condensation with HMF. The rate-determining step in this pathway is the aldol-addition reaction between the DHH-derived enols with 5-HMF. Within the implicit solvation approximation, the formation of the 5-HMF-DHH dimer is slightly endergonic, whereas the 5-HMF rehydration leading to DHH is thermodynamically downhill. This mechanistic understanding of initiation reactions for humins could pave the way to screen and design solvent and catalyst systems to deter their formation.

Catalytic Hydrotreatment of Humins Waste over Bifunctional Pd-Based Zeolite Catalysts

The catalytic hydrotreatment of humins, the solid byproduct produced from the conversion of C6 sugars (glucose, fructose) to 5-hydroxymethylfurfural (HMF), using supported Pd@zeolite (Beta, Y, and USY) catalysts with different amounts of Pd (i.e., 0.5, 1.0 and 1.5 wt%) was investigated under molecular hydrogen pressure. The highest conversion of humins (52.0%) was obtained on 1.5Pd@USY catalyst while the highest amount of humins oil (27.3%) was obtained in the presence of the 1Pd@Beta zeolite sample, at PH2 = 30 bars and T = 250 °C. The major compounds in the humins oil evidenced by GC-MS are alcohols, organic acids, ethers, and alkyl-phenolics. However, although all these classes of compounds are obtained regardless of the nature of the catalyst used, the composition of the mixture differs from one catalyst to another. Furanic compounds were not identified in the reaction products. A possible explanation may be related to their high reactivity under the reaction conditions, in the presence of the Pd-based catalysts these compounds lead to alkyl phenolics, important intermediates in the petrochemical industry.

Humic Substances Derived From Biomass Waste During Aerobic Composting and Hydrothermal Treatment: A Review

Humic substances (HSs) occupy 80% of organic matter in soil and have been widely applied for soil remediation agents, potential battery materials, and adsorbents. Since the HS extraction rate is very low by microbial degradation in nature, artificial humification processes such as aerobic composting (AC) and hydrothermal treatment (HT) have attracted a great deal of attention as the most important strategies in HS production. This article aims to provide a state-of-the-art review on the development of conversion of biomass waste into HSs based on AC and HT for the first time in terms of mechanisms, characteristics of HSs’ molecular structure, and influencing factors. In addition, some differences based on the aforementioned information between AC and HT are reviewed and discussed in the conversion of biomass waste into HSs in a pioneering way. For biomass waste conversion, a feasible strategy on effective humification processes by combining AC with HT is proposed.

Physico-Chemical Properties and Principal Component Analysis of Biobased Thermosets Developed with Different Batches of Industrial Humins

Humins have already shown their potential as thermosetting resins to produce crosslinked networks and composites, with a large variety of properties depending on the used macromolecular approach. Our group has shown that a very interesting class of materials with tunable flexibility can be made by humins co-polymerization with glycerol diglycidyl ether (GDE). To create a clearer picture on structure-reactivity-properties-application interdependent relationship, a principal component analysis (PCA) was applied on several humins batches. The PCA allowed to obtain a clear discrimination between the humins/GDE resins samples in 3 groups which correlate very well with the results of copolymerization reactivity (DSC) and thermosets properties: crosslink density, thermal stability, tan δ, Shore D hardness values, etc.

Humins Blending in Thermoreversible Diels-Alder Networks for Stiffness Tuning and Enhanced Healing Performance for Soft Robotics

Humins waste valorization is considered to be an essential pathway to improve the economic viability of many biorefinery processes and further promote their circularity by avoiding waste formation. In this research, the incorporation of humins in a Diels-Alder (DA) polymer network based on furan-maleimide thermoreversible crosslinks was studied. A considerable enhancement of the healing efficiency was observed by just healing for 1 h at 60 °C at the expense of a reduction of the material mechanical properties, while the unfilled material showed no healing under the same conditions. Nevertheless, the thermal healing step favored the irreversible humins polycondensation, thus strengthening the material while keeping the enhanced healing performance. Our hypothesis states a synergistic healing mechanism based on humins flowing throughout the damage, followed by thermal humins crosslinking during the healing trigger, together with DA thermoreversible bonds recombination. A multi-material soft robotic gripper was manufactured out of the proposed material, showing not only improved recovery of the functional performance upon healing but also stiffness-tunable features by means of humins thermal crosslinking. For the first time, both damage healing and zone reinforcement for further damage prevention are achieved in a single intrinsic self-healing system.

Identification of Crucial Intermediates in the Formation of Humins from Cellulose-Derived Platform Chemicals Under Brønsted Acid Catalyzed Reaction Conditions

Humins are one of the undesirable products formed during the dehydration of sugars as well as the conversion of 5-hydroxymethylfurfural (HMF) to value-added products. Thus, reducing the formation of humins is an important strategy for improving the yield of the aforementioned reactions. Even after a plethora of studies, the mechanism of formation and the structure of humins are still elusive. In this regard, we have employed density functional theory-based mechanistic studies and microkinetic analysis to identify crucial intermediates formed from glucose, fructose, and HMF that can initiate the polymerization reactions resulting in humins under Brønsted acid-catalyzed reaction conditions. This study brings light into crucial elementary reaction steps that can be targeted for controlling humins formation. Moreover, this work provides a rationale for the experimentally observed aliphatic chains and HMF condensation products in the humins structure. Different possible polymerization routes that could contribute to the structure of humins are also suggested based on the results. Importantly, the findings of this work indicate that increasing the rate of isomerization of glucose to fructose and reducing the rate of reaction between HMF molecules could be an efficient strategy for reducing humins formation.

Designing FeO@graphite@C Nanocomposites Based on Humins as Efficient Catalysts for Reverse Water-Gas Shift

Acid-catalyzed conversion of biomass into bio-based platform chemicals such as levulinic acid and 5-hydroxymethylfurfural is an important route in biorefineries, which has attracted much attention in recent years. Such a route however unavoidably yields massive recalcitrant byproducts called humins, which are now broadly considered as waste and are limited to combustion, causing unfavorable energy and environmental processes. Therefore, the development of a value-added utilization approach for such humin byproducts is crucial for making the biorefineries economical and environmentally viable. In this work, we present a starting point for valorization of humins via the preparation of carbon-based iron oxide nanocomposites of FeO@graphite@C by using the humins as carbon resources and material templates via a facile synthesis strategy. The as-prepared catalyst is capable of promoting the reverse water-gas shift reaction and reaching a high CO₂ conversion ratio with excellent CO selectivity (> 99%) at 500-700 °C, enabling an efficient utilization of waste CO₂. The unique graphite-capsuled FeO structure of FeO@graphite@C was found to be the origin of its excellent catalytic activity toward CO₂ reduction into CO, which shifts electrons from the graphite layer to FeO, reconstructing the Fe electron structure. This strengthened the electrophilic attack ability toward CO₂ and weakened the bond with the derived CO* species of the Fe active sites, associated with the excellent CO₂ conversion and CO selectivity.

Heterogeneous Catalysis to Drive the Waste-to-Pharma Concept: From Furanics to Active Pharmaceutical Ingredients

A perspective on the use of heterogeneous catalysis to drive the waste-to-pharma concept is provided in this contribution based on the conversion of furanics to active pharmaceutical ingredients (APIs). The provided overview of the concept in this perspective article has been exemplified for two key molecule examples: Ancarolol and Furosemide.

Understanding the Effect of Solvent Environment on the Interaction of Hydronium Ion with Biomass Derived Species: A Molecular Dynamics and Metadynamics Investigation

The addition of aprotic solvents results in higher reactivities and selectivities in many key aqueous phase biomass reactions, including the acid-catalyzed conversion of fructose to 5-hydroxyl methyl furfural (HMF). The addition of certain co-solvents inhibits the formation of humins via preferential solvation of key functional groups and can alter reaction kinetics. An important factor in this context is the relative stability of the hydronium ion (the catalyst) in the vicinity of the biomass moiety as compared to that in bulk, as it could determine its efficacy in the protonation step. Hence, in the present work, molecular dynamics (MD) simulations of HMF (the model product) and fructose (the model reactant) in acidic water and water-DMSO mixtures are performed to analyze their interaction with the hydronium ions. We show that the presence of DMSO favors the interaction of the hydronium ion with fructose, whereas it has a detrimental effect on the interaction of hydronium ion with HMF. Well-tempered metadynamics (WT-MTD) simulations are performed to determine the relative stability of the hydronium ion in the immediate vicinity of fructose and HMF, as compared to that in the bulk solvent phase, as a function of solvent composition. We find that DMSO improves the stabilization of the hydronium ions in the first solvation shell of fructose compared to that in the bulk solvent. On the other hand, hydronium ions become less stable in the immediate vicinity of HMF, as the concentration of DMSO increases.

Valorization of humins from food waste biorefinery for synthesis of biochar-supported Lewis acid catalysts

To close the carbon loop of biomass waste valorization, it is imperative to utilize the unavoidable by-products such as humins, a carbonaceous residue with complex and heterogeneous composition. In this study, starch-rich rice waste was effectively converted into value-added chemicals (e.g., 5-hydroxymethylfurfural) under microwave heating at 160 °C using AlCl₃ as the catalyst. The solid by-products, i.e., humins, were then valorized as a raw material for fabricating biochar-supported Lewis acid catalysts. The humins were collected and pretreated by AlCl₃ as the impregnation agent, followed by carbonization. Detailed characterization revealed several AlO species on the biochar surface plausibly in the amorphous state. The oxygen-containing functional groups of humins might serve as anchoring sites for the Al species during impregnation. The humins-derived biochars exhibited good catalytic activity toward glucose-to-fructose isomerization, a common biorefinery reaction catalyzed by Lewis acids. A fructose yield of up to 14 Cmol% could be achieved under microwave heating at 160 °C for 20 min in water as the greenest solvent. Such catalytic performance was comparable with the previously reported Al-based catalysts derived from wood waste and graphene/graphitic oxide. This study herein highlights humins as a low-cost alternative source of carbon for the preparation of renewable solid catalysts, proposing a novel practice for recycling by-products from food waste valorization to foster circular economy and sustainable development.

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.

Manufacture of Platform Chemicals from Pine Wood Polysaccharides in Media Containing Acidic Ionic Liquids

Pinus pinaster wood samples were subjected to chemical processing for manufacturing furans and organic acids from the polysaccharide fractions (cellulose and hemicellulose). The operation was performed in a single reaction stage at 180 or 190 °C, using a microwave reactor. The reaction media contained wood, water, methyl isobutyl ketone, and an acidic ionic liquid, which acted as a catalyst. In media catalyzed with 1-butyl-3-methylimidazolium hydrogen sulfate, up to 60.5% pentosan conversion into furfural was achieved, but the conversions of cellulose and (galacto) glucomannan in levulinic acid were low. Improved results were achieved when AILs bearing a sulfonated alkyl chain were employed as catalysts. In media containing 1-(3-sulfopropyl)-3-methylimidazolium hydrogen sulfate as a catalyst, near quantitative conversion of pentosans into furfural was achieved at a short reaction time (7.5 min), together with 32.8% conversion of hexosans into levulinic acid. Longer reaction times improved the production of organic acids, but resulted in some furfural consumption. A similar reaction pattern was observed in experiments using 1-(3-sulfobutyl)-3-methylimidazolium hydrogen sulfate as a catalyst.

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.

Kinetics and Chemorheological Analysis of Cross-Linking Reactions in Humins

Humins is a biomass-derived material, co-product of the acid-catalyzed conversion of cellulose and hemicellulose to platform chemicals. This work presents a thorough study concerning the crosslinking kinetics of humins by chemorheological analysis and model-free kinetics under isothermal and non-isothermal curing. Humins can auto-crosslink under the effect of temperature, and the reaction can be fastener when adding an acidic initiator. Thus, the effect of P-Toluenesulfonic acid monohydrate (pTSA) on the crosslinking kinetics was also studied. The dependencies of the effective activation energy (E_α-dependencies) were determined by an advanced isoconversional method and correlated with the variation of complex viscosity during curing. It is shown that humins curing involves multi-step complex reactions and that the use of an acidic initiator allows faster crosslinking at lower temperatures, involving lower E_α. The shift from chemical to diffusion control was also estimated.

How Pseudo-lignin Is Generated during Dilute Sulfuric Acid Pretreatment

Pseudo-lignin is generated from lignocellulose biomass during pretreatment with dilute sulfuric acid and has a significant inhibitory effect on cellulase. However, the mechanism of pseudo-lignin generation remains unclear. The following main points have been addressed to help elucidate the pseudo-lignin generation pathway. Cellulose and xylan were pretreated with sulfuric acid at different concentrations; aliquots were periodically collected; and the changes in the byproducts of the prehydrolysate were quantified. Milled wood lignin (MWL) mixed with cellulose and xylan was pretreated to evaluate the impact of lignin on pseudo-lignin generation. Furfural, 5-hydroxymethylfurfural, and MWL were pretreated as model compounds to investigate pseudo-lignin generation. The result indicated that the increasing acid concentration significantly promoted the generation of pseudo-lignin. When the acid concentration was increased from 0 to 1.00 wt %, pseudo-lignin was increased from 1.36 to 4.05 g. In addition, lignin promoted the pseudo-lignin generation through the condensation between lignin and the generated intermediates.

Humins from Biorefineries as Thermoreactive Macromolecular Systems

Conversion of lignocellulosic biomass often brings about the formation of several side products. Among these, a black and viscous coproduct known as humins is formed on acidic treatment of polysaccharides. To improve the efficiency of this process from an economical and environmental perspective, new solutions for humins valorization are urgently needed. This work focuses on the comprehensive understanding of humins with special emphasis on their structure/properties relationships. Humins were subjected to different thermal treatments and characterized by means of structural, thermoanalytical, and rheological investigations. The structure and composition of humins are very diverse and depend on the thermochemical conditions. On sufficient heating, humins change into a nonreversible and more branched furanic structure with a relatively high glass-transition temperature (T_g >65 °C). Thus, humins can be easily processed for preparing thermoset-like resins.

Catalytic Hydrotreatment of Humins to Bio-Oil in Methanol over Supported Metal Catalysts

Valorization of humins, the polymeric byproducts formed during the acid-catalyzed production of HMF (5-hydroxymethylfurfural) or furfural, is necessary to improve process economics and make biorefineries viable. We report the one-step catalytic hydrotreatment of humins in methanol to humin oil containing fully or partially deoxygenated compounds. First, we compare four commercial noble-metal catalysts (Ru/C, Rh/C, Pt/C, and Pd/C). Aromatic hydrocarbons, phenols, and esters are the main products detected by GC. Rh/C achieves the best GC-detectable oil yield and 75 % humins conversion in 3 h at 400 °C, 30 bar H₂ , and a catalyst-to-humins mass ratio of 1:10. High H₂ pressures and intermediate temperatures, reaction times, and catalyst loadings enhance GC-detectable oil yields. In contrast, high temperatures and long reaction times enhance gasification. Aromatics and phenols are found at high temperatures and long reaction times, whereas esters are the major species at short reaction times and high catalyst loading. ¹³ C-isotopic labeling studies confirm, for the first time, that methanol participates in the alkylation and esterification reactions to form aromatic, phenolic and ester products. The reactivity in isopropanol is also discussed.

Sustainable Utilization of Biomass Refinery Wastes for Accessing Activated Carbons and Supercapacitor Electrode Materials

Biomass processing wastes (humins) are anticipated to become a large-tonnage solid waste in the near future, owing to the accelerated development of renewable technologies based on utilization of carbohydrates. In this work, the utility of humins as a feedstock for the production of activated carbon by various methods (pyrolysis, physical and chemical activation, or combined approaches) was evaluated. The obtained activated carbons were tested as potential electrode materials for supercapacitor applications and demonstrated combined micro- and mesoporous structures with a good capacitance of 370 F g^-1 (at a current density of 0.5 A g^-1 ) and good cycling stability with a capacitance retention of 92 % after 10 000 charge/discharge cycles (at 10 A g^-1 in 6 m aqueous KOH electrolyte). The applicability of the developed activated carbon for practical usage as a supercapacitor electrode material was demonstrated by its successful utilization in symmetric two-electrode cells and by powering electric devices. These findings provide a new approach to deal with the problem of sustainable wastes utilization and to advance challenging energy storage applications.

Sequential Production of Levulinic Acid and Porous Carbon Material from Cellulose

A sequential production of levulinic acid (LA) and porous carbon material (CM) from cellulose was conducted by a two-step process. The cellulose was first acid hydrolyzed, and the preferred reaction conditions required a severity factor of 4.0⁻4.5, in which the yields of LA, formic acid, and solid residue were 38 ± 3 wt%, 17 ± 3 wt%, and 15 ± 3 wt%, respectively. The solid residue was further used for CM preparation through pyrolysis, with or without ZnCl₂ activation. The ZnCl₂ activation promoted the formation of CMs with improved thermal stability, high surface area (1184⁻2510 m²/g), and excellent phenol adsorption capacity (136⁻172 mg/g). The used CM can be easily regenerated by a simple methanol Soxhlet extraction process, and a comparable phenol adsorption capacity of 97 mg/g was maintained for the 5th reusing. Finally, 100 g cellulose produced 40.5 g LA, 18.9 g formic acid and 8.5 g porous CM, with a total carbon utilization ratio reaching 74.4%.

Towards the photophysical studies of humin by-products

Photophysical studies on humins and separated humin fractions were carried out using steady-state and time-resolve fluorescence techniques.

Exploratory catalyst screening studies on the liquefaction of model humins from C6 sugars

A catalyst screening study is reported on the liquefaction of humins, the solid byproducts from C6 sugar biorefineries for levulinic acid and 5-hydroxymethylfurfural production.

Catalytic Hydrotreatment of Humins in Mixtures of Formic Acid/2-Propanol with Supported Ruthenium Catalysts

The catalytic hydrotreatment of humins, which are the solid byproducts from the conversion of C6 sugars (glucose, fructose) into 5-hydroxymethylfurfural (HMF) and levulinic acid (LA), by using supported ruthenium catalysts has been investigated. Reactions were carried out in a batch setup at elevated temperatures (400 °C) by using a hydrogen donor (formic acid (FA) in isopropanol (IPA) or hydrogen gas), with humins obtained from d-glucose. Humin conversions of up to 69 % were achieved with Ru/C and FA, whereas the performance for Ru on alumina was slightly poorer (59 % humin conversion). Humin oils were characterized by using a range of analytical techniques (GC, GC-MS, GCxGC, gel permeation chromatography) and were shown to consist of monomers, mainly alkyl phenolics (>45 % based on compounds detectable by GC) and higher oligomers. A reaction network for the reaction is proposed based on structural proposals for humins and the main reaction products.