Synthesis of sulfonated lignin-derived ordered mesoporous carbon for catalytic production of furfural from xylose

Efficient separation of lignocellulose component and furfural production from hemicellulose using a γ-valerolactone/H2O system

This study investigates a one-step process for the simultaneous separation of cellulose, hemicellulose, and lignin from lignocellulosic biomass using γ-valerolactone (GVL)/H2O pretreatment, which also converts hemicellulose to furfural (FF). A response surface methodology (RSM) was applied to optimize the process parameters. Under optimal conditions (163 °C for 1.5 h), the maximum FF yield reached 85.36 %, and cellulose purity was 80.80 %. The extracted GVL-lignin was characterized as low-molecular-weight guaiacyl-syringyl (G-S) type nanospheres with significant antioxidant activity. The conversion of hemicellulose to FF was enhanced by the synergistic interaction of Lewis acid (MgCl2) and Brønsted acid (H2SO4), which promoted the isomerization of xylose and dehydration to FF. The high-purity cellulose yielded 18.87 g/L ethanol through separate hydrolysis and fermentation (SHF), 27 times higher than untreated solids. Additionally, GVL exhibited consistent performance in lignocellulose separation after six cycles. This method offers an efficient and sustainable approach to valorize lignocellulosic biomass, advancing the production of high-value products.

Functionalized covalent organic frameworks for catalytic conversion of biomass-derived xylan to furfural

A direct synthesis strategy was employed to prepare functionalized COFs enriched with acidic sites, using various precursor monomers. The functionalized COFs were applied in the catalytic conversion of biomass-derived xylan to furfural in the liquid phase. The study further assessed the recyclability and reusability of these COFs, explored the relationship between their structural features and catalytic performance, and investigated the reaction mechanism underlying the COF-catalyzed conversion of xylan to furfural. The results revealed the successful solvothermal synthesis of four COFs (COF-LZU1, TP-PA, TB-DAB, and TP-DAB). Among them, TP-DAB exhibited the highest acidity, reaching 2.092 mmol/g, due to its rich content of -OH and -COOH. Additionally, TP-DAB demonstrated a well-developed porous structure and excellent thermal stability, essential characteristics for a highly efficient solid acid catalyst. When employed as a catalyst in a mixed solvent system of H2O/THF at 160 °C for 180 min, TP-DAB achieved complete xylan conversion with furfural yield of 63.49 %. Moreover, TP-DAB maintained good stability and reusability, being effective for at least five cycles. This study presents a novel and highly effective green catalyst for the sustainable conversion of biomass-derived sugars into furfural, providing new avenues for the efficient conversion of biomass into fine chemicals.

Integrated production of xylose and docosahexaenoic acid from hemicellulose and cellulose in corncob

Exploring efficient and comprehensive utilization of agricultural waste to produce high value-added products has been global research hotspot. In this study, a novel process for integrated production of xylose and docosahexaenoic acid (DHA) from hemicellulose and cellulose in corncob was developed. Corncob was treated with dilute H2SO4 at 121 °C for 1 h and xylose was readily produced with a recovery yield of 79.35 %. The corncob residue was then subject to alkali pretreatment under optimized conditions of 0.1 g NaOH/g dry solid, 60 °C for 2 h, and the contents of cellulose, hemicellulose, and lignin in the resulting residue were 87.49 %, 7.58 % and 2.31 %, respectively. The cellulose in the residue was easily hydrolyzed by cellulase, yielding 74.87 g/L glucose with hydrolysis efficiency of 77.02 %. Remarkably, the corncob residue hydrolysate supported cell growth and DHA production in Schizochytrium sp. ATCC 20888 well, and the maximum biomass of 32.71 g/L and DHA yield of 4.63 g/L were obtained, with DHA percentage in total fatty acids of 36.89 %. This study demonstrates that the corncob residue generated during xylose production, rich in cellulose, can be effectively utilized for DHA production by Schizochytrium sp., offering a cost-effective and sustainable alternative to pure glucose.

Advancing mesoporous carbon synthesis for supercapacitors: a systematic investigation of cross-linking agent effects on pore structure and functionality

Soft-templating synthesis provides an effective route to prepare ordered mesoporous carbons (MCs) that can be used for supercapacitors. During this process, the cross-linking of carbon precursors is critical to obtain tailored pore structural MCs, thus careful selection of appropriate cross-linking agents is required. Despite the shift from the prevailing cross-linker formaldehyde to its more environmentally friendly alternatives, detailed understanding on the influence of different cross-linking agents on templating synthesis is still lacking. Therefore, it remains challenging to draw a conclusion regarding which cross-linker can effectively enable an ideal cross-linking and a robust templating synthesis of ordered MCs. This work presents a systematic study, by comparing three typical cross-linkers (formaldehyde, glyoxal, and glyoxylic acid), on the pore architecture, surface functionality, and electrochemical performance of resulting MCs. Both the type of cross-linker and its ratio with precursor monomer were found to be crucial for the pore architecture and electrochemical performance of resulting MCs. Glyoxal showed to be a promising cross-linker for easily generating ordered mesopores between 3.3-6.1 nm when the molar ratio between cross-linker and carbon precursor ranged from 1 to 2, whereas glyoxylic acid and formaldehyde induced interrupted or disordered mesopores. When the resulting MCs were used as supercapacitor electrodes, those cross-linked with glyoxal also led to overall higher capacitance in both 6 M KOH aqueous and ionic liquid [N2220][NTf2]/acetonitrile electrolytes thanks to the dominance of ordered mesopore channels, especially MC prepared at glyoxal/precursor molar ratio of 1.5. These findings on the effect of cross-linking on templating synthesis can be used to guide the customisation of MCs for supercapacitors and other applications by smartly choosing a suitable cross-linking agent and its ratio with the precursor.

Function of Brønsted and Lewis acid sites in xylose conversion into furfural

In this work, the xylose conversion and the selectivity to furfural were assessed over mesoporous sulfonic silica SBA-15-(X)SO3H catalysts doped with metal ions (X = Al(iii), Ti(iv) or Zr(iv)). The type and amount of acid sites were analyzed by adsorption of pivalonitrile. The SBA-15-(X)SO3H materials show Lewis acid sites (LAS) and two types of Brønsted acid sites (BAS) with different strengths. Type I (BAS I) belongs to terminal silanol groups, type II (BAS II) is ascribed to hydroxyl groups bonded to sulfur or transition metal, and the LAS is related to M-O bonds. Optimal reaction conditions for the most active catalyst (SBA-15-(Zr)SO3H) were 120 minutes of reaction at 160 °C, 20 wt% of catalyst, and 2.5% of xylose/solvent. Additionally, a kinetic study was carried out to calculate the rate constants, the activation energy, and the pre-exponential factor for the xylose dehydration reaction. It was found that the selectivity to furfural in sulfonic silica SBA-15-(X)SO3H catalysts was directly related to the BAS II fraction. While LAS negatively impacts the selectivity to furfural leading to the undesired reaction between furfural and xylose obtaining humins as secondary products.

Exploration of Converting Food Waste into Value-Added Products via Insect Pretreatment-Assisted Hydrothermal Catalysis

The environmental burden of food waste (FW) disposal coupled with natural resource scarcity has aroused interest in FW valorization; however, transforming FW into valuable products remains a challenge because of its heterogeneous nature. In this study, a two-stage method involving black soldier fly (BSF)-based insect pretreatment and subsequent hydrothermal catalysis over a single-atom cerium-incorporated hydroxyapatite (Ce-HAP) was explored to convert FW into high added-value furfurals (furfural and 5-hydroxymethylfurfural). FW consisting of cereal, vegetables, meat, eggs, oil, and salt was initially degraded by BSF larvae to generate homogeneous BSF biomass, and then, crucial parameters impacting the conversion of BSF biomass into furfurals were investigated. Under the optimized conditions, 9.3 wt % yield of furfurals was attained, and repeated trials confirmed the recyclability of Ce-HAP. It was proved that the revenue of furfural production from FW by this two-stage method ranged from 3.14 to 584.4 USD/tonne. This study provides a potential technical orientation for FW resource utilization.

Thermal Treatment to Obtain 5-Hydroxymethyl Furfural (5-HMF), Furfural and Phenolic Compounds from Vinasse Waste from Agave

Vinasses represent important final disposal problems due to their physical-chemical composition. This work analyzed the composition of tequila vinasses and increased 5-hydroxymethylfurfural, furfural, and phenolic compounds using thermal hydrolysis with hydrogen peroxide as a catalyst. A statistical Taguchi design was used, and a UPLC-MS (XEVO TQS Micro) analysis determined the presence and increase of the components. The treatment at 130 °C, 40 min, and 0.5% of catalyst presented the highest increase for 5-HMF (127 mg/L), furfural (3.07 mg/L), and phenol compounds as chlorogenic (0.36 mg/L), and vanillic acid (2.75 mg/L). Additionally, the highest removal of total sugars (57.3%), sucrose (99.3%), and COD (32.9%). For the treatment T130:30m:0P the syringic (0.74 mg/L) and coumaric (0.013 mg/L) acids obtained the highest increase, and the treatment T120:30m:1P increased 3-hydroxybenzoic (1.30 mg/L) and sinapic (0.06 mg/L) acid. The revaluation of vinasses through thermal treatments provides guidelines to reduce the impact generated on the environment.

Recent advances in lignin-based carbon materials and their applications: A review

As the most abundant natural aromatic polymer, tens of million of tons of lignin produced in paper-making or biorefinery industry are used as fuel annually, which is a low-value utilization. Moreover, burning lignin results in large amounts of carbon dioxide and pollutants in the air. The potential of lignin is far from being fully exploited and the search for high value-added application of lignin is highly pursued. Because of the high carbon content of lignin, converting lignin into advanced carbon-based structural or functional materials is regarded as one of the most promising solutions for both environmental protection and utilization of renewable resources. Significant progresses in lignin-based carbon materials (LCMs) including porous carbon, activated carbon, carbon fiber, carbon aerogel, nanostructured carbon, etc., for various valued applications have been witnessed in recent years. Here, this review summarized the recent advances in LCMs from the perspectives of preparation, structure, and applications. In particular, this review attempts to figure out the intrinsic relationship between the structure and functionalities of LCMs from their recent applications. Hopefully, some thoughts and discussions on the structure-property relationship of LCMs can inspire researchers to stride over the present barriers in the preparation and applications of LCMs.

Towards efficient and greener processes for furfural production from biomass: A review of the recent trends

As mentioned in several recent reviews, biomass-based furfural is attracting increasing interest as a feasible alternative for the synthesis of a wide range of non-petroleum-derived compounds. However, the lack of environmentally friendly, cost-effective, and sustainable industrial procedures is still evident. This review describes the chemical and biological routes for furfural production. The mechanisms proposed for the chemical transformation of xylose to furfural are detailed, as are the current advances in the manufacture of furfural from biomass. The main goal is to overview the different ways of improving the furfural synthesis process. A pretreatment process, particularly chemical and physico-chemical, enhances the digestibility of biomass, leading to the production of >70 % of available sugars for the production of valuable products. The combination of heterogeneous (zeolite and polymeric solid) catalyst and biphasic solvent system (water/GVL and water/CPME) is regarded as an attractive approach, affording >75 % furfural yield for over 80 % of selectivity with the possibility of catalyst reuse. Microwave heating as an activation technique reduces reaction time at least tenfold, making the process more sustainable. The state of the art in industrial processes is also discussed. It shows that, when sulfuric acid is used, the furfural yields do not exceed 55 % for temperatures close to 180 °C. However, the MTC process recently achieved an 83 % yield by continuously removing furfural from the liquid phase. Finally, the CIMV process, using a formic acid/acetic acid mixture, has been developed. The economic aspects of furfural production are then addressed. Future research will be needed to investigate scaling-up and biological techniques that produce acceptable yields and productivities to become commercially viable and competitive in furfural production from biomass.

Hierarchical nanoarchitectonics of ordered mesoporous carbon from lignin for high-performance supercapacitors

The synthesis of ordered mesoporous carbons (OMCs) with hierarchical pore structure is significant for supercapacitor applications as electrode material. In this study, the ordered mesoporous carbons with hierarchical pore structure (HOMC) are synthesized via solvent evaporation induced self-assembly (EISA) method using lignin from walnut shell as carbon precursor and Co²⁺ ion as crosslinking agent, followed by removal of metal by diluted acid and chemical activation with KHCO₃. The prepared HOMC material has a large specific surface area of 2033 m² g^-1 and high pore volume of 1.59 cm³ g^-1, and it shows good electrochemical performance as the electrode of supercapacitor with high specific supercapacitances of 286 and 206 F g^-1 in 6 M KOH aqueous solutions at 0.2 and 20 A g^-1, respectively. The assembled HOMC-based symmetric supercapacitors provides a specific energy density of 13.5 Wh kg^-1 at a high power density of 44.3 kW kg^-1 and keep good cycling stability after 5000 cycle tests. The superior electrochemical performance is ascribed to the long range ordered parallel mesoporous channels, hierarchical porous structure, high specific surface area and appropriate microporous/mesoporous ratio. The materials prepared in this study have the potential to be used in the fields of adsorption, energy storage and capacitance deionization.

Recent progress in direct production of furfural from lignocellulosic residues and hemicellulose

Furfural is a vital biomass-derived platform molecule, which can be used to synthesize a wide range of value-added chemicals. Furfural and its derivatives are promising alternatives to conventional petroleum chemicals. However, recent industrial production of furfural existed some thorny problems, including low efficiency, energy waste, and environmental pollution. Therefore, tremendous and continuous efforts have been made by researchers to develop novel furfural production processes with high economic viability, production efficiency, and sustainability. This review summarized the merits and shortcomings of disparate catalytic systems for the synthesis of furfural from biomass and biomass pretreatment hydrolysate on the basis of recently published literature. Furthermore, the suggestions for furfural production research were put forward.

Continuous hydrothermal furfural production from xylose in a microreactor with dual-acid catalysts

An effective continuous furfural production from xylose in a microreactor over dual-acid catalysts was proposed. In this work, furfural was synthesized in an organic solvent-free system using formic acid and aluminum chloride as catalyst. The role of these catalysts in the consecutive reactions was examined and verified. The influence of operating conditions including xylose concentration, reaction temperature, residence time, total catalyst concentration, and catalyst ratio on the yield of furfural was investigated and optimized. The furfural yield of 92.2% was achieved at the reaction temperature of 180 °C, residence time of 15 min, catalyst molar ratio of 1 : 1, xylose concentration of 1 g L⁻¹, and total catalyst concentration of 16 mM. The superior production performance of our process was highlighted in terms of the low catalyst concentration and short residence time compared to those of other systems based on the literature. In addition, a continuous in situ catalyst removal (purification) was demonstrated, providing further insights into the practical development of continuous furfural production.

An effective continuous furfural production from xylose in a microreactor over dual-acid catalysts was proposed. In this work, furfural was synthesized in an organic solvent-free system using formic acid and aluminum chloride as catalyst.