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

The effect of ultrasound on birch sawdust during simultaneous pretreatment and hemicellulose's chemical conversion

The effect of low-frequency ultrasound on the treatment of birch sawdust with hot water and diluted acid was studied for the first time under high pressure and temperature. When treated with diluted formic acid solution, the production of furfural dramatically increased, emphasizing the straightforward hydrolysis of hemicellulose. The highest furfural yield (43-44 %) was achieved with 5 % formic acid. The most significant decrease in crystallinity index (from 56 % to 50 %) compared to treatment without ultrasound was observed with 2.5 % formic acid, using a 70:30 pulse mode with 70 % amplitude of the nominal power deliverable by the generator and an additional pressure of 3 bar. In diluted acid experiments, the remaining solid fraction, which presumably contained mainly cellulose and lignin, exhibited a completely different shape compared to the starting material, resulting in a kind of "wooden paste" with reduced particle size. The impact of additional pressure appeared to be significant, and this is further discussed in relation to the determination of the acoustic power under such rigorous experimental conditions. Based on the results obtained, ultrasound combined with hot water / diluted acid treatment shows potential for the efficient utilization of birch sawdust for platform chemicals.

Effective pretreatment of tea stem via poly-deep eutectic solvent for promoting platform molecule production and obtaining fluorescent lignin

In this study, polyethylene glycol 200 (PEG200) was employed as hydrogen bond acceptor, while organic acids served as hydrogen bond donors, to formulate poly-deep eutectic solvents (PDESs), which were utilized to pretreat tea stem. Specially, combining PEG200 and oxalic acid (OA) exhibited a notably high cellulose retention (82.03 %) and most efficient hemicellulose (97.02 %) and lignin removal (70.89 %). The removal of amorphous lignin enhanced the crystallinity of the residues and improved the conversion efficiency of cellulose into levulinic acid. Additionally, the structural alterations in lignin samples were analyzed in comparison to milled wood lignin (MWL). The PEG200-OA system facilitated the cleavage of β-O-4 and β-5 linkages and resulted in the degradation of S-type lignin, accompanied by increased condensation of G units. The resulting lignin displayed a reduced molecular weight (Mw of 1283 g/mol, Mn value 531 g/mol) and nanoscale particle size (D50 212 nm). Furthermore, fluorescent lignin was synthesized through simple oxidation and was used to detect metal ions. Density functional theory (DFT) calculations supported that both PEG200 and OA played a significant role in lignin dissolution, with the weak interactions between DES and lignin primarily driven by hydrogen bonding (characterized as weak, closed-shell, and electrostatic) and van der Waals forces.

Ultra-high-pressure homogenization combined with ionic liquid-organic acid solvent for effective pretreatment of lignocellulose biomass

The complex structure of lignocellulose necessitates advanced pretreatment techniques to effectively separate its three primary components for further conversion into valuable products. This study introduced an innovative approach to pretreating bagasse by commencing with ultra-high-pressure homogenization (UHPH) applied to raw bagasse, which maintained chemical integrity while reducing intermolecular bonds, crystallinity, and particle size. Subsequently, UHPH-bagasse underwent pretreatment using a synergistic solution of ionic liquid ([Bmim]Cl) and organic acid (oxalic acid: OA). This combination achieved a remarkable 90.26 % lignin removal rate, surpassing many conventional methods. The influence of temperature on pretreatment efficiency was also explored, demonstrating effective lignin removal at temperatures below 130 °C without compromising cellulose integrity. This performance greatly enhanced cellulose conversion into levulinic acid (from 38.8 % to 57.5). However, temperatures exceeding 140 °C led to lignin depolymerization and subsequent re-aggregation on the residue's surface, hindering cellulose conversion. The [Bmim]Cl-OA system not only aided bagasse delignification but also promoted cleavage of β-O-4' linkages, especially at higher temperatures. The resulting lignin exhibited reduced molecular weight and nanoscale particle size, enhancing its antioxidant properties and suggesting potential applications in lignin-based chemicals and materials.

Catalytic Production and Upgrading of Furfural: A Platform Compound

Furfural is a renewable platform compound that can be derived from lignocellulosic biomass. The highly functionalized molecular structure of furfural enables us to prepare a variety of high value-added chemicals, which will help realize biomass high-value utilization, and alleviate energy and environmental problems. This paper reviews the research progress on furfural production and upgrading to C5 chemicals from the catalyst perspective. The emphasis is placed on summarizing and refining the catalytic mechanism and in-depth analysis of available data. Specifically, the reaction mechanism of furfural production and upgrading is summarized firstly from the perspective of reaction pathways and reaction kinetics. Then, the available data are further processed to evaluate the actual reaction efficiency of different catalytic systems from multiple dimensions. Finally, based on statistical analysis, the challenges and opportunities of furfural-based research are proposed.

Sucrose-derived porous carbon catalyzed lignin depolymerization to obtain a product with application in type 2 diabetes mellitus

As the most important phenolic biopolymer in nature, lignin shows promising application potentialities in various bioactivities in vivo and in vitro, mainly including antioxidant, anti-inflammatory, hypolipidemic, and antidiabetic control. In this work, several carbon-based solid acids were synthesized to catalyze the fragmentation of organosolv lignin (OL). The generated lignin fragments, with controllable molecular weight and functional groups, were further evaluated for their application in the prevention and treatment of type 2 diabetes mellitus (T2DM). The results suggested that the urea-doped catalyst (SUPC) showed a more excellent catalytic performance in producing diethyl ether insoluble lignin (DEIL) and diethyl ether soluble lignin (DESL). In addition, the lignin fragments have a good therapeutic effect on the cell model of T2DM. Compared with the insulin resistance model, DEIL obtained by catalytic depolymerization of OL with SUPC could improve the glucose consumption of insulin-resistant cells. Moreover, low-concentration samples (50 μg/mL) can promote glucose consumption (19.7 mM) more than the traditional drug rosiglitazone (17.5 mM). This work demonstrates the prospect of depolymerized lignin for the prevention and treatment of T2DM and provides a new application field for lignin degradation products.

Hemicellulose-Based Sensors: When Sustainability Meets Complexity

Hemicelluloses (HCs) are promising sustainable biopolymers with a great natural abundance, excellent biocompatibility, and biodegradability. Yet, their potential sensing applications remain limited due to intrinsic challenges in their heterogeneous chemical composition, structure, and physicochemical properties. Herein, recent advances in the development of HC-based sensors for different chemical analytes and physical stimuli using different transduction mechanisms are reviewed and discussed. HCs can be utilized as carbonaceous precursors, reducing, capping, and stabilizing agents, binders, and active components for sensing applications. In addition, different strategies to develop and improve the sensing capacity of HC-based sensors are also highlighted.

Diels-Alder Cycloaddition of 2,5-Bis(hydroxymethyl)furan (BHMF) and N-Phenylmaleimide Derivatives

Currently, amidst atmospheric menace where natural calamities such as wildfire and floods are becoming more frequent than ever, biobased derivatives offer a sustainable alternative to conventional ways, for instance, petrochemical commodities. Biobased products, obtained from agricultural waste, including 5-(hydroxymethyl)furfural (HMF), 2,5-bis(hydroxymethyl)furan (BHMF), and 2,5-furandicarboxylic acid (FDCA) are promising chemical platforms in the biorefinery, which is yet to be explored. The Diels-Alder cycloaddition of BHMF and N-phenylmaleimide derivatives under optimal reaction conditions is investigated in this report. First, HMF is reduced to BHMF in the presence of NaBH4, and then the Diels-Alder reaction of BHMF and N-phenylmaleimide derivatives is investigated to produce Diels-Alder adducts. All novel compounds are synthesized in acceptable yields and effectively characterized by employing important techniques such as one-dimensional (1D) NMR spectroscopy (1H, 13C, DEPT-90, and DEPT- 135), two-dimensional (2D) NMR spectroscopy (1H-1H COSY, 1H-13C HSQC, and 1H-13C HMBC), IR spectroscopy, elemental analysis, mass spectrum (QTOF), and single-crystal X-ray diffraction (SC-XRD). Furthermore, this study underlines the necessity of sustainable synthetic methodologies and gives critical insights into the progress of ecologically friendly methodologies, providing a new avenue as a tunable precursor for the challenging functionalized polymer in the future.

Furfural as a low-volume, high-value asset from agricultural residues: A review on production, agricultural applications and environmental sustainability

This comprehensive review explores furfural production from agricultural residues, focusing on its significance as a low-volume, high-value asset crucial for environmental sustainability. It covers diverse production technologies, recent advancements, and applications in agriculture, evaluating furfural's potential to enhance crop resilience and yield. Showing its role in a circular economy, the review discusses how furfural can replace conventional petrochemical processes, thereby reducing environmental impact. Case studies, such as successful implementations with cotton biomass byproducts, illustrate furfural's practical applications and environmental benefits. The study underscores the need for ongoing research, supportive policies, and furfural's growing role in sustainable agriculture and industry. It is focused on furfural's essential contribution to promoting environmental stewardship and sustainable practices. By examining furfural's role as a value-added product from agricultural residues, this review provides insights into its economic viability and potential challenges.

Enhanced carboxylation of furoic salt with CO2 by ZnCl2 coordination for efficient production of 2,5-furandicarboxylic acid

C-H carboxylation of furoic acid (FA) with CO2 is an atom-efficient strategy to produce 2,5-furandicarboxylic acid (2,5-FDCA) from lignocellulose. The existing carbonate-promoted CO2 carboxylation processes rely on the use of large amounts of expensive Cs2CO3 as a deprotonating reagent and molten salt. Substitution of Cs with other cheap and abundant alkali ions (such as K and Na) can reduce the use of Cs, but it faces the problem of a low yield of 2,5-FDCA. This study found that the addition of catalytic amounts of ZnCl2 as a Lewis acid can increase the yield of 2,5-FDCA in the CO2 carboxylation reaction of Na/K-FA in a molten salt reaction system. 1H NMR analysis and DFT calculations confirmed that ZnCl2 coordinates with the furan ring through electron transfer from the conjugated furan ring to Zn2+, thereby activating the H at the C5 position of Na/K-FA. This coordination lengthened the C5-H bond and lowered its heterolytic dissociation energy, making it more susceptible to being deprotonated by CO32- and subsequently carboxylated by CO2. The developed Lewis acid coordination strategy provides a new idea for the efficient construction of C-C bonds between CO2 and aromatics through carbonate-promoted C-H carboxylation.

Efficient co-production of xylooligosaccharides, furfural and reducing sugars from yellow bamboo via the pretreatment with biochar-based catalyst

The research on the efficient use of biomass to produce chemical products has received extensive attention. In this work, a novel heterogeneous biocarbon-based heterogeneous catalyst AT-Sn-YB was prepared using yellow bamboo (YB) as a carrier, and its physical properties were proved to be good by various characterization and stability experiments. In the γ-valerolactone/water (3:1, v/v) medium containing 100 mM CuCl2, the use of AT-Sn-YB (3.6 wt%) under 170 °C for 20 min was applied to catalyze YB into furfural (80.3% yield), accompanied with 2.8 g/L xylooligosaccharides. The YB solid residue obtained from treatment was efficiently saccharified to reducing sugars (17.2 g/L). Accordingly, comprehensive understanding of efficiently co-producing xylooligosaccharides, furfural and reducing sugars from YB was demonstrated via the pretreatment with biochar-based catalyst. This study innovatively used a new type of solid acid to complete the efficient co-production of chemical products, and realized the value-added utilization of yellow bamboo.

Chemobiocatalytic transfromation of biomass into furfurylamine with mixed amine donor in an eco-friendly medium

Biobased furfurylamine (FAM) is a versatile platform molecule for producing additives, pharmaceuticals, and pesticides. Recombinant E. coli HNND-AlaDH was created by co-expressing L-alanine dehydrogenase (AlaDH) and mutated Aspergillus terreus ω-transaminase (HNND), aiming to convert furfural (FUR) into FAM using inexpensive L-alanine and isopropylamine as mixed amine donors. In ChCl:FA:OA (10 wt%), pineapple peel, bagasse, barley shell, peanut shell, and corn stalk could be efficiently transformed into FUR under 170 °C for 10 min. Pineapple peel produced a high titer of FUR (183.3 mM). Additionally, the viscosity, surface tension and polarity of ChCl:FA:OA were explored. The biomass-derived FUR was fully transformed to FAM by HNND-AlaDH with amine donor (1:1:1 of L-Ala/isopropylamine/FUR mol/mol/mol) within 300 min. Accordingly, the FAM productivity was 0.58 g/(g xylan in pineapple peel). This chemobiocatalytic strategy established through the combination of chemocatalysis and biocatalysis could be applied to convert renewable biomass into valuable organic amines.

Ionic liquid recovery and recycling via electrodialysis in biomass processing: An economical assessment

Extravagant price and lack of high-efficiency recovery technology limited scale-up utilization of ionic liquids. Ionic liquids recovery with electrodialysis-based techniques has caught wide concern due to membrane-based characteristic. Economical assessment for electrodialysis-based ionic liquid recovery and recycling in biomass processing was performed by determining influence of equipment-related and financial-related factors with sensitivity analysis for each factor. Overall recovery cost of 1-ethyl-3-methylimidazolium acetate, choline acetate, 1-butyl-3-methylimidazolium hydrogen sulphate and 1-ethyl-3-methylimidazolium hydrogen sulfate varied within 0.75-1.96 $/Kg, 0.99-3.00 $/Kg, 1.37-2.74 $/Kg and 1.15-2.89 $/Kg when factors changed within investigated range. Fold of membrane cost, factor of membrane stack cost, factor of auxiliary equipment cost, factor of annual maintenance cost and annual interest rate of loan were positively related with recovery cost. While percentage of annual elapsed time and loan period were negatively correlated with recovery cost. Economical assessment confirmed economic efficiency of electrodialysis for ionic liquids recovery and recycling in biomass processing.

Ti/Zr/O Mixed Oxides for the Catalytic Transfer Hydrogenation of Furfural to GVL in a Liquid-Phase Continuous-Flow Reactor

This work aims to develop an efficient catalyst for the cascade reaction from furfural to γ-valerolactone in a liquid-phase continuous reactor. This process requires both Lewis and Brønsted acidity; hence, a bifunctional catalyst is necessary to complete the one-pot reaction. Ti/Zr/O mixed oxide-based catalysts were chosen to this end as balancing metal oxide composition allows the acidity characteristics of the overall material to be modulated. Oxides with different compositions were then synthesized using the co-precipitation method. After characterization via porosimetry and NH3-TPD, the catalyst with equimolar quantities of the two components was demonstrated to be the best one in terms of superficial area (279 m2/g) and acid site density (0.67 mmol/g). The synthesized materials were then tested using a plug flow reactor at 180 °C, with a 10 min contact time. Ti/Zr/O (1:1) was demonstrated to be the most promising catalyst during the recycling tests as it allowed obtaining the highest selectivities in the desired products (about 45% in furfuryl isopropyl ether and 20% in γ-valerolactone) contemporaneously with 100% furfural conversion.

Model-based process intensification of dilute acid pre-hydrolysis of oil palm empty fruit bunch biomass for pretreatment and furfural production

A novel process for simultaneous production of furfural and pretreatment of oil palm empty fruit bunch (EFB) by dilute acid pre-hydrolysis was developed based on non-isothermal kinetic modeling. Mass transfer analysis suggested that the internal diffusion could be neglected as diffusion time of sulfuric acid in EFB particles was significantly shorter than the pre-hydrolysis period, whereas the heating stage could not be neglected due to a significant part of xylan was solubilized at the stage. A strategy for increasing furfural yield was developed by intermittent discharging of steam, resulting in 71.4 % furfural yield. The pretreated solids showed good enzymatic digestibility. 136.3 g/L glucose corresponding to 81.6 % yield was obtained by high-solid loading hydrolysis. 95.4 g furfural and 212 g glucose could be obtained from 1 kg dry EFB. Therefore, non-isothermal effects on polysaccharide hydrolysis and pentose decomposition should be considered carefully for an efficient process design of EFB biorefining.

Sustainable lignocellulose fractionation by integrating p-toluenesulfonic acid/pentanol pretreatment with mannitol for efficient production of glucose, native-like lignin, and furfural

A new cutting-edge lignocellulose fractionation technology for the co-production of glucose, native-like lignin, and furfural was introduced using mannitol (MT)-assisted p-toluenesulfonic acid/pentanol pretreatment, as an eco-friendly process. The addition of optimized 5% MT in pretreatment enhanced the delignification rate by 29% and enlarged the surface area and biomass porosity by 1.07-1.80 folds. This increased the glucose yield by 45% (from 65.34 to 94.54%) after enzymatic hydrolysis relative to those without MT. The extracted lignin in the organic phase of pretreatment exhibited β-O-4 bonds (61.54/100 Ar) properties of native cellulosic enzyme lignin. Lignin characterization and molecular docking analyses revealed that the hydroxyl tails of MT were incorporated with lignin and formed etherified lignin, which preserved high lignin integrity. The solubilized hemicellulose (96%) in the liquid phase of pretreatment was converted into furfural with a yield of 83.99%. The MT-assisted pretreatment could contribute to a waste-free biorefinery pathway toward a circular bioeconomy.

Progress of Reactions between Furfural and Aliphatic Alcohols via Catalytic Oxidation Processes: Reaction Routes, Catalysts, and Perspectives

Furfural is one of the most important biomass platform compounds and can be used to prepare various high-value-added chemicals. The reactions of furfural with aliphatic alcohols via an oxidative esterification reaction or oxidative condensation reaction can bond two carbon molecules together and produce longer hydrocarbon chains chemicals, including methylfuroate and some low-volatility liquid biomass fuels. Thus, these reactions are considered significant utilization routes of furfural, and many inspiring catalytic systems have been designed to promoted these reactions. In this work, the reported catalytic systems for the oxidative esterification and oxidative condensation reactions are reviewed separately. The catalysts for the oxidative esterification reaction are reviewed for the classification of noble metal catalysts and non-noble metal catalysts, according to the active metals in the catalysts. For the oxidative condensation reactions, the studies using oxygen as the oxidant are reviewed firstly, and then the studies conducted using the hydrogen transfer process are analyzed subsequently. Furthermore, suggestions for future research directions for the oxidative esterification and oxidative condensation reactions are put forward.

Microwave-assisted choline chloride/1,2-propanediol/methyl isobutyl ketone biphasic system for one-pot fractionation and valorization of Eucalyptus biomass

The developing of pretreatment method to break the biomass barrier of lignocellulosic is a challenging task for achieve high value utilization. A fast microwave-assisted choline chloride/1,2-propanediol/methyl isobutyl ketone biphasic system was constructed for pretreating Eucalyptus to the production of furfural and cellulose-rich residues and the extraction of lignin. Results showed that the combination of AlCl₃·6H₂O and HCl had the best catalytic ability for furfural production among the examined catalysts. Under the optimal conditions (140 °C, 15 min, 0.075 M AlCl₃·6H₂O, 0.05 M HCl), the furfural yield of 55.4 %, the glucose yield of 90.3 % and the delignification rate of 92.4 % could be achieved. Moreover, the extracted lignin samples with a low polydispersity (1.55-1.73) and molecular weight (1380-2040 g/mol) are promising to act as precursor for the value-add products processing. These findings demonstrated an ultrafast pretreatment process with excellent results in biomass fractionation and comprehensive utilization of biomass components.

New concept for conversion of lignocellulose to ethanol and furfural

Studies on the chemical mechanisms of furfural formation showed the possibility to apply a new differential catalysis of hemicellulose - its depolymerisation and pentose dehydration to furfural. This change led to the increase in furfural yield and essential decrease of cellulose destruction. The lignocellulose residue that remains after the production of furfural may be subjected to enzymatic hydrolysis to glucose and the subsequent fermentation to ethanol. The remaining lignin appeared to be suitable for the production of additional various value-added products including medicinal mushrooms and laccase-containing enzyme complexes. Based on these developments, an innovative concept is proposed for the waste-free use of lignocellulose to obtain various valuable products. KEY POINTS: • New chemical mechanism of furfural production. • New lignocellulose pretreatment does not damage cellulose and lignin. • Lignocellulose may be processed using waste-free technology.

Potential of Staphylea holocarpa Wood for Renewable Bioenergy

Energy is indispensable in human life and social development, but this has led to an overconsumption of non-renewable energy. Sustainable energy is needed to maintain the global energy balance. Lignocellulose from agriculture or forestry is often discarded or directly incinerated. It is abundantly available to be discovered and studied as a biomass energy source. Therefore, this research uses Staphylea holocarpa wood as feedstock to evaluate its potential as energy source. We characterized Staphylea holocarpa wood by utilizing FT-IR, GC-MS, TGA, Py/GC-MS and NMR. The results showed that Staphylea holocarpa wood contained a large amount of oxygenated volatiles, indicating that it has the ability to act as biomass energy sources which can achieve green chemistry and sustainable development.

One pot bioprocessing in lignocellulosic biorefinery: A review

Practically, high-yield conversion of biomass into value-added products at low cost is a primary goal for any lignocellulosic refinery. In the industrial context, the limitation in the practical adaptation of the conventional techniques practically involves multiple reactors for the conversion of biomass to bioproducts. Therefore, the present manuscript critically reviewed the advancements in one-pot reaction systems with a major focus on the scientific production of value-added products from lignocellulosic biomass. In view of that, the novelty of one-pot reactions is shown during the fractionation of biomass into their individual constituents. The importance of the direct conversion of cellulose and lignin into a range of valuable products including organic acids and platform chemicals are separately discussed. Finally, the article is concluded with the opportunities, existing troubles, and possible solutions to overcome the challenges in lignocellulosic biorefinery. This article will assist the readers to identify the economic-friendly-one-pot conversion of lignocellulosic biomass.

Peroxyacetic Acid Pretreatment: A Potentially Promising Strategy towards Lignocellulose Biorefinery

The stubborn and complex structure of lignocellulose hinders the valorization of each component of cellulose, hemicellulose, and lignin in the biorefinery industries. Therefore, efficient pretreatment is an essential and prerequisite step for lignocellulose biorefinery. Recently, a considerable number of studies have focused on peroxyacetic acid (PAA) pretreatment in lignocellulose fractionation and some breakthroughs have been achieved in recent decades. In this article, we aim to highlight the challenges of PAA pretreatment and propose a roadmap towards lignocellulose fractionation by PAA for future research. As a novel promising pretreatment method towards lignocellulosic fractionation, PAA is a strong oxidizing agent that can selectively remove lignin and hemicellulose from lignocellulose, retaining intact cellulose for downstream upgrading. PAA in lignocellulose pretreatment can be divided into commercial PAA, chemical activation PAA, and enzymatic in-situ generation of PAA. Each PAA for lignocellulose fractionation shows its own advantages and disadvantages. To meet the theme of green chemistry, enzymatic in-situ generation of PAA has aroused a great deal of enthusiasm in lignocellulose fractionation. Furthermore, mass balance and techno-economic analyses are discussed in order to evaluate the feasibility of PAA pretreatment in lignocellulose fractionation. Ultimately, some perspectives and opportunities are proposed to address the existing limitations in PAA pretreatment towards biomass biorefinery valorization. In summary, from the views of green chemistry, enzymatic in-situ generation of PAA will become a cutting-edge topic research in the lignocellulose fractionation in future.