Selectively transform lignin into value-added chemicals

A lignin/castor oil-based polyamide autonomous self-healing composite materials

Reconciling high toughness and autonomous self-healing ability at a low cost remains a formidable challenge in the development of bio-based self-healing elastomers. Herein, lignin was incorporated into castor oil-based polyamide (PBUDA) as a rigid filler and hydrogen bond donor through solution method. The lignin was uniformly dispersed in PBUDA, forming a phase separation structure that significantly improved the mechanical properties of polyamide materials. The mechanical strength of blends coating 40 % (wt%) lignin was 22.7 ± 1.84 MPa, which was five times higher than that of pure PBUDA. Meanwhile the toughness and Young's modulus were also increased by four times and fourteen times, respectively. Moreover, the activate dynamic hydrogen bond and low glass transition temperature (Tg) endowed the PBUDA-lignin blends excellent self-healing ability at room temperature. This study not only provides a viable pathway for the valorization of high-added lignin, but also facilitates the advancement of self-healing castor oil-based polyamides, thereby contributing to the promotion of sustainable materials.

Development and structural comparison of alkaline and organosolv coconut husks lignin as an eco-friendly lignin-phenol-glyoxal (LPG) wood adhesives

The development of eco-friendly wood adhesives have gained more interest among adhesives industries due to the concerns about using carcinogenic formaldehyde and petroleum-based phenol in commercially available adhesives. Therefore, many studies have been done by using lignin to partially replace phenol and completely substitute formaldehyde with non-toxic glyoxal in a wood adhesive formulation. This study focused on using different percentages of lignin substitution (10 %, 30 % and 50 wt%) of alkaline and organosolv coconut husk lignin into soda lignin-phenol-glyoxal (SLPG), Kraft lignin-phenol-glyoxal (KLPG) and organosolv lignin-phenol-glyoxal (OLPG) adhesives. The adhesives were further characterized using various analyses and it showed that 50 % lignin substitution was the optimum rate percentage with 50 % SLPG adhesive giving the highest solid content, shorter gel time and more viscosity compared to control (PF and PG), KLPG and OLPG adhesives. Mechanical properties revealed that 50 % SLPG adhesive showed an improvement performance of tensile strength (TS: 68.98 ± 0.19 MPa), internal bonding (IB: 17.01 ± 1.07 Nmm-2), and cross-linking density panels (775.51 ± 8.15 kg m-3) due to the higher amount of molecular weight (Mw) as well as higher phenolic-OH that improved the cross-linking reaction between phenol-glyoxal with G-type unit in lignin structure.

Collaborative performance of enzymatic saccharification and organic pollutant degradation from PHP (phosphoric acid coupled with hydrogen peroxide) pretreatment of lignocellulose

As a newly developed technology, lignocellulose pretreatment of PHP (phosphoric acid coupled with hydrogen peroxide) can facilitate the enzymatic hydrolysis of pretreated lignocellulose for glucose production. It also has been found that the derived oxidative tail gas from pretreatment can facilely degrade organic pollutant. To balance the pollutant degradation and the glucose yield, the collaborative optimization on pretreatment was investigated. Results indicated that temperature, H3PO4 and H2O2 concentration were positively correlated with the model pollutant degradation (methylene blue) and enzymatic hydrolysis. Under the optimized conditions of temperature (55 °C), H3PO4 concentration (65%), and H2O2 concentration (7%), three typical agricultural residues, including wheat straw, Jerusalem artichoke stalks and corn stover, achieved 95.2%, 94.0% and 98.3% methylene blue degradation, and the corresponding cellulose-glucose conversion was 100%, 97.6% and 100.0%, respectively. While two typical woody residues of oak and birch sawdust achieved methylene blue degradation of 70.2% and 68.0%, and the corresponding cellulose-glucose conversion reached 88.3% and 84.0%, respectively. 90.2-93.6% H3PO4 could be recovered with a stable performance of methylene blue degradation of 98.8-99.7% and cellulose-glucose conversion of 96.1-99.8% in the 5 recycling batches. Overall, this work achieved the "win-win" function on pollutant removal and glucose production, and efficient solvent recycling, which further improved the applicability of PHP pretreatment.

One-Pot Production of Cinnamonitriles from Lignin β-O-4 Segments Induced by Selective Oxidation of the γ-OH Group

The construction of N-containing aromatic compounds from lignin is of great importance to expanding the boundary of the biorefinery and meeting the demand for value-added biorefinery. However, it remains a huge challenge due to the complex lignin structure and the incompatible catalysis for C-O/C-C bond cleavage and C-N formation. Herein, sustainable synthesis of cinnamonitrile derivatives from lignin β-O-4 model compounds in the presence of 2,2,6,6-tetramethylpiperidine oxide (TEMPO), (diacetoxyiodo)benzene (BAIB), and a strong base has been achieved in a one-pot, two-step fashion under transition-metal-free conditions. Mechanistic studies suggest that this transformation starts from selective oxidation of Cγ-OH of the β-O-4 model compound, followed by retro-aldol condensation, resulting in the cleavage of the Cα-Cβ bond to afford veratraldehyde. Whereafter, the aldol condensation reaction allows coupling of veratraldehyde with nitriles to provide cinnamonitriles. With this protocol, 3,4-dimethoxycinnamonitrile and 3,4-dimethoxyphenyl-2-phenylacrylonitrile were synthesized from lignin β-O-4 model compounds and showed good antibacterial or antifungal activity, showcasing the application potential of lignin in pharmaceutical synthesis.

Review of the application of bimetallic catalysts coupled with internal hydrogen donor for catalytic hydrogenolysis of lignin to produce phenolic fine chemicals

Lignocellulosic biomass contains lignin, an aromatic and oxygenated substance and a potential method for lignin utilization is achieved through catalytic conversion into useful phenolic and aromatic monomers. The application of monometallic catalysts for lignin hydrogenolysis reaction remains one of the major reasons for the underutilization of lignin to produce valuable chemicals. Monometallic catalysts have many limitations such as limited catalytic sites for interacting with different lignin linkages, poor catalytic activity, low lignin conversion, and low product selectivity. It is due to lack of synergy with other metallic catalysts that can enhance the catalytic activity, stability, selectivity, and overall catalytic performance. To overcome these limitations, works on the application of bimetallic catalysts that can offer higher activity, selectivity, and stability have been initiated. In this review, cutting-edge insights into the catalytic hydrogenolysis of lignin, focusing on the production of phenolic and aromatic monomers using bimetallic catalysts within an internal hydrogen donor solvent are discussed. The contribution of this work lies in a critical discussion of recent reported findings, in-depth analyses of reaction mechanisms, optimal conditions, and emerging trends in lignin catalytic hydrogenolysis. The specific effects of catalytic active components on the reaction outcomes are also explored. Additionally, this review extends beyond current knowledge, offering forward-looking suggestions for utilizing lignin as a raw material in the production of valuable products across various industrial processes. This work not only consolidates existing knowledge but also introduces novel perspectives, paving the way for future advancements in lignin utilization and catalytic processes.

Eco-friendly regeneration of lignin with acidic deep eutectic solvent for adsorption of pollutant dyes for water cleanup

In this study, a simple and eco-friendly method was used to treat alkaline lignin with an acidic deep eutectic solvent (DES) to obtain regenerated lignin for the efficient adsorption of pollutant dyes from aqueous environment. Based on the yield and adsorption capacity of the sorbent for these dyes, conditions such as the type and concentration of DES component, solid-to-liquid ratio, reaction time, and temperature were optimized. By characterizing and comparing alkali lignin with regenerated lignin, a series of reactions were demonstrated to occur during the DES treatment process. The performance and mechanism of methylene blue and rhodamine B adsorption on regenerated lignin were studied systematically, and the maximum adsorbed amounts were 348.29 and 551.05 mg/g at 323 K, respectively. This study provides a new strategy for the green preparation of functionalized lignin and its use in the water pollutant treatment.

Advances in green materials derived from wood for detecting and removing mercury ions in water

The issue of mercury pollution in environmental remediation has garnered significant attention due to its severe health hazards to humans. Various strategies have been devised to mitigate the impact of toxic mercury ions, including coagulation, ion exchange, adsorption, membrane technology, and electrochemical treatment. Among these approaches, adsorption has emerged as an efficient and widely employed method for the uptake of low concentrations of mercury ions. It offers convenient operation, high removal efficiency, and facile regeneration of the adsorbent. Wood, being the most abundant renewable and sustainable bioresource, has garnered attention as a promising material for treating heavy metal wastewater. This is attributed to its unique physical and chemical characteristics, encompassing hierarchical pores, aligned channels, active functional groups, biodegradability, and cost-effectiveness. However, a comprehensive examination of the cutting-edge applications of wood and wood-derived biopolymers in the detection and removal of mercury ions from wastewater has yet to be undertaken. Consequently, this article presents a chronological overview of recent advancements in materials and structures derived from bulk wood and its constituents, including cellulose, lignin, hemicellulose, and tannin, with a specific focus on their utility in detecting and eliminating mercury from water sources. Subsequently, the most promising techniques and strategies involving wood and wood-derived biopolymers in addressing the predicament of mercury pollution are explored. Furthermore, this piece offers insights into the existing challenges and future prospects concerning environmentally friendly materials derived from wood, aiming to foster the development of cost-effective mercury adsorbents and detection devices.

Continuous Flow Hydrogenation of Lignin-model Aromatic Compounds over Carbon-supported Noble Metals

An efficient continuous-flow (CF) protocol was designed for the hydrogenation of lignin-derived aromatics to the corresponding cycloalkanes derivatives. A parametric analysis of the reaction was carried out by tuning the temperature, the H2 pressure and the flow rate, and using diphenyl ether (DPE) as a model substrate, commercial Ru/C as a catalyst, and isopropanol as a solvent: at 25 °C, 50 bar H2 , and a flow rate of 0.1 mL min-1 , dicyclohexyl ether was achieved in an 86 % selectivity, at quantitative conversion. By-products from the competitive C-O bond cleavage of DPE, cyclohexanol and cyclohexane, did not exceed 14 % in total. Remarkably, prolonged experiments demonstrated an excellent stability of the catalyst whose performance was unaltered for up to 420 min of time-of-stream. A substrate scope evaluation proved that under the same conditions used for DPE, a variety of substrates including alkoxy-, allyl-, and carbonyl-functionalized phenols, biphenyl, aryl benzyl- and phenethyl ethers (10 examples) yielded the ring-hydrogenated products with selectivity up to 99 % at complete conversion.

Modifications of Ganoderma lucidum spores into digestive-tissue highly adherent porous carriers with selective affinity to hydrophilic or hydrophobic drugs

Ganoderma lucidum spores (GLSs) have been suggested to provide optimal structures for transporting orally bioavailable drugs. However, the double-layer wall and cavities of GLSs are naturally closed. This study aimed to modify GLSs into porous carriers by opening the layers and internal cavity with iturin A (IA) followed by potassium hydroxide (KOH) or hydrochloric acid (HCl). The (IA + KOH)- and (IA + HCl)-treated GLS carriers exhibited a high loading rate of 301.50 ± 2.33 and 268.18 ± 7.72 mg/g for the hydrophilic methylene blue (MB) and hydrophobic rifampicin (RF), respectively. The mechanisms underlying the modification involved the enhancement of the specific surface area with IA and the exposure of hydrophilic groups or hydrophobic groups of the GLSs with KOH or HCl. The sustained 48-h molecule-release profiles of the MB- and RF-loaded GLS carriers were best fitted using a first-order kinetics model in simulated gastric (or intestinal) fluid compared with other models. In mice, the designed GLS carriers had high adhesion capacities onto the mucosa of the digestive tract and long retention times (120 h), and even promoted the secretion of mucus and expression of several key intestinal barrier proteins. This study provided a new method to modify GLSs into oral carriers with selective drug affinity, high loading capacity, sustained drug release, and high adhesion to the digestive tract.

In-depth investigation of formic acid pretreatment for various biomasses: Chemical properties, structural features, and enzymatic hydrolysis

Formic acid pretreatment is a promising approach for fractionating biomass, and it has the advantages of efficient recycling and removal of hemicellulose and lignin. Biomass is one of the most plentiful resources on earth, yet its chemical structure differs significantly between woody and herbaceous biomass. The influence of formic acid pretreatment on the fractionation of woody and herbaceous biomasses, as well as changes in physical-chemical properties, was investigated in this study. The results indicated that formic acid is universal in the biorefinery of different biomass, however, herbaceous biomass had greater xylan and lignin removal than woody biomass (especially softwood). Formic acid pretreatment not only considerably improved the enzymatic efficiency of herbaceous biomass, but also had a good effect on the enzymatic efficiency of poplar. This study also found that the correlation between residual xylan content and enzymatic efficiency after pretreatment was much higher than that of lignin content.

Application of Pyrolysis for the Evaluation of Organic Compounds in Medical Plastic Waste Generated in the City of Cartagena-Colombia Applying TG-GC/MS

In this study, the thermal degradation and pyrolysis of hospital plastic waste consisting of polyethylene (PE), polystyrene (PS), and polypropylene (PP) were investigated using TG-GC/MS. The identified molecules with the functional groups of alkanes, alkenes, alkynes, alcohols, aromatics, phenols, CO and CO2 were found in the gas stream from pyrolysis and oxidation, and are chemical structures with derivatives of aromatic rings. They are mainly related to the degradation of PS hospital waste, and the alkanes and alkenes groups originate mainly from PP and PE-based medical waste. The pyrolysis of this hospital waste did not show the presence of derivatives of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans, which is an advantage over classical incineration methodologies. CO, CO2, phenol, acetic acid and benzoic acid concentrations were higher in the gases from the oxidative degradation than in those generated in the pyrolysis with helium. In this article, we propose different pathways of reaction mechanisms that allow us to explain the presence of molecules with other functional groups, such as alkanes, alkenes, carboxylic acids, alcohols, aromatics and permanent gases.

Lignin-Based Materials for Additive Manufacturing: Chemistry, Processing, Structures, Properties, and Applications

The utilization of lignin, the most abundant aromatic biomass component, is at the forefront of sustainable engineering, energy, and environment research, where its abundance and low-cost features enable widespread application. Constructing lignin into material parts with controlled and desired macro- and microstructures and properties via additive manufacturing has been recognized as a promising technology and paves the way to the practical application of lignin. Considering the rapid development and significant progress recently achieved in this field, a comprehensive and critical review and outlook on three-dimensional (3D) printing of lignin is highly desirable. This article fulfils this demand with an overview on the structure of lignin and presents the state-of-the-art of 3D printing of pristine lignin and lignin-based composites, and highlights the key challenges. It is attempted to deliver better fundamental understanding of the impacts of morphology, microstructure, physical, chemical, and biological modifications, and composition/hybrids on the rheological behavior of lignin/polymer blends, as well as, on the mechanical, physical, and chemical performance of the 3D printed lignin-based materials. The main points toward future developments involve hybrid manufacturing, in situ polymerization, and surface tension or energy driven molecular segregation are also elaborated and discussed to promote the high-value utilization of lignin.

Multilamellar spherical micelles of alkali lignin: dissipative particle dynamics simulations

CONTEXT

Lignin has an immense potential for the production of lignin-based functional materials. In this work, effect of 2-chloro-ethyltrimethyl ammonium chloride (AC)-grafted alkali lignin (AL) on the morphologies in water was investigated by dissipative particle dynamics (DPD) simulations. The results showed that AL molecules formed spherical micelles, but the corresponding phenylpropane units of AL were randomly distributed in spherical micelles. However, AC-grafted modification of phenolic hydroxyl groups in AL led to the formation of multilamellar spherical micelles. The formation of multilamellar spherical micelles of AL mainly went through four stages: small clusters, larger aggregates with a core-shell structure, trilaminar, and multilamellar spherical micelles. AL molecules resulted in dimethomorph molecules being randomly distributed in the spherical micelle, while the dimethomorph molecules were perfectly entrapped into the spherical micelles of AC-grafted AL. Various molecular weights of AL had no effect on the formation and size of multilamellar spherical micelles. With increasing the content of AC-grafted AL, small clusters, multilamellar spherical micelles, tube-like, and lamellar aggregates were observed successively. This work highlights the potential of lignin to prepare monodispersed lignin-based functional colloidal spheres.

METHODS

Coarse-grained beads were performed energy minimization, geometric optimization, NPT ensemble (298 K and 1.0 bar), and NVT ensemble (298 K) calculations. DPD simulations were carried out at 300,000 steps in a 30×30×30 Rc³ cubic box with Materials Studio 7.0 program.

Value-Added Products from Catalytic Pyrolysis of Lignocellulosic Biomass and Waste Plastics over Biochar-Based Catalyst: A State-of-the-Art Review

As the only renewable carbon resource on Earth, lignocellulosic biomass is abundant in reserves and has the advantages of environmental friendliness, low price, and easy availability. The pyrolysis of lignocellulosic biomass can generate solid biochar with a large specific surface area, well-developed pores, and plentiful surface functional groups. Therefore, it can be considered as a catalyst for upgrading the other two products, syngas and liquid bio-oil, from lignocellulosic biomass pyrolysis, which has the potential to be an alternative to some non-renewable and expensive conventional catalysts. In addition, as another carbon resource, waste plastics can also use biochar-based catalysts for catalytic pyrolysis to solve the problem of accumulation and produce fuels simultaneously. This review systematically introduces the formation mechanism of biochar from lignocellulosic biomass pyrolysis. Subsequently, the activation and modification methods of biochar catalysts, including physical activation, chemical activation, metal modification, and nonmetallic modification, are summarized. Finally, the application of biochar-based catalysts for lignocellulosic biomass and waste plastics pyrolysis is discussed in detail and the catalytic mechanism of biochar-based catalysts is also investigated.

Microwave co-pyrolysis for simultaneous disposal of environmentally hazardous hospital plastic waste, lignocellulosic, and triglyceride biowaste

Microwave co-pyrolysis was examined as an approach for simultaneous reduction and treatment of environmentally hazardous hospital plastic waste (HPW), lignocellulosic (palm kernel shell, PKS) and triglycerides (waste vegetable oil, WVO) biowaste as co-feedstock. The co-pyrolysis demonstrated faster heating rate (16-43 °C/min) compared to microwave pyrolysis of single feedstock (9-17 °C/min). Microwave co-pyrolysis of HPW/WVO performed at 1:1 ratio produced a higher yield (80.5 wt%) of hydrocarbon liquid fuel compared to HPW/PKS (78.2 wt%). The liquid oil possessed a low nitrogen content (< 4 wt%) and free of sulfur that could reduce the release of hazardous pollutants during its use as fuel in combustion. In particular, the liquid oil obtained from co-pyrolysis of HPW/WVO has low oxygenated compounds (< 16%) leading to reduction in generation of potentially hazardous sludge or problematic acidic tar during oil storage. Insignificant amount of benzene derivatives (< 1%) was also found in the liquid oil, indicating the desirable feature of this pyrolysis approach to suppress the formation of toxic polycyclic aromatic hydrocarbons (PAHs). Microwave co-pyrolysis of HPW/WVO improved the yield and properties of liquid oil for potential use as a cleaner fuel, whereas the liquid oil from co-pyrolysis of HPW/PKS is applicable in the synthesis of phenolic resin.

Strategic hazard mitigation of waste furniture boards via pyrolysis: Pyrolysis behavior, mechanisms, and value-added products

Waste furniture boards (WFBs) contain hazardous formaldehyde and volatile organic compounds when left unmanaged or improperly disposed through landfilling and open burning. In this study, pyrolysis was examined as a disposal and recovery approach to convert three types of WFBs (i.e., particleboard, plywood, and fiberboard) into value-added chemicals using thermogravimetric analysis coupled with Fourier-transform infrared spectrometry (TG-FTIR) and pyrolysis coupled with gas chromatography/mass spectrometry (Py-GC/MS). TG-FTIR analysis shows that pyrolysis performed at an optimum temperature of 250-550 °C produced volatile products mainly consisting of carbon dioxide, carbon monoxide, and light hydrocarbons, such as methane. Py-GC/MS shows that pyrolysis at different final temperatures and heating rates recovered mainly phenols (25.9-54.7%) for potential use as additives in gasoline, colorants, and food. The calorific value of WFBs ranged from 16 to 18 MJ/kg but the WFBs showed high H/C (1.7-1.8) and O/C (0.8-1.0) ratios that provide low chemical energy during combustion. This result indicates that WFBs are not recommended to be burned directly as fuel, however, they can be pyrolyzed and converted into solid pyrolytic products such as biochar with improved properties for fuel application. Hazardous components, such as cyclopropylmethanol, were removed and converted into value-added compounds, such as 1,4:3,6-dianhydro-d-glucopyranose, for use in pharmaceuticals. These results show that the pyrolysis of WFBs at high temperature and low heating rate is a promising feature to produce value-added chemicals and reduce the formation of harmful chemical species. Thus, the release of hazardous formaldehyde and greenhouse gases into the environment is redirected.

Sulfonic acid-functionalized PCP(Cr) catalysts with Cr3+ and -SO3H sites for 5-ethoxymethylfurfural production from glucose

5-Ethoxymethylfurfural (EMF) has been identified as a potential biofuel and fuel additive, for which the production from glucose (the most abundant and inexpensive monosaccharide) in a one-step process would be highly desirable. Here, the synthesis of sulfonic acid-functionalized porous coordination polymers (PCPs) and their application as catalysts for EMF synthesis are reported. PCP(Cr)-BA (PCP material with Cr3+ ions and H2BDC-SO3H linkers) and PCP(Cr)-NA (PCP material with Cr3+ ions and H2NDC(SO3H)2 linkers) materials containing both Cr3+ sites and Brønsted-acidic -SO3H sites were prepared. The morphology, pore structure, acidity, chemical composition, and thermal stability of the two functionalized PCP(Cr) catalysts were analyzed by systematic characterization. The catalysts featured a porous morphology and dual Cr3+ and -SO3H sites, which enabled the cascade conversion of glucose to EMF. PCP(Cr)-BA exhibited higher performance than PCP(Cr)-NA with an EMF yield of 23.1% in the conversion of glucose at 140 °C after 22 h in an ethanol/water system. In addition, the as-prepared catalyst exhibited a high stability in the current catalytic system for EMF production from glucose with a constant catalytic activity in a four-run recycling test without an intermediate regeneration step.

Acid-based lignocellulosic biomass biorefinery for bioenergy production: Advantages, application constraints, and perspectives

The production of chemicals and fuels from renewable biomass with the primary aim of reducing carbon footprints has recently become one of the central points of interest. The use of lignocellulosic biomass for energy production is believed to meet the main criteria of maximizing the available global energy source and minimizing pollutant emissions. However, before usage in bioenergy production, lignocellulosic biomass needs to undergo several processes, among which biomass pretreatment plays an important role in the yield, productivity, and quality of the products. Acid-based pretreatment, one of the existing methods applied for lignocellulosic biomass pretreatment, has several advantages, such as short operating time and high efficiency. A thorough analysis of the characteristics of acid-based biomass pretreatment is presented in this review. The environmental concerns and future challenges involved in using acid pretreatment methods are discussed in detail to achieve clean and sustainable bioenergy production. The application of acid to biomass pretreatment is considered an effective process for biorefineries that aim to optimize the production of desired products while minimizing the by-products.

Lignin-Based High-Performance Fibers by Textile Spinning Techniques

As a major component of lignocellulosic biomass, lignin is one of the largest natural resources of biopolymers and, thus, an abundant and renewable raw material for products, such as high-performance fibers for industrial applications. Direct conversion of lignin has long been investigated, but the fiber spinning process for lignin is difficult and the obtained fibers exhibit unsatisfactory mechanical performance mainly due to the amorphous chemical structure, low molecular weight of lignin, and broad molecular weight distribution. Therefore, different textile spinning techniques, modifications of lignin, and incorporation of lignin into polymers have been and are being developed to increase lignin's spinnability and compatibility with existing materials to yield fibers with better mechanical performance. This review presents the latest advances in the textile fabrication techniques, modified lignin-based high-performance fibers, and their potential in the enhancement of the mechanical performance.

Advances in Versatile Nanoscale Catalyst for the Reductive Catalytic Fractionation of Lignin

In the past five years, biomass-derived biofuels and biochemicals were widely studied both in academia and industry as promising alternatives to petroleum. In this Review, the latest progress of the synthesis and fabrication of porous nanocatalysts that are used in catalytic transformations involving hydrogenolysis of lignin is reviewed in terms of their textural properties, catalytic activities, and stabilities. A particular emphasis is made with regard to the catalyst design for the hydrogenolysis of lignin and/or lignin model compounds. Furthermore, the effects of different supports on the lignin hydrogenolysis/hydrogenation are discussed in detail. Finally, the challenges and future opportunities of lignin hydrogenolysis over nanomaterial-supported catalysts are also presented.

Recent advances in the valorization of plant biomass

Plant biomass is a highly abundant renewable resource that can be converted into several types of high-value-added products, including chemicals, biofuels and advanced materials. In the last few decades, an increasing number of biomass species and processing techniques have been developed to enhance the application of plant biomass followed by the industrial application of some of the products, during which varied technologies have been successfully developed. In this review, we summarize the different sources of plant biomass, the evolving technologies for treating it, and the various products derived from plant biomass. Moreover, the challenges inherent in the valorization of plant biomass used in high-value-added products are also discussed. Overall, with the increased use of plant biomass, the development of treatment technologies, and the solution of the challenges raised during plant biomass valorization, the value-added products derived from plant biomass will become greater in number and more valuable.

Hetero-Porous, High-Surface Area Green Carbon Aerogels for the Next-Generation Energy Storage Applications

Various carbon materials have been developed for energy storage applications to address the increasing energy demand in the world. However, the environmentally friendly, renewable, and nontoxic bio-based carbon resources have not been extensively investigated towards high-performance energy storage materials. Here, we report an anisotropic, hetero-porous, high-surface area carbon aerogel prepared from renewable resources achieving an excellent electrical double-layer capacitance. Two different green, abundant, and carbon-rich lignins which can be extracted from various biomasses, have been selected as raw materials, i.e., kraft and soda lignins, resulting in clearly distinct physical, structural as well as electrochemical characteristics of the carbon aerogels after carbonization. The obtained green carbon aerogel based on kraft lignin not only demonstrates a competitive specific capacitance as high as 163 F g⁻¹ and energy density of 5.67 Wh kg⁻¹ at a power density of 50 W kg⁻¹ when assembled as a two-electrode symmetric supercapacitor, but also shows outstanding compressive mechanical properties. This reveals the great potential of the carbon aerogels developed in this study for the next-generation energy storage applications requiring green and renewable resources, lightweight, robust storage ability, and reliable mechanical integrity.

Microwave-assisted catalytic depolymerization of lignin from birch sawdust to produce phenolic monomers utilizing a hydrogen-free strategy

Catalytic hydrogenolysis of lignin to obtain value-added phenolic chemicals is a sustainable and cost-effective strategy for the efficient valorization of biomass derived wastes. Herein, an innovative approach by using a single-step microwave assisted depolymerization of lignin from birch sawdust without external hydrogen in the mixture of water-alcohol (methanol, ethanol, isopropanol) co-solvents over commercial catalysts (Pd/C, Pt/C, Ru/C) was investigated. A 65 wt% yield of phenolic monomers was obtained based on 43.8 wt% of delignification (190 °C, 3 h). The solid residues retained 92.0 wt% of cellulose and 57.3 wt% of hemicellulose, which could be further used for fermentation or in the pulp industry. Analysis of the lignin oil revealed that in-situ hydrogen generated from methanol decomposition promoted the hydrogenolysis of βO4 ether linkage and selective hydrogenation of unsaturated side-chains of phenolic monomers. This work introduces new perspectives for the efficient and cost-effective production of value-added phenolic compounds from lignin in agro-industrial wastes without external hydrogen assisted by microwave heating.

Recent Advances in the Catalytic Depolymerization of Lignin towards Phenolic Chemicals: A Review

The efficient valorization of lignin could dictate the success of the 2nd generation biorefinery. Lignin, accounting for on average a third of the lignocellulosic biomass, is the most promising candidate for sustainable production of value-added phenolics. However, the structural alteration induced during lignin isolation is often depleting its potential for value-added chemicals. Recently, catalytic reductive depolymerization of lignin has appeared to be a promising and effective method for its valorization to obtain phenolic monomers. The present study systematically summarizes the far-reaching and state-of-the-art lignin valorization strategies during different stages, including conventional catalytic depolymerization of technical lignin, emerging reductive catalytic fractionation of protolignin, stabilization strategies to inhibit the undesired condensation reactions, and further catalytic upgrading of lignin-derived monomers. Finally, the potential challenges for the future researches on the efficient valorization of lignin and possible solutions are proposed.

Product-oriented Direct Cleavage of Chemical Linkages in Lignin

Lignin is one of the most important biomacromolecules in the plant biomass and the largest renewable source of aromatic building blocks in nature. Selectively producing value-added chemicals from the catalytic transformation of renewable lignin is of strategic significance and meet sustainability targets owing to the excessive consumption of non-renewable petroleum resource, but remains a long-term challenge owing to the complexity of lignin structure. This Minireview provides a summary and perspective of the extensive research that provides insight into selectively catalytic transformations of lignin and its derived monomers via directed scissor of chemical linkages (C-O and C-C bonds) with product-oriented targets. Furthermore, some challenges and opportunities of lignin catalytic transformation are provided based on existing problems in this field for readers to discuss future research directions.

Novel recyclable deep eutectic solvent boost biomass pretreatment for enzymatic hydrolysis

Deep eutectic solvent (DES) with protonic acid shows the great potential for biomass valorization. However, the acid corrosion and recycling are still severe challenges in biorefinery. Herein, a novel DES by coordinating FeCl₃ in choline chloride/glycerol DES was designed for effective and recyclable pretreatment. As compared to DESs with FeCl₂, ZnCl₂, AlCl₃ and CuCl₂, DES with FeCl₃ approvingly retained most of cellulose in pretreated Hybrid Pennisetum (95.2%). Meanwhile, the cellulose saccharification significantly increased to 99.5%, which was six-fold higher than that of raw biomass. The excellent pretreatment performance was mainly attributed to the high removal of lignin (78.88 wt%) and hemicelluloses (93.63 wt%) under the synergistic effect of Lewis acid and proper hydrogen-bond interaction of DES with FeCl₃. Furthermore, almost all cellulose still can be converted into glucose after five recycling process. Overall, the process demonstrated designed pretreatment was great potential for the low-cost biorefinery and boost the biofuel development.

Fast and Efficient Method to Evaluate the Potential of Eutectic Solvents to Dissolve Lignocellulosic Components

The application of eutectic solvents (ESs) in lignocellulosic biomass fractionation has been demonstrated as a promising approach to accomplish efficient and environmentally friendly biomass valorization. In general, ESs are a combination of two components, a hydrogen-bonding donor and a hydrogen-bonding acceptor, in which the melting point of the mixture is lower than that of the individual components. However, there are plenty of possible combinations to form ESs with the potential to apply in biomass processing. Therefore, the development of fast and effective screening methods to find combinations capable to dissolve the main biomass components—namely cellulose, hemicelluloses, and lignin—is highly required. An accurate and simple technique based on optical microscopy with or without polarized lenses was used in this study to quickly screen and monitor the dissolution of cellulose, xylose (a monomer of hemicelluloses), and lignin in several ESs. The dissolution of these solutes were investigated in different choline-chloride-based ESs (ChCl:UREA, ChCl:PROP, ChCl:EtGLY, ChCl:OXA, ChCl:GLY, ChCl:LAC). Small amounts of solute and solvent with temperature control were applied and the dissolution process was monitored in real time. The results obtained in this study showed that cellulose was insoluble in these ESs, while lignin and xylose were progressively dissolved.

Techno-economic analysis of vanillin production from Kraft lignin: Feasibility study of lignin valorization

Kraft lignin waste is valorized by converting it into vanillin via the oxidation process. To obtain the highest yield of vanillin, feed concentration of lignin, reaction temperature, and oxygen partial pressure are optimized. Three separation cases, i.e. solvent extraction followed by distillation (Case I), solvent extraction (Case II), and vacuum distillation (Case III) are simulated and compared to identify the most suitable separation process. The results reveal that the highest vanillin yield of 9.25% is attainable using feed concentration of Kraft lignin of 30 g/l, operating temperature of 110 °C, and oxygen partial pressure of 5 bars. Case I appears to be the most suitable method of separation since it consumes the lowest amount of energy and gives the best economic returns, with a payback period of 6.19 years and internal rate of return (IRR) of 22.63%.

From cellulose to 1,2,4-benzenetriol via catalytic degradation over a wood-based activated carbon catalyst

1,2,4-Benzenetriol was obtained from cellulose hydrothermal degradation using phosphoric acid-activated wood-based AC as the catalyst.

Selective utilization of methoxy groups in lignin for N-methylation reaction of anilines

The utilization of lignin as a feedstock to produce valuable chemicals is of great importance. However, it is a great challenge to produce pure chemicals because of the complex structure of lignin. The selective utilization of specific groups on lignin molecules offers the possibility of preparing chemicals with high selectivity, but this strategy has not attracted attention. In this work, we propose a protocol to produce methyl-substituted amines by the selective reaction of the methoxy groups of lignin and aniline compounds. It was found that LiI in the ionic liquid 1-hexyl-3-methylimidazolium tetrafluoroborate could catalyze the reaction efficiently and the selectivity to the N-methylation product could be as high as 98%. Moreover, the lignin was not depolymerized in the reaction. As it was rich in hydroxyl groups, the residual material left over after the reaction was used as an efficient co-catalyst for the cycloaddition of epoxy propane with CO2, using KI as the catalyst.