Advances in lignin valorization towards bio-based chemicals and fuels: Lignin biorefinery

Selective Oxidation Cleavage of Cα-Cβ Bonds between Lignin Aromatic Units via Phosphomolybdic Acid-Ionic Liquid

Lignin, the most abundant renewable resource of aromatics in nature, is recognized as an alternative to fossil-based fuels and chemicals. In this study, a phosphomolybdic acid-ionic liquid (PMA-IL) [BSHMIM]H2PMo12O40 was synthesized and used as a catalyst for further oxidative depolymerization of extracted lignin to prepare valuable chemicals. Under optimized conditions, the conversion of lignin reached 61.33%, and the total yield of target products (vanillin, vanillic acid, and methyl vanillate) was 28.00 mg·g-1, where the selectivity of methyl vanillate reached 56.43%. The liquid products and residues obtained under the optimum conditions were analyzed, further confirming the advantages of PMA-IL compared with single PMA. In addition, this method also has an excellent catalytic effect for other types of lignin and presents a good substrate applicability. Finally, based on the research results of model compounds, the possible reaction pathway of the formation of vanillin, vanillic acid, and methyl vanillate was proposed.

Tunning antisolvent precipitation for the synthesis of lignin nanoparticles using lignin extracted from different agro-industrial wastes

Lignin nanoparticles (LNPs) show great potential in UV-protectants, drugs carriers, encapsulation, supercapacitors, and others. This study proposes the development of an optimised LNP synthesis method by antisolvent precipitation, using lignin from persimmon tree pruning waste, green coconut waste, and sugarcane bagasse. The best synthesis conditions were determined evaluating the chemical composition and the physicochemical properties of the LNPs, by varying the antisolvent addition rate, initial lignin concentration and antisolvent pH. Optimal precipitation conditions - 250 μL·s-1, 5 mg·mL-1 of lignin, pH 7.0 (antisolvent), 250 μL·s-1 adding antisolvent - converted the persimmon, coconut, and the sugarcane lignin into nanometric structures (Ø = 130-192 nm), with a spherical morphology, which were stable during storage at 5 °C for 90 days. Particle formation did not cause significant changes in the chemical composition of the lignins, and regardless of the plant origin, the LNPs showed higher UV absorption and thermal stability than the original corresponding lignins.

Structural and molecular insights into diisocyanate functionalized lignosulfonate for improving asphaltic aging resistance

Lignosulfonate (LS) is used to improve asphaltic aging resistance owing to absorbing ultraviolet (UV) light and trapping free radicals. However, excessive addition of LS disrupts uniform dispersion in the asphaltic matrix due to polarity mismatch, causing aggregation, phase separation, and matrix hardening, which collectively reduces anti-aging effectiveness. Herein, we demonstrate a strategy of diisocyanate to enhance LS on asphaltic compatibility with asphalt by synergistically reducing hydrophilic groups and surface free energy. In detail, three diisocyanate functionalized LSs (DFLSs) were prepared via covalent binding of hydroxyl and isocyanate groups, and their structural properties were characterized using various techniques. The results indicated that DFLS had larger particle sizes, greater hydrophobicity, and improved UV absorption than LS. Subsequently, DFLS was utilized to modify asphalt (DFLS-MA), demonstrating superior aging resistance compared to LS-modified asphalt (LS-MA) and pristine asphalt (PA). Beyond the compatibility test, the interaction between DFLS and asphalt was elucidated using molecular simulations (MS). Through functioning of diisocyanates, the surface energy value of LS declined from 34.034 to 8.470 mJ/m2 maximumly, stating that the aggregation of LS was inhibited markedly. Meanwhile, Binding energy calculations revealed that DFLS exhibited higher absolute values than LS, indicating that the functionalization of improved LS dispersion in asphalt and contributed valid aging protection. Furthermore, 4,4'-diphenylmethane diisocyanate (MDI) illustrating the most effective enhancement among all, highlighting that the introduction of benzene ring was pivotal in improving LS compatibility with asphalt. This finding presents a novel approach to enhancing asphalt aging resistance through the structural organization of lignin materials.

Alkaline catalytic liquefaction of pig manure fermentation residue in ethanol solvent for the production of high-quality biocrude oil

The widespread application of biogas projects generates substantial amounts of waste fermentation residue. Further treatment of fermentation residues facilitates resource utilization, ensures safe disposal, and is anticipated to enhance the economic returns of biogas projects. Herein, catalytic liquefaction of pig manure fermentation residue to produce biocrude oil was investigated using various alkaline catalysts at 340 ℃ with ethanol as the solvent. Biocrude oils were analyzed by elemental analysis, gas chromatography-mass spectrometry (GC-MS), thermogravimetric analysis, and kinetic analysis. The maximum biocrude oil yield (45.24 wt%) was obtained with the KOH catalyst. Additionally, the biocrude oil produced by the catalysis of CaO exhibited the maximum higher heating value at 44.18 MJ/kg. GC-MS results showed that KOH and K2CO3 considerably increased the content of phenols and hydrocarbons in the biocrude while reducing nitrogenous compounds. All alkaline catalysts effectively reduced the activation energy of biocrude oil compared to biocrude oil without catalyst. The maximum reduction in activation energy (18.73 %) was achieved with the addition of Na2CO3. More importantly, adding CaO not only increased the yield and higher heating value of biocrude oil but also reduced nitrogenous compounds and activation energy, improving the overall yield and quality. Overall, this work provides an effective and promising method to convert pig manure fermentation residue into green high-quality biocrude oil, simultaneously providing an economical and environmentally friendly waste management strategy for the fermentation industry.

Study of Ni-ZSM-5 Catalysts in the Hydrogenolysis of Benzyl Phenyl Ether: Effects of Ni Loading, Morphology, and Reaction Conditions

This work investigates the activity of a series of Ni catalysts under a range of reaction conditions for the conversion of a lignin model compound (benzyl phenyl ether) to aromatic compounds. A series of transition metal-based catalysts (Ni-ZSM-5) have been prepared with different metal loadings (5, 10 and 20%) via an excess impregnation method. The materials were characterized using power X-ray diffraction (p-XRD), transmission electron microscopy (TEM) and Brunauer-Emmett-Teller (BET) confirming the formation of a set of dispersed, metallic and spherical nanoparticles on all materials. On a 10% Ni-ZSM-5 material, the formation of a set of nanoparticles with a tetrahedral shape was noted. The materials were applied in the cleavage of the ether bond of a lignin model compound (benzyl phenyl ether) via hydrogenolysis in a range of organic solvents (1-butanol, ethanol, 2-propanol and pentane) and under two different atmospheres (H2 and Ar). 2-Propanol was shown to be the optimal solvent for the reaction confirming its propensity to act as a H-transfer material and the morphology of the supported nanoparticles was shown to have an important effect on the reactivity of the catalysts.

Unlocking Lignin's Potential: Engineered Bacterial Laccases to Produce Biologically Active Molecules

Laccases are biocatalysts with immense potential in lignocellulose biorefineries to valorize emerging lignin monomers for sustainable chemicals. Despite reduced costs over the past two decades, enzymes remain a major expense in biorefining. Protein engineering can enhance enzyme properties and lower costs further. In this study, we used enzyme engineering tools to improve >400-fold the catalytic efficiency (kcat/Km) of a hyperthermostable bacterial laccase for 2,6-dimethoxyphenol, a lignin-related phenolic compound. Furthermore, this evolved variant showed improved activity at neutral to alkaline pH for hydroxycinnamyl alcohols, hydrocinnamic acids, phenylpropanoid and vanillyl derivatives. We optimized conditions for the synthesis of syringaresinol, dehydrodiconiferyl alcohol, thomasidioic acid, biseugenol, dehydrodiisoeugenol, and diapocynin, detailing the pH, catalyst concentration, reaction time, temperature, and oxygenation of the reaction mixtures. Our biocatalytic system offers several advantages, including being free of organic solvents, achieving faster reaction times, using lower amounts of enzymes and delivering excellent yields (up to 100 %) than reported methods. Additionally, we provide insights that advance the state-of-the-art in lignin combinatory chemistry. This progress marks a significant step forward in valorizing the lignin chemicals platform, enabling high yields of dimeric compounds with structural scaffolds that can be exploited in various biotechnological areas, such as medicinal chemistry and polymer synthesis.

Comprehensive characterization of lignins in the context of their valorization: A combination of NMR/2D-COS IR spectroscopy

The widespread development of lignin valorization is hindered by a number of challenges. In particular, efficient valorization necessitates comprehensive characterization of initial lignins. In this work, the structural features of lignins from birch wood (Bétula péndula), obtained by various methods of hard and mild fractionation of biomass: hydrolysis (Hyd-L), kraft (Kraft-L), soda (Soda-L), and soda-ethanol (SodaEt-L) processes, as well as organosolv processes with dioxane (MWL, DL) and dimethyl sulfoxide (DMSO-L) have been comprehensively studied. The main novelty of this study is the first-time application of Two-Dimensional Correlation Infrared Spectroscopy (2D-COS IR) for rapidly and comprehensively assessing structural transformations of lignins, in combination with 31P NMR. It has been established that changing delignification conditions primarily affects the processes of demethoxylation, dehydration and polymerization/condensation of lignin, and then the breaking of lignin-carbohydrates linkages. An approach to evaluating the potential of different types of lignin for valorization (valorization index), based on their structural characteristics, has been proposed. The applied approach allowed for the arrangement of the studied lignins in order of decreasing valorization index: DMSO-L, MWL, DL, SodaEt-L, Soda-L, Kraft-L.

Catalytic depolymerization of Camellia oleifera shell lignin to phenolic monomers: Insights into the effects of solvent, catalyst and atmosphere

Camellia oleifera shell (COS) is a renewable biomass resource abundant in lignin with significant potential for producing phenolic monomers. However, the dearth of research has led to considerable resource wastage and environmental pollution. Herein, reductive catalytic fractionation (RCF) of COS was performed using noble metal catalysts in different solvents. An 11.1 wt% yield of phenolic monomers was achieved with 91% selectivity toward propylene-substituted monomers in H2O/EtOH (3:7, v/v) cosolvent under N2 atmosphere. Notably, the highest phenolic monomer yield of 17.0 wt% was obtained with impressive selectivity (86.9%) toward propanol-substituted monomers in the presence of H2. The GPC analysis and 2D HSQC NMR spectra indicated the effective depolymerization of lignin oligomers with catalysts. Phenolic monomers with ethyl, propyl, or propanol side chain could be produced from lignin-derived oligomers through hydrogenolysis, hydrogenation, and decarboxylation reactions. Overall, this study has paved the way for the valorization of COS lignin through the RCF strategy.

Lignin: An Adaptable Biodegradable Polymer Used in Different Formulation Processes

INTRODUCTION

LIG is a biopolymer found in vascular plant cell walls that is created by networks of hydroxylated and methoxylated phenylpropane that are randomly crosslinked. Plant cell walls contain LIG, a biopolymer with significant potential for usage in modern industrial and pharmaceutical applications. It is a renewable raw resource. The plant is mechanically protected by this substance, which may increase its durability. Because it has antibacterial and antioxidant qualities, LIG also shields plants from biological and chemical challenges from the outside world. Researchers have done a great deal of work to create new materials and substances based on LIG. Numerous applications, including those involving antibacterial agents, antioxidant additives, UV protection agents, hydrogel-forming molecules, nanoparticles, and solid dosage forms, have been made with this biopolymer.

METHODS

For this review, a consistent literature screening using the Pubmed database from 2019-2024 has been performed.

RESULTS

The results showed that there is an increase in interest in lignin as an adaptable biomolecule. The most recent studies are focused on the biosynthesis and antimicrobial properties of lignin-derived molecules. Also, the use of lignin in conjunction with nanostructures is actively explored.

CONCLUSIONS

Overall, lignin is a versatile molecule with multiple uses in industry and medical science.

Oxidative Catalytic Depolymerization of Lignin into Value-Added Monophenols by Carbon Nanotube-Supported Cu-Based Catalysts

Lignin valorisation into chemicals and fuels is of great importance in addressing energy challenges and advancing biorefining in a sustainable manner. In this study, on the basis of the high microwave absorption performance of carbon nanotubes (CNTs), a series of copper-oxide-loaded CNT catalysts (CuO/CNT) were developed to facilitate the oxidative depolymerization of lignin under microwave heating. This catalyst can promote the activation of hydrogen peroxide and air, effectively generating a range of reactive oxygen species (ROS). Through the application of electron paramagnetic resonance techniques, these ROS generated under different oxidation conditions were detected to elucidate the oxidation mechanism. The results demonstrate that the •OH and O2•- play a crucial role in the formation of aldehyde and ketone products through the cleavage of lignin Cβ-O and Cα-Cβ bonds. We further evaluated the catalytic performance of the CuO/CNT catalysts with three typical lignin feedstocks to determine their applicability for lignin biorefinery. The bio-enzymatic lignin produced a 13.9% monophenol yield at 200 °C for 20 min under microwave heating, which was higher than the 7% yield via hydrothermal heating conversion. The selectivity of G-/H-/S-type products was slightly affected, while lignin substrate had a noticeable effect on the selective production. Overall, this study explored the structural characteristics of CuO/CNT catalysts and their implications for lignin conversion and offered an efficient oxidation approach that holds promise for sustainable biorefining practices.

Improving the Monophenolic Yield of Lignin Depolymerization in Dualistic Aprotic Solvent System by Organic Solvent Fractionation

Converting lignin into aromatic chemicals is a promising strategy for the high-value utilization of lignocellulosic feedstock. However, the inherent heterogeneity of lignin poses a significant obstacle to achieving efficient conversion and optimal product yields within bio-refinery systems. Herein, we employed a one-step fractionation method to enhance lignin homogeneity and utilized the THF/DMSO-EtONa (tetrahydrofuran/dimethyl sulfoxide-sodium ethoxide) system to depolymerize the fractionated lignin. Three protic and three aprotic solvents were used for fractionation. The impact of the solvent properties on the structure and the depolymerization efficiency of the fractionated lignin was investigated. Methanol-fractionated lignin generated the benzoic acid compounds with a yield of 30 wt%, 50 % higher than that of the unfractionated lignin. The polarities (δP), hydrogen bonding abilities (δH), and viscosities (η) of selected protic solvents showed strong linear correlation with molecular weight (Mw), polymer dispersity index (PDI), and syringyl/guaiacyl ratio (S/G ratio) of the fractionated lignin, as well as the total yield of benzoic acid compounds derived from the β-O-4 bond cleavage. This study elucidates the relationship between solvent properties and lignin structure and proposes a promising approach for refining lignin to enhance utilization efficiency, thereby presenting a potential strategy for value-added application of complex lignin polymers.

Lignin-Based Composite Film and Its Application for Agricultural Mulching

Agricultural mulching is an important input for modern agricultural production and plays an important role in guaranteeing food security worldwide. At present, polyethylene (PE) mulching is still commonly used in agricultural production in most countries around the world, which is non-biodegradable, and years of mulching have caused serious agricultural white pollution. Lignin is one of the three major components of plant cell walls, and it is also the main renewable natural aromatic compounds in nature. Lignin-based composite film materials are green, biodegradable, and show good prospects for development in the field of agricultural mulch. This paper introduces the types, structure, and application status of lignin, summarizes the preparation of lignin-based composite film materials and its latest research progress, focuses on the types, preparation methods, and application examples of lignin-based agricultural mulching, and looks forward to the future development prospects of lignin-based agricultural mulching.

Perspective on Lignin Conversion Strategies That Enable Next Generation Biorefineries

The valorization of lignin, a currently underutilized component of lignocellulosic biomass, has attracted attention to promote a stable and circular bioeconomy. Successful approaches including thermochemical, biological, and catalytic lignin depolymerization have been demonstrated, enabling opportunities for lignino-refineries and lignocellulosic biorefineries. Although significant progress in lignin valorization has been made, this review describes unexplored opportunities in chemical and biological routes for lignin depolymerization and thereby contributes to economically and environmentally sustainable lignin-utilizing biorefineries. This review also highlights the integration of chemical and biological lignin depolymerization and identifies research gaps while also recommending future directions for scaling processes to establish a lignino-chemical industry.

Sustainable Calcite Scale Inhibitors via Oxidation of Lignosulfonates

Deposition of inorganic scales in wells, flow lines, and equipment is a major problem in the water treatment, geothermal, or upstream oil and gas industries. Deployment of scale inhibitors has been adopted worldwide for oilfield scale prevention. Commercial synthetic scale inhibitors such as polymeric carboxylates and sulfonates or nonpolymeric phosphonates offer good scale inhibition performance but often suffer from one or more limitations including biodegradability, calcium compatibility, and thermal stability. Lignin-based biomaterials such as sodium lignosulfonates are natural, sustainable, and widely available polymers that are accepted for use in environmentally sensitive areas. Here we show that, although lignosulfonates perform relatively poorly as calcite scale inhibitors in dynamic tube blocking tests, oxidized lignosulfonates show a much improved inhibition effect by a factor of 20-fold. The oxidized lignosulfonates are easy to prepare in a 1-step reaction and show excellent calcium compatibility and thermal stability, useful for downhole squeeze treatments in high temperature wells. This present study unequivocally establishes oxidized lignosulfonates as a new class of sustainable green scale inhibitors, thereby bridging the gap between materials derived directly from nature and the classic synthetic polymeric scale inhibitors.

Selective adsorption of anionic dyes by a macropore magnetic lignin-chitosan adsorbent

Dyes pollution is well known for their hazardous impacts on human health and the environment. The removal of dyes from wastewater has become an important issue. In this study, magnetic micrometer-sized particles AL-CTS@MNPs were synthesized from alkaline lignin (AL) and chitosan (CTS) by "one-pot method". The adsorbent presented higher selectivity adsorption effect on anionic dyes than amphoteric and cationic dyes, and even no adsorption effect on cationic methylene blue (MB), which showed that the anionic dyes could be better separated from the other two types of dyes. The adsorption isotherms of the dyes were highly consistent with the Langmuir model, and the maximum adsorption capacity was 329.50 mg/g for methyl orange (MO) and 20.00 mg/g for rhodamine B (RhB). AL-CTS@MNPs showed good adsorption of anionic dyes (MO) in the pH range of 3-9. Meanwhile, the adsorbent AL-CTS@MNPs were also characterized, showing rough surface with specific surface areas of 37.38 m2/g, pore diameter of 95.8 nm and porosity of 17.62 %. The particle sizes were ranged from 800 μm to 1300 μm. The electrostatic attraction and π-π* electron donor-acceptor interactions were the main forces between the adsorbent and anionic dyes. While the electrostatic repulsive force between the adsorbent and the cationic dyes resulted in the non-absorption of MB by AL-CTS@MNPs. Subsequently, the adsorbent maintained a removal rate of >95 % after five adsorption-desorption cycles, demonstrating its excellent stability and recoverability. Ultimately, the prepared AL-CTS@MNPs illuminated good prospect on complex components dyes wastewater treatment.

Fabrication modulation of lignin-derived carbon nanosphere supported Pd nanoparticle via lignin fractionation for improved catalytic performance in vanillin hydrodeoxygenation

Nano-lignin presents great potential in advanced carbon materials preparation since it integrates the advantages of nanomaterials as well the preferable properties of lignin (e.g. high carbon content and highly aromatic structure). Herein, lignin-derived carbon nanosphere supported Pd catalysts (Pd@LCNS) were prepared via a two-step carbonization of Pd2+ adsorbed lignin nanospheres (LNS) and applied in vanillin hydrodeoxygenation. The effect lignin heterogeneity on the synthesis of Pd@LCNS as well as its catalytic performance was further investigated through the synthesis of Pd@LCNS using three lignin fractions with different molecular weight. The results showed that the three Pd@LCNSs exhibited significant differences in the morphology of both carbon support and Pd nanoparticles. Pd@LCNS-3 prepared from high molecular weight lignin fraction (L-3) presented stable carbon nanosphere support with the smallest particle size (∼150 nm) and the highest Pd loading amount (3.78 %) with the smallest Pd NPs size (∼1.6 nm). Therefore, Pd@LCNS-3 displayed superior catalytic activity for vanillin hydrodeoxygenation (99.34 % of vanillin conversion and 99.47 % of 2-methoxy-4-methylphenol selectivity) at 90 °C without H2. Consequently, this work provides a sustainable strategy to prepare uniformly dispersed lignin-based carbon-supported Pd catalyst using high molecular weight lignin as the feedstock and further demonstrate its superior applicability in the selective transfer hydrogenation of vanillin.

Constructing lignin based nanoparticles towards flame retardant thermoplastic polyurethane composites with improved mechanical and oxidation resistant properties

A multifunctional lignin derivative nanoparticle (C-P-Lignin) was synthesized by grafting phenyl dichloro sphosphineoxid and 1, 4-dimethoxyacetylene stepwise on the lignin, then it was applied to prepare the thermoplastic polyurethane (TPU) composite with improved mechanical properties, oxidation resistance, and flame retardancy. The tensile strength, the elongation at break, and the toughness of the TPU/2C-P-Lignin sample reached 28.3 MPa, 941 %, and 139.0 MJ/m2 respectively, which were increased by 39.0 %, 3.4 %, and 33.9 % respectively compared with that of the control TPU sample. The anti-fatigue property was also improved. More importantly, the mechanism of the improved mechanical properties was also calculated and simulated by FTIR and Materials Studio software. The TPU/2C-P-Lignin sample exhibited superior oxidation resistance during the process of photoaging and thermal oxidative aging. Furthermore, the peak heat release rate and the smoke production rate for theTPU/2C-P-Lignin sample was reduced by 50.0 % and 53.8 % compared with that of the control TPU. The reason was that the C-P-Lignin is conducive to the formation of uniformly distributed carbon layers. It is expected that this work can provide a new method for expanding the utilization of waste wood as a multifunctional lignin-based filler to improve fire safety and extend the service life of TPU polymers.

Lignin Extraction by Using Two-Step Fractionation: A Review

Lignocellulosic biomass represents the most abundant renewable carbon source on earth and is already used for energy and biofuel production. The pivotal step in the conversion process involving lignocellulosic biomass is pretreatment, which aims to disrupt the lignocellulose matrix. For effective pretreatment, a comprehensive understanding of the intricate structure of lignocellulose and its compositional properties during component disintegration and subsequent conversion is essential. The presence of lignin-carbohydrate complexes and covalent interactions between them within the lignocellulosic matrix confers a distinctively labile nature to hemicellulose. Meanwhile, the recalcitrant characteristics of lignin pose challenges in the fractionation process, particularly during delignification. Delignification is a critical step that directly impacts the purity of lignin and facilitates the breakdown of bonds involving lignin and lignin-carbohydrate complexes surrounding cellulose. This article discusses a two-step fractionation approach for efficient lignin extraction, providing viable paths for lignin-based valorization described in the literature. This approach allows for the creation of individual process streams for each component, tailored to extract their corresponding compounds.

A wide array of lignin-related phenolics are oxidized by an evolved bacterial dye-decolourising peroxidase

Lignin is the second most abundant natural polymer next to cellulose and by far the largest renewable source of aromatic compounds on the planet. Dye-decolourising peroxidases (DyPs) are biocatalysts with immense potential in lignocellulose biorefineries to valorize emerging lignin building blocks for environmentally friendly chemicals and materials. This work investigates the catalytic potential of the engineered PpDyP variant 6E10 for the oxidation of 24 syringyl, guaiacyl and hydroxybenzene lignin-phenolic derivatives. Variant 6E10 exhibited up to 100-fold higher oxidation rates at pH 8 for all the tested phenolic substrates compared to the wild-type enzyme and other acidic DyPs described in the literature. The main products of reactions were dimeric isomers with molecular weights of (2 × MWsubstrate - 2 H). Their structure depends on the substitution pattern of the aromatic ring of substrates, i.e., of the coupling possibilities of the primarily formed radicals upon enzymatic oxidation. Among the dimers identified were syringaresinol, divanillin and diapocynin, important sources of structural scaffolds exploitable in medicinal chemistry, food additives and polymers.

Selective Depolymerization of Lignin Towards Isolated Phenolic Acids Under Mild Conditions

The selective transformation of lignin to value-added biochemicals (e. g., phenolic acids) in high yields is incredibly challenging due to its structural complexity and many possible reaction pathways. Phenolic acids (PA) are key building blocks for various aromatic polymers, but the isolation of PAs from lignin is below 5 wt.% and requires harsh reaction conditions. Herein, we demonstrate an effective route to selectively convert lignin extracted from sweet sorghum and poplar into isolated PA in a high yield (up to 20 wt.% of lignin) using a low-cost graphene oxide-urea hydrogen peroxide (GO-UHP) catalyst under mild conditions (<120 °C). The lignin conversion yield is up to 95 %, and the remaining low molecular weight organic oils are ready for aviation fuel production to complete lignin utilization. Mechanistic studies demonstrate that pre-acetylation allows the selective depolymerization of lignin to aromatic aldehydes with a decent yield by GO through the Cα activation of β-O-4 cleavage. A urea-hydrogen peroxide (UHP) oxidative process is followed to transform aldehydes in the depolymerized product to PAs by avoiding the undesired Dakin side reaction due to the electron-withdrawing effect of the acetyl group. This study opens a new way to selectively cleave lignin side chains to isolated biochemicals under mild conditions.

Recent advancements and challenges in emerging applications of biochar-based catalysts

The sustainable utilization of biochar produced from biomass waste could substantially promote the development of carbon neutrality and a circular economy. Due to their cost-effectiveness, multiple functionalities, tailorable porous structure, and thermal stability, biochar-based catalysts play a vital role in sustainable biorefineries and environmental protection, contributing to a positive, planet-level impact. This review provides an overview of emerging synthesis routes for multifunctional biochar-based catalysts. It discusses recent advances in biorefinery and pollutant degradation in air, soil, and water, providing deeper and more comprehensive information of the catalysts, such as physicochemical properties and surface chemistry. The catalytic performance and deactivation mechanisms under different catalytic systems were critically reviewed, providing new insights into developing efficient and practical biochar-based catalysts for large-scale use in various applications. Machine learning (ML)-based predictions and inverse design have addressed the innovation of biochar-based catalysts with high-performance applications, as ML efficiently predicts the properties and performance of biochar, interprets the underlying mechanisms and complicated relationships, and guides biochar synthesis. Finally, environmental benefit and economic feasibility assessments are proposed for science-based guidelines for industries and policymakers. With concerted effort, upgrading biomass waste into high-performance catalysts for biorefinery and environmental protection could reduce environmental pollution, increase energy safety, and achieve sustainable biomass management, all of which are beneficial for attaining several of the United Nations Sustainable Development Goals (UN SDGs) and Environmental, Social and Governance (ESG).

Depolymerization of lignin: Recent progress towards value-added chemicals and biohydrogen production

The need for alternative sources of energy became increasingly urgent as demand for energy and the use of fossil fuels both soared. When processed into aromatic compounds, lignin can be utilized as an alternative to fossil fuels, however, lignin's complex structure and recalcitrance make depolymerization impractical. This article presented an overview of the most recent advances in lignin conversion, including process technology, catalyst advancement, and case study-based end products. In addition to the three established methods (thermochemical, biochemical, and catalytic depolymerization), a lignin-first strategy was presented. Depolymerizing different forms of lignin into smaller phenolic molecules has been suggested using homogeneous and heterogeneous catalysts for oxidation or reduction. Limitations and future prospects of lignin depolymerization have been discussed which suggests that solar-driven catalytic depolymerization through photocatalysts including quantum dots offers a unique pathway to obtain the highly catalytic conversion of lignin.

Advances of Modified Lignin as Substitute to Develop Lignin-Based Phenol-Formaldehyde Resin Adhesives

Traditionally, phenols used to prepare phenol-formaldehyde (PF) resin adhesives are obtained from phenolic compounds and various chemicals, which are extracted from petroleum-based raw materials. Lignin, a sustainable phenolic macromolecule in the cell wall of biomass with an aromatic ring and a phenolic hydroxyl group similar to those of phenol, can be an ideal substitute for phenol in PF resin adhesives. However, only a few lignin-based adhesives are produced on a large scale in industry, mainly because of the low activity of lignin. Preparing lignin-based PF resin adhesives with exceptional achievements by modifying lignin instead of phenol is an efficient method to improve the economic benefits and protect the environment. In this review, the latest progress in the preparation of PF resin adhesives via lignin modification, including chemical, physical, and biological modifications, is discussed. In addition, the advantages and disadvantages of different lignin modification methods for adhesives are compared and discussed, and future research directions for the synthesis of lignin-based PF resin adhesives are proposed.

Recent advances in bio-based polybenzoxazines as an interesting adhesive coating

Polybenzoxazine (PBz) is an excellent and highly intriguing resin for various sophisticated uses. Benzoxazines have piqued the curiosity of academics worldwide because of their peculiar properties. Nonetheless, most benzoxazine resin manufacturing and processing methods, notably bisphenol A-based benzoxazine, rely on petroleum resources. Because of the environmental consequences, bio-based benzoxazines are being researched as alternatives to petroleum-based benzoxazines. As a result of the environmental implications, bio-based benzoxazines are being developed to replace petroleum-based benzoxazines, and they are gaining traction. Bio-based polybenzoxazine, epoxy, and polysiloxane-based resins have piqued the interest of researchers in coatings, adhesives, and flame-retardant thermosets in recent years due to their anticorrosion, ecologically friendly, affordable, and low water absorption properties. As a result, numerous scientific studies and patents on polybenzoxazine continues to rise in polymer research. Based on its mechanical, thermal, and chemical characteristics, bio-based polybenzoxazine has several applications, including coatings (anticorrosion and antifouling), adhesives (highly crosslinked network, outstanding mechanical and thermal capabilities), and flame retardants (with the high charring capability). This review reports an overview of polybenzoxazine, highlighting the current advances and progress in synthesizing bio-based polybenzoxazine, their properties, and their use in coating applications.

Utilization Perspectives of Lignin Biochar from Industrial Biomass Residue

The present study aimed at utilizing technically hydrolyzed lignin (THL), industrial biomass residue, derived in high-temperature diluted sulfuric acid hydrolysis of softwood and hardwood chips to sugars. The THL was carbonized in a horizontal tube furnace at atmospheric pressure, in inert atmosphere and at three different temperatures (500, 600, and 700 °C). Biochar chemical composition was investigated along with its HHV, thermal stability (thermogravimetric analysis), and textural properties. Surface area and pore volume were measured with nitrogen physisorption analysis often named upon Brunauer-Emmett-Teller (BET). Increasing the carbonization temperature reduced volatile organic compounds (40 ÷ 96 wt. %), increased fixed carbon (2.11 to 3.68 times the wt. % of fixed carbon in THL), ash, and C-content. Moreover, H and O were reduced, while N- and S-content were below the detection limit. This suggested biochar application as solid biofuel. The biochar Fourier-transform infrared (FTIR) spectra revealed that the functional groups were gradually lost, thus forming materials having merely polycyclic aromatic structures and high condensation rate. The biochar obtained at 600 and 700 °C proved having properties typical for microporous adsorbents, suitable for selective adsorption purposes. Based on the latest observations, another biochar application was proposed-as a catalyst.

The Study of Potentially Lignocellulolytic Actinobacteria Pseudonocardia sp. AI2

The search for microorganisms with potential for bioconversion of lignocellulose is now of immediate interest. Industrial waste is a source of various microorganisms. This paper describes results of the research of potentially lignocellulolytic actinobacteria isolated from activated sludge of the wastewater treatment plant of a pulp and paper mill located in Komi Republic (Russia). One strain of actinobacteria, AI2, was found to be sufficiently active in terms of degradation of lignocellulose-containing materials. Testing of the AI2 isolate demonstrated its ability to synthesize cellulase, dehydrogenase and protease to various extents. The AI2 strain was found capable of biosynthesizing cellulase to 5.5 U/ml. In case of solid-phase fermentation using treated softwood and hardwood sawdust, the content of main components changed most significantly in aspen sawdust: from initial concentration of 20.4% down to 15.6% for lignin, and from 50.6% down to 31.8% for cellulose. In case of liquid-phase fermentation, the content of lignin components decreased significantly in the treated aqueous medium that contained lignosulfonates: from initial concentration of 3.6 g down to 2.1g. Taxonomic study of the AI2 strain of actinobacteria confirmed that it belongs to the rare Pseudonocardia genus of actinomycetes. Based on the results of 16S rRNA sequencing, the AI2 strain is most similar to the species Pseudonocardia carboxydivorans.

Preparation of High-Toughness Lignin Phenolic Resin Biomaterials Based via Polybutylene Succinate Molecular Intercalation

Lignin has many potential applications and is a biopolymer with a three-dimensional network structure. It is composed of three phenylpropane units, p-hydroxyphenyl, guaiacyl, and syringyl, connected by ether bonds and carbon-carbon bonds, and it contains a large number of phenol or aldehyde structural units, resulting in complex lignin structures. This limits the application of lignin. To expand the application range of lignin, we prepared lignin thermoplastic phenolic resins (LPRs) by using lignin instead of phenol; these LPRs had molecular weights of up to 1917 g/mol, a molecular weight distribution of 1.451, and an O/P value of up to 2.73. Due to the complex structure of the lignin, the synthetic lignin thermoplastic phenolic resins were not very tough, which greatly affected the performance of the material. If the lignin phenolic resins were toughened, their application range would be substantially expanded. Polybutylene succinate (PBS) has excellent processability and excellent mechanical properties. The toughening effects of different PBS contents in the LPRs were investigated. PBS was found to be compatible with the LPRs, and the flexible chain segments of the small PBS molecules were embedded in the molecular chain segments of the LPRs, thus reducing the crystallinities of the LPRs. The good compatibility between the two materials promoted hydrogen bond formation between the PBS and LPRs. Rheological data showed good interfacial bonding between the materials, and the modulus of the high-melting PBS made the LPRs more damage resistant. When PBS was added at 30%, the tensile strength of the LPRs was increased by 2.8 times to 1.65 MPa, and the elongation at break increased by 31 times to 93%. This work demonstrates the potential of lignin thermoplastic phenolic resins for industrial applications and provides novel concepts for toughening biobased aromatic resins with PBS.

Exploring the Oxidative Effects of the Microbial Electro-Fenton Process on the Depolymerization of Lignin Extracted from Rice Straw in a Bio-Electrochemical System Coupled with Wastewater Treatment

Lignin is a potential renewable feedstock to produce value-added compounds, but the overwhelming bulk of it is either burned for energy or discarded as waste. This paper addressed two critical issues: waste-to-value generation and management by demonstrating the in situ depolymerization of lignin extracted from waste rice straw utilizing the microbial electro-Fenton process in a microbial peroxide-producing cell (MPPC), a type of bio-electrochemical cell, for value addition while synchronously treating wastewater. The MPPC electrochemical voltage yields of 0.171 ± 0.05-0.497 ± 0.2 V produced 9 ± 0.43-34 ± 0.11 mM of H₂O₂, which was utilized to depolymerize lignin at various concentrations. Interestingly, a direct correlation was observed between lignin depolymerization and H₂O₂ concentration, while Fourier-transform infrared spectroscopy data revealed a constant disruption of the lignin structure accurately in the wavenumber region of 1000-1750 cm^-1 irrespective of the H₂O₂ concentration. Carboxylic acid derivatives, benzopyran, hexanoic acid, and other valuable compounds were detected in the LC QTOF MS data from the depolymerized lignin mixture. Remarkably, SEM analysis demonstrated morphological changes in depolymerized lignin induced by the oxidative effects of hydroxyl radicals. Biochemical oxygen demand and chemical oxygen demand removal was 60 ± 3-85 ± 1% in anodic wastewater treatment. This research provides a sustainable and efficient technique for lignin valorization and wastewater treatment.

Bio-separation of value-added products from Kraft lignin: A promising two-stage lignin biorefinery via microbial electrochemical technology

The most ubiquitous aromatic biopolymer in nature, lignin offers a promising foundation for the development of bio-based chemicals with wide-ranging industrial uses attributable to its aromatic structure. Lignin must first be depolymerized into smaller oligomeric and monomeric units at the initial stage of lignin bioconversion, followed by separation to recover valuable products. This study demonstrates an integrative biorefinery idea based on in-situ depolymerization of the lignin via microbial electro-Fenton reaction in a microbial peroxide-producing cell and recovery of the identified products i.e., phenolic or aromatic monomers by one step high throughput chromatography. The yield percentage of acetovanillone, ethylvanillin, and ferulic acid recovered from the depolymerized lignin using the integrative biorefinery strategy were 2.1 %, 9.1 %, and 9.04 %, respectively. These products have diverse industrial usage and can be employed as platform chemicals. The development of a novel system for efficient simultaneous lignin depolymerization and subsequent quality separation are demonstrated in this study.

Characteristics of calcium lignin from pulping waste liquor and application for the treatment middle-stage wastewater of paper making

In order to obtain a lignin-based adsorbent with low cost, simple operation and no further modification, a calcium lignin adsorbent was prepared from chemical mechanical pulping (CMP) waste liquor by directly calcification from lime. The calcium lignin was characterized by BET, SEM, TEM, FT-IR and solid-state NMR analyses. The results showed that the molecular structure of the calcium lignin particles did not change when compared to sodium lignin, the formation mechanism of calcium lignin was revealed. The initial COD and lignin contents of CMP waste liquid were 54858 mg/L and 24.39 g/L, the conversion rate of lignin can reach 71.36% when was deal with lime. Thus, most of the lignin resources in the waste liquid were recovered. The middle-stage wastewater (MSWW) of pulping and papermaking was dealt with calcium lignin, the COD removal rate was up to 85.83%. The adsorption isotherms and kinetics were well fitted by the Langmuir model and pseudo-second-order kinetic model, respectively. Lime was regenerated from the used calcium lignin with high-temperature calcination, the conversion rate of calcium ions can reach 83.56%. Overall, the calcium lignin prepared by the one-step method exhibited great potential for effectively removing COD from middle-stage wastewater.

Efficient depolymerization of lignin through microwave-assisted Ru/C catalyst cooperated with metal chloride in methanol/formic acid media

Lignin, an abundant aromatic biopolymer, has the potential to produce various biofuels and chemicals through biorefinery activities and is expected to benefit the future circular economy. Microwave-assisted efficient degradation of lignin in methanol/formic acid over Ru/C catalyst cooperated with metal chloride was investigated, concerning the effect of type and dosage of metal chloride, dosage of Ru/C, reaction temperature, and reaction time on depolymerized product yield and distribution. Results showed that 91.1 wt% yield of bio-oil including 13.4 wt% monomers was obtained under the optimum condition. Yields of guaiacol-type compounds and 2,3-dihydrobenzofuran were promoted in the presence of ZnCl₂. Formic acid played two roles: (1) acid-catalyzed cleavage of linkages; (2) acted as an in situ hydrogen donor for hydrodeoxygenation in the presence of Ru/C. A possible mechanism for lignin degradation was proposed. This work will provide a beneficial approach for efficient depolymerization of lignin and controllable product distribution.

Techno-economic optimization of a process superstructure for lignin valorization

Lignin, the most abundant aromatic biopolymer on Earth, is often considered a biorefinery by-product, despite its potential to be valorized into high-added-value chemicals and fuels. In this work, an integrated superstructure-based optimization model was set up and optimized using mixed-integer non-linear programming for the conversion of technical lignin to three main biobased products: aromatic monomers, phenol-formaldehyde resins, and aromatic aldehydes/acids. Several alternative conversion pathways were simultaneously compared to assess the profitability of lignins-based processes by predicting the performance of technologies with different TRL. Upon employing key technologies such as hydrothermal liquefaction, dissolution in solvent, or high-temperature electrolysis, the technical lignins could have a market value of 200 €/t when the market price for aromatic monomers, resins, and vanillin is at least 2.0, 0.8, and 15.0 €/kg, respectively. When lower product selling prices were considered, the aromatic monomers and the resins were not profitable as target products.

Recent Advancements and Challenges in Lignin Valorization: Green Routes towards Sustainable Bioproducts

The aromatic hetero-polymer lignin is industrially processed in the paper/pulp and lignocellulose biorefinery, acting as a major energy source. It has been proven to be a natural resource for useful bioproducts; however, its depolymerization and conversion into high-value-added chemicals is the major challenge due to the complicated structure and heterogeneity. Conversely, the various pre-treatments techniques and valorization strategies offers a potential solution for developing a biomass-based biorefinery. Thus, the current review focus on the new isolation techniques for lignin, various pre-treatment approaches and biocatalytic methods for the synthesis of sustainable value-added products. Meanwhile, the challenges and prospective for the green synthesis of various biomolecules via utilizing the complicated hetero-polymer lignin are also discussed.

Identifying ligninolytic bacteria for lignin valorization to bioplastics

Biological valorization of lignin to bioplastics is a promising route to improve biorefinery efficiency and address environmental challenges. A two-stage screening procedure had been designed to successfully identify four ligninolytic bacteria from soil samples. The isolated bacteria displayed substrate preference of guaiacyl- and hydroxyphenyl-based aromatics, but they effectively synthesized polyhydroxyalkanoates (PHAs). B. cepacia B1-2 and P. putida KT3-1 accumulated 27.3% and 20.9% PHA in cells and achieved a titer of 280.9 and 204.1 mg/L, respectively, from p-hydroxybenzoic acid. The isolated bacteria exhibited good ligninolytic performance indicated by the degradation of β-O-4 linkage and small molecules. B. cepacia B1-2 grew well on actual lignin substrate and yielded a PHA titer of 87.2 mg/L. With the design of fed-batch mode, B. cepacia B1-2 produced the highest PHA titer of 1420 mg/L from lignin-derived aromatics. Overall, isolated ligninolytic bacteria show good PHA accumulation capacity, which are the promising host strains for lignin valorization.

Technology Overview of Fast Pyrolysis of Lignin: Current State and Potential for Scale-Up

Lignin is an abundant natural polymer obtained from lignocellulosic biomass and rich in aromatic substructures. When efficiently depolymerized, it has great potential in the production of value-added chemicals. Fast pyrolysis is a promising depolymerization method, but current studies focus mainly on small quantities of lignin. In this Review, to determine the potential for upscaling, systems used in the most relevant unit operations of fast pyrolysis of lignin are evaluated. Fluidized-bed reactors have the most potential. It would be beneficial to combine them with the following: slug injectors for feeding, hot particle filters, cyclones, and fractional condensation for product separation and recovery. Moreover, upgrading lignin pyrolysis oil would allow the necessary quality parameters for particular applications to be reached.

Preparation, characterization and formation mechanism of size-controlled lignin nanoparticles

Lignin is a renewable raw material with excellent adsorption, biodegradability, and non-toxicity. As a new, green nanomaterial, lignin nanoparticles (LNPs) have been explored as high-value renewable materials for applications in many fields. Herein, we provide a simple, rapid approach for the fabrication of size-controlled LNPs using a titrimetric nanoprecipitation method. The prepared LNPs were formed through a layer-by-layer self-assembly approach from inside to outside based on π-π interactions and had spherical shapes with porous surfaces and particle sizes from 272.0 to 915.4 nm. The average particle size of LNPs varied with stirring speed and decreased as the volume of deionized water increased. Compared with those of the original lignin, the chemical structural characteristics of LNPs did not change significantly. The proposed scheme for the preparation of LNPs is simple, inexpensive, and possesses the properties of both lignin and nanomaterials. The sizes of LNPs were controlled. Therefore, this is a good scheme for high-value applications of lignin.

The Consistency of Yields and Chemical Composition of HTL Bio-Oils from Lignins Produced by Different Preprocessing Technologies

This work evaluates the effect of feedstock type and composition on the conversion of lignin to liquid by solvolysis with formic acid as hydrogen donor (LtL), by analyzing the yields and molecular composition of the liquid products and interpreting them in terms of both the type and the preprocessing of the lignocellulosic biomass using chemometric data analysis. Lignin samples of different types and purities from softwood, hardwood, and grasses (rice straw and corn stover) have been converted to bio-oil, and the molecular composition analyzed and quantified using GC-MS. LtL solvolysis was found to be a robust method for lignin conversion in terms of converting all samples into bio-oils rich in phenolic compounds regardless of the purity of the lignin sample. The bio-oil yields ranged from 24–94 wt.% relative to lignin input and could be modelled well as a function of the elemental composition of the feedstock. On a molecular basis, the softwood-derived bio-oil contained the most guaiacol-derivatives, and syringol was correlated to hardwood. However, the connection between compounds in the bio-oil and lignin origin was less pronounced than the effects of the methods for biomass fractionation, showing that the pretreatment of the biomass dominates both the yield and molecular composition of the bio-oil and must be addressed as a primary concern when utilization of lignin in a biorefinery is planned.

Response surface methodology (RSM) and artificial neural network (ANN) approach to optimize the photocatalytic conversion of rice straw hydrolysis residue (RSHR) into vanillin and 4-hydroxybenzaldehyde

Effective use of waste lignin is always a challenging task, technologies have been applied in the past to get value-added compounds from waste lignin. However, the existing technologies are not economical and efficient to produce the value-added chemicals. Alkali soluble lignin from rice straw hydrolysis residue (RSHR) is subjected to photocatalytic conversion into value-added compounds. Photocatalysis is one of the multifarious advanced oxidation processes (AOPs), carried out with TiO2 nanoparticles under a 125 W UV bulb. Gas chromatography mass spectroscopy (GCMS) confirmed the formation of vanillin and 4-hydroxybenzaldehyde. RSM and ANN techniques are adopted to optimize the process conditions for the maximization of the products. The response one (Y 1) vanillin (24.61 mg) and second response (Y 2) 4-hydroxybenzaldehyde (19.51 mg) is obtained at the optimal conditions as 7.0 h irradiation time, 2.763 g/L catalyst dose, 15 g/L lignin concentration, and 14.26 g/L NaOH dose for alkali treatment, suggested by face-centered central composite design (CCD). RSM and ANN models are statistically analyzed in terms of RMSE, R 2 and AAD. For RSM the R 2 0.9864 and 0.9787 while for ANN 0.9875 and 0.9847, closer to one warrant the good fitting of the models. Therefore, in terms of higher precision and predictive ability of both models the ANN model showed excellence for both responses as compared to the RSM model.

One-Step Lignin Refining Process: The Influence of the Solvent Nature on the Properties and Quality of Fractions

Heterogeneity of kraft lignin is one of the main limitations for the development of high-performance applications. Therefore, refining lignin using organic solvents is a promising strategy to obtain homogenous fractions with controlled quality in terms of structure and properties. In this work, one-step refining processes for hardwood kraft lignin using nine organic solvents of different chemical nature and polarity were carried out with the aim of investigating and understanding the effect of the type of organic solvent on the quality of resulting fractions. Structural features of both soluble and insoluble lignin fractions were assessed by GPC, Py-GC-MS, and FTIR linked to PCA analysis. Moreover, functional properties such as physical appearance, hygroscopicity, antioxidant capacity, and thermal properties were evaluated. The results evidenced the relationship between the nature and polarity of the solvents and the properties of the obtained soluble and insoluble fractions.

Kraft Lignin with Improved Homogeneity Recovered Directly from Black Liquor and Its Application in Flexible Polyurethane Foams

An effective method that can produce a large amount of Kraft lignin with improved homogeneity is strongly desired for Kraft lignin's high-value applications and scientific advancements. Herein, a one-pot acid-catalyzed liquefaction method was developed to recover Kraft lignin directly from black liquor. The recovery rate and properties of the recovered lignin were affected by the reaction time, reaction temperature, moisture content (MC), pH, and acid categories. The highest lignin recovery rate of 75% was achieved when the concentrated black liquor (MC = 25%) reacted with methanol at pH = 7 and 160 °C for 10 min using acetic acid as the catalyst. Most of the recovered lignin from this method showed an average molecular weight (Mw) value less than 2000 Da and a polydispersity (PDI) value less than 2.0. Such a PDI value was lower than that of current acid precipitated lignin (around 2.2-5.4). The recovered lignin was directly used to replace 20% of the petroleum-based polyol in the formula of a flexible polyurethane (PU) foam, and it was found that the molecular weight characteristics of the lignin affected the physical and mechanical properties of the flexible PU foams. The recovered lignin with the Mw value of 1600 Da and the PDI value of 1.8 was able to maintain the major physical and mechanical properties of the flexible PU foams. This study provided a promising way to recover lignin with improved homogeneity from black liquor with the potential to customize lignin properties to meet the requirements of downstream processes.

Technoeconomic evaluation of recent process improvements in production of sugar and high-value lignin co-products via two-stage Cu-catalyzed alkaline-oxidative pretreatment

BACKGROUND

A lignocellulose-to-biofuel biorefinery process that enables multiple product streams is recognized as a promising strategy to improve the economics of this biorefinery and to accelerate technology commercialization. We recently identified an innovative pretreatment technology that enables of the production of sugars at high yields while simultaneously generating a high-quality lignin stream that has been demonstrated as both a promising renewable polyol replacement for polyurethane applications and is highly susceptible to depolymerization into monomers. This technology comprises a two-stage pretreatment approach that includes an alkaline pre-extraction followed by a metal-catalyzed alkaline-oxidative pretreatment. Our recent work demonstrated that H₂O₂ and O₂ act synergistically as co-oxidants during the alkaline-oxidative pretreatment and could significantly reduce the pretreatment chemical input while maintaining high sugar yields (~ 95% glucose and ~ 100% xylose of initial sugar composition), high lignin yields (~ 75% of initial lignin), and improvements in lignin usage.

RESULTS

This study considers the economic impact of these advances and provides strategies that could lead to additional economic improvements for future commercialization. The results of the technoeconomic analysis (TEA) demonstrated that adding O₂ as a co-oxidant at 50 psig for the alkaline-oxidative pretreatment and reducing the raw material input reduced the minimum fuel selling price from $1.08/L to $0.85/L, assuming recoverable lignin is used as a polyol replacement. If additional lignin can be recovered and sold as more valuable monomers, the minimum fuel selling price (MFSP) can be further reduced to $0.73/L.

CONCLUSIONS

The present work demonstrated that high sugar and lignin yields combined with low raw material inputs and increasing the value of lignin could greatly increase the economic viability of a poplar-based biorefinery. Continued research on integrating sugar production with lignin valorization is thus warranted to confirm this economic potential as the technology matures.

Engineered biochar: A multifunctional material for energy and environment

Biochar is a stable carbon-rich product loaded with upgraded properties obtained by thermal cracking of biomasses in an oxygen-free atmosphere. The pristine biochar is further modified to produce engineered biochar via various physical, mechanical, and chemical methods. The hasty advancement in engineered biochar synthesis via different technologies and their application in the field of energy and environment is a topical issue that required an up-to-date review. Therefore, this review deals with comprehensive and recent mechanistic approaches of engineered biochar synthesis and its further application in the field of energy and the environment. Synthesis and activation of engineered biochar via various methods has been deliberated in brief. Furthermore, this review systematically covered the impacts of engineered biochar amendment in the composting process, anaerobic digestion (AD), soil microbial community encouragement, and their enzymatic activities. Finally, this review provided a glimpse of the knowledge gaps and challenges associated with application of engineered biochar in various fields, which needs urgent attention in future research.

The application of green solvent in a biorefinery using lignocellulosic biomass as a feedstock

The high dependence on crude oil for energy utilization leads to a necessity of finding alternative sustainable resources. Solvents are often employed in valorizing the biomass into bioproducts and other value-added chemicals during treatment stages. Unfortunately, despite the effectiveness of conventional solvents, hindrances such as expensive solvents, unfavourable environmental ramifications, and complicated downstream separation systems often occur. Therefore, the scientific community has been actively investigating more cost-effective, environmentally friendly alternatives and possess the excellent dissolving capability for biomass processing. Generally, 'green' solvents are attractive due to their low toxicity, economic value, and biodegradability. Nonetheless, green solvents are not without disadvantages due to their complicated product recovery, recyclability, and high operational cost. This review summarizes and evaluates the recent contributions, including potential advantages, challenges, and drawbacks of green solvents, namely ionic liquids, deep eutectic solvents, water, biomass-derived solvents and carbon dioxide in transforming the lignocellulosic biomass into high-value products. Moreover, research opportunities for future developments and potential upscale implementation of green solvents are also critically discussed.

Microwave-Assisted Lignin Wet Peroxide Oxidation to C4 Dicarboxylic Acids

Innovative methodologies, such as microwave-assisted reaction, can help to valorize lignin with higher productivity and better energy efficiency. In this work, microwave heating was tested in the wet peroxide oxidation of three lignins (Indulin AT, Lignol, and Eucalyptus globulus lignins) as a novel methodology to obtain C₄ dicarboxylic acids. The effect of temperature, time, and catalyst type (TS-1 or Fe-TS1) was evaluated in the production of these acids. The TS-1 catalyst improved succinic acid yield, achieving up to 9.4 wt % for Lignol lignin. Moreover, the microwave heating specifically enhanced Lignol conversion to malic acid (34 wt %), even without catalyst, showing to be an attractive path for the future valorization of organosolv lignins. Overall, compared to conventional heating, microwave heating originated a rapid lignin conversion. Nevertheless, for prolonged times, conventional heating led to better results for some target products, e.g., malic and succinic acids.

Biochemical biorefinery: A low-cost and non-waste concept for promoting sustainable circular bioeconomy

The transition from a fossil-based linear economy to a circular bioeconomy is no longer an option but rather imperative, given worldwide concerns about the depletion of fossil resources and the demand for innovative products that are ecocompatible. As a critical component of sustainable development, this discourse has attracted wide attention at the regional and international levels. Biorefinery is an indispensable technology to implement the blueprint of the circular bioeconomy. As a low-cost, non-waste innovative concept, the biorefinery concept will spur a myriad of new economic opportunities across a wide range of sectors. Consequently, scaling up biorefinery processes is of the essence. Despite several decades of research and development channeled into upscaling biorefinery processes, the commercialization of biorefinery technology appears unrealizable. In this review, challenges limiting the commercialization of biorefinery technologies are discussed, with a particular focus on biofuels, biochemicals, and biomaterials. To counteract these challenges, various process intensification strategies such as consolidated bioprocessing, integrated biorefinery configurations, the use of highly efficient bioreactors, simultaneous saccharification and fermentation, have been explored. This study also includes an overview of biomass pretreatment-generated inhibitory compounds as platform chemicals to produce other essential biocommodities. There is a detailed examination of the technological, economic, and environmental considerations of a sustainable biorefinery. Finally, the prospects for establishing a viable circular bioeconomy in Nigeria are briefly discussed.

A recent advancement on preparation, characterization and application of nanolignin

Each year, 50 to 70 million tonnes of lignin are produced worldwide as by-products from pulp industries and biorefineries through numerous processes. Nevertheless, about 98% of lignin is directly burnt to produce steam to generate energy for the pulp mills and only a handful of isolated lignin is used as a raw material for the chemical conversion and for the preparation of various substances as well as modification of lignin into nanomaterials. Thus, thanks to its complex structure, the conversion of lignin to nanolignin, attracting growing attention and generating considerable interest in the scientific community. The objective of this review is to provide a complete understanding and knowledge of the synthesis methods and functionalization of various lignin nanoparticles (LNP). The characterization of LNP such as structural, thermal, molecular weight properties together with macromolecule and quantification assessments are also reviewed. In particular, emerging applications in different areas such as UV barriers, antimicrobials, drug administration, agriculture, anticorrosives, the environment, wood protection, enzymatic immobilization and others were highlighted. In addition, future perspectives and challenges related to the development of LNP are discussed.