Production of monomeric phenols by thermochemical conversion of biomass: a review

Selective Cleavage of Cβ-O-4 Bond for Lignin Depolymerization via Paired-Electrolysis in an Undivided Cell

The cleavage of C-O bonds is one of the most promising strategies for lignin-to-chemicals conversion, which has attracted considerable attention in recent years. However, current catalytic system capable of selectively breaking C-O bonds in lignin often requires a precious metal catalyst and/or harsh conditions such as high-pressure H2 and elevated temperatures. Herein, we report a novel protocol of paired electrolysis to effectively cleave the Cβ-O-4 bond of lignin model compounds and real lignin at room temperature and ambient pressure. For the first time, "cathodic hydrogenolysis of Cβ-O-4 linkage" and "anodic C-H/N-H cross-coupling reaction" are paired in an undivided cell, thus the cleavage of C-O bonds and the synthesis of valuable triarylamine derivatives could be simultaneously achieved in an energy-effective manner. This protocol features mild reaction conditions, high atom economy, remarkable yield with excellent chemoselectivity, and feasibility for large-scale synthesis. Mechanistic studies indicate that indirect H* (chemical absorbed hydrogen) reduction instead of direct electron transfer might be the pathway for the cathodic hydrogenolysis of Cβ-O-4 linkage.

Balancing the Components of Biomass and the Reactivity of Pyrolysis Gas: Biomass-Assisted Recycling of Spent LiCoO2 Batteries

Waste biomass is one of the promising feedstocks to supply syngas that can be used as fuels, chemicals, reductants, etc. However, the relationship between the component of biomass and the constituent of pyrolysis gas remains unclear. Here, we study the pyrolysis behaviors of various biomasses and reveal the relationship between the biomass components and gas compositions. Further, different pyrolysis gases are applied for the reduction of spent lithium cobalt oxide (LiCoO2) below 500 °C. The pyrolysis gas with a higher concentration of CO has a higher reductivity to convert LiCoO2 to CoO and Li2CO3 with a conversion rate close to 100% in 1 h at 500 °C. The biomass rich in cellulose and with a lower content of lignin tends to produce pyrolysis gas with a high concentration of CO, which comes from the deliberate breakdown of carboxyl, carbonyl, ether, and ester linkages. Moreover, LiCoO2 exerts catalytic functions over the deoxygenation and enhancement of oxygenates and single-ring aromatics. Overall, this paper offers a tailored approach to regulating biomass pyrolysis gases, enabling highly efficient battery recycling and syngas production.

Lignin-based composites with enhanced mechanical properties by acetone fractionation and epoxidation modification

Epoxy resin is widely used in various fields of the national economy due to its excellent chemical and mechanical properties. Lignin is mainly derived from lignocelluloses as one of the most abundant renewable bioresources. Due to the diversity of lignin sources and the complexity as well as heterogeneity of its structure, the value of lignin has not been fully realized. Herein, we report the utilization of industrial alkali lignin for the preparation of low-carbon and environmentally friendly bio-based epoxy thermosetting materials. Specifically, epoxidized lignin with substituted petroleum-based chemical bisphenol A diglycidyl ether (BADGE) in various proportions was cross-linked to fabricate thermosetting epoxies. The cured thermosetting resin revealed enhanced tensile strength (4.6 MPa) and elongation (315.5%) in comparison with the common BADGE polymers. Overall, this work provides a practicable approach for lignin valorization toward tailored sustainable bioplastics in the context of a circular bioeconomy.

Semi-VOCs of Wood Vinegar Display Strong Antifungal Activities against Oomycete Species Globisporangium ultimum and Pythium aphanidermatum

Plant disease outbreaks are increasingly exacerbated by climate change and the conditions of stress combinations. They are negatively affecting crop yield and driving threats to food security in many areas of the world. Although synthetic pesticides offer relative success in the control of pests and plant diseases, they are often overused, and this method faces numerous drawbacks, including environmental toxicity, soil degradation, and adverse effects on human health. Therefore, alternatives are being developed and examined, including the biocontrol of pests and pathogens and biomass pyrolysis leading to wood vinegar that has shown great promise in agriculture and organic farming. However, while wood vinegar use is expanding and allows the control of numerous pests and bacterial and fungal diseases, its application to control oomycete diseases is limited. This study aimed to test wood vinegar for the control of oomycete plant pathogens from which six wood vinegars of pistachio, pomegranate, almond, pine, cypress, and walnut were produced. The inhibitory effects of volatile metabolites (semi-VOCs) of different wood vinegars concentrations (100%, 50%, 25%, 12.5%, and 6.25%) were examined against the hyphal growth of Globisporangium ultimum and Pythium aphanidermatum isolates. An in vitro analysis unambiguously demonstrated that for Globisporangium ultimum, the wood vinegar semi-VOCs of almond, pistachio (C 100% and 50%), and walnut (C 100%) totally inhibited mycelial growth. On the other hand, Pythium aphanidermatum, pistachio (C 100%, 50%, and 25%), and cypress (C 100%) expressed their abilities to completely inhibit the mycelial growth. Other treatments, including relevant concentrations of pine and pomegranate significantly inhibited the growth of mycelia of both species compared to the control (p ≤ 0.05). Therefore, wood vinegar could be considered a natural and organic product to use in agriculture to cope not only against pests, bacterial and fungal pests but also against emerging oomycete plant diseases.

The Fate of Protonated Guaiacol and Its Derivatives in the Gas Phase

Guaiacol (2-methoxyphenol) and its derivatives are a class of semivolatile polar organic molecules possessing low molecular weights. Owing to their volatility, guaiacol and its derivatives can interact with atmospheric water and form protonated methoxyphenols through proton transfer. The aim of the present work is to study the dissociation of these protonated ions and hence, potentially, their atmospheric fate. Tandem mass spectrometry was employed to analyze the unimolecular dissociation of the protonated forms of guaiacol (2-methoxyphenol, 1), creosol (2-methoxy-4-methylphenol, 2), 4-ethylguaiacol (4-ethyl-2-methoxyphenol, 3), 4-vinylguaiacol (2-methoxy-4-vinylphenol, 4), eugenol (2-methoxy-4-prop-2-enylphenol, 5), and vanillin (4-hydroxy-3-methoxybenzaldehyde, 6). Density functional theory at the B3LYP/6-31G(d) (1-5) and B3LYP/6-311+G(d,p) (6) levels of theory were applied to determine the observed minimum energy reaction pathways, and reliable energetics were acquired using CBS-QB3 single-point energy calculations. All the protonated ions, with the exception of 6, exhibit the loss of CH₃OH via a series of hydrogen transfers, followed by ring contraction to lose CO. This common dissociation pathway leads to the formation of a cyclopentadienyl ion as the main dissociation product. Conversely, 6 first exhibits the loss of CO, followed by sequential losses of CH₃OH and CO to generate a cyclopentadienyl ion. Additionally, minor fragmentation channels are also observed for the different protonated ions: CH₂ loss in 1; CH₄ and H₂O losses in 3; CH₃ loss in 4, 5, and 6; C₂H₄ and CH₂CHCH₂ losses in 5; H loss in 6. Altogether, the protonated ions primarily lose CH₃OH and CO as neutral molecules and generate a cyclopentadienyl ion as a dissociation product.

Diphenoquinhydrones and Related Hydrogen-Bonded Charge-Transfer Complexes

Benzoquinone and hydroquinone cocrystallize to form quinhydrone, a 1:1 complex with a characteristic structure in which the components are positioned by hydrogen bonds and charge-transfer interactions. We have found that analogous diphenoquinhydrones can be made by combining 4,4'-diphenoquinones with the corresponding 4,4'-dihydroxybiphenyls. In addition, mixed diphenoquinhydrones can be assembled from components with different substituents, and mismatched quinhydrones can be made from benzoquinones and dihydroxybiphenyls. In all cases, the components of the resulting structures are linked in alternation by O-H···O hydrogen bonds to form essentially planar chains, which stack to produce layers in which π-donors and π-acceptors are aligned by charge-transfer interactions. Geometric parameters, computational studies, and spectroscopic properties of diphenoquinhydrones show that the key intermolecular interactions are stronger than those in simple quinhydrone analogues. These findings demonstrate that the principles of modular construction underlying the formation of classical quinhydrones can be generalized to produce a broad range of hydrogen-bonded charge-transfer materials in which the components are positioned by design.

Diphenoquinones Redux

Benzoquinones can undergo reversible reductions and are attractive candidates for use as active materials in green carbon-based batteries. Related compounds of potential utility include 4,4'-diphenoquinones, which have extended quinonoid structures with two carbonyl groups in different rings. Diphenoquinones are a poorly explored class of compounds, but a wide variety can be synthesized, isolated, crystallized, and fully characterized. Experimental and computational approaches have established that typical 4,4'-diphenoquinones have nearly planar cores in which two cyclohexadienone rings are joined by an unusually long interannular C═C bond. Derivatives unsubstituted at the 3,3',5,5'-positions react readily by hydration, dimerization, and other processes. Association of diphenoquinones in the solid state normally produces chains or sheets held together by multiple C-H···O interactions, giving structures that differ markedly from those of the corresponding 4,4'-dihydroxybiphenyls. Electrochemical studies in solution and in the solid state show that diphenoquinones are reduced rapidly and reversibly at potentials higher than those of analogous benzoquinones. Together, these results help bring diphenoquinones into the mainstream of modern chemistry and provide a foundation for developing redox-active derivatives for use in carbon-based electrochemical devices.

Lignocellulosic Materials for the Production of Biofuels, Biochemicals and Biomaterials and Applications of Lignocellulose-Based Polyurethanes: A Review

The present review is devoted to the description of the state-of-the-art techniques and procedures concerning treatments and modifications of lignocellulosic materials in order to use them as precursors for biomaterials, biochemicals and biofuels, with particular focus on lignin and lignin-based products. Four different main pretreatment types are outlined, i.e., thermal, mechanical, chemical and biological, with special emphasis on the biological action of fungi and bacteria. Therefore, by selecting a determined type of fungi or bacteria, some of the fractions may remain unaltered, while others may be decomposed. In this sense, the possibilities to obtain different final products are massive, depending on the type of microorganism and the biomass selected. Biofuels, biochemicals and biomaterials derived from lignocellulose are extensively described, covering those obtained from the lignocellulose as a whole, but also from the main biopolymers that comprise its structure, i.e., cellulose, hemicellulose and lignin. In addition, special attention has been paid to the formulation of bio-polyurethanes from lignocellulosic materials, focusing more specifically on their applications in the lubricant, adhesive and cushioning material fields. High-performance alternatives to petroleum-derived products have been reported, such as adhesives that substantially exceed the adhesion performance of those commercially available in different surfaces, lubricating greases with tribological behaviour superior to those in lithium and calcium soap and elastomers with excellent static and dynamic performance.

A critical review on metal-based catalysts used in the pyrolysis of lignocellulosic biomass materials

This review discusses the technical aspects of improving the efficiency of the pyrolysis of lignocellulosic materials to increase the yield of the main products, which are bio-oil, biochar, and syngas. The latest aspects of catalyst development in the biomass pyrolysis process are presented focusing on the various catalyst structures, the physical and chemical performance of the catalysts, and the mode of the catalytic reaction. In bio-oil upgrading, atmospheric catalytic cracking is shown to be more economical than catalytic hydrotreating. Catalysts help in the upgrading process by facilitating several reaction pathways such as polymerization, aromatization, and alkyl condensation. However, the grade of bio-oil must be similar to that of diesel fuel. Hence, the properties of the pyrolysis liquid such as viscosity, kinematic viscosity, density, and boiling point are important and have been highlighted. Switching between types of catalysts has a significant influence on the final product yields and exhibits different levels of durability. Various catalysts have been shown to enhance gas yield at the expense of the yields of bio-oil and biochar that shift the overall purpose of pyrolysis. Therefore, the catalytic activity as a function of temperature, pressure, and catalyst biomass ratio is discussed in detail. These operational parameters are crucial because they determine the overall yield as well as the ratio of the oil, char, and gas products. Although significant progress has been made in catalytic pyrolysis, the economic feasibility of the process and the catalyst cost remain the major obstacles. This review concludes that the catalytic process would be feasible when the fuel selling price is reduced to less than US $ 4 per gallon of gasoline-equivalent, and when the selectivity of catalysts is further enhanced.

Improving UV Curing in Organosolv Lignin-Containing Photopolymers for Stereolithography by Reduction and Acylation

Despite recent successes in incorporating lignin into photoactive resins, lignin photo-properties can be detrimental to its application in UV-curable photopolymers, especially in specialized engineered resins for use in stereolithography printing. We report on chemical modification techniques employed to reduce UV absorption by lignin and the resulting mechanical, thermal, and cure properties of these modified lignin materials. Lignin was modified using reduction and acylation reactions and incorporated into a 3D printable resin formulation. UV–Vis absorption at the 3D printing range of 405 nm was reduced in all modified lignins compared to the unmodified sample by 25% to ≥ 60%. Resins made with the modified lignins showed an increase in stiffness and strength with lower thermal stability. Studying these techniques is an important step in developing lignin for use in UV-curing applications and further the effort to valorize lignin towards commercial use.

Sugarcane bagasse - A source of cellulosic fiber for diverse applications

Sugarcane bagasse is a fibrous material containing cellulose as its main component. It is produced in large quantities across the world. It is a kind of waste material that comes from the sugar industry. It is most commonly used in paper industries, but researchers have suggested that different mechanical and chemical treatments can help to extract cellulosic fibers, pure cellulose, cellulose nanofibers, and cellulose nanocrystals. These extracted materials have diverse applications in regenerated cellulosic fiber and composite material production. This paper will discuss the extraction procedures and typical applications in composite industries of these extracted materials. And an assessment will also be done on the production process and the properties of the end products to find out some common factors which can control the properties of these extracted material reinforced composites to some extent.

Choosing the Right Lignin to Fully Replace Bisphenol A in Epoxy Resin Formulation

Thirteen unmodified lignin samples from different biomass sources and isolation processes were characterized and used to entirely replace bisphenol A (BPA) in the formulation of solubilized epoxy resins using a developed novel method. The objective was to measure the reactivity of different lignins toward bio-based epichlorohydrin (ECH). The epoxy contents of various bio-based epoxidized lignins were measured by titration and 1 H NMR spectroscopy methods. A partial least square regression (PLS-R) model with 92 % fitting accuracy and 90 % prediction ability was developed to find correlations between lignin properties and their epoxy contents. The results showed that lignins with higher phenolic hydroxy content and lower molecular weights were more suitable for replacing 100 % of toxic BPA in the formulation of epoxy resins. Additionally, two epoxidized lignin samples (highest epoxy contents) cured by using a bio-based hardener (Cardolite GX-3090) were found to show comparable thermomechanical performances and thermal stabilities to a petroleum-based (DGEBA) epoxy system.

Torrefaction at 200 °C of Pubescens Pretreated with AlCl3 Aqueous Solution at Room Temperature

Metal salt soaking-torrefaction conversion technology was investigated. It was found that AlCl₃ pretreatment of pubescens favored observably the yield of liquid and small-molecular products in torrefaction via changing the composition and structure of the raw material. The maximum conversion of pretreated samples, washed (PSW) and Y _liquid were 15.5 and 10.8 wt % (with 0.26 wt % monosaccharides, 0.26 wt % carboxylic acids, 0.38 wt % furan compounds, and 1.28 wt % phenols), where 20.4 wt % hemicellulose, 22.9 wt % cellulose, and 5.7 wt % lignin were converted, respectively. However, for pretreated samples (PS), the maximum conversion and Y _liquid reached 44.2 and 32.1 wt %, respectively, along with 96.0 wt % hemicellulose and 31.8 wt % cellulose converted, yielding 2.39 wt % monosaccharides, 5.14 wt % carboxylic acids, 2.60 wt % furan compounds and 10.52 wt % phenols, indicating obvious catalytic effects of residual AlCl₃ on the decomposition of the three major components in torrefaction. Two-dimensional HSQC and electrospray ionization mass spectrometry (ESI-MS) characterizations further confirmed the dominant formation of oligomers derived from holocellulose, lignin, and cross-linkage involving the lignin-carbohydrate complex, indicating that the catalytic thermal cleavage of β-O-4, C-O-C, β-β, 5-5, 4-O-5, C_α-C_β, and α-O-4 linkages by aluminum species in the samples benefited the yield of liquid as well as monophenols.

The influence of torrefaction on pyrolysed biomass: The relationship of bio-oil composition with the torrefaction severity

In this study, three types of biomass were torrefied at different times (0.5, 1, 1.5 h) and temperature (200, 240, 280, 320 °C), which were further pyrolyzed at 550 °C after torrefaction. CEI (carbon element index), which was established based on the carbon content of the torrefied biomass, was chosen as an indicator for reflecting torrefaction severity. The results showed that there was a curvilinear relationship between CEI and the physicochemical characteristics, energy recovery of torrefied biomass, which obtained an average goodness of fit was higher than 0.93. Moreover, the goodness of fit between CEI and pyrolysis carbon and bio-oil yield was higher than 0.95 and 0.91, respectively. Especially, the bio-oil composition and CEI were fitted by a quadratic function (y = a + bx + cx²). Based on the function, the yield of phenols could be predicted based on the CEI value, which would benefit for the preparation of higher quality bio-oil directionally.

Molecular Oxygen Lignin Depolymerization: An Insight into the Stability of Phenolic Monomers

During oxidative depolymerization of lignin in aqueous alkaline medium using molecular oxygen as oxidant, the highly functionalized primary phenolic monomers are not stable products, owing to various not fully identified secondary reaction mechanisms. However, better understanding of the mechanisms responsible for the instability of the main part of the products of interest derived from lignin is of much interest. Evaluation of their individual reactivities under oxidative conditions should significantly help to find a better way to valorize the lignin polymer and to maximize the yields of target value-added products. Consequently, the main objective of this study is to assess the individual stabilities of some selected lignin-based phenolic compounds, such as vanillin, vanillic acid, and acetovanillone, together with some other pure chemical compounds such as phenol and anisole to give an insight into the mechanisms responsible for the simultaneous formation and repolymerization of those products and the influence of the oxidation conditions. Various complementary strategies of stabilization are proposed, discussed, and applied for the oxidative depolymerization reactions of a technical lignin extracted from pinewood with a high content of β-O-4 interconnecting bonds to try to obtain enhanced yields of value-added products.

Lignin Depolymerization: A Comparison of Methods to Analyze Monomers and Oligomers

Catalytic liquefaction of lignin is an attractive process to produce fuels and chemicals, but it forms a wide range of liquid products from monomers to oligomers. Oligomers represent an important fraction of the products and their analysis is complex. Therefore, rapid characterization methods are needed to screen liquefaction conditions based on the distribution in monomers and oligomers. For this purpose, UV spectroscopy is proposed as a fast and simple method to assess the composition of lignin-derived liquids. UV absorption and fluorescence were studied on various model compounds and liquefaction products. Liquefaction of Soda lignin was conducted in an autoclave, in ethanol and with Pt/C catalyst (H₂ , 250 °C, 110 bar). Liquids were sampled at isothermal conditions every 30 min for 4 h. UV fluorescence spectroscopy is related to GC-MS, gel-permeation chromatography (GPC), MALDI-TOF MS, and NMR characterizations. A depolymerization index is proposed from UV spectroscopy to rapidly assess the relative distribution of monomers and oligomers.

VS2 and its doped composition: Catalytic depolymerization of alkali lignin for increased bio-oil production

VS₂ spheres and VS₂ sheets with doped compositions (Mo, Ag and graphite) were successfully prepared by one-step hydrothermal method and characterized by different techniques including X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and N₂ adsorption isotherms. Catalysts were applied for the depolymerization of alkali lignin. VS₂ spheres exhibited lower yield of degraded lignin and bio-oil than those with VS₂ sheets and VS₂ flowers heated to 250 °C and held for 1.5 h with 2.0 MPa H₂. The catalytic depolymerization performance was markedly affected by the dopant in the VS₂ sheets, with the highest degraded lignin yield of 81.22%, achieved over 5 wt% Ag-VS₂ at 290 °C under 2.0 MPa H₂ for 1.5 h, yielding 61.23% bio-oil. The VS₂-based catalysts show excellent selectivity in the interruption of the lignin structure and target production of bio-oil. The bio-oil showed that the relevant contents of a phenolic-type compound changes significantly according to the dopant in the VS₂ catalyst.

Quantum chemical calculations on the mechanism and kinetics of ozone-initiated removal of p-coumaryl alcohol in the atmosphere

p-Coumaryl alcohol (p-CMA), as the simplest lignin precursor, was determined in the process of lignin polymer degradation and wood smoke. However, its transformation and migration in the atmosphere have not been well clarified. In this work, the gas-phase reaction mechanisms and kinetic parameters of ozone-initiated removal of p-CMA were performed by using quantum chemical calculations. Seven primary addition reaction pathways were summarized. A more comprehensive and detailed reaction routes of the favorable Criegee intermediate (IM9) were presented, including the reactions with small molecules, as well as its own isomerization and decomposition reactions. p-Hydroxybenzaldehyde (P1) is the most dominant product in the further reactions of IM9 and the subsequent ozonolysis mechanisms of P1 also were elucidated. All thermodynamic calculations were investigated on the density functional theory (DFT) method at the M06-2X/6-311 + G (3df, 2p)//M06-2X/6-311 + G (d,p) level. The overall and individual rate constants have estimated by using the KiSThelP under typical atmospheric temperature (198-338 K) and pressure. The total rate constant is 3.37 × 10^-16 cm³ molecule^-1 s^-1 at 298 K and 1 atm. In addition, the atmospheric lifetime of p-CMA by ozone-determined is 1.18 h under the average ozone concentration of 7 × 10¹¹ molecules cm^-3. The short lifetime indicates that the degradation processes of p-CMA determined by O₃ cannot be ignored, especially in areas where the tip concentration of O₃ molecules is high. The present study provides a synthetical investigation on ozonolysis of p-CMA for the first time and enriches our understanding of atmospheric oxidation processes of other lignin compounds.

OH-Initiated Reactions of para-Coumaryl Alcohol Relevant to the Lignin Pyrolysis. Part III. Kinetics of H-Abstraction by H, OH, and CH3 Radicals

Lignin is the most complex component of biomass, and development of a detailed chemical kinetic model for biomass pyrolysis mainly relies on the understanding of the lignin decomposition kinetics. para-Coumaryl alcohol (p-CMA, HOPh-CH═CH-CH₂OH), the focus of our analysis, is the simplest of the lignin monomers (monolignols) containing a typical side-chain double bond and both alkyl- and phenolic-type OH-groups. In parts I and II of our work (Asatryan, R. J. Phys. Chem. A 2019, 123, 2570-2585; Hudzik, J. M. J. Phys. Chem. A 2020, current issue), we created a detailed potential energy surface (PES) and performed a kinetic analysis of chemically activated, unimolecular, and bimolecular reactions pathways for p-CMA + OH. Reaction pathways analyzed include dissociation, intramolecular abstraction, group transfer, and elimination processes. The α- and β-carbon addition reactions generate 1,3- (RA1) and 1,2-diol (RB1) adduct radicals, respectively. Well depths are approximately 29 and 41 kcal/mol below the p-CMA + OH entrance level. Kinetic analysis aides in determining the major pathways for our conventional and fractional pyrolysis experiments. The current paper focuses on the H-abstraction reactions via H, OH, and CH₃ light ("pool") radicals from p-CMA. The thermochemical properties of all stable, radical, and transition-state species were determined using the ωB97XD density functional theory (DFT) and higher-level CBS-QB3 composite methods. Barrier heights from the prereaction complexes, for OH-radical abstractions, to the transition states for the propanoid side chain are compared to the model H-abstraction reactions of allyl alcohol (AA) with OH and p-CMA with H and CH₃ radicals. The lowest-energy, most stable, p-CMA radical formed is at the C9 allylic position (p-CMA-C9j) with exothermicity of 26.63, 41.32, and 27.34 kcal/mol for H, OH, and CH₃, respectively. For OH-radical abstraction at this position, our findings are consistent with corresponding data on AA + OH at 37.44 kcal/mol and similar to that of RB1. A similar stable radical with an exothermicity of 34.95 kcal/mol occurs for the phenol hydroxyl group, generating the p-CMA-O4j radical. H-abstraction pathways are considered in relation to other major pathways previously considered for p-CMA + OH reactions including H-atom shifts, dehydration, and β-scission reactions. Derived rate coefficients for substituted phenols can be utilized in detailed kinetic models for lignin/biomass pyrolysis.

Effect of cobalt on titania, ceria and zirconia oxide supported catalysts on the oxidative depolymerization of prot and alkali lignin

The production of phenolics by oxidative depolymerization of prot lignin and alkali lignin were studied in the presence of cobalt impregnated TiO₂, CeO₂ and ZrO₂ catalysts at 140 °C for 1 h. Maximum bio-oil yield of 78.0 and 60.2 wt% were observed with Co/CeO₂ catalyst for prot lignin and alkali lignin, respectively. The characterizations of the bio-oils were carried out using GC-MS, FTIR, and ¹H NMR. The GC-MS compounds have been classified into four categories (G, H, S-type and others). The depolymerization of prot lignin showed a mixture of G, H and S type phenolic monomers. Interestingly, higher selectivity of acetosyringone (47.1%) was obtained in the presence of Co/TiO₂ catalyst with prot lignin. The depolymerization of alkali lignin exhibited only G-type phenolic monomers production, and was effectively produced 67.4% (G-type monomer) in the presence of Co/ZrO₂ catalyst.

A Review of Non-Soil Biochar Applications

Biochar is the solid residue that is recovered after the thermal cracking of biomasses in an oxygen-free atmosphere. Biochar has been used for many years as a soil amendment and in general soil applications. Nonetheless, biochar is far more than a mere soil amendment. In this review, we report all the non-soil applications of biochar including environmental remediation, energy storage, composites, and catalyst production. We provide a general overview of the recent uses of biochar in material science, thus presenting this cheap and waste-derived material as a high value-added and carbonaceous source.

Synthesis of Chitosan-Ignosulfonate Composite as an Adsorbent for Dyes and Metal Ions Removal from Wastewater

Sodium lignosulfonate is a polymer with extensive sources and abundant functional groups. Therefore, it has potential value for research and wide utilization. In this study, the adsorption material was prepared by blending sodium lignosulfonate and chitosan, which could adsorb anionic and cationic dyes and metal ions. The composite was characterized by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and thermogravimetry (TG). The results showed that the composite was cross-linked mainly by the strong electrostatic interaction between the protonated amino group in chitosan and the sulfonate group in sodium lignosulfonate. Moreover, the effects of initial concentration, adsorption time, initial pH, and mass ratio of chitosan to sodium lignosulfonate on the adsorption performance of the composite were investigated. Meanwhile, the adsorption processes were agreed well with the pseudo-second-order kinetic model and Langmuir isotherm model. The adsorption mechanism was that the electrostatic interaction between the protonated amino and hydroxyl groups of the composite with anionic (SO3 -) and HCrO4 - groups of Congo red and Cr(VI), respectively. In addition, the electrostatic interaction between SO3 - of the composite and positively charged group of Rhodamine B played an important role in the adsorption of Rhodamine B.

Catalytic pyrolysis of soda lignin over zeolites using pyrolysis gas chromatography-mass spectrometry

Catalytic fast pyrolysis of soda lignin was examined at different temperatures (500,600,700,800 and 900 °C) in the presence of three zeolites with different Si/Al ratio using the Py-GC/MS in order to investigate best catalytic system. The three zeolites are y-zeolite (8-9), mordenite (15-17), ZSM-5 (30-40), which have static pore sizes 0.74, 0.65, and 0.59 nm respectively. The shape and acidity of zeolites, as well as pyrolysis temperature, have a significant effect on product distribution in catalytic fast pyrolysis. Y-zeolite was the most effective catalytic system among all catalysts for deomethoxylation and dehydroxylation of small oxygenates as well as bulky oxygenates to produce aromatics. However, mordenite and ZSM-5 could not convert the large oxygenates due to size exclusion and pore blockage. Highest yield of aromatics with significant amount of aromatic dimers was obtained over y-zeolite and then yield of aromatics followed in order by mordenite and ZSM-5 at 800 °C.

Catalytic fast pyrolysis of maize straw with a core-shell ZSM-5@SBA-15 catalyst for producing phenols and hydrocarbons

Zeolites have been widely used as catalysts in the catalytic pyrolysis of biomass to produce biofuels and/or bio-based chemicals, which could lead to the replacement of fossil sources by renewable ones. However, conventional zeolites often suffer from diffusion resistance for large intermediate oxygenates. To solve this problem, a micro/mesoporous core-shell composite zeolite ZSM-5@SBA-15 was prepared and employed as a catalyst in the catalytic pyrolysis of maize straw. ZSM-5@SBA-15 was synthesized by crystallizing mesoporous silica on the external surface of ZSM-5 using the triblock copolymer Plunoric P123 as the template. The core-shell and hierarchical structures were verified using PXRD, TEM, and N₂ sorption experiments. In the catalytic pyrolysis of maize straw, ZSM-5@SBA-15 significantly enhanced the yield of valuable phenols and hydrocarbons in bio-oil, compared to ZSM-5 and SBA-15. The results demonstrated the potential application of micro@mesoporous core-shell composite zeolites in the catalytic pyrolysis of biomass.

New sight on the lignin torrefaction pretreatment: Relevance between the evolution of chemical structure and the properties of torrefied gaseous, liquid, and solid products

In order to reveal the deoxygenation mechanism of lignin torrefaction, the relevance between evolution of chemical structure of torrefied lignin and the properties of torrefied gaseous, liquid, and solid products was established in this study. Results showed that the contents of oxygen element, βO4 linkages, oxygen-containing functional groups (aliphatic OH, aliphatic COOH, aromatic OCH₃) in lignin decreased with the increase of the torrefaction temperature from 210 to 300 °C. The oxygen removal efficiency of lignin torrefaction reached the maximum value of 25.53% at 300 °C. The removed oxygen in the torrefied lignin was transferred into the torrefied gaseous product (e.g. CO₂, H₂O, and CO) and torrefied liquid product (e.g. G-type and P-type phenols, acids). Among the torrefied gaseous products, CO₂ was the dominant oxygen carrier, followed by CO and H₂O. Among the torrefied liquid products, G-type phenols were the dominant oxygen carrier, followed by P-type phenols and acids.

Theoretical Elucidation of β-O-4 Bond Cleavage of Lignin Model Compound Promoted by Sulfonic Acid-Functionalized Ionic Liquid

While the depolymerization of lignin to chemicals catalyzed by ionic liquids has attracted significant attention, the relevant molecular mechanism, especially the cleavage of specific bonds related to efficient depolymerization, still needs to be deeply understood for the complexity of this natural aromatic polymer. This work presents a detailed understanding of the cleavage of the most abundant β-O-4 bond in the model system, guaiacylglycerol β-guaiacyl ether, by a Brønsted acidic IL (1-methyl-3-(propyl-3-sulfonate) imidazolium bisulfate ([C₃SO₃Hmim][HSO₄]) using density functional theory calculation and molecular dynamics simulation. It has been found that [C₃SO₃Hmim][HSO₄] generates zwitterion/H₂SO₄via proton transfer with an energy barrier of 0.38 kcal/mol, which plays a dominant role in the lignin depolymerization process. Subsequently, the reaction can be carried out via three potential pathways, including (1) the dehydration of α-C-OH, (2) dehydration of γ-C-OH, and (3) the protonation of β-O. The electrophilic attack of H₂SO₄ and the hydrogen-bonding interaction between GG and zwitterion are the two most important factors to promote the depolymerization reaction. In all steps, the dehydration of α-C-OH route is computed to be favored for the experiment. The relatively higher energy barrier for β-O-4 bond dissociation among these reaction steps is attributed to the hindrance of the self-assembled clusters of GG in the mixed system. Further, the dense distribution of H13([C₃SO₃Hmim]) surrounding O21(GG), indicated by sharp peaks in RDFs, reveals that -SO₃H in cations plays a substantial role in solvating lignin. Hopefully, this work will demonstrate new insights into lignin depolymerization by functionalized ILs in biomass conversion chemistry.

Solar binary chemical depolymerization of lignin for efficient production of small molecules and hydrogen

In this paper, solar binary chemical depolymerization, that is Solar Thermal Electrochemical Process (STEP), was implemented for an effective breaking of lignin into small molecules and hydrogen. Compared with the conventional unitary chemical thermolysis, solar binary chemical depolymerization of lignin has high efficiencies of the liquefaction and gasification with the low coke, and accompanied by the abundant production of hydrogen. And the reaction temperature of the STEP process was greatly lowered by an intervention of the electrolysis. The results showed that the total conversion and liquefaction of the lignin yielded 87.22% and 57.72% under a constant current of 0.4 A at 340 °C. Further characterizations show that lignin has been successfully decomposed into small molecules with high added-value and hydrogen by a combination of the thermolysis and electrolysis. And the particle size of aggregates and the color degree in the lignin aqueous solution was obviously decreased after the STEP process.

CuSO4/H2O2-Catalyzed Lignin Depolymerization under the Irradiation of Microwaves

The increasing demand for renewable materials in the world has resulted in sustained efforts to utilize biomass in a better way. Lignin, a natural and abundant polymer in plants, has provided an ongoing challenge for many researchers seeking ways to better utilize this abundant resource. Here, we report a very efficient lignin depolymerization strategy with the assistant of microwave radiation. Copper sulphate (CuSO₄) and hydrogen peroxide (H₂O₂) were used to generate hydroxyl radicals to depolymerize lignin under the irradiation of microwaves. Three different types of lignin, organosolv lignin, kraft lignin, and alkali lignin, were all successfully depolymerized using microwave irradiation at a temperature of 110 °C for 7 min. The use of ¹H/¹³C two-dimensional nuclear magnetic resonance spectroscopy enabled the confirmation of structural changes, comparing before and after depolymerization. Liquid chromatography-mass spectrometry was used to characterize the products. Both monomers and oligomers were detected after depolymerization.

Biodegradation of Endocrine-Disrupting Chemicals and Residual Organic Pollutants of Pulp and Paper Mill Effluent by Biostimulation

Effluent discharged from the pulp and paper industry contains various refractory and androgenic compounds, even after secondary treatment by activated processes. Detailed knowledge is not yet available regarding the properties of organic pollutants and methods for their bioremediation. This study focused on detecting residual organic pollutants of pulp and paper mill effluent after biological treatment and assessing their degradability by biostimulation. The major compounds identified in the effluent were 2,3,6-trimethylphenol, 2-methoxyphenol (guaiacol), 2,6-dimethoxyphenol (syringol), methoxycinnamic acid, pentadecane, octadecanoic acid, trimethylsilyl ester, cyclotetracosane, 5,8-dimethoxy-6-methyl-2,4-bis(phenylmethyl)napthalen-1-ol, and 1,2-benzendicarboxylic acid diisononyl ester. Most of these compounds are classified as endocrine-disrupting chemicals and environmental toxicants. Some compounds are lignin monomers that are metabolic products from secondary treatment of the discharged effluent. This indicated that the existing industrial process could not further degrade the effluent. Supplementation by carbon (glucose 1.0%) and nitrogen (peptone 0.5%) bio-stimulated the degradation process. The degraded sample after biostimulation showed either disappearance or generation of metabolic products under optimized conditions, i.e., a stirring rate of 150 rpm and temperature of 37 ± 1°C after 3 and 6 days of bacterial incubation. Isolated potential autochthonous bacteria were identified as Klebsiella pneumoniae IITRCP04 (KU715839), Enterobacter cloacae strain IITRCP11 (KU715840), Enterobacter cloacae IITRCP14 (KU715841), and Acinetobacter pittii strain IITRCP19 (KU715842). Lactic acid, benzoic acid, and vanillin, resulting from residual chlorolignin compounds, were generated as potential value-added products during the detoxification of effluent in the biostimulation process, supporting the commercial importance of this process.

Chemicals from lignin: an interplay of lignocellulose fractionation, depolymerisation, and upgrading

In pursuit of more sustainable and competitive biorefineries, the effective valorisation of lignin is key. An alluring opportunity is the exploitation of lignin as a resource for chemicals. Three technological biorefinery aspects will determine the realisation of a successful lignin-to-chemicals valorisation chain, namely (i) lignocellulose fractionation, (ii) lignin depolymerisation, and (iii) upgrading towards targeted chemicals. This review provides a summary and perspective of the extensive research that has been devoted to each of these three interconnected biorefinery aspects, ranging from industrially well-established techniques to the latest cutting edge innovations. To navigate the reader through the overwhelming collection of literature on each topic, distinct strategies/topics were delineated and summarised in comprehensive overview figures. Upon closer inspection, conceptual principles arise that rationalise the success of certain methodologies, and more importantly, can guide future research to further expand the portfolio of promising technologies. When targeting chemicals, a key objective during the fractionation and depolymerisation stage is to minimise lignin condensation (i.e. formation of resistive carbon-carbon linkages). During fractionation, this can be achieved by either (i) preserving the (native) lignin structure or (ii) by tolerating depolymerisation of the lignin polymer but preventing condensation through chemical quenching or physical removal of reactive intermediates. The latter strategy is also commonly applied in the lignin depolymerisation stage, while an alternative approach is to augment the relative rate of depolymerisation vs. condensation by enhancing the reactivity of the lignin structure towards depolymerisation. Finally, because depolymerised lignins often consist of a complex mixture of various compounds, upgrading of the raw product mixture through convergent transformations embodies a promising approach to decrease the complexity. This particular upgrading approach is termed funneling, and includes both chemocatalytic and biological strategies.

Protic Ionic Liquids for Lignin Extraction-A Lignin Characterization Study

Protic ionic liquids (PILs) have been established as effective solvents for the selective extraction and recovery of lignin from lignocellulosic biomass. In this study, we utilize extensive analytical techniques to characterize the PIL-extracted lignins to (1) expand on the physical/chemical structure, and to (2) develop a better understanding of the mechanism behind the lignin dissolution process. The PIL-lignins were characterized using elemental and FT-IR analyses, alongside molecular weight distribution and chemical modeling via MM2. For the more ionic pyrrolidinium acetate ([Pyrr][Ac]), there is an increase in the fragmentation of lignin, resulting in lignin with a smaller average molecular weight and a more uniform dispersity. This lends better understanding to previous findings indicating that higher ionicity in a PIL leads to increased lignin extraction.