Catalytic Depolymerization of Lignin and Woody Biomass in Supercritical Ethanol: Influence of Reaction Temperature and Feedstock

Hydrogen-transfer strategy in lignin refinery: Towards sustainable and versatile value-added biochemicals

Lignin, the most prevalent natural source of polyphenols on Earth, offers substantial possibilities for the conversion into aromatic compounds, which is critical for attaining sustainability and carbon neutrality. The hydrogen-transfer method has garnered significant interest owing to its environmental compatibility and economic viability. The efficacy of this approach is contingent upon the careful selection of catalytic and hydrogen-donating systems that decisively affect the yield and selectivity of the monomeric products resulting from lignin degradation. This paper highlights the hydrogen-transfer technique in lignin refinery, with a specific focus on the influence of hydrogen donors on the depolymerization pathways of lignin. It delineates the correlation between the structure and activity of catalytic hydrogen-transfer arrangements and the gamut of lignin-derived biochemicals, utilizing data from lignin model compounds, separated lignin, and lignocellulosic biomass. Additionally, the paper delves into the advantages and future directions of employing the hydrogen-transfer approach for lignin conversion. In essence, this concept investigation illuminates the efficacy of the hydrogen-transfer paradigm in lignin valorization, offering key insights and strategic directives to maximize lignin's value sustainably.

Biomass Derived Biofluorescent Carbon Dots for Energy Applications: Current Progress and Prospects

Biomass resources are often disposed of inefficiently and it causes environmental degradation. These wastes can be turned into bio-products using effective conversion techniques. The synthesis of high-value bio-products from biomass adheres to the principles of a sustainable circular economy in a variety of industries, including agriculture. Recently, fluorescent carbon dots (C-dots) derived from biowastes have emerged as a breakthrough in the field, showcasing outstanding fluorescence properties and biocompatibility. The C-dots exhibit unique quantum confinement properties due to their small size, contributing to their exceptional fluorescence. The significance of their fluorescent properties lies in their versatile applications, particularly in bio-imaging and energy devices. Their rapid and straight-forward production using green/chemical precursors has further accelerated their adoption in diverse applications. The use of green precursors for C-dot not only addresses the biomass disposal issue through a scientific approach, but also establishes a path for a circular economy. This approach not only minimizes biowaste, which also harnesses the potential of fluorescent C-dots to contribute to sustainable practices in agriculture. This review explores recent developments and challenges in synthesizing high-quality C-dots from agro-residues, shedding light on their crucial role in advancing technologies for a cleaner and more sustainable future.

Optimizing Catalytic Depolymerization of Lignin in Ethanol with a Day-Clustered Box-Behnken Design

Lignin is a potential resource for biobased aromatics with applications in the field of fuel additives, resins, and bioplastics. Via a catalytic depolymerization process using supercritical ethanol and a mixed metal oxide catalyst (CuMgAlO_x), lignin can be converted into a lignin oil, containing phenolic monomers that are intermediates to the mentioned applications. Herein, we evaluated the viability of this lignin conversion technology through a stage-gate scale-up methodology. Optimization was done with a day-clustered Box-Behnken design to accommodate the large number of experimental runs in which five input factors (temperature, lignin-to-ethanol ratio, catalyst particle size, catalyst concentration, and reaction time) and three output product streams (monomer yield, yield of THF-soluble fragments, and yield of THF-insoluble fragments and char) were considered. Qualitative relationships between the studied process parameters and the product streams were determined based on mass balances and product analyses. Linear mixed models with random intercept were employed to study quantitative relationships between the input factors and the outcomes through maximum likelihood estimation. The response surface methodology study reveals that the selected input factors, together with higher order interactions, are highly significant for the determination of the three response surfaces. The good agreement between the predicted and experimental yield of the three output streams is a validation of the response surface methodology analysis discussed in this contribution.

Generation and characterization of bio-oil obtained from the slow pyrolysis of cooked food waste at various temperatures

Bio-oil was generated from slow pyrolysis of cooked food waste (CFW) at various temperatures (300-500 °C). Then NMR analysis was used as a qualitative means to characterize the bio-oil for its nature (aliphatic or aromatic), and then the compounds were confirmed and quantified using the GC-MS. This analysis indicated that the pyrolysis at low temperature (300 °C) mainly generated carbonyl compounds (Aldehydes, Ketones, Esters, and Oxo groups), Levoglucosans, and Furans (17%, 24%, and 38%, respectively) considered as typical pyrolysis chemicals. Similarly, the pyrolysis at medium temperature (400 °C) generated other compounds that were present in significant quantity, including sugars, aliphatic compounds, nitrogen compounds, acids, phenolic compounds, and alcohols. However, their fraction decreased with an increase in pyrolysis temperature to 500 °C and the fraction of aromatics increased significantly (>60%). This aromatics fraction was much more than that in a bio-oil from typical biomass which can be attributed to distinctively different chemical characteristics of CFW due to presence of additional compounds such as starch, proteins, waxes and oils in CFW. Moreover, the composition of aromatic fraction was better because a very high percentage of aromatic ethers (>58%) e.g. Benzene, 1,3-bis (3-phenoxyphenoxy), was found at 500 °C which can be converted into aliphatic alkanes, aliphatic alcohols, aromatic derivatives and platform chemicals by means of catalyst addition.

Modular Flow Reactors for Valorization of Kraft Lignin and Low-Voltage Hydrogen Production

Recent studies have found that green hydrogen production and biomass utilization technologies can be combined to efficiently produce both hydrogen and value-added chemicals using biomass as an electron and proton source. However, the majority of them have been limited to proof-of-concept demonstrations based on batch systems. Here the authors report the design of modular flow systems for the continuous depolymerization and valorization of lignin and low-voltage hydrogen production. A redox-active phosphomolybdic acid is used as a catalyst to depolymerize lignin with the production of aromatic compounds and extraction of electrons for hydrogen production. Individual processes for lignin depolymerization, byproduct separation, and hydrogen production with catalyst reactivation are modularized and integrated to perform the entire process in the serial flow. Consequently, this work enabled a one-flow process from biomass conversion to hydrogen gas generation under a cyclic loop. In addition, the unique advantages of the fluidic system (i.e., effective mass and heat transfer) substantially improved the yield and efficiency, leading to hydrogen production at a higher current density (20.5 mA cm^-2 ) at a lower voltage (1.5 V) without oxygen evolution. This sustainable eco-chemical platform envisages scalable co-production of valuable chemicals and green hydrogen for industrial purposes in an energy-saving and safe manner.

Catalytic Wood Fractionation into Chemicals in Supercritical Ethanol and n-Heptane: Potential and Limitations

Direct selective wood fractionation into chemicals is an approach that has attracted recent attention. The application of sub- and supercritical (SC) alcohols to fractionate wood into solid cellulose and liquefy phenolic monomers is a process now widely known as “lignin first”. It is justified to study the potential of other SC organic solvents of variable polarities. Herein, we compare the abilities of SC ethanol and SC n-heptane to fractionate pine wood near their critical point. While near-critical ethanol has more affinity for lignin fraction, we show that near-critical n-heptane has preference for carbohydrate deconstruction. If SC ethanol favors biooil formation which contains important ethyl/ethoxy groups, the alkane greatly favors solid carbon products. The impact of addition of heterogeneous catalysts (acid, basic and Cu-based catalysts) on wood fractionation and light chemicals formation was investigated deeply in SC ethanol. In SC ethanol, catalysts favor light liquid products such as esters at the expense of biooil with a total oxygenates yield of 33 wt% relative to carbohydrates over β zeolite. However, we show that depending on the catalysts’ nature, wood components fractionation was completely changed, and this is particularly true with solid acid catalysts which promote cellulose deconstruction and the formation of solid carbon products. It is proposed that liquid products’ accumulation in the autoclave, in particular water, is at the origin of the wood fractionation changes which preclude its control by the choice of the SC organic solvent and conditions. Moreover, all the catalysts underwent severe leaching, which also contributed to the wood component fractionation changes.

Extraction methodology of lignin from biomass waste influences the quality of bio-oil obtained by solvothermal depolymerization process

Lignin from sugarcane bagasse was extracted using three different methods such as Alkaline, Ethanosolv, and Hydrotropic extraction and the effect of each method on yield and quality of bio-oil obtained when the lignin was depolymerized through solvothermal liquefaction was studied using ethanol as solvent. The maximum lignin yield was obtained in the hydrotropic extraction method when Sodium Xylene Sulfonate was used as the hydrotropic solvent at a concentration of 1.43 M and a temperature of 90 °C. Hydrothermal experiments were performed at temperature of 250 °C with a residence time of 30 min and lignin to ethanol ratio of 1:200 g/mL respectively. Among the methods used, the Ethanosolv lignin showed the highest extent of depolymerization (86.7%) to yield bio-oil at 250 °C with reduced biochar formation at lignin to solvent ratio of 1:200. Biochar obtained was used in adsorption studies of Cadmium (Cd), Lead (Pb), Nickel (Ni), and Zinc (Zn) and results showed that more than 85% removal of all the metals under lower concentration levels.

Advancements in the Conversion of Lipid-Rich Biowastes and Lignocellulosic Residues into High-Quality Road and Jet Biofuels Using Nanomaterials as Catalysts

At present, the majority of available road and jet biofuels are produced from oleochemical feedstocks that include vegetable oils and biowastes such as waste cooking oils and animal fats. Additionally, one of the most promising ways to achieve long-term environmental goals is to sustainably use lignocellulosic residues. These resources must be treated through a deoxygenation process and subsequent upgrading processes to obtain high-quality road and jet biofuels. Accordingly, in this review, we explore recent advancements in the deoxygenation of oleochemical and lignocellulosic feedstocks in the absence of hydrogen to produce high-quality road and jet biofuels, mainly focusing on the use of nanomaterials as catalysts and the valorization of lipid-rich biowastes and lignocellulosic residues. As a result, we found that regardless of the catalyst particle size, the coexistence of basic sites and weak/medium acid sites is highly important in catalytic systems. Basic sites can enhance the removal of oxygenates via decarboxylation and decarbonylation reactions and inhibit coke formation, while weak/medium acid sites can enhance the cracking reaction. Additionally, the extraction of value-added derivatives from lignocellulosic residues and their subsequent upgrade require the use of advanced methods such as the lignin-first approach and condensation reactions.

Lignin-Derived Syringol and Acetosyringone from Palm Bunch Using Heterogeneous Oxidative Depolymerization over Mixed Metal Oxide Catalysts under Microwave Heating

Biomass valorization to building block chemicals in food and pharmaceutical industries has tremendously gained attention. To produce monophenolic compounds from palm empty fruit bunch (EFB), EFB was subjected to alkaline hydrothermal extraction using NaOH or K2CO3 as a promotor. Subsequently, EFB-derived lignin was subjected to an oxidative depolymerization using Cu(II) and Fe(III) mixed metal oxides catalyst supported on γ-Al2O3 or SiO2 as the catalyst in the presence of hydrogen peroxide. The highest percentage of total phenolic compounds of 63.87 wt% was obtained from microwave-induced oxidative degradation of K2CO3 extracted lignin catalyzed by Cu-Fe/SiO2 catalyst. Main products from the aforementioned condition included 27.29 wt% of 2,4-di-tert-butylphenol, 19.21 wt% of syringol, 9.36 wt% of acetosyringone, 3.69 wt% of acetovanillone, 2.16 wt% of syringaldehyde, and 2.16 wt% of vanillin. Although the total phenolic compound from Cu-Fe/Al2O3 catalyst was lower (49.52 wt%) compared with that from Cu-Fe/SiO2 catalyst (63.87 wt%), Cu-Fe/Al2O3 catalyst provided the greater selectivity of main two value-added products, syringol and acetosyrigone, at 54.64% and 23.65%, respectively (78.29% total selectivity of two products) from the NaOH extracted lignin. The findings suggested a promising method for syringol and acetosyringone production from the oxidative heterogeneous lignin depolymerization under low power intensity microwave heating within a short reaction time of 30 min.

Could preoxidation always promote the subsequent hydroconversion of lignin? Two counterexamples catalyzed by Cu/CuMgAlOx in supercritical ethanol

In this study, two counterexamples of lignin preoxidation-hydroconversion were reported. First, two lignin feedstocks were preoxidized with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) in acetonitrile with various dosages (15%, 30%, and 60%). Then, these preoxidized lignins (HELOs and MWLOs) were hydroconverted in supercritical ethanol catalyzed by Cu/CuMgAlO_x. Total yields from HELOs were all higher than those from HEL, indicating the good promotion of DDQ preoxidation on the subsequent hydroconversion of HELOs, especially with the DDQ dosage of 15%. Differently, the promotion effect of DDQ preoxidation on the hydroconversion of MWLOs depended on the DDQ dosage as well as the reaction time. Through the comparison of two counterexamples, this work bursted the myth that preoxidation can always promote the subsequent hydroconversion of lignin, revealed the influence of lignin property, preoxidation degree, and reaction conditions on the subsequent hydroconversion of preoxidized lignin, and presented the new insight into the preoxidation-hydroconversion strategy for lignin.

Catalytic conversion of enzymatic hydrolysis lignin into cycloalkanes over a gamma-alumina supported nickel molybdenum alloy catalyst

The efficient depolymerization and hydrodeoxygenation of enzymatic hydrolysis lignin are achieved in cyclohexane solvents over a gamma-alumina supported nickel molybdenum alloy catalyst in a single step. Under initial 3 MPa hydrogen at 320 °C, the highest overall cycloalkane yield of 104.4 mg/g enzymatic hydrolysis lignin with 44.4 wt% selectivity of ethyl-cyclohexane was obtained. The reaction atmosphere and temperature have significant effects on enzymatic hydrolysis lignin conversion, product type and distribution. The conversion of enzymatic hydrolysis lignin was also investigated over different nickel and molybdenum-based catalysts, and the gamma-alumina supported nickel molybdenum alloy catalyst exhibited the highest activity among those catalysts. To reveal the reaction pathways of alkylphenol hydrodeoxygenation, 4-ethylphenol was tested as a model compound. Complete conversion of 4-ethylphenol into cycloalkanes was achieved. A two-step mechanism of 4-ethylphenol dihydroxylation - hydrogenation is proposed, in which the benzene ring saturation is deemed as the rate-determining step.

Directional depolymerization of lignin into high added-value chemical with synergistic effect of binary solvents

This work exploits a one-pot method for directional depolymerizing organosolv lignin into high added-value phenolic monomers with synergistic reaction system consisted of methanol-dimethoxymethane binary solvents and acid catalyst. The influence of solvent composition and reaction parameters such as different catalyst, binary solvents ratio, time, and temperature on the conversion of lignin and yield of products were investigated carefully, the optimum yield of liquid products and phenolic monomers were achieved at 67.39% and 27.67% at 200 °C kept for 60 min with low amount of acid catalyst. The plausible mechanism on the depolymerization of lignin was proposed in view of product distributions. Moreover, the combination of co-solvents and acidic catalyst was also suitable for converting different types of lignin into phenolic monomers, and the recyclability of joint reaction system was satisfactory. These results can provide promising prospects on developing an effective method for achieving high added-value phenolic compounds from lignin.

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

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

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.

Effect of HCOOK/Ethanol on Fe/HUSY, Ni/HUSY, and Ni-Fe/HUSY Catalysts on Lignin Depolymerization to Benzyl Alcohols and Bioaromatics

We have investigated the production of benzyl alcohols and bioaromatics via the reductive lignin depolymerization process over Fe/H-style ultrastable Y (HUSY), Ni/HUSY, and Ni-Fe/HUSY catalysts using HCOOK/ETOH in air. Synergy effect between HCOOK and the catalysts improved the depolymerization process, resulting in a higher bio-oil recovery. HCOOK does not act solely as an in situ hydrogen source; it also interacts with lignin to enable its initial depolymerization via a base-catalyzed mechanism to low-molecular-weight fragments, and in tandem with the catalyst, the hydrogenolysis rate of the depolymerized lignin monomers was enhanced. Fe/HUSY displayed an excellent activity for the catalytic reductive step in contrast to Ni/HUSY and Ni-Fe/HUSY by facilitating methoxy group removal via hydrogenolysis, thereby contributing to the yield and stabilization of the low-molecular-weight aromatics [diethyl ether (DEE)-soluble products]. Fe/HUSY gave the highest DEE product yield of >99 wt % and a total benzyl alcohol yield of 16 wt % with a total selectivity of 47 wt % (60 wt % for aromatic alcohols). Fe/HUSY was reused for the lignin depolymerization reaction without much loss of its initial activity, giving 13 wt % yield of benzyl alcohols with a selectivity of 58 wt % (77 wt % for aromatic alcohols).

Methanolysis Fractionation and Catalytic Conversion of Poplar Wood toward Methyl Levulinate, Phenolics, and Glucose

In the present study, methanolysis of poplar biomass was conducted for the selective transformation of hemicellulose and lignin, which leads to methyl glycosides (mainly C5 glycosides) and lignin fragments in the liquefied products that can be separated according to their difference in hydrophilicity. The distribution of methyl glycosides and delignification was dependent on the presence of acid catalysts and reaction temperatures. The obtained lignin fraction was separated into solid lignin fragments and liquid lignin oil according to their molecular weight distribution. Subsequently, directional conversion of methyl C5 glycosides into methyl levulinate was performed with dimethoxymethane/methanol as the cosolvent. A yield of 12-30% of methyl levulinate yield (based on the methyl glycoside) was achieved under these conditions. The remaining cellulose-rich substrate showed enhanced susceptibility to enzymatic hydrolysis, resulting in a yield of glucose of above 70%. Overall, the described strategy shows practical implications for the effective valorization of biomass.

One-pot transformation of lignocellulosic biomass into crude bio-oil with metal chlorides via hydrothermal and supercritical ethanol processing

Grape seeds were deconstructed in both hydrothermal and supercritical ethanol media with a combination of two metal chlorides (TiCl₄:MgCl₂) to produce bio-oils. The use of metal chloride additives in supercritical ethanol achieved the highest bio-oil yield of 49.2 wt% (300 °C, 30 min). Both the hydrothermal and supercritical ethanol deconstruction with the additives (TiCl₄:MgCl₂ = 4 mmol:4mmol) produced the bio-oils with a higher heating value (HHV) of 35 MJ/Kg. Gas chromatography-mass spectrometry (GC-MS) analysis of the bio-oils showed that the major products in bio-oils from the hydrothermal deconstruction were acids while the majority products in bio-oils form the supercritical ethanol deconstruction were esters. Nuclear magnetic resonance (NMR) data of the bio-oils suggested that both hydrothermal and supercritical ethanol deconstruction with metal chlorides significantly reduced the non-condensed OH and oxygenated lignin sub-units in bio-oils; while only supercritical ethanol deconstruction with metal chlorides reduced the aliphatic OH and O-alkylated structures in bio-oils.

Catalytic Transfer Hydrogenolysis Reactions for Lignin Valorization to Fuels and Chemicals

Lignocellulosic biomass is an abundant renewable source of chemicals and fuels. Lignin, one of biomass main structural components being widely available as by-product in the pulp and paper industry and in the process of second generation bioethanol, can provide phenolic and aromatic compounds that can be utilized for the manufacture of a wide variety of polymers, fuels, and other high added value products. The effective depolymerisation of lignin into its primary building blocks remains a challenge with regard to conversion degree and monomers selectivity and stability. This review article focuses on the state of the art in the liquid phase reductive depolymerisation of lignin under relatively mild conditions via catalytic hydrogenolysis/hydrogenation reactions, discussing the effect of lignin type/origin, hydrogen donor solvents, and related transfer hydrogenation or reforming pathways, catalysts, and reaction conditions.

Plasma-deposition of α-FeOOH particles on biochar using a gliding arc discharge in humid air: a green and sustainable route for producing oxidation catalysts

Non-thermal atmospheric plasma of the gliding arc type was used as a tool for goethite-on-biochar hybrid material preparation. Biochars were first prepared by carbonizing raffia bamboo (the leafstalk of raffia palm) pith at 300 °C (BC3), 500 °C (BC5) and 700 °C (BC7). A suspension of each biochar in Fe²⁺ aqueous solution was then exposed to a plasma discharge burning in humid air. α-FeOOH particles were thus formed and spontaneously deposited on the biochar surface. In order to investigate the effect of plasma species on the support during goethite deposition, biochars were also treated with plasma in the absence of Fe²⁺ ions and then characterized. Results revealed a substantial hydroxylation and slight N-doping of biochar after plasma treatment. The prepared composite materials were tested in oxidative degradation of nitroresorcinol. The catalytic performances were in the order Fe-BC3 < Fe-BC7 < Fe-BC5 according to the abatement efficiency and half-time values obtained for each catalyst. This study establishes that waste biomass and atmospheric air can be simultaneously valorised for green production of heterogeneous catalysts.

Non-thermal atmospheric plasma of the gliding arc type was used as a tool for goethite-on-biochar hybrid material preparation.

Ethanol: A Promising Green Solvent for the Deconstruction of Lignocellulose

Growing energy demand, environmental impact, energy security issues, and rural economic development have encouraged the development of sustainable renewable fuels. Nonfood lignocellulosic biomass is a suitable source for sustainable energy because the biomass feedstocks are low cost, abundant, and carbon neutral. Recent thermochemical conversion studies are frequently directed at converting biomass into high-quality liquid fuel precursors or chemicals in a single step. Supercritical ethanol has been selected as a promising solvent medium to deconstruct lignocellulosic biomass because ethanol has extraordinary solubility towards lignocellulosic biomass and can be resourced from cellulosic ethanol facilities. This review provides a critical insight into both catalytic and noncatalytic strategies of lignocellulose deconstruction. In this context, the supercritical ethanol deconstruction pathways are thoroughly reviewed; GC-MS, 1D and 2D NMR spectroscopy, and elemental analysis strategies towards liquid biomass deconstruction products are also critically presented. This review aims to provide readers a broad and accurate roadmap of novel biomass to biofuel conversion techniques.

Alternatives for Chemical and Biochemical Lignin Valorization: Hot Topics from a Bibliometric Analysis of the Research Published During the 2000–2016 Period

A complete bibliometric analysis of the Scopus database was performed to identify the research trends related to lignin valorization from 2000 to 2016. The results from this analysis revealed an exponentially increasing number of publications and a high relevance of interdisciplinary collaboration. The simultaneous valorization of the three main components of lignocellulosic biomass (cellulose, hemicellulose, and lignin) has been revealed as a key aspect and optimal pretreatment is required for the subsequent lignin valorization. Research covers the determination of the lignin structure, isolation, and characterization; depolymerization by thermal and thermochemical methods; chemical, biochemical and biological conversion of depolymerized lignin; and lignin applications. Most methods for lignin depolymerization are focused on the selective cleavage of the β-O-4 linkage. Although many depolymerization methods have been developed, depolymerization with sodium hydroxide is the dominant process at industrial scale. Oxidative conversion of lignin is the most used method for the chemical lignin upgrading. Lignin uses can be classified according to its structure into lignin-derived aromatic compounds, lignin-derived carbon materials and lignin-derived polymeric materials. There are many advances in all approaches, but lignin-derived polymeric materials appear as a promising option.

Hydrotreatment Upgrading of Bio-oil from Torrefaction of Pubescens in Alcohol over Pd/NbOPO4

Pd/NbOPO₄ multifunctional catalyst was prepared and used for catalytic hydrotreatment upgrading of bio-oil, which was obtained from low-temperature torrefaction (LTT) of pubescens and contained mainly lignin oligomers. The upgrading temperatures were investigated at 220-280 °C. Pd/NbOPO₄ exhibited good performance for the effective depolymerization of oligomers with increasing temperature. It was revealed that both Brönsted acid sites and Lewis acid sites existed on NbO _x , which contributed to the cleavage of the C-O-C bond. Furthermore, esterification, hydrogenation, and O-alkylation of monomeric derivatives also occurred simultaneously during the depolymerization process. After hydrotreatment upgrading, the average molecular weight of bio-oil decreased from M _w = 320 Da (M _n = 298 Da) to M _w = 273 Da (M _n = 254 Da) and the bio-oil quality was improved dramatically. The oxygen content decreased from 29.53 to 9.78 wt %. The upgraded bio-oil obtained at 280 °C had a heating value of 40.48 MJ kg^-1, which was much higher than that of the original bio-oil (26.96 MJ kg^-1).

Synthesis of CoFeO mixed oxides via an alginate gelation process as efficient heterogeneous catalysts for lignin depolymerization in water

CoFeO mixed oxide, an efficient catalyst for lignin depolymerization in water to functional phenols.