Catalytic Depolymerization Of Lignin Research Articles

Synchronous catalytic depolymerization of alkaline lignin to monophenols with in situ-converted hierarchical zeolite for bio-polyurethane production

Catalytic depolymerization of lignin to high-value chemicals is crucial to the comprehensive achievement of sustainable and economic concerns. Herein, we propose a green, practical, and economic strategy for the synchronous catalytic depolymerization of lignin based on in situ conversion of geopolymer precursor to hierarchical zeolite, using water as a mild solvent and without external H2, additives, co-catalysts or co-solvents. The in situ-converted hierarchical analcime (ANA) zeolite outperformed previously reported representative catalysts, such as PTA/MCM-41 and CuAlMgOx in lignin depolymerization with a high monophenol yield (95.61 ± 7.89 mg/g). The synergetic effect of the micro-mesoporous structure and enhanced acidic sites of the ANA played a vital role in regulating the monomer composition and the yield of monophenols. The obtained monophenols are rich in -OH groups and can be utilized as a substitute for petroleum resources, such as ethylene glycol or glycerin for the synthesis of bio-polyurethane foams (bio-PUFs). This work expands the scope of using biomass in a sustainable manner to make high-value chemicals and biomaterials.

Possible use as biofuels of monoaromatic oxygenates produced by lignin catalytic conversion: A review

Small aromatic molecules with oxygen-containing functional groups (monoaromatic oxygenates) are common products of the catalytic depolymerization of lignin, which can be considered as a promising class of fuel additives. This mini-review article starts with an introduction of second generation (2G) of biofuel production from lignocellulose and the further conversion of lignin into fuel performance boosting blends. The discussion is divided into four parts. The first part gives a brief overview of the production of aromatic oxygenates from the catalytic conversion of lignin of different origin. The three following parts are focused on the aromatic oxygenates, for which combustion data can be found. The second part describes their chemical structure and physical properties. The third part is dominated by their global combustion performance, i.e., the commercial fuel parameters as lower heating value, octane and cetane numbers. A few studies on ignition delay times and laminar flame velocities are also described. The fourth part shortly reviews the kinetic studies presenting product quantifications, the proposed detailed kinetic models and the influence of the structure of the aromatic reactant on soot formation. To finish, a perspective on future research directions is given.

Catalytic conversion of Kraft lignin into platform chemicals in supercritical ethanol over a Mo(OCH2CH3)x/NaCl catalyst

A Mo(OCH2CH3)x/NaCl catalyst showed high efficiency in supercritical ethanol without adding H2 in the conversion of Kraft lignin to chemicals, including C6 alcohols, C8-C10 esters, benzyl alcohols and arenes. Control experiments were done with MoCl5, NaOC2H5 and the physical mixture of them. The Mo(OCH2CH3)x/NaCl catalyst exhibited superior activity among the samples examined. The overall yield increased as the reaction temperature increased from 260° to 300°C. The yield of aromatic compounds achieved 303 mg/g lignin over the Mo(OCH2CH3)x/NaCl catalyst at 300 °C for 6 h. MoCl5 and NaOC2H5 forms Mo(OCH2CH3)x in the catalyst preparation, which behaves as the active species in Kraft lignin conversion. The primary aromatics formed from the catalytic lignin depolymerization steps may undergo secondary reactions to form the final products.

Ni12P5/P-N-C Derived from Natural Single-Celled Chlorella for Catalytic Depolymerization of Lignin into Monophenols.

Lignin is exceptionally abundant in nature and is regarded as a renewable, cheap, and environmentally friendly resource for the manufacture of aromatic chemicals. A novel Ni12P5/P–N–C catalyst for catalytic hydrogenolysis of lignin was synthesized. The catalysts were prepared by simple impregnation and carbonization using the nonprecious metal Ni taken up by the cell wall of Chlorella in Ni(NO3)2 solution. There were only two steps in this process, making the whole process very simple, efficient, and economical. Ni12P5 was uniformly distributed in the catalyst. During the hydrogenolysis of lignin, after 4 h reaction at 270 °C, the yield of bio-oil reached 65.26%, the yield of monomer reached 9.60%, and the selectivity to alkylphenol reached 76.15%. The mixed solvent of ethanol/isopropanol (1:1, v/v) is used as the solvent for the hydrogenolysis of lignin, which not only had excellent hydrogen transferability but also improved the yield of bio-oil, inhibiting the generation of char. No external hydrogen was used, thus avoiding safety issues in hydrogen transport and storage.

Metal-based ionic liquids: effective catalysts in aqueous media for the selective production of vanillin from alkali lignin at room temperature

Catalytic depolymerization of lignin to value-added compounds is receiving increasing interest as part of the circular bioeconomy.

Metal Supported Hydrotalcite Catalytic Depolymerization of Lignin: Effects of Reaction Parameter on Compounds Distribution

Metal Supported Hydrotalcite Catalytic Depolymerization of Lignin: Effects of Reaction Parameter on Compounds Distribution

Catalytic depolymerization of lignin into monophenols over an amorphous mesoporous geopolymer monolith

A new economical, stable, and recyclable amorphous mesoporous geopolymer monolith (GM) was prepared from metakaolin and slag. The obtained GM contained a porous structure mainly with mesopores, and rich Brønsted and Lewis acid sites, which showed higher activity than Ni/MCM-41 and Pt/NiAl2O4, etc. Over 45 aromatic compounds, including guaiacol, syringol, isovanillin, 3,4-dimethoxybenzyl alcohol, etc., were found in the bio-oil. Under optimal conditions, the total yield of 10 major monophenols reached 74.69 ± 1.00 mg/g, half of which was 4-ethyl guaiacol (36.77 ± 1.89 mg/g). Moreover, the GM was easy to regenerate and reuse. In three consecutive runs, the catalytic activity of GM was only reduced by 6.69% per cycle. The synergism of Brønsted and Lewis acidic sites and mesopores of GM was responsible for the high catalytic activity. These indicate the GM is low-cost, easy to prepare, environmentally benign, stable, recyclable, and has great potential in depolymerizing lignin into monophenols.

Machine learning based analysis of reaction phenomena in catalytic lignin depolymerization

Heterogeneously catalyzed lignin solvolysis opens the possibility of transforming low value biomass into high value, useful aromatic chemicals, however, its reaction behavior is poorly understood due to the many possible interactions between reaction parameters. In this study, a novel predictive model for bio-oil yield, char yield and reaction time is developed using Random Forest (RF) regression method using data available from the literature to study the impact of surface properties of the catalyst and the weight averaged molecular weight of the lignin (Mw) used in the reaction. The models achieved a coefficient of determination (R2) score of 0.9062, 0.9428 and 0.8327, respectively, and feature importance for each case was explained and tied to studies that provide a mechanistic explanation for the performance of the model. Surface properties and lignin Mw showed no importance to the prediction of bio-oil yield and average pore diameter contributed 3% of feature importance to reaction time.

Catalytic depolymerization of kraft lignin for liquid fuels and phenolic monomers over molybdenum-based catalysts: The effect of supports

Catalytic lignin depolymerization (CCLD) for liquid fuels and phenolic monomers was investigated over various supports including clays (e.g., sepiolite (SEP), attapulgite (ATP), and montmorillonite (MTM)), and oxides (e.g., Al2O3 and SiO2) as well as their supported Mo-based catalysts under supercritical ethanol. The characterization results demonstrated that different supports with diverse structural properties could affect the textural structures, surface Mo5+ content, and acid sites distribution. Clay-based supports had more strong acid sites as compared with Al2O3 and SiO2, which went against the production of lignin oil (LO) and led to form more solid products during CLD experiments. Meanwhile, the obtained petroleum ether-soluble product (PEsp) in LO catalyzed by sole supports was mainly alkyl/alkoxy substituted phenols. Additionally, Mo species (especially Mo5+) significantly increased the yields of LO and PEsp. Mo/SiO2 had the highest surface Mo5+ species, showing the highest LO yield of 85.2%, in which the produced alkyl/alkoxy substituted phenols reached 450.3 mg/glignin. Among the clay-supported Mo catalysts, Mo/SEP presented superior LO (82.3%) and PEsp (70.8%) yields and the generated substituted phenols reached 398.8 mg/glignin. This paper systematically reported the application of green and environmentally friendly clay-based materials in lignin conversion, which provides some key information for the development of clay catalysts for biomass conversion.

Recent advances of lignin valorization techniques toward sustainable aromatics and potential benchmarks to fossil refinery products

Aromatic compounds are important fuels and key chemical precursors for organic synthesis, however the current aromatics market are mainly relying on fossil resources which will eventually contribute to carbon emissions. Lignin has been recognized as a drop-in substitution to conventional aromatics, with its values gradually realized after tremendous research efforts in the recent five years. To facilitate the development of a possible lignin economics, this study overviewed the recent advances of various biorefinery techniques and the remaining challenging for lignin valorization. Starting with recent discovery of unexplored lignin structures, the potential functions of lignin related chemical structures were emphasized. The important breakthrough of lignin-first pretreatment, catalytic lignin depolymerization, and the high value products with possible benchmark with modern aromatics were reviewed with possible future targets. Possible retrofit of conventional petroleum refinery for lignin products were also introduced and hopefully paving a way to progressively migrate the industry towards carbon neutrality.

Calcium oxide derived from eggshells supported on titanium oxide green catalysts for lignin hydrogenolysis under supercritical alcohol solvents

Catalytic depolymerization of lignin has been investigated in the presence of egg shell derived CaO/TiO2 catalysts. Reaction was carried out for different reaction temperatures (250, 280 and 310 °C) at different reaction holding time at presence of N2 and H2 gas under ethanol, methanol and water solvent. Highest bio-oil yield was found with CaO/TiO2-800 catalyst in ethanol solvent under N2 (74.8 wt%), and H2 (82.8 wt%) environment compared to the water solvent. Under hydrogen environment very less amount of unreacted residue was produced. Bio-oil analysis showed that in under nitrogen environment catalytic depolymerization of lignin produced alkyl phenolic monomer compounds 68.0% with methoxy phenolic compounds 24.0%. Interestingly hydrogen promoted the deoxygenating and hydrogenation reaction which produced higher cyclohexane compounds 38.2% and aromatic hydrocarbon 19%. This is suggesting that the effectively breaking of β-O-4 bond by the catalysts which has an excellence character for the industrial application. Elemental analysis shows that hydrogen enhanced the bio-oil quality compared to the nitrogen environment. This work introduces new perspectives for the efficient production of functional compounds from lignin assisted by egg shell derived green catalysts.

Reductive or oxidative catalytic lignin depolymerization: An overview of recent advances

Lignin, one of the main biopolymers in lignocellulosic biomass, is a promising feedstock for producing aromatic chemicals and BTX-fuels. Despite high availability, lignin remains under-valorized to chemical formation motivating research towards upgrading through depolymerization. Catalytic approaches are particularly studied since they can influence the selectivity of depolymerization. Next to thermal or acid/base depolymerization, catalytic routes under either oxidative or reductive atmosphere represent a very attractive way to produce aromatics for fine chemistry and energy. This literature overview shows that the depolymerization outcome depends strongly on the reaction conditions. While under oxidative atmosphere highly functionalized high-added value chemicals like vanillin are obtained, alkylphenolics and BTX are mainly observed when conducting the reaction under reductive atmosphere. Additionally, results depend mainly on the nature of the catalyst for the former approach, whereas reaction conditions play an essential role when operating under hydrogen. Understanding and comparing these quite complex methodologies over the last ten years constitutes the focus of this review.

A Genetic Algorithmic Approach to Determine the Structure of Li-Al Layered Double Hydroxides.

Layered double hydroxides (LDH) demonstrate significant potential across a range of applications, including as catalysts, delivery vehicles for pharmaceuticals, environmental remediation, and supercapacitors. Explaining the mechanism of LDH action at the atomic scale in these and other applications is challenging, however, due to the difficulty in precisely defining the bulk and surface structure and chemical compositions. Here, we focus on the determination of the structure of lithium-aluminum (Li-Al) LDH, which has shown promise in the catalytic depolymerization of lignin, both directly as the catalyst and as a support for gold nanoparticles. While the relative positions of the Li and Al metals are generally well resolved by X-ray crystallography, it is the structures of the anionic layers, consisting of water and carbonate, that are less well established. Combinatorial analyses of all possible positions and rotations of the water and carbonate in the three-layered Li-AL LDH polytope reveals that the phase space is much too large to examine in any reasonable time frame in a one-by-one structure exploration. To overcome this limitation, we develop and deploy a genetic algorithm (GA) wherein fitness is determined by matching a calculated X-ray diffraction (XRD) pattern for a given structure to the known experimental XRD pattern. The GA approach results in structures of high fitness that portend the bulk Li-Al LDH structure. Importantly, the GA approach offers the potential to determine the structures of other LDH, and more generally layered materials, which are generally difficult to describe given the large chemical and structural space to be explored.

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.

I-Propylammonium Lead Chloride Based Perovskite Photocatalysts for Depolymerization of Lignin Under UV Light.

Lignin depolymerization for the purpose of synthesizing aromatic molecules is a growing focus of research to find alternative energy sources. In current studies, the photocatalytic depolymerization of lignin has been investigated by two new iso-propylamine-based lead chloride perovskite nanomaterials (SK9 and SK10), synthesized by the facile hydrothermal method. Characterization was done by Powder X-Ray Diffraction (PXRD), Scanning Electron Microscopy (SEM), UV-Visible (UV-Vis), Photoluminescence (PL), and Fourier-Transform Infrared (FTIR) Spectroscopy and was used for the photocatalytic depolymerization of lignin under UV light. Lignin depolymerization was monitored by taking absorption spectra and catalytic paths studied by applying kinetic models. The %depolymerization was calculated for factors such as catalyst dose variation, initial concentration of lignin, and varying temperatures. Pseudo-second order was the best suited kinetic model, exhibiting a mechanism for lignin depolymerization that was chemically rate controlled. The activation energy (Ea) for the depolymerization reaction was found to be 15 kJ/mol, which is remarkably less than conventional depolymerization of the lignin, i.e., 59.75 kJ/mol, exhibiting significant catalytic efficiencies of synthesized perovskites. Products of lignin depolymerization obtained after photocatalytic activity at room temperature (20 °C) and at 90 °C were characterized by GC-MS analysis, indicating an increase in catalytic lignin depolymerization structural subunits into small monomeric functionalities at higher temperatures. Specifically, 2-methoxy-4-methylphenol (39%), benzene (17%), phenol (10%) and catechol (7%) were detected by GC-MS analysis of lignin depolymerization products.

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

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

Catalytic depolymerization of lignin from wood waste biomass over natural sourced ZSM-5 catalysts

Lignin isolated from wood waste biomass, contains 61.07 % of lignin, was converted to vanillin using ZSM-5 catalysts. Prior to use, wood waste biomass was delignified to enrich its lignin contents followed by added 10 % H2SO4 to isolate the lignin such as solid black material. Three types of ZSM-5 catalysts i.e. hierarchical ZSM-5, NiO/hierarchical ZSM-5 and CuO/hierarchical ZSM-5 zeolites were used as catalysts in this study. Hierarchical ZSM-5 zeolite was prepared through TPAOH template synthesis methods followed by PDDAM as secondary template. Silicate and aluminate source based on a natural source to form hierarchical ZSM-5 zeolite. Hierarchical ZSM-5 zeolite is modified with NiO and CuO by using impregnation method with Ni nitrate and Cu nitrate solution followed by calcination at 550 °C. The characterization of catalysts employed FTIR, XRD, andSEM-EDX. The reaction was carried out in 200 mL-batch reactor at 100 °C, 150 °C, 200 °C, 250 °C and 300 °C in the presence of ethanol and water (v/v) for 30 min. CuO/hierarchical ZSM-5 zeolite gave the highest % yield of vanillin as product (4.68 %) followed by NiO/hierarchical ZSM-5 zeolite (3.82 %) for the variation of temperature, compared to other ZSM-5 catalysts.

In-situ extraction of depolymerization products by membrane filtration against lignin condensation

Catalytic depolymerization of lignin is a challenging process due to competitive repolymerization reactions. In this paper, the oxidative depolymerization of lignin was catalyzed by a commercial laccase both in a batch experiment and in a membrane bioreactor using the same catalytic conditions. The membrane bioreactor was previously optimized to reach high permeation flux (25 L.h−1.m−2) during lignin diafiltration. While the lignin was exclusively condensed in the batch experiment leading to high molecular weight macromolecules (from 9 to 16 kDa), its depolymerization was effective in the bioreactor producing fragments of less than 1 kDa thanks to the in-situ extraction of the reaction products. This paper demonstrates that the reactor configuration is playing an essential role in triggering or preventing lignin condensation. It also reports the first proof-of-concept demonstrating that in-situ membrane extraction of the reactive fragments of lignin from the bulk medium can be useful against detrimental repolymerization reactions.

Identification of the cleavage mechanisms and hydrogenation activity of the β-O-4 linkage in a lignin model compound over Ni-CeO2/H-ZSM-5

Strategies for catalytic lignin depolymerization to yield ethylbenzene chemicals are green, sustainable and environmentally friendly methods. In this study, a series of Ni-CeO2/H-ZSM-5 catalysts were prepared via the precipitation method, which catalytically degraded the β-O-4 chemical bonding structure to yield ethylbenzene chemicals. The 2-(2-methoxy-phenoxy)-1-phenylethanol substance (β-O-4) was selected as a typical lignin model compound for the investigation of the intrinsic depolymerization mechanism and the catalytic performance. The results demonstrated that the introduced CeO2 active phase can effectively promote the catalytic conversion of the β-O-4 chemical bonding structure to ethylbenzene chemicals. Physicochemical data demonstrate that the reaction pathways and hydrogenation selectivity were effectively regulated and controlled by the tuning of the dehydration and hydrogenolysis processes via the introduction of CeO2, which realized the selective adjustment of the redox properties and the surface valence states of active species in the catalytic process due to its excellent oxygen transfer performance.

Catalytic Lignin Depolymerization to Aromatic Chemicals.

In recent decades, research on lignin depolymerization and its downstream product transformation has drawn an enormous amount of attention from academia to industry worldwide, aiming at harvesting aromatic compounds from this abundant and renewable biomass resource. Although the lignin conversion can be traced back to the 1930s and various noncatalytic and catalytic methods have been explored to depolymerize lignin via direct lignin conversion research or lignin models conversion studies, the complexity of the lignin structure, various linkages, the high stability of lignin bonds, and the diverse fragments condensation process make lignin depolymerization to monomers a highly challenging task. For the potential practical utilization of lignin, compared with lignin conversion to liquid fuel with extra H2 consumption, maintaining the aromatic structure and preparing high-value aromatic chemicals from renewable lignin is more profitable. Therefore, lignin depolymerization to easy-to-handle aromatic monomers with acceptable conversion and selectivity is of great importance. In this article, we present our recent studies on lignin's catalytic conversion to aromatic chemicals. First, we introduce our research on protolignin depolymerization via a fragmentation-hydrogenolysis process in alcohol solvents. Then, focusing on the catalytic cleavage of lignin C-C and C-O bonds, we shed light on a recapitulative adjacent functional group modification (AFGM) strategy for the conversion of lignin models. AFGM strategy begins with the adjacent functional group modification of the target C-C or C-O bond to directly decrease the bond dissociation enthalpy (BDE) of targeted bonds or generate new substrate sites to introduce the cleavage reagent for further conversion. Subsequently, on the basis of these two concepts from AFGM, we summarize our strategies on lignin depolymerization, which highlight the effects of lignin structure, catalyst character, and reaction conditions on the efficiency of strategies. In short, the key point for lignin depolymerization to aromatics is promoting the lignin conversion and restraining the condensation. Compared with the complex research on direct lignin conversion, this bottom-up research approach, beginning with lignin model research, can make the conversion mechanism study clear and provide potential methods for the protolignin/technical lignin conversion. In addition, one of our perspectives for lignin utilization is that the products from lignin conversion can be used as monomers for artificial polymerization, such as the simple phenol (PhOH) and other potential acid compounds, or that lignin derivative molecules can be used to synthesize high-value synthetic building blocks.