Catalytic Lignin Research Articles

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.

Catalytic depolymerization of Kraft lignin towards liquid fuels over bifunctional molybdenum oxide based supported catalyst

Catalytic depolymerization of Kraft lignin towards valuable liquid fuels and monomeric phenols has been a significant and extremely attractive target, but it remains a great challenge. Herein, we report a catalytic system consisted of bifunctional molybdenum oxide based supported catalyst for catalytic lignin hydroconversion into alkylated benzenes and phenols. In the meantime, the achieved yield of liquid product was 95% and petroleum ether extracted product was 65% at 300℃ for 12 h over 20%MoOx/ZIF-8@ZIF-67 catalyst. The calorific value was increased from 25.66 MJ/ Kg to 34.31 MJ/Kg. The characterization studies show the incorporation of MoOx species leads to the synergy between redox sites and acid sites. The product analysis and catalytic studies demonstrate its synergism to promote catalytic cleavage of C-O linkages via the coupled hydrodeoxygenation and alkylation reaction. The reasonable catalytic mechanism and redox cycle route of catalyst indicate that the cooperative catalytic system paves the way for high-efficiency waste lignin utilization.

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.

Catalytic lignin valorization over HSZ-supported CuNiAl-based catalysts with microwave heating

Microwave assisted lignin depolymerization was investigated over HSZ-supported CuNiAl-based catalysts.

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.

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.

Structure-antioxidant activity relationship of active oxygen catalytic lignin and lignin-carbohydrate complex

Lignin, as a natural antioxidant, has a great potential to replace the chemosynthetic ones due to this material benefits of being biodegradable, eco-friendly, abundant and low-cost. However, the commonly-used lignins, such as acid, kraft and alkali lignins, have the poor antioxidant ability, and their antioxidative mechanism and kinetics remain poorly understood. Moreover, the understanding of the effect of polysaccharides in lignin-carbohydrate complex (LCC) on lignin antioxidant activity is also extremely insufficient. Herein, we isolated lignin and LCC from rice straw and its alkali-oxygen spent liquor to investigate their structure-antioxidant activity relationship and antioxidative mechanism. Experimental results illustrated that the alkali-oxygen treatment can significantly enhance the antioxidant activity of lignin. Demethoxylation, ring-opening and the cleavage of aryl ether bonds occur to lignin structure leading to the decrease of molecular weight, while the more stable condensed β-1′, 5–5′ and β-5′ linkages maintain the thermostability of this antioxidant. The synergistic effect of adjacent methoxyl with phenolic hydroxyl is the key factor that endows lignin with the outstanding antioxidant activity. In contrast, oligosaccharides formed by alkali-oxygen treatment have a negative influence on the antioxidant activity of lignin. This work demonstrates that alkali-oxygen lignin is a promising antioxidant to replace chemosynthetic ones for polymeric materials.

Lignin catalytic hydroconversion in a semi-continuous reactor: An experimental study

The valorization of lignin coming from pulp industry or bio-ethanol refineries into renewable chemicals is one of the great challenges of the biorefinery concept. Among the several processes proposed to depolymerize lignin, catalytic hydroconversion appeared efficient to get high liquid yield and can provide targeted aromatic monomers. A new semi-continuous set-up consisting in a batch reactor opened on the gas-phase was implemented to carry out the catalytic lignin liquefaction into phenolic and deoxygenated aromatic compounds with continuous H2 feeding. The interest of this equipment is the continuous removing of light products and water from the reacting mixture whereas the hydrogen donor solvent is reintroduced in the reactor via a reflux/condensing system. A Co-promoted Mo sulfide catalyst was used and thanks to efficient separation and extensive analysis, the components of the different gaseous, liquid and solid fractions obtained were identified and quantified. The evolution of the various fractions in function of the time and the deep investigation of the composition, allowed to propose a reaction scheme for the lignin depolymerization in those operating conditions.

Metamorphic meta isomer: carbon dioxide and ketenes are formed via retro-Diels-Alder reactions in the decomposition of meta-benzenediol.

The deoxygenation reaction of m-benzenediol (resorcinol), an important lignin model compound, was studied in a hot microreactor. We revealed three decomposition channels by detecting elusive and reactive intermediates and product isomers selectively and found that resorcinol, similarly to catechol (o-benzenediol) and hydroquinone (p-benzenediol), (i) gets decarbonylated to yield hydroxycyclopentadiene. Additionally, (ii) decarboxylation (CO2 loss) yields C5H6 species in a retro-Diels-Alder reaction from a lactone species. Only acyclic products are detected at lower reactor temperatures and the most stable C5H6 isomer, cyclopentadiene (c-C5H6), is only observed at higher temperatures. Finally, (iii) two reactive ketene species, ethenone and buta-1,3-dienal, were observed in a third reaction channel. Both decarboxylation and ketene formation channels are unique among benzenediols for the meta-isomer, resorcinol. We have explored the resorcinol potential energy surface to rationalize the observed reactions. These findings may help to understand the source of ketenes in catalytic lignin depolymerization and give new insight into isomer-specific deoxygenation processes.

Analysis of gas chromatography/mass spectrometry data for catalytic lignin depolymerization using positive matrix factorization

Various catalytic technologies are being developed to efficiently convert lignin into renewable chemicals.

Thermocatalytic conversion of lignin in an ethanol/formic acid medium with NiMo catalysts: Role of the metal and acid sites

NiMo catalysts supported on different sulfated and non-sulfated aluminas and zirconias were studied for the catalytic conversion of lignin in a formic acid/ethanol medium. All the pre-reduced NiMo-support combinations resulted in high conversion of lignin into bio-oil, with over 60% yield (mass%). The NiMo-sulfated alumina catalyst exhibited the highest activity among all the catalysts studied. The overall reaction mechanism of the catalytic lignin conversion was found to be especially complex. The oil yield and its properties are affected by a combination of successive catalytic reactions that are part of the lignin conversion process. Lignin is first de-polymerized into smaller fragments through the cleavage of the aliphatic ether bonds. This reaction can be either catalyzed by Ni0 species and strong Lewis acid sites within the alumina supports. In the presence of both active species, the Ni0 catalyzed ether bond cleavage is the prevailing reaction mechanism. In a second step, the smaller lignin fragments can be stabilized by catalytic hydrodeoxygenation (HDO) and alkylation reactions that hinder their re-polymerization into char. Mo was found to be especially active for HDO reactions while all the catalysts studied exhibited significant alkylation activity. The final bio-oil yield is strongly dependent on the aliphatic ether bond cleavage rate; the contribution of those monomer stabilization reactions (i.e. HDO and alkylation) being secondary.

ChemInform Abstract: Recent Developments in Chemical Degradation of Lignin: Catalytic Oxidation and Ionic Liquids

AbstractReview: 60 refs.

Catalytic Lignin Valorization Process for the Production of Aromatic Chemicals and Hydrogen

With dwindling reserves of fossil feedstock as a resource for chemicals production, the fraction of chemicals and energy supplied by alternative, renewable resources, such as lignin, can be expected to increase in the foreseeable future. Here, we demonstrate a catalytic process to valorize lignin (exemplified with kraft, organosolv, and sugarcane bagasse lignin) using a mixture of cheap, bio-renewable ethanol and water as solvent. Ethanol/water mixtures readily solubilize lignin under moderate temperatures and pressures with little residual solids. The molecular weight of the dissolved lignins was shown to be reduced by gel permeation chromatography and quantitative HSQC NMR methods. The use of liquid-phase reforming of the solubilized lignin over a Pt/Al(2)O(3) catalyst at 498 K and 58 bar is introduced to yield up to 17 % combined yield of monomeric aromatic oxygenates such as guaiacol and substituted guaiacols generating hydrogen as a useful by-product. Reduction of the lignin dissolved in ethanol/water using a supported transition metal catalyst at 473 K and 30 bar hydrogen yields up to 6 % of cyclic hydrocarbons and aromatics.

Towards Quantitative Catalytic Lignin Depolymerization

The products of base-catalyzed liquid-phase hydrolysis of lignin depend markedly on the operating conditions. By varying temperature, pressure, catalyst concentration, and residence time, the yield of monomers and oligomers from depolymerized lignin can be adjusted. It is shown that monomers of phenolic derivatives are the only primary products of base-catalyzed hydrolysis and that oligomers form as secondary products. Oligomerization and polymerization of these highly reactive products, however, limit the amount of obtainable product oil containing low-molecular-weight phenolic products. Therefore, inhibition of concurrent oligomerization and polymerization reactions during hydrothermal lignin depolymerization is important to enhance product yields. Applying boric acid as a capping agent to suppress addition and condensation reactions of initially formed products is presented as a successful approach in this direction. Combination of base-catalyzed lignin hydrolysis with addition of boric acid protecting agent shifts the product distribution to lower molecular weight compounds and increases product yields beyond 85%.

Reaction pathway analysis of thermal and catalytic lignin fragmentation by use of model compounds

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTReaction pathway analysis of thermal and catalytic lignin fragmentation by use of model compoundsStephen J. Hurff and Michael T. KleinCite this: Ind. Eng. Chem. Fundamen. 1983, 22, 4, 426–430Publication Date (Print):November 1, 1983Publication History Published online1 May 2002Published inissue 1 November 1983https://doi.org/10.1021/i100012a012RIGHTS & PERMISSIONSArticle Views1053Altmetric-Citations79LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (688 KB) Get e-Alerts