Lignin-derived Phenolic Monomers Research Articles

Self-Hydrogen Supplied Catalytic Fractionation of Raw Biomass into Lignin-Derived Phenolic Monomers and Cellulose-Rich Pulps.

Lignocellulosic biomass is one of the most well-studied and promising green carbon sources. The fullest utilization of lignocellulosic biomass in hydrogen-free and mild conditions to produce phenolic monomers while preserving cellulose-rich pulps is challenging and has far-reaching significance. Here, we report an innovative strategy to convert lignocellulosic biomass into lignin oils and cellulose-rich pulps without exogenous hydrogen under mild conditions over a Pt/NiAl2O4 catalyst. In this process, the structural hydrogens in hemicellulose acted as a hydrogen source to realize the fractionation and depolymerization of lignin into phenolic monomers while keeping the cellulose intact, which is named self-hydrogen supplied catalytic fractionation (SCF). By using water as a solvent, the theoretical yield of phenolic monomers (46.6 wt %, with propyl(ethyl) end-chained syringol and guaiacol as main products) is achieved at 140 °C for 24 h, with 90% cellulose intact in birch sawdust. This H2-free process can be extended to other biomass (hardwood, softwood, and grass) and can be scaled up. The Pt/NiAl2O4 catalyst also shows good stability in recycling as well as regeneration treatment. This work provides a new strategy to achieve high utilization of lignocellulosic biomass for sustainable biorefinery by using water as a solvent without exogenous hydrogen under mild conditions.

Total chemocatalytic cascade conversion of lignocellulosic biomass into biochemicals

Because of its complexity, selective conversion of lignocellulosic biomass into platform chemicals presents significant challenges. Herein, we converted birch wood into high-yield lignin-derived phenolic monomers and dimers and holocellulose-derived polyols and monocarboxylic acids via a two-step cascade reaction using 0.1 wt% Pd on N-doped carbon (Pd0.1/CNx) and passivated alumina-coated Ni on activated carbon (Ni2 @Al2O3/AC) catalysts. The catalytic fractionation of birch sawdust using Pd0.1/CNx produced 11.1 wt% monomers, 5.6% dimers, and 63.4 wt% pulp-rich solid (PRS) based on feed weight. The subsequent conversion of PRS over passivated Ni2 @Al2O3/AC produced 21.6 wt% C2–C6 polyols and 7.9 wt% monocarboxylic acids. After the whole biomass conversion reaction, the Pd0.1/CNx and Ni2 @Al2O3/AC catalysts were separated using their different magnetic responses and reused three times without activity loss. The structure–performance relationships of the Pd0.1/CNx catalysts synthesized using different methods and effect of passivation on the performance of the Ni2 @Al2O3/AC catalyst were analyzed.

Low-pressure two-stage catalytic hydropyrolysis of lignin and lignin-derived phenolic monomers using zeolite-based bifunctional catalysts

In the present study, a two-stage catalytic hydropyrolysis of lignin was investigated by converting lignin extracted from corn stover, loblolly pine and red oak using HZSM-5, MoO3/ZSM-5 and Ni/ZSM-5 as catalysts. Compared to the catalytic pyrolysis with inert gas, the presence of atmospheric-pressure hydrogen significantly enhanced the formation of hydrocarbon from lignin whereas dramatically reducing coke yield. In comparison to HZSM-5, MoO3/ZSM-5 increased the production of aromatic hydrocarbons, while Ni/ZSM-5 enhanced the formation of aliphatic hydrocarbons. Coke yields decreased with both MoO3/ZSM-5 and Ni/ZSM-5, which corresponds to the suppression of polyaromatic formation and increased selectivity to single ring aromatics. Corn stover lignin produced the highest yield of aromatic hydrocarbons with all three catalysts, followed by loblolly pine and red oak lignins. Particularly, up to 42.24 C% of corn stover lignin was converted into aromatic and aliphatic hydrocarbons with MoO3/ZSM-5. In this study, reaction pathways of lignin-derived pyrolysis vapor during catalytic hydropyrolysis were further studied using phenol, guaiacol, and syringol as the model compounds. Results suggest that demethoxylation followed by the hydrodeoxygenation of methoxyl radicals and subsequent alkylation of the phenolic ring to produce cresol, and dimethyl phenol as intermediates prior to the intermediate phenolics were further hydrodeoxygenated to produce benzene and alkylated benzene. MoO3/ZSM-5 showed strong ability for both demethoxylation and hydrodeoxygenation. In comparison, the ability of Ni/ZSM-5 for phenolic-hydroxyl removal was much inferior. Based on the results obtained from the conversions of lignin and the model compounds, a negative correlation between the total yields of aromatic hydrocarbons from lignin and the abundancy of phenolic methoxyls in the lignin-derived pyrolysis vapor was found. It was also found that the pyrolysis vapors of simple H, G, or S-based monomers tend to produce more aromatic hydrocarbons than the vapors composed of more complex monomers and oligomers from their corresponding H, G or S group. However, the yield differences were less significant among G and S-based monomers and oligomers.

Complete Genome Sequence of Rhodococcus ruber R1, a Novel Strain Showing a Broad Catabolic Potential toward Lignin-Derived Aromatics.

Rhodococcus ruber R1 was isolated from a pulp mill wastewater treatment plant because of its ability to use methoxylated aromatics as growth substrates. We report the 5.56-Mb genome sequence of strain R1, which can provide insights into the biodegradation of lignin-derived phenolic monomers and potentially support processes for lignocellulose conversion.

Fractionation of Lignocellulosic Biomass over Core-Shell Ni@Al2 O3 Catalysts with Formic Acid as a Cocatalyst and Hydrogen Source.

Highly dispersed, core-shell Ni@Al2 O3 on activated carbon (AC) catalysts were prepared to develop an effective, external-hydrogen-free fractionation process for various types of lignocellulosic biomass. In a mixture of formic acid, ethanol, and water at 190 °C, the conversion of oak wood produced 23.4 C% lignin-derived phenolic monomers (LDPMs) and highly delignified pulp-rich solid. At an early stage, formic acid acted as a cocatalyst to enhance the delignification by solvolysis, and at a later stage, it acted as a hydrogen source to stabilize the phenolic monomers by hydrodeoxygenation and hydrogenation. Based on the positive correlation between spillover hydrogen on the catalysts and LDPM yields, a new suite of catalyst design criteria was proposed to develop highly active, non-noble-metal based catalysts for realizing economically viable biorefineries. Enzymatic saccharification of the pulp-rich solid indicated that the pulp-rich solid is an excellent source of fermentable sugars.

Single-step conversion of lignin monomers to phenol: Bridging the gap between lignin and high-value chemicals

Transformation of lignin into high-value chemicals is hampered by the complexity of monomers obtained from lignin depolymerization. Here we report a strategy, composed of hydro-demethoxylation and de-alkylation reactions, that is able to chemically converge various lignin-derived phenolic monomers into phenol in a single-step. Using 2-methoxy-4-propylphenol as a model compound, Pt/C exhibited the best performance in hydro-demethoxylation reaction affording >80% 4-propylphenol from 2-methoxy-4-propylphenol, while H-ZSM-5 was identified as the most suitable catalyst for de-alkylation, achieving 83% yield of phenol from 4-propylphenol. Since the two catalysts operate under compatible conditions, combining the two catalysts to simultaneously promote both hydro-demethoxylation and de-alkylation reactions was achieved. Configuration of how to organize the catalysts is a critical parameter, where the physical mixture of the two was most effective, providing over 60% phenol from 2-methoxy-4-propylphenol in a single-step.

Hydrodeoxygenation of lignin-derived phenolic compounds over bi-functional Ru/H-Beta under mild conditions

Bifunctional ruthenium catalysts supported on H-Beta zeolite were designed and applied in the hydrodeoxygenation of lignin-derived phenolic compounds for bio-oil upgrading. The oxygen-containing groups in lignin-derived phenolic monomers and dimers could be efficiently removed through aqueous phase hydrodeoxygenation catalyzed by Ru/H-Beta under very mild conditions, i.e. at 413K and 4MPa H2. Characterization results revealed that ruthenium species existed in the form of highly dispersed nanoparticles on H-Beta zeolite, while the presence of both Brønsted and Lewis acid sites in zeolite was crucial for the remarkable hydrodeoxygenation activity. The effects of reaction conditions and catalyst constitution on the catalytic performance of Ru/H-Beta in hydrodeoxygenation were systematically investigated. The hydrodeoxygenation pathway of diphenyl ether as a model compound catalyzed by optimized 0.5%Ru/H-Beta was discussed and the structure-activity relationship in hydrodeoxygenation was proposed.

Abundance and composition of free and aggregate-occluded carbohydrates and lignin in two forest soils as affected by wildfires of different severity

Organic matter is the soil component most affected by wildfires, both in terms of abundance and composition. Fire-induced alteration of soil organic matter (SOM) depends on heating intensity and duration, oxygen availability and other factors related to topography, climate, soil and vegetation features. Particularly affected by fire is the litter layer, but SOM from the uppermost mineral soil can also experience some major changes. In this study, we investigated the direct impact of fire on molecular SOM parameters in density fractions isolated from the top 2.5cm of mineral soil in two forests that recently experienced wildfires of different severity. One, located in Tuscany, Central Italy, is a mixed forest of Downy oak and Maritime pine, developed on Acrisols formed on sandy lacustrine deposits, affected by a moderately severe fire. The other, located in Victoria, South-East Australia, is a mixed-species eucalypt forest, developed on a Cambisol formed on sandy Devonian sediments, affected by an extremely severe fire (the infamous ‘Black Saturday’ fire). The purpose of this study was the assessment of fire-induced changes on amount and composition of the bulk SOM and SOM associated to soil fractions having different densities. We used 1.8Mgm−3 as density cut-off and distinguished between free and aggregate-occluded SOM. In particular, the analyses focused on abundance and composition of two major SOM components, proposed as molecular indicators of fire severity: the non-cellulosic neutral sugars, digested by trifluoroacetic acid (TFA), and the lignin-derived phenolic monomers, released by cupric oxide (CuO) oxidation. The chemical structure of both bulk SOM and SOM fractions were analysed by solid-state 13C nuclear magnetic resonance spectroscopy.In contrast to the moderately severe fire affecting the Italian site, the extremely severe fire at the Australian site caused substantial loss of SOM from the top mineral soil. Both fires had major effects on SOM composition. In spite of the evident impact they experienced, neither hydrolysable sugars nor lignin phenols resulted to be reliable indicators of fire severity. Moreover, both fires apparently broke up soil aggregates, hence promoting the release of some occluded organic matter. The fire-induced changes of SOM observed have implications for the C cycle, so highlighting the critical role of wildfire occurrence and severity in climate change.

Reductive lignocellulose fractionation into soluble lignin-derived phenolic monomers and dimers and processable carbohydrate pulps

A new generation lignocellulose biorefinery uses heterogeneous catalysis for the high-yield production of a handful of chemicals from wood.

Hydrodeoxygenation of Lignin-Derived Phenolic Monomers and Dimers to Alkane Fuels over Bifunctional Zeolite-Supported Metal Catalysts

A bifunctional catalyst of Ru supported in zeolite HZSM-5, Ru/HZSM-5 (Si/Al = 25), exhibited excellent hydrodeoxygenation activity toward the conversion of lignin-derived phenolic monomers and dimers to cycloalkanes in aqueous solution. The oxygen-containing groups in mono- and binuclear phenols were removed through a cleavage of C–O bonds in phenolics followed by an integrated metal- and acid-catalyzed hydrogenation and dehydration. As a bifunctional catalyst Ru/HZSM-5, the presence of both the Bronsted acid site in the pores of HZSM-5 for dehydration and a metallic function of Ru for hydrogenation was indispensible for the formation of alkanes from lignin-derived phenolics. Our findings also reveal that the Ru/HZSM-5 with the lowest Si/Al ratio of HZSM-5 proved to be most selective to cycloalkanes, indicating that more acid sites over zeolite are favorable for the dehydration of cyclohexanol during hydrodeoxygenation process, which leads higher selectivity to hydrocarbons. This approach for the construc...

Effect of lignin-derived phenolic monomers on the growth of the edible mushrooms Lentinus edodes, Pleurotus sajor-caju and Volvariella volvacea

Pleurotus sajor-caju was generally more tolerant to lignin-related phenolic monomers and tannin derivatives than Lentinus edodes and the straw mushroom, Volvariella volvacea. Several phenols, at up to 5 mM, enhanced mycelial growth of P. sajor-caju. No clear pattern was evident when the effects of phenols and tannins on the growth of V. volvacea and L. edodes were compared, but the lower concentrations of 4-hydroxybenzaldehyde and vanillin which were tested were markedly more toxic to the straw mushroom. The distribution of phenolic monomers and tannin derivatives in the agricultural wastes used for mushroom cultivation may be an important growth determinant. However, the differences in the growth inhibition profiles of L. edodes, P. sajor-caju and V. volvacea suggest that, alone, the effect of these compounds on fungal growth is unlikely to account for the varying abilities of the three mushroom species to grow and fruit on a particular lignocellulosic substrate.

Separation and quantification of lignin-derived phenolic monomers using high-resolution gas chromatography

Mode operatoire d'une methode de dosage de cette fraction extraite de parois cellulaires vegetales. Cette methode permet d'effectuer la separation des monomeres phenoliques sous forme de derives trimethylsilyles. Elle est rapide, peu onereuse et a une sensibilite egale ou superieure a celles des autres methodes