Lignin-derived Phenolic Compounds Research Articles

Water-Assisted Selective Hydrodeoxygenation of Guaiacol to Cyclohexanol over Supported Ni and Co Bimetallic Catalysts

Hydrodeoxygenation (HDO) of guaiacol, a typical lignin-derived phenolic compound, at relatively mild conditions was studied over γ-Al2O3 and ZSM-5 supported catalysts with Ni and/or Co as active metal. Among various catalysts, NiCo/γ-Al2O3 catalysts exhibited better guaiacol conversion up to 96.1% with cyclohexanol as the main product in aqueous, due to the proper acidity and interaction between metal particles and support. The effects of process parameters on guaiacol conversion and product distribution were investigated in detail associated with solvent effect. The cleavage of C–O bonds in guaiacol was investigated over NiCo/γ-Al2O3 catalysts in aqueous phase. Phenol was found as the main intermediate with 1-methyl-1,2-cyclohexanediol as another intermediate instead of 2-methoxy-cyclohexanol. The demethoxylation first happened to form phenol, and then, the aromatic ring was hydrogenated to give cyclohexanol after further hydrogenation of cyclohexanone.

Biotransformation of ferulic acid to protocatechuic acid by Corynebacterium glutamicum ATCC 21420 engineered to express vanillate O-demethylase

Ferulic acid (4-hydroxy-3-methoxycinnamic acid, FA) is a lignin-derived phenolic compound abundant in plant biomass. The utilization of FA and its conversion to valuable compounds is desired. Protocatechuic acid (3,4-dihydroxybenzoic acid, PCA) is a precursor of polymers and plastics and a constituent of food. A microbial conversion system to produce PCA from FA was developed in this study using a PCA-producing strain of Corynebacterium glutamicum F (ATCC 21420). C. glutamicum strain F grown at 30 °C for 48 h utilized 2 mM each of FA and vanillic acid (4-hydroxy-3-methoxybenzoic acid, VA) to produce PCA, which was secreted into the medium. FA may be catabolized by C. glutamicum through proposed (I) non-β-oxidative, CoA-dependent or (II) β-oxidative, CoA-dependent phenylpropanoid pathways. The conversion of VA to PCA is the last step in each pathway. Therefore, the vanillate O-demethylase gene (vanAB) from Corynebacterium efficiens NBRC 100395 was expressed in C. glutamicum F (designated strain FVan) cultured at 30 °C in AF medium containing FA. Strain C. glutamicum FVan converted 4.57 ± 0.07 mM of FA into 2.87 ± 0.01 mM PCA after 48 h with yields of 62.8% (mol/mol), and 6.91 mM (1064 mg/L) of PCA was produced from 16.0 mM of FA after 12 h of fed-batch biotransformation. Genomic analysis of C. glutamicum ATCC 21420 revealed that the PCA-utilization genes (pca cluster) were conserved in strain ATCC 21420 and that mutations were present in the PCA importer gene pcaK.

Hydrocarbons Production from Lignin-derived Phenolic Compounds over Ni/SiO 2 Catalyst

Abstract Ni-based catalysts supported on different supports (γ-Al2O3 and SiO2) were prepared by impregnation. Catalyst characterization was carried out by multiple methods. Effects of supports on catalytic performance were tested though the HDO of phenol. Experiment result shows that single phenolic compounds can be efficiently converted over Ni/SiO2 and Ni/γ-Al2O3 at 300 oC. The hydrocarbons yields are in the range of 60∼90%. When mixed phenolic compounds were used as feedstock, Ni/SiO2 catalyst also exhibits high catalytic activity and excellent repeatability. However, the catalytic activity of Ni/γ-Al2O3 decreased obviously in the HDO of mixed phenolic compounds. Deteriorated repeatability was also exhibited due to the formation of coke in the HDO process.

Analysis of lignin-derived phenolic compounds and their transformations in aged wine distillates

Aromatic aldehydes and acids derived from lignin were studied by capillary zone electrophoresis in barrel matured wine distillates used in brandy production. Different conditions of analysis were applied to set up the best separation and reproducibility. The optimal separation was performed using 25 mM borate buffer containing 8% v/v ethanol as modifier. Total amount of guaiacol-type compounds (coniferaldehyde, vanillin, and vanillic acid) and syringol-type compounds (sinapaldehyde, syringaldehyde, and syringic acid) increased with increasing ageing time for distillates aged from 1 to 25 years. Sum of concentrations of syringic and vanillic acids can be also used for characterizing aged distillates according to their ageing level. The developed analysis method is simple, precise and cost efficient. It provides good separation efficiency, and it is ideally suited for the analysis of aged wine distillates for determination of their overall quality, approximate ageing time and signs of counterfeiting.

Direct fast pyrolysis bio-oil fuel cell

Bio-oil derived from the pyrolysis of lignocellulosic biomass shows a great promise, however, needs further upgrading to potentially serve as an alternative to fossil fuels. Herein, we demonstrate that crude fast pyrolysis bio-oil can be directly used as a fuel for anion exchange membrane fuel cells (AEMFCs) to generate high power density electrical energy at low temperature (⩽80°C). A simple aqueous-phase reduction method was used to prepare carbon nanotube (CNT) supported noble metal (Pt, Pd, Au, and Ag) nanoparticles with average particle sizes: 1.4nm, 2.0nm, 3.8nm, and 12.9nm for Pt/CNT, Pd/CNT, Au/CNT, and Ag/CNT, respectively. Direct fast pyrolysis bio-oil AEMFCs with the Pd/CNT anode catalyst and a commercial Fe-based cathode catalyst exhibit a remarkable peak power density of 42.7mWcm−2 at 80°C using 30wt% bio-oil+6.0M KOH electrolyte. Levoglucosan was identified as the major sugar compound with 11.1wt% of the bio-oil composition, along with disaccharides, pyrolytic lignin, and oligomer of lignin-derived phenolic compounds. Cyclic voltammetry (CV) studies investigated the electrocatalytic oxidation of high purity levoglucosan over the four noble metal catalysts in half cell, as levoglucosan is the dominant sugar component in bio-oil. Pd/CNT, compared to other catalysts, displayed the highest activity and lowest onset potential of electrocatalytic oxidation of levoglucosan. AEMFC with high purity sugars shows ∼1.2 to 3 times higher power density than that with fast pyrolysis bio-oil fuel.

Ultra-high performance supercritical fluid chromatography of lignin-derived phenols from alkaline cupric oxide oxidation.

Traditional chromatographic methods for the analysis of lignin‐derived phenolic compounds in environmental samples are generally time consuming. In this work, an ultra‐high performance supercritical fluid chromatography method with a diode array detector for the analysis of major lignin‐derived phenolic compounds produced by alkaline cupric oxide oxidation was developed. In an analysis of a collection of 11 representative monomeric lignin phenolic compounds, all compounds were clearly separated within 6 min with excellent peak shapes, with a limit of detection of 0.5–2.5 μM, a limit of quantification of 2.5–5.0 μM, and a dynamic range of 5.0–2.0 mM (R 2 > 0.997). The new ultra‐high performance supercritical fluid chromatography method was also applied for the qualitative and quantitative analysis of lignin‐derived phenolic compounds obtained upon alkaline cupric oxide oxidation of a commercial humic acid. Ten out of the previous eleven model compounds could be quantified in the oxidized humic acid sample. The high separation power and short analysis time obtained demonstrate for the first time that supercritical fluid chromatography is a fast and reliable technique for the analysis of lignin‐derived phenols in complex environmental samples.

Using decalin and tetralin as hydrogen source for transfer hydrogenation of renewable lignin-derived phenolics over activated carbon supported Pd and Pt catalysts

Catalytic hydrogenation is considered as an efficient technique for upgrading pyrolysis bio-oil. High flammability of hydrogen gas in contact with air leads to difficult control of high pressurized hydrogen gas in large-scale systems. Meanwhile, molecular hydrogen production is a costly industrial process. Thus, hydrogenation study using hydrogen donor (H-donor) material as alternative for hydrogen gas could be useful in terms of cost and safety control. In this study, the potential of decalin and tetralin for use as hydrogen source was investigated in transfer hydrogenation of renewable lignin-derived phenolic compounds (phenol, o-cresol and guaiacol) and a simulated phenolic bio-oil over Pd/C and Pt/C catalysts. Reaction mechanisms of H-donor dehydrogenation and phenolics hydrogenation were studied. Catalytic activity of Pt/C for transfer hydrogenation of the phenolic compounds was higher than that of Pd/C at reaction temperature of 275 °C. Decalin as hydrogen source showed to be more efficient for hydrogenation of the phenolic compounds compared to tetralin. In addition, the influence of water content on transfer hydrogenation activity was studied by employing the water to donor ratios of 0/100, 25/75, 50/50 and 75/25 g/g. Maximum hydrogenation of phenol as bio-oil model compound was observed at water to donor ratio of 50/50 g/g.

Inhibition of lignin-derived phenolic compounds to cellulase.

BackgroundLignin-derived phenolic compounds are universal in the hydrolysate of pretreated lignocellulosic biomass. The phenolics reduce the efficiency of enzymatic hydrolysis and increase the cost of ethanol production. We investigated inhibition of phenolics on cellulase during enzymatic hydrolysis using vanillin as one of the typical lignin-derived phenolics and Avicel as cellulose substrate.ResultsAs vanillin concentration increased from 0 to 10 mg/mL, cellulose conversion after 72-h enzymatic hydrolysis decreased from 53 to 26 %. Enzyme deactivation and precipitation were detected with the vanillin addition. The enzyme concentration and activity consecutively decreased during hydrolysis, but the inhibition degree, expressed as the ratio of the cellulose conversion without vanillin to the conversion with vanillin (A0/A), was almost independent on hydrolysis time. Inhibition can be mitigated by increasing cellulose loading or cellulase concentration. The inhibition degree showed linear relationship with the vanillin concentration and exponential relationship with the cellulose loading and the cellulase concentration. The addition of calcium chloride, BSA, and Tween 80 did not release the inhibition of vanillin significantly. pH and temperature for hydrolysis also showed no significant impact on inhibition degree. The presence of hydroxyl group, carbonyl group, and methoxy group in phenolics affected the inhibition degree.ConclusionBesides phenolics concentration, other factors such as cellulose loading, enzyme concentration, and phenolic structure also affect the inhibition of cellulose conversion. Lignin-blocking agents have little effect on the inhibition effect of soluble phenolics, indicating that the inhibition mechanism of phenolics to enzyme is likely different from insoluble lignin. The inhibition of soluble phenolics can hardly be entirely removed by increasing enzyme concentration or adding blocking proteins due to the dispersity and multiple binding sites of phenolics than insoluble lignin.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-016-0485-2) contains supplementary material, which is available to authorized users.

Potential of genetically engineered hybrid poplar for pyrolytic production of bio-based phenolic compounds

Wild-type and two genetically engineered hybrid poplar lines were pyrolyzed in a micro-pyrolysis (Py-GC/MS) and a bench scale setup for fast and intermediate pyrolysis studies. Principal component analysis showed that the pyrolysis vapors obtained by micro-pyrolysis from wood of caffeic acid O-methyltransferase (COMT) and caffeoyl-CoA O-methyltransferase (CCoAOMT) down-regulated poplar trees differed significantly from the pyrolysis vapors obtained from non-transgenic control trees. Both fast micro-pyrolysis and intermediate pyrolysis of transgenic hybrid poplars showed that down-regulation of COMT can enhance the relative yield of guaiacyl lignin-derived products, while the relative yield of syringyl lignin-derived products was up to a factor 3 lower. This study indicates that lignin engineering via genetic modifications of genes involved in the phenylpropanoid and monolignol biosynthetic pathways can help to steer the pyrolytic production of guaiacyl and syringyl lignin-derived phenolic compounds such as guaiacol, 4-methylguaiacol, 4-ethylguaiacol, 4-vinylguaiacol, syringol, 4-vinylsyringol, and syringaldehyde present in the bio-oil.

Hydrogenation of lignin-derived phenolic compounds over step by step precipitated Ni/SiO2

An efficient and mild process for the hydrogenation of phenolic compounds over step by step precipitated Ni/SiO2 catalyst was presented.

Vapor-phase hydrodeoxygenation of guaiacol on Al-MCM-41 supported Ni and Co catalysts

Vapor-phase hydrodeoxygenation (HDO) of guaiacol, a typical lignin-derived phenolic compound, was studied on Al-MCM-41 supported Ni and Co catalysts at 400°C and atmospheric pressure. Ni was found as an active metal for ring opening activity while Co favored the deoxygenation activity. Besides benzene and phenol were observed as the major deoxygenation products, the existence of toluene, cresol and other methylated C7–12 products was the result of methyl transfer reaction over the acidic function of support. Co/Al-MCM-41 catalyzed not only HDO to remove oxygen but also transalkylation to prevent the carbon loss via methanization. In addition, coke deposit mainly gathered on the surrounding area of cobalt particles, leading to the faster deactivation in HDO activity than transalykation.

Mo2C catalyzed vapor phase hydrodeoxygenation of lignin-derived phenolic compound mixtures to aromatics under ambient pressure

High aromatics yield (>90%, benzene and toluene) was obtained from vapor phase hydrodeoxygenation (HDO) of phenolic compound mixtures containing m-cresol, anisole, 1,2-dimethoxybenzene, and guaiacol over molybdenum carbide catalysts (Mo2C) under atmospheric pressure at 533–553K, even with H2 to phenolic compound molar ratios of ∼3,300. Toluene selectivity increased proportionately (4%–66%) to m-cresol content in HDO of phenolic compound mixtures (molar composition: 0%–70%) at quantitative conversion. Phenol selectivity increased with decreasing conversion, implying that the aryl-methoxyl bond in guaiacol is cleaved first, before the aryl-hydroxyl bond. Low selectivity to cyclohexane and methylcyclohexane (<10%) across the conversions investigated (18–94%) demonstrates that undesired successive hydrogenation reactions of aromatics over Mo2C were inhibited, presumably due to in situ oxygen modification, as inferred from titration studies of aromatic hydrogenation reactions using methanol and water as titrants.

Stabilization of bio-oils using low temperature, low pressure hydrogenation

The superficial similarities between petroleum and bio-oil have encouraged efforts to employ petroleum hydroprocessing in the upgrading of bio-oil. Any facile comparison is overshadowed by the fact that petroleum consists of non-polar hydrocarbons that are relatively stable, requiring elevated temperatures and pressures to encourage chemical transformations, whereas bio-oil consists of oxygenated organic compounds whose high degree of functionality makes them chemically reactive even at low temperatures and pressures. Lignin-derived phenolic compounds readily polymerize and dehydrate to coke when hydroprocessed, resulting in low carbon yields of fuel range molecules and catalyst deactivation. In light of the limitations of conventional hydroprocessing, we explore low-temperature, low-pressure (LTLP) hydrogenation of pyrolysis-derived phenolics over 10% palladium on activated carbon (Pd/C) at 21°C and 1bar pressure as a way to produce stabilized bio-oil at high yields.

Production of Alkanes from Lignin-derived Phenolic Compounds over In Situ Formed Ni Catalyst with Solid Acid

Abstract In situ formed Ni catalyst combined with added solid acids is highly active for the hydrodeoxygenation of lignin-derived phenolic compounds. In the heterogeneous catalysts, in situ formed Ni acts as the hydrogenation and hydrogenolysis catalyst and solid acid acts as the dehydration catalyst.

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.

Production of Hydrocarbons via Hydrodeoxygenation of Lignin-Derived Phenolic Compounds

Lignin is the component with the highest carbon content in biomass. The transformation of lignin to high-grade liquid fuels can be achieved via hydrodeoxygenation(HDO) of phenolic intermediates derived from the products of lignin depolymerization. The octane numbers of the hydrodeoxygenation products of phenolic intermediates are quite high. They have vapor pressures and carbon atom number (C6 similar to C10) within the range of gasoline. Thus, these hydrodeoxygenation products would be the most desirable components for a fungible liquid transportation fuel. This is very meaningful to application of lignin. Recently, researches about the hydrodeoxygenation of phenolic compounds develop rapidly. In this paper, the HDO reactions of phenolic compounds using sulfided Mo-based catalyst, noble metal catalyst and inexpensive non-sulfided catalyst are reviewed in detail. It is found that most of the investigated catalysts are bifunctional catalysts, combining the hydrogenation function of active metal with hydrolysis and dehydration of support. The catalytic mechanism for the HDO of phenolic compounds is sketched, and the effects of catalyst supporter on the catalytic activity are also discussed. Furthermore, the current technique challenges are summarized, and future technologic explorations for the efficient hydrodeoxygenation of lignin-derived phenolic compounds are proposed.

Effects of Carbohydrates on the Hydrodeoxygenation of Lignin-Derived Phenolic Compounds

Simulating lignocellulose-derived pyrolysis oil, the effects of carbohydrate derivatives on the hydrodeoxygenation of lignin-derived phenolic compounds, guaiacol in this study, were observed using supported ruthenium catalysts. Among several carbohydrate derivatives which possibly exist in the pyrolysis oil, the addition of furfural and 5-hydroxymethylfurfural (5-HMF) significantly decreased the conversion of guaiacol, with density functional theory (DFT) calculations indicating that guaiacol competes with furfural and 5-HMF to adsorb onto the ruthenium nanoparticle surface, thus suppressing the hydrogenation of guaiacol.

Detailed characterization of red oak-derived pyrolysis oil: Integrated use of GC, HPLC, IC, GPC and Karl-Fischer

Red oak bio-oil obtained from fast pyrolysis in a fluidized bed reactor was fully analyzed using gas chromatography/mass spectrometry (GC/MS), high-performance liquid chromatography (HPLC), ion chromatography (IC), gel permeation chromatography (GPC) and Karl-Fischer titration. Based on the chemical speciation, we achieved a high mass balance closure of bio-oil (92wt%). Of the analytical techniques, GC accounted for the largest portion of the bio-oil (25.7wt%), followed by HPLC (15.4wt%) and IC (8.1wt%). Monosaccharides and disaccharides (not detected by GC) were characterized by HPLC, and total sugars present in bio-oil were estimated by running acid-hydrolysable sugars in the HPLC. Quantity of pyrolytic lignin, oligomer of lignin-derived phenolic compounds, was determined as a GC-undetected portion of water-insolubles of a whole bio-oil. Small standard deviation of each compound between duplicate runs indicated a reproducibility of pyrolysis experiments and bio-oil characterizations validating the detailed analytical approach used.

Towards Rational Design of Nanoparticle Catalysis in Ionic Liquids

This feature article introduces the strategies on the design of highly efficient nanoparticle (NP) catalytic systems in ionic liquids (ILs). The employment of functional ILs as the media for NP preparation and catalysis could prove advantageous in terms of enhancing both NP stability and catalytic activity. Hydroxyl group functionalized ILs, in particular, exhibited a remarkable promotion effect on a variety of reactions catalyzed by NPs, such as hydrogenation over Rh NPs, hydrodehalogenation over Pt NPs and Suzuki reaction over Pd NPs. In some cases, tailor-made stabilizer is used in addition to keep the NPs sufficiently stable. For example, a carboxylic group modified polyvinylpyrrolidone endows NPs three-fold stabilization, including steric, electrostatic and ligand stabilizations, which leads to excellent stability of the NPs. The catalytic activities of these NPs, on the other hand, are not compromised, as each of these stabilizations is not too strong. Following that, the article describes our recent work on the rational design of bimetallic NPs in ILs and the development of multifunctional systems involving NPs for a tandem reaction sequence that convert lignin-derived phenolic compounds into fuels.

Hydrodeoxygenation of lignin-derived phenolic compounds to hydrocarbons over Ni/SiO2–ZrO2 catalysts

Inexpensive non-sulfided Ni-based catalysts were evaluated for hydrodeoxygenation (HDO) using guaiacol as model compound. SiO2–ZrO2 (SZ), a complex oxide synthesized by precipitation method with different ratio of Si/Zr, was impregnated with Ni(NO3)2·6H2O and calcined at 500°C. Conversion rates and product distribution for guaiacol HDO at 200–340°C were determined. Guaiacol conversion reached the maximum at 300°C in the presence of Ni/SZ-3. When HDO reaction was carried out with real lignin-derived phenolic compounds under the optimal conditions determined for guaiacol, the total yield of hydrocarbons was 62.81%. These hydrocarbons were comprised of cyclohexane, alkyl-substituted cyclohexane and alkyl-substituted benzene. They have high octane number, would be the most desirable components for fungible liquid transportation fuel.