Lignin-derived Compounds Research Articles

The selective hydrodeoxygenation of guaiacol to cyclohexanol over cobalt-modified TS-1 catalysts

A Co-modified zeolite (Co/TS-1) catalyst is prepared and evaluated for the catalytic hydrodeoxygenation (HDO) of the lignin-derived model compound guaiacol under mild conditions at 1 MPa H2 and 200 °C. According to the systemic experimental investigations including reduction temperatures, metal loading and reaction time, it is found that the guaiacol conversion and cyclohexanol selectivity over guaiacol HDO are significantly improved by regulating the Ti content, Co content and reduction temperature, in which 5.0%Co/TS-1 (Si/Ti = 110) reduced in 600 °C shows the superior HDO performance with 94.3% guaiacol conversion and 88.7% cyclohexanol selectivity. Combined with XRD, TEM, BET, NH3-TPD, Py-IR, H2-TPR, UV–Vis and XPS characterizations, it is confirmed that the introduction of appropriate Ti could modulate the catalyst Lewis acid sites and the interaction between Co and support to affect the metal reduction degree, to realize the improvement of the substrate adsorption and exposing more metallic Co0 active sites, resulting in higher HDO performance. In addition, the reaction pathway of guaiacol HDO to cyclohexanol over Co/TS-1 is proposed via demethoxylation of guaiacol to generate reaction intermediate phenol.

Structure- and computational-aided engineering of an oxidase to produce isoeugenol from a lignin-derived compound

Various 4-alkylphenols can be easily obtained through reductive catalytic fractionation of lignocellulosic biomass. Selective dehydrogenation of 4-n-propylguaiacol results in the formation of isoeugenol, a valuable flavor and fragrance molecule and versatile precursor compound. Here we present the engineering of a bacterial eugenol oxidase to catalyze this reaction. Five mutations, identified from computational predictions, are first introduced to render the enzyme more thermostable. Other mutations are then added and analyzed to enhance chemoselectivity and activity. Structural insight demonstrates that the slow catalytic activity of an otherwise promising enzyme variant is due the formation of a slowly-decaying covalent substrate-flavin cofactor adduct that can be remedied by targeted residue changes. The final engineered variant comprises eight mutations, is thermostable, displays good activity and acts as a highly chemoselective 4-n-propylguaiacol oxidase. We lastly use our engineered biocatalyst in an illustrative preparative reaction at gram-scale. Our findings show that a natural enzyme can be redesigned into a tailored biocatalyst capable of valorizing lignin-based monophenols.

Crop rotational diversity alters the composition of stabilized soil organic matter compounds in soil physical fractions

Crop rotational diversity is an important part of sustainable agricultural and soil management to improve crop yield and soil fertility including enhancing soil organic matter (SOM) stabilization. Because of the physical protection via interactions with soil minerals, SOM in mineral-associated fractions is believed to be longer-lived and more stable relative to SOM in particulate (light) fractions. However, it is still unclear how crop rotational diversity alters soil carbon distribution, composition and stabilization in soil physical fractions. To address this, we studied a 37 years’ agricultural site with different crop rotational diversity (from continuous corn or alfalfa up to four species (corn, soybean, winter wheat, and red clover)). Soil carbon analysis, targeted compound analysis and nuclear magnetic resonance spectroscopy methods were used to obtain the distribution and degradation of SOM components in light and mineral-associated (F53–2000 µm, F2–53 µm, and F<2 µm) fractions. Higher soil organic carbon (SOC) concentrations were observed in F<2 µm with relatively high diversified crop rotations (three and four types of crops) compared to monoculture or two crops in the rotations, which suggests that carbon storage is enhanced in mineral-stabilized pools. Higher concentrations of long-chain aliphatic compounds as well as increased accumulation and preservation of lignin-derived compounds in fine aggregates (<53 µm) were also observed with relatively high diversified crop rotations. Overall, the increased concentration and preservation of specific SOM compounds as well as increased SOC in finer mineral-associated fractions (<53 µm) suggests that crop rotational diversity may enhance the long-term stability of SOM in agroecosystems.

Energy-Resolved Mass Spectrometry as a Tool for Identification of Lignin Depolymerization Products.

Lignin is the largest source of bio-based aromatic compounds in nature, and its valorization is essential to the sustainability of lignocellulosic biorefining. Characterizing lignin-derived compounds remains challenging due to the heterogeneity of this biopolymer. Tandem mass spectrometry is a promising tool for lignin structural analytics, as fragmentation patterns of model compounds can be extrapolated to identify characteristic moieties in complex samples. This work extended previous resonance excitation-type collision-induced dissociation (CID) methods that identified lignin oligomers containing β-O-4, β-5, and β-β bonds, to also identify characteristics of 5-5, β-1, and 4-O-5 dimers, enabled by quadrupole time-of-flight (QTOF) CID with energy-resolved mass spectrometry (ERMS). Overall, QTOF-ERMS offers in-depth structural information and could ultimately contribute to tools for high-throughput lignin dimer identification.

Unveiling the role of surface basic sites on ruthenium-based nanocatalysts for enhanced hydrodeoxygenation of guaiacol

Presently, it is well-recognized that surface acidic sites on supported metal catalysts play an important role in promoting the hydrodeoxygenation (HDO) of lignin-derived phenolic compounds. In the present work, new insights into the promotion role of surface basic sites on the catalytic performance of MgO-decorated nanostructured ZrO2 supported Ru nanocatalysts in the HDO of guaiacol were attained. It was found that the adsorption capacity of guaiacol and the HDO ability increased with the density of surface basic sites on as-modified Ru-based catalysts. Combining surface-interface microstructural characterizations of Ru-based catalysts and catalytic testing results with in-situ diffused reflectance infrared Fourier transform spectroscopy of guaiacol adsorption, it was unveiled that surface basic sites induced by the introduction of MgO on the ZrO2 surface could favor the preferential adsorption of guaiacol through the hydroxyl group interacting with surface basic sites and thus simultaneously the indirect activation of the Cring-OCH3 bond, thereby boosting the guaiacol HDO to produce cyclohexanol via the demethoxylation and following ring-hydrogenation processes. The present study may provide a promising strategy to design next generation supported metal catalysts with the improved surface basicity for the HDO of lignocellulose-derived phenolic derivates.

An integrated olive stone biorefinery based on a two-step fractionation strategy

Olive stones (OS) constitute a waste lignocellulosic material produced by the olive oil industry in great amounts, that currently is only used as a low-value energy source for industrial or domestic boilers. Having in view its full valorization, this work proposes and validates an integrated strategy aiming to obtain three different streams of sugars / lignin-derived compounds. Dilute acid hydrolysis was used to obtain a xylose-rich hydroysate that was chemically converted into furfural with a 48.7 % yield. The resulting acid-pretreated solid biomass that consisted mainly of lignin and cellulose, was subjected to a catalyzed ethanol-based organosolv delignification. Temperature, time, and sulphuric acid concentration were optimized in order to recover added-value lignin products and digestible cellulose.

리그노셀룰로오스의 혐기성 분해에 의한 탄수화물과 방향족 화합물의 축적속도 평가

This study evaluated the degradation properties of lignocellulose in methanogenic and sulfate-reducing environment. Carbohydrates and aromatic compounds, which are lignocellulosic degradation products, were analyzed and the accumulation rates were calculated. Seeding microorganisms, as well as leachate from a model landfill reactor composed of a methanogenic and sulfate-reducing environment that hadbeen operatingfor more than three years wereused. To calculate the accumulation rates of carbohydrates and aromatic compounds, serum vials cultured for 12 days were subjected to 3% (volume ratio) toluene. Toluene was used to selectively inhibit the activity of microorganisms while maintaining the activity of the extracellular degrading enzyme. Galactose, glucose, xylose and mannose produced from holocellulose such as office paper and newspaper in the presence of 3% toluene showed a linear increase in carbohydrate accumulation with time in a sulfate-reducing environment. The accumulation rates of glucose and xylose in the sulfate-reducing environment were faster than in the methanogenic environment, indicating that holocellulose decomposition was faster in the sulfate-reducing environment than in the methanogenic environment. For the lignin-derived aromatic compounds produced in newspapers in the presence of 3% toluene, 7 aromatic compounds were identified in the sulfate-reducing environment, compared to 3 aromatic compounds identified in the methanogenic environment. Accumulation rates of benzoic acid and vanillin were faster in the sulfate-reducing environment than in the methanogenic environment, indicating that lignin degradation was faster in the sulfate-reducing environment than in the methanogenic environment.

Measurement and summary of photoionization data for biomass-derived compounds.

Biomass is a potential feedstock for making liquid fuels and valuable chemicals. Quantitative analysis of biomass conversion in real time by photoionization mass spectrometry (PIMS) is an important way to understand the reaction process. However, the lack of photoionization data for biomass-derived compounds limits the research using PIMS. Measurements of photoionization data were performed with synchrotron vacuum ultraviolet PIMS. Toluene and methanol were used as calibrated references and solvents in this experiment since their photoionization cross-sections (PICS) are well documented in the literature. The ionization energies (IEs) of 23 biomass-derived compounds were measured. Among them, the PICSs of 14 compounds were calibrated and presented. Besides, the IEs of 95 other biomass-derived compounds and their typical fragment ions were also summarized. A photoionization database related to IEs and PICSs of biomass-derived compounds (m/z < 200) is established. PICSs of most biomass-derived compounds have low values at the most frequently used photoionization energy of 10.5eV. Lignin-derived compounds have lower IEs than carbohydrate-derived compounds.

Improving liquid chromatography-mass spectrometry sensitivity for characterization of lignin oligomers and phenolic compounds using acetic acid as a mobile phase additive

Characterization of complex lignin degradation products by liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) requires a high sensitivity, which can be improved by use of optimized mobile phase additive. In this study, chromatographic separation and ionization efficiency for LC-MS analysis of lignin oligomers and lignin-derived phenolic compounds were compared among six different mobile phase additives. We found that acetic acid exhibits analytical performance superior to the other mobile phase additives for characterization of lignin degradation products by LC-(−)-ESI-MS/MS. The retention of phenolic compounds (PCs) containing carboxylic group was improved by using acidic additives instead of their ammonium salts. The use of acetic acid as an LC mobile phase additive enhanced the ionization efficiency of PCs in (−)-ESI-MS about 2 to 4 times higher than the other additives. The improved MS sensitivity with acetic acid yielded a higher coverage of fragment ions in LC-MS/MS analysis, leading to identification of four additional synthetic G-type lignin oligomers (LOs) than ammonium acetate. A similar degree of sensitivity enhancement was also demonstrated for degradation products from rice straw lignin using acetic acid additive over the others. The increased chromatographic retention and enhanced sensitivity of PCs and LOs provided by the use of acetic acid as an LC-(−)-ESI-MS mobile phase additive will facilitate structural analysis of lignin degradation products without relying on additional instrumentation.

Hydrodeoxygenation of lignin-derived phenolic compounds over Ru/TiO2 catalyst: Effect of TiO2 morphology

Hydrodeoxygenation (HDO) reaction is a necessary refinery process for lignin-derived phenolic compounds to be used as high quality liquid fuels. Catalyst morphology makes a big difference on the HDO performance through changing the properties of metal site and acid site, while the catalytic mechanism is still not very clear. In this work, four kinds of Ru/TiO2 catalysts with different morphology were prepared by photochemical method and all of them achieved a high Ru metal dispersion. A series of catalyst characterizations were carried out, including XRD, BET, SEM, TEM, H2-TPD and NH3-TPD, in order to explore the crystal structure, surface property, Ru metal dispersion, hydrogen adsorption capacity as well as acid properties. Results showed that Ru/TNP catalyst possessed a large surface area, an abundance of medium strength acid sites and a good hydrogen adsorption capacity. The HDO performances on lignin-derived phenolic compounds were also compared, in which Ru/TNP catalyst presented the best HDO performance. The guaiacol conversion and the selectivity of cyclohexane product were both close to 100 % at 250 °C under 1 MPa hydrogen pressure. Moreover, the content of hydrocarbons increased from 11.1 % to 60.8 % in the lignin-oil upgrading process.

Bacterial catabolism of acetovanillone, a lignin-derived compound

Bacterial catabolic pathways have considerable potential as industrial biocatalysts for the valorization of lignin, a major component of plant-derived biomass. Here, we describe a pathway responsible for the catabolism of acetovanillone, a major component of several industrial lignin streams. Rhodococcus rhodochrous GD02 was previously isolated for growth on acetovanillone. A high-quality genome sequence of GD02 was generated. Transcriptomic analyses revealed a cluster of eight genes up-regulated during growth on acetovanillone and 4-hydroxyacetophenone, as well as a two-gene cluster up-regulated during growth on acetophenone. Bioinformatic analyses predicted that the hydroxyphenylethanone (Hpe) pathway proceeds via phosphorylation and carboxylation, before β-elimination yields vanillate from acetovanillone or 4-hydroxybenzoate from 4-hydroxyacetophenone. Consistent with this prediction, the kinase, HpeHI, phosphorylated acetovanillone and 4-hydroxyacetophenone. Furthermore, HpeCBA, a biotin-dependent enzyme, catalyzed the ATP-dependent carboxylation of 4-phospho-acetovanillone but not acetovanillone. The carboxylase's specificity for 4-phospho-acetophenone (kcat/KM = 34 ± 2 mM-1 s-1) was approximately an order of magnitude higher than for 4-phospho-acetovanillone. HpeD catalyzed the efficient dephosphorylation of the carboxylated products. GD02 grew on a preparation of pine lignin produced by oxidative catalytic fractionation, depleting all of the acetovanillone, vanillin, and vanillate. Genomic and metagenomic searches indicated that the Hpe pathway occurs in a relatively small number of bacteria. This study facilitates the design of bacterial strains for biocatalytic applications by identifying a pathway for the degradation of acetovanillone.

Effect of the Support on Rhenium Carbide in the Hydrodeoxygenation of Guaiacol as Lignin-Derived Model Compound

The effect of support on the formation of rhenium carbide in the hydrodeoxygenation (HDO) of guaiacol as a lignin-derived compound was evaluated. Catalysts were prepared by incipient wetness impregnation, carburized at 650 °C under a mixture 25/75 of ethylene/hydrogen, and characterized by XRD, N2-physisorption, TPR, TPD of NH3 or isopropylamine (IPA), and XPS. The results have demonstrated that the support choice affects the carburization of rhenium. Indeed, over non-acidic support (e.g., SiO2), limited carburization of the metal was observed, while over ZrO2 and Al2O3, carburization of rhenium occurred, and different carbidic species were obtained depending on the surface and chemical identity of the support. The rhenium carbide species obtained over ZrO2 was the most active and selective toward benzene (22% at 98% of conversion).

Bacterial diversity in aerated facultative lagoon treating kraft cellulose effluent with bioaugmentation

The microbiological diversity was evaluated in an aerated facultative lagoon system with organic loading rates of 0.2 and 0.6 kgCODm-3d-1 treating effluent from the kraft pulp industry for bioaugmentation purposes. Samples were taken from a laboratory-scale lagoon at steady state treating kraft pulp effluent and operated with two different rates for 120 days. The analysis was performed by 16S rDNA sequencing. The autochthonous bacteria were identified through statistical similarity obtained from the NCBI-BLAST database. The lagoon performance was assessed based on the removal efficiency of biochemical oxygen demand (94% and 80%), chemical oxygen demand (51% and 44%), total organic carbon (49% and 41%), lignin-derived compounds (13% and 27%), turbidity (94% and 87%), for the low and high rates used respectively. Color and TPC were not significantly removed during the biological treatment of the industrial matrix. In the biomass samples collected at a steady state, 9 and 12 species of bacteria were identified at the applied rates. The species Bacillus cereus, Bacillus thuringiensis, and Paenibacillus glucanolyticus found in this matrix presented significant removal of the parameters in the kraft effluent. The three referred species show great promise in the removal of specific parameters in an AFL biological treatment system using bioaugmentation.

Continuous hydrodeoxygenation of lignin to jet-range aromatic hydrocarbons

<h2>Summary</h2> Sustainable aviation fuel (SAF) is essential to decrease the carbon footprint of the aviation industry. Although many strategies have been developed to provide the linear and branched aliphatic components of SAF, few viable strategies have been demonstrated to supply the aromatic and cycloalkane fraction of the SAF at the necessary scale from bio-based feedstocks. Lignin is the largest natural source of renewable aromatic compounds; however, major challenges in deoxygenation have prevented its use as a feedstock for SAFs. Here, we report a continuous, two-stage catalytic process using molybdenum carbide to deoxygenate lignin from poplar into aromatic hydrocarbons with 87.5% selectivity toward aromatic hydrocarbons at 86% of the theoretical carbon recovery. Tier α fuel property testing indicates that the SAF-range lignin-derived aromatic compounds are likely performance-advantaged across multiple properties relative to conventional jet fuel aromatic compounds. This work demonstrates an effective approach to convert lignin into aromatic SAF blendstocks.

Novel bacterial taxa in a minimal lignocellulolytic consortium and their potential for lignin and plastics transformation.

The understanding and manipulation of microbial communities toward the conversion of lignocellulose and plastics are topics of interest in microbial ecology and biotechnology. In this study, the polymer-degrading capability of a minimal lignocellulolytic microbial consortium (MELMC) was explored by genome-resolved metagenomics. The MELMC was mostly composed (>90%) of three bacterial members (Pseudomonas protegens; Pristimantibacillus lignocellulolyticus gen. nov., sp. nov; and Ochrobactrum gambitense sp. nov) recognized by their high-quality metagenome-assembled genomes (MAGs). Functional annotation of these MAGs revealed that Pr. lignocellulolyticus could be involved in cellulose and xylan deconstruction, whereas Ps. protegens could catabolize lignin-derived chemical compounds. The capacity of the MELMC to transform synthetic plastics was assessed by two strategies: (i) annotation of MAGs against databases containing plastic-transforming enzymes; and (ii) predicting enzymatic activity based on chemical structural similarities between lignin- and plastics-derived chemical compounds, using Simplified Molecular-Input Line-Entry System and Tanimoto coefficients. Enzymes involved in the depolymerization of polyurethane and polybutylene adipate terephthalate were found to be encoded by Ps. protegens, which could catabolize phthalates and terephthalic acid. The axenic culture of Ps. protegens grew on polyhydroxyalkanoate (PHA) nanoparticles and might be a suitable species for the industrial production of PHAs in the context of lignin and plastic upcycling.

Toward Value-Added Arenes from Lignin-Derived Phenolic Compounds via Catalytic Hydrodeoxygenation

Toward Value-Added Arenes from Lignin-Derived Phenolic Compounds via Catalytic Hydrodeoxygenation

Selective production of aromatics from catalytic pyrolysis of biomass wastes: Effects of feedstock properties and key oxygenated intermediates on aromatics formation

The catalytic pyrolysis is a promising method for obtaining value-added aromatics, especially benzene, toluene and xylene (BTX). For different biomass-based materials, the dual catalyst system composed of CaO-based and ZSM-5-based catalysts showed an obvious selectivity for the BTX production. This study chose CaO derived from organic calcium precursors (Org-CaO) and nano-sized ZSM-5 (NZSM-5), and comprehensively investigated the effects mechanism of biomass components on the formation pathways of BTX via Py-GC/MS. Under the catalysis of NZSM-5, the BTX yields were only 7.8–30%. The BTX yields on Org-CaO/NZSM-5 were as follows: lipid (63.1%) > hemicellulose (55.4%) > cellulose (40.2%) > lignin (21.7%). Typical pyrolysis intermediates were employed to quantitatively reveal the intermediate reactions. Pyrolysis intermediates exhibited low BTX-forming reactivity over NZSM-5. The pre-catalysis of Org-CaO selectively converted part undesired intermediates (fatty acids and furans) into BTX precursors (short-chain olefins and ketones), facilitating the remarkable increase of BTX yield in the subsequent NZSM-5 catalysis process. However, the pre-catalysis of Org-CaO can hardly make the ring opening reaction of lignin-derived phenolic compounds that have very low reactivity on NZSM-5, and thence high-lignin biomass obtained low BTX production during catalytic pyrolysis by Org-CaO/NZSM-5. These findings afforded a new route for increasing the BTX yields by directionally forming BTX precursors or controlling biomass components.

Superhydrophobic Ru Catalyst for Highly Efficient Hydrogenation of Phenol under Mild Aqueous Conditions

Selective hydrogenations of lignin-derived phenolic compounds represent essential processes in the chemical industry, especially for production of a multitude of fine chemicals. However, selective hydrogenation of phenolic compounds in water phase suffers from low conversion. Here we report a catalyst of well-dispersed Ru clusters fixed in N-doped mesoporous hollow carbon spheres (Ru@N-CS) for enhanced cyclohexanol productivity in phenol hydrogenation at mild aqueous condition. This superhydrophobicity carbon spheres appear to selectively allow diffusion of phenol and hydrogen molecules to the electron-rich coordination unsaturated Ru active sites, while confining the reactants there to enhance its reaction probability. The Ru@N-CS catalyst can selectively hydrogenate phenol at 80 °C and 0.5 MPa of H2 in 30 min in aqueous medium with phenol conversions of 100% and ~100% cyclohexanol selectivity, corresponding to cyclohexanol productivity up to 471 per g of Ru per minute. The TOF value is up to 9980 h−1, which 14 times more than Ru nanoparticles supported on N-doped carbon hollow spheres (Ru/N-CS). This work provides an important catalytic system for upgrading of bio-oil into value-added chemicals under mild aqueous-phase.

Dynamic and single cell characterization of a CRISPR-interference toolset in Pseudomonas putida KT2440 for β-ketoadipate production from p-coumarate

Pseudomonas putida KT2440 is a well-studied bacterium for the conversion of lignin-derived aromatic compounds to bioproducts. The development of advanced genetic tools in P. putida has reduced the turnaround time for hypothesis testing and enabled the construction of strains capable of producing various products of interest. Here, we evaluate an inducible CRISPR-interference (CRISPRi) toolset on fluorescent, essential, and metabolic targets. Nuclease-deficient Cas9 (dCas9) expressed with the arabinose (8K)-inducible promoter was shown to be tightly regulated across various media conditions and when targeting essential genes. In addition to bulk growth data, single cell time lapse microscopy was conducted, which revealed intrinsic heterogeneity in knockdown rate within an isoclonal population. The dynamics of knockdown were studied across genomic targets in exponentially-growing cells, revealing a universal 1.75 ± 0.38 h quiescent phase after induction where 1.5 ± 0.35 doublings occur before a phenotypic response is observed. To demonstrate application of this CRISPRi toolset, β-ketoadipate, a monomer for performance-advantaged nylon, was produced at a 4.39 ± 0.5 g/L and yield of 0.76 ± 0.10 mol/mol from p-coumarate, a hydroxycinnamic acid that can be derived from grasses. These cultivation metrics were achieved by using the higher strength IPTG (1K)-inducible promoter to knockdown the pcaIJ operon in the βKA pathway during early exponential phase. This allowed the majority of the carbon to be shunted into the desired product while eliminating the need for a supplemental carbon and energy source to support growth and maintenance.

Funneling lignin-derived compounds into polyhydroxyalkanoate by Halomonas sp. Y3

Lignin-derived compounds (LDCs) biological funneling for polyhydroxyalkanoate (PHA) synthesis has been attractive but elusive. Herein, the Halomonas sp. Y3 is isolated and developed for PHA production from LDCs. Of the tested 13 LDCs, 4-hydroxybenzoic acid (4-HBA), protocatechuate (PA), catechol (CAT), and vanillic acid (VA) exhibit a hyper-degradation and production with 87.2 %, 85.8 %, 84.7 %, and 83.4 % TOC removal rate and 535.2 mg/L, 506.5 mg/L, 435.6 mg/L, and 440.8 mg/L PHA concentration, respectively. The Halomonas sp. Y3 genome is sequenced by identifying numerous genes responsible for LDCs funneling, stress response, and PHA biosynthesis. An open unsterilized fermentation with optimal conditions of pH 9.0 and NaCl 60 g/L is investigated, achieving a completely aseptic effect and significantly improved PHA production from LDCs. Overall, the results indicate that the Halomonas sp. Y3 is an ideal candidate for LDC bioconversion and exhibits a great potential to realize black liquor valorization.