Phenolic Monomers Research Articles

1-ethyl-3-methyl imidazolium acetate, hemicellulolytic enzymes and laccase-mediator system: Toward an integrated co-valorization of polysaccharides and lignin from Miscanthus

The pretreatment of Miscanthus x giganteus with the ionic liquid 1-ethyl-3-methylimidazolium acetate ([Emim][OAc]), followed by enzymatic hydrolysis and oxidative depolymerization, resulted in the efficient production of monomeric sugars and selective production of phenolic intermediates. The liquid fractions containing monomeric sugars were obtained with high yields (>80%), while a solid fraction enriched with lignin (>50% w.w−1) was isolated. The phenolic monomers released during [Emim][OAc]-pretreatment were identified and quantified by HPLC. A decrease in the content of vanillin, vanillic acid, and p-hydroxybenzaldehyde was observed during pretreatment, suggesting a selective solubilization of guaicyl and p-hydroxyphenyl units from the lignin polymer in [Emim][OAc]. The decrease in p-coumaric and ferulic acids content suggested a cleavage of lignin-carbohydrate complexes during pretreatment. Both pretreatment and enzymatic hydrolysis affected the content of ferulic acid ether and ester bonds. The NMR structural study (2D HSQC) of the isolated lignin showed the preservation of β-O-4′ interunit bonds, while 31P NMR analysis revealed a high content of aliphatic hydroxyl groups. The oxidative depolymerization of the isolated lignin, catalyzed by the laccase mediator system in the presence of 5% v.v−1 recycled [Emim][OAc] in buffer, mainly led to the production of free p-hydroxybenzaldehyde as a promising platform molecule. The mass balance of glucan, xylan and lignin from Miscanthus was validated throughout this strategy.

Selective Conversion of Lignin Catalyzed by Palladium Supported on N-Doped Carbon

Highly selective conversion of lignin is essential to enable high-value utilization of lignin. Herein, we have prepared a palladium supported on N-doped carbon catalyst modified by 1,3,5-trimethylbenzene (TMB). The Pd nanoparticles are better dispersed on the TMB-modified catalyst than on the original catalyst. Therefore, the catalyst modified by TMB is more effective than the original catalyst in selectively converting lignin. When the organosolv lignin is catalyzed by 3 wt % Pd/CBFS-26-TMB (1:2) at 280 °C for 5 h, the yield of phenolic acid is 25.71 wt % and the biochar yield is only 4.5 wt %. Significantly, 52.59% of the phenolic acid monomers are 4-hydroxy-3,5-dimethoxyphenylacetic acid with a yield of 13.52 wt %. Thus, the catalyst 3 wt % Pd/CBFS-26-TMB (1:2) can effectively break the C–C and C–O bonds in the β–O–4 structure to convert lignin into 4-hydroxy-3,5-dimethoxyphenylacetic acid. We have also discussed the possible mechanism of lignin conversion into main products. This provides an essential approach for the high-value utilization of lignin.

A Na+-Dependent Mechanism Is Involved in Mucosal Uptake of Cinnamic Acid across the Jejunal Brush Border in Rats

Phenolic acids are present in all plant-derived foods and in most diets. Indirect evidence indicates substantial absorption of phenolic monomers from the gastrointestinal tract. However, the mechanisms involved in the absorptive process are unknown. The present study investigates mucosal uptake of radioactively labeled cinnamic acid as a model substance for monomeric cinnamic acid derivatives (e.g., cinnamic, ferulic or caffeic acid) in the rat jejunum using an in vitro mucosal uptake technique. The results indicate the existence of a Na+-dependent saturable transport mechanism for uptake of cinnamic acid across the jejunal brush border membrane. The observed Na+ dependence of jejunal cinnamate uptake seems not to be related to the activity of the Na+, H+ exchanger. Lowering the pH of the incubation medium resulted in a pronounced increase in mucosal cinnamate uptake that can be only partially explained by an increase in nonionic diffusion of cinnamic acid. Furthermore, jejunal uptake of cinnamate seems to be influenced by intracellular HCO3- and/or pH, since the addition of methazolamide to a HCO3- and CO2-free incubation medium significantly inhibited mucosal cinnamate uptake, whereas methazolamide was without an effect in the presence of HCO3- and CO2 in the incubation medium. Unlabeled cinnamic and ferulic acid as well as short-chain fatty acids (acetic, propionic and butyric acid) significantly inhibited Na+-dependent uptake of radioactively labeled cinnamic acid. Taken together, the results indicate the involvement of a Na+-dependent, carrier-mediated transport process in the uptake of cinnamic acid and structurally related substrates such as ferulic acid across the brush border membrane of rat jejunum.

High-performance depolymerization of lignin by bimetallic Cu-Ni@C catalysts prepared with MOF as a carrier under mild conditions

In this study, Cu was loaded on the surface of Ni-MOF by impregnation, and significantly improved the catalytic activity on lignin and its derivatives. The characterization showed that the non-noble bimetallic catalyst owned good dispersion, rich acid sites and stable structure was successfully synthesized. The introduced Cu reduced the reduction temperature of Ni, increased the acidity of the catalyst, and thus improved the catalytic performance and product selectivity of the catalyst. Under the mild conditions (120 °C), the conversion percentage of BPE was as high as 89.6 % using isopropyl alcohol as the hydrogen source. When the reaction temperature was 260 °C, the depolymerization percentage of corn cob lignin was 81.12 %, and the yield of phenol monomer could reach 11.46 wt. %. This work may provide an effective strategy for the preparation of efficient bimetallic catalysts for lignin hydrogenolysis.

Investigating wine astringency profiles by characterizing tannin fractions in Cabernet Sauvignon wines and model wines

Contribution of various phenols on wine astringency profiles was far from clear explanations. To effectively describe wine astringency profiles and determined the function of tannins/matrix (pH and ethanol), multiple chemical analyses combined RATA (Rate-all-that-apply) sensory method were applied in Cabernet Sauvignon and model wines. Results showed that polymeric flavanols determined the bulk of wine astringency intensity, oligomeric tannins enriched the smoothness and periodontium astringency, and monomeric phenol enhanced overall astringency intensity through synergistic effect. Astringency balance was effectively quantification, and its potential correlation relationship with epicatechin extension subunit (0.83) and fluorescence peak shift (0.75) cannot be ignored. The astringency profiles of condensed tannins with anthocyanins were enhanced. Low-pH (from 3.8 to 3.0) enhanced astringency by increasing the tannins affinity to proteins, while ethanol (from 10.0 % ∼ 15.0 %) decreased the hydrophobicity bond between tannins-protein interaction. This paper provided new insights to explain wine astringency profiles and a reference for astringency modification during winemaking.

Catalytic Depolymerization of Lignin for the Selective Production of Phenolic Monomers over Cobalt-Supported Calcium Catalysts

Catalytic Depolymerization of Lignin for the Selective Production of Phenolic Monomers over Cobalt-Supported Calcium Catalysts

Thiourea dioxide as a green reductant for selective depolymerization of lignin to guaiacol

Selective depolymerization of lignin is a key strategy for realizing high-value utilization of this natural renewable aromatic biopolymer. Degradation of lignin by the traditional technologies usually requires costly metal complex catalysts, and encounters poor monomer selectivity at present. Herein, a novel eco-friendly reduction system for high selectivity production of guaiacol directly from technical lignin by thiourea dioxide (TDO) assisted sodium hydroxide was reported. The experimental results of lignin and 2-phenoxy-1-phenylethanol depolymerization confirmed that the addition of TDO effectively promoted the cleavage of C-O bond of β-O-4-alcohols, and lignin was completely converted with minimal char formation of 2.73 wt% under relatively mild conditions. In addition, 4.91 wt% of phenolic monomers and 55.29 wt% of re-lignin were generated, and all with improved yields compared to the environment in the absence of TDO. Notably, the selectivity of guaiacol could amount to 64.77% in this reduction system, which is significantly higher than most reports of lignin depolymerization using noble metals, enabling value-increment utilization of technical lignin by means of low cost.

Complete Low-Temperature Transformation and Dissolution of the Three Main Components in Corn Straw.

The conversion of biomass faces the challenge of mass and heat transfer, as well as the exertion of heterogeneous catalyst, because raw biomass exists usually in solid state. In this work, the simultaneous transformation and dissolution of the three main components (hemicellulose, cellulose, lignin) in corn straw were achieved in ethanol/ valerolactone (GVL)/H2 O (10 : 10 : 40, v/v/v) co-solvent system. With the assistance of AlCl3 ⋅ 6H2 O, the conversion of hemicellulose, lignin and cellulose was >96 % at 170 °C. The conversion of solid biomass into fluid, overcoming the mass transfer restrictions between solid biomass and solid catalysts, provides new raw materials to further upgrading. H2 O could penetrate inside the crystalline cellulose to swell even dissolve it, while ethanol and GVL acted as media to dissolve especially the G unit in lignin. The H+ derived from AlCl3 ⋅ 6H2 O hydrolysis could break the linkages of lignin-hemicellulose and glycosidic bond in saccharides, and aluminum chloride promoted the next degradation of polysaccharides to small molecules. Consequently, as high as 33.2 % yield of levulinic acid and 42.2 % yield of furfural were obtained. The cleavage of β-O-4 and Cβ -Cγ bonds in lignin produced large amounts of lignin-derived dimers and trimers. The total yield of monomeric phenols is up to 8 %.

Metal supported hydrotalcite catalytic depolymerization of lignin: Effects of reaction parameter on compounds distribution

In this study different metal (Ni, Co and Fe) supported hydrotalcite catalysts were synthesis and it was used for lignin depolymerization. Catalytic pyrolysis reactions have been carried out at reaction temperature range of 400 to 550 °C, reaction time 30 to 120 min. with the presence of different amount of metal supported catalysts. From product distribution, it has been found that reaction temperature 500 °C was the optimal temperature for the production of maximum bio-oil yield of 32.4 wt% at reaction time of 60 min reaction. With the addition of the catalysts in pyrolysis, bio-oil significantly increased and maximum bio-oil (47.4 wt%) was found with cobalt supported hydrotalcite catalyst (Co/MgAl2O4). Other catalysts for example Ni/MgAl2O4 and Fe/MgAl2O4 catalyst exhibited bio-oil yield of 42.1 and 43.2 wt%. Different metals on MgAl2O4 showed different properties, which is affecting the lignin depolymerization during the pyrolysis. Catalytic pyrolysis produced higher amount of G-types phenolic monomer with higher bio-oil yield. This is suggesting that Co supported MgAl2O4 catalyst effectively breakdown the ether bond (COC) in the lignin. Elemental analysis and GPC of bio-oil was specified that the macromolecules structure of lignin depolymerized effectively with the using of catalysts. breaking of lignin macromolecule into small monomers phenolic compounds. Co/MgAl2O4 and Fe/MgAl2O4 was effectively encouraged the breaking of raw lignin into low molecular weight monomers as compared to others catalyst. Higher Mw and PDI were obtained for the Fe/MgAl2O4 catalytic pyrolysis reactions due to the repolymerization of monomers are promoted during pyrolysis.

Multicomponent graphene based catalysts for guaiacol upgrading in hydrothermal conditions: Exploring "H2-free" alternatives for bio-compounds hydrodeoxygenation

Catalytic hydrodeoxygenation (HDO) is a critical technique for upgrading biomass derivatives to deoxygenated fuels or other high-value compounds. Phenol, guaiacol, anisole, p-cresol, m-cresol and vanillin are all monomeric phenolics produced from lignin. Guaiacol is often utilised as a model lignin compound to deduce mechanistic information about the bio-oil upgrading process. Typically, a source of H2 is supplied as reactant for the HDO reaction. However, the H2 supply, due to the high cost of production and additional safety precautions needed for storage and transportation, imposes significant economic infeasibilities on the HDO process's scaling up. We investigated a novel H2-free hydrodeoxygenation (HDO) reaction of guaiacol at low temperatures and pressures, using water as both a reaction medium and hydrogen source. A variety of Ni catalysts supported on zirconia/graphene/with/without nitrogen doping were synthesised and evaluated at 250 °C and 300 °C in a batch reactor, with the goal of performing a multi-step tandem reaction including water splitting followed by HDO. The catalysts were characterised using H2-TPR, XRD, TEM and XPS to better understand the physicochemical properties and their correlation with catalytic performance of the samples in the HDO process. Indeed, our NiZr2O/Gr-n present the best activity/selectivity balance and it is deemed as a promising catalyst to conduct the H2-free HDO reaction. The catalyst reached commendable conversion levels and selectivity to mono-oxygenated compounds considering the very challenging reaction conditions. This innovative HDO approach provides a new avenue for cost-effective biomass upgrading.

Abatement of Aromatic Contaminants from Wastewater by a Heat/Persulfate Process Based on a Polymerization Mechanism.

A novel approach to the abatement of pollutants consisting of their conversion to separable solid polymers is explored by a heat/persulfate (PDS) process for the treatment of high-temperature wastewaters. During this process, a simultaneous decontamination and carbon recovery can be achieved with minimal use of PDS, which is significantly different from conventional degradation processes. The feasibility of this process is demonstrated by eight kinds of typical organic pollutants and by a real coking wastewater. For the treatment of the selected pollutants, 30.2-91.9% DOC abatement was achieved with 24.8-91.2% carbon recovery; meanwhile, only 5.2-47.0% of PDS was consumed compared to a conventional degradation process. For the treatment of a real coking wastewater, 71.0% DOC abatement was achieved with 66.0% carbon recovery. With phenol as a representative compound, our polymerization-based heat/PDS process is applicable in a wide pH range (3.5-9.0) with a carbon recovery of >87%. Both SO4•- and HO• can be initiators for polymerization, with different contribution ratios under various conditions. Phenol monomers are semioxidized to form phenolic radicals, which are polymerized via chain transfer or chain growth processes to form separable solid phenol polymers, benzenediol polymers, and cross-linked polymers.

Catalytic depolymerization of Kraft lignin to high yield alkylated-phenols over CoMo/SBA-15 catalyst in supercritical ethanol.

Lignin is generally considered to be a renewable and sustainable resource of aromatic chemicals. However, the depolymerization of Kraft lignin (KL) for the production of selective phenolic monomers presents a significant challenge due to its highly recalcitrant nature. Therefore, in this work, we investigated the effect of metal sites and acid active sites on Mo/SBA-15, Co/SBA-15 and CoMo/SBA-15 catalysts in supercritical ethanol for the depolymerization of KL to produce phenolic monomers. Ethanol was used as a hydrogen donor solvent instead of using external hydrogen. Results showed that the bimetallic CoMo/SBA-15 catalyst exhibited significantly higher catalytic activity compared to the monometallic, Co/SBA-15, Mo/SBA-15 or bare SBA-15. The highest phenolic monomers yield of 27.04 wt% was achieved at 290 °C for 4 h over CoMo/SBA-15 catalyst. The inter-unit linkages such as β-O-4', β-β and α-O-4' in lignin were considerably cleaved during the catalytic depolymerization in supercritical ethanol. Meanwhile, higher functionality of carbonyl compounds was present in the non-catalytic bio-oil, while more alkylated phenols were produced over CoMo/SBA-15 catalyst. The major phenolic monomers identified in the catalytic bio-oil were 4-ethylguaiacol (9.15 wt%), 4-methylguaiacol (6.80 wt%), and 4-propylguaiacol (2.85 wt%). These findings suggest that the metal sites and abundant acid active sites of CoMo/SBA-15 had a synergistic effect toward the degradation of different linkages of lignin and production of selective phenolic monomers in bio-oils.

Metal–organic framework-derived CuO catalysts for the efficient hydrogenolysis of hardwood lignin into phenolic monomers

The synergistic effects of the fabricated CuO/c-UiO-66 catalyst and hydrogen lead to the efficient scission of C–O bonds of the methoxylated β-O-4′ intermediates, transforming hardwood lignins into monophenols.

New insights into the base catalyzed depolymerization of technical lignins: a systematic comparison.

A first systematic approach on the base catalyzed depolymerization (BCD) of five technical lignins derived from various botanical origins (herbaceous, hardwood and softwood) and covering the main three industrial pulping methods (soda, kraft and organosolv) is reported. This study provides a first of its kind in-depth quantification and structural characterization of two main BCD fractions namely lignin oil and lignin residue, describing the influence of the BCD process conditions. Depolymerization is evaluated in terms of lignin conversion, lignin oil yield, phenolic monomer selectivity and the production of lignin residue and char. Lignin oils were extensively characterized by size exclusion chromatography (SEC), GC-MS, GC-FID, 13C-NMR, HSQC NMR and elemental analysis. GC × GC-FID was used to identify and quantify distinct groups of monomeric compounds (methoxy phenols, phenols, dihydroxy-benzenes) in the lignin oil. The lignin oil yields (w/w) ranged from 20-31% with total monomer contents ranging from 48 to 57% w/w. SEC analysis indicated the presence of dimers/oligomers in the lignin oil, which through HSQC NMR analysis were confirmed to contain new, non-native interunit linkages. 13C NMR analyses of the lignin oils suggest the presence of diaryl type linkages (i.e. aryl-aryl, aryl C-O) evidencing deconstruction and recombination of lignin fragments during BCD. Irrespective of the lignin source, a residue, often regarded as 'unreacted' residual lignin was the main product of BCD (43 to 70% w/w). Our study highlights that this residue has different structural properties and should not be considered as unreacted lignin, but rather as an alkali soluble condensed aromatic material. HSQC, DEPT-135, 13C, and 31P NMR and SEC analyses confirm that the BCD residues are indeed more condensed, with increased phenolic hydroxyl content and lower molecular weights compared to all feed lignins. Subsequent BCD of solid residual fractions produced only low oil yields (6-9% w/w) with lower phenolic monomer yields (4% w/w) compared to original lignin, confirming the significantly more recalcitrant structure. Our study improves the overall understanding of the BCD process, highlights important feedstock-dependent outcomes and ultimately contributes to the complete valorization of BCD-derived lignin streams.

Use of Ionic Liquid-Based Ultrasound Assisted Liquid-Liquid Extraction of Phenols from Aqueous Fractions of Seed Bio-Oil

The liquid product of the pyrolysis of biomass is a mixture of an organic phase and other aqueous, being the last one rich in phenol monomers which can be used in industrial chemistry as input for plastic and resin production. This work aimed to develop a method for extracting phenols present in the aqueous fraction obtained from the pyrolysis of guava seeds, using ultrasonic assisted liquid-liquid extraction (UALLE) with ethyl acetate and ionic liquids (ILs) as co-solvents (1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl) amide (BMIM.NTF2) and 1-butyl-3-methylimidazolinium hexafluorophosphate (BMIM.PF6)). The percentage IL, ultrasonic bath potency, temperature, and pH were studied. Quantification of twelve phenol monomers was performed using gas chromatography-mass spectrometry (GC-MS) and the total phenol concentration (TPC) was performed using UV-Vis spectrophotometer. The ionic liquid BMIM.NTF2 was more efficient for phenol extraction than BMIM.PF6. The phenolic extractions were influenced by the pH of the aqueous fraction (higher extraction yields at pH ≤ 7), and thus, presented recoveries above 80% for both ionic liquids.

Hydrodeoxygenation of guaiacol to phenol using endogenous hydrogen induced by chemo-splitting of water over a versatile nano-porous Ni catalyst

In this work, an innovative route for upgrading biomass-derived phenolic monomers by “hydrogen-free” hydrodeoxygenation (HDO) was proposed and evaluated.

Ultrasound-assisted low-temperature catalytic lignin-first depolymerization of pine wood biomass to selectively produce propyl guaiacol

Lignin-first depolymerization of biomass using reductive catalytic fractionation is a promising option for the biorefinery as it selectively converts lignin to value-added phenolic monomers while preserving the carbohydrate fraction.

Lignin-first biorefinery approach for the valorization of cotton stalks to phenolic monomers

Cotton stalks were fractionated using a lignin-first biorefinery approach by converting lignin to phenolic monomers and carbohydrates to functional carbon(s).

Acid-promoted lignin reductive depolymerization under mild conditions via a condensation minimizing approach: From organosolv lignin to woody biomass

Lignin reductive depolymerization into phenolic monomers is a critical step for the scale-conversion of lignin into liquid fuels but its scale-up is still compromised by harsh reaction conditions (e.g. high temperature and high external H2 pressure) and inevitable condensations. Herein, we present an efficient acid-promoted reductive depolymerization of lignin over Ni/C without external H2 via a condensation minimizing approach using lignin monomer analogue (p-hydroxybenzyl alcohol, HBA) as the capping agent. With addition of 0.4 % H2SO4 and 0.4 mmol/g HBA, 20.42 % of phenolic monomer yield along with 31.70 % oligomer yield was achieved at 160 °C while the condensated/undepolymerized lignin yield was less than 10 %. HBA inhibited the acid-induced condensation by competitive reaction with the nucleophilic C6 in guaiacyl unit. When the approach was applied in lignin-first reductive fractionation of poplar, 32.72 % of phenolic monomer yield and 76.59 % of delignification were achieved at 160 °C in the presence of acid and HBA. Additionally, xylan was dissociated concurrently owing to the acid-catalyzed hydrolysis, resulting in a cellulose-rich solid residue. Consequently, this work proposes an efficient approach for lignin reductive depolymerization and lignin-first biomass fractionation under mild conditions through the synergism of acid and capping agent.

Biosynthetic melanin with excellent performance can be used for heavy metal adsorption

Melanin is a complex polymer composed of indole and/or phenolic monomers, which show the potential to adsorb heavy metals in water due to their numerous functional groups. However, the artificial synthesis of melanin is difficult and the natural sources are limited. In this study, we screened the filamentous fungus Stachybotrys sp. HSS-1 to produce 11.56 g/L melanin M1 after fermentation optimization. M1 was identified as eumelanin using UV spectroscopy, elemental analysis, HPLC-MS, infrared spectroscopy, and nuclear magnetic resonance. Melanin M1 nano-materials showed the ability to adsorb the heavy metals Cd2+, Cu2+ and Pb2+ in water; in particular, the adsorption upper limit of Pb2+ reached 45 mg/g. Melanin M1 nano-materials also exhibited excellent thermal stability and radiation resistance, with a residual rate of 96.46% after heating at 100 °C for 2 h and more than 98% after 60 min of UV irradiation and 5 d of sunlight exposure. In addition, melanin M1 nano-materials strongly inhibited Staphylococcus aureus, Bacillus megaterium, and Salmonella, and the scavenging rates of 1 g/L M1 on superoxide radicals and hydroxyl radicals in the solution reached 97.33% and 98.59%, respectively. Therefore, melanin M1 nano-materials can not only adsorb heavy metals but also show the ability to resist the complex natural environment. Overall, this study developed high-yield, stable microbial melanin nano-materials that was shown to be an excellent adsorbent for heavy metal removal from water.