Biomass Model Compounds Research Articles

Cu(II) Coordination Polymers for the Selective Oxidation of Biomass-Derived Veratryl Alcohol in Green Solvents: A Sustainable Catalytic Approach.

Four air-stable one-dimensional copper(II) coordination polymers (CP1-CP4) with azide linkers were synthesized using tridentate NNS and NNN ligands. Single-crystal X-ray diffraction (XRD) analysis confirmed the molecular structures of CP1, CP3, and CP4. In the presence of TEMPO, all four coordination polymers demonstrated effective catalytic activity for the selective aerobic oxidation of veratryl alcohol, a biomass model compound, under base-free conditions. CP4 exhibited the best catalytic efficiency. Oxidations were conducted at ambient temperature (40 °C) utilizing air as a sustainable oxidant. Selective oxidation of veratryl alcohol to veratraldehyde was also conducted in the presence of a catalytic amount of base (5 mol %), and enhanced reactivity was observed. The green solvents, acetone, and water, were used to maximize sustainability. The optimized reaction conditions were applied to broaden the substrate scope of various lignin model alcohols and substituted benzylic alcohols with wide electronic variability. CP4 exhibited high recyclability, consistently providing quantitative yields even after ten consecutive runs. The catalytic protocol demonstrated sustainability and environmental compatibility, as evidenced by a low E-factor (4.29) and a high Eco-scale score (90). Based on experimental evidence and theoretical calculations, a plausible catalytic cycle was proposed. Finally, the sustainability credentials of the different optimized reaction protocols were evaluated using the CHEM21 green metrics toolkit.

Supercritical Water Gasification of Ethanol as Biomass Model Compound in Tandem with Steam Reforming: Kinetic Modeling of the Reforming Step and Techno-Economic Analysis of the Integrated Concept

Supercritical Water Gasification of Ethanol as Biomass Model Compound in Tandem with Steam Reforming: Kinetic Modeling of the Reforming Step and Techno-Economic Analysis of the Integrated Concept

Enhancing oil production via radical reactions during hydrothermal coliquefaction of biomass model compounds and plastics: A molecular dynamic simulation study

Recently, hydrothermal coliquefaction of biomass and plastic waste has attracted considerable research interest. However, there is a notable gap in understanding the fundamental reaction mechanisms between biomass and plastics during coliquefaction. This study focused on the coliquefaction of biomass model compounds and plastic polymers using ReaxFF molecular dynamics simulations under both subcritical and supercritical water conditions. Molecular-level tracking and probing of the reaction mechanisms between biomass model compounds and plastics were conducted to purposefully enhance oil production. The study observed related radical reactions between by-product molecules, with detailed mechanisms primarily involving (1) ▪OH radicals released by aqueous phase molecules from biomolecules, transferring as H2O molecules and facilitating plastic depolymerization, and (2) C1–C4 radicals in the gaseous phase, emitted from biomolecule and plastic, colliding and subsequently recombining to form oil molecules. Moreover, the yield of multiple products from various mixtures were evaluated by considering the key reaction parameters including reaction temperature and feedstock blended ratio. An exploration into the effect of coliquefaction on oil yield was conducted to precisely identify the optimal coliquefaction conditions. The positive effect of coliquefaction was more pronounced between biomass model compounds and aromatic polymers compared to aliphatic polymers. Analysis of reaction mechanisms and product outcomes has shown that hydrothermal coliquefaction is a viable approach to improving oil production from multi-source organic solid waste.

Investigation on the influences of CaO on tar of biomass model compounds by Boltzmann-Monte Carlo-Percolation (BMCP) model

CaO have been widely used in biomass thermal conversion processes to deal with tar of biomass. The influences of the CaO on the function groups or intermediates of the bio tars are crucial because strategies on refining bio tars can be determined. The pyrolysis experiments of three typical model compounds, lignin, cellulose, hemicellulose, are carried out in a multi-stage tube followed by a cold trap. The influence of CaO can be analyzing the products distribution and components obtained from Nuclear Magnetic Resonance and Gas Chromatography-Mass Spectrometry technologies with and without CaO-loaded honeycombs. As the adsorbed matters on CaO-loaded honeycombs are hardly to be analyzed, the Boltzmann-Monte Carlo-Percolation model is introduced to make further investigations on the possible influence of CaO. The experimental results suggest that generations of unsaturated structures are inhibited by CaO, and the comparison of simulation and experimental results suggest that aliphatic carbon-centered radicals rather than oxygen-centered radicals are adsorbed and stabilized by CaO.

Using ethanol and isopropanol as biomass model compounds for understanding bond scission mechanisms over Cu/Mo2N catalysts

The conversion of biomass compounds into fuels and chemicals is an important step towards a more sustainable future. This work combines results from model surfaces and powder catalysts to demonstrate Cu-modified molybdenum nitride (Cu/Mo2N) as a selective catalyst for dehydrogenation of the biomass model compounds, ethanol and isopropanol. Results from model surfaces showed that while Mo2N led to unselective decomposition via both dehydrogenation and dehydration, the addition of Cu increased the dehydrogenation activity and selectivity. DFT calculations showed how Cu influenced the structures of active sites, adsorbate interactions, and thus the product selectivity. Batch reactor studies on corresponding powder catalysts confirmed the trend that Cu modification increased dehydrogenation activity, and in situ X-ray absorption spectroscopy elucidated the Cu oxidation state under reaction conditions. This work demonstrates a strategy for promoting dehydrogenation over Mo2N-based catalysts, as well as the feasibility of using model surfaces to guide the design of industrially relevant catalysts.

Hydrogen production from aqueous‐phase reforming of glycerol, sorbitol, and glycine over Pt/Al2O3 catalyst in a fixed‐bed reactor

AbstractAqueous‐phase reforming (APR) is an interesting technique for generating hydrogen (H2) from biofeeds. In this work, APR of model compounds of wet biomass for H2 production was investigated. Glycerol, sorbitol, and glycine were the chosen model compounds. They represent polyols and amino acids in wet biomass such as waste sludge and microalgal biomass. The Pt/Al2O3 catalyst was preferred and it was characterized using nitrogen adsorption–desorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), x‐ray diffraction (XRD), and x‐ray photoelectron spectroscopy (XPS) techniques. APR trials were performed in a continuous fixed‐bed reactor. The reaction conditions chosen for this work were: temperature (T) 453–498 K, pressure (P) 1.2–2.4 MPa, feed concentration 5–15 wt%, and weight hourly space velocity (WHSV) 0.15–0.6 g reactant/(g catalyst h). The best conditions for H2 production by the APR process were found to be T = 498 K, P = 2.4 MPa, and feed concentration = 15 wt%. Among the chosen model compounds, glycerol exhibited the highest H2 selectivity (82.7%) and H2 yield (21.6%) at 498 K. The analysis of kinetic data suggested first‐order reaction kinetics for all the model compounds. The values of activation energy for the reactions with glycerol (55.4 kJ/mol), sorbitol (51.6 kJ/mol), and glycine (45.7 kJ/mol) were determined. Thus, APR is a promising route for effectively producing H2‐bearing gaseous products with high heating value from wet biomass.

Iron complexation by biomass model compounds

Biomass-based renewable, biodegradable Fe(ii) and Fe(iii) chelators investigated using model compounds in DMSO where flavonol compounds showed greatest binding affiinity and cooperativity.

Aqueous‐phase reforming of model compounds of wet biomass to hydrogen on alumina‐supported metal catalysts

AbstractCatalytic aqueous‐phase reforming (APR) of wet biomass such as microalgae and activated sludge is a potential technique for the production of H2‐rich gaseous products. In the present work, model compounds such as ethylene glycol, xylose and alanine were selected as representatives of the polyols, carbohydrates and proteins in wet biomass. APR trials were performed in a stirred batch reactor using commercial Pt/Al2O3 and Ru/Al2O3 catalysts. The reforming reactions were investigated at different conditions: temperature (T), 498 to 518 K, feed concentration, 1 to 5 wt. %, catalyst loading (ω), 2 to 6 kg/m3, and reaction time (t), 1 to 6 h. The commercial Pt/Al2O3 catalyst exhibited higher reforming activity. The influence of reaction parameters on turnover frequency (TOFH₂), hydrogen yield (Y‐H2) and carbon‐to‐gas conversion (C to G conversion) was studied. The values of TOFH₂ for Pt/Al2O3 were measured at T = 518 K, ω = 2 kg/m3 and t = 3 h using 1 wt% feed and these values were 19.2, 4 and 6 1/min for ethylene glycol, xylose and alanine. The values of TOFH₂ over Ru/Al2O3 under identical conditions were: ethylene glycol–12.4, xylose–1.4 and alanine–5.4 1/min. The activation energies for H2 production from ethylene glycol, xylose and alanine over Pt/Al2O3 and Ru/Al2O3 catalysts were determined. APR of the mixture of model compounds was also studied over laboratory‐made Pt/Al2O3 and Ru/Al2O3 catalysts at the optimum reaction conditions. Thus, this work has provided crucial insights into the production of H2 from model compounds of wet biomass using Al2O3‐supported catalysts.

The impact of H-ZSM-5 catalyst on the mechanism of fuel-N conversion during glutamic acid pyrolysis

During the pyrolysis of biomass, Fuel-bound Nitrogen (Fuel-N) is converted into N-containing compounds present in bio-oil and biochar. These compounds are easily oxidized into NOx during subsequent utilization, causing ecological damage. Catalytic fast pyrolysis has emerged as a promising method for denitrogenation in recent years, but the underlying catalyst mechanism still needs to be determined. This study analyzed the impact of catalyst H-ZSM-5 on the mechanism of Fuel-N conversion during the pyrolysis of glutamic acid, a model compound for nitrogenous biomass, through experimental studies and theoretical calculations. According to literature data, the pyrolysis of glutamic acid predominantly yielded the N-containing products pyrrole, glutarimide, and pyrrolidone. The H-ZSM-5 catalyst showed optimum denitrification at 600 ℃, resulting in a 49.62% reduction in the proportion of N-containing compounds. In the catalytic pyrolysis products, the generation of toluene and naphthalene increased. In-situ DRIFTS experiments were consistent with the results of Py-GC-MS experiments, with catalytic pyrolysis promoting deaminations and decarboxylations, decreased imines and nitriles, and increased aromatic hydrocarbons. Additionally, the energy barrier changes of each pyrolysis pathway were calculated based on Density Functional Theory (DFT). The results showed that the H-ZSM-5 catalyst primarily promoted the deamination reaction, followed by the decarboxylation and dehydration condensation reactions, while inhibiting the dehydrogenation reaction. Moreover, the energy barrier for unsaturated hydrocarbon addition reactions was reduced, facilitating the formation of aromatic compounds. The acid sites inside the H-ZSM-5 catalyst weakly interacted with the reactants, making it easier to detach the amino group during catalytic pyrolysis. This study provides a reference for the denitrification of bio-oil and biochar. Subsequent work can realize the regulation of nitrogen conversion by changing the acidity and concentration of catalyst acid sites.

Distributed activation energy model of pyrolysis kinetics of starch and lignin with blast furnace slag as heat carriers

Molten blast furnace slag (BFS) can be used as heat carrier for biomass pyrolysis, which has high industrial value. Lignin (LG) and starch (ST) were chosen as model compounds of lignocellulosic biomass, which were mixed with different proportions of BFS, respectively. Thermogravimetry-process mass spectrometry studied the characteristics of LG-BFS and ST-BFS pyrolysis. The activation energies were obtained by Kissinger-Akahira-Sunose (KAS) method and four kinds of Distributed Activation Energy Model (DAEM) methods. The results showed BFS has little effect on the temperature of LG and ST pyrolysis. The average activation energy of LG-BFS-30% and ST-BFS-50% calculated by KAS method was 167.74 and 155.57 kJ∙mol−1 respectively, which meant the addition of 30% and 50% BFS promoted the pyrolysis of LG and ST, respectively. The activation energy distribution (AED) obtained by the four kinds of DAEM methods could reflect the actual pyrolysis process more completely. The results showed that the Double Gaussian distribution (GAUSS-2)and the distribution-free method (DAEM-NM) were more closer to the pyrolysis process of LG-BFS and ST-BFS. Compared with the pure LG, the CO2 content in pyrolysis gas decreased by 9.61%, and the CO content increased by 22.14% in the LG-BFS-30% pyrolysis. Compared with ST-BFS and LG-BFS, LG-BFS-30% was more conducive to the generation of CO.

Development of a global kinetic model based on chemical compositions of lignocellulosic biomass for predicting product yields from hydrothermal liquefaction

This study aimed to develop a global kinetic model to predict product yields from hydrothermal liquefaction (HTL) of lignocellulosic biomass based on its chemical compositions (contents of cellulose, hemicellulose, and lignin). HTL experiments were carried out with biomass model compounds (cellulose, xylan, and lignin) and lignocellulosic biomass (bamboo, cornstalk, and pinewood) at various temperatures (225–300 °C) and reaction times (10–60 min) with K2CO3 catalyst. Out of the three major components of lignocellulosic biomass, lignin was found to be the main contributor to bio-oil formation. A universal reaction network was proposed, and a kinetic model was developed based on the experimental results obtained from HTL of biomass model compounds. The kinetic parameters were determined by the lease-squares method using a MATLAB optimization function. Assuming no interactions among the components (cellulose, hemicellulose, and lignin) of lignocellulosic biomass during HTL, a global kinetic model was developed based on the chemical compositions of lignocellulosic biomass and the kinetic parameters obtained from the model compound. The developed model was validated with our experimental results from HTL of bamboo, cornstalk, and pinewood and the publicly available HTL data in literature obtained with lignocellulosic biomass feedstocks.

Water-assisted HDO of biomass model compounds enabled by Ru-based catalysts

Biofuels upgrading gathering momentum in view of the gradual depletion of fossil fuels and the pursuit of renewable energy sources to mitigate global warming. Hydrodeoxygenation (HDO) is a key reaction in the upgrading of bio-oil to produce hydrocarbon fuels or high-value chemicals. Oxygen removal in bio-oil increases its calorific value, improve thermal and chemical stability, reduce corrosiveness, etc., making the upgraded bio-oil suitable as a fuel or blending fuel. However, the dependence on high-pressure hydrogen is a serious disadvantage, as it is an expensive resource whose use also poses safety concerns. In this scenario, we propose a pioneering route for model biomass compounds upgrading via H2-free HDO. Herein we have developed multifunctional catalysts based on Ru and ceria supported on carbon able conduct the hydrodeoxygenation reaction using water as hydrogen source. We found that cerium oxide improves ruthenium metallic dispersion and the overall redox properties of the multicomponent system leading to enhanced catalytic performance. Along with the successful catalytic formulation we identify 300 °C as an optimal temperature validating the H2-free HDO route for bio-compounds upgrading.

L-Lysine Stabilized FeNi Nanoparticles for the Catalytic Reduction of Biomass-Derived Substrates in Water Using Magnetic Induction.

The reduction of biomass-derived compounds gives access to valuable chemicals from renewable sources, circumventing the use of fossil feedstocks. Herein, we describe the use of iron-nickel magnetic nanoparticles for the reduction of biomass model compounds in aqueous media under magnetic induction. Nanoparticles with a hydrophobic ligand (FeNi3 -PA, PA=palmitic acid) have been employed successfully, and their catalytic performance is intended to improve by ligand exchange with lysine (FeNi3 -Lys and FeNi3 @Ni-Lys NPs) to enhance water dispersibility. All three catalysts have been used to hydrogenate 5-hydroxymethylfurfural into 2,5-bis(hydroxymethyl)furan with complete selectivity and almost quantitative yields, using 3 bar of H2 and a magnetic field of 65 mT in water. These catalysts have been recycled up to 10 times maintaining high conversions. Under the same conditions, levulinic acid has been hydrogenated to γ-valerolactone, and 4'-hydroxyacetophenone hydrodeoxygenated to 4-ethylphenol, with conversions up to 70 % using FeNi3 -Lys, and selectivities above 85 % in both cases. This promising catalytic system improves biomass reduction sustainability by avoiding noble metals and expensive ligands, increasing energy efficiency via magnetic induction heating, using low H2 pressure, and proving good reusability while working in an aqueous medium.

Front Cover: Catalytic Transfer Hydrogenation of Lignocellulosic Biomass Model Compounds Furfural and Vanillin with Ethanol by an Air‐stable Iron(II) Complex (ChemCatChem 3/2023)

Front Cover: Catalytic Transfer Hydrogenation of Lignocellulosic Biomass Model Compounds Furfural and Vanillin with Ethanol by an Air‐stable Iron(II) Complex (ChemCatChem 3/2023)

Selective aerobic oxidation of biomass model compound veratryl alcohol catalyzed by air-stable copper(ii) complexes in water

Three new copper(ii) complexes were synthesized and successfully utilized as effective catalysts for the selective aerobic oxidation of biomass derived veratryl alcohol to veratraldehyde in water as a green and sustainable reaction medium.

Catalytic Transfer Hydrogenation of Lignocellulosic Biomass Model Compounds Furfural and Vanillin with Ethanol by an Air‐stable Iron(II) Complex

AbstractThe chemical transformation of lignocellulosic biomass into various fine chemicals is the necessity for sustainable developments. A significant research interest has been devoted to develop catalysts for the reduction of cellulose and lignin model compounds furfural and vanillin, respectively. An iron(II) complex (1) was readily synthesized by facile coordination of NNO pincer ligand with FeCl2.4H2O. The air‐stable complex 1 was efficiently utilized for the catalytic transfer hydrogenation of furfural and vanillin using ecologically benign but challenging primary alcohol ethanol. Secondary alcohol isopropanol was also utilized. Various other biomass model compounds and structurally related aldehydes were also effectively reduced. Kinetic studies suggested first order kinetics in catalyst and zeroth order in substrate. Based on the experimental evidences and published reports, a catalytic cycle is proposed which proceed via iron(II)‐dialkoxides and alkoxide‐hydride intermediates. Finally, CHEM21 green metrics toolkit was utilized to evaluate the sustainable and green credentials of the catalytic protocols.

Carbon nanotube as catalyst support in supercritical water

Carbon nanotubes (CNT) are possible catalyst supports for biomass gasification. In this study, glucose (5 wt%), a typical model compound of biomass, was gasified with a 0.5 wt% ruthenium catalyst on a CNT support. Only 0.15 g of catalyst containing 0.5 wt% Ru was sufficient to achieve complete gasification. High stability was observed in supercritical water at 600 °C and 25 MPa using a packed bed reactor. Compared with previous studies, the amount of Ru used in this study was one to two orders of magnitude lower than that on other catalyst supports. This makes CNT a promising catalyst support for supercritical water gasification.

Hydrogen Production by Aqueous-Phase Reforming of Model Compounds of Wet Biomass over Platinum Catalysts

Hydrogen Production by Aqueous-Phase Reforming of Model Compounds of Wet Biomass over Platinum Catalysts

Microwave pyrolysis of biomass model compounds for bio-oil: Formation mechanisms of the nitrogenous chemicals and DFT calculations

Microwave pyrolysis of nitrogen-rich biomass for bio-oil is a green and sustainable pathway to realize energy conversion and produce high-value nitrogenous chemicals. This work selected three typical amino acids (serine (Ser), glutamic acid (Glu), and phenylalanine (Phe)) as nitrogenous model compounds for biomass, and the distribution characteristics and formation mechanisms of the nitrogenous chemicals in bio-oil were studied in depth. Results showed that the amino acid structure and pyrolysis temperature were the crucial factors affecting the distribution and selectivity of nitrogenous chemicals. The nitrogenous chemicals were mainly produced at 200–500 °C from the model amino acids, and the nitrogen in Ser was more prone to accumulating in bio-oil compared with Glu and Phe. At 300 °C, the model amino acids generated numerous amines and cyclic amides through decarboxylation, decarbonylation, and dehydration. Higher temperatures (400 and 500 °C) promoted amines/amides to form nitriles and N-heterocycles, with the releasing of H2. Nitriles (including propionitrile and phenylacetonitrile) were typically produced by the straight-chain dehydrogenation of amines. Ser, Glu, and Phe produced N-heterocycles (including pyrazine, pyrrole, 2-pyrrolidone, and indole) based on the cyclization and dehydration between carbonyl and amino compounds, intramolecular dehydration, and cyclization dehydrogenation of phenethylamine, respectively. Finally, the possible formation pathways of the main nitrogenous chemicals were proposed, and the kinetics and thermodynamic analyses were performed through density functional theory (DFT) calculations. The findings could provide theoretical support for the nitrogenous chemicals production from microwave pyrolysis of amino acids and biomass.

Supercritical water gasification of lignocellulosic biomass: Development of a general kinetic model for prediction of gas yield

• A general kinetic model of biomass supercritical water gasification was developed. • The kinetic model was validated successfully based on results from real biomass. • Temperature played the most important role in producing gaseous species. • The effect of residence time on gas formation was found to be minor. • SCWG of lignin produced the highest yield of hydrogen. Supercritical water gasification (SCWG) utilizes water as the reaction medium to convert biomass into a mixture of gases (i.e., H 2 , CO 2 , CO, CH 4 , and other short-chain hydrocarbons) at typical operating temperature ≥ 400 °C and pressure ≥ 23 MPa. Understanding kinetics of SCWG processes is critically important for future development and scale-up application of the SCWG technology. Thus, this study aimed to develop a general kinetic model to predict the yields of gases from SCWG of various lignocellulosic feedstocks with varying contents of cellulose, hemicellulose and lignin. The model was established based on the experimental results from K 2 CO 3 -catalyzed SCWG of various biomass model compounds including cellulose, xylan and lignin at 450–550 °C for 10–50 min, followed by validation of the model using the experimental data obtained from SCWG of real biomass (i.e., corn stalk and pinewood) under same reaction conditions. The validation results showed that the general kinetic model developed could accurately predict the yields of gases from real biomass SCWG and the quantitative influences of temperature and residence time on the gas yield in biomass SCWG. Additionally, the kinetic model has been validated other SCWG data in the literature obtained with various facilities and different lignocellulosic biomass feedstocks. The development of the general kinetic model provides an applicable way to assess the potential of SCWG of various lignocellulosic biomass feedstocks for producing combustible gases at various conditions.